C. J. Naito Main

Executive Summary
Due to the catastrophic failure of bridge systems in the earthquakes of Loma Prieta, Northridge, and Kobe, there has been a great effort directed towards safer civil infrastructure in the United States and Japan. This has taken the form of retrofitting or strengthening existing bridges and increasing the design requirements for new bridge systems. While strengthening techniques and design requirements for beams and columns are well established [Park 1975], methods for designing or evaluating the connection between the two are still in contention.

The current methods of joint design are based either on a two-dimensional evaluation of the flow of stresses within the joint or through strut and tie methods which often neglect compatibility in their formulation. In general, reinforced concrete bridges are subjected to multi-directional ground motion. Therefore, response of bridge beam-column joints is predominantly three-dimensional (3D). Evaluation of existing bridges and development of appropriate design requirements for beam-column joints can be enhanced through the the use of 3D-models which take into account compatibility, equilibrium and the constitutive properties of the system.

Many computational methods exist for modeling systems in three-dimensions; however, how well these models reflect the actual behavior of reinforced concrete bridges, particularly systems subjected to seismic loading, is not clear. This study investigates 3D finite element modeling methods for application on reinforced concrete bridges using available techniques and solution strategies. An effective procedure for modeling these systems in three-dimensions is presented. The results of these modeling techniques are compared to the response of reduced scale experimental bridge subassembly tests.

This research focused on the performance and design of innovative reinforced concrete joints. The project involved the investigation of existing design practices and evaluation of new reinforcing strategies through experimental testing and analytical modeling. Headed reinforcement was one strategy that was tested as a means of decreasing joint congestion. This project was part of a larger investigative effort. The phases, presented here, that focused on the T-joint connections, were called 'Group A' and 'Group B.'

Findings in the form of global and local load-deformation relationships, crack patterns, modes of failure, and stress-strain relations are presented. The observed damage initiation and propagation reflected the flexibility of the tested waffle slab/circular column subassembly and the brittle nature of failure of the tested waffle slab/infilled frame subassembly. The provided idealized relations for the different aspects of the performance of these subassemblies are readily usable for finite element modeling of structural systems where these subassemblies may represent parts of the whole system.

Research Team
Clay Naito, Lead Researcher
Professor Jack P. Moehle, Principal Investigator
Assistant Professor Khalid Mosalam, Co-Principal Investigator

Publications
1. C. J. Naito, J. P. Moehle, and K. M. Mosalam, "Evaluation of Bridge Beam-Column Joints Under Simulated Seismic Loading," ACI Structural Journal, Vol.99, No.1, Jan. 2002.
2. K. M. Mosalam, C. J. Naito, S. Khaykina, "Bidirectional Cyclic Performance of Reinforced Concrete Bridge Column-Superstructure Subassemblies," Earthquake Spectra, Vol.18, No.4, Nov 2002, pp.663-687.
3. C. J. Naito, J. P. Moehle, and K. M. Mosalam, "Experimental and Computational Evaluation of Reinforced Concrete Bridge Beam-Column Connections for Seismic Performance," PEER Report No.2001/08, Berkeley: Pacific Earthquake Engineering Research Center, University of California, Nov. 2001, 232 pages.

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