Direct shear test on UHPC key-wet-joints and the unified calculation formula of direct shear capacity of UHPC wet-joints [UHPC键齿湿接缝直剪试验及湿接缝直剪承载力统一公式]

Abstract

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°) are basically 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.