1. Warning: More Than 12 DOF With Zero Stiffness
2. Warning when using the command: list-of-joints Elastic mat Dir YONLY SUB 10000 
3. I have analyzed a structure and find that there are instability messages in the .anl (output) file
4. If there are instability messages, does it mean my analysis results may be unsatisfactory?
5. If there are instability messages, are there any simple checks to verify whether my analysis results are satisfactory?
6. What does a zero stiffness warning message in the STAAD output file mean?
7. Spurious Degrees of Freedom
8. [[Zero stiffness/instability warnings at nodes of solid elements]]

See Also

RAM Instability In Finite Element Analysis

Structural Product TechNotes And FAQs

Is there a Customized curtailment provision in RCDC ?

• Each beam is divided and designed at-least at 13 stations i.e. 12 section; along the length of the beam.
• Each section is designed for each load combination to arrive at required areas of longitudinal reinforcement at top and bottom and shear reinforcement.
• Further, the lapping locations are available as per user inputs. Default location for lapping of top reinforcement is L/4. As RCDC design the beam for 12 zones, the options of L/3, L/4 and L/6 are available for lapping at top and bottom reinforcement.  User can choose the lapping location as per design requirements.
  • For any beam under consideration, as the bending moment is parabolic in nature and not a linear one, it is not feasible in RCDC to interpolate the BM "in between the section length". So, the lapping locations provided in RCDC are all multiple of 12 i.e. L/3, L/4 & L/6 ---- where 12 is the number of section in which a beam is divided.
• RCDC provides all the Lapping location as mentioned in SP34 except for L/10 so as to avoid the interpolation of Bending moment in between a section length. 

• At top location, the lapping is provided at curtailment locations. i.e. L/3,L/4 or L/6 distance from column face. Here the distance 2xD is not checked for curtailment. If we start providing curtailments for beams as per the beam depth, it would be complicated. The curtailment location will vary as per the beam depth. The location of curtailments might fall between two stations. Checking reinforcement curtailments at any location as per 2D would not be simple and might not give the desire result. Interpolation of forces is not possible for in between values. Even if we consider on higher side, it would not be consistent to all beams and curtailments will not match the distance 2D for all beams. Also, it is very difficult to handle Ast calculations and shear check location for individual beams.
• For Bottom location, RCDC provides the lapping at face of the beam. The higher diameter rebars extends to lower diameter to make sure that the it satisfies the bending and shear check criteria. Also, the confining of the reinforcement exists up to twice the distance from the column face.
  • If we provide lapping away from the twice the beam depth, it might reach in the middle zone of the beam which is also needs to avoid as it is governed by permanent loads. In this case we might need to handle ductile and Non-ductile beams separately. For ductile beam lapping will place away from the 2D and for Non-ductile it is possible to provide within 2D.

Note that there is an option in RCDC to perform local curtailment by modifying the reinforcement locally for any station of a zone. On the design output window, you can click on the 'Detail' feature and by double click on each zone, you can modify the 'Top reinforcement', 'Bottom reinforcement' & 'Shear reinforcement' also. 

Further, in case you want to use the same reinforcement configuration for other zone by avoiding this step, there is further tool available to 'copy reinforcement' & then 'paste reinforcement' to other beam with same size and same material used for design.

Refer the attached video for understanding how this can be done.

communities.bentley.com/.../2210.2021_2D00_08_2D00_20_5F00_13_2D00_21_2D00_42.mp4

In RAM Connection when trying to generate the report, I am getting below error. Can you please help?

This issue is related to printer settings. Please change the default printer and try again.

In RCDC, we can group columns and design them. But, when we go on creating elevation there is no way to create a single elevation for all the columns in a group. This feature is available only for detailed drawing. Can we incorporate the same for elevation drawings also? If not, can you please let me know the reason?

[[Detailed explanation for Gravity column design in RCDC]]

[[Why only 50% of longitudinal reinforcement considered For Column Shear Calculation?]]

[[Why RCDC shows message of “Elevation of Column has been Omitted” while generating elevation of combined wall?]]

[[There is option under shear wall for detailing as Boundary Element or Equi Spaced rebar. I wish to have detailing as equi-spaced rebar, but it never gives detailing as equi spaced and redesign consume lot of time]]

[[Does RCDC calculate the effective length factor based on ACI 318M -14 Fig. R6.2.5 (b) for sway frames?]]

[[On what basis does RCDC perform the Joint shear check based on the Aspect ratio of vertical member as per Clause 7.1.2 IS13920 - 2016 & Amendment no.1 - 2017?]]

[[Can RCDC handle columns of shape L, T and other odd shapes?]]

[[When equal number of bars are provided in all columns from plinth to top floors, after design it’s showing lesser bars at the bottom and more at top]]

[[Some of the columns are missing at lower level even if they have exist in Staad model]]

[[Forces for column do not match with analysis]]

[[In edit link arrangement all the internal links can be removed. It doesn’t affect the design of links in column design. Please clarify]]

[[Does RCDC calculate the Effective length factor automatically or it is user defined? Is it same for all columns in model or different?]]

[[Spacing of confining reinforcement for column as per IS13920 2016]]

[[In RCDC, we can group columns and design them. But, when we go on creating elevation there is no way to create a single elevation for all the columns in a group. This feature is available only for detailed drawing. Can we incorporate the same for elevation]]

• 1. Can RCDC handle columns of shape L, T and other odd shapes?
  • Yes. RCDC can design any shape of column like L, T, I, E, Capsule and polygons up to 12 edges. It also has an option to create user defined sections. For more information refer Topic “Irregular Shaped Column” for column from help Content.

• 2. When equal number of bars are provided in all columns from plinth to top floors. After design it’s showing lesser bars at the bottom and more at top.
  • RCDC designs the column floor-wise. If percentage reinforcement required at a given level is more than the lower floor then it could be because of higher moment at that floor. Normally this happens at terrace floor where moments are more as compared to lower floors. This can be checked as per efficiency ratios in the design table.

• 3. Some of the columns are missing at lower level even if they have exist in Staad model.
  • If the model has column members with no joints at in between levels, then these columns will appear ‘Missing’ in those levels. This can be checked by generating column elevation.

• 4. Forces for column do not match with analysis.
  • RCDC reads the forces only for Primary load cases. These will match with the analysis forces. The forces for combinations are computed within RCDC as per load factors and other conditions like (LLR) Live load reduction. If the conditions of LLR are matched in analysis and RCDC, the design forces will match. For foundation design, RCDC uses member forces and not support reactions. In case of rotated columns or columns with offset, the support reactions do not match with member forces.

• 5. In edit link arrangement all the internal links can be removed. It doesn’t affect the design of links in column design. Please clarify.
  • Option of Edit link arrangement is provided to change the link arrangement. It is provided only as detailing tool and not linked to design. User is expected to check the shear requirements before modifying it. Also it may be noted that, diameter and spacing of links is not recalculated after editing of links. For more information refer Topic “Edit Link Arrangement” for column from help Content.

• 6. Does RCDC calculate the Effective length factor automatically or it is user defined? Is it same for all columns in model or different?
  • RCDC identifies the sway or Non-sway frames factor as per storey stiffness and storey index. It calculates relative stiffness of the beams and columns as per column orientation. It calculates the effective length factors as per available charts for Sway and Non-sway. Effective length factor would be different for all columns as per calculations. Option of overriding effective factor is available to user. User also can apply single factor to all columns on one click. For more information refer Topic “Effective Length Factor” for column from help Content.

• 7. Does RCDC designs shear wall for out of plane moments in addition to in plane moments?
  • RCDC designs the sections as per the forces from analysis. In addition to the forces from analysis, RCDC calculates moments due to minimum eccentricity in both major and minor directions and performs section design. If applicable, slenderness moments are added in the final design moments. For cross-section design of walls same principles as column design are followed.

• 8. Can we design shear wall/wall with single layer (mesh) of reinforcement?
  • No. Shear wall design with single mesh is not available as it is designed for the axial force and biaxial moments.

• 9. RCDC uses the formula of column for the “Minimum Eccentricity Calculation” (in IS code), though it is different for shear walls as per Clause: 32.2.2 of IS 456-2000.
  • Clause 32.2 in IS 456-2000, is for Empirical Design Method of walls. Clause 32.3 is for design of walls subjected to horizontal and vertical loads and same has been followed in design of wall in RCDC.

• 10. Please clarify the braced and un-braced design conditions.
  • These are design principles chosen by structural engineer for design of buildings. These are beyond purview of RCDC. RCDC captures this as information for further calculations.

    As per clause 39.7.1 (Notes), IS code allows user to design column based on Braced and Un-braced conditions. The end moments are calculated based on end conditions given in this clause.

    In Euro code, the braced and Unbraced option is available for calculation of effective length factor.

• 11. Lateral ties diameter, spacing & no. of columns main bars are correlated by formula given in IS: 13920 for rectangular and circular column. Can any single parameter be provided to calculate remaining two parameters in RCDC, once the initial design is complete?
  • Yes. After initial design is completed, user can change the numbers and diameter of main reinforcement in redesign option. Diameter and spacing of links can be changed. For any parameter changed in redesign process, RCDC would design/ check the column with all relevant clauses. For more information refer “Edit Local Column Design” from help Content.

• 12. Pl refer to Annexure A off IS 13920 which states walls are to be designed for uniaxial bending. Columns are considered as biaxial. Hence, their design cannot be clubbed under one set.
  • Annex A of IS 13920 is about the calculation of moment of resistance of the web portion of rectangular wall section. This is further used only in calculation of effective axial force in boundary element due to major axis moment. It may please also be noted in IS 456 which is the main code for design there is no separate procedure for design of walls. Clause no 39.6 of IS 456 refers to members subjected combined axial and biaxial bending which includes column and walls. Thus for biaxial design RCDC follows the basic principle of plotting P-M curve for design and checks for boundary element using annex-A provided in IS 13920. For more information refer Topic “Technical discussion” for column from help Content.

