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部分预应力混凝土结构通常是从预应力和非预应力钢筋共同来加强的。在使用荷载作用了,受弯截面的拉力区允许出现细小的裂缝,截面设计是在假定受拉区已经开裂的前题下进行的。这种结构形式较之普通钢筋混凝土和全预应力结构具有明显的优越性:由于只有细小的裂缝,挠度就比钢筋混凝土结构要小些;由于没有很高的预应力,因而避免了在结构中有不利的变形发生;这种结构对破坏还具有较高的延性和吸收能量的能力,在某些情况下能降低造价。 建立在满足极限强度要求和耐久性标准的设计方法已经有好几种了,这些设计方法都是用所谓的“部分预应力率”或“预应力度”作参数得出的。本文所述方法则以满足极限强度要求和使用荷载下钢筋应力限值作参数的,而后一参数又是与最大裂缝宽度,疲劳强度及挠度有关的重要参数。当确定了上述标准后,就可针对已知截面和材料条件写出两个联立方程:
Partially prestressed concrete structures are commonly reinforced with prestressed and non-prestressed reinforcing bars. Under load, the tensile zone of the bent section allows for small cracks, the cross-section design being based on the assumption that the tension zone has been cracked. This kind of structure has obvious superiority compared with ordinary reinforced concrete and full prestressed structure: the deflection is smaller than the reinforced concrete structure because of the small cracks; because there is no high prestress, it is avoided in the structure There are adverse deformations; this structure also has high ductility and energy absorption capacity, in some cases can reduce the cost. There are several design approaches based on meeting the ultimate strength requirements and durability criteria, all of which are based on so-called “partial prestress rates” or “pre-stress levels”. The method described in this paper satisfies the ultimate strength requirement and the steel reinforcement stress limit under service load as parameters, and the latter parameter is an important parameter related to the maximum crack width, fatigue strength and deflection. Once the above criteria have been established, two simultaneous equations can be written for the known cross-section and material conditions: