Active Shear Reinforcement Technology Of Pre-stressed Steel Plate-Experimental Study On Stress Holding Of Bolted Steel Plate And Tensioning Technology

With the increasing improvement of the highway network in China,the bridge construction will enter a stage of “construction and maintenance”.The maintenance and reinforcement of old bridge has been paid more attention to for its practicality and economy.In terms of the reinforcement concept,the active reinforcement technology shows obvious advantages compared with traditional reinforcement technology because it can improve the structural mechanical performance in using stage,however,its research on shear reinforcement is relatively weak,and there are many deficiencies in reinforcement materials and construction technology.Therefore,a new type of “Active Shear Reinforcement Technology of Pre-stressed Steel Plates” is put forward,and there will be of great practical significance to study this technology.Based on its first subproject's results of experimental study on shear anchoring behavior of bolted steel plate,the experimental study on stress holding of bolted steel plate and tensioning technology is carried out in this paper.Taking into account the factors of prestress level,steel plate material and tensioning numbers,the effect of anchorage releasing and the development law of steel plates' stress with time increasing is mainly studied through the test of concrete component,then the influence of repeated tensioning technology on above two aspects is also considered and the time selection is discussed as well,finally,some suggestions about design and construction technology are put forward.The main results of this paper are as follows:(1)The test of tension-anchorage on different prestress levels and steel plate materials is carried out,the results show that the anchorage releasing effect is mainly related to the design prestress level applied to steel plate,not the steel material.(2)During the process of stress holding,the strain data of steel plate is collected in a long period of time,and the law of the data shows that the stresses on the test steel plates decrease with time and they tend to be stable eventually;its stress variation process is divided into three stages: the fast variation period,the gentle period and the stable period.(3)By comparing the data of stress holding on different prestress levels and steel plate materials,it can be known that the range and rate of stress variation with time are related to the prestress level and steel material.In the same steel material,the higher prestress level is applied,the greater range and rate will be;and the range and rate of Q345 are all greater than those of Q235 under the same proportion of prestress level for the yield strength.(4)The second tensioning and third tensioning are carried out for some components,and the law of the strain data under different tensioning numbers shows that the repeated tensioning technology is beneficial to reduce the effect of anchorage releasing and the stress loss with time increasing,but its weakening ability gradually decreases with the increase of tensioning times.And there should be theoretical minimum values of stress loss to anchorage releasing and stress holding,they cannot be realized accurately for their theoretical property,but can be approximated gradually by the increasing number of tensioning in real projects.(5)Through analyzing the law of the strain data under different tensioning numbers of the same test group,the repeated tensioning time should be selected at the end of the fast variation period.The result of this experiment shows that the second tensioning can be carried out within 3~5 days after the first tensioning,and the third tensioning can be carried out at about 5 days after the second tensioning.