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Ⅰ.我们知道,预应力高强度钢丝之延伸率ε和应力σ在一定的范围内是成直线变化的,超过一定的限度即出现残余变形。有的国家规定钢丝的弹限为σ_(0.01),即产生0.01%残余变形时的应力叫弹限。σ_(0.01)一般在0.4σ_b左右。我国对预应力钢丝只规定了条件流限,没有弹限的规定。在预施应力时,临时超拉应力往往达(0.75～0.8)σ_b,超过0.4σ_b很多。超出弹限后,拉伸曲线开始偏离直线。E值开始变化,弹性模量不是一个常数。因此,在后张法预应力梁中计算钢丝的伸长
Ⅰ. We know that the elongation ε and the stress σ of the prestressed high strength steel wire change linearly within a certain range, and the residual deformation occurs beyond a certain limit. In some countries, the limit of the steel wire is σ_ (0.01), that is, the stress at the residual deformation of 0.01% is called the elastic limit. σ_ (0.01) is generally around 0.4σ_b. China pre-stressed steel only provides the conditions of the current limit, there is no limit of the provisions. In the prestress, the temporary super-tensile stress often reaches (0.75 ~ 0.8) σ_b, exceeding 0.4σ_b much. Beyond the limit, the tensile curve began to deviate from the straight line. The value of E starts to change and the modulus of elasticity is not a constant. Therefore, the elongation of the wire is calculated in the post-tensioned prestress beam