huangyhg

how to select the seismic response coefficient (cs) in asce/
hi all
i have been implementing seismic analysis following asce7/sei 7-05 and i meet a big confusion these days when i plan to calculate the equivalent lateral force procedure base shear to scale design values of combined response for modal response spectrum analysis (section 12.9 of asce/sei 7-05).
according to section 12.8.1.1 of asce/sei 7-05 (page 129) we can get this relationship shown in the following:
when t<=tl,s1>=0.6g
0.5s1/(r/i)<=cs<=sd1/t/(r/i);cs=sds/(r/i)
now we have a project:
ss=1.981;s1=0.926;sds =1.32;sd1 =0.93:r=1.5;i=1.0;t=2.807s;tl=8s
so we can get these following results:
0.5s1/(r/i)=0.5*0.926/(1.5/1)=0.309
sds/(r/i)=1.32/(1.5/1)=0.88
sd1/t/(r/i)=0.93/2.807/(1.5/1)=0.221
that means csmax <csmin,it is very clear that there is a conflict.0.5s1/(r/i)=0.309<cs=0.88>sd1/t/(r/i)=0.221
then i am confused which number should select for cs,0.221? or 0.309?
this is an urgent project for me.could you please help me clarify this confusion? i am very appreciated for your quick reply!
br
henry

my interpretation is the following:
cs is the minimum value of 12.8-2 and 12.8-3(or 12.8-4). but in addition where s1>0.6, cs cannot be less than 12.8-6.
so in your case 12.8-6 would govern.

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