Specification for Installation of Prestressed Steel Strand

Prestressed steel strand is an indispensable material in engineering construction, and it is also widely used in highways, bridges, pillow rails, large sports venues, high-rise buildings, airports, seaports, docks, nuclear power plants, urban overhead roads, light rails, and other projects, but this does not mean that it can be installed at will. There are also certain specifications for the installation of steel strands. The following editor will introduce you to the installation specifications of prestressed steel strands, I hope it will be helpful to everyone.

The position of the prestressed steel strands and whether the steel strands are twisted are the key to quality control. The inaccurate position of the duct will change the stress state of the structure. If the elevation change section of the curved duct is not round, it will increase the friction loss of the prestressed duct. Therefore, the accuracy of the location of the duct is directly related to whether the prestress degree of the construction is consistent with the prestress degree of the design, and it has a deep impact on the safety of the structure and whether there will be cracks in the engineering use stage.

If multiple steel strands are twisted together, the stress of each steel strand will be uneven during tension, which will increase the friction between the steel strands and cause the loss of prestress to increase. In the actual construction, if these details are not paid attention to, the position of the scaffolding tower of the fixed steel beam is inaccurate or the spacing is not arranged in accordance with the specification and design, it will cause the position of the steel beam to be inconsistent with the design, and some will produce sharp bends in the curve change section (the radius is too small) or the local deviation of the channel is too large.

At present, there are still projects that use manual pulling of steel strands, especially for the long bundles of multiple steel strands, which are very heavy. Manual pulling of steel strands takes time and effort, and it is easy to cause workers to rotate the steel strands to penetrate and make the steel strands twist together.

There are nine continuous beams in Section Four of an expressway (overpass) project in Shenyang. The spacing of the well-frames used to fix the steel beams during construction is 1 meter and the beam height is 1.6 meters. Therefore, the vertical bending change is not large, and the spacing meets the requirements. However, the coordinates of the derrick frame were inaccurate due to the poor work of the workers during the construction, and manual pulling of steel strands was used. The beam lengths ranged from 100 to 120 meters.

During tensioning, it was found that the elongation value of most of the steel strands did not match the theoretical elongation value (some were 11% less than the theoretical value). During the tensioning process, the sound of the internal steel strands being twisted and twisted was often heard. At that time, the equipment was verified immediately. When there was no problem with the equipment, the design unit, the supervision unit and the construction unit began to analyze the problem together. The measured elastic modulus was used when calculating the elongation value of the steel strand, and the values of μ and K were according to the recommended values of the specifications. The design unit rechecked the structure. Finally, it is determined that the error of the elongation value is guaranteed to be within 12% under the condition of ensuring the tension, which undoubtedly reduces structural safety.

The D ramp of the Sujiatun Interchange of Shenyang-Dalian Expressway is a 4-hole continuous curved beam with a length of 220 meters and a curve radius of 55 meters. Therefore, the steel beam has both horizontal and vertical bends. The well-shaped frame is arranged at a distance of 50cm and the coordinates are accurate. Manually coordinated and mechanically pulling of the steel strand. The same method was applied in two-linked 100-meter continuous beam  construction of  the Mark Super Bridge of Section 14 of the Guangzhou Southern Expressway Project. Due to special attention to the control of the duct coordinates and the smooth line of the duct, and to avoid the twisting of the steel strands. During the tensioning process, the elongation values of steel strands in the above two projects all meet the requirements.

The above installation specifications for steel strands are hoped to be helpful to everyone, and serious attention must be paid to related matters during construction to avoid related errors. Henan Zhongjiao Road&Bridge Engineering Materials Co., Ltd specializes in producing the post-tensioning system for over 10 years. If you want to know more information about prestressed anchorages, welcome to consult sales@zjmaterials.com.