Abstract: Based on the experiment of a 30 m-span prestressed concrete thin-wall box-beams, the reason why the longitudinal cracks appear along prestressed steel during the tensioning is analysed. For thin-wall box-beams prestressed element, the disadvantaged influences resulted from both possion effect and opposite acting force due to the deformation of beams is considered while the needed longitudinal prestress is acquired. And the model from the engineering design's viewpoint is established. And a formulation of the protective thickness of the concrete under the prestressed steel has been suggested.

Key words: thin-wall box-beams, longitudinal crack, poisson effectl, opposite acting force, the protective thickness of concrete under the prestressed steel

摘要： 依据30 m跨径预应力砼足尺薄壁箱梁的试验研究,分析了其在张拉阶段底板沿预应力钢束纵向开裂的原因,对薄壁箱形预应力砼构件,提出在考虑获得所需纵向预应力的同时,应计入泊松效应和预应力钢束对构件变形产生的反向作用力的不利影响,并从工程设计角度建立了分析模型,提出了确定预应力钢束下保护层厚度的建议公式.

关键词: 薄壁箱梁, 纵向裂缝, 泊松效应, 反向作用力, 下保护层厚度