Mechanical behavior of PPC member with a vertical joint and the influence of PC grout quality assessment

为了研究带竖向施工缝的部分预应力混凝土（PPC）结构的抗弯和抗剪性能，进行了45根尺寸为30 cm × 60 cm × 360 cm的试件的抗弯强度试验。实验工作的参数按以下因素分类：竖缝2个质量等级，混凝土抗压强度为35和70 N/mm^2，施加预应力量为φ 13 mm预应力钢筋0.2%偏置屈服强度的60%和80%，灌浆水泥砂浆抗压强度为20，40，60 N/mm^2。试验中还考虑了普通钢筋和PC钢筋的布置方式。另外，梁试件中竖向接缝的位置可分为三个位置：等弯矩区、剪跨中点、上跨中点， 关于我们 从抗弯强度试验结果来看，试验参数对试验结果有很大的影响。裂缝应力和裂缝宽度在竖缝处有较大的影响。预应力的大小和竖向接缝的质量对试验结果也有很大的影响。此外，弯曲裂缝宽度表现出较大的值的PC灌浆水泥的抗压强度较低的情况下，无论施加的预应力量。弯曲裂缝往往发生在位于剪切跨度的垂直缝的位置最初。这种弯曲裂缝导致接缝混凝土的抗剪强度降低。由于弯曲裂缝和剪切阻力降低的相互作用，接头处可能发生滑移。这种滑移现象在施加的预应力量较低且竖向接缝质量较差的情况下会变得非常显著。在此基础上，提出了一个新的设计公式，该公式基于考虑弯曲裂缝的纤维模型和考虑剪切裂缝宽度的压缩场有限元法，对剪切裂缝宽度进行了解析计算。少

In this study, in order to experimentally investigate the flexural and shear behaviors of the Partially Prestressed Concrete(PPC) structure with vertical construction joints, the bending strength tests are carried out for 45 beam specimens of size of 30cm×60cm×360cm. The parameters for the experimental work have been classified by the following factors ; 2 quality classes of the vertical joints, 35 and 70 N/mm^2 of compressive strength of concrete, the amounts of applied prestressing forces are 60% and 80% of the 0.2% offset yield strength of φ 13mm prestressing steel bar, the compressive strength of the grout cement mortar are 20,40,60 N/mm^2. However, the layouts of the ordinary reinforcing steel bar and that of the PC steel bar are also considered as the experimental parameters. In addition, the positions of a vertical joint in the beam specimens are classified into 3 places of followings ; constant bending moment area, or the center point of shear span, or the mid point between sup … More port and the center point of shear span.From the experimental results of bending strength tests, it is obvious that the results are greatly influenced by the testing parameters. The flexural crack stress and the flexural crack width are significant in the position of vertical joint. These experimental results are also remarkably influenced by the amount of applied prestressing force, and the quality of the vertical joint. Moreover, the flexural crack width exhibited larger value for a case of low compressive strength of PC grout cement despite the amount of applied prestressing force.The flexural crack tends to occur initially in the position of vertical joint located in the shear span. This flexural crack results in the reduction of the shear resistance of the joint concrete. The slippage at the joint can occur due to a mutual effect of the flexural crack and reduction of shear resistance. This phenomenon of slippage can become very remarkable in the case of low amount of applied prestressing force accompanied by the poor quality of vertical joint. The slippage eventually causes to the diagonal shear crack which will be further significantly developed in such case.As a result, a new design equation is proposed to analytically clarify the shear crack width which based on the fiber model concerning to the flexural crack, and the FEM of the compression field theory concerning to the shear crack width. Less