• 13. Can we have calculations for boundary zone length in wall design?
  • Boundary elements are provided for ductile walls as per IS 13920. Governing Criteria to provide Boundary element is if stress is more than 0.2*fck and Boundary wall terminates (along the height of wall) if stress is less than 0.15fck. Zoning of reinforcement is done around the boundary element. The initial length of the boundary element is arrived at as per procedure discussed in help. For more information refer Topic “Technical discussion” for column from help Content.

• 14. RCDC follows ductile detailing as per 13920 for outer ring of boundary element but reduces link dia. & spacing for inner links.
  • As per ductile detailing, for the calculation of confining links (outer links in BE – BE main) of boundary zone, formulation of Ash as per IS 13920, clause 7.4.8 is used. The internal links (BE others) are provided at same spacing with lowest possible diameter to maintain the “h” value in calculation of Ash. At middle zone, the links are provided as per IS 456. As a standard practice RCDC provided links to all longitudinal reinforcement.

• 15. What is the basis for only 20% of vertical reinforcement is considered for the calculation of Shear capacity (Tc)?
  • Based on the IS 456, Only tension reinforcement is to be considered for shear capacity (Tc) calculation. We can assume at- least 30 to 40% reinforcement would be under tension in a given load combinations.  Also, the effective depth as per code is suggested to be considered as 0.8 x the total depth for the shear calculation. Considering both the criteria, it is assumed that the only 20% of the main reinforcement of entire wall would be in tension.  It is also very difficult to identify the % tension reinforcement in wall for combination which is critical in shear. This has been discussed with the professor on the code panel in technical presentation of IS 13920-2016 and suggested to use only 20%of the main reinforcement in the shear calculation.

• 16. How and when Modulus of rupture check performed in RCDC?
  • Modulus of rupture check is performed as per clause 6.2.2 of IS 456-2002. The option of performing this check is available in RCDC as per user’s choice. This check is performed only for the tensile axial force in the column against the tensile capacity of the column. Effect of moment is not considered as this check is for tensile strength of concrete. If the axial tension is more than 0.7xsqrt(fck) then RCDC shows the column failure. It is just a check performed in the RCDC, there is no impact on the final design of the column.

• 17. In which cases we should not consider perform slenderness check - When to and when not to consider slenderness?

  • Slenderness check is an option given in RCDC. If the structure is analyzed with the Non-linear load cases (P-Delta) it is not recommended to consider this check. If the structure is analyzed with linear load cases, it is recommended to consider this check. If this check is selected, slenderness check will be performed, and additional slenderness moments will be calculated if column is slender.If this check is not selected, slenderness check will not be performed.

• 18. Provide detailed explanation for identification of section as a wall with respect to Depth and Width of member in RCDC

  • Please note the points below followed in RCDC for design of Columns based on provisions of IS 13920 (2016). This is as per our understanding of the code and based on discussions with some experts on the code –

    1. Columns should be B/D >= 0.4 (or D/B <= 2.5 – clause 7.1.2)
    2. Columns with as B/D < 0.4 to be designed as per provisions of wall (Clause 7.1.2)
    3. Walls to be considered if D/B > 4 (Or B/D <= 0.25) (Clause 10.1.3)
    4. As per experts, 2.5 < D/B < 4 should be avoided as these elements exhibit partial wall-column behavior
    You would notice that, in RCDC we allow users a bit of flexibility in defining the ratio for differentiation of wall and column. By default, the value is set at 4 as per the provisions of code. We hope this explains, the reason for defining the section to qualify as wall. For example, if you want sections with D/B > 5 to be designed as column. So, in RCDC, you have to set the qualifier for this as 6. This will segregate the cross-sections in 2 categories – 1) All sections with D/B <=6 would be treated as columns, 2) All sections with D/B > 6 would be treated as walls. You would appreciate that; we would not be able to provide this option to be changed for individual member. It would not be possible for us to handle that.

• 19. Provide detailed explanation for Gravity column design in RCDC.

  • Gravity columns is a choice that you as structural engineer have to make in your system. To reflect this correctly in analysis, ideally these columns should not participate in lateral load resistance in carrying shear and bending moments. These should be defined as ‘pinned’ ends in lateral load analysis. As per current limitations in E-tabs and STAAD, this is not easily manageable. Hence, we have allowed the users to select the required columns in RCDC and treat them as ‘Gravity’ columns. RAM software has the option to analyse the structure with combination of Lateral and Gravity columns.

    As per code, the Gravity columns should be designed for the forces from analysis as well as effects of lateral displacement (known as ‘displacement compatibility’). This is done by considering moment due to Pu (Axial load from Gravity load combinations with DL +LL) acting at R*Delta distance away (Delta is displacement due to lateral loads). We would request you to go through Clause 11 of IS 13920 (2016) for more details on this.

    In RCDC, we follow the above procedure in detail. Please check detailed design calculation report for Gravity columns for more information.

    Please note that, in RCDC the member can be defined as ‘Gravity column’ only if that qualifies as column based on D/B ratio. Walls can’t be design as Gravity members. It can be either Non-ductile or Ductile. Further, the Gravity columns are designed for Vertical gravity loads with effect of later displacement due to lateral loads as explained earlier. Click on below link to understand the implementation of Gravity column in RCDC.

    https://communities.bentley.com/products/ram-staad/m/structural_analysis_and_design_gallery/274370

• 20.Why only 50% of longitudinal reinforcement considered For Column Shear Calculation?
  • for column shear calculation, Tc shall be calculated for tension reinforcement. As column is mainly axial force carrying member, all the rebar would not be in tension. Also, when column is designed, rebars below the neutral axis are in tension. For shear check, identifying rebars those are in tension for combination which is critical in shear would be critical. Thus, RCDC assumes the 50% of the tension reinforcement for shear calculation

• 21. Why RCDC shows message of “Elevation of Column has been Omitted” while generating elevation of combined wall?

  • Combined walls are consisting of more than one walls. If the wall shape and size is same at all floors, RCDC generally generates the elevation of combined wall showing one face only.

    If the wall shape and size is not same throughout the height of all floors, it is difficult to generate elevation of these walls. The combined junctions of walls are detailed separately to satisfy the percentage reinforcement in both the walls. Also showing elevation of each face of combined wall would be difficult in case of thickness changes, thus RCDC generally ignore or omit the elevation of combined walls for elevation. Cases like major variation of reinforcement along height of wall and if combined wall consist of column are omitted.

    Generally, elevations are generated to show typical reinforcement detailing along the height of column/wall. User can still generate elevation of column and single walls for typical reinforcement details.

• 22.There is option under shear wall for detailing as Boundary Element or Equi Spaced rebar. I wish to have detailing as equi-spaced rebar, but it never gives detailing as equi spaced and redesign consume lot of time

  • When you select the option of “Detail with Equi-spaced rebar arrangement" RCDC design and detail the wall with Zones, however rebar spacing in all zones are maintain same. refer below snap showing rebar arrangement with same setting,

if you unselect "Detail wall with Boundary element" it will design as a ductile wall without Boundary element but it will try to provide zones to optimized the reinforcement.

when you select both the options i.e. Boundary element and Equi-spaced, it will design as Boundary wall with equi-spaced rebar arrangement. This setting is applicable for Non-ductile wall if you want t provide equal spacing.

if you want to design wall as column and with same rebar having equal spacing, then you have to perform the redesign step, however in redesign column tool allows user to change the type from "Zonal" to "Equi" in one step for wall along height. refer below snap,

for wall, RCDC tries to optimize the reinforcement by providing higher diameter at edges.

23.Does RCDC calculate the effective length factor based on ACI 318M -14 Fig. R6.2.5 (b) for sway frames?

Reply:    

Reply: RCDC calculates the column effective length factors as per above charts based on type of frame.

Type of frame is identified as per story height, axial load, relative displacement and story shear. Refer below snap,

Based on the column at top and bottom along with beam stiffness of story considered, value of Ѱ is calculated. Refer below snap,

As per Ѱ, effective length factor (k) is calculated based on fig. 6.2.5

24.On what basis does RCDC perform the Joint shear check based on the Aspect ratio of vertical member as per Clause 7.1.2 IS:13920 - 2016 & Amendment no.1 - 2017 ?

As per clause 7.1.2 IS;13920 - 2016, the vertical members of structure whose B/D >= 0.4 (or D/B <= 2.5), shall be designed as per requirements of Clause 9.

The first print of IS;13920 - 2016, 'Clause 8' talks about 'special confining reinforcement'. Later in Amendment no.1 - 2017 to IS;13920 - 2016 , this clause was renamed as 7.6. Hence, the old clause 9 now automatically becomes 8 and clause 10 (which is for shear walls) becomes 9.

Further, in the same amendment, they have mentioned that 0.45 in 7.1.2 should be replaced by 0.4. With this background, one can interpret 7.1.2 as below - It is preferred to provide D/B as 2.5 or less (B/D 0.4 or more) for columns. In clause for walls it is very clearly mentioned that D/B should be more than 4. Also, 

So, for D/B between 2.5 and 4, the behavior is in between and should be avoided. However, if one has to use these ratios then those members can be designed as walls as per clause 9, and can be done in RCDC by changing the D/B ratio in Design Settings form.

25.In RCDC, we can group columns and design them. But, when we go on creating elevation there is no way to create a single elevation for all the columns in a group. This feature is available only for detailed drawing. Can we incorporate the same for elevation drawings also? If not, can you please let me know the reason?

26.How can we change the Un-supported length in RCDC when column is tied in one direction and is free in another direction?

Reply:

Considering below example when there is a case where a column is not tied along one direction and is tied along another direction, the unsupported length of the column along the direction where it is not tied is to be manually entered in RCDC using the 'Redesign Section' tool available in RCDC.

With this option, the actual unsupported length = (Floor height - the Beam depth) needs to be manually entered in RCDC.

