Effect of bidirectional excitation on seismic performance of regular RC frame buildings designed for modern codes

Abstract

The existing practice to estimate seismic performance of a regular building is to carry out nonlinear time history analysis using two-dimensional models subjected to unidirectional excitations, even though the multiple components of ground motion can affect the seismic response, significantly. During seismic shaking, columns are invariably subjected to bending in two orthogonal vertical planes, which leads to a complex interaction of axial force with the biaxial bending moments. This article compares the seismic performance of regular and symmetric RC moment frame buildings for unidirectional and bidirectional ground motions. The buildings are designed and detailed according to the Indian codes, which are at par with the other modern seismic codes. A fiber-hinge model, duly calibrated with the biaxial experimental results, is utilized to simulate the inelastic behavior of columns under bidirectional bending. A comparison of the estimated seismic collapse capacity is presented, illustrating the importance of considering the bidirectional effects. The results from fragility analysis indicate that the failure probabilities of buildings under the bidirectional excitation are significantly higher as compared to those obtained under the unidirectional excitation.

Seismic vulnerability of reinforced concrete buildings with discontinuity in columns

“…A column is considered to have reached significant damage state if the strain in any of the reinforcement fibers exceeds 0.050 in tension or 0.025 in compression. These are the average strain values observed in the extreme fibers of steel reinforcement at the ultimate drift in the columns considered in the calibration study by Gwalani et al 32 …”

“…The effect of cyclic strength and stiffness deterioration is considered in the materials using energy based "concrete" hysteresis model and "degrading" hysteresis model for concrete and steel reinforcement, respectively. The parameters of these material hysteresis models have been calibrated against experimental results on columns subjected to bidirectional earthquake loading in a previous study by Gwalani et al 32 The same parameters (f = 0.90, f 1 = 1, f 2 = 0.90, and s = 1) are used in the present study. Two damage limits are used to identify the state of columns in nonlinear analysis, that is, yield and significant damage.…”

“…However, during an earthquake, columns of a building are subjected to variable axial force demand and biaxial bending moment. The need to consider the effect of bidirectional excitation on the seismic response of columns has been highlighted in several past studies 28–32 . This effect may be even more pronounced in case of buildings with discontinuous columns.…”

“…The need to consider the effect of bidirectional excitation on the seismic response of columns has been highlighted in several past studies. [28][29][30][31][32] This effect may be even more pronounced in case of buildings with discontinuous columns. Further, the application of the vertical component of ground motion significantly affects the axial load demand in columns.…”

Bi-axially Loaded RC Beam-Column Joints and Haunch Retrofit

“…columns (e.g. the most recent five works, to the Authors' knowledge, are Lucchini et al (2022); Gwalani et al (2021); Salami et al (2021); Zhang and Tao (2021); Opabola et al (2020)), shear walls (e.g. the most recent five works, to the Authors' knowledge, are Wang et al (2023Wang et al ( , 2022; Niroomandi et al (2021); Behrouzi et al (2020); Beyer et al (2008)).…”