Behavior of Bridge Asphalt Plug Joints under Thermal and Traffic Loads

An asphalt plug joint (APJ) is a type of expansion joint providing quick, easy, and cheap installation along with good surface flatness. However, APJs are known to suffer from premature failure, and their behavior, especially under thermal movement, has not yet been fully established. In this paper, the behavior of a typical APJ subjected to thermal and traffic loads is examined through a series of finite element analyzes employing a temperature-dependent viscoplastic material model. The material parameters are calibrated by using previously published test data, and the model is validated by comparing simulated responses to APJ test data. The developed models are then used to investigate stress and strain distributions, vulnerable locations to cracking failure, and local demands at those locations when a prototype APJ is subjected to various loading and temperature conditions. Sensitivity studies are also conducted to quantify the effect of debonding the bottom of the APJ and loading rate. The model results shed light about APJ response under traffic and thermal loading and provide new, fundamental information that can be used to improve the durability of APJs. For example, the simulation results suggest that intentionally debonding the interface between the gap plate and the APJ is a practical and low cost solution to mitigate the risk of premature APJ failure.     

Improved Longitudinal Joint Details in Decked Bulb Tees for Accelerated Bridge Construction: Concept Development

This paper focuses on an investigation of improved continuous longitudinal joint details for decked precast prestressed concrete girder bridge systems. Precast concrete girders with an integral deck that is cast and prestressed with the girder provide benefits of rapid construction along with improved structural performance and durability. Despite these advantages, use of this type of construction has been limited to isolated regions of the United States. One of the issues limiting more widespread use is a perceived problem with durability of longitudinal joints used to connect adjacent girders. This paper presents the results of a study to assess potential alternate joint details based on constructability, followed by testing of selected details. Seven reinforced concrete beam specimens connected with either lapped headed reinforcement or lapped welded wire reinforcement were tested along with a specimen reinforced by continuous bars for comparison. Test results were evaluated based on flexural capacity, curvature at failure, cracking, deflection, and steel strain. Based on the survey and the experimental program, a headed bar detail with a 152 mm (6 in.) lap length was recommended for replacing the current welded steel connector detail.     

State of Research on Seismic Retrofit of RC Beam-Column Joints with Externally Bonded FRP

A considerable amount of research has been directed recently toward understanding and promoting the use of externally applied fiber-reinforced polymer (FRP) for the seismic retrofit of reinforced concrete (RC) structures. In this paper, a comprehensive review and synthesis of published experimental studies on the seismic rehabilitation of RC frame beam-column joints with FRP is presented, and the issues that need to be addressed for further research are discussed. In addition, the paper presents a simple design model for predicting the contribution of the FRP to the shear strength of retrofitted joints. The key element in the model is the derivation of an expression for the effective FRP strain, based on the calibration of test data reported in the literature. A total of 54 tests carried out worldwide were considered in the review, and a database of the published studies, encompassing all relevant design parameters, was assembled. The reported test results confirm the structural effectiveness of the FRP strengthening technique for the seismic retrofit of RC joints. However, there are some gaps which need to be addressed. For instance, there is a lack of a rationale explanation of the resistance mechanisms involved in the beam-column joints retrofitted with FRP. Such a rational explanation is a prerequisite for the development of more comprehensive and rigorous design procedure.     

钢筋混凝土框架夹心节点设计方法

为给出钢筋混凝土框架夹心节点的设计方法,依据试件破坏特征等试验结果提出了验算内容与设计准则,通过对夹心节点抗震性能影响因素的分析及其与传统节点的对比提出了设计参数限值,基于试验试件的承载力并结合非线性有限元模拟的结果提出了核心区承栽力验算公式。结果表明：为达到所需的位移延性并满足承载力要求,需设置剪压比、轴压比、柱梁混凝土强度比、最小配箍量等参数限值约束夹心节点适用范围;通过核心区受压验算、受剪验算保障节点的承载力,必要时可采取适当的加强措施;此外需要采取合理的构造措施避免梁筋过度的粘结退化。