螺旋肋GFRP筋与UHPC黏结强度试验及计算方法

Experimental Study and Calculating Method for Bond Strength Between Helically Ribbed GFRP Bar and UHPC

为研究螺旋肋GFRP筋与UHPC黏结强度,以钢纤维掺量、保护层厚度、锚固长度及GFRP筋直径为试验参数,对60个螺旋肋GFRP筋与UHPC试件展开拉拔试验,获得了各参数对GFRP筋与UHPC黏结强度的影响规律。结果表明:GFRP筋UHPC试件的拔出破坏主要呈现直接拔出和劈裂拔出2种模式,直接拔出破坏主要出现于钢纤维掺量≥2%且保护层厚度较大的试件中;在不同参数情况下,直径18 mm及22 mm GFRP筋与UHPC黏结强度为19.6~53.7 MPa,同时黏结强度整体上随钢纤维掺量及保护层厚度的增加而增大,随锚固长度的增加而减小;当UHPC钢纤维掺量从0%增加至2%时,GFRP筋与UHPC黏结强度提高幅度达71.4%~74.1%,但钢纤维掺量由2%增加至3%时,出现黏结强度增长减缓甚至不增长现象;保护层厚度对黏结强度的增强作用存在“上限效应”,即当其小于临界保护层厚度时,黏结强度随保护层厚度增加而增长,但当其大于该临界值,增强作用显著减弱;直径18 mm、锚固长度1倍直径的GFRP筋在UHPC中的临界保护层厚度约为3倍直径。基于弹塑性力学中的厚壁圆筒理论,建立了GFRP筋与UHPC黏结强度理论计算公式,并用试验结果验证了所提公式的适用性。

To determine the bond strength of helically ribbed glass-fiber-reinforced polymer(GFRP)bars to ultrahigh-performance concrete(UHPC),pull-out tests were carried out on 60 GFRP-bar-UHPC specimens with the test parameters including the steel fiber content,cover thickness,and embedment length.The effects of these parameters on the bond strength were evaluated.The results indicate that the GFRP-bar-UHPC specimens have two types of failure mode:direct pulling-out failure and splitting pulling-out failure.The direct pulling-out failure happens in specimens with steel fiber content≥2%and with a large cover thickness.For different test parameters,the bond strengths of the GFRP rebars with diameters of 18 and 22 mm to UHPC are 19.6-53.7 MPa.Generally,the bond strength increases with an increase in the steel fiber content and cover thickness,whereas it decreases with an increase in the embedment length.When the steel fiber content in UHPC increases from 0%to 2%,the bond strength between the GFRP bars and UHPC increases by 71.4%-74.1%.However,the bond strength experiences little or no increase when the steel fiber content increases from 2%to 3%.There is an"upper limit effect"in the improvement action of the cover thickness on the bond strength.When it is less than the critical cover thickness,the bond strength increases with increasing cover thickness.However,the improvement is significantly weakened when it exceeds the critical value.The critical cover thickness of GFRP bars with a diameter of 18 mm and an embedment length of 18 mm embedded in UHPC is approximately three times the rebar diameter.Based on the elastoplastic theory of thick-walled cylinders,a theoretical formula was developed to predict the bond strength between the GFRP bar and the UHPC,and the proposed formula was verified by experimental results.