Load Combination

[monchie]

I am modelling a 30 story building(rectangular shape) with the following static load cases;
DL 1,LL 0, WINDY 0 and Load Combination(SLS) COMB4(DL + WINDY) COMB5(DL + 0.5LL +WINDY)

But when I check the max. point displacement(@ 30th floor), I noticed that load case WINDY, COMB4 & COMB5 have almost the same value of 160 mm!What I have in mind is that COMB4 is similar to load case WINDY(Does ETABS consider automatically the self weight of the building when finding the displacement for WINDY<windy+DL>?)

Also, why COMB5 yields the same result with both WINDY and COMB4 when additional load of 0.5LL(LL=2.5 kN/m2) was added to retard the displacement. Did I miss something here?Can somebody help me on this?

 

[slickdeals]

I don't think your gravity load will have much influence on your lateral displacement, unless your structure has a tendency to "lean" under gravity loading. So for a very symmetric structure, your gravity load contribution to lateral deflection will be very small, almost negligible.