Abstract:Through the Tensile testing, the acoustic emission characteristic parameters of the whole damage process of the steel strand were obtained. The test results show that the correlation point graph of count, energy, duration, amplitude and time is used to comprehensively characterize the damage, which can not only track the whole process of damage, but also accurately determine the broken wire signal, non broken wire signal and broken wire position. It is found that the acoustic emission characteristic parameters of the steel strand are not obvious before the yield deformation, and after the yield stage, The characteristic parameters of acoustic emission gradually increase, and as the fracture approaches, the characteristic parameters of acoustic emission rapidly increase. Finally, the time series fractal theory of acoustic emission characteristic parameters is used to study the damage evolution law of steel strand. In the middle stage of loading, the Fractal dimension changes little. When the crack of steel strand enters the rapid growth stage, the Fractal dimension changes in a "maximum minimum" mode, which can provide a new criterion for the critical damage of steel strand

Abstract:The traditional clamp type anchor must be improved when applied to CFRP (Carbon Fiber Reinforced Polymer/Plastics) prestressed tendons. The improved clamp type anchor consists of concave toothed curved clamps, anchor cups, plastic films, and thin-walled aluminum sleeves. In the design process of clip type anchors, the stress formula of the anchor cup is first derived through static analysis of the anchor. Then, the minimum thickness of the anchor cup is determined based on the Von Mises yield criterion, and the geometric size of the clip is obtained from the geometric relationship between the anchor cup and the clip. Experimental research shows that when the inclination angle of the anchor cup is 3 °, the pre tightening force of the clip is 100kN, the thickness of the aluminum sheet is 1mm, the spacing between the concave teeth is 12.85mm, and the depth of the concave teeth is 0.3mm, the clip type anchor shows good anchoring performance, with an ultimate load of 185kN and a corresponding anchoring efficiency coefficient of 96.4%. The experimental parameters such as anchor cup length, anchor cup inclination angle, pre tightening force of the clip, spacing between concave teeth, depth and width, and thickness of the aluminum sleeve all have a significant impact on the ultimate bearing capacity of the clip type anchor and the sliding amount between the CFRP reinforcement and the clip. The measured values of anchor cup stress are in good agreement with the theoretical values, verifying the reliability of anchor stress analysis. The calculation formula for ultimate load has good applicability

Abstract:Carbon fiber reinforced polymer (CFRP) bars have excellent physical and mechanical properties and can be used to replace traditional prestressed steel bars. A model of prestressed concrete box girder with externally configured carbon fiber reinforcement was made, and experimental observations were conducted for 1001 days on the stress redistribution, long-term deflection deformation, and crack development of the box girder under continuous uniform load. Based on the measured creep coefficient of plain concrete columns, the bilinear method and curvature method were used to predict the long-term bending deformation of the test box beam. The experimental results show that the strain of compressive steel bars increases by 225% to 268% compared to the initial value, the strain of tensile steel bars increases by 36.2% to 38.6% compared to the initial value, and the compressive strain of concrete surface increases by 164% to 224% compared to the initial value. According to the current design specifications, the characteristic crack width under long-term load action is 11.8%~55.5% smaller than the measured value. The measured value of long-term bending deformation in the mid span is 2.32-2.42 times the initial deformation, which is 18.5% larger than the current design specifications

Abstract:Prestressed cables are widely used in bridges and some large building structures. HDPE is commonly used as the outer sheath of cables and is an important protective layer for cables, playing a protective and anti-corrosion role, directly affecting the safe use of bridges and the lifespan of cables. The wear durability of HDPE was explored through fatigue wear performance tests of prestressed cables and steering gear, as well as friction loss tests with large sliding distances. The former focuses on micro vibration wear and conducts 2 million pulse vibration slip tests under bending stress and deflection stress to detect the degree of HDPE wear; The latter tests the friction rate between the steering gear and the HDPE sheath of the steel strand, simulating the actual force conditions, for vibration wear with a large sliding distance. Both sets of test results indicate that the wear rate of HDPE is very low, indicating that it has sufficient wear durability and can meet the general usage requirements of bridge cables. The test results can provide a certain reference for determining the design service life of bridge cables

Abstract:Experimental research was conducted on the mechanical properties of the overall cable and its constituent steel wires after a fire in the bridge steel wire cable. The conclusion was drawn on the impact of cable fire on the mechanical properties of the cable, and maintenance suggestions were given for the cable after fire. This provides a basis for evaluating the performance of cables after a fire and can serve as a reference for evaluating similar engineering accidents

Abstract:The currently used soil nail support design software saves designers a lot of time. But for muddy soil layer and two types of soil layer C φ When there is a significant difference in values, the software calculates results with greater distortion. This article analyzes the mechanical models of soil anchors and soil nails based on previous studies, and considers the problem from another perspective, which is to use anchor pipes to strengthen the soil and improve its C φ The value stabilizes the soil. At the same time, the effect of soil nail reinforcement on soil was also discussed

Abstract:Through the analysis of the settlement characteristics of sparse Pile foundation, this paper proposes three representative settlement calculation methods (building pile foundation code method, settlement as control index method, double-layer stress method) for comparison and analysis.

Abstract:This article introduces the current application status of single-layer flat cable mesh in glass curtain wall engineering in China, as well as the issues and suggestions that should be paid attention to.