10.1.4.2 Two Methods of Prestressing. Pre-tensioning(先张法) ●Post-tensioning :(后张法)
l Pre-tensioning (先张法） l Post-tensioning （后张法）
Tendons(预应力钢筋或钢绞线) Anchorages(锚具) (a) Abutment(台座) (b) (e) 6个 会术 (d) 预力梁。(a)用千斤顶预拉钢索；(b)等混凝土凝固；(c)混凝土凝固后剪 断钢索，如果钢索是分布在混凝土的底部，剪断钢索会使得这部分受压 力，梁会拱起并往上变形；(d)正好平衡因载重所受的变形
Tendons (预应力钢筋或钢绞线) Anchorages (锚具) Abutment (台座)
Two concepts: 注意：仅 使用于有 Transfer and Transmission length. 粘结预应 力混凝土 When the tendons is (a) released,the force in the 简化为直线分布 tendons is transferred to concrete by bond stress..“自 锚” (b) Ope 简化为直线分布 The length required to transmit the full tendon (c) stress to the concrete is t=0 called the transmission length.Ltr (d)
W h e n t h e t e n d o n s is released, the force in the tendons is transferred to concrete by bond stress. “自 锚” 。 The l ength r equir ed to transmit the full tendon stress to the concrete is called the transmission length. Ltr. 注意：仅 使用于有 粘结预应 力混凝土
Pre-tensioning is more suitable for mass production(工业化大生产)of standard members in factory. Usually straight tendons are used
Pre-tensioning is more suitable for mass production （工业化大生产）of standard members in factory. Usually straight tendons are used
Post-tensioning method