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This report presents the research conducted as part of an investigation for the California Department of Transportation (Caltrans) regarding the seismic response and overall moment capacity of precast I-girder to inverted-T bent cap bridge connections for seismic applications. The current design practice, as outlined by Caltrans' Seismic Design Criteria, assumes that the connection between the precast I-girders and the inverted-T bent cap will degrade in a seismic event and shall therefore be designed as a pinned connection, making the precast girder option for seismic bridges inefficient. A prototype I-girder to inverted-T bent cap bridge and a 50% scale test unit was designed in order to investigate the behavior of the as-built girder-to-cap connection region. Additionally, per the request of Caltrans, an improved girder-to-cap connection detail was developed in order to ensure a fully continuous moment connection between the I-girders and inverted-T bent cap.
This report presents the research conducted as part of an investigation for the California Department of Transportation (Caltrans) regarding the seismic response and overall moment capacity of precast I-girder to inverted-T bent cap bridge connections for seismic applications. The current design practice, as outlined by Caltrans' Seismic Design Criteria, assumes that the connection between the precast I-girders and the inverted-T bent cap will degrade in a seismic event and shall therefore be designed as a pinned connection, making the precast girder option for seismic bridges inefficient. A prototype I-girder to inverted-T bent cap bridge and a 50% scale test unit was designed in order to investigate the behavior of the as-built girder-to-cap connection region. Additionally, per the request of Caltrans, an improved girder-to-cap connection detail was developed in order to ensure a fully continuous moment connection between the I-girders and inverted-T bent cap.
TRB’s National Cooperative Highway Research Program (NCHRP) Report 698: Application of Accelerated Bridge Construction Connections in Moderate-to-High Seismic Regions evaluates the performance of connection details for bridge members in accelerated bridge construction in medium-to-high seismic regions and offers suggestions for further research.
In seismic design practice, hollow concrete columns offer an efficient alternative especially for tall bridge columns. The confinement in critical regions of these columns is not well understood and the confinement models developed for solid concrete sections are used to characterize these columns. This report identifies several shortcomings in current practice associated with hollow column design. Using experimental and analytical means, it is shown that the confined concrete behavior in hollow concrete columns is different from that established for solid sections. Recommendations to improve analysis and design of hollow columns are presented with experimental verification. Modification to alter the confinement models developed for solid sections and a design example are also provided.
In bridges with precast prestressed concrete girders, the resistance to seismic effects is achieved by the interaction between the columns, the cap beam and the girders. Said components must be connected such that flexural resistance is provided. Under the impact of longitudinal seismic motion, the bottom flanges of the two girders, meeting end-to-end at the cap beam, will be under tension and compression, respectively. The tension connection is presently made by extending some of the bottom strands into the cast-in-place diaphragm. At this location, the space available is too small for development by bond in the straight strands alone. Since concrete in the diaphragm is highly confined, it can probably carry high bearing stress and a small bearing area may be possible. Thus, the goal of this project is to create a reliable, effective, as well as practically applicable way of anchoring strands extended from the girder into the cap beam. The first stage in the development of the girder-diaphragm seismic connection consists of establishing the adequacy of the smallest possible strand anchor capacity such that a strand ductile failure due to yielding and fracture is achieved before the strand anchor fails by crushing the concrete at the bearing surface. As a second stage, the impact of the possible failure mechanisms of the strands embedded in the diaphragm on the development of the girder-cap beam positive moment connection was investigated. Finally, the distribution of girder bending moments across the bridge deck was evaluated, while investigating the influence on that distribution of the most important bridge parame- ters, such as cracking of bridge components, as well as varying cross sectional dimensions.
Unified Theory of Concrete Structures develops an integrated theory that encompasses the various stress states experienced by both RC & PC structures under the various loading conditions of bending, axial load, shear and torsion. Upon synthesis, the new rational theories replace the many empirical formulas currently in use for shear, torsion and membrane stress. The unified theory is divided into six model components: a) the struts-and-ties model, b) the equilibrium (plasticity) truss model, c) the Bernoulli compatibility truss model, d) the Mohr compatibility truss model, e) the softened truss model, and f) the softened membrane model. Hsu presents the six models as rational tools for the solution of the four basic types of stress, focusing on the significance of their intrinsic consistencies and their inter-relationships. Because of its inherent rationality, this unified theory of reinforced concrete can serve as the basis for the formulation of a universal and international design code. Includes an appendix and accompanying website hosting the authors’ finite element program SCS along with instructions and examples Offers comprehensive coverage of content ranging from fundamentals of flexure, shear and torsion all the way to non-linear finite element analysis and design of wall-type structures under earthquake loading. Authored by world-leading experts on torsion and shear
This report describes research conducted to enable evaluation of existing vintage bent cap beams in reinforced concrete deck girder bridges. The report is organized into two parts: 1) flexural anchorage capacity response and prediction of reduced development length due to beneficial column axial compression and 2) structural performance of bent cap systems and their analytical evaluation. Each of these parts including descriptions of the experimental specimens and results of analytical studies is described separately. The research results from both studies are combined and used in an example to demonstrate the rating of an actual 1950's vintage RCDG bent cap beam for continuous and single trip permit loads.