M. Shahria Alam

Shape memory alloy wire-based smart natural rubber bearing

In this study, two types of smart elastomeric bearings are presented using shape memory alloy (SMA) wires. Due to the unique characteristics of SMAs, such as the superelastic effect and the recentering capability, the residual deformation in SMA-based natural rubber bearings (SMA-NRBs) is significantly reduced whereas the energy dissipation capacity is increased. Two different configurations of SMA wires incorporated in elastomeric bearings are considered. The effect of several parameters, including the shear strain amplitude, the type of SMA, the aspect ratio of the base isolator, the thickness of SMA wire, and the amount of pre-strain in the wires on the performance of SMA-NRBs is investigated. Rubber bearings are composed of natural rubber layers bonded to steel shims as reinforcement. Results show that ferrous SMA wire, FeNiCuAlTaB, with 13.5% superelastic strain and a very low austenite finish temperature (?62??C), is the best candidate to be used in SMA-NRBs subjected to high shear strain amplitudes. In terms of the lateral flexibility and wire strain level, the smart rubber bearing with a cross configuration of SMA wires is more efficient. Moreover, the cross configuration can be implemented in high-aspect-ratio elastomeric bearings since the strain induced in the wire does not exceed the superelastic range. When cross SMA wires with 2% pre-strain are used in a smart NRB, the dissipated energy is increased by 74% and the residual deformation is decreased by 15%.

Seismic fragility assessment of highway bridges: a state-of-the-art review

Safety and serviceability of highway bridges, during and after an earthquake, is a prerequisite to ensure continuous transport facilities, emergency and evacuation routes. Recently, fragility curves have emerged as important decision support tools to identify the potential seismic risk and consequences during and after an earthquake. There has been a substantial increase in interest among researchers in the topic of seismic fragility assessment of highway bridges as evidenced by the growing number of published literature. Advanced computational techniques and available resources have led to the development of different methodologies for fragility assessment. This study presents a review of the different methodologies developed for seismic fragility assessment of highway bridges along with their features, limitations and applications. This study presents a review of available methodologies and identifies opportunities for future development. This study mainly focuses on the key features of different method...Safety and serviceability of highway bridges, during and after an earthquake, is a prerequisite to ensure continuous transport facilities, emergency and evacuation routes. Recently, fragility curves have emerged as important decision support tools to identify the potential seismic risk and consequences during and after an earthquake. There has been a substantial increase in interest among researchers in the topic of seismic fragility assessment of highway bridges as evidenced by the growing number of published literature. Advanced computational techniques and available resources have led to the development of different methodologies for fragility assessment. This study presents a review of the different methodologies developed for seismic fragility assessment of highway bridges along with their features, limitations and applications. This study presents a review of available methodologies and identifies opportunities for future development. This study mainly focuses on the key features of different methods and applications rather than penetrating down to a critique of the associated analysis procedure or mathematical framework. It synthesises the existing information on fragility analysis, presents it in concise and useful tables, and explains different applications for different purposes, which would motivate decision-makers and stake holders to extend the application of fragility curves for more informed decision-making.

Fragility Analysis of Retrofitted Multicolumn Bridge Bent Subjected to Near-Fault and Far-Field Ground Motion

AbstractThis paper focuses on the fragility-based seismic vulnerability assessment of retrofitted multicolumn bridge bents. Fragility curves are developed to assess the relative performance of various retrofit methods under both near-fault and far-field ground motions. A probabilistic seismic demand model (PSDM) is used in generating the fragility functions. Through nonlinear dynamic analysis, fragility curves are developed for multicolumn bridge bents retrofitted with four different retrofit techniques, specifically carbon fiber–reinforced polymer (CFRP) jacketing, steel jacketing, concrete jacketing, and engineered cementitious composite (ECC) jacketing. Following the performance-based evaluation approach, this study aims to investigate the effectiveness of different retrofitting methods to minimize the overall seismic vulnerability of deficient bridge bents. To investigate the seismic responses of the retrofitted bridge bents, a total of 40 earthquake excitations, of which 20 are near-fault and 20 are ...

Seismic Fragility Assessment of Concrete Bridge Pier Reinforced with Superelastic Shape Memory Alloy

In an attempt to reduce permanent displacement and damage, a hybrid reinforced concrete (RC) bridge pier configuration is considered in the present study. The plastic hinge region of the bridge pier is reinforced with superelastic shape memory alloy (SMA) and the remaining portion with regular steel. This paper focuses on fragility-based seismic vulnerability assessment for a SMA-RC bridge pier considering residual displacement, displacement ductility, and performance criteria as the demand parameters. Fragility curves are developed to assess the relative vulnerability of a SMA-RC bridge pier and a conventional steel-RC bridge pier using probabilistic seismic demand model (PSDM). The fragility curves are developed with a suite of 20 near-fault ground motions using incremental dynamic analysis. The fragility curves provide insight into the failure probability of the bridge piers and aid in expressing the impact of SMA on the bridge pier vulnerability.

Seismic Vulnerability Assessment of a Multi-Span Continuous Highway Bridge Fitted with Shape Memory Alloy Bars and Laminated Rubber Bearings

This study performs seismic vulnerability assessment in the longitudinal direction of a three-span continuous highway bridge, restrained by shape memory alloy (SMA) bars and isolated with laminated rubber bearings. The analytical simulation method based on incremental dynamic analyses is used in evaluating the seismic fragility functions of the bridge components (pier and isolation bearing) and the system. A two-dimensional finite element model scheme with nonlinear force-displacement relationships is used for the bridge piers and bearings. This study shows that the bridge piers with SMA bars have led to relatively higher seismic vulnerability over the bridge piers without SMA bars, which is also reflected in the bridge system. The isolation bearings with SMA bars have revealed comparatively less seismic vulnerability than those without SMA bars. From the numerical results, it is recognized that the failure probability of the bridge system is dictated by the bridge pier over the isolation bearing.

