带肋钢板加固腹板开大洞口RC梁的受剪承载力试验研究

Experimental research on shear capacity of RC beams with large web openings strengthened by ribbed steel plate

设计并制作24根腹板开矩形大洞口钢筋混凝土梁,分别进行外贴钢板和带肋钢板加固,对比分析不同开洞尺寸、开洞位置、多洞口分布和锚栓构造等因素对钢板加固有效性的影响。结果表明:带肋钢板加固能有效改善洞口角部的受力性状,约束钢板不发生平面外屈曲失稳,使得钢板加固梁的洞口上肢整体压溃的脆性破坏模式转变为混凝土局部压碎的延性破坏模式,大幅提高了开洞梁的承载力、刚度及变形能力;开洞高度为0.4h(h为梁截面高度)、洞口宽高比为2的情况下,带肋钢板加固基本能使开洞梁的受力性能恢复至不开洞情况,随洞口尺寸的进一步增大,带肋钢板的相对加固效率更高,但加固梁的受剪承载力恢复水平会逐渐降低;高洞口、大弯矩以及开洞位置偏向受压区均会削弱洞口上肢,使上肢混凝土压碎成为梁承载失效的控制因素;多洞口相邻角部裂缝易贯通发展,使洞口区域受力复杂,可偏于安全地取多洞口外包络作为边界,将其近似为单一大洞口考虑;锚栓对约束带肋钢板剥离和提高加固系统整体性有一定作用,可作为构造措施但在受剪计算中不予考虑。根据试验结果与分析,建立带肋钢板加固梁的受剪承载力计算模型,其计算结果与试验结果吻合较好。

A total of 24 reinforced concrete( RC) beams with large web openings were prepared,and some were strengthened with externally bonded plain steel plates and ribbed steel plates to investigate their strengthening effectiveness under different conditions including varied opening size,position and configuration as well as anchoring measure. The test results show that externally bonded ribbed plates can effectively alleviate stress concentration at the opening corners,restrain the plates from buckling out of plane and transform the brittle failure of plain plate strengthening,which is abrupt crushing of upper chord,into a more ductile failure of local concrete crushing. As a consequence,extra improvements of ultimate load,flexural stiffness and deformation ability of the strengthened beams are acquired over the corresponding plain plate strengthening ones. The load bearing performance could be basically restored by ribbed plate strengthening in case of the web opening depth as large as 0. 4 times of the beam depth and width to depth ratio of 2. With further increase of opening size,the relative strengthening effect can be even higher,whereas the absolute restoration level will gradually decrease. The increasing of opening depth and bending moment impairing the upper chord in compression as well as the opening vertically moving towards compression zone,all make the crushing of upper chord become a critical factor of ultimate failure. Diagonal cracks of adjacent multi-openings tend to develop through the interval concrete which further complicate the stress condition,thus it is convenient to take the outer envelope as a boundary of a single large opening without unacceptable loss of accuracy. Anchor rods restrain the debonding of ribbed plate and improve the integrity of the strengthening system,whereas its contribution to shear resistance is suggested to be ignored as a safety margin. Based on the test results and analysis,a calculation model is built for RC beams with large web openings strengthened with ribbed plate and validated by test results.