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PC strand arise slide wires and broken wires reason

2018-07-16 18:36:02

For large-span concrete continuous steel bridges, continuous beam bridges or steel-continuous beam composite bridges (hereinafter collectively referred to as continuous beam bridges), prestressing technology is not only a structural method but also a combination of construction methods to form a complete set. The prestressed construction method with segmental construction as the main body. As the span of these bridges becomes larger and larger, and the superstructure of the bridge is being cast cantilever one by one, the length of the prestressed steel strands will be longer and longer due to the existence of a large number of segments. The problems such as breakage of wires, slipping wire and lack of actual elongation are more likely to occur. It is increasingly decisive for the quality of the entire structure and the construction period. Therefore, the prestressed construction quality should be improved to a special position and the correct choice must be made. The construction process and strict quality control measures are taken to ensure the prestressed construction quality. The three-way prestressed concrete box girder with a single box and a single chamber in the upper part of the main bridge of the Heng-Liang Super Bridge under the Nansha Port Expressway in Guangzhou is constructed with a light-weight hanging basket and a cantilever balanced cast construction. The longitudinal steel beams are of large tonnage. ×d 15.24 mm~15×d 15.24 mm low relaxation high strength prestressed steel strand bundle, VLM15-9~15 post-tensioned prestressed system, longitudinal prestressed bundles are arranged in the horizontal curve of vertical and horizontal combination, using The corrugated metal tube is made into a hole, and the length of the steel beam stretched at both ends is up to 101.2 m. The main bridge box girder prestressed construction was analyzed for the prone problems, and some effective control measures were taken in the construction and good results were obtained. The results are summarized as follows and provide reference for similar prestressed engineering construction.

Analysis of Causes of Problems and Control Measures

When the prestressed steel strand bundle is tensioned, in order to achieve the expected effective stress value of the design, it is required to use the double control measures of tension control and extension value checking. When the actual tension reaches the design tension, the deviation of the actual elongation value is required. Should be in the range of -6% to +6%, and the number of slip wires or breakage per strand is controlled to be 1 filament, and the slip wire or breakage rate of each cross section must not be greater than 1% of the total number of filaments in the cross section. During the process of tensioning and anchoring the long strands of steel strands, due to various reasons, the main problems that easily arise are: individual strands are slipped and broken; as the length of the strands increases, actual deviation of the elongation is presented. From positive to negative trends, the greater the beam length, the greater the negative deviation, even exceeding the allowable negative deviation of -6%.

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