AISC seismic provision

[loveearth]

I am working on design ordinary brace frame steel Building that locate in Seismic category D. I'm using ASD method. AISC require to design all bracing connection to resist full tensile strength of member.
I got some problem on Vertical brace design. Those member are quite big due to compression buckling case. Actual force in Member is not high but design force determined by using Ry x Ag x fy is very high.

For example, the biggest size for Vertical brace is W14x145. This force occured in this member is 500 kips. but we need to design connection to resist 2349 kips (1.1 x 50ksi x 42.7in^2). It couldn't be possible to design connection with this very high load.

Are there any exception for the case that full tensile is significanly higher that actual forces?

 

[whyun]

1997 UBC Section 2213.8.3.1 and 2213.9.3.1 talks about three forces and you design the connection for the least of the three.

1997 AISC Seismic Section 13.3a and 14.3a read similar.

It is often the maximum force that can be delivered to the brace by the system that control the design.

 

[loveearth]

I am using IBC2003 and ASCE 7-02 for model code. I will check in similar section on Monday.

In AISC 341-02, they specified to use full tensile of member to design their connections. This make me in knightmare. I'm not sure if three times of force can be allowed to use as upper limit of design force or not. I will check it.

Thanks,

 

[whyun]

ALso look into the 1999 SEAOC Bluebook (Recommended Lateral Force Requirements and Commentary) Section C704.6.

It gives more detailed information and commentary related to the three force levels described in the AISC and UBC Sections.

 

[loveearth]

Thanks. I talked with my boss. Only IBC 2003 and Aisc 341-02 can be use as reference for this project. Therefore, I need to design those connections with full tensile strength of member.

Thanks again