Studying the Effect of Earthquake Excitation Angle on the Internal Forces of Steel Building’s Elements by Using Nonlinear Time History Analyses

Abstract eng:
It has been claimed by many researchers that the direction of dominant excitation might be none of the main directions of the building axes. However, the researches performed in this regard are mostly limited to buildings with elastic behavior. In this paper two 5-story steel buildings with moment frames, one with square and the other with rectangular plan, have been designed base on the seismic design code for steel buildings, and then have been analyzed by a Nonlinear Time History Analysis (NLTHA) program using simultaneously the accelerograms of two horizontal components of some earthquakes. The used earthquakes are almost of the same PGA level, but have different frequency contents. A set of values from 0 to 90 degrees, with an increment of 10 degrees, have been used for angle of excitation. Buildings’ columns have been divided into three main categories, including corner, side, and internal columns, and axial force and bending moment values in different columns, and moment values in girders, as well as the total base shear forces of the buildings, have been investigated in all cases. The results show that the columns’ axial forces may exceed the ordinary cases up to 50% by varying the angle of excitation, and that this variation is more in buildings with rectangular plans. Furthermore, each column gets its maximum axial force with a specific angle of excitation, which is not 0 or 90 necessarily, and is different from column to column, and that specific angle is not the same for different earthquakes.

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