Proper design of reinforced concrete bridge beam-column connections is imperative for the behavior of the bridge structure. While in the past this area was overlooked, resulting in bridge structure damage and in some cases collapse, current methods have overcompensated for these shortcomings. The presented research shows that current joint design requirements in the state of California produce conservative designs (i.e., joints with excessive amounts of reinforcement). The joints in these systems are capable of supporting the intended flexural mechanism, but at the cost of constructability. The goal of this report is to evaluate current methods, identify shortcomings, and develop methods or techniques for joint performance improvement.
The research was carried out in three phases. In the first, current design requirements, constructability improvement techniques, and joint force transfer mechanisms were experimentally investigated. This was accomplished with four large-scale experiments on cap beam to column subassemblies of typical geometry. Following analysis of the force transfer mechanisms and determination of the shortcomings, a second experimental phase was undertaken to evaluate joints subjected to high joint demands. This consisted of two subassemblies with reduced beam depths and increased column strengths. Furthermore, the effectiveness of the joint spiral reinforcement versus the use of lateral and vertical joint transverse reinforcement was evaluated. In the third phase, the effectiveness of the reinforcement in these designs was evaluated analytically using developed three-dimensional finite element models. The study strives to develop a set of joint design requirements based on damage criteria; two performance criteria are suggested. The first criterion determines a level of lateral reinforcement necessary to activate the joint width in shear resistance. The second criterion determines a level of vertical joint reinforcement necessary to limit crack formation in the joint.
The results of these phases show that the intended design mechanism does not completely occur, suggesting that the placement of reinforcement under current requirements may be ineffective. Furthermore, it is shown that the use of a joint spiral is not necessary for good joint performance and may be removed as a means of improving constructability. Headed reinforcement was shown effective when used as joint transverse reinforcement, thus providing additional means of construction improvement. Three-dimensional finite element models were found to provide a reliable estimation of global and local joint response. As a conclusion to this work, the results of parametric finite element analyses are used to develop possible damage-based joint design requirements.
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