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(07.18.2012 / 09.11.2012) Bentley - SACS Precede Modeling eSeminar Attendee Questions The SACS Executive eSeminar was hosted in July for users in Americas and Europe, as well as one for our Asia and the Middle East users in September. The following questions and answers are from offerings. You can view the recording online at our BeConnected site (Click (Click Here ). ). The following are the product-related questions and corresponding answers from the eSeminar. 1. Q: What's the difference between adding a weight and adding a load? A: For a static analysis it is the same thing. Using loads gives a force in the Z direction only where as a weight would be in all three directions. Using a weight would be beneficial with other analysis, for example a transportation analysis where the structure is turned on its side or if you will use the model for a dynamic analysis. 2. Q: Does Seastate generate a dead load? A: You can add the dead weight through the seastate load generation feature in precede. 3. Q: How do you apply the wind load? A: A wind load is defined through the seastate load generation box in precede. You would check off the wind box and then input the information you are given for the wind. This load is applied to the structure for the degree you specify. 4. Q: How should we create and define the property for the piles? A: The piles are created when you use the structural definition wizard. The property is to be defined through the Property manage box in precede. 5. Q: What’s the A/B release? A: This is the member end releases at the beginning or end of the member. 6. Q: Can you define soil structure interaction (stiffness) for the foundation elements? A: Yes, through a PSI file, not in Precede. 7. Q: Is it possible to create duplicated du plicated beams? A: You can have the different members with the same group name and same member properties. Also, you can have members with different group names that are the same member type with the same properties. 8. Q: How do you input i nput current speed profile over water depth?
A: You specify the profile in the seastate load generation box. See picture below:
9. Q: Are the piles connected at the intermediate node points? A: Yes, at every joint that ends in “P” is a joint to a pile member. The Piles are divided at the same location as the Jacket Legs. 10. Q: Should the Pile and Legs be created as 2 members? A: Yes, the leg will be one member and the pile will be one member if it is un-grouted. These members will be at the same location and will display on top of each other. If the leg is grouted it will only display one member instead of two.
11. Q: How do you model the connection between conductors and the deck? A: You will connect the conductor to the conductor framing using dummy members. 12. Q: Can you show how space load applied to node. Basically how does it calculate the load? A: The load is distributed out to the joints selected. It gets distributed depending on the distance from the load to the joint (like rigid connection between the load point and the distributed joints).
13. Q: How do you define member offsets? A: There is a member offset option which you could use. Also if you select member- details/modify and select a member you can change the offset through this box. Using Joint- Automatic Design, precede can automatically calculate the brace offsets to the outside of the cords. 14. Q: What depth below the mudline is normally assumed to be fully fixed….ex. clay soil? A: Precede doesn’t do anything regarding soil and pile. This work is done using single pile program.
15. Q: How is self-weight generated? A: All the members input have a density. Precede will then take the amount of steel for each member and multiply that by the density and give the structural self-weight.
16. Q: How many codes are covered in sacs? i.e. API, NORSOK, etc? A: Please open Precede, go to Options/Analysis, all included codes are listed for Code Check Option.
17. Q: Should I put fixities like 222000 in every joint as in the samples? A: For a model created for a static analysis you would not use that. This type of fixity is used for dynamic analysis. It is restrained degrees of freedom. 18. Q: How do we analyze local stresses at the joint assembly? A: After you run the static analysis you can look at the stresses.
19. Q: Could you show me how to define boundary conditions (i.e all fixed, hinged)? A: If you use the structural wizard it will automatically put the fixities at the bottom of the legs as well as the bottom of the conductors. To define fixities you can go to joint/fixity and input it through there.
20. Q: Can you show how equipment load applied to node. Basically how it calculates? A: A skid load is applied to the member as a concentrated load. The skid beams that cross the deck members is the location when the load will be applied. The load is distributed to these points depending on where the load is located.
The following are the product-related questions and corresponding answers from the September 11th eSeminar.
21. Q: Why you did not model wish-bone for pile and leg connection? A: Time did not permit me to show the wishbone modelling but you can add a wishbone between the leg and pile. Use the Wishbone command from the Member menu. 22. Q: I saw you have a card where you can select master and slave? May I know what is this for and how is this affect the analysis please? A: This allows you to simulate the in-plane rigidity of a planar part of the structure. One example would be a deck stiffened by deck plate. If you don’t model the deck plates, the master-slave will ensure all the joints on the deck move as a rigid body and can also improve performance in dynamic analysis. 23. Q: Will the master and slave definition affect the design if we don't define this? A: If the deck plates are not modelled and transverse loads are applied which cause the deck members to deflect, then these deflections will not actually occur in practise. Using the master-slave constraint will give a better result. 24. Q: Where and when should we use Gap elements? A: Gap elements are used to simulate tension or compression only elements or to simulate friction. A common example would be the support for a jacket on a barge which only provide upwards support but can lift off if upwards force is applied. 25. Q: How do we model a Joint Can? A: The thicker portion at the ends of a member which form the joint can should be defined as segments within the member. Give the end segments larger. 26. Q: Is there any option to define offsets with single command? A: Yes. The Offsets command from the Member menu allows you to automatically specify the offset to align top or bottom of steel of adjacent members. You can also define a distance relative to these locations.