Erratum to: Seismic fragility assessment of SMA-bar restrained multi-span continuous highway bridge isolated by different laminated rubber bearings in medium to strong seismic risk zones

This study analytically determines the seismic fragility of a three-span continuous highway bridge fitted with laminated rubber bearings and shape memory alloy (SMA) restrainers. Fragility function, which expresses the likelihood of exceeding a damage state conditioned at a given earthquake intensity, has been derived based on SeismoStruct’s nonlinear incremental dynamic analysis results of the bridge subjected to medium to strong earthquake excitation records. A total of 20 excitation records with peak ground acceleration values ranging from 0.45 to 1.07 g, are used in the nonlinear dynamic analysis of the bridge. A 2-D finite element model scheme is used in this study considering nonlinearity in the bridge piers and the isolation bearings. Two types of laminated rubber bearings are used in the bridge system in addition to the SMA restrainers: high damping rubber bearings and lead rubber bearings. The fragility curves are constructed for two bridge components (i.e. piers and isolation bearings), and the system as well. The component fragility curves are combined to evaluate the fragility curves for the entire bridge system at different damage states. The bridge system, for simplicity, considers the bridge deck, isolation bearings with SMA restrainer and bridge piers but excluding the bridge foundations and the abutments. The numerical results show that the failure probability of the bridge system is dominated by the bridge piers over the isolation bearings. Moreover, the inclusion of SMA restrainers in the bridge system exhibits high probability of failure, especially, when the system is isolated with lead rubber bearings.

Feasibility study of utilizing superelastic shape memory alloy plates in steel beam–column connections for improved seismic performance

Steel moment-resisting frames are prone to extensive damage in seismically active zones. Large permanent deformations in structural members following strong earthquakes can be mitigated using smart materials such as shape memory alloys. In this article, three-dimensional finite element analyses are conducted to study the seismic performance of beam–column connections incorporating shape memory alloy plates. Eight beam–column connection subassemblies with shape memory alloy plates in the plastic hinge of beam were analyzed under cyclic loading. Based on the numerical results, the recentering properties of superelastic shape memory alloy plates were found to be effective in reducing the residual drifts of a flange plate beam–column connection, while displaying an excellent ductility. In addition, shape memory alloy plates could prevent the occurrence of local buckling and damage in structural members. The new self-centering connections could also exhibit a good energy dissipation capability.

Green Concrete Made with RCA and FRP Scrap Aggregate: Fresh and Hardened Properties

AbstractBecause global landfills are filling at a fast rate with waste that can potentially be recycled, it is now time for the development and implementation of sustainable materials in construction. This article investigates the properties of a new generation concrete containing fiber reinforced polymer (FRP), fiber scrap aggregate (FSA), and recycled concrete aggregate (RCA). Although previous research has been undertaken for the use of RCA in concrete, the use of FSA is a new research area and has been found in this study to have exciting potential. Through different replacements of these aggregates in the concrete, both individually and in combination, conclusive test results were produced. The results indicate that both the fresh and hardened RCA concrete properties were similar to those of the control concrete containing only natural aggregate. In the case of fresh properties, the RCA concrete experienced slightly lower slump than the control concrete. The FSA concrete had a lower compressive stren...

Finite-Element Simulation of Posttensioned Steel Connections with Bolted Angles under Cyclic Loading

AbstractSteel beam-column connections with posttensioned (PT) elements are proven systems that can provide adequate stiffness, strength, and ductility, while eliminating permanent deformations in a moment-resisting frame subjected to seismic loading. In this study, detailed three-dimensional finite-element (FE) models of steel beam-column connections with PT strands are developed and analyzed under cyclic loading. Efforts are made to overcome challenges in performing the nonlinear FE analysis of large-scale PT connections, which involves gap opening and closing behavior as well as contact and sliding phenomena. Geometric and material nonlinearities, preloaded bolts and strands are also considered in the modeling. Through a verification study, the results from the FE models are validated against prior experiments on interior PT connections with top-and-seat angles. Parametric studies are also conducted to investigate the effects of three factors on the cyclic performance of PT connections. The factors inve...

Buildings’ seismic vulnerability assessment methods: a comparative study

A critical review and comparison of existing seismic vulnerability assessment techniques for buildings are carried out to evaluate their suitability for use in seismic risk assessment. The methods considered are “Hybrid” vulnerability assessment method, FEMA 154 (Rapid Visual Screening), Euro Code 8, New Zealand Guidelines, Modified Turkish method and NRC Guidelines. A scoring system is proposed to select the suitable vulnerability assessment technique to be utilized for three different case studies conducted in different seismicity and geological zones, that is, Dhaka, and Rangamati cities, in Bangladesh, and Kelowna, in Canada. The ranking considers general description of vulnerability, building response factors, variance in output, applicability and ease of use, which are identified as the key characteristics required for vulnerability scales used in seismic risk evaluation. A sensitivity analysis has been carried out for the different methods with regard to different weighting criteria. Furthermore, a multi-criteria decision-making tool AHP has also been utilized to find out the suitable alternatives for seismic vulnerability assessment of buildings. It was observed that the Hybrid method adequately satisfies all the criteria necessary for their use in seismic risk assessment. Vulnerability maps of different study areas using Hybrid method have been integrated into a GIS framework to visualize the building vulnerabilities in a spatial manner, which will facilitate the authority to manage effective seismic hazard risk reduction measures, including upgrading, repairing and retrofitting of structures.