An SMA cable-based negative stiffness seismic isolator: Development, experimental characterization, and numerical modeling

Shape memory alloy (SMA)-based seismic isolation systems can successfully reduce the peak and residual displacements of bridges during strong earthquake, but they commonly lead to an increased force demands in substructure. This study explores the development of an SMA cable-based negative stiffness isolator to alleviate this problem. The proposed isolator is composed of superelastic SMA cables and a frictional sliding bearing with convex surfaces. The frictional sliding bearing limit the forces transferred to the superstructure and provides energy dissipation, while its built-in negative stiffness mechanism reduces the force demands in substructure. SMA cables provide critical restoring forces, additional energy dissipation, and displacement-limiting capacity. Based on the force balance, the negative stiffness and restoring requirements of the SMA cable-based negative stiffness isolator were analyzed first. Then, a prototype large-scale isolator was designed and fabricated. Next, the experimental testing of the developed isolator was performed under two different vertical load levels. Finally, finite element modeling of the proposed isolator was conducted, and the simulation results and experimental results were compared and discussed. The proposed isolator generates lower forces than the SMA-based zero and positive stiffness isolators and can exhibit stable energy dissipation capabilities with very good displacement-limiting and self-centering capabilities.

Experimental and Numerical Investigation of a Dissipative Connection for the Seismic Retrofit of Precast RC Industrial Sheds

Past earthquakes have highlighted the seismic vulnerability of prefabricated industrial sheds typical of past Italian building practices. Such buildings typically exhibited rigid collapse mechanisms due to the absence of rigid links between columns, beams, and roof elements. This study aims at presenting the experimental and numerical assessment of a novel dissipative connection system (DCS) designed to improve the seismic performance of prefabricated sheds. The device, which is placed on the top of columns, exploits the movement of a rigid slider on a sloped surface to dissipate seismic energy and control the lateral displacement of the beam, and to provide a recentering effect at the end of the earthquake. The backbone curve of the DCS, and the effect of vertical load, sliding velocity, and number of cycles were assessed in experimental tests conducted on a scaled prototype, according to a test protocol designed accounting for similarity requirements. In the second part of the study, non-linear dynamic analyses were performed on a finite element model of a portal frame implementing, at beam-column joints, either the DCS or a pure friction connection. The results highlighted the effectiveness of the DCS in controlling beam-to-column displacements, reducing shear forces on the top of columns, and limiting residual displacements that can accrue during ground motion sequences.

Residual displacement estimation of the bilinear SDOF systems under the near-fault ground motions using the BP neural network

This paper presents a comprehensive study of residual displacements of the bilinear single degree of freedom (SDOF) systems under the near-fault ground motions (NFGMs). Five sets of NFGMs were constructed in this study, in which the natural ones as well as the synthesized ones were both considered. By way of the nonlinear time history analyses, three different residual displacement spectrums were obtained and analyzed in detail. Utilizing the calculated data, a back propagation (BP) neural network was established to predict the residual displacements of the bilinear SDOF systems under the NFGMs. The results show that the structural parameters, including the strength reduction factor and the post-yield strength ratio, have significant and relatively consistent impacts on the residual displacement spectrum. However, the ground motion characteristics, including the fault type, the closest distance from the site to the fault rupture, the earthquake magnitude, and the site soil condition, exhibit more complex effects on the residual displacement spectrum. In addition, the proposed BP neural network can fully incorporate the parameters affecting the residual displacements of the bilinear SDOF systems under the NFGMs, while having a fairly good accuracy in predicting the residual displacements.

Seismic Response of Resilient Bridges with SMA-Based Rocking ECC-Reinforced Piers

Post-earthquake investigation shows that numerous reinforced concrete (RC) bridges were demolished because of large residual displacements. Improving the self-centering capability and hence resilience of these bridges located in earthquake-prone regions is essential. In this regard, a resilient bridge system incorporating engineered cementitious composites (ECC) reinforced piers and shape memory alloy (SMA) energy dissipation components, i.e., SMA washers, is proposed to enhance its resilience when subjected to strong earthquakes. This study commences with a detailed introduction of the resilient SMA-washer-based rocking bridge system with ECC-reinforced piers. Subsequently, a constitutive model of the ECC material is implemented into OpenSees and the constitutive model is validated by test data. The working principle and constitutive model of the SMA washers are also introduced. A series of dynamic analysis on the conventional and resilient rocking bridge systems with ECC-reinforced piers under a suite of ground motions at E1 and E2 earthquake levels are conducted. The analysis results indicate that the resilient rocking bridge system with ECC-reinforced piers has superior resilience and damage control capacities over the conventional one.

CIRCULAR DOUBLE SKIN STAINLESS STEEL TUBULAR COLUMN FILLED WITH UHPFRC SUBJECTED TO IMPACT LOAD

Concrete filled steel tube (CFST) column is an important type of structural member and its protective design is essential to enhance its structural performance under various dynamic loads. Previously carried out studies on CFST columns tried to determine how to improve their structural response under various loadings, such as axial compression, lateral impact, blast, seismic, etc. Apart from investigations on transverse impact loading, the majority of the other studies on CFST under various loads established solutions and protective measures. Therefore, this study aim is to improve the performance of CFST under transverse impact loads. The geometrical and mechanical properties, boundary conditions, impact loading and dynamic explicit analysis employed in that study. This paper proposes a novel design in terms of cross-sectional configuration and smart materials to be applied on the CFST in order to improve its performance under lateral impact loading. The proposed investigation is exclusively numerical and its results were verified with the experimental results from literature. The considered three main variables were including (1) concrete-filled double skin steel tubular – CFDST with both first sandwich layer and internal carbon steel tube filled with normal strength concrete – NSC, (2) CFDST with first sandwich layer filled with Ultra High-Performance Fiber-Reinforced Concrete – UHPFRC. a. The parameters including failure modes, maximum mid-span deflection, and residual displacements were presented.

