INFLUENCE OF HIGHER MODES ON THE RESPONSE OF IRREGULAR BUILDINGS SUBJECTED TO NARROW-BAND RECORDS Chapter in Scopus uri icon

abstract

  • Higher-mode effects have been studied during the last decades for purposes that have evolved through time. Initially, these effects were studied so that they could be taken into account within the context of code-based static design methodologies. Two considerations were made: an increase in the lateral force corresponding to the top story; and the formulation of modification factors to raise the tail of the design spectra. This paper presents the results of a study aimed to assess the higher mode effect on the nonlinear dynamic response of an irregular 20-story reinforced concrete (RC) framed building. For this purpose, an analytical model of the building that considers elasto-plastic hysteretic behavior was used, 20 seismic excitations with a dominant period of motion of 1 sec, recorded at the Transitional Zone of Mexico City, were used for the nonlinear dynamic analyses. While the fundamental period of vibration of the building is equal to 3 sec; its second period, is close to 1 sec, this results in that the selected seismic excitations stimulate the participation of the second mode in the overall dynamic response of the building. In terms of the response of the building, it was observed that the method used to scale the ground motions significantly affects the variability along height associated to the dynamic response of the different stories. Then, the circumstances under which the effect of higher modes gives place to an excessive response of the upper stories is identified, and quantitative measures are offered to anticipate these cases. Finally, the analysis cases which show a lengthening of first and/or second building period are discussed and it is concluded that this period lengthening promotes damage in upper and/or lower story levels. © 2024, International Association for Earthquake Engineering. All rights reserved.

publication date

  • January 1, 2024