Once this height is entered; the column section is redesigned and the redesigned data is accepted, the revised height of the column at selected floor will be displayed in the design calculation report as well.

Below are the snips for reference;

27. IN FAILURE DIAGNOSTIC WE CAN GET ONLY REASON OF FAILURE BUT  NOT GET THE CALCULATION. HOW WE KNOW THE FAILURE CALCULATION OF COLUMN? 

Reply:

RCDC provides the reason for failure in the Failure Diagnostics report. There are multiple type of Failure suggested by RCDC as follows:

1. Axial Failure -  When the Average Stress in Column (Pu / Ag) for Pumax from seismic Load Combination exceeds 0.4 fck, then there is Axial Failure. 
   • This can be tackled by either Increasing the Column Size or by Increasing the Grade of Concrete. As both these parameters are set by user, RCDC cannot modify these parameters and shows as a Failure condition.
2. Joint Flexure Failure - As per Clause 7.2 (IS:13920-2016), for a considered Beam Column Junction, when the Column Capacity is found to be Less the 1.4 Beam Capacity (considering all the beams at the joint), then there is Joint Flexure Failure. 
   • In this case, RCDC tries to increase the Ast provided for Column up to Maximum Pt considering the Max Diameter - Min spacing parameters that are set in RCDC. If still there is failure after increasing the Pt, then RCDC shows it as Failure only. 
   • You can handle this by either increasing the Column sizing or by controlling the moments in beam by providing some partial releases in beam or by decreasing the beam sizing to control the stiffness.
3. Joint Shear Failure - As per Clause 9.1 (IS 13920-2016), the Nominal shear strength of concrete in the Beam - Column Joint is checked as mentioned in the code. Below image for reference:
   • This check depends on the Beam-Column Joint area and the Concrete Grade. So, this can be tackled by either Increasing the Column Size or by Increasing the Grade of Concrete. As, RCDC cannot modify both these parameters it is shown as a Failure condition.
4. Detailing Failure - This type of Failure occurs in RCDC when the 'Maximum Diameter' and 'Maximum allowable bars' for a column section is provided and still with this configuration of Pt provided is less than the Max Pt allowed. 
   • In this case RCDC has already tried to reach the maximum possible diameter and number of bars. So, this can be further handled from user's end by allowing the Maximum diameter available in the list and / or increasing the Number of Bars for the column section. The number of bars for column section can be increased from the Zone & Rebar settings in RCDC. 
5. Rupture Failure - Modulus of rupture check is performed as per clause 6.2.2 of IS 456-2002. The option of performing this check is available in RCDC as per user’s choice. This check is performed only for the tensile axial force in the column against the tensile capacity of the column. Effect of moment is not considered as this check is for tensile strength of concrete. If the axial tension is more than 0.7xsqrt(fck) then RCDC shows the column failure. It is just a check performed in the RCDC, there is no impact on the final design of the column.
   • In this case, the check is performed only when user selects to perform this check and there is tension in the column.

28. RCDC consider 0.4% reinforcement for column minimum reinforcement by default. Is there any clause in IS code to reduce column minimum reinforcement from 0.8% to 0.4%?

As per code, Min As = 0.8% of the required C/s area of the column. RCDC follows the same.

RCDC internally calculates the c/s area required for the Maximum Pu and then takes 0.8% of the Required c/s area.

The 0.4% mentioned on the reinforcement setting form is used to calculate the Asmin with the Provided c/s area of the column.

Finally the Asmin is considered as Max (0.8*Required c/s area of column, 0.4*Provided c/s area of column) where the required c/s area of column is calculated in RCDC internally with Max Pu.

29. A parametric wall is having different thickness at different levels. RCDC is unable to show the correct thickness. What may be the cause?

        Note that whenever a single parametric surface is modeled and 2 different plate thicknesses are found to be assigned to a single surface, RCDC considers the minimum of the thicknesses obtained. If it is desired to have different thicknesses at different levels, then you should model separate parametric surfaces and then assign the desired thickness to different surfaces. Then only RCDC will read and show the correct thickness at different levels.

30. In my model I have grouped the columns. Instead of column name I want to see group names. How to do that?

   This can be achieved by changing the Drawing Style. To do that go to Modify > Drawing Style > Modify Drawing Style as shown below. 

Now a new window will open. There you need to check the box against "Use Group Names in Output" under Display Style. This will show the group names instead of column names.

How can we change the Un-supported length in RCDC when column is tied in one direction and is free in another direction?

Reply:

Considering below example when there is a case where a column is not tied along one direction and is tied along another direction, the unsupported length of the column along the direction where it is not tied is to be manually entered in RCDC using the 'Redesign Section' tool available in RCDC.

With this option, the actual unsupported length = (Floor height - the Beam depth) needs to be manually entered in RCDC.

Once this height is entered; the column section is redesigned and the redesigned data is accepted, the revised height of the column at selected floor will be displayed in the design calculation report as well.

Below are the snips for reference;

IN FAILURE DIAGNOSTIC WE CAN GET ONLY REASON OF FAILURE BUT  NOT GET THE CALCULATION. HOW WE KNOW THE FAILURE CALCULATION OF COLUMN? 

Reply:

RCDC provides the reason for failure in the Failure Diagnostics report. There are multiple type of Failure suggested by RCDC as follows:

1. Axial Failure -  When the Average Stress in Column (Pu / Ag) for Pumax from seismic Load Combination exceeds 0.4 fck, then there is Axial Failure. 
   • This can be tackled by either Increasing the Column Size or by Increasing the Grade of Concrete. As both these parameters are set by user, RCDC cannot modify these parameters and shows as a Failure condition.
2. Joint Flexure Failure - As per Clause 7.2 (IS:13920-2016), for a considered Beam Column Junction, when the Column Capacity is found to be Less the 1.4 Beam Capacity (considering all the beams at the joint), then there is Joint Flexure Failure. 
   • In this case, RCDC tries to increase the Ast provided for Column up to Maximum Pt considering the Max Diameter - Min spacing parameters that are set in RCDC. If still there is failure after increasing the Pt, then RCDC shows it as Failure only. 
   • You can handle this by either increasing the Column sizing or by controlling the moments in beam by providing some partial releases in beam or by decreasing the beam sizing to control the stiffness.
3. Joint Shear Failure - As per Clause 9.1 (IS 13920-2016), the Nominal shear strength of concrete in the Beam - Column Joint is checked as mentioned in the code. Below image for reference:
   • This check depends on the Beam-Column Joint area and the Concrete Grade. So, this can be tackled by either Increasing the Column Size or by Increasing the Grade of Concrete. As, RCDC cannot modify both these parameters it is shown as a Failure condition.
4. Detailing Failure - This type of Failure occurs in RCDC when the 'Maximum Diameter' and 'Maximum allowable bars' for a column section is provided and still with this configuration of Pt provided is less than the Max Pt allowed. 
   • In this case RCDC has already tried to reach the maximum possible diameter and number of bars. So, this can be further handled from user's end by allowing the Maximum diameter available in the list and / or increasing the Number of Bars for the column section. The number of bars for column section can be increased from the Zone & Rebar settings in RCDC. 
5. Rupture Failure - Modulus of rupture check is performed as per clause 6.2.2 of IS 456-2002. The option of performing this check is available in RCDC as per user’s choice. This check is performed only for the tensile axial force in the column against the tensile capacity of the column. Effect of moment is not considered as this check is for tensile strength of concrete. If the axial tension is more than 0.7xsqrt(fck) then RCDC shows the column failure. It is just a check performed in the RCDC, there is no impact on the final design of the column.
   • In this case, the check is performed only when user selects to perform this check and there is tension in the column.

RCDC consider 0.4% reinforcement for column minimum reinforcement by default. Is there any clause in IS code to reduce column minimum reinforcement from 0.8% to 0.4%?

As per code, Min As = 0.8% of the required C/s area of the column. RCDC follows the same.

RCDC internally calculates the c/s area required for the Maximum Pu and then takes 0.8% of the Required c/s area.

The 0.4% mentioned on the reinforcement setting form is used to calculate the Asmin with the Provided c/s area of the column.

Finally the Asmin is considered as Max (0.8*Required c/s area of column, 0.4*Provided c/s area of column) where the required c/s area of column is calculated in RCDC internally with Max Pu.

A parametric wall is having different thickness at different levels. RCDC is unable to show the correct thickness. What may be the cause?

Note that whenever a single parametric surface is modeled and 2 different plate thicknesses are found to be assigned to a single surface, RCDC considers the minimum of the thicknesses obtained. If it is desired to have different thicknesses at different levels, then you should model separate parametric surfaces and then assign the desired thickness to different surfaces. Then only RCDC will read and show the correct thickness at different levels.

In my model I have grouped the columns. Instead of column name I want to see group names. How to do that?

This can be achieved by changing the Drawing Style. To do that go to Modify > Drawing Style > Modify Drawing Style as shown below. 

Now a new window will open. There you need to check the box against "Use Group Names in Output" under Display Style. This will show the group names instead of column names.

Where are the reported member forces acting?

The member forces for walls are for a horizontal section at the base of the story. The Major Shear force is the force along this slice, the Axial force is the vertical force normal to this slice, and the Major Moment is the "overturning moment" about the mid length (centroid) location of the slice. Minor Shear forces are the out-of-plane shear forces, and the Minor Moments are the moments about the long axis of the wall (i.e. out-of-plane moments). Those will generally be 0 unless the wall out-of-plane stiffness is considered in the analysis. 

For more on the wall sign convention refer to the Ram Frame Analysis program manual section "7.3 Sign Convention". 

To obtain forces acting on other sections use the Shear Wall Forces mode. 

What is the difference between "Cracked Factor (membrane)" and "Cracked Factor (bending)?"

Wall element stiffness in RAM Structural System is separated into membrane stiffness (in-plane behavior) and plate bending stiffness (out-of-plane behavior). In RAM Modeler, Cracked Factor (membrane) and Cracked Factor (bending) can be used to adjust each of these behaviors.