Modeling and Design Exploration of Tensegrity Plate Mechanisms With Energy Dissipation Capabilities Enabled by Shape Memory Alloys

This paper presents the modeling and design exploration of tensegrity plate mechanisms with the ability of dissipating energy arising from compressive loads. The tensegrity plates are comprised of an assembly of tensegrity prisms, each formed by three compressive bars self-equilibrated by a network of tensile strings. The plates transfer a uniform compressive surface load applied along their planform area to uniaxial tension and compression within their members. The energy dissipation capabilities of plates with strings formed by three different elastoplastic metals and a pseudoelastic shape memory alloy (SMA) are explored. The constitutive parameters of these materials are calibrated from experimental data, and finite element models of the plates are created. A Taguchi design of experiments is used to evaluate the main effects of different design parameters of the plates on their energy dissipation and residual deformation responses. Results indicate that plates of larger thickness, lower diameter, and higher complexities provide higher energy dissipation per unit mass. Pseudoelastic SMA strings were the only type of strings that provided cyclic energy dissipation without the emergence of residual displacements. The studied energy absorbing mechanisms can potentially be integrated in aerospace, automotive, and civil components designed to absorb and dissipate energy from vibrations or distributed compressive loads.

Seismic cracking mechanism and control for pre-stressed concrete box girders of continuous rigid-frame bridges: Miaoziping bridge in Wenchuan earthquake as an example

The box girder of the Miaoziping Bridge, a three-span prestressed concrete continuous rigid-frame bridge, suffered a serious crack in its box section’s web near the 1/6 to 1/2 length of the side span and the middle-span length of 1/4 to 3/4, as a result of the 2008 Wenchuan earthquake, which also caused large lateral residual displacements at both ends of the side span. In this study, eight strong-motion records near the bridge site and two other records (El Centro and Taft) are selected as inputs for time-history analysis of the bridge. The cantilever construction process and initial stress of the box girder are considered in a bridge model for seismic numerical simulation. Further, the simulation results are compared with the actual earthquake damage. The cracking mechanism, influencing factors and control of the girder crack damage are discussed. The high-stress zones of the box girder agree with the seismic damage observed, even various seismic inputs are considered. The findings reveal that the maximum (principal) tensile stress of the girder exceeds the tensile strength of the concrete under the seismic excitations, and cracks occur. Under various input directions of ground motions, the proportion of the main girder stresses induced by the earthquake shows differences. After the failure of the shear keys in the transverse direction of the bridge, the stresses of the girder decrease in the mid-span. However, the beams at both ends of the side spans revealed large lateral displacements. Considering that the uplift of the beam ends, stress and axial torque of the girder’s side span are greatly reduced. Setting bi-directional friction pendulum bearings on the transition pier is an effective damping measure to control web cracking of the mid-span and lateral drifts of the beam ends.

Novel Method for Probabilistic Evaluation of the Post-Earthquake Functionality of a Bridge

While modern overpass bridges are safe against collapse, their functionality will likely be compromised in case of design-level or beyond design-level earthquake, which may generate excessive residual displacements of the bridge deck. Presently, there is no validated, quantitative approach for estimating the operational level of the bridge after an earthquake due to the difficulty of accurately simulating residual displacements. This research develops a novel method for probabilistic evaluation of the post-earthquake functionality state of the bridge; the approach is founded on an explicit evaluation of bridge residual displacements and associated traffic capacity by considering realistic traffic load scenarios. This research proposes a high-fidelity finite-element model for bridge columns, developed and calibrated using existing experimental data from the shake table tests of a full-scale bridge column. This finite-element model of the bridge column is further expanded to enable evaluation of the axial load-carrying capacity of damaged columns, which is critical for an accurate evaluation of the traffic capacity of the bridge. Existing experimental data from the crushing tests on the columns with earthquake-induced damage support this phase of the finite-element model development. To properly evaluate the bridge's post-earthquake functionality state, realistic traffic loadings representative of different bridge conditions (e.g., immediate access, emergency traffic only, closed) are applied in the proposed model following an earthquake simulation. The traffic loadings in the finite-element model consider the distribution of the vehicles on the bridge causing the largest forces in the bridge columns.

Deformation due to sliding of single and woven carbon tows in dry and epoxy-lubricated conditions

This experimental work focuses on the evaluation of deformation mechanisms due to sliding between carbon fiber tows with a flat tool in dry and lubricated with liquid resin conditions. The experiments were carried out on manually woven and single tows. The effect of angle between tow axes and sliding direction was also studied. The topography of the tows in contact with a sliding transparent glass plate was measured with a 3D optical microscope before and after sliding. These measurements revealed a decrease of roughness with sliding in all tested conditions, a contraction of lubricated single tows in perpendicular to sliding orientation, and high residual displacements in lubricated woven tows in 0°/90° orientation and dry single tows in perpendicular to sliding orientation.