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2、张拉预应力筋的张拉是生产预应力构件的关键。必须按照现行《钢筋混凝土工程施工及验收规范》中有关规定进行。下面就预应力筋张拉时对构件强度的要求、张拉顺序及张拉制度、预应力校核及伸长值测定三个问题分别叙述。 1.张拉时对构件的强度要求用后张法张拉预应力筋时,构件混凝土强度必须达到设计规定的强度,一般情况下混凝土强度达到标号R_(28)的100％后方能张拉。对于块体拼装的预应力构件,其立缝处混凝土或砂浆强度也必须达到设计规定的强度;如设计无规定时,不应低于块体混凝土设计标号的40％,也不得低于15兆帕。这是为了减少由于张拉预应力筋时混凝土和块体拼缝处的变形,防止由于混凝土强度不够,在张拉预应力筋
2. The tension of tensioned prestressed tendons is the key to producing prestressed components. Must be in accordance with the relevant provisions of the current “Code for the Construction and Acceptance of Reinforced Concrete Works.” In the following, the requirements on the strength of components, the tension sequence, the tension system, the pre-stress check, and the determination of the elongation value during the tensioning of prestressed tendons are separately described. 1. When the tensile strength of the component is required to tension the prestressed tendons by the post-tensioning method, the strength of the structural concrete must reach the strength specified in the design. Generally, the concrete strength reaches 100% of the reference number R_(28) and can be stretched. For prestressed members assembled with blocks, the strength of the concrete or mortar at the vertical joints must also reach the designed strength; if the design is not specified, it should not be less than 40% of the design number of the block concrete, nor should it be less than 15 trillion. Pa. This is to reduce the deformation of the joint between the concrete and the block due to tensioning of the prestressed tendons, and to prevent the tension of the prestressed tendons due to insufficient strength of the concrete.