Seismic response analysis of multiple-frame bridges with unseating restrainers considering ground motion spatial variation and SSI

Unseating damages of bridge decks have been observed in many previous major earthquakes due to large relative displacement exceeding the available seat length. Steel cable restrainers are often used to limit such relative displacements. Present restrainer design methods are based on the relative displacements caused by the different dynamic characteristics of adjacent bridge structures. However, the relative displacements in bridge structures are not only caused by different dynamic characteristics of adjacent bridge segments. Recent studies indicated that differential ground motions at supports of bridge piers and Soil Structure Interaction (SSI) could have a significant influence on the relative displacement of adjacent bridge components. Thus the present design methods could significantly underestimate the relative displacement responses of the adjacent bridge components and the stiffness of the restrainers required to limit these displacements. None of the previous investigations considered the effects of spatially varying ground motions in evaluating the adequacy of the restrainers design methods. Moreover, the code recommendation of adjusting the fundamental frequencies of adjacent bridge structures close to each other to mitigate relative displacement induced damages is developed based on the uniform ground motion assumption. Investigations on its effectiveness to mitigate the relative displacement induced damages on the bridge structures subjected to spatially varying ground motion and SSI are made. This paper discusses the effects of spatially varying ground motions and SSI on the responses of the multiple-frame bridges with unseating restrainers through inelastic bridge response analysis

Parametric study of seismic performance of super-elastic shape memory alloy-reinforced bridge piers

One of the important measures of post-earthquake functionality of bridges after a major earthquake is residual displacement. In many recent major earthquakes, large residual displacements resulted in demolition of bridge piers due to the loss of functionality. Replacing the conventional longitudinal steel reinforcement in the plastic hinge regions of bridge piers with super-elastic shape memory alloy (SMA) could significantly reduce residual deformations. In this study, numerical investigations on the performance of SMA-reinforced concrete (RC) bridge bents to monotonic and seismic loadings are presented. Incremental dynamic analyses are conducted to compare the response of SMA RC bents with steel RC bents considering the peak and the residual deformations after seismic events. Numerical study on multiple prototype bridge bents with single and multiple piers reinforced with super-elastic SMA or conventional steel bars in plastic hinge regions is conducted. Effects of replacement of the steel rebar by SMA rebar on the performance of the bridge bents are studied. This paper presents results of the parametrical analyses on the effects of various design and geometric parameters, such as the number and geometry of piers and reinforcement ratio of the RC SMA bridge bents on its performance

Seismic Evaluation of Steel Joints for UCLA Center for Health Science Westwood Replacement Hospital

Report No. CCEER-00-5The Northridge earthquake of January 17, 1994, dramatically demonstrated that welded moment connections in Special Moment Resisting Frames (SMRF) were susceptible to damage during earthquakes. This damage initiated the requirements for qualifying cyclic tests of beam-to-column connections. The purpose of these requirements is to provide evidence that moment connections satisfy the code requirements of strength and inelastic rotations. Realizing this fact, John A. Martin, Inc. engineers initiated a study to evaluate experimentally the response of the moment connections of the UCLA Center for Health Science Westwood replacement hospital. The JAMA moment connection utilized a variety of concepts including bottom haunch, top cover plate, beam web stiffener, and reduced beam section (RBS). In this concept, the cross section of the beam is intentionally reduced within a segment to produce an intended plastic hinge zone, located within the beam span away from the column face. While the bottom haunch and the top cover plate substantially reduces the seismic demand at the face of the column by the added strength and stiffness. The buckling of the web at the plastic hinge region is effectively postponed via the horizontal web stiffeners

