UHPC键齿湿接缝直剪试验及湿接缝直剪承载力统一公式

Direct shear test on UHPC key-wet-joints and the unified calculation formula of direct shear capacity of UHPC wet-joints

为得到UHPC键齿湿接缝的直剪受力性能及直剪承载力统一公式,开展17个UHPC试件的直剪推出试验,考察键齿形状、侧向应力等对UHPC键齿湿接缝直剪破坏模式、裂纹发展情况、直剪强度以及剪切滑移性能的影响,并结合前期24个UHPC整体浇筑试件和24个UHPC平(湿)接缝试件的试验结果对UHPC界面直剪承载力计算方法进行研究。结果表明:UHPC键齿接缝试件的剪切破坏过程可分为线弹性阶段、裂纹发展阶段、破坏阶段和残余应力阶段;各键齿接缝直剪破坏界面与剪切界面几乎重合;梯形(键齿夹角113°)、矩形、倒梯形(键齿夹角65°)等三种键齿形式的直剪性能基本相同,为方便施工,工程中键齿宜选用梯形;键齿接缝试件的初裂强度、峰值强度提升值(相对于平接缝)与整体试件相应强度提升值之比远小于两者剪切面的整体面积之比;无侧向应力下,UHPC键齿接缝试件的剪切刚度和峰值强度均大于平接缝试件,逊于整体试件,且差距较大;键齿接缝试件峰值强度为整体试件的52.5%;在5MPa侧向应力下,平接缝试件与各键齿接缝试件剪切刚度已差别不大,峰值强度差值变小;键齿接缝试件的峰裂比(峰值强度与初裂强度之比)为1.173~1.319;键齿接缝试件的剪切刚度、延性系数、初裂强度、峰值强度及剪切滑移能力均随着侧向应力的增大而增大;UHPC湿接缝试件初裂强度和峰值强度随侧向应力的增长规律符合库伦准则,其摩擦系数可取1.26。最后,建立物理意义明确、形式简单、精度较高的可适用于未配抗剪钢筋UHPC整体界面、平湿接缝界面和键齿湿接缝界面的直剪承载力计算统一公式。

To obtain the direct shear performance and the unified formula of direct shear capacity of the UHPC key-wet-joints,direct shear pushout tests of 17 UHPC specimens were carried out.The influences of the key-joint shape and lateral stress on the failure mode,crack development,shear strength and shear-slip performance of the UHPC key-wet-joints were investigated.Besides,in combination with previous test results of 24 monolithic UHPC specimens and 24 UHPC flat-joint specimens,the calculation method for direct shear capacity of the UHPC interface was analyzed.The results indicated that the failure process of the UHPC key-wet-joint specimens can be divided into linear-elastic,crack-development,failure and residual-stress stages.The direct shear failure interfaces of the key-joint specimens almost coincide with the shear plane.The direct shear performances of three kinds of key-joint specimens with key-joint shapes of trapezoid(key-joint included angle of 113°),rectangle and inverted trapezoid(key-joint included angle of 65°)arebasically the same.To facilitate construction,the key-joint shape should be the trapezoidal shape in the actual project.The ratios of the increment values of the initial cracking strength and peak strength of the key-joint specimens(compared with the flat-joint specimens)to those of the monolithic specimens were far less than the ratio of the complete area in the shear plane of the two kind of specimens.Under the condition without lateral stress,the shear stiffness and peak strength of the UHPC key-joint specimens were larger than those of the flat-joint specimens,but smaller than those of the monolithic specimens.The peak strength of the UHPC key-joint specimens is 52.5%of that of monolithic specimen.Under the condition with lateral stress of 5 MPa,the difference in the shear stiffness between the flat-joint specimen and the key-joint specimen is not evident,and the difference in the peak strength tends to be smaller.The peak-to-crack ratios(the ratio of direct shear peak strength to cracking strength)of the key-joint specimens range from 1.173 to 1.319.The shear stiffness,ductility coefficient,initial cracking strength,peak strength and the shear-slip performance of the key-joint specimens increase with the increase of the lateral stress.The growth laws of the initial cracking and peak strengths of the UHPC wet-joint specimens with the lateral stress conform to the Coulomb criterion,and the friction coefficient can be taken as 1.26.Finally,a unified formula with clear physical meaning,simple form and high precision for calculating the direct shear capacities of the monolithic UHPC interface,flat-wet-joint interface and key-wet-joint interface was established.