Steel Stair Seismic Design

[courtnvm]

I have a project that I will be submitting calculations on. I have a typical straight parallel steel stair with 2" filled concrete pans and 3" concrete landings. I am required to design the steel tower for seismic load effects. I have all the design criteria for Ss and S1, etc. The project is under the 2000 IBC.

My difficulty is finding the correct design procedure under the code for steel stairs. I don't think they really classify to be calculated under section 1617 (Earthquake Loads-Minimum Design Lateral Force and Related Effects).

It seems like you could calculate the forces under section 9.6 of the ASCE7-02 (Architectural, Mechanical, and Electrical Components and Systems), but it seems that this section is for more isolated cases rather than a stair tower.

Furthermore, it appears that the steel stair tower could be designed under section 9.14 of the ASCE7-02 (NonBuilding Structures), but which category does the steel stairs belong to.

Does anyone have experience/advice on this topic? Any help would be appreciated.

Also, is there special connection considerations that must be accounted for?

Thank You,
Val

 

[JAE]

I would design stairs under 1621. This gives you an Fp value which then is used for Q_E for section 1617.1 with [ρ] = 1

Read through the entire text of 1621.1.4 (IBC 2000) and especially the last few paragraphs.

For stairs, the difficulty is determining an R_p and an a_p. For metal stairs, perhaps a flexible component with both values = 2.5.

 

[courtnvm]

Thanks JAE. I was talking to an engineering buddy of mine and he thought it would also be acceptable to design the steel stairs under section 1620.1.4. This section gives an Fp for a smaller portion of the structure, which should be transferred into the main structure. I could see how 1621 could be used. Its not real cut and dry for sure. I might go with 1621 because it seems to be more conservative.

Val