- 1. Does RCDC design the irregular slab like L, T shapes and slab having more than four edges?
- Yes. Rectangular and odd shaped slabs can be designed in RCDC. RCDC designs the two way and irregular slab based on yield line theory. For odd shaped slab RCDC considers the largest span as shorter direction for design. For Aspect ratio (L/B) RCDC considers the outer-most dimensions of the irregular slab. As per the aspect ratio of irregular slab it identifies whether the slab is one way or two way. For design using ACI, the two way and irregular slab are based on direct design method. For more information refer “Technical Discussion” of slab from help Content.
- 2. For square/rectangular panels of slab, can RCDC transfer the load to two adjacent edges (beams) only as per user choice?
- No. RCDC designs the slab as per relevant clauses and based on explanation provided in relevant codes. RCDC automatically identifies continuity based on the edge conditions. User can change end conditions as per requirements. User can change the type of slab like one way or two way as per choice. RCDC will design the slab accordingly. For more information refer “Technical Discussion” of slab from help Content.
- 3. RCDC is considering some slabs as cut-outs but actually we have modelled those slab instead of cut-outs in E-tabs.
- In E-tabs, sometimes user models single membrane or shell for many number of slabs combined in one large entity. Thus in this case, individual slabs bounded by beams can’t be read by RCDC. For more information refer “Slab auto-detection” of slab from help Content.
- 4. Tensile factor for deflection of slabs is limited to 2.0 in IS 456 but RCDC provides value 2.26 in the design calculations. Please clarify.
- Calculation of tensile factor is based on the formulation available in SP24 clause 22.2.1. IS 456 has provided the graph up to value 2.0 but it is not restricted as far as formulation is concerned. Higher values can be considered in design to control the deflection.
5. Which method is used for Two way slab design in ACI 318 (Metric and English) code available in RCDC?
RCDC has used Direct design method available in ACI code.
- 6. We are designing slab in RCDC but some slab portion is not considered for design which are shown by black screen between slab.
Reply:
RCDC identifies the slab based on closed polygons. The close polygons are identified based on the periphery beams.
In your case, beams B13 and B29 are overlaps each other. Due to overlapping of beams there are no close polygons are identified.
We would suggest you intersect these beams as shown below. This will not impact analysis of the structure.
After intersecting the beams, RCDC is now able to read the slab properly,
7. There is a form in RCDC (IS 456) slab design to input the permissible limit of l/d ratio for two-way slabs. (With defaults as 28 for SS and 32 for continuous.). However, these values are not valid if the loading class in more than 3 kPa and spans up to 3.5 m. Please clarify.
Reply:
RCDC is a design software. the recommended values of L/D are available in design settings. i.e. for Two way simply supported slab it is 35 x 0.8 = 28 and for continuous slab it is 40 x 0.8 = 32. refer below snap from IS code.
please note that option of changing the L/D factors are available in software as per user requirements. we understand that the above ratio available in code has certain limitation of span and loadings. thus L/D ratio are available to modify by user. User can take the decision on the same and proceed with the design. it is always a user choice to select the L/D ratio which suits the design.