Browsing by Author "DesRoches, Reginald"
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Item Application of Compact, Geometrically Complex Shape Memory Alloy Devices for Seismic Enhancement of Highway Bridge Expansion Joints(2014-04-25) McCarthy, Emily Ruth; Padgett, Jamie E.; Stanciulescu, Ilinca; Lou, Jun; DesRoches, ReginaldHighway bridges are an important part of transportation networks. They provide connectivity across waterways, ravines and other roadways, reducing commuting times and facilitating social community. The disruption of their effective operation caused by earthquake damage has lasting effects based on repair costs, road closure times, traffic rerouting causing extended commute times and additional CO2 emissions, and the potential prevention of emergency responders being able to reach affected regions. Bridge expansion joints have historically been recognized as the most vulnerable component in the bridge system during these seismic events, causing dramatic disruption to bridge functionality because of their location in bridges (points of discontinuity in deck systems). Expansion joint systems are placed in these locations of discontinuity and accommodate bridge movements from thermal effects while facilitating safe driving surfaces across large gaps in the roadway. Commonly installed systems are not designed to survive seismic events, instead failure is assumed and replacement necessary to return the bridge to its functional state. When damaged, the large gaps they span can be un-crossable without external intervention, resulting in non-functioning bridges even when the structural system remains sound. Expensive and complex expansion systems exist, which prevent seismic damage, however they are used mostly in highly seismic regions and limitedly elsewhere. This dissertation provides an expansion joint design that is economical and superior in seismic performance to the commonly installed service level expansion joints so that more bridges in moderate seismic regions can be equipped with expansion systems able to accommodate large longitudinal displacement demands from earthquakes. The use of innovative shape memory alloy (SMA) springs enables a single support bar modular bridge expansion joint (one type of large capacity expansion joint) to accommodate seismic level longitudinal displacements while maintaining existing performance behavior for service level thermal expansion demands. Through limited alteration of the existing configuration, costs are minimized. The resulting design is experimentally and analytically shown to be superior in performance and able to prevent expansion joint system failure during dynamic loading. The use of fragility curves, which are probabilistic statements of demand exceeding capacity, offers a means of measuring performance over a range of earthquake intensities. Convolution with seismic hazard curves for some moderate seismic zones in the US over a range of time intervals provide information on lifetime seismic risk, valuable information for a cost benefit analysis that concludes investment in SMA springs for enhancement of modular bridge expansion joints is worthwhile for the cost reduction they offer over the life of the bridge.Item Reflections on Juneteenth: Session One(Rice University, 2020-06-19) DesRoches, Reginald; Byrd, Alexander; Bratter, JeniferItem Seismic Design and Performance Assessment of Bridges with SMA-Restrained Rocking Columns(2023-04-06) Akbarnezhad, Miles; DesRoches, ReginaldDuring the last three decades, multiple studies have been conducted to develop bridge columns that either sustain low damage or remain fully functional during moderate to strong earthquakes. Among such bridge columns, which are compatible with Accelerated Bridge Construction (ABC) and also offer self-centering, are precast concrete rocking columns. This dissertation intends to propose and evaluate an innovative class of seismically resilient precast concrete rocking columns using shape memory alloys (SMA). The proposed precast concrete bridge columns, which are termed SMA-restrained rocking (SRR) columns, are connected to their adjacent substructure components through two series of unbonded links, namely, SMA links (to achieve self-centering) and replaceable energy dissipation (ED) links. After introducing three SRR column design variations, a displacement-based procedure is proposed for their effective seismic design. To investigate the performance of the proposed columns under monotonic and cyclic lateral loading and to examine the effective ranges of two key design parameters, nonlinear 3D solid finite element (FE) models are used. Following the initial evaluations of SRR columns under monotonic/cyclic loading, the seismic performances of two reinforced concrete (RC) bridges with SRR columns are evaluated through multiple time history analyses. To examine the potential effects of ground motion characteristics, three ensembles of ground motions including far-field, near-fault without velocity