What ap/Rp would you use for a suspended catwalk with lateral bracing?

[TDIengineer]

The catwalk is suspended from a steel structure with tube hangers with lateral bracing at about 7'-6" above the catwalk elevation.

Catwalk will have C6x stringers at 5'-0" o.c. with 1/4" diamond steel plate and L2x2 @ 30"o.c.

Code = ASCE 7-05.

Previous engineer used a ratio of 1/2.5.. I am thinking this is more of a flexible component with high deformability and use 2.5 / 3.5.
I believe the fundamental period of the braced structure needs to be less than 0.07 seconds to be considered "rigid" and I don't think this layout would be rigid, therefore and ap value of 1.0 may not be appropriate.

I would prefer tho to use the lower coefficient and let this element be very flexible as deflection isn't really an issue. So I am torn...

 

[TDIengineer]

Any seismic engineers out there?

 

[SAIL3]

this is an engineering judgement call....it being a suspended walkway, the issue of safety would influence my decision and would tend to go with the more consevative value...anyway, the difference between the two values is not that significant....I certainly would pay special attention to the connection of the walkway to the main structure...

 

[wannabeSE]

I might be inclined to be even more conservative. The catwalk is hanging with a brace half way between the catwalk deck and the structure above. I might use a_p=2.5 and R_p=2.5 (or shave down the load a little by using a_p=2.5 and R_p=2.5 for everything below the brace and a_p=1 and R_p=2.5 for everything at the brace and above). Perhaps I am too conservative, but it may act similar to other things in the table with the same factors (cantilevered elements, appendages, and signs). Maybe, a_p=2.5 and R_p=3.5 is a good compromise. But, how much cost is added with the more conservative loading.

I don't know what your loads are. But assume F_p=2W_p, W_p=100 plf and brace spacing at 40', the horizontal force is only 8 kips. That is less than 12 kips axial load into the HSS 4x4 brace.

 

[wannabeSE]

Oopps - double the brace force because it is half way up the hanger.

 

[TDIengineer]

Thank you guys for the response. I agree I will use a higher design load.