Understanding the wall element stiffness formulation used in RAM Frame is key to understanding how the cracked factors are applied. The wall element stiffness formulation is discussed in Section 6.4.4 of the RAM Frame Analysis Manual v14.06. The shells used in the program are 4-sided elements with 6 degrees of freedom at each node. When determining the element stiffness, the stiffness associated with these degrees of freedom are separated into a membrane stiffness matrix and a plate bending stiffness matrix. The membrane stiffness include stiffness associated with the two in-plane translational degrees of freedom and the drilling degree of freedom (in-plane rotation). The plate stiffness matrix includes stiffness associated with the remaining two rotational degrees of freedom and the out-of-plane translational degree of freedom. The membrane cracked section factor is applied to membrane stiffness matrix and affects in-plane translational (horizontal and vertical) and in-plane rotation. The plate cracked section factor is applied to the plate bending stiffness matrix and affects out-of-plane rotations and translation. Note that the out-of-plane stiffness can also be completely ignored in the Ram Frame analysis under Criteria - General - Wall Element by unchecking the option to "Include out-of-plane stiffness (bending)":

In summary,

Cracked Factor (membrane) applies to in-plane wall stiffness. It affects behavior associated with axial forces, overturning moments and major axis shear (the shear stiffness is related to the membrane stiffness by Poisson's ratio and Hooke's Law) .

Cracked Factor (bending) applies to out-of-plane wall stiffness, which also can be ignored in the analysis.

3-Dimensional (3D) Effects of Wall Groups

The following example illustrates how the finite element analysis of connected walls produces drastically different results than a simple two-dimensional approach. When walls are modeled in RAM Structural System such that they form a corner, it is important to understand what is happening at the point of intersection.  Because the walls frame into a common node, they will both affect the stiffness of that node.  In the RAM Frame manual, on Page 78, it states, “Since RAM Frame assembles the stiffness coefficients of its elements in a 3-Dimensional Fashion, walls that intersect at an angle (and hence share common nodes) form a 3-D system and the 3-D behavior is captured by the analysis.”  This is correct and consistent with proper Finite Element Analysis.

Typical 3-Dimensional FE-based analysis programs all Consider the 3-dimensional nature of connected walls this way. The member force output, however, is reported for the individual walls segments.

Case 1 - Consider the example of a simple building is 20 ft square with 10’ high shear walls all the way around the perimeter. A 100k lateral load is applied at the center of the rigid diaphragm and the wall forces are as follows:

Thus the overturning moment from the lateral load (100k x 10ft = 1000k-ft) is resisted by the parallel walls in the form of overturning moment, and in the end walls in the form of coupled axial forces:

220.33k-ft + 220.33k-ft + (27.97k x 20ft) = 1000k-ft

It should be noted that the percentage of the total overturning resisted by the walls parallel to the load can be dramatically affected by the size of the mesh. In this example, the walls were all meshed in 2.5’ squares).

Case 2 - The results change drastically if we place a small gap between the four wall elements so that they no longer share common nodes. Now the wall forces are as follows:

Here, the overturning moment is resisted entirely by the walls oriented parallel to the force.

Note, the wall elements considered in this example have zero out-of-plane stiffness, so the walls perpendicular to the load offer no resistance. For FE analysis which does include out-of-plane stiffness in walls, the results may differ slightly.

Also note, in Ram SS, it is required to place a gravity beam in the gaps to prevent a framing tables error. Starting with version 17 an option to automatically place gaps at the ends of walls was introduced, but only for tilt-up walls. For more on that see [[RAM Structural System Tilt-Up Workflow]].

With RAM Frame, an option is available to assign Wall Group Numbers to multiple walls. If a wall group is assigned to all four walls in either Case 1 or 2, the reported wall group forces will be the same. The total shear on the wall group is 100k, and the total overturning moment is 1000k’ as expected. It's important to note that assigning wall groups does not change any of the behavior, member forces, etc. For more on Wall Groups see [[RAM Frame Wall Groups FAQ]].

This example outlines above is the simplest case, but the same general principles apply no matter how the walls connect. Walls that intersect like an “L” or “T” also interact in a 3-dimension fashion. The story height and relationship between the walls of one floor and another also have a significant impact on the force distribution.

Lintel Beams

There are 2 approaches for modeling lintels beams in walls. The first approach is to model the whole wall and then place an opening in the wall. The second approach is to model walls on each side of the opening, and then span across the opening with a beam.

Walls with opening

When a wall opening is used the area above the opening is meshed along with the rest of the wall using shell elements and using the mesh parameters set under Criteria - General. The beam is assigned the same properties and cracked section factors as the rest of the wall.

Lintel beams of this type can be designed as Coupling Beams in the Ram Concrete Shear wall Module only, though you can cut sections through the beam to get forces at specific sections.

Generally speaking this approach gives you the stiffest overall wall compared to other methods. For that reason it's preferred for beams that are fairly stout, i.e. when the depth of the beam is > 1/4 the span.

Beam between walls

When modeling the lintel as a beam, the linear finite element of the beam connects to the corner nodes of the wall only. Consequently, the total stiffness of two walls coupled with a beam is less than the method above. There is an option within the Ram Frame - Criteria - General to control if the beam is virtually extended into the wall with a rigid link. 

Using this option will result in a more rigidly fixed connection of the beam to the wall, and is not recommended for models with tilt-up walls using gaps. For further details refer to the program manual, RamFrameAnalysis.pdf, section 7.21.3 Moderately Deep Coupling Beams.

Beams modeled this way can be designed in the Ram Concrete Beam module only, though forces are reported the same as other frame beams.

Generally speaking, this approach is recommended for long and skinny beams between walls, e.g. when the beam depth is < 1/4 of the span.

Note, a continuous two-way slab between walls (or a semi-rigid diaphragm with out-of-plane stiffness considered) will also couple walls together in a similar fashion. A rigid diaphragm will tie walls together and can provide for shear force transfer from one wall to another, but a rigid diaphragm alone without any out-of-plane stiffness does not actually couple the walls together.

Combining Columns and Walls

In the Modeler, you can freely model a column at the end of any wall without warning.

Where a column pilaster like this is modeled it's important to note that:

1. The full self weight of both will be counted.
2. If the columns and wall are lateral, then they will be meshed together and act compositely in Ram Frame (this is also true of gravity members analyzed in Ram Concrete.)
3. The design of the wall is based on the forces in the wall only, while the design of the column is based on the forces in the column only.
4. Where boundary element design is intended, it is better to model using walls only.

The presence of pilasters inside shear wall systems introduces a much different distribution of loads that has to be looked at closely.  In the Figure below, P1, P2, P3, P4, P5, P7, P9 and P11 represent the axial loads in the columns whereas P6, P8 and P10 represent axial loads in walls 1, 2 and 3 respectively. R1, R2, R3 and R4 are the external reactions. 

 Axial forces in Walls with Pilasters

A finite element analysis of the wall system shown in the figure above will give axial loads P5, P7, P9 and P11 which are much smaller than P1, P2, P3 and P4 respectively, because these loads are transferred not only to the columns also to the shear walls below.  In fact, the shear walls will often take most of the load leaving the column pilasters with very small internal forces. Many engineers want the pilasters to be designed for at least the loads that come directly from the columns above. There is no single tool to accomplish this in the program, so we recommend hand-checking that the pilaster below has at least the same size and area of reinforcement as the column above.

The frame reactions are the total reaction at a node. These reactions include the forces from the columns and the walls supported. For this system shown, the sum of R1-R4 is equal to the sum of column loads P1-P4, but forces will be distributed differently due to the presence of the walls.

It is worth noting that the walls themselves are further subdvided into a Finite Element mesh and if you prefer to view the individual nodal reactions, rather than the wall net reactions, use Process - Results - Reactions and toggle on the option to "Show Reactions at All Nodes"

Walls on Beams

When a wall is being supported by a beam, it is important to understand the way forces are transferred through the walls and into the supporting structure.

Gravity Walls

Starting in version 10 of RAM Structural System, gravity walls can be used to transfer loads from level to level.

When using Ram Steel analysis methods, any load is applied to the top of a gravity wall, that load is transferred straight down to the supporting member below (another wall or a beam for example). The applied loads are not fanned out or redistributed in any way.

This simplistic approach works nicely for simple bearing walls.

When using Ram Concrete analysis, the gravity members are part of the finite element analysis and the behavior is similar to that of lateral walls described below.

Live Load Reduction is not considered for both gravity and lateral walls in RAM Concrete due to  Defect #119766. However, LL reduction is taken into account in RAM Frame Analysis for lateral walls only.

Lateral Walls

Loads are tracked down through lateral through finite element analysis in RAM Frame (or RAM Concrete).

A frame wall is a shell element capable of spanning from support-to-support. If a frame wall on an upper level is supported by frame columns on a lower level, then that wall is able to span from column to column like a very deep beam. Consequently, if a beam is modeled on the lower level from column to column as well, that beam will not be directly loaded by the wall. Think of it like a small flange welded to the bottom of a very deep plate.

Bending forces in the beam still occur because the wall is meshed (based on the settings under Criteria - General) and bending deformation of the whole system is still possible. Axial tension under gravity load is expected, though a rigid diaphragm or stiff two-way slab would inhibit those forces as well.

To reiterate, the forces within a frame wall from the RAM Frame analysis are not delivered to the supporting beam in the form of an external line load. The only external loads shown on the Report - Gravity Loads are:

1. member self weight
2. line loads applied directly to the beam
3. the loads applied to the deck supported by the beam
4. reactions of gravity members supported by the beam

If the supporting beam is longer than the wall above, then the beam still acts like a flange but we can expect sudden increases in the shear and moment beyond the end of the wall.

