PPC斜拉桥主梁多状态疲劳及疲劳后静力性能试验研究

Experimental study on multiple-state fatigue and post-fatigue static performance of girder of PPC cable-stayed bridge

为研究大跨径部分预应力混凝土(PPC)斜拉桥主梁的抗疲劳性能,进一步探究混凝土斜拉桥主梁采用部分预应力设计的可行性及合理性,制作了斜拉桥缩尺节段模型,并对主梁采用部分预应力设计,开展4轮共4×250万次主梁具有不同初始损伤及带裂缝工作状态下的疲劳试验;疲劳试验结束后,以4种不同主梁裂缝宽度(0.1mm、0.2mm、0.3mm和0.5mm)为控制工序,反复加载一定倍数的等效活载至主梁裂缝宽度逐步达到0.5mm,以全面研究PPC斜拉桥主梁多状态疲劳后的受力性能。试验结果表明:在等效设计疲劳荷载作用下,主梁无初始损伤时,体系刚度基本无退化,主梁最大裂缝宽度预损伤分别为0.1mm、0.2mm时,跨中截面体系刚度下降量仅为3.35%、4.44%,且未发现裂缝张开;主梁带裂缝工作状态下,跨中截面体系刚度平缓下降7.46%,上峰值静载下,裂缝数量及高度略有增加,但卸载后裂缝均闭合,说明PPC斜拉桥具有良好的抗疲劳性能;疲劳后主梁大损伤静载试验中,主梁裂缝平稳发展,各工序反复加载过程中,主梁挠度、裂缝状态及斜拉索索力均具有较好的恢复能力,当主梁最大裂缝宽度为0.5mm时,荷载达到了7.49倍活载,斜拉桥体系仍然具有较大的剩余承载力。该文试验研究结果表明混凝土斜拉桥主梁采用部分预应力设计具有工程应用的可行性。

In order to study the fatigue resistance of the girder of long-span partially prestressed concrete(PPC)cable-stayed bridge and explore the feasibility and rationality of partially prestressed design of concrete cable-stayed bridge girder,the scaled segment model of cable-stayed bridge was fabricated and then the girder was partially prestressed.A total of4×2.5 million fatigue tests in four rounds on girder under different initial damages and working conditions with cracks were carried out.After the fatigue tests,with 4 different crack widths(0.1,0.2,0.3 and 0.5mm)as the control procedure,the equivalent live load of a certain multiple was repeatedly applied until the crack width of the girder gradually reached 0.5 mm,so the mechanical properties of PPC cable-stayed bridge after multi-state fatigue were comprehensive studied.The results show that under the equivalent design fatigue load,the stiffness of the system basically does not degrade if there is no initial damage in girder.When the maximum crack width of the girder was 0.1 mm and 0.2 mm respectively,the stiffness of mid-span section may decrease only by 3.35%and 4.44%,respectively,and no crack opening is found.For the girder with crack,the stiffness of the mid-span section decreases gently by 7.46%.Under static load with the upper peak,the number and height of cracks may increase slightly,but after unloading all the cracks may close,indicating that PPC cable-stayed bridge possesses good fatigue resistance.In the static load test of the girder with large damage after fatigue,the cracks of the girder develop steadily.In the process of repeated loading,there are good recoveries in the deflection of the girder,the states of cracks and the cable force of the stay cable.When the maximum crack width of the girder was 0.5 mm,the load was about 7.49 times the live load,and the cable-stayed bridge system still had a large residual bearing capacity.The experimental results reveal that the partial prestressing design of the girder in concrete cable-stayed bridge is feasible in practical applications.