Abstract
The design philosophy of a strong-column weak-beam (SCWB), commonly used in seismic design codes for reinforced concrete (RC) moment-resisting frame structures, permits plastic deformation in beams while keeping columns elastic. SCWB frames are designed according to beam-to-column flexural capacity ratio requirements in order to ensure the beam-hinge mechanism during large earthquakes and without considering the influence of the beam-to-column stiffness ratio on the failure modes of global structures. The beam-to-column linear stiffness ratio is a comprehensive indicator of flexural stiffness, story height, and span. This study proposes limit values for different aseismic grades based on a governing equation deduced from the perspective of member ductility. The mathematical expression shows that the structural yielding mechanism strongly depends on parameters such as material strength, section size, reinforcement ratio, and axial compression ratio. The beam-hinge mechanism can be achieved if the actual beam-to-column linear stiffness ratio is smaller than the recommended limit values. Two 1/3-scale models of 3-bay, 3-story RC frames were constructed and tested under low reversed cyclic loading to verify the theoretical analysis and investigate the influence of the beam-to-column linear stiffness ratio on the structural failure patterns. A series of nonlinear dynamic analyses were conducted on the numerical models, both nonconforming and conforming to the beam-to-column linear stiffness ratio limit values. The test results indicated that seismic damage tends to occur at the columns in structures with larger beam-to-column linear stiffness ratios, which inhibits the energy dissipation. The dynamic analysis suggests that considering the beam-to-column linear stiffness ratio during the design of structures leads to a transition from a column-hinge mechanism to a beam-hinge mechanism.
Highlights
Reinforced concrete (RC) frames are the most widely used structural systems for multistory industrial and civil buildings around the world
E design philosophy of strong-column weak-beam (SCWB) is applied to ensure that the sum of the ultimate flexural capacity of all columns should be larger than that of the beams at the beam-to-column joints locally. is requirement can be expressed as ΣMuc/ΣMub>ηamp, where Muc and Mub represent the ultimate flexural capacity of the columns and beams, respectively, and ηamp represents the amplification factor, which varies from code to code
There are no specific provisions for the beam-to-column linear stiffness ratio in the seismic design of RC frame buildings. e beam-to-column linear stiffness ratio could reflect the variation of flexural stiffness, story height, and span comprehensively and have significant effects on the seismic behavior of RC frame structures. e main objective of this study is to investigate the influence of the beam-to-column linear stiffness ratio on the failure modes of RC frame structures
Summary
Reinforced concrete (RC) frames are the most widely used structural systems for multistory industrial and civil buildings around the world. Numerous studies have shown that these seismic design code provisions may not be adequate to prevent the column-hinge mechanism; that is, the demand values of the SCWB ratio are usually larger than the code specifications. Dooley and Bracci [8] compared the seismic response of 3- and 6-story RC frame structures with different SCWB ratios varying from 0.8 to 2.4 and found that a minimum strength ratio of 2.0 was effective to prevent the column-hinge mechanism. Ibarra and Krawinkler [11] studied the seismic behavior of 9- and 18story RC frame buildings and suggested that a SCWB ratio of 3.0 was needed to prevent the column-hinge mechanism. A governing equation for controlling the structural yielding mechanism is deduced considering member ductility, and various limit values of beam-to-column linear stiffness ratio are suggested for different aseismic grades. Plastic hinge distribution and component plastic deformation are compared to highlight the significance of the beam-to-column linear stiffness ratio
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