Study On The Shear Resistant Performance Of RC Columns Subjected To Axial Velocity Pulse-like Ground Motions

Near-fault velocity pulse-like ground motion leads to the serious velocity anddisplacement impact of engineering structures. It makes the shear-resistance capacityof reinforced concrete (RC) column decrease, which leads to shear brittle failure andcollapse in building structures. Employing the nonlinear dynamic time historyanalysis method, this paper studies the effect of the vertical velocity pulse-like groundmotion on the influences of the shear resistance of RC frame columns. Thequantitative expression of the shear-resistance performance of column is obtainedbased on a large number of the nonlinear regression analysis data. The main contentsof the research, as well as the conclusions are as following:1. Based on nonlinear dynamic time history analysis，18velocity pulseearthquake records considering3different near-fault distances in Chi-Chi earthquakeare selected to study the shear-resistant behavior of RC columns subjected to verticalvelocity pulse-like earthquake action. The influences of fault distance, vertical andhorizontal acceleration spectral ratio, as well as initial axial load ratio and shear spanratio on the shear resistant behavior of RC columns are studied. The resultsdemonstrate that near-fault vertical velocity pulse-like ground motion affects greatlythe shear-resistant behavior of RC columns, and the ratio of shear resistance capacityand shear demand decreases with the increasing of the ratio of the accelerationspectrum. Initial axial load ratio and fault distance, and shear span ratio and near faultdistance (0—10km) have coupling influences on the shear-resistant behavior of RCcolumns.2. The bottom columns of RC frame structure are taken as the research object,and the equivalent velocity pulse excitations are chosen to study the effects ofhorizontal and vertical velocity pulse-like excitations on shear behavior of concretecolumns, based on the time history analysis. Vertical-to-horizontal peak accelerationratio, arrival time interval of peak acceleration between vertical and horizontalexcitations, initial axial load ratio, shear span ratio, as well as fundamental periods onthe effects of both shear demand and shear-resistant capacity are studied. The resultsdemonstrate that shear demand of RC columns increases with the increasing of theintensity of velocity pulse, and shear-resistant capacity decrease with increasingvertical-to-horizontal peak acceleration ratio. Arrival time interval between verticaland horizontal excitations has an important influence on the most unfavorable shear behavior of concrete frame columns. With the increasing of shear span ratio, velocitypulse-like excitations have more influence on the shear-resistance behavior of RCframes columns.3. By the multiple nonlinear regression analysis on a large number of analyticaldata, the expression of shear-resistance behavior is established to provide effectivereference for seismic engineering, which considers the influence of both near-faultvelocity pulse ground motion and coupling factors.