Seismic performance of skewed and curved RC bridges

2013 Summer.Includes bibliographical references.Explicit knowledge of the behavioral response of complex reinforced concrete (RC) highway bridges to seismic events is essential to designing safe transportation systems. In the past, a number of skewed and curved highway bridges have experienced damage or suffered collapse due to earthquakes; and have most recently been observed during the Chile earthquake in 2010. Yet, there is very limited information on the combined effects of skew and curvature on the seismic response of RC bridges, and in particular identifying critical vulnerabilities to localized failures or system collapse. Recent research has also shown that the vertical component of earthquake ground motion, previously not considered, may have significant bearing on the response of highway bridges, particularly in near-fault regions. This study is comprised of two parts, including an examination of skewed and curved RC bridges of various configurations representative of a low seismic region, and an evaluation of the effect of vertical ground motion on complex geometry bridges in a moderate, near-fault, seismic region. Detailed numerical models are developed for various configurations of skew and curvature, and subjected to earthquake ground motion using nonlinear time-history analysis. In part one, detailed finite element models are developed and analyzed for eight bridge configurations of various degrees of skew and curvature, with consistent structural and geometric components. The bridge designs and earthquake hazard level are characteristic of the Mountain West region where the seismic risk is typically classified as low to moderate. Nonlinear time-history analysis is conducted on each bridge configuration for seven sets of earthquake records scaled to a site location in Denver, Colorado. The effects of earthquake input loading direction and abutment support condition, including integral and bearing supports, are also considered. The results show significant impacts on the seismic performance due to the effects of skew and curvature with stacking effects observed in the combined geometries. Insights on the complexities of curvature, skew, loading direction and support condition are made, which may lend themselves to more informed design decisions in the future. Part two of this study presents an assessment of the effect of vertical ground motion on horizontally skewed and curved highway bridges in moderate-to-high seismic regions. A numerical model of a skewed and curved, three-span bridge located in Tacoma, Washington is subjected to a suite of ground motions using non-linear time-history analysis. The ground motions selected represent a range of near-fault records with varying characteristics such as site condition, fault distance, and vertical-to-horizontal acceleration component ratios. The scenario developed characterizes the behavior of a bridge with a short fundamental period of vibration in a moderate seismic zone, where vertical ground motion effects may be applicable yet not considered by structural code. The results of the numerical simulations depict a significant impact from vertical ground motion in the substructure and superstructure, including responses typically not documented in existing studies. The implications of the results for structural designers may be to reconsider the current design approach involving vertical ground motion, particularly with shorter period bridges involving configurations of skew and curvature

Devices for protecting bridge superstructure from pounding and unseating damages: an overview

Previous earthquakes have highlighted the seismic vulnerability of bridges due to excessive movements at expansion joints. This movement could lead to the catastrophic unseating failure if the provided seat width is inadequate. Moreover, seismic pounding is inevitable during a strong earthquake due to the limited gap size normally provided at the expansion joints. Various types of restrainers, dampers and other devices have been proposed to limit the joint movement or to accommodate the joint movement so that the damages caused by excessive relative displacements could be mitigated. To select and design appropriate devices to mitigate the relative displacement-induced damages to bridge structures during earthquake shaking, it is important that results from the previous studies are well understood. This paper presents an overview on various pounding and unseating mitigation devices that have been proposed by various researchers. Based on an extensive review of up-to-date literatures, the merits and limitations of these devices are discussed

Numerical and Experimental study of pounding damages in adjacent bridge structures subjected to spatially varying ground motion and its mitigation method

Bridge infrastructure is an integral component of the transportation network with significant strategic value and is expected to remain functional in the damaged area immediately after a strong earthquake. However, previous experiences have shown that keeping the bridges operational after a strong earthquake is very challenging. This study investigates the damages resulting from pounding and unseating at bridge superstructure and residual deformation of bridge substructure subjected to earthquake loading, and the possible mitigation methods

Master of Science

thesisDamage to bridges has been evident during many earthquakes, even when the structure was designed according to model codes. Abutments act like a retaining wall during a seismic event. Past studies show that there have been several incidents of damage to abutments and shear keys due to pounding. This research attempts to study the performance of an existing multispan curved bridge supported on rigidly capped vertical pile groups which pass through a deep layer of soft clay. The soil-structure interaction (SSI) between the pile group and soil is idealized as linear springs in two perpendicular horizontal directions. At the expansion joints and abutments, steel shear walls are provided to improve the performance and concrete shear keys are utilized to restrain the lateral movement of the girders and deck during seismic events. A seismic retrofit scheme using Buckling Restrained Braces (BRB) is implemented at the abutments to prevent pounding damage. It is observed that the soft soil surrounding the piles has a significant effect on the dynamic response of the bridge; in addition, the bearing displacements are underestimated if SSI is ignored. Damage to the abutments and the deck due to pounding can be prevented by using a combination of BRBs. Similarly, pounding between steel girders at the expansion joints can be prevented by using BRBs instead of seismic restrainer rods. BRBs are idealized using bilinear plastic link elements with a backbone curve adopted from actual experiments. A sensitivity analysis is carried out for modeling the BRBs using two different software packages

Model Validation and Simulation

The Bauhaus Summer School series provides an international forum for an exchange of methods and skills related to the interaction between different disciplines of modern engineering science. The 2012 civil engineering course was held in August over two weeks at Bauhaus-Universität Weimar. The overall aim was the exchange of research and modern scientific approaches in the field of model validation and simulation between well-known experts acting as lecturers and active students. Besides these educational intentions the social and cultural component of the meeting has been in the focus. 48 graduate and doctoral students from 20 different countries and 22 lecturers from 12 countries attended this summer school. Among other aspects, this activity can be considered successful as it raised the sensitivity towards both the significance of research in civil engineering and the role of intercultural exchange. This volume summarizes and publishes some of the results: abstracts of key note papers presented by the experts and selected student research works. The overview reflects the quality of this summer school. Furthermore the individual contributions confirm that for active students this event has been a research forum and a special opportunity to learn from the experiences of the researchers in terms of methodology and strategies for research implementation in their current work

Experimental and three-dimensional finite element method studies on pounding responses of bridge structures subjected to spatially varying ground motions

Pounding and unseating damages to bridge superstructures have been commonly observed in many previous major earthquakes. These damages can essentially attribute to the large closing or opening relative displacement between adjacent structures. This article carries out an experimental study on the pounding responses of adjacent bridge structures considering spatially varying ground motions using a shaking table array system. Two sets of large-scale (1:6) bridge models involving two bridge frames were constructed. The bridge models were subjected to the stochastically simulated ground motions in bi-direction based on the response spectra of Chinese Guideline for Seismic Design of Highway Bridge for three different site conditions, considering three coherency levels. Two types of boundary conditions, that is, the fixed foundation and rocking foundation, were applied to investigate the influence of the foundation type. In addition, a detailed three-dimensional finite element model was constructed to simulate an experimental case. The nonlinear material behavior including strain rate effects of concrete and steel reinforcement is included. The applicability and accuracy of the finite element model in simulating bridge pounding responses subjected to spatially varying ground motions are discussed. The experimental and numerical results demonstrate that non-uniform excitations and foundation rocking can affect the relative displacements and pounding responses significantly

MECHANICAL BEHAVIOR OF HORIZONTAL SWIVEL SYSTEM WITH UHPC SPHERICAL HINGE UNDER SEISMIC ACTION

In the process of rotation, the total weight of the bridge structure is jointly supported by the spherical hinge and the supporting structure, and its lateral stability is poor. It is easy to lose stability under the action of dynamic loads such as seismic action effect. The present paper takes a 10,000-ton continuous rigid frame swivel bridge as the re-search object, analyzes the dynamic response of the seismic action to the horizontal swivel system, and establishes several structure simulation models. Eighteen seismic waves in three directions that meet the calculation requirements are screened for time history analysis and compared with the response spectrum method. Finally, an optimization algorithm for the seismic response of the bridge under horizontal swivel system is proposed based on the mode superposition method. The UHPC spherical hinge bears all the vertical forces and 20% of the bending moment caused by the seismic action, the support structure bearing the remaining 80% of the bending moment. The optimization algorithm proposed in this paper features high accuracy

Seismic Vulnerability of the Italian Roadway Bridge Stock

This study focuses on the seismic vulnerability evaluation of the Italian roadway bridge stock, within the framework of a Civil Protection sponsored project. A comprehensive database of existing bridges (17,000 bridges with different level of knowledge) was implemented. At the core of the study stands a procedure for automatically carrying out state-of-the-art analytical evaluation of fragility curves for two performance levels – damage and collapse – on an individual bridge basis. A webGIS was developed to handle data and results. The main outputs are maps of bridge seismic risk (from the fragilities and the hazard maps) at the national level and real-time scenario damage-probability maps (from the fragilities and the scenario shake maps). In the latter case the webGIS also performs network analysis to identify routes to be followed by rescue teams. Consistency of the fragility derivation over the entire bridge stock is regarded as a major advantage of the adopted approach

SEISMIC VULNERABILITY ANALYSIS OF CABLE-STAYED BRIDGE DURING ROTATION CONSTRUCTION

          Due to the swivel construction, the structural redundancy of cable-stayed bridge is reduced, and its seismic vulnerability is significantly higher than that of non-swirling construction structure and its own state of formation. Therefore, it is particularly important to study the damage changes of each component and stage system during the swivel construction of cable-stayed bridge under different horizontal earthquakes. Based on the construction of Rotary Cable-stayed Bridge in Haxi Street, the calculation formula of damage exceeding probability is established based on reliability theory, and the damage calibration of cable-stayed bridge components is carried out, and the finite element model of cable-stayed bridge rotating structure is established. The vulnerable parts of the main tower and the stay cable components of the cable-stayed bridge are identified and the incremental dynamic analysis is carried out. Finally, the seismic vulnerability curves of the main tower section, the stay cable and the rotating system are established. The results of the study show that the vulnerable areas of the H-shaped bridge towers are the abrupt changes in the main tower section near the upper and lower beams, and the vulnerable diagonal cables are the long cables anchored to the beam ends and the short cables near the main tower；At the same seismic level, the damage exceedance probability of main tower vulnerable section of cable-stayed bridge under transverse earthquake is greater than that under longitudinal earthquake, the damage exceedance probability of vulnerable stay cables under transverse seismic action is less than that under longitudinal seismic action；On the premise of the same damage probability, the required ground motion intensity of the system can be reduced by 0.35g at most compared with the component；Under the same seismic intensity, the system damage probability is 6.60 % higher than the component damage probability at most. The research results have reference significance for the construction of rotating cable-stayed bridges in areas lacking seismic records