Sir,
I am a structural designer in Oil Field equipment. I design land oil rigs. I have couple of doubts. The entire Mast section is manufactured in segments due to transport constraint and assembled at site by use of PIN joints. How do I model this junction? The entire structure is placed on the concrete foundation. How to resemble this in the model? I have attached my model and couple of photographs as to how it looks. Kindly enlighten me. I would appreciate a reply from those who are familiar with API 4F and similar structures. Thank you in advance. Mast_Vertical_AC Rigs_AISC_ASD.stdgn product with API 4F standard.
Hi,
Here are some suggestions for your queries:
How do I model this junction?
You can use Member Release option from General > Specs > Beam. To simulate a pinned connection you may release or partially release in MY and MZ at the member ends. As these parameter are in respect to local axis of the member, MX should not be released as this would mean that it is allowed to rotate about its own axis.
How to resemble this in the model?
Though you are stating that the entire structure is supported by concrete foundation but in your model pinned supports are used. This depends on how you are connecting your member with concrete foundation. Some of the questions here: Base plate connection? No. of bolts? etc. On the other hand to model concrete foundation, you can use Mat Support option from General > Support > Create > Foundation but this would mean that all your members are fixedly supported with concrete foundation.
Thank you Mr. Kush for your reply.
As I said, the complete structure just rests on the concrete floor. No firm joint with bolts to the concrete floor. By virtue of its own dead weight, loads are transferred to the floor. The bottom section consists of 2 wide flanges beams placed side by side and connected by cross members, which directly rests on the concrete floor. How do I model support for such type. Also let me know if you are familiar with API-4F specification so that I can ask some more queries. And if I give offset to any of the members to resemble actual situation, will the model analyse the members with the centre lines connected or according to offset?
Let say I have analysed my model and I got failure ratios more than one. Is ht e motto of designer is to see that all the members ratio falls below 1?
I have the following queries w.r.t API-4F specification:
1. What are the differences between PSL1 and PSL2 as far as API-4F is concerned?
2. Are structures classified according to their SSL's specified according to wind speed only?
3. What is meant by " As applicable" in design loadings section (Table 7) of cases 3a, 4 and 5
4. Does it mean to do all the design calculations manually according to cl. 8.3.3 Member by Member method? We do all the design in Staad Pro. only. Only few members are manually checked for their cross section. Cl. 11.8.2 says use FEM only for Design verification. What does this mean?
5. Cl. 8.4 Dynamic loads applicable only for Offshore rigs?