Here the program creates additional nodes on the beam where the two finite elements are connected together and alone the length of the wall based on the mesh criteria. As the wall is vertically loaded, assuming everything is symmetric, the basic deformed shape of the beam will now look like a trapezoid (although the true deformed shape is actually a continuous curve and not “kinked”). Nodes N2 and N3 remain level and the same distance apart, thus there will be large shear forces and moments in the end segments of the beam, at the face of the wall. If the wall is broken up into smaller elements, then there will be additional nodes between N2 and N3. In this case, there can be relative displacement between the ends of the wall, but the deformed shape will still be basically the same when the wall is stiff in comparison to the beam.

Behavior of a Wall Supported by a Beam – Centered

For situations where the wall is not centered upon the beam, or where the system is otherwise asymmetric, the situation is further complicated. Where the beam supports one end of the wall, significant vertical displacements can be expected, as opposed to the column support which is presumably much stiffer. A net rotation of the wall results throwing shear and overturning moments into that wall and the supported structure. When a rigid diaphragm is present, other frames may even experience lateral shear due to this rotation.

Behavior of a Wall Supported by a Beam - Off Center

If there is another level of framing or a rigid diaphragm at the top of the wall, that could limit the rotation and affect the forces throughout the whole system as well.

Special Considerations for Ram Concrete Analysis

As noted in the Analysis Types wiki, Ram Concrete Analysis is also a finite element analysis, but it works by analyzing one floor at a time. Consequently some of the complex multi-story, truss like effects from having multiple levels of walls transferred on one slab with not be captured by the Ram Concrete analysis.

RAM Concrete Analysis has a useful analysis option for ignoring the stiffness of walls that are supported by beams below (see discussion in previous section). Check the box for "Ignore Wall Stiffness on Above Story" in RAM Concrete - Concrete Analysis mode - Criteria - General to minimize the deep beam effect of walls above. For the design of frame beams and columns, choose to use the gravity forces from the RAM Concrete Analysis and not the RAM Frame Analysis. This is an option in the Criteria pull down menu in both RAM Concrete Beam and RAM Concrete Column.

See Also

RAM SS Analysis Types

[[RAM Frame wall Groups FAQ]]

Modeling Podium Slabs

RAM SS - Rigid Diaphragm Constraints and Frame Shear [TN]

I am not able to open my STAAD model anymore. What can I do ?

STAAD.Pro creates a number of auxiliary data files in the same folder as the STAAD model and if any of these get corrupted or locked up, the model may fail to open and sometimes the software may even crash when trying to open the file

Here are a set of steps that you can try out

Create a new folder in your local machine (NOT on any network drive)

Open up File Explorer and browse to the folder where your STAAD.Pro model file (.std) is.

Copy ONLY the .std file into the new folder. DO NOT do a File Save As from within STAAD.Pro to copy the file.

Launch STAAD.Pro and try to open the model

If you still cannot open the file, please get in touch with STAAD.Pro Technical support.

Warning message in output file: This structure is disjointed, accompanied by several instability warnings.

The error message, "this structure is disjointed..." is caused by multiple structures in the model. Multiple structures exist when one portion of the model does not have any way of transferring forces to another portion. It is possible to create a model that visually appears to be a single structure, but upon closer inspection it is revealed that the model contains two or more unconnected structures. Instability warnings may also appear in the output file, due to the fact that the structure appears to be properly supported when, in fact, it is not. Multiple disjointed structures can be detected by selecting the top menu option Utilities > Structure Tools > Multiple Structures ( In older versions of STAAD.Pro like v8i Tools > Check Multiple Structures).

What do we mean by member connectivity? What determines whether two members are connected so that one can transfer loading to another? Consider two lines that intersect in 3D space, with the starting point of one line lying on the longitudinal axis of the other line. The fact that the end of one member lies on the axis of another is not sufficient to ensure connectivity. Connectivity is ensured only when intersecting members are divided into segments that meet at a single, common node. ("Common node" means a single node number. 

The following wiki contains more information on connectivity related issues

How the effective self-weight of the footing is calculated?

Effective self-weight of footing is calculated as additional load of footing volume with respect to difference in density of concrete and soil. For more information refer “Technical discussion” of footing from help Content.

[[While designing for reinforcement requirement]]

[[Footing Design with tension in Column]]

[[Eccentric Footing design in RCDC]]

[[Footing Design with loss of contact condition in RCDC]]

[[Base pressure calculation in RCDC]]

[[How the effective self-weight of the footing is calculated?]]

• 1. How the effective self-weight of the footing is calculated?
  • Effective self-weight of footing is calculated as additional load of footing volume with respect to difference in density of concrete and soil. For more information refer “Technical discussion” of footing from help Content.

• 2. For calculation of two way (punching) shear, footing self-weight is not added to axial load.
  • Concept of Footing punching shear criteria is column punches in the footing. Load from the column punches the column in footing. Self-weight of footing, overburden load do not participate in punching of column as it is a uniformly distributed load, thus it is not considered in design. For more information refer “Technical discussion” of footing from help Content.

• 3. As per design, required reinforcement is 1478/1528 sqmm along L/B direction. Provided reinforcement is T12@175 mm which amounts to 1453 sqmm only for 2.25 m width of footing, whereas the calculation report shows Ast provided as 1583sqmm. Please clarify.
  • Width = 2250 mm Ast required = 1478 sqmm Reinforcement provided = T12@175 mm In RCDC the number of bars required are calculated and spacing is calculated. While presenting the spacing rounded to 5 mm. In this example, number of bars as per spacing would be calculated as below – (2250 / 175 = 12.86 which is 13 spaces). Hence number of bars would be 14. Thus actual Ast-provided would be (14x113.097 = 1584) 1584 sqmm which is more than required.

• 4. Please clarify the footing type “on raft” given in RCDC.
  • RCDC designs the isolated footings. The purpose of this options is to maintain the same thickness of first step for all footings if all footing are connected by common raft. This type of footing mostly use in the basement structures. The concept of this type of footing is similar to stepped footing.

• 5. How is the volume of trapezoidal footing calculated in RCDC?
  • RCDC calculates the weight of trapezoidal footing as per following formulations, Self-wt. of footing Volume of footing = ((L*B*D) + ((((L*B) + (Lt*Bt))/2)*(D-d))/1000^3 Where, L= Length of footing B= Width of footing D= Depth of footing Lt= Length of footing top Bt= Width of footing top d= depth of sloping area.

• 6.In RCDC, the minimum rebar’s in Bottom are calculation based on effective Depth of the Foundation (Dff),whereas as per Clause 26.5.2.1 the minimum %Pt  is 0.12 of the Gross cross section area. Ast (minimum) as per IS456-200 Clause 26.5.2.1 is 0.12% of the Gross Cross section area.Therefore,  for  F4 1800 x 1800 x 500 thk. : Ast mini = (0.12/100) x 500 x 1800 = 1080 Sqmm. RCDC Calculations. Area calculation based on Deff. { (0.12/100) x 411 x 1800 = 887.76 Sqmm }. Actually we end up providing less %Pt than required. < 1080 sqmm actual requirement vs 888 sqmm Provided>
  • Please refer below snap extracted from IS 456,

Minimum reinforcement is for the total cross section area, thus 0.12% steel is to be provided at top and bottom.

In your case, top reinforcement is selected and below is the reinforcement given,

The minimum bottom reinforcement is given as 0.12% and top as 0.06%. Thus In your case, the RCDC will check the total reinforcement to be provided at a given cross section area as 0.12%. here, 0.06% is already provided at top, thus at bottom it will provided as per the 0.12% given by you with deff. Refer below snap of calculation  report.

Now, don’t select the top reinforcement and maintain the same reinforcement, below is the output

Reinforcement is provided indirectly as 0.12% with total depth. 0.12 x 500 x 1800/100 = 1080 sqmm.  If we take Deff, then 0.141 x 427 x 1800/100 = 1083.72 sqmm. So the final reinforcement required is 1080 sqmm.

Here, the required pt has increased to match with the 0.12% with total D.

If you want to reduce the Bottom reinforcement, please provide bottom reinforcement as 0.06%

What is the purpose of the Ignore Torsion feature available in RCDC Design settings and how does RCDC Consider it while designing any beam with Torsion ?

​

​

1.[[If Beam shows Failure]]

2. [[Can RCDC design Curved beams? Will it convert the curved beam composed of many parts to a single physical beam?]]

3. [[Can RCDC provide bottom bar without curtailment in single span?]]

4. [[Designing Group of Beams can be done if the Beam arrangement is similar at all Floors.]]

5. [[Can RCDC provide the detailing of beam with lowest diameter throughout the length and balance area of steel with higher diameter in other layer?]]

6. [[Does RCDC allow to provide only 2 bars for top reinforcement?]]

7. [[What is the purpose of mirror & straight option in group/ungroup tab?]]

8. [[Why specifically only 13 stations (for beams) can be imported from E-tabs to RCDC?]]

9. [[Side face reinforcement (SFR) is designed for beams even though the depth is less than 750mm, whether there are any options to enable/ disable side face reinforcement?]]

10.[[For Non ductile and Ductile Beam]]

11.[[How to calculate reinforcement of beam at face of column in RCDC?]]

12.[[The Building is designed including EQ loads and STAAD RCDC is giving more reinforcement at bottom near supports as curtailed bars. Why?]]

13.[[Which option can be used to save the reinforcement for long span beams in RCDC?]]

14.[[In RCDC Detailing option is available in Design Settings.]]

15.[[Clarification regarding the curtailment of 100% top reinforcement.]]

16.[[In BBS for ductile beams, there should be no lap splice within the joint and within 2D from the face of the column. (ACI 318M – 14 cl. 18.6.3.3)]]

17. [[Please give clarification of failure type for beam element. Failure type – Shear –Tc max]]

18.[[Does RCDC perform the Serviceability check for allowable deflections from ACI 318M-14 Table 24.2.2 by using the effective moment of inertia from ACI 318M-14 cl. 24.2.3.5 ?]]

19.[[RCDC is considering 'Zero" bending moment at left and right support despite there being some Bending moment at the support.]]

