Bending Moment diagram for response spectrum loading

A portal frame was analysed by equivalent Static load and Response spectrum method. My doubt is that a. The Bending moment diagram for the static load method is different from that of the response spectrum method. Why is it so? b. Is there any error in my application of response spectrum load, if so, how it is to be corrected. I request your kind attention on the above issue please, awaiting your kind replies urgently.”

NIHESH.N Sat, Apr 25 2009 4:48 PM
Please go through the attached word file. I hope this helps.
Negative value of Force at member end in a Response Spectrum Analysis.zip
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Ambrish Wed, Apr 29 2009 10:01 AM in reply to NIHESH.N

Thank you very much Mr. Nihesh Response spectrum analysis gives absolute values of forces and moments. that is ok. The BMD for response spectrum case does not change the sign at the midspan of beam as all the values are positive. Thus, beam and column support moments are obtained correctly by using + and - sign in load combinations but the values at midspan of beams can not be directly used in design as it is also getting added and subtracted. In reality, for lateral load case, the midspan moment in beams is nearly zero. How to take care of this during the combination of loads, to obtain actual span moments. awaiting your reply with warmest regards Ambrish
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