What are the characteristics of prestressed concrete?

【Advantages】 1. Good crack resistance and high stiffness. By applying prestress to the members, **the appearance of cracks is delayed; under service loads, the members may not develop cracks at all, or the occurrence of cracks is postponed. As a result, the stiffness of the members increases and the durability of the structure is enhanced. 　　2. Save materials and reduce self-weight. Due to the need to use high-strength materials in its structure, it allows for a reduction in the amount of rebar required as well as in the cross-sectional dimensions of the components, thereby saving steel and concrete and reducing the structural weight. This gives it significant advantages for large-span and heavily loaded structures. 　　3. Improve the shear resistance of components. Tests have shown that the longitudinal prestressed rebar acts as anchor bolts, preventing the occurrence and progression of diagonal cracks in the members; moreover, the vertical component of the resultant force of the curved rebar (strands) in the prestressed concrete beam partially offsets the shear force. 　　4. Improve the stability of compressed members. When a compressed member has a high slenderness ratio, it is prone to bending under certain pressure, resulting in a loss of stability and failure. If prestress is applied to a reinforced concrete column, tightening the longitudinal load-bearing rebar not only makes it difficult for the prestressed rebar itself to bend under compression, but also helps the surrounding concrete improve its resistance to compressive bending. 　　5. Improve the fatigue resistance of components. Because of the high prestress in the rebar, the magnitude of stress changes caused by loading or unloading during service is relatively small; this enhances the fatigue resistance, which is highly advantageous for structures subjected to dynamic loads. 　　【Disadvantages】 1. The manufacturing process is relatively complex and high quality standards are required, which necessitates the use of a highly skilled professional team. 　　2. Certain specialized equipment is required, such as tensioning tools and grouting equipment. 　　3. The initial costs for prestressed concrete structures are high, resulting in higher project costs for projects with a small number of components. Source: http://baike.baidu.com/view/354117.htm This post was last edited by brucehan on 2009-4-2 08:28]

Characteristics of prestressed concrete: The ultimate tensile strain of ordinary reinforced concrete members is only 0.0001~0.00015. When the concrete of a member does not crack under tension, the stress in the tensile steel bars within that member is only 20–30 N/mm2 ； Even in components where cracks are allowed, due to the limitation imposed by the crack width, the stress on the tensile steel bars only reaches 150–200 N/mm2, preventing the tensile strength of the steel bars from being fully utilized. Prestressed concrete is an effective solution to this problem, that is, prestress is applied to the concrete in the tensile zone of the member in advance, before the member is subjected to external loads. When tensile stresses are generated in a member under external loads during its service life, the pre-compression stress must first be offsetted. This delays the appearance of cracks in the concrete and also limits their propagation, thereby improving the crack resistance and stiffness of the member. The method of applying prestress to the tensile zone of concrete members involves tensioning the prestressed steel bars in that zone; through these steel bars or anchors, the elastic contraction force of the prestressed bars is transmitted to the concrete member, thereby generating prestress. Reinforcement bars are generally processed in a reinforcement bar workshop or a processing shed at the construction site, and then transported to the site for installation or binding. The steel bar processing process depends on the type of finished product; common processing methods include cold drawing, cold extrusion, straightening, cutting, heading, bending, welding, and binding.