20.[[How the effective depth is calculated in beam design and what is the impact of “maximum Aggregate 2 Size” on effective depth?]]

21.[[Why is RCDC taking wind load shears to do ductile detailing for earthquake loads? ]]

22.[[Does STAAD advanced concrete design (RCDC) consider the contributing effects of the slab flanges in RC beam design?]]

23.[[ Is there a Customized curtailment provision in RCDC ?]]

24[[What is the purpose of the Ignore Torsion feature available in RCDC Design setting?]]

• 1. Can RCDC design Curved beams? Will it convert the curved beam composed of many parts to a single physical beam?
  • Yes. If curved beam is modelled in sufficient small parts then RCDC identifies it as single beam as per the geometry and support conditions. The beam is designed for Bending, shear and torsion as per regular beam.

• 2. Can RCDC provide bottom bar without curtailment in single span?
  • RCDC has the option of detailing bottom reinforcement as Best fit and Max dia. user can use option of Max diameter to maintain the same number of bars at bottom most layer. For Best fit it curtails the bars at support if it is allowed as per detailing requirements.

• 3.Can number of bars for the given width of beam be edited?
  • Yes, User can set the number of bars as per width of section in "zone bar setting" option. It also checks the minimum and maximum spacing criteria at the same time. For more information refer Topic “Preferred Bar Spacing” for beam from help Content.

• 4.Can RCDC provide the detailing of beam with lowest diameter throughout the length and balance area of steel with higher diameter in other layer?
  • Yes. It can handle this only for top reinforcement. To maintain the lowest bar at top user can select “min dia.” option in general setting. Lowest Bar diameter and numbers will be provided across the length of the beam and remainder will be provided at next layer of reinforcement. This option will result in detailing like 2-T12 at first layer and 2-T25 at second layer. For more information refer Topic “General and Reinforcement Settings” for beam from help Content.

• 5.Does RCDC allow to provide only 2 bars for top reinforcement?
  • The Number of Bars suggested by RCDC are as per beam width and maximum spacing criteria given in codes. User can change the numbers of bars prior to design subjected to spacing criteria given in code. For zero bending moment zone RCDC can provide minimum two bars with minimum bar diameter. For more information refer Topic “Preferred Bar Spacing” for beam from help Content.

• 6. What is the purpose of mirror & straight option in group/ungroup tab?
  • Mirror grouping option can be used if beams are mirror in arrangement with same geometrical properties. So beam on one side can be mirror in detailing of the beam on other side. Similarly if beams are identical in plan i.e. beam geometry is similar at a given level and repetitive then these beams can be grouped. For more information refer Topic “In Plan Grouping” for beam from help Content.

• 7. Why specifically only 13 stations (for beams) can be imported from E-tabs to RCDC?
  • 13 stations divides the element in to twelve parts. As per standard practice of all codes, curtailments of reinforcement lies at L/4, L/6 and L/3 of span where L is the span of the element. Dividing the element in to 13 station satisfies all the requirements of curtailments. Curtailment of reinforcement helps in beam detailing thus it is mandatory to provide 13 stations to all beams in the analysis. Staad automatically provides the results at 13 stations. E-tabs can provide results at any stations as per user requirements Thus in E-tabs user has to assign output stations as 13 before exporting the results. For more information refer topic “Technical Discussion” of beam and Column from help Content.

• 8. Side face reinforcement (SFR) is designed for beams even though the depth is less than 750mm, whether there are any options to enable/ disable side face reinforcement?
  • In RCDC, SFR is calculated as per design requirements including torsion. User can provide the SFR even it is not required in design. In many cases for beams with depth less than 750 mm, there may be torsion, which would result in SFR. User may check the detailed calculation report for clarification.

• 9. Please give clarification of failure type for beam element. Failure type – Shear –Tc max
  • Tc max failure means Tv exceeds the maximum permissible shear stress.

• 10. Even after opting best fit for top reinforcement, why does RCDC provides higher reinforcement (as per minimum Pt) at top at mid-span?
  • This would be typically doubly reinforced section which causes more reinforcement at top even when moment at that location is nominal. In the calculation report it can be clearly checked where Asc-required at mid-span is captured. This is the top reinforcement required at that section.

• 11. Why default 0.2% is provided for nominal steel in RCDC? Does it have any reference?
  • RCDC provides the nominal steel where bending moment is ZERO. Default value provided in RCDC for nominal steel is 0.2 %. This is an approximate Value and we have kept the value close to minimum steel in beam. The above value is editable and can be put as per user requirements. For zone with no Bending Moment, RCDC uses nominal steel and for detailing, it would adopt 2 bars with minimum diameter possible.

• 12. Is there any option to disregard the contribution of concrete in resisting shear for beam when IS: 13920 is used?
  • No. Beam shear design is as per IS 456. Shear induced due to Sway action is calculated as per IS 13920. For Sway shear also the part of shear is arrived from the dead and live load. Thus RCDC does not allow to ignore the concrete for shear design.

• 13. When IS: 13920 is selected, does RCDC consider required rebar or provided rebar to calculate capacity (plastic) shear force (or moment capacity) for beam?
  • Yes. RCDC designs the beam shear as per Clause 6.3.3 of IS 13920 and consider the reinforcement provided to calculate the moment capacity. For more information refer Topic “Calculation of Ductile Shear” for beam from help Content.

• 14. Does RCDC calculates moment capacity for sway shear calculations as per rectangular section or flanged section for beam?
  • For moment capacity of section RCDC always considered as a Rectangular section as Flange section is not applicable at support. Also to get the flange action, flange has to at compression side which is not the case at support. For more information refer Topic “Flanged Beam” for beam from help Content.

• 15. If Beam is designed for axial plus biaxial forces, ideally if axial force in beam is less than the permissible value given in IS 13920 code, the member should be designed as beam only both for strength and crack width and check as per columns should not be applicable.
  • Whenever design for ‘Biaxial Bending’ is selected, RCDC would treat the design of beam like a column. There is possibility where axial forces would be negligible but lateral moment and shear would be high. In this case this member should be designed as a column only. Axial forces will not govern whether to details the member like beam or column.IS 13920 suggest to design/ details member like column as per clause 7 if axial stress exceeds 0.08ck. here the section will be detail as a column. shear (ductile) links should be calculated as per column.if axial stress less than 0.08 fck the section would be details as beam. All the links calculations would be as per beam. Further depending on Pu-threshold value set by user (the value is considered as compressive), RCDC will design the section with Pu, Mu-major and Mu-minor. If Pu for a given combination is less than Pu-threshold, it simply assumed.Pu = 0. This is only for ‘design combinations’ or limit state of collapse.For crack-width, there is no input for threshold value (currently there is no provision for it) of axial force. The crack-width is checked for service combinations. In this case, the values as per combinations are used for crack-width check.

• 16. We accept that concrete capacity shall be ignored as per clause 6.3.4 of IS 13920-2016 but this can be logically ok if only Ductile shear governs the design.In cases where DL+LL shear governs the design (i.e. no plastic hinge evidently formed) it will be very conservative to ignore shear capacity of concrete in beam.
  • The requirement of ignoring concrete capacity is due to unpredicted forces during earthquake. The earthquake forces are instantaneous, the concrete will crack, and plastic hinge will be formed. Even after the earthquake loads, the beams will be loaded with the Dead and live loads. The cracking of concrete, the shear capacity of the bean will be depending on the shear reinforcements only. Thus, ignoring concrete capacity of the beam for shear check is applicable to all load combinations. So even the critical combination is DL+LL, the concrete capacity should be ignored

• 17. In Beam design output of stirrups, what is 2L-T8 (H)?

  • 2L-T8 (H) is the horizontal link (stirrups) provided in the beam in case if Beam is designed for Axial+ Biaxial forces.

    Based on the axial stress (0.08 fck) type of beam detailing is performed in RCDC. If section selected for Axial + Biaxial design in RCDC then section will be designed as a column. If the section requires stirrups for horizontal shear in case of beam detailing, RCDC provides horizontal links. In case of section is detail as a column, RCDC provides the horizontal link to tie all the rebars along all faces of the section.

• 18. If the Beams exists at support level of the structure, can it be design in RCDC?
  • Yes. if the Beams are present at support level, RCDC can read and design these beams. After reading the analysis file for beams, RCDC shows all the levels available in analysis file. User can select the support level for beam design. Column above the support level are considered as support for beam and accordingly beam drawings are generated.

• 19. Three beams are failed due to shear since no links were designed and also, I am not able to add in any by manual means.

  • If the beam shown failure due to stress exceeds the maximum permissible stress for Shear and Torsion, then it’s a section failure. User can increase the size or Material grade to pass the beam in design. As it is section failure, there is no option available to change the reinforcement diameter to pass the design.

• 20. While designing beams of a group a floor together for a multi-story building, the software error. There is no problem if I design for each floor level separately.
  • There are some missing beams marked in snap below. Please note that the levels can be grouped only if the beam arrangement is similar at all floors.As RCDC is design and detailing software, it generates the Beam elevation. If the Beam are not same at all grouped levels, then it would not be possible to perform the beam design and generate the design calculation reports including drawings.

• 21. It is noticed that when ductile design is done (even only near supports), that there is a big jump in shears in the “Mid” span.  Let me know if this is unexpected

               Reply:

              For Non ductile and Ductile beam, Shear force at end is depend on the following settings,

              .

As per above settings, for ductile beam the end shear would be considered as per 2xDepth of beam. For Non ductile it would be L/3. It is purely depend on the depth of the beam and length of the Beam. If the Beam L/3 is more than the 2xD then it is possible that  at mid zones shear would be less as compared to ductile beam.

RCDC provides following two options for Sway shear check in Beam design.

For Ductile Shear at Support      : Sway shear would be calculated only at ends.

For At All Station                           : Sway shear would be calculated at all 13 stations for which beam is designed. Maximum of Shear due to sway at mid zones would be considered as critical in design.

