Disadvantages of prestressed concrete structures

 

Concrete Steel Structure

1. The process is more complex, high quality requirements, thus requiring a more skilled professional team, and there are problems of interspersed types of work.

2. Sub-stress. Secondary stresses due to prestressing, creep and shrinkage effects, temperature variations, and bearing subsidence can be severe in continuous structures unless these are controlled or accounted for in the design. In prestressed continuous structures, it is interesting to note that these secondary stresses can often be exploited advantageously, and thus the secondary stresses will increase the economy of the structure.

3. Friction losses in continuous force bars. Friction losses can be significant if there are many reverse curves, if the curves have large deflection angles, or if the force bars are too long. In beams with corrugations or added axils, friction losses can be minimised by using straighter cables. The usual methods of over-tensioning and tensioning from both ends can also be used to minimise friction losses.

4. Certain specialised equipment is required, such as tensioning rigs and grouting equipment. Pre-tensioning method requires a tensioning pedestal; post-tensioning method also consumes a larger number of reliable quality of anchorage, etc.. However, now the more widely used slow bond prestressing is a great improvement on this basis.

5. The start-up cost of prestressed concrete structure is larger, and the cost is higher for projects with a small number of members.

6. Prestressed reverse arch is not easy to control. It increases with the increase of concrete creep, causing the structure to finish unevenly. Especially the pre-stressed prefabricated members are more significant, the anti-arch is not coordinated, and the cracking problem of the members brings more difficulties to the site.

7. Under high temperature conditions, the strength of reinforced concrete after applying prestressing will be significantly reduced, leading to a decrease in its fire resistance limit, so there are safety hazards in building fire protection.