How to ensure the tension accuracy of prestressed tensioning equipment under high pressure?
Publish Time: 2025-12-08
In modern large-scale infrastructure construction, prestressed technology is widely used in critical structures such as bridges, high-rise buildings, and nuclear power plant containment vessels. Prestressed tensioning equipment—composed of tensioning jacks and electric hydraulic pumps—is the core tool for applying prestress, and its tension accuracy directly affects the safety and durability of the structure. Excessive tension deviation can lead to concrete cracking, abnormal arching, or even structural failure.
1. System Calibration: The Prerequisite Guarantee of Accuracy
The foundation of tension accuracy lies in the accuracy of the equipment itself. Prestressed tensioning equipment must undergo "whole-machine joint calibration," that is, force value calibration of the complete system consisting of jacks, hydraulic pumps, pressure gauges, and hydraulic pipes on a standard testing machine. Calibration needs to cover 20%–100% of the commonly used tensioning range and establish an accurate correspondence curve between hydraulic pressure and output force. This curve is the sole basis for force value conversion during subsequent construction. After more than 6 months of use or 200 tensioning cycles, the equipment must be recalibrated to eliminate system drift caused by factors such as seal aging and oil contamination.
2. High-Precision Sensing and Intelligent Closed-Loop Control
Traditional methods relying on mechanical pressure gauge readings suffer from large errors and slow response. Modern high-precision tensioning equipment generally uses digital pressure and displacement sensors to collect real-time data on oil pressure and steel strand elongation, achieving closed-loop feedback through an embedded control system. The system dynamically compares the measured force value with the set target value, automatically adjusting the output of the electric oil pump to achieve micron-level flow control. This "sensing-judgment-adjustment" mechanism effectively suppresses pressure fluctuations, improving tension force control accuracy to within ±0.5%, far superior to manual operation.
3. High-Quality Hydraulic System: The Core of Stable Power Supply
The performance of the electric oil pump directly affects the smoothness of the tensioning process. High-precision equipment typically uses variable displacement piston pumps or servo motor-driven pumps, offering advantages such as low pressure fluctuations, fast response, and adjustable flow. Meanwhile, the cleanliness of the hydraulic oil must be strictly controlled below NAS 8 to prevent impurities from wearing down the valve core or clogging the throttle orifice. Furthermore, oil temperature significantly affects viscosity; high-end equipment often integrates oil temperature monitoring and cooling modules to ensure stable hydraulic performance during long-term continuous operation.
4. Optimization of Synchronous Tensioning and Staged Loading Processes
For multi-strand symmetrical tensioning (such as box girder webs), an intelligent synchronous tensioning system is used. A central controller coordinates the synchronous loading of multiple jacks, ensuring that the difference in prestress between each strand does not exceed 2%. This effectively eliminates inelastic deformations such as steel strand slack and wedge slippage, making the final locking force closer to the theoretical design value.
5. Standardized Operation and Environmental Factor Control
Even with advanced equipment, improper operation can still lead to inaccuracies. During construction, it is necessary to ensure that the jack axis is completely concentric with the prestressing tendons to avoid eccentric stress; the length and bends of the oil pipes should be as consistent as possible to reduce pressure loss differences; in extreme temperature environments, temperature correction or suspension of operation should be performed. Furthermore, structural factors such as anchor friction and duct friction also require pre-correction of tension values through friction testing.
High-precision control of prestressed tensioning equipment is the result of the synergistic effect of materials, equipment, processes, and management. From system calibration to intelligent control, from hydraulic stability to construction specifications, every link is indispensable. Only by treating every kilonewton of tension with a scientific attitude can we truly achieve "precise prestressing" and lay a solid safety foundation for projects that will last a century.
