Reinforced concrete Intermediate Diaphragms (IDs) are currently being used in prestressed concrete (PC) girder bridges in Louisiana. Some of the advantages of providing IDs are disputed in the bridge community because the use of IDs increases the cost and time of construction. There is no consistency in the practice of providing IDs among various states and codes of practice, and the overall effectiveness of IDs, as well as the need for them in prestressed concrete bridges, is unclear. The objectives of this research were (1) to assess the need of reinforced concrete (RC) IDs in PC girder bridges and to determine their effectiveness, and (2) to search for a possible alternative steel diaphragm configuration that could replace concrete diaphragms if necessary. The research team has examined and reviewed state-of-the-art technology and current practices from many sources of information on IDs. Through a survey questionnaire and review of the Louisiana Department of Transportation and Development (LADOTD) Bridge Design Manual, the research team obtained relevant information regarding the ID practices in Louisiana. Through the LADOTD data base for all state bridges, and from direct interaction with district engineers, several of the bridges that are of interest for this study were selected for field inspection. From these field trips to various bridge locations, much information has been acquired from the bridges themselves, as well as from the district engineers. Systematic parametric studies for various bridge configurations, which are representative of an entire range of bridge geometries with different parameters, were analyzed through simplified and solid finite element models. This study was performed on right and skewed bridges, which are simply supported and continuous. A reduction factor that could be multiplied by the AASHTO load distribution factor to account for the influence of the diaphragm in load distribution was developed. A finite element analysis was carried out using 3-D solid models to assess the effectiveness of various diaphragms in protecting the girders against the lateral impact and to determine the design forces in the steel bracing members during construction of deck. The results from the parametric studies indicated that several parameters such as skew, span length, spacing, stiffness of diaphragm and girder have different levels of influence on the effectiveness of diaphragms in live load distribution for bridges. Correction factors that could quantify the ID influence on load distribution were developed. Results from various studies indicated that a steel diaphragm section can possibly replace the RC diaphragms. A prestressed concrete bridge was tested in the field. This bridge was selected by an inspection team comprised of personnel from FHWA, LADOTD, and the LSU research team and is located over Cypress Bayou on LA 408 East, in District 61. A comprehensive instrumentation and loading scheme is presented and illustrated in this report. The instrumentation consists of LVDTs – Linear Variable Differential Transformers (to measure the midspan deflection of each girder), accelerometers, strain gauges, and acoustic emission sensors. The measured results are presented, and comparisons are made between the finite element model and the field tests.
To overcome the drawbacks of bond-type anchors for carbon fiber–reinforced polymer (CFRP) cables, an innovative bonded anchor with steel wedges at the free end is developed in this study. The new anchor features high compressive stresses in the free end zone and relatively low radial stresses in the loaded end zone. Theoretical methods for assessing the carrying capacity and mechanical behaviors of this new bond-type anchor are established after analyzing the working mechanism of the new anchor. Furthermore, an optimal design method for the new anchor is developed. The optimal design and mechanical behavior for different cable specifications of the new anchorage system are analyzed, and the optimal design parameters are provided. Experimental studies were conducted on the static and fatigue properties of the new anchor, which is designed with 19 CFRP wires. The results show that the cone angle of the barrel has a significant effect on the mechanical behaviors of the anchor. The theoretical results match the test results well. The experiments show that the new anchor with 19 CFRP wires reached a failure load of up to 97% of the CFRP cable's total capacity, and it is capable of resisting bear over 2 million load cycles with a stress amplitude of 161 MPa. In addition, the static load-carrying capacity of the new anchor increases after the fatigue test.
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