平钢板-UHPC组合桥面板疲劳性能与疲劳损伤机理

Fatigue performance and fatigue damage mechanism of steel plate-UHPC composite bridge deck

以国内某在建双塔双索面混合梁斜拉桥为工程背景,针对首次提出并使用的8mm平钢板+15cm UHPC层+PBL剪力键的平钢板-UHPC组合桥面板,进行三块足尺组合桥面板负弯矩疲劳荷载试验及其研究。试验过程中,每间隔一定疲劳加载次数停机进行静载测试,采集静载作用下试件的裂缝宽度、跨中挠度、UHPC表面应变、钢底板应变、受拉钢筋应变等。试验结果表明:①UHPC受拉区纵筋配筋率1.58%的钢UHPC组合桥面板在荷载比0.25、循环最大荷载为静开裂荷载0.8倍的荷载作用下,以裂纹宽度0.10mm为寿命标准,其疲劳寿命超过4000万次或无限长;而纵筋配筋率0.89%者,其疲劳寿命仅908万次;②UHPC受拉区纵筋配筋率1.58%的钢-UHPC组合桥面板刚度随循环次数增加缓慢下降,经循环加载4000万次,仅下降17.2%;而配筋率为0.89%者的刚度,在循环加载908万次时,突然大幅度下降,共下降了51.6%;③平钢板-UHPC组合桥面板抗负弯疲劳性能及剩余承载力衰减基本由UHPC抗拉层的疲劳衰减(疲劳损伤)所致;受拉区纵筋配筋率越大,越能减轻UHPC抗拉层的疲劳衰减,当超过一定值后,可使得UHPC抗拉层在某种循环荷载下几乎不衰减;④平钢板-UHPC组合桥面板的疲劳设计应不再是强度控制,而是耐久性控制。

Based on a hybrid girder cable-stayed bridge with two towers and double cable planes in China,full-scale fatigue tests of three steel plate-UHPC composite bridge deck(8 mm steel plate+15 cm UHPC layer+PBL shear connectors)were conducted to investigate the fatigue behavior of the composite bridge deck under hogging moment.During the test,the static load tests were conducted every certain fatigue circles to collect the crack width,mid-span deflection,strains in UHPC,strains in steel plate,strains in the reinforcements,etc.Test results showed that:(1)When the fatigue loading ratio is 0.25 with the maximum load of 0.8 times of the static cracking load,and the steel-UHPC composite deck with the longitudinal reinforcement ratio of 1.58%in the tensile zone has a fatigue life of over 40 million or infinite circles by use of the crack width of 0.10 mm as the fatigue failure criterion.However,when the longitudinal reinforcement ratio decreases to 0.89%,the fatigue life of the composite bridge deck is only 9.08 million circles.(2)The stiffness of steel-UHPC composite bridge deck with the longitudinal reinforcement ratio of 1.58%decreases slowly with the increase of fatigue cycles and only decreases by 17.2%after 40 million cycles.Nevertheless,the stiffness of that with the longitudinal reinforcement ratio of 0.89%suddenly drops by 51.6%when the cyclic loading reaches 9.08 million times.(3)The degradation of the fatigue resistance and residual capacity of steel plate-UHPC composite bridge deck is primarily caused by the fatigue degradation of the UHPC tensile layer.Larger longitudinal reinforcement ratio may reduce the fatigue degradation of UHPC tensile layer.When the ratio exceeds a certain value,the UHPC tensile layer can remain almost no fatigue degradation under a certain cyclic load.(4)The fatigue design of the steel plate-UHPC composite bridge deck should be controlled by the durability rather than the strength.