1. Since the STAAD Offshore loads already include a static component should the static (gravity) loads in the STAAD Pro load combinations be excluded when analysing for  transportation cases?
2. Can we specify Marine Growth above the Still Water Level in STAAD.Offshore?
3. When I generate the STAAD file with wave loads using the STAAD.Offshore module, the file throws up errors while opening in STAAD.Pro and the Wave Load Cases are messed up.
4. I have specified the added mass coefficient and the drag coefficient as zero. However, STAAD is still generating Wave Loads in the Vertical direction.
5. When I try to open my staad.pro model in offshore, I receive the error: “Structure file has syntax errors. check the <filename>.err file for reasons”. What is the cause of this error ?
6.  I added a section to the STAAD.Pro section database and used it in my model. Now I am trying to open the STAAD.Pro model in STAAD.Offshore and I am getting error messages saying “structure file has syntax errors”. How do I get Offshore to recognize my defined sections ?
7. Is it possible to specify the heave + roll and heave –roll in the same load case?

1.Regarding the Transportation module in STAAD Offshore, there is a Gravity/Tilt option on the Transport Definition/General page. When this is turned on it appears that STAAD Offshore generates static load components in the vertical and horizontal directions based on the tilted position of the structure on the ship. These static components are included in the overall inertia loads and transferred into STAAD Pro. Our question is: since the STAAD Offshore loads already include a static component should the static (gravity) loads in the STAAD Pro load combinations be excluded when analysing for  transportation cases? If they are included it appears that we are "double-dipping" on the static loads and resultant vertical loads are too high.

When you are analyzing with the transport loads in STAAD.Pro, you need not consider the self-weight loads separately in the load combinations because you have already considered the inertia force due to acceleration due to gravity in the STAAD.Offshore Module, which is the selfweight of the structure. This is in addition to the inertia force generated due to acceleration of the barge on which the structure is being transported.

2. Can we specify Marine Growth above the Still Water Level in STAAD.Offshore?

No, we cannot. As per the API code clause 1.3.8, the Marine Growth is the most near the Mean Water Level but can be significant 200 feet or below the Mean Sea Level. The STAAD.Offshore is designed to take the marine growth data at and below the Still Water Level.

3. When I generate the STAAD file with wave loads using the STAAD.Offshore module, the file throws up errors while opening in STAAD.Pro and the Wave Load Cases are messed up.

This is most likely due to the fact that you have specified the first wave load case number such that either that case number or the subsequent wave load case numbers match with primary or combination load case numbers in the original file. If this is the reason then you need to specify the wave load case number in such a way that there is no duplication.

4. I have specified the added mass coefficient and the drag coefficient as zero. However, STAAD is still generating Wave Loads in the Vertical direction.

The answer to your question as to why the wave loads are generated inspite of the drag and the added mass coefficients defined as zero is inherent in the Morison’s equation. If you look into the Morison’s equation, you will see the following:

Here,  C_m= Inertia coefficient = 1 + C_a

               C_a =Added Mass Coefficient

          C_d = Drag Coefficient

The first term on the right side of the equation is the inertial force and the second term is the drag force.

The inertia force is again the sum of Froude-Krylov Force and Hydrodynamic Mass Force. Expressing the Morison’s equation in these terms, we have the following:

The first term on the right hand side of the equation above is the Froude-Krylov Force and is not dependent on the added mass coefficient and the drag coefficient. So, even if you specify the added mass coefficient and the drag coefficient as zero, it is not necessary that the Force will be zero.

Also you have specified a 0 degree wave, the fluid particle acceleration is only in the vertical direction. Hence, we will have the force in the vertical direction of the structure.

5. When I try to open my staad.pro model in offshore, I receive the error: “Structure file has syntax errors. check the <filename>.err file for reasons”. What is the cause of this error ?

The error indicates that there is some problem in the command input in the .std that you are trying to open. A (filename).err file is created inside the same folder from where you are trying to open the .std file. This file can be opened using Wordpad or notepad and should indicate specifically where the software is failing to read the input.

6. I added a section to the STAAD.Pro section database and used it in my model. Now I am trying to open the STAAD.Pro model in STAAD.Offshore and I am getting error messages saying “structure file has syntax errors”. How do I get Offshore to recognize my defined sections ?

When you add a section to the STAAD.pro section database, it gets added to the mdb file corresponding to that country database. For example if you added a section to the American Section database, this data would be added to the AISCSections.mdb file. These mdb files can be found within the X:\SProV8i\STAAD\Sections folder where X represents the local drive in which STAAD.Pro is installed. You need select the appropriate mdb and copy it to the folder C:\Users\(user name)\AppData\Roaming\Bentley\OpenSTAADOEM\Sections from where Offshore reads the sections. There would be an existing file by the same name and that file needs to be replaced by the file you are trying to copy. You would then be able to open the file in STAAD.Offshore.

It is better to have STAAD.Pro and STAAD.Offshore closed when you do these external file transfers. Moreover it is always a good idea to keep a backup whenever you are trying to replace or modify any standard mdbs.

7. Is it possible to specify the heave + roll and heave –
roll in the same load case?

You cannot create heave + roll and heave – roll in the same load group. You need to create two different groups with the directional factor as + 1 for heave + roll case and -1 for heave – roll case.

In the STAAD file however, you can manually edit the load cases two specify all the load items in the same load case – however, doing that you run the risk of under estimating the inertial forces.

 8. What does the message “The section Type PIPE/TUBE/OPEN/PRISMATIC cannot be established for some members. These members have been shown in red. The property table contents of these members will also be shown in red.” means while opening the STAAD.Pro model in STAAD.Offshore and how does this affect?

If you are using a transportation module, the aforementioned message does not make a difference as only the lumped masses are used for calculation of inertial forces. But it does affect in case the Wave Loading module is used. The Wave loading is calculated using the shapes of the members. Currently the STAAD.Offshore program is able to account for the following sections only:

1- Pipe, 2- Rectangle hollow (including square hollow), 3- Wide flange or Channel, 4- Rectangular Solid and 5- Circular solid

If the STAAD.Pro model has sections other than the aforementioned ones, their shapes wil not be accounted for leading to an erroneous calculation of wave loads.