基于多种规范的PC箱梁顶板纵向裂缝影响参数

Influence parameters of longitudinal cracks of PC box girder roof based on multiple specifications

为有效防止和改善箱梁纵向开裂,优化实际工程中对中小跨径PC箱梁设计参数的取值,以某三跨PC箱梁桥为背景,采用实体单元模型,分析了中、美、欧、日4种设计规范所采用的温度梯度模式、预应力钢束布置形式、顶板厚度、材料强度、保护层厚度对箱梁顶板应力和纵向开裂的影响。分析结果表明:美国规范采用的温度梯度模式下顶板拉压应力最大,顶板纵向裂缝最大,较有利于抗裂设计;日本规范采用的预应力钢束布置形式及美国和欧洲规范顶板厚度取值下的顶板拉压应力最小,顶板纵向裂缝最小,较有利于抗裂设计;各规范材料强度和保护层厚度取值下顶板拉压应力基本相同,但日本和美国的材料强度取值及日本和欧洲规范的保护层厚度取值下纵向裂缝宽度更小,较有利于抗裂设计。对30~100 m跨径PC箱梁桥设计规范提出优化建议:采用双线性温度梯度模式,预应力钢束面积取25~28 cm^(2),顶板厚度取35~38 cm,宜采用C50以上较高强度混凝土材料,保护层厚度宜取35~45 mm。

In order to prevent and improve the longitudinal cracking of box girder effectively,the parameters of the design of the PC box girder with small and medium spans in the actual project should be optimized.In this paper,with a three-span PC box girder bridge as the background,a solid element model is used to analyze the influences of temperature gradient mode, prestressed steel beam layout, roof thickness, material strength,protective layer on roof stress and longitudinal cracking of box girder in the four design specifications of China,the United States,Europe,and Japan.The analysis shows that under the temperature gradient mode adopted by the US specification,the roof tensile and compressive stresses are the largest,and the longitudinal cracks of the roof are the largest, which is more conducive to crack resistance design. With the pre-stressed steel beam arrangement form adopted by the Japanese specification and the roof thickness of the American and European specifications, the tensile and compressive stresses are the smallest, and the longitudinal cracks of the roof are the smallest,which is more conducive to crack resistance design.The tensile or compressive stress of the roof is basically the same under the values of material strength and protective layer thickness of all specifications,but the longitudinal crack width under the material strength values of Japan and the United States and the protective layer thickness of Japanese and European specifications is smaller, which is more conducive to the design of crack resistance. According to the analysis results, optimization recommendations are proposed for the design specifications of the PC box girder bridge with a span of 30~100 m:the bilinear temperature gradient model is adopted, the area of the pre-stressed steel beam is 25~28 cm;,the thickness of the top plate is 35~38 cm,the high-strength concrete materials above C50 should be adopted,and the thickness of the protective layer should be 35~45 mm.