不同持荷下自密实混凝土加固既有RC梁抗弯性能试验

Experiment of flexural behavior of an existing RC beam reinforced by self-compacting concrete under different continuous loading

针对自密实混凝土加固既有混凝土桥梁时结构初始损伤和持荷加固等对加固梁抗弯性能的影响,设计和制作了8片钢筋混凝土T梁,对其进行加载造成初始损伤,然后在不同持荷水平下对其进行自密实混凝土增大截面加固,并对加固梁进行抗弯性能测试,以明确持荷水平和自密实混凝土加固厚度对RC梁抗弯性能的影响,包括构件裂缝分布形态、破坏形式、挠度变形和混凝土应变发展等,最后探讨了加固梁抗弯承载力计算方法。研究结果表明:该试验采用的自密实混凝土增大截面加固方法能有效提高构件的抗弯刚度,增大抗弯承载力约1倍,并且加固梁均表现出良好的延性破坏特征;混凝土梁底加固厚度能在一定程度上提高构件抗弯承载力,但效果不明显,其提高程度小于加固截面自重的增长;低持荷水平对加固梁抗弯承载力退化影响不大,甚至略有提高,但高持荷水平会引起加固梁抗弯承载力在一定程度退化,持荷水平对加固梁抗弯刚度的影响依赖于其引起的梁表面裂缝张合情况,裂缝闭合时,一定的持荷对于加固梁的抗弯刚度具有促进作用,但高持荷加固梁表面存在开口裂缝时会引起其抗弯刚度退化;对于适筋加固梁,基于平截面假定和塑性极限方法,忽略二次受力的影响,直接按受拉钢筋屈服对加固梁抗弯承载力计算具有较高的精度。

To investigate the effects of initial damage and sustained load on the flexural behavior of structures strengthened using the enlarge section method with self-compacting concrete,eight reinforcement concrete T beams were designed and constructed.These beams were first loaded to simulate the initial damage.Then,they were strengthened using the enlarge section method with self-compacting concrete under different sustained loads.Thereafter,the beams were tested under a flexural load to investigate the effects of sustained load and the strengthening thickness below the T beams on the flexural capacity and the section stiffness of the strengthened reinforced concrete beams.The crack distributions,failure modes,load-deflection curves and concrete strain developments were assessed in the test study.Finally,a method is discussed based on the experimental test for flexural capacity prediction of the strengthened structures.The results show that the used reinforcement method of self-compacting concrete significantly increases the beam section stiffness.The beam flexural capacity increases approximately one time and nearly all the reinforced beams show the expected ductile failures.The flexural capacity of the beams somewhat increases with an increase in the thickness of the self-compacting concrete below the beams.The increase in the flexural capacity,however,is slow compared to the weight increase of the strengthened members.The low continuous load during the reinforcement procedure has little effect on beam flexural capacity degradation,which can slightly increase the flexural capacity.The high continuous load,however,deteriorates the beam flexural capacity.The effects of continuous load on beam section stiffness also depends on the condition of the initial cracks on the beam surface.For the beams with the closed initial cracks on the surface,a certain degree of continuous load can increase the beam section stiffness.A high continuous load can lead to the opening of initial cracks during the reinforcement procedure,which results in the degradation of the beam section stiffness.For beams strengthened with appropriate steel reinforcement,it is feasible to predict the beam flexural capacity based on the plastic limit analysis method and neglecting the strain-lag effects caused by the sustained load during the strengthening process.2 tabs,10 figs,25 refs.