1. Composite Action in Steel Girder Bridge Superstructures Subjected to Transverse Earthquake Loading
Research Assistant: Francisco Garcia-Alvarez
Experiments were performed on 2/5 scale model of a steel girder bridge superstructures with reinforced concrete deck to investigate means of improving the seismic performance of typical slab and girder bridges. During the early stage of experimentation, the need to understand the influence of composite action became apparent. The figure below shows the test set-up that was used for this investigation. It was found out that the shear connectors in a fully composite model were sufficient to ensure composite action when subjected to transverse loading and provided an adequate load path through the superstructure and into the substructure. However, the lack of shear connectors in the negative moment regions caused the load to be transferred into the steel girders at the point of contra-flexure, resulting in damage to the girders and inadequate formation of the ultimate limit state in the columns.
View of Test Set-up Used to Determine the Load Path in Steel Plate Girder Bridges
2. Seismic Performance of Steel Girder Bridges with Ductile Cross Frames Using Single Angle X-Braces
Research Assistant: Lyle P. Carden
Ductile end cross frames have been proposed in the past a seismic design and retrofit strategy for steel plate girder bridges. Large scale shake table experiments were performed on a straight steel I-girder bridge model to evaluate the performance of a superstructure with ductile end cross frames using single angle X-braces. The figure below shows the test set-up that was used in this investigation. The cross frames exhibited no apparent overall strength degradation, but also comparatively low post yield stiffness, allowing the cross frames to act as effectives structural fuse.
View of Plate Girder Bridge on the Earthquake Simulators
3. Seismic Performance of Steel Girder Bridges with Ductile Cross Frames Using Buckling Restrained Braces
Research Assistant: Lyle P. Carden
Large shake table experiments investigated the performance of braces with both pin-ended connections and fixed-end connections. The figure below shows the BRB at end cross frame. Despite slippage, the pin ended connections are considered more effective as flexural action in the relatively short braces is prevented. The relatively large deformation capacity of the BRBs, although not as great as the X-braces is necessary to achieve a significant reduction in the base shear. The maximum cross frame displacements with the BRBs are consistently smaller than those in the X-braces at the same level of base shear.
View of BRB at the End Cross Frame of the Plate Girder Bridge
Cyclic Behavior of Steel Plate Girder Bridge End Cross Frames
Research Assistant: Hamid Bahrami
The end cross frames of steel plate girder bridges play an important role in transferring the seismic forces to the substructures. The diagonal members of the end cross frames can be designed and detailed to withstand large cyclic inelastic deformation thus reducing limiting the lateral forces that can be transferred to the substructure. An experimental investigation was conducted on several types of end cross frames to determine the load path and cyclic deformation. The figure below shows the set-up that was used for this investigation. The results of these experiments showed the importance of shear connectors in transferring the seismic forces to the bearings.
View of Test set-up Used for End Cross Frame Experiments
5. Fatigue Behavior of a Riveted Open-Deck Railroad Plate Girder Span
Research Assistant: Philip C. He
A full scale specimen representing an existing railroad bridge was subjected to 5.5 million cycles of dynamic heavy loading. These cycles represented 200 million gross ton of rail traffic. The figure below shows the test set-up used in the fatigue testing of plate girder. The top flange and the web of the plate girder experienced out-of-plane deformations due to the eccentric location of the applied load from the center of the plate girder. The measured strains on the flange and the web correlated well with the strains obtained using linear finite element analysis.
View of Open Deck Plate Girder Under Applied Loading
6. Bridge Column Rebar Cage Stability during Construction
Research Assistant: J. Camilo Builes-Mejia
Collapse of rebar cages has been problematic costing bridge owners, contractors, and the public substantial time and money. The lateral stiffness and strength of rebar cages depends on the connections between the longitudinal and transverse bars and on the presence of internal braces. Experimental investigation was conducted on various tie wire connections to determine their capacity. These results were then used in sophisticated nonlinear finite element analyses to determine the significance of tie wire connections and bracing. The results have shown the internal braces and their configurations are the primary contributors to the stability of rebar cages. To calibrate the finite element models, large scale rebar cage models were tested to failure (Fig. 4). Based on this investigation, guidelines are being established for the assembly and construction of bridge column rebar cages to keep them stable.
Collapse of Full-Scale Rebar Cage