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

Precarious rock methodology for seismic hazard: Physical testing, numerical modeling and coherence studies

This report covers the following projects: Shake table tests of precarious rock methodology, field tests of precarious rocks at Yucca Mountain and comparison of the results with PSHA predictions, study of the coherence of the wave field in the ESF, and a limited survey of precarious rocks south of the proposed repository footprint. A series of shake table experiments have been carried out at the University of Nevada, Reno Large Scale Structures Laboratory. The bulk of the experiments involved scaling acceleration time histories (uniaxial forcing) from 0.1g to the point where the objects on the shake table overturned a specified number of times. The results of these experiments have been compared with numerical overturning predictions. Numerical predictions for toppling of large objects with simple contact conditions (e.g., I-beams with sharp basal edges) agree well with shake-table results. The numerical model slightly underpredicts the overturning of small rectangular blocks. It overpredicts the overturning PGA for asymmetric granite boulders with complex basal contact conditions. In general the results confirm the approximate predictions of previous studies. Field testing of several rocks at Yucca Mountain has approximately confirmed the preliminary results from previous studies, suggesting that the PSHA predictions are too high, possibly because the uncertainty in the mean of the attenuation relations. Study of the coherence of wavefields in the ESF has provided results which will be very important in design of the canisters distribution, in particular a preliminary estimate of the wavelengths at which the wavefields become incoherent. No evidence was found for extreme focusing by lens-like inhomogeneities. A limited survey for precarious rocks confirmed that they extend south of the repository, and one of these has been field tested

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

PEER Arizona strong-motion database and GMPEs evaluation

This report summarizes the products and results of a study on the collection, processing, and analysis of earthquake ground-motions recorded in Arizona at several recording stations within 200 km from the Palo Verde Nuclear Generating Station in central Arizona. The recorded ground motion in Arizona were compiled and processed according to the Pacific Earthquake Engineering Research Center’s (PEER) record-processing standards. Shear wave velocity profiles at ten recording stations were measured through the spectral analysis of surface wave dispersion technique. Additionally, “kappa” a measure of energy dissipation in the top 1 to 2 km of the crust, was estimated by three methodologies. The average κ0 (kappa at zero-kilometer distance) was estimated from all sites as 0.033 sec. Finally, response spectra of the recorded ground motions in Arizona were compared with those predicted by the NGA-West2 ground motion prediction equations at large distances in Arizona. The comparison showed that overall the recorded 5% damped response spectral ordinates were over predicted by the NGA-West2 models by a range of 0-0.35 natural log units for events occurring in Central California, and by a range of 0.2-0.7 natural log units for events occurring in Southern California and the Gulf of California

Torsional Ground Motion Effects on the Seismic Response of Continuous Box-girder Highway Bridges