It is not clearly mentioned in the IS code up to which location the sway shear is to be considered. The Option is added as per our discussion with the IIT professors. Professors is in opinion that, Earthquake loads are impact loads and shear due to Lateral loads might extend up to the mid span of beam. To avoid this kind on un-foreseen condition he has suggested us to add the option of checking sway shear at all stations.  Thus, these two options are available in RCDC. But It would be user’s choice

22.How to calculate reinforcement of beam at face of column in RCDC?

In STAAD generally we design the beam as centre to centre of column and from output we interpolate the beam reinforcement at the face of the column. How we can do the same in the RCDC. Because in boiler supporting structure where column size is 900x900 mm difference in beam reinforcement at centre of column & at face of the column is around 1000 mm².  Like in attached STAAD file for beam member no. 105, reinf. At centre of column is 3297 mm². Whereas by interpolation at face of the column its around 2722 mm².

Reply :

RCDC design the Beam based on geometry and forces available from the analysis file. It doesn’t modify the forces. In you case, the beams are modelled up to centre of the column and beam need to design at face of the column.

We would suggest following methods to add the beam at face of the column, so that beam will get design at moment available at face of the column,

User can assign Member offset command available in STAAD. RCDC will read the beam length and force available in STAAD as per the offset beam length.

User can define the rigid member within the column extent. The property of this member can such that the stiffness is more than the beam stiffness. i.e. YD = 3m and ZD = 0.45 m

The density of this member can be assigned as Zero. RCDC auto ignores the member within the column and with zero density.

The beam can be designed as per moment available at face of the column. Refer below snap

Below is the snap from the RCDC,

• 23.The Building is designed including EQ loads and STAAD RCDC is giving more reinforcement at bottom near supports as curtailed bars. Why?
  • RCDC design the beams as per section forces available from analysis. it designs the beams at 13 stations for given load combinations. when lateral loads are applied, due to sway effect end moment exists at end of the beam. So generally for +ve Eq and -ve Eq loads, the heavy moment exists at top or bottom of the end of the beam. we would request you to check the detailed design calculation report to get more information about the design of the beam. You will get the information about the for which moment end reinforcement is calculated.

• 24. I showed best fit beam reinforcement drawings to client, but he categorically said that I have never seen this type of detailing and it’s not practically possible. Why RCDC gives this type of detailing? 
  • Best fit detailing option is used by most of the structural consultant in Metro cities. it is generally used for the commercial, office and shopping malls where beam spans are larger. Best fit option can be used to save the reinforcement for long span beams. there are other options available in RCDC. i.e. Maximum Dia & Min. Dia which gives flexibility to users to detail the beams as per design and detailing requirements. Beams having shorter spans, maximum or minimum diameter option can be used to avoid lapping.

• 25. STAAD adv. Concrete designer RCDC provides top bars with lapping in output beam reinf. near supports but I want through bars at top without lapping and with curtailed bars near supports. How to do it?
  • Please select Min OR Max diameter detailing option in design settings in RCDC. refer below snap,
    
    

26.Can you provide clarification regarding the curtailment of 100% top reinforcement at a certain location from column as per IS code?

Reply:

RCDC design the reinforcement as per the forces available at all sections in the beam. It takes 13 stations (i.e. 12 zones) for design of beams. Based on the forces available in each zone, reinforcement is calculated. Lapping locations are available as per user inputs. Default location for lapping of top reinforcement is L/4. As RCDC design the beam for 12 zones, the options of L/3,L/4 and L/6 are available for lapping at top and bottom reinforcement.  User can change the lapping location as per design requirements.

Lapping of top reinforcement is available to optimized the reinforcement. Curtailment location is available in SP 34. Refer below snap,. As far are rebar are lapped with the development length, lapping is permitted for top reinforcement.

RCDC provided various option for top and bottom reinforcement detailing. This option is available in General and reinforcement settings,

If user doesn’t want to provide lapping for top reinforcement, we would suggest you to use Max Dia and Min Dia option of detailing.

27.In BBS for ductile beams, there should be no lap splice within the joint and within 2D from the face of the column. (ACI 318M – 14 cl. 18.6.3.3)

(Currently, lap splices are still drawn within the restricted locations.)

Reply:

RCDC design the reinforcement as per the forces available at all sections in the beam. It takes 13 stations (i.e. 12 zones) for design of beams. Based on the forces available in each zone, reinforcement is calculated. Lapping locations are available as per user inputs. Default location for lapping of top reinforcement is L/4. As RCDC design the beam for 12 zones, the options of L/3,L/4 and L/6 are available for lapping at top and bottom reinforcement

At top location, the lapping is provided at curtailment locations. i.e. L/3,L/4 or L/6 distance from column face. Here the distance 2xD is not checked for curtailment. If we start providing curtailments for beams as per the beam depth, it would be complicated. The curtailment location will vary as per the beam depth. The location of curtailments might fall between two stations. Checking reinforcement curtailments at any location as per 2D would not be simple and might not give the desire result. Interpolation of forces is not possible for in between values. Even if we consider on higher side, it would not be consistent to all beams and curtailments will not match the distance 2D for all beams. Also, it is very difficult to handle Ast calculations and shear check location for individual beams.

For Bottom location, RCDC provides the lapping at face of the beam. The higher diameter rebars extends to lower diameter to make sure that the it satisfies the bending and shear check criteria. Also, the confining of the reinforcement exists up to twice the distance from the column face.

If we provide lapping away from the twice the beam depth, it might reach in the middle zone of the beam which is also needs to avoid as it is governed by permanent loads. In this case we might need to handle ductile and Non-ductile beams separately. For ductile beam lapping will place away from the 2D and for Non-ductile it is possible to provide within 2D.

For such cases, we would recommend user to use detailing options available in RCDC.

For Top rebars use max dia. Option: here the same diameter rebar is continued at outer most layer to avoid lapping.

For Bottom rebars use max dia. Option and try to provide same rebar numbers and diameter to adjacent beams to avoid lapping.

28. Does RCDC perform the Serviceability check for allowable deflections from ACI 318M-14 Table 24.2.2 by using the effective moment of inertia from ACI 318M-14 cl. 24.2.3.5 ?

Reply:

Presently deflection values are not read by RCDC and deflection check is not performed. There would be simple check for deflection as per the deflection values available from analysis for given load cases. This would-be short-term deflection check.

Other is long term deflection check which is depend on the creep and shrinkage of concrete.

 We will try and take this as an enhancement in RCD for future release.

29.  RCDC is considering 'Zero" bending moment at left and right support despite there being some Bending moment at the support.

Reply:

Below is the step by step process which explains why and how RCDC shows Zero BM at supports to satisfy max Ast requirement:

Step 1: RCDC bifurcates the beam in Left, Mid and Right zone and identifies the length of each zone.

Step 2: Based on the length of each zone, RCDC further identifies the number of stations that will fall in each zone.

Step 3: For each station, identifies +ve moment as Top moment and -ve moment as Bottom moment

Step 4: RCDC Calculates As,reqd for each station as follows:

As,reqd = Max{B,B', A+D/2, A+C x (fsc / fyd)+D/2} (for Mu > 0)

As,reqd = Bn (for Mu = 0)

Where, 

A = As = Tension reinforcement required for bending moment

B = As,min (flex) = Min area of flexural reinforcement

Bn = As,nominal = Nominal area of reinforcement

Step 5: After identifying Max As,reqd (as per above step) for each station individually, RCDC provides the Max Ast for all the stations of a particular zone under consideration.

Step 6:"If As reqd is governed by As nominal, the RCDC shows Zero BM value in the design calculation report."

Refer attached excel which explains a solved example. 

 communities.bentley.com/.../RCDC-Logic-of-designing-Beams.xlsx

30.  How the effective depth is calculated in beam design and what is the impact of “maximum Aggregate 2 Size” on effective depth?

Reply:

RCDC assumes the number of rebars layers for the effective depth calculation based on the following,

Assumption of number of layers of reinforcement:

At design time the number of layers of reinforcement is assumed as under to arrive at the effective depth, d:

D < 400 mm                                                                   1 layer

400 mm >=   D <=1200 mm                                        2 layers

1200mm > D <= 1350 mm                                          3 layers

1350 mm > D <= 1800 mm                                        4 layers

1800 mm > D <= 2250 mm                                        5 layers

2250 mm > D <= 2700 mm                                        6 layers

2700 mm > D <= 3250 mm                                        7 layers

D > 3250 mm                                                               8 layers

Effective depth is calculated as follows,

Example-1

Beam Depth (D)                               = 600 mm

Clear cover (Cc)                               = 25 mm (this includes diameter of link/stirrups/fitment)

Maximum Aggregate 2 Size (M)  = 25 mm

 Assumed Diameter (d1)                 = 20 mm

Number of layers                            = 2 Nos (for 400 mm >=  D <=1200 mm)

Space between two rebars           = if  -- d1 > 2 * M / 3

                                                        Then  d1 is considered

                                                        Else, 2 * M / 3  is considered

In the example considered, 

               20 > 2*25/3

               20 > 16.67mm

Thus, spacing between rebars is 20mm.

& 

Effective depth = D – Cc - d1 – M/2

                              = 600 – 25 – 20 – 20/2

                              = 545 mm

Example-2

Beam Depth (D)                               = 600 mm

Clear cover (Cc)                               = 25 mm (this includes diameter of link/stirrups/fitment)

Maximum Aggregate 2 Size (M)  = 40 mm

Assumed Diameter (d1)                 = 20 mm

Number of layers                            = 2 Nos.

Space between two rebars           = if  --- d1 < 2 * M / 3

                                                        Then  d1

                                                        Else, 2 * M / 3            

In the example considered, 

               20 < 2*40/3

               20 < 26.67mm

Thus, space between rebars is 26.67 mm

 &

Effective depth = D – Cc - d1 – M/2

                              = 600 – 25 – 20 – 26.67/2

                              = 541.665 mm

Thus, if user expects clear spacing between rebars to be 25mm, it is recommended user to provide value of Maximum Aggregate 2 Size (M) equal to 37.5mm. (2 x 37.5 / 3 = 25mm)

31. Why is RCDC taking wind load shears to do ductile detailing for earthquake loads? It should take hogging and sagging moments of receiving frame beams for the earthquake loads and calculate the sway shears for comparison of shear force with the static analysis shear force.

