《混凝土结构设计原理》双语 (15).ppt

Prestressed Concrete Structure. 10.1 Basic concepts 10.1.1 Concept of prestress 预应力技术再其它结构中的运用 Membrane Structure 10.1.2 Why select prestressing in R.C structure? Flew （缺陷）of R.C.  抗拉强度低： 极限拉应变小（破坏前没有明显征兆） Cracking Stress steel σs=20～40MPa The stress of steel under service load: σs=200～250Mpa ωmax=0.2～0.3mm ： 普通钢筋混凝土带裂缝工作，美观性、耐久性、刚度下降。 如果在普通混凝土中用高强钢材，在使用荷载下钢筋应力更高，裂缝宽度更大，往往不能满足使用要求。 小结： 钢筋混凝土虽然能弥补混凝土抗拉强度太低的缺点，但并不能解决由于混凝土抗拉强度太低而引起的另一个本质上的缺陷——裂缝问题。 Prestressed concrete can be defined as concrete in which internal stresses of such magnitude and distribution have been introduced that the stresses resulting from the given applied loading are counteracted to a desired degree. （最有效的方法是预应力，根据需要人为地引入一定数值与分布的内应力，以部分或全部抵消外荷载的一种加筋混凝土。达到避免过早开裂，有效利用高强钢材的目的） 10.1.3 Concept of prestressed Concrete 10.1.4 Classification of Prestressed concrete 预加应力程度： Fully prestressed members and partial prestressed members全预应力混凝土、部分预应力混凝土 Prestressing method: Pre-tensioning先张法； Post-tensioning后张法 钢筋与混凝土之间的粘结情况： 有粘结预应力混凝土、无粘结预应力混凝土、体外预应力混凝土 10.1.4 .1 Fully prestressed members and partial prestressed members No tensile stress is permitted. “Fully prestressed members 全” The permissible tensile stress is kept sufficiently low so that no visible cracking occurs. “限值” The tensile stress are restricted such that crack width do not exceed 0.1mm or 0.2mm . “Partial prestressed members 部分” 10.1.4 .2 Two methods of prestressing. Pre-tensioning (先张法） Post-tensioning （后张法） Pre-tensioning method Two concepts:Transfer and Transmission length. 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 Effectively bonded prestressed beam（有效粘结预应力梁） Un-bonded prestressed beam（无粘结预应力梁） Out－body prestressed beam（体外预应力）  第一次课到此 10.2 Basic behavior of P.C State of zero stress Consider the loss of prestress caused by concrete shrinkage and creep