钢筋在超高性能混凝土中的锚固与搭接性能试验研究

Test study on anchorage and lap splicing performance of rebars in UHPC

为研究超高性能混凝土(ultra-high performance concrete,UHPC)与钢筋间的黏结受力性能,设计并制作了45个锚固试件和39个包含新旧UHPC界面的对称搭接试件,研究钢筋直径、保护层厚度、锚固/搭接长度、荷载形式、箍筋配置以及界面处理方式对黏结性能的影响规律。结果表明:对于锚固试件,其破坏模式和黏结强度主要由保护层厚度和锚固长度共同影响,当保护层厚度小于3d(d为钢筋直径)时,均发生UHPC劈裂破坏,黏结强度均较小;保护层厚度达3d及以上时,锚固长度为5d的试件均发生钢筋屈服后的拔出破坏,黏结强度较大;锚固长度达10d及以上时,试件均发生钢筋拉断破坏,同时黏结强度平均降低幅度达50%以上;对于搭接试件,无箍筋配置的试件均发生界面劈裂破坏;当体积配箍率不低于0.2%时,搭接试件的破坏模式及黏结强度主要受搭接长度的影响,搭接长度大于6d时,破坏模式由钢筋拔出破坏转变为钢筋拉断破坏,且黏结强度明显降低。依据试验结果,对于拔出试件,建议保护层厚度取值为3d~5d,同时建立了最小锚固/搭接长度计算公式,并给出了临界黏结长度系数α的取值建议。

To study the bonding performance between ultra-high performance concrete(UHPC)and rebars,45 directpull-out specimens and 39 lap-splicing specimens containing new and old UHPC interfaces were designed.The effects of rebar diameter,UHPC cover thickness,anchorage and lap splicing length,loading form,stirrup configuration and interface treatment on the bonding performance were studied through pull-out tests and lap-splicing tests.The results show that for anchorage specimens,the failure mode and bonding strength are mainly influenced by the cover thicknessand anchorage length.When cover thickness is less than 3d(d represents the diameter of rebar),all specimens exhibit UHPC splitting failure,and the bonding strengths are relatively small.When cover thickness reaches 3d or above,specimens with the anchorage length of 5d show pull-out failure after rebar yielding,resulting in a higher bond strength.When the anchorage length reaches 10d or more,all specimens fail in the fracture of rebar,and the averagedecrease of bonding strength is more than 50%.For lap-splicing tests,specimens without stirrups all exhibit interfacesplitting failure.For specimens with volumetric stirrup ratio no less than 0.2%,bonding performance is mainlyinfluenced by lap splicing length.When the lap splicing length is longer than 6d,the failure mode changes from pullout failure to fracture of rebar,and the bond strength significantly decreases.Based on the test results,it isrecommended that the UHPC cover thickness should be within the range of 3d-5d for pull-out specimens.Besides,design formula of the minimum anchorage/lap splicing length is proposed and recommended values of the critical bonding length coefficient are given.