Journal of Structural Engineering

This paper puts forward an indirect bridge monitoring method using Mel-frequency cepstral analysis of inverse-filtered drive-by acceleration signals collected through smartphones. Crowdsensing-based approaches using data collected by smart cars and smartphones opened a new chapter in bridge monitoring by reducing the costs and increasing the efficiency of the bridge monitoring process. However, the major challenge of the dominancy of the operational effects in the recorded drive-by vibrations overshadows the bridge monitoring objective. This paper proposes an inverse filtering-based monitoring approach to suppress operational effects. The inverse-filtered spectrum is later employed in a Mel-frequency cepstral analysis, leading to the calculation of the abnormality index, which is then used to detect the change in the bridge state. The performance of the proposed method in suppressing operational effects is assessed through a series of laboratory and real-life experiments. Afterward, the damage detection capability of the method is investigated for two damage levels at different locations along the bridge, modeled in a laboratory environment. The results provide evidence for the capability of the proposed method in drive-by damage detection of bridges. Moreover, using the smartphone as the data acquisition device paves the path toward the implementation of the method for crowdsensing-based bridge monitoring in future smart cities, although more operational factors such as passenger interactions and resulting smartphone motions need to be considered in future studies.

Buckling of slender members due to gravity loading or thermal effects is influenced by the member’s geometric imperfections, boundary conditions, and intermediate lateral supports. When assessing the capacity of such members, these parameters are often unknown (e.g., the rotational stiffness of end connections in a truss or the lateral support provided by the ties to a rail track), and conservative assumptions must be made resulting in conservative assessments. Distributed fiber optic sensors (DFOS) can potentially be used to determine these parameters with greater accuracy using strain measurements along the length of a member. A series of buckling experiments was conducted on a slender member instrumented with DFOS subjected to axial load with varying levels of lateral restraint or to increasing temperature. The distributed strain data were then used to evaluate the geometric imperfections, boundary conditions, and lateral support stiffness. These inputs were used to create a finite-element model to estimate the ultimate load response of the member using data acquired at service loads.

The present paper deals with the optimal design of nonprismatic beams, i.e., beams with variable cross section. To set the optimization problem, Euler-Bernoulli unshearable beam theory is considered and the elastica equation expressing the transverse displacement as a function of the applied loads is reformulated into a system of four differential equations involving kinematic components and internal forces. The optimal solution (in terms of volume) must satisfy two constraints: the maximum Von Mises equivalent stress must not exceed an (ideal) strength, and the maximum vertical displacement is limited to a fraction of beam length. To evaluate the maximum equivalent stress in the beam, normal and shear stresses have been considered. The former was evaluated through the Navier formula, and the latter through a formula derived from Jourawsky and holding for straight and untwisted beams with bisymmetric variable cross sections. The optimal solutions as function of material unit weight, maximum strength, and applied load are presented and discussed. It is shown that the binding constraint is usually represented by the maximum stress in the beam, and that applied load and strength affect the solution more than material unit weight. To maintain the generality of the solution, the nondimensionalization according to Buckingham $\mathrm{\Pi }$-theorem is implemented and a design abacus is proposed.

This paper presents experimental investigations on the lateral performance of cross-laminated timber (CLT) shear walls with customized self-tapping screw (STS) connections. The panel-to-base (hold-downs and shear brackets) and panel-to-panel (spline) connections were tested under quasi-static monotonic and reversed cyclic loading to derive design values of STS, which were shown to be 2.8–3.6 times higher than those calculated using the current Canadian timber design standard. Then, a total of 26 CLT shear walls, including single-, double- and triple-panel configurations, were tested, again under quasi-static monotonic and reversed cyclic loading. The shear walls consisted of five-ply, 139-mm-thick and 3-m-high CLT panels with aspect ratio of either $2:1$ or $3:1$, and different numbers of STS in the connections. The shear wall strength and corresponding displacements increased with the number of screws in hold-downs and spline joints; further, it increased with number of connected panels and decreased as a function of aspect ratio. The data can be used for developing and calibrating numerical models to investigate the lateral responses of CLT shear walls with different configurations.

