Cer tain in for ma tion about each response spectrum Load Case is avail able for print ing from the SAP2000 graphi cal in ter face. This in for ma tion is de scribed in the fol -low ing sub top ics.
Damping and Accelerations
The mo dal damp ing and the ground ac cel era tions act ing in each di rec tion are given for every Mode. The damp ing value printed for each Mode is just the speci fied damp ing ra tio, damp, spec i fied for the load case (un less ad vanced damp ing is de -fined for the the model, in which case it will be larger.)
The ac cel era tions printed for each Mode are the ac tual val ues as in ter po lated at the mo dal pe riod from the response- spectrum curves af ter scal ing by the speci fied value of sf. The ac cel era tions are al ways re ferred to the lo cal axes of the spectrum analy sis. They are iden ti fied in the out put as U1, U2, and U3.
Modal Amplitudes
The re sponse-spec trum modal am pli tudes give the mul ti pli ers of the mode shapes that con trib ute to the dis placed shape of the struc ture for each di rec tion of Ac cel er a tion Load. For a given Mode and a given di rec tion of ac cel er a tion, this is the prod uct of the modal par tic i pa tion fac tor and the re sponsespec trum ac cel er a tion, di -vided by the eigenvalue, w2, of the Mode.
This am pli tude, mul ti plied by any modal re sponse quan tity (dis place ment, force, stress, etc.), gives the con tri bu tion of that mode to the value of the same re sponse quan tity re ported for the re sponse-spec trum load case.
The ac cel era tion di rec tions are al ways re ferred to the lo cal axes of the spectrum analy sis. They are iden ti fied in the out put as U1, U2, and U3.
For more in for ma tion:
• See the pre vi ous Sub topic “Damp ing and Ac cel era tion” for the defi ni tion of the response- spectrum ac cel era tions.
• See Topic “Mo dal Analy sis Re sults” (page 73) in this chap ter for the defi ni tion of the mo dal par tici pa tion fac tors and the ei gen val ues.
Base Reactions
The base re ac tions are the to tal forces and mo ments about the global ori gin re quired of the sup ports (re straints and springs) to re sist the in er tia forces due to spectrum load ing. These are printed for each in di vid ual Mode af ter per form ing only di rec tional com bi na tion, and then summed for all Modes af ter per form ing mo -dal com bi na tion and di rec tional com bi na tion.
The re ac tion forces and mo ments are al ways re ferred to the lo cal axes of the response- spectrum analy sis. They are iden ti fied in the out put as F1, F2, F3, M1, M2, and M3.
84 Response-Spectrum Analysis
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90
B
I sec tion, 20
lo cal co or di nate sys tem, 17 ma te rial prop er ties, 17 mo ment of in er tia, 17 pipe sec tion, 20 rect an gu lar sec tion, 20 shape, 18
shear area, 17
shear de for ma tion, 17 solid cir cu lar sec tion, 20 T sec tion, 20
tor sional con stant, 17
T
Truss
see Frame el e ment
Ty po graph i cal con ven tions, 2
92