A Study of Fiber Reinforced Plastics for Seismic Bridge Restrainers

Report No. CCEER-05-2Abstract: Easily installed and inspected fiber reinforced plastic (FRP) as an alternative to steel for restrainer construction to reduce bridge hinge movements during earthquakes was examined. Glass, carbon, and hybrid (glass/carbon) restrainers were constructed and dynamically tested in the large-scale structures laboratory. Work included: 1. Tensile tests on FRP strips and on FRP/concrete bond versus loading rate 2. FRP restrainer development, including dynamic testing 3. Shake table data analysis and comparisons of FRP, steel, and SMA restrainer performance 4. Development of a FRP restrainer design method. Findings confirm FRP restrainer potential for future implementation to structures Results include: 1. FRP strength is strain-rate insensitive 2. FRP/concrete bond strength is a function of concrete shear strength and is strain rate sensitive 3. Flexible restrainer construction and restrainer/concrete bond methods are demonstrated 4. A simplified FRP restrainer design method, more realistic than AASHTO, and that considers bridge structure dynamic characteristics, is propose

Experimental and Analytical Seismic Studies of a Two-Span Bridge System with Precast Concrete Elements and ABC Connections

Report No. CCEER-19-02Missin

Seismic Performance of Precast Full-Depth Decks in Accelerated Bridge Construction

Report No. CCEER-17-05Cast-in-place (CIP) concrete construction is time intensive and require many on-site construction procedures that creates negative impacts on traffic flow, work zone safety, and the environment. Accelerated bridge construction (ABC) offers a viable alternative to CIP construction since significant construction time can be reduced by using prefabricated decks for new construction or replacement projects. They can be quickly assembled and reduce onsite construction time, minimizing traffic disruption, reducing environmental impact, improving worker and motorist safety, improving constructability, and increasing the quality of final product. Prefabricated deck panels provide the opportunity to replace decks during the life span of the bridge while keeping part of the bridge in service. The primary objective of this study was to evaluate different grout types for dowel connection between prefabricated precast bridge decks that are compositely connected to precast longitudinal girders and to determine the effect of earthquake forces on these connections. The study consisted of experimental work on headed anchor and analytical investigation using the results from the experimental study. The research included construction and testing of shear and pullout test specimens to evaluate the shear and pullout behavior of the selected anchor. Various parameters such as group effect of anchor, type of grout and head area of the anchors were also studied. Experimental results indicated that type of grout and head area of the anchors had an insignificant effect on the shear and pullout capacity of the anchor. It was concluded that the current provisions in AASHTO LRFD Specifications for CIP decks are applicable to the seismic analysis of precast deck panels. The results from the experiments were used to perform nonlinear analyses of a two-span bridge. A computational model for headed anchor was recommended and a numerical study was performed to investigate the seismic response of decks with shear pockets placed at 4 ft and 6 ft spacing. The nonlinear response history analysis was performed for eight different ground motion corresponding to 100% design level and 150% maximum considered earthquake (MCE) level. Insignificant difference was observed in the seismic behavior due to the increase in pocket spacing from 4 ft to 6 ft. It was also found that the forces in the headed anchors for both spacing were below ultimate strength of the connectors

Nonlinear Seismic Response of Isolated Bridges and Effects of Pier Ductility Demand

Report No. CCEER-95-6A nonlinear computer program to predict the dynamic response of base isolated bridges to orthogonal, horizontal earthquake ground motions was developed. The computer program can model multi-span bridges with straight, continuous superstructures and multi-column bents. Hysteretic behavior of elastomeric or lead-rubber isolators, abutments, shear keys, and columns can be modeled. Nonlinear analysis of the six-span Verdi bridge near Reno, Nevada showed that column ductility demands can be eliminated using isolation. Contrary to linear elastic theory, the superstructure displacements were controlled. Studies were conducted to show that seismic isolation may not be effective in bridges with long columns and located on deep soil deposits. The AASHTO Guide Specifications for Seismic Isolation Design were evaluated. Results of the simplified linear methods compared well with nonlinear analysis in the longitudinal direction but were in error by 21% transversely (Abstract by authors)

Development and Seismic Evaluation of Pier Systems w/Pocket Connections, CFRP Tendons, and ECC/UHPC Columns