Reply:

As per above sentence all the beams on which seismic forces are applied or the beams that behaves as a part of seismic force resisting system needs to be designed for ductility. But the critical load combination can be any one; which imposes Max Flexure or Max shear on the beam.

So, based on same, when Seismic forces are applied in the analysis file and also when Seismic load cases are selected for design of beams in RCDC, ductility criteria is applied.

Also, there is an option in RCDC where user can select the beams which needs to be designed for Ductility. By default, when ‘Ductile Design’ option is selected from Design settings, RCDC selects all Primary column to column beams to be designed for Ductility criteria.

Going ahead, for shear design of Beams, RCDC follows below mentioned steps:

1. RCDC identifies the ‘Max Shear’ value for the considered beam from all the available load combinations. This happens for Left Mid and Right zone of the beam.
   1. To this max shear, the additional shear due to torsion is added:

Vut = Vu (from analysis) + Vtu (Shear induced due to torsion)

2. Once the Max shear is determined, RCDC will trace the load combination from where Max Shear is found and take it as critical load combination.
3. The sway shear (Vu sway) is calculated as below (as per IS 13920 – 2016).

The simply supported shear is calculated as below for the DL and LL cases independently and added when calculating ductile shear –

V-left = Shear at left end from analysis

V-left-ss (Shear at left end as per simply-supported action) =

= V-left – M-left/L + M-right/L

Calculation of ductile-shear at any section from left to right can be worked out as below -

V-x = Shear at ‘x’ left end from analysis

V-x-ductile = Maximum of (V-x – M-left/L + M-right/L – Sway shear-right), (V-x – M-left/L + M-right/L + Sway shear-left)

4. The final Design Shear i.e. Vud = Max (Vut, Vusway) is used for the shear design of stirrups.

32. Does staad advanced concrete design (RCDC) consider the contributing effects of the slab flanges in RC beam design? I examined the calculation report for some beams and realized  the beams are designed completely as rectangular beams even when you specify them as flange beams.

Reply;

RCDC can design beams with flanged action (T or L). As per design principles of flanged beam, RCDC uses this action only for mid-span bottom reinforcement.

Effective width of flange-action is calculated as per the provisions in code for simply-supported and continuous beams.

Below snip shows difference where same Beam is designed with Flanged action and without Flanged action, using Indian Code as an example.

33. Is there a Customized curtailment provision in RCDC ?

• Each beam is divided and designed at-least at 13 stations i.e. 12 section; along the length of the beam.
• Each section is designed for each load combination to arrive at required areas of longitudinal reinforcement at top and bottom and shear reinforcement.
• Further, the lapping locations are available as per user inputs. Default location for lapping of top reinforcement is L/4. As RCDC design the beam for 12 zones, the options of L/3, L/4 and L/6 are available for lapping at top and bottom reinforcement.  User can choose the lapping location as per design requirements.
  • For any beam under consideration, as the bending moment is parabolic in nature and not a linear one, it is not feasible in RCDC to interpolate the BM "in between the section length". So, the lapping locations provided in RCDC are all multiple of 12 i.e. L/3, L/4 & L/6 ---- where 12 is the number of section in which a beam is divided.
• RCDC provides all the Lapping location as mentioned in SP34 except for L/10 so as to avoid the interpolation of Bending moment in between a section length. 

• At top location, the lapping is provided at curtailment locations. i.e. L/3,L/4 or L/6 distance from column face. Here the distance 2xD is not checked for curtailment. If we start providing curtailments for beams as per the beam depth, it would be complicated. The curtailment location will vary as per the beam depth. The location of curtailments might fall between two stations. Checking reinforcement curtailments at any location as per 2D would not be simple and might not give the desire result. Interpolation of forces is not possible for in between values. Even if we consider on higher side, it would not be consistent to all beams and curtailments will not match the distance 2D for all beams. Also, it is very difficult to handle Ast calculations and shear check location for individual beams.
• For Bottom location, RCDC provides the lapping at face of the beam. The higher diameter rebars extends to lower diameter to make sure that the it satisfies the bending and shear check criteria. Also, the confining of the reinforcement exists up to twice the distance from the column face.
  • If we provide lapping away from the twice the beam depth, it might reach in the middle zone of the beam which is also needs to avoid as it is governed by permanent loads. In this case we might need to handle ductile and Non-ductile beams separately. For ductile beam lapping will place away from the 2D and for Non-ductile it is possible to provide within 2D.

Note that there is an option in RCDC to perform local curtailment by modifying the reinforcement locally for any station of a zone. On the design output window, you can click on the 'Detail' feature and by double click on each zone, you can modify the 'Top reinforcement', 'Bottom reinforcement' & 'Shear reinforcement' also. 

Further, in case you want to use the same reinforcement configuration for other zone by avoiding this step, there is further tool available to 'copy reinforcement' & then 'paste reinforcement' to other beam with same size and same material used for design.

Refer the attached video for understanding how this can be done.

communities.bentley.com/.../2021_2D00_08_2D00_20_5F00_13_2D00_21_2D00_42.mp4

34. What is the purpose of the Ignore Torsion feature available in RCDC Design settings and how does RCDC Consider it while designing any beam with Torsion ?

RCDC reads the design forces from analysis and performs the design based on that. We are not making any changes to force values that we get.

The feature for 'Ignore Torsion' was introduced because many users argued that the torsion value we are getting from analysis may be unreal as effect of the slabs is often ignored in the analysis.

To cater for such cases, we allow users to set a value of torsion, so that while designing RCDC ignores all the values below that value.

If we allow users to 'deduct' any value from the analysis values, that would mean we are tampering with the analysis results for design, which we want to avoid.

We would not be introducing any such feature.

We would suggest using 'Stiffness Modifiers' or 'Member End Releases' appropriately in the analysis to actually release the effect of torsion.

35.RCDC is providing steel for beams in several layers of 12mm dia. for some beams. Instead of using greater diameter of bar and less number of layers, software is providing all layers with T12 bars.

      This scenario happens when we select ductile design for beams. As per IS13920:2016 clause 7.1.1 (a) the largest diameter of longitudinal bar in the beam passing through or anchoring at the column.

In RCDC as we design every element type in different module, this check was not available earlier. In recent updates we have provided this check in beam module. So, now the highest reinforcement dia permissible in beam is not greater than column dimension in the direction of beam spanning /20. So, if the dimension of column is 300mm, maximum allowable bar dia is 300 /20 = 15mm. But as 12mm and 16mm are the diameter available practically, we will use 12mm dia. If you want to use higher diameter rebar then you need to increase the size of column.

36.Asv required for is greater than Asv provided.

Refer to the attached excel sheet and the corresponding Design Calculation Report from RCDC to validate what is explained in the attached excel. 

communities.bentley.com/.../B274-Design-calculation-report-from-RCDC.html

communities.bentley.com/.../Asv-calculation-explanation.xlsx

Is there a Customized curtailment provision in RCDC ?

• Each beam is divided and designed at-least at 13 stations i.e. 12 section; along the length of the beam.
• Each section is designed for each load combination to arrive at required areas of longitudinal reinforcement at top and bottom and shear reinforcement.
• Further, the lapping locations are available as per user inputs. Default location for lapping of top reinforcement is L/4. As RCDC design the beam for 12 zones, the options of L/3, L/4 and L/6 are available for lapping at top and bottom reinforcement.  User can choose the lapping location as per design requirements.
  • For any beam under consideration, as the bending moment is parabolic in nature and not a linear one, it is not feasible in RCDC to interpolate the BM "in between the section length". So, the lapping locations provided in RCDC are all multiple of 12 i.e. L/3, L/4 & L/6 ---- where 12 is the number of section in which a beam is divided.
• RCDC provides all the Lapping location as mentioned in SP34 except for L/10 so as to avoid the interpolation of Bending moment in between a section length. 

• At top location, the lapping is provided at curtailment locations. i.e. L/3,L/4 or L/6 distance from column face. Here the distance 2xD is not checked for curtailment. If we start providing curtailments for beams as per the beam depth, it would be complicated. The curtailment location will vary as per the beam depth. The location of curtailments might fall between two stations. Checking reinforcement curtailments at any location as per 2D would not be simple and might not give the desire result. Interpolation of forces is not possible for in between values. Even if we consider on higher side, it would not be consistent to all beams and curtailments will not match the distance 2D for all beams. Also, it is very difficult to handle Ast calculations and shear check location for individual beams.
• For Bottom location, RCDC provides the lapping at face of the beam. The higher diameter rebars extends to lower diameter to make sure that the it satisfies the bending and shear check criteria. Also, the confining of the reinforcement exists up to twice the distance from the column face.
  • If we provide lapping away from the twice the beam depth, it might reach in the middle zone of the beam which is also needs to avoid as it is governed by permanent loads. In this case we might need to handle ductile and Non-ductile beams separately. For ductile beam lapping will place away from the 2D and for Non-ductile it is possible to provide within 2D.

Note that there is an option in RCDC to perform local curtailment by modifying the reinforcement locally for any station of a zone. On the design output window, you can click on the 'Detail' feature and by double click on each zone, you can modify the 'Top reinforcement', 'Bottom reinforcement' & 'Shear reinforcement' also. 

Further, in case you want to use the same reinforcement configuration for other zone by avoiding this step, there is further tool available to 'copy reinforcement' & then 'paste reinforcement' to other beam with same size and same material used for design.

Refer the attached video for understanding how this can be done.

communities.bentley.com/.../7382.2021_2D00_08_2D00_20_5F00_13_2D00_21_2D00_42.mp4