| The pre-stressed threaded steel reinforcement with an embedded anchor plate is one of the main components used for connecting prefabricated bridge piers and foundations.It is also widely applied in preventing uplift in raft foundations.However,there is limited experimental research on its anchorage performance in thick reinforced concrete slabs or foundations.In this study,ten vertical pull-out specimens of pre-stressed threaded steel reinforcement were designed and manufactured for testing in thick reinforced concrete slabs or foundations.The experimental parameters included effective anchorage length,presence of a sleeve,anchor plate dimensions,surface reinforcement ratio,and number of structural reinforcements.The failure characteristics of the specimens were investigated,and load-displacement curves,pull-out bearing capacity characteristics,and load-strain curves were analyzed.Finite element simulations were also conducted,and a calculation formula for the pull-out bearing capacity of pre-stressed threaded steel reinforcement with an anchor plate was proposed.The main research findings are as follows:(1)The experimental results showed that the pull-out bearing capacity increased by 50% and79% when the effective anchorage length increased from 150 mm to 200 mm and 250 mm,respectively.When the effective anchorage length was sufficient,the ultimate pull-out bearing capacity depended on the ultimate bearing capacity of the pre-stressed threaded steel reinforcement.Increasing the anchor plate width from 120 mm to 140 mm increased the cracking load by 1.33 times.The increase in the number of structural reinforcements had no significant effect on the cracking load,but it improved the pull-out resistance performance of pre-stressed threaded steel reinforcement with an anchor plate.Increasing the diameter of surface reinforcements slightly increased the cracking load of the specimens.The use of a sleeve increased the cracking load by 3.66 times compared to specimens without a sleeve.(2)Comparative analysis of calculation formulas: Compared with the requirement in Article 8.3of the "Code for Design of Concrete Structures," which specifies an anchorage length of 1200 mm or48 times the diameter of the steel reinforcement,the experimental results indicated that pre-stressed threaded steel reinforcement yielded when the required anchorage length was 13.2 times the diameter of the steel reinforcement.Therefore,the anchorage length required by the "Code for Design of Concrete Structures" appears to be conservative.Based on the experimental results and relevant literature,the experimental values and calculated values of the pull-out bearing capacity of prestressed threaded steel reinforcement with an anchor plate were compared.The calculated values using the CCD method,Nilforoush’s proposed formula,the shear calculation formula in the "Code for Design of Concrete Structures," and the shear calculation formula in the Japanese JSCE specification were,on average,64%,20%,34%,and 12% lower than the experimental values,respectively.The formulas used can predict the pull-out bearing capacity of pre-stressed threaded steel reinforcement with an anchor plate with reasonable safety.However,they may overestimate the pull-out bearing capacity for some specimens.Therefore,this study proposes a calculation formula for the pull-out bearing capacity of pre-stressed threaded steel reinforcement with an anchor plate based on the failure of concrete in the anchor zone.(3)Finite element analysis: ABAQUS finite element software was used to analyze the prestressed threaded steel reinforcement with an anchor plate,and the simulation results were compared with the experimental data.The results showed good agreement between the finite element analysis and experimental data,and the influential parameters such as effective anchorage length,anchor plate width,diameter of surface reinforcements,and diameter of structural reinforcements were further analyzed.(4)The pre-stressed threaded steel reinforcement with an anchor plate studied in this research is similar to the Type III anchor bolt in the "Design Manual for Steel Structure Connections." The manual only requires the anchor plate thickness to be greater than 20 mm,and pre-stressed threaded steel reinforcement manufacturers also recommend using a 20 mm thick anchor plate.However,during the pull-out tests of pre-stressed threaded steel reinforcement with an anchor plate,it was found that the pull-out bearing capacity of some specimens was significantly lower due to insufficient flexural stiffness of the anchor plate.Therefore,it is recommended to follow the requirements of the "Technical Regulations for Anchor Plate Applications," which state that the anchor plate thickness should be greater than the diameter of the pre-stressed threaded steel reinforcement. |