pulse, and near-fault with velocity pulse are considered. In addition, the effects of ambient temperature on the behavior of SRR columns due to the thermomechanical properties of SMA links are studied. The analysis results show that the SRR columns' capability of sustaining damage is practically insensitive to site-to-source distance and velocity pulse content of ground motions and ambient temperature. In order to evaluate the seismic fragility of bridges with SRR columns, a two-span RC bridge is considered. To produce seismic fragility functions, initially, multi-parameter probabilistic seismic demand models (PSDMs) are generated through different machine learning techniques and considering various sources of uncertainty. Subsequently, multi-parameter fragility functions are developed for various bridge damage states using neural networks. After examining the effects of the two SRR column design parameters on the seismic fragility of the bridge, its seismic fragility is compared with those of the same bridge with monolithic RC and posttensioned (PT) rocking columns.Item Seismic fragilities of single‐column highway bridges with rocking column‐footing(Wiley, 2019) Xie, Yazhou; Zhang, Jian; DesRoches, Reginald; Padgett, Jamie E.Rocking isolation has been increasingly studied as a promising design concept to limit the earthquake damage of civil structures. Despite the difficulties and uncertainties of predicting the rocking response under individual earthquake excitations (due to negative rotational stiffness and complex impact energy loss), in a statistical sense, the seismic performance of rocking structures has been shown to be generally consistent with the experimental outcomes. To this end, this study assesses, in a probabilistic manner, the effectiveness of using rocking isolation as a retrofit strategy for single‐column concrete box‐girder highway bridges in California. Under earthquake excitation, the rocking bridge could experience multi‐class responses (eg, full contacted or uplifting foundation) and multi‐mode damage (eg, overturning, uplift impact, and column nonlinearity). A multi‐step machine learning framework is developed to estimate the damage probability associated with each damage scenario. The framework consists of the dimensionally consistent generalized linear model for regression of seismic demand, the logistic regression for classification of distinct response classes, and the stepwise regression for feature selection of significant ground motion and structural parameters. Fragility curves are derived to predict the response class probabilities of rocking uplift and overturning, and the conditional damage probabilities such as column vibrational damage and rocking uplift impact damage. The fragility estimates of rocking bridges are compared with those for as‐built bridges, indicating that rocking isolation is capable of reducing column damage potential. Additionally, there exists an optimal slenderness angle range that enables the studied bridges to experience much lower overturning tendencies and significantly reduced column damage probabilities at the same time.Item Sensitivity of seismic demands and fragility estimates of a typical California highway bridge to uncertainties in its soil-structure interaction modeling(Elsevier, 2019) Xie, Yazhou; DesRoches, ReginaldThis study investigates the sensitivity of seismic demands and fragility estimates of a typical highway bridge in California to variation in its soil-structure interaction (SSI) modeling parameters. A rigorous p-y spring based modeling approach is developed and validated for an instrumented highway overcrossing that provides a dependable screening of each modeling parameter. Modifications are made to benchmark the overcrossing against typical bridge designs in California, including the consideration of diaphragm and seat abutments. Plausible variation in SSI modeling parameters is established using 18 random variables that cover different soil zones. Influential SSI parameters are identified for the seismic demands of bridge components through two regression techniques such as stepwise and LASSO regressions. Concurring results from both regressions indicate that bridge demand models tend to be sensitive to the modeling parameters associated with near-ground soils. Furthermore, the relative importance of the uncertainty in SSI modeling parameters is assessed with respect to the fragility estimates in both component and system levels. The study reveals that the bridge performance and fragility curves of bridge columns and decks are dominated by the uncertainty in the ground motion. However, the propagation of the potentially variable SSI parameters plays a significant role in the fragility estimates of bridge foundations and abutment components such as span unseating, bearings and shear keys. The results offer insights to guide future uncertainty treatment in SSI modeling and investment in refined soil parameter estimates through field testing or other measures.