Report No. CCEER-17-02Deployment of accelerated bridge construction (ABC) technology has been gaining momentum in recent years. ABC offers many advantages over conventional bridge construction by expediting onsite construction while shortening traffic delays and road closures, thus better serving the traveling public. The use of prefabricated reinforced concrete members is essential in ABC because these members can be fabricated concurrently while field preparation is in progress. ABC provides the opportunity for advanced and low-damage materials to be incorporated in the design of the prefabricated bridge components under controlled environmental conditions to provide superior bridge seismic performance and improve resiliency. ABC has been widely used in low seismic regions mostly in superstructures. The application of ABC in high seismic zones has been limited due to insufficient research results and guidelines for seismic design of prefabricated members and connections. The primary aim of this study was to help address this gap. The main objectives of this study were to evaluate seismic performance of precast bridge columns with pocket connections and develop seismic design methods to facilitate the use of ABC in practice. Another objective of the study was to incorporate advanced materials, such as carbon fiber reinforced polymer (CFRP) tendon, ultra-high performance concrete (UHPC), and engineered cementitious composite (ECC), in design of bridge columns to improve the seismic performance and post-earthquake serviceability of precast bridges. This study consisted of three parts, experimental studies, analytical studies, and design method development. The experimental studies involved shake table testing of a 0.33-scale model of a square column and a two-column bent. For the first time, unbonded CFRP tendons and UHPC were incorporated in design of a precast square column. Unbonded CFRP tendons were used to post-tension the column, and UHPC was used in the plastic hinge zone of the column and conventional concrete elsewhere. The column model was connected to a precast footing with a square pocket (also known as socket) connection. Successive motions simulating scaled versions of the 1994 Northridge-Rinaldi earthquake were used in the shake table tests. Results showed that the drift ratio and displacement ductility capacity of the column were 6.9% and 13.8, respectively, and the residual displacement was negligible. The column-footing pocket connection was effective in forming the plastic hinge in the column with no connection damage. The objectives of studying the two-column bent model were to evaluate the seismic response of cap-beam column pocket connections and the relative merit of UHPC and ECC in reducing damage in column plastic hinges. The columns were connected to a precast footing and a precast cap beam using pocket connections. The bent was subjected to successive motions simulating scaled versions of the 1994 Northridge-Sylmar earthquake until failure. Results showed that pocket connections performed well and the structural integrity was maintained up to drift ratio of 9.6% and displacement ductility of 12. UHPC and ECC effectively reduced the column plastic hinge damage, although the extent and location of damage for the two materials were different at failure. The analytical models presented in this study for both single column model and two-column bent model were found to be relatively simple and sufficiently accurate to capture the global seismic response of the models. ii To facilitate the use of ABC in practice, preliminary seismic design methods were developed based on the experimental results and the analytical investigations of this project and previous studies and were integrated with the AASHTO provisions. The design methods were practical as demonstrated in three design examples

Influence of new Bridge Configurations on Seismic Performance

Report No. CCEER-97-5After the dramatic failure of a connector bridge at the lnterstate-5/State Route-14 interchange during the Northridge earthquake of 1994 in Southern California, designers re-evaluated the overall configuration of the bridge and incorporated new concepts in the replacement structure. The new concepts departed from the norm in three fronts: (1) it used equal column heights within each frame regardless of the terrains, (2) it reduced the number of in-span hinges, and (3) it eliminated intermediate hinge seats and instead placed columns adjacent to the hinge on either sides. While these steps appeared to be logical, the replacement bridge had to be constructed rapidly and no detailed evaluation of the concepts was carried out before the design. This report presents an evaluation of the effects of these changes on the nonlinear seismic response of the bridge based on an extensive three-dimensional analysis of a straight version of the actual structure which is curved. Computer program Drain-3DX was used along with five earthquake records with different spectral characteristics. Both the new bridge and a conventional bridge were analyzed. The conventional bridge had variable columns heights that followed the terrains, had more in-span hinges than the new bridge, and had hinge seats. Displacements, column shears, and column ductilities were used to evaluate the effectiveness of the changes in improving the seismic performance. The study revealed that the changes can improve the earthquake response only if abutment shear keys are designed to yield at relatively low forces so that the superstructure can move in the transverse direction of the bridge. Otherwise excessive transverse displacements could occur due to the pivoting action of the abutments on the superstructure. It was also found that the eccentricity between the superstructure mass center and substructure stiffness center should be considered and minimized at the design stage to obtain a more uniform distribution of displacements and column shears (Abstract by authors)