某預(yù)應(yīng)力混凝土梁長(zhǎng)21m,預(yù)應(yīng)力鋼筋直徑φ20,彈性模量E=2×105N/mm2,抗拉強(qiáng)度標(biāo)準(zhǔn)值fpuk=500N/mm2;采用后張法施工,張拉控制應(yīng)力σcon=0.65fpuk,張拉程序0→1.03σcon,試計(jì)算