Abstract

Recent amendments to design ground snow load requirements in current US standards have reduced the size of case-study regions by 91% from what they were in previous standards, primarily in western states. This reduction is made possible through the development of highly accurate regional generalized additive models (RGAMs), stitched together with a novel smoothing scheme implemented in the R software package remap, to produce the continental-scale maps of reliability-targeted design ground snow loads available in current standards. This approach allows for better characterizations of the changing relationship between temperature, elevation, and ground snow loads across the conterminous US (CONUS). RGAMs are shown to have 10% or better improvement in mean absolute mapping error in two independently created data sets when compared with traditional mapping techniques.

Practical Applications

Structures must be able to withstand environmental stresses without collapsing, including snow. Design ground snow loads are estimated using snow measurements taken at weather stations throughout the US. Mapping techniques allow design ground snow loads to be estimated at regions between weather stations. This paper describes a regional approach for mapping design ground snow loads in CONUS and demonstrates the improved accuracy of the approach, relative to previous methods, on two independently created national data sets.

Balloon-type mass timber shear walls are one of the most efficient structural systems to resist lateral loads induced by earthquakes or high winds. They are a viable solution for high-rise buildings because they have several key advantages, such as reducing connections and avoiding accumulating compression perpendicular to grain in the floors. This system, however, is not included in current Canadian building code and has no design guidelines in the Canadian timber standard, so it is out of reach of most designers. A multiyear research project has been initiated to quantify the system performance and develop the necessary technical information to codify balloon-type mass timber shear walls. In this paper, the limits for the building height of balloon mass timber shear walls were investigated theoretically. A mechanics-based analytical model was developed to analyze the building height limits governed mainly by the mass timber panels. The influence of loading types (seismic versus wind loads), lateral load levels, panel deformation contribution, seismic force modification factors, and vertical joints between panels on the building heights was investigated using the developed model. The results of this study will give a valuable insight into the seismic performance of balloon type cross-laminated timber (CLT) shear walls.

Bridges have recently been exposed to an increasing number of natural hazards such as earthquakes and tsunamis. These extreme events have resulted in transverse offsets, overturning moments, and even dropping-off of superstructures due to their weak connection to substructures. These outcomes are potentially prevented or mitigated by developing and deploying sliding, modular, adaptive, replaceable, and two-dimensional (SMART) shear keys as fuse elements between superstructures and substructures. The novelty of SMART shear keys is to enable an adaptive control of both the force and displacement of bridges under different types of loads. In this study, the performance of SMART shear keys under tsunami loading was investigated through a 1/5-scale six-girder concrete bridge model. Four levels of tsunami-like solitary waves 0.27, 0.42, 0.57, and 0.72 m in height were generated in the large wave flume at Oregon State University and applied on the reinforced concrete bridge. To evaluate the performance of the shear keys, the dynamic responses of the bridge model were measured from accelerometers, load cells, and displacement sensors. The shear keys were prestressed to 0, 100, and 200 MPa to represent flexible, medium, and fixed superstructure-substructure connections, respectively. The test results indicated that the residual displacements of the SMART shear keys were less than 1 mm in the vertical direction and zero in the horizontal direction. The energy dissipated by the SMART shear keys was up to 32.5% of the input energy that the bridge received from the tsunami loading. The natural frequency and energy dissipation of the bridge were respectively modified up to 18% and 14.2% by changing the prestress level of the SMART shear keys from 0 to 200 MPa.

Exposed column-base connections are commonly overtopped with concrete to provide an even surface with the surrounding floor slab. To facilitate construction, this concrete is poured, after construction of the floor slab, into a blocked out region of the slab in which the column is placed. The result is a shallowly embedded connection that has significantly higher lateral strength and stiffness with respect to the exposed column-base plate connection without the embedment. This has implications for design and, more importantly, seismic performance assessment. Three large-scale experiments are presented to examine the response of such connections. The connections were subjected to combinations of axial compression and cyclic lateral deformation representative of seismic loading. Significant increases in both strength and stiffness (relative to exposed base plate connections) are noted, arising from the block-out concrete resisting the uplift of the base plate. Stable and ductile hysteretic response (similar to exposed column-base plate connections) is also noted. Failure modes include concrete breakout above the base plate and fracture of the anchors. Results from this study are synthesized with results from previous studies on similar connections to propose a strength model, and to evaluate previously proposed models for stiffness.

Large infrastructure projects can efficiently use large diameter bars as longitudinal reinforcement in reinforced concrete elements. In earthquake-prone zones, critical regions of these elements must be detailed for ductility and hysteretic energy dissipation. Longitudinal bars in these