高强轻骨料混凝土深受弯构件受剪性能及尺寸效应试验研究

Experimental study on shear behavior and size effect of high strength lightweight aggregate concrete deep flexural members

为避免实际结构与缩尺模型因尺寸效应引起的安全隐患,应对剪切作用下轻骨料混凝土深受弯构件的破坏机理、承载能力和设计方法进行研究,为此,完成了对称集中荷载作用下截面高度在500~1 400 mm、剪跨比为0. 85~1. 73的15根LC60级的高强轻骨料混凝土深受弯构件受剪性能试验,观察破坏过程与破坏形态,分析了荷载-跨中挠度曲线、特征荷载、钢筋应变、斜裂缝等的发展趋势,研究其尺寸效应作用机理,分析了典型模型和计算方法的适用性。试验结果表明:试件破坏形态与尺寸大小无关,主要包括剪压和斜向劈裂两种破坏模式;随截面高度增大其尺寸效应作用显著,截面高度由500 mm增大至1 400 mm,归一化极限荷载降低约37%;随剪跨比减小,归一化开裂荷载/极限荷载均呈降低趋势。计算表明,对轻骨料混凝土强度未进行折减时,采用我国GB 50010-2010《混凝土结构设计规范》中未准确考虑尺寸效应影响的计算公式,结果较为保守,未合理考虑尺寸效应对深受弯构件抗剪强度的影响,采用欧洲EC2规范、美国ACI 318规范、TanCheng及Tang-Tan等基于拉压杆的受剪承载力模型进行计算时,其预测值与试验值吻合良好。而采用加拿大CSA规范计算时,应根据剪跨比合理选取有效压杆系数。

To avoid the potentially dangers caused by size discrepancies between actual structure and scaled model,a total of 15 lightweight aggregate concrete( LWAC) deep flexural members with section height of 500-1 400 mm and shear span-effective depth ratio of 0. 85-1. 73,was tested to study the size effect,failure mechanism,shear bearing capacity and design method. The shear behavior,including failure process,failure modes,load-deflection curves,loads at characteristic points,reinforcement strains and inclined crack propagation,were systematically analyzed. The accuracy and applicability of strut-and-tie model-based code provisions and shear models for specimens were verified.The test results indicate that there are two different failure modes,namely,shear-compression failure and diagonal splitting failure,which are independent of beam section sizes. With the increase in section height from 500 mm to1 400 mm,significant size effect on normalized ultimate shear stress is manifested with an approximately 37%decrease. Instead,the increasing shear span-effective depth ratio leads to an appreciable reduction in both the normalized cracking and ultimate shear stresses. Calculation results show that,the GB 50010-2010‘Code for design of concrete structures’ without reasonable consideration of size effect on the strength of LWAC leads to conservative results. The predictions obtained from EC2,ACI 318,Tan-Cheng and Tang-Tan models show good agreement to the test results. It is suggested that a rational effective struts coefficient shall be considered when using CSA code.