Research On Shear Behavior Of RC Frame Structures Subjected To Horizontal And Vertical Ground Motion

Comparing to the far-field ground motions, the near-field ground motions aremuch complex. For its significant pulse ingredient and strong vertical component,bulking damage or shear failure can easily occur in the RC column, which maybeleads to the structural brittle collapse. To investigate the mechanism of seismicbehavior degeneration and the storey pancake collapse of the structure, thedistribution mode of axial force for RC frame column, as well as the shear behavior ofthe RC frame beam and column subjected to the coupled horizontal and verticalground motions, ia studied by dynamic analysis. The major research and conclusionsin this paper are as follows:1. Employing a10-storey3-span planar RC frame as the analytical objective, thedynamic history analyses are performed to investigate the distribution mode of theincremental axial force of the frame column under coupled horizontal and groundmotions. The results show that the compression force of column can be2~3times ofthe initial static force due to the strong vertical ground motions, and it can also resultin tension forces for the columns. Generally, the maximal tension force occurs in theupper story for the interior columns and in the lower story for the exterior columns.The vertical ground motion has greater effects on the exterior frame columns and theupper columns of structure. The frequency content of the vertical excitation hasimportant effects on the column axial force; the vertical earthquake analysis using thescaled horizontal ground motions recommended in current seismic codes shallunder-estimate the effect of vertical excitation.2. Taking a4-storey large-span frame structures as the research objects, usingthe orthogonal design method, the influence of the PGA ratio (the ratio of the verticalto horizontal peak acceleration), shear span ratio, structural vertical vibration periodand initial axial compression ratio on the shear behavior of the RC frame beams andcolumns for the frame structure subjected to coupled horizontal and vertical groundmotion are studied. The results show that the shear resistant behavior factors of thebeam and column decreases with the increase of the PGA ratio. The factors of thebeam and column increase first then decrease with the increase in the shear span ratio,and the peak values occur when the shear span ratio is3.0. The increase of thestructural vibration period can significantly weaken the shear resistant behavior of thebeam and column. Both of the factor of the beam and column increase first thendecrease with the increase in the initial compression ratio, while the peak value factor for the beam and column occur when the initial compression ratio are0.45and0.40,respectively. For the frame structure subjected to horizontal and vertical groundmotion, the columns can experience shear failure prior to the beams, which belongs tostrong-beam and weak-column failure mode.