About the cause of loss of prestressed anchorage to use
Prestressed anchorage for some operating procedures in use tend to be strengthened, it is because the construction of very tall to the requirement of strengthening safety performance as a result, the prestressed anchorage will more or less some losses, but what is the cause of the damage?How to solve this article show you talk about?
First talk about prestressed tensioning
The first in a pedestal in accordance with the provisions, the design requirements Reinforced tensioned to control stress - and temporary fixed anchorage to pouring concrete, to meet the design concrete strength by more than 75% cut to relax the cohesive force of steel on steel and concrete delivery pressure.Construction simple, since by bond anchor, don't have to take special anchorage, temporary anchorage can reuse (commonly called tool type anchorage or jig), the economy when mass production, quality and stability.Used in small and medium sized components factory production.
Zhang method after
For the embedded control hole to casting concrete, smoke tube to maintenance in muscle tension, anchoring and grouting (to prevent the steel bar rust).Rely on anchorage block reinforced elastic rebound, give section concrete preloading stress.This method is simple in equipment, do not need a pedestal, flexible production, but need reliable anchorage and jack, large amount of anchorage steel, apply to the construction of large components.
Measures:
1) choose deformation small or narrow inside prestressed anchorage, minimize the plate number;(2) the first tensioning component, select the pedestal.
2. The friction loss speed 12: reason: in the process of tensioning prestressed reinforcement, the method of post-tensioned prestressed reinforcement and the friction between the channel wall, first with tensioning prestressed anchorage and fold point of friction between, also can make the tensile stress.
Steps: (1) can be tensioned in both ends of a long component;(2) is made of super tension.
3. The temperature loss/s13: reason: first a method of the temperature loss caused by thermal curing measures: (1) the secondary heat curing.(2) on the steel tensioning prestressed reinforcement.Prestressed anchorage at www.ytyuyingli.com
4. The stress relaxation loss sigma l4 reasons: the length of the prestressed reinforcement unchanged, under the long-term effects of high stress will produce relaxation, can lead to loss of prestress.
Measures: the tension or small prestressed relaxation.
5. The shrinkage and creep of concrete cause the loss of sigma l5: hard when volume shrinkage of concrete, the under the effect of preloading effect, the concrete creep will happen, it will make component, component of the prestressed reinforcement with retraction, resulting in loss of prestress.
Steps: (1) using high grade cement, reduce the dosage of cement, reduce the water cement ratio;(2) the good gradation of aggregate, strengthen vibrating, improve the compactness of concrete;(3) strengthen the maintenance, in order to reduce the shrinkage of concrete, concrete stress (4) control sigma PC, requirements in order to prevent the happen of nonlinear creep.
6 sigma l6 circular reinforcement loss reasons: with spiral prestressed reinforcement ring artifacts due to the local compression of concrete prestress loss.