## ASCE7-02 Table 9.5.2.8 vs Section 9.5.5.7.2

## ASCE7-02 Table 9.5.2.8 vs Section 9.5.5.7.2

(OP)

Hello

I have a 7-story concrete structure with a combined lateral resisting system in the x direction of shear walls and ordinary moment resisting frames.

based on section 9.5.5.7.2 of ASCE 7-02 my thetamax = 0.1

which also happens to be the limit at which you should consider p-delta effects.

My issue stems from the theoretical limit on my inter story deflections now set at hsx/1188-2865, in order to meet a thetamax =0.1, which is considerable higher than the limit from table 9.5.2.8 of hsx/100.

Can anyone provide any guidance on how to procede because as it stands now I am at h/400, considering p-delta, but my stability coeeficient, theta, exceeds theta max by a considerable amount. Is the structure really going to be unstable under these circumstances?

thank you for any help

I have a 7-story concrete structure with a combined lateral resisting system in the x direction of shear walls and ordinary moment resisting frames.

based on section 9.5.5.7.2 of ASCE 7-02 my thetamax = 0.1

which also happens to be the limit at which you should consider p-delta effects.

My issue stems from the theoretical limit on my inter story deflections now set at hsx/1188-2865, in order to meet a thetamax =0.1, which is considerable higher than the limit from table 9.5.2.8 of hsx/100.

Can anyone provide any guidance on how to procede because as it stands now I am at h/400, considering p-delta, but my stability coeeficient, theta, exceeds theta max by a considerable amount. Is the structure really going to be unstable under these circumstances?

thank you for any help

## RE: ASCE7-02 Table 9.5.2.8 vs Section 9.5.5.7.2

hsx/1188-2865

??

Tell us your ratio of Px/Vx and your Cd value.

If you take a Table 9.5.2.8 allowable story drift Δ = 0.01hsx and a Cd = 4.5 (I'm guessing here) and then plug it into the Θ equation:

((Px/Vx)(0.01hsx)) / ((hsx)(4.5)) <= 0.10

The hsx value cancels out and you get:

Px/Vx <= 45

Θmax = 0.5 / (0.8 x 4.5) = 0.139 using β = 0.8

or if Cd = 2.5 then Θmax = 0.25.

According to ASCE 7, yes - if you exceed Θmax you are unstable.

Verify your calculation values.

## RE: ASCE7-02 Table 9.5.2.8 vs Section 9.5.5.7.2

My Px/Vx ratios vary from 119 at the roof to 287 at the lowest level and Cd = 5

## RE: ASCE7-02 Table 9.5.2.8 vs Section 9.5.5.7.2

Those ratios seem to imply you have a very low seismic demand.

## RE: ASCE7-02 Table 9.5.2.8 vs Section 9.5.5.7.2

I am comparing my results with a ram frame analysis and it appears ram frame is only considering the the applied story shear for its theta calcs.

Can anyone confirm that Vx should be the sum as oulined in the first paragraph of this post?

Either way I will need to do further investigation at the very least at my upper levels to make sure beta is such that theta max is higher than theta.

## RE: ASCE7-02 Table 9.5.2.8 vs Section 9.5.5.7.2

## RE: ASCE7-02 Table 9.5.2.8 vs Section 9.5.5.7.2