摘要
本文针对低、多层剪力墙结构房屋的受力特点,在研究、分析国内外已有相关研究成果的基础上,进行了8片足尺墙片在静力反复加载下的试验研究。试验墙片的墙肢宽度为2000mm,高度为1600mm,厚度为130mm；分布钢筋采用双向单排配筋方式,通过改变分布钢筋间距控制水平及竖向分布钢筋配筋率为0.1%-0.2%；试验轴压比为0.08。通过试验,重点研究了单排配筋情况下,不同分布钢筋间距(也即配筋率)对于墙体承载能力、耗能能力、延性、刚度、破坏模式等的影响。并且分别采用大型有限元程序ABAQUS、ANSYS对试验模型进行了非线性数值分析,分析结果与试验结果吻合较好。
通过试验研究和数值分析,得出以下主要结论：
1、墙片以弯曲破坏为主,在形成对角斜裂缝前,混凝土已经被压碎。分布钢筋配筋率大于0.1%的墙片,裂缝主要以距离墙底600mm以下的三条与水平面约35°夹角的斜裂缝为主；配筋率等于0.1%的墙片,仅在距墙底200mm处形成一条斜裂缝。
2、试件的试验承载力均高于按行业标准《高层建筑混凝土结构技术规程》相关公式计算的抗弯承载力及抗剪承载力,并且准确预见了墙片的破坏形态。采用现行规范公式进行低轴压比、低剪跨比、低配筋率的单排配筋剪力墙结构设计偏于安全。
3、分布钢筋配筋率自0.2%降低至0.1%,屈服荷载约下降9%,极限荷载约下降13%,试件的刚度和延性变化不明显。在低轴压比下,试件刚度和延性受混凝土强度、截面尺寸以及边缘构件纵向钢筋及箍筋设计控制；分布钢筋对试件的承载力贡献不明显。
4、采用ABAQUS程序分离式建模,采用塑性损伤本构模型,应力应变曲线按《混凝土结构设计规范》附录C规定取值,损伤参数指标按Mazars模型计算。分析结果表明,ABAQUS软件能较好的模拟试件屈服前的荷载位移(P-△)曲线,计算极限荷载低于试验极限荷载,分布钢筋变化的影响不明显。
5、采用ANSYS软件整体式建模,仅考虑垂直于单元坐标系x轴方向的单元划分定义实常数,能较好的模拟试件开裂前的荷载位移(P-△)曲线状态,模拟计算的极限荷载结果低于试验值。
根据研究结果,低、多层建筑采用单排双向、低配筋率分布钢筋配筋方式的剪力墙,具有适宜的承载力、刚度和延性,可以达到一定的节材目的,具有较大的应用前景。
This paper considers the mechanical characteristics of low rise and multi-story building shear wall structures based on analyses of related domestic and foreign research achievements. Eight full-scale specimens of reinforced concrete shear walls were tested and studied under static-cyclic loading. The wall specimens'width, height and thickness dimensions were 2000mm,1600mm and 130mm respectively. The horizontal and vertical distribution reinforcement of the wall was arranged in separate single layers. The distribution reinforcement ratio was controlled at 0.1%-0.2% by changing the reinforcement spacing. The ratio of axial force to the product of the concrete section area and compressive strength of the wall was equal to 0.08. Using the single reinforcement layers and different distributions of the reinforcement spacing (through the variation of the reinforcement ratio) the study focuses on the influence the variations had on the bearing capacity, energy dissipation capacity, ductility, stiffness and failure modes of the wall specimens. In addition, nonlinear numerical analyses of the tested specimens were made via the large finite element program ABAQUS and ANSYS respectively. The analytical results match the experimental ones well.
Based on the experimental and analytical results the main conclusions that are reached in this paper are as follows:
(1) The failure mode of the specimen belongs to bending. The concrete was crushed before the diagonal cracks occurred. For the wall specimens of reinforcement ratio more than 0.1%, three main cracks formed below 600 mm from the bottom of the wall with a diagonal angle of about 35°to the horizontal; and for the wall specimens of reinforcement ratio equal to 0.1%, only one diagonal crack formed 200 mm from the bottom of the wall.
(2) The flexural strength and shear capacity of the wall specimens calculated by the formulas of the Chinese code, the Technical Specification for Concrete Structures of Tall Buildings, was lower than the tested practical capacity and the Specification can predict the failure mode correctly. Accordingly, it is safe to design using the current codes for shear walls with single layered reinforcement, low axial compressive force ratios, low shear-span ratios and low reinforcement ratios.
(3) With the distribution reinforcement ratio of the wall decreasing from 0.2% to 0.1%, the yield load falls nearly by 9%, the ultimate load falls by about 13%, but the stiffness and ductility do not change significantly. With the low axial compressive force ratio, the stiffness and the ductility of the walls are controlled by the strength of the concrete, the section size and the longitudinal reinforcement and stirrups of the edge element. The contribution of the distribution reinforcement to the bearing capacity is not obvious.
(4) Nonlinear analysis was done using ABAQUS with the separated modeling and plastic damage constitutive model. The stress-strain curve was calculated by means of Appendix C of the Chinese National Code for Design of Concrete Structures and the damage parameter index value was obtained by Mazars model. The analytic results show that ABAQUS simulates well the load-displacement curve of the specimens before the yield displacement. The calculated ultimate load is lower than the experimental result and the change of the distribution reinforcement ratio of the specimens has nearly no influence.
(5) Nonlinear analysis was also done using ANSYS with the integral modeling of concrete. The real constant was defined by taking only the meshing of the plane vertical to the X axis of the coordinate system. The analytic results show that ANSYS can simulate well the load-displacement curve before the cracking displacement. The calculated ultimate load is also lower than the experimental one.
According to the results of the study shear wall design with bi-directional single layered reinforcement and low reinforcement ratio applied to low rise and multistory buildings has appropriate load bearing capacity, stiffness and ductility. This type of shear wall can, to an appreciable extent, save material and has a reasonable application prospect.
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