Highway bridges are particularly vulnerable to seismically-induced deformations and forces due to their complex dynamic characteristics. Therefore, many studies have been conducted to provide insight into their seismic response characteristics under various types of ground motions. Undoubtedly, investigations relating to both structural components as well as the strong ground motion characteristics play major roles in providing reliable design guidelines for highway bridges. It is generally accepted that ground motion characteristics such as spatial variability may result in differential excitations at the supports of relatively longer span highway bridges which may induce adverse interactions. In addition, the propagation characteristics of seismic waves along different wave paths result in rotational deformations on the ground surface which remains unaccounted, however, studies on implications for the seismic response of structural systems are rare. Therefore, the primary objective of the present study is to investigate force and deformation demands on highway bridge components particularly due to torsional components of earthquake ground motions, which are not considered explicitly in design codes. For this purpose, continuous concrete box-girder highway bridges were considered and torsional ground motion effects on these bridges were investigated in two phases. Firstly, the upper and lower bound effects of torsional ground motions (TGMs) on the seismic response of highway bridges were investigated through simplified computational models with varying skew angles, eccentricity between the centers of mass and rigidity, gap sizes between the deck and abutment, and overall dynamic characteristics. It is noted that highly nonlinear impact elements were included explicitly in the computational models to ensure that consistent deck rotations are accounted for. Furthermore, the translational ground motions accompanying with TGMs were applied with different incident angles. The results were compared for the cases with and without TGM and observations revealed that larger deck rotations due to TGMs lead to larger impact forces, which further amplifies the deck rotations. The observations from the first phase warranted a more comprehensive investigation that utilized three-dimensional finite element (3D FE) models of typical highway bridges. In this second phase of the study, the inelastic response characteristics of bent columns and abutment components such as shear keys, bearings, piles as well as the impact between deck and abutment, and abutment soil-structure interaction were explicitly included in OpenSees models. Furthermore, 3D FE models with a range of standard dimensions were altered to carry out an investigation on bridges with varying skew angles, number of bent columns, and column height-to-diameter ratios. Inelastic seismic responses of bridges subjected to only translational and both translational and torsional ground motions were compared. The most unfavorable TGM effects were observed when TGMs resulted in uneven and asymmetric shear key failure, in which, an instantaneous eccentricity was induced when the deck comes in contact with the shear key(s). Subsequently, the deck rotations amplified directly due to TGMs as well as due to more frequent occurrence of impact and larger impact forces. Furthermore, it was noted that TGM-induced torsional moment demand combined with axial-flexure-shear interactions may result in complex failure modes, high shear stresses, and reduction in lateral deformation and flexural capacity of the bridge columns. Finally, the observations relative to the shear key failure mechanisms suggested that superstructure displacement demands can be restrained by either preventing or delaying the failure of shear keys. In this regard, a design method that ensures effectiveness of shear keys while preventing asymmetric failure mechanisms to form, in mitigating seismic response of highway bridges was proposed. The proposed method follows the conventional approach to ensure that substructure components are capacity-protected, however formalizes a practical procedure to specify desired deformation limits associated with i) gap size between the superstructure and shear keys, and ii) ultimate deformation capacity of shear keys. The efficacy of the method was demonstrated through nonlinear response history analyses of a series of benchmark bridges. It was demonstrated that excessive in-plane deck rotations and extent of damage can be limited when the effectiveness of shear keys is maintained throughout the duration of seismic excitation

Experimental Seismic Evaluation of Ceiling-Piping-Partition Nonstructural Systems

The seismic performance of nonstructural components plays a significant role during and after an earthquake. Damage to these systems can leave buildings inoperable, causing economic losses and extensive downtime. Therefore, it is necessary to better understand the response of these systems in order to enhance the seismic resilience of buildings. A series of full-scale system-level experiments conducted at the University of Nevada, Reno Network for Earthquake Engineering Simulation site aimed to investigate the seismic performance of integrated ceiling-piping-partition systems. A full-scale, two-story, two-by-one bay steel braced-frame test-bed structure that spanned over three biaxial shake tables was used to house the nonstructural systems. The test-bed structure was subjected to over 50 generated ground motions in a series of eight tests. The test-bed structure could be constructed into two configurations, one to produce large floor accelerations and the other to produce large inter-story drifts, affecting both acceleration and drift sensitive nonstructural systems. The responses and behaviors of ceiling-piping-partition systems were critically assessed through several design variables, configurations, and materials. The degree of damage observed during testing was used as an evaluation of the performance of nonstructural components.Post processing of experimental data led to results including acceleration amplification factors, seismic fragility analysis, and overall performance of nonstructural systems. Three significant findings from this experiment are as follows: 1) ceiling systems with pop rivet connections have a lower probability of failure compared to seismic clips, 2) pipe joints with 2.0 in. (50.8 mm) diameter pipes have the greatest probability of rotation failure compared to other diameter pipes, and 3) acceleration amplification factors for out-of-plane partition walls are comparable with the recommended amplification suggested by the ASCE 7-10 code for flexible components