摘要
理论研究与震害经验表明,地震时地面运动和结构的反应均是复杂的多维运动。目前有关涉及结构非线性地震反应的研究中,地震动主要是沿着结构的主轴单向输入和沿结构主轴双向输入,这显然是一种特殊情况。实际上,更为普遍的情况是地面运动可以沿建筑物的任意一个水平方向输入。因此,地震波以何种角度输入对结构地震反应的影响最不利是有待澄清的问题。
本文利用严格按照我国规范GB50010-2002和GB50011-2001设计的三个典型钢筋混凝土空间框架,在非线性动力分析平台OpenSees上对空间框架进行了多条地震动(单向)不同输入角度下罕遇地震作用的非线性反应分析。主要考察地震波不同输入角度对空间框架顶点位移、层间位移以及层间位移角分布的影响,且重点研究对空间框架塑性铰分布规律,包括杆端纤维应变、塑性铰的分布、塑性铰转动以及结构延性需求的影响。
通过以上分析,本文得出了以下主要结论:从整体反应来看,九度(0.4g)区空间框架的顶点最大位移和层间位移角,地震波(从0度至180度)以15度的增量变化输入,沿结构主轴方向输入时最大,另一主轴方向接近于零,输入角度从0度至90度变化时,结构的纵轴方向依次成递减趋势,横轴方向依次成递增趋势,105度至180度输入时的规律与0度至90类似。8度(0.2g)区和七度(0.1g)区空间框架的顶点最大位移和层间位移角的规律与九度(0.4g)区类似。
从局部反应来看,九度(0.4g)区空间框架的梁、柱塑性铰分布规律是,从0度至90度梁、柱铰在纵轴方向数量上逐渐减少、转动大小也在减小;在横轴方向数量上逐渐增加、转动大小也在增大。其中45度方向输入时,梁、柱端塑性铰在两个主轴方向的出铰数量、转动大小均较为均衡,且数量变化不大。从层累积转角和转角延性需求看, 0度和15度方向输入时框架梁的损伤明显大于框架柱,这表明是以梁铰为主的耗能机制。30度和45度方向输入时框架梁、柱的损伤基本相当,尤其是45度方向输入时框架梁、柱的损伤更为接近,形成了梁柱铰均衡地参与塑形耗能的状态。60度至90度方向输入时框架梁的损伤明显大于框架柱,也是以梁铰为主的耗能机制。90度至180度则与0度至90度规律类似。
八度(0.2g)区空间框架的梁、柱塑性铰分布规律与九度(0.4g)区类似,层累积转角和转角延性需求,各框架柱的层累积转角显著大于框架梁,表明框架柱沿层的损伤要比框架梁严重的多。各框架柱的延性需求远大于框架梁。其中45度方向输入时完全以柱端塑形耗能的方式抗震,其耗能方式仍然较0度和90度方向输入时更为不利。
七度(0.1g)区空间框架,0度、45度和90度方向输入时均以柱端出铰为主,且数量都很少,梁端基本没有出铰。各框架柱的层累积转角只有在个别楼层大于框架梁层累积转角,总体上框架柱和框架梁沿层的损伤均很小。
It is indicated by theoretical research and damage experience that the ground motion and the reaction of the structure under seismic action are both complex multi-dimensional. At present, in the area of researching the nonlinear seismic response of the structure, the main transmitting orientation is along the principal axis, including the unidirectional input and bidirectional input along the principal axises of the structure, however, this is just a special case. In fact, a more common case is that the input direction of the ground motion would along any horizontal direction of the building. Consequently, there arises a problem, which should be clarified, is that what angle of the seismic wave should input would do the most harmful influence to the structure.
In this thesis, the author utilized three typical reinforced concrete spatial frames, which were strictly designed according to the code for concrete structure design (GB50010-2002) and the code for seismic design of buildings (GB50011-2001), and then completed the nonlinear response analysis of the spatial frames suffering from several seismic emotions (unidirectional) from different angles under rare earthquake in the nonlinear dynamic analysis platform named OpenSees. The chief investigations are the top displacement, inner-story drift and the distribution of story lateral displacement of the spatial frame under seismic wave from different enter angles. And the main point is the influence to the plastic hinge distribution law, for instance, the fibre strain of the member ends, the plastic hinge distribution, the plastic hinge rotation value and the ductility demand of the structure.
Several conclusions can be achieved through the above analyses,
In the global response, the topmost displacement and inner-story drift ratio of the spatial frames in Intensity Region 9(0.4g) are as following: With the seismic wave’s input angle increment of 15°(from 0°to 180°), the values reach the maximum when the wave input along the principal axis while the values are close to zero along another principal axis. When the input angles change from 0°to 90°, the values along the vertical axis decrease progressively while increasing progressively along the horizontal axis, as well as the input angles change from 105°to 180°. The laws for the topmost displacement and inner-story drift ratio of the spatial frames in Intensity Region 8(0.2g) are similar with the above.
In the local response, the laws of beam hinges and column hinges of the spatial frames in Intensity Region 9(0.4g) are as following: From 0°to 90°, the number and rotation values of beam hinges and column hinges decrease progressively along the vertical axis while increasing progressively along the horizontal axis. Among them, with the input angle of 45°, either the number or rotation values of the beam hinges and column hinges reach balance within little change in amount. The story accumulated rotation angle and the ductility demand of the rotation angle, with the input angles of 0°and 15°, the damage of the frame beams are greater than frame columns obviously, which indicates that the major energy dissipation mechanism is based on beam hinges. The damage of frame beams and columns are quite the same with the input angles of 30°and 45°, especially in the case of 45°, which shows the status of beam hinges and column hinges involving in the dissipation mechanism evenly. From input angles of 60°to 90°, the damage of the frame beams are greater than frame columns, which indicates that the major energy dissipation mechanism is based on beam hinges too. The law is the same as the above with the input angles from 90°to 180°.
The distribution laws of beam hinges and column hinges of spatial frames in Intensity Region 8(0.2g) are similar to that in Intensity Region 9(0.4g). For the story accumulated rotation angles and the ductility demand of the rotation angles, the story accumulated rotation angle of each column is larger than beam, which indicates that the damage of the columns along the story is greater than beams. The ductility demand of each column is larger than beam. And the main energy dissipation mechanism of seismic resistance is based on column hinges at the ends when the input angle is 45°, which’s still less disadvantageous than the input angles of 0°and 90°.
The spatial frames in Intensity Region 7(0.1g) with the input angles of 0°, 45°and 90°show column hinges at the ends mostly, few in amount and basically with no hinges at the ends of beams. The story accumulated rotation angle of each column is larger than beam in some story, in general, the damages of columns and beams along the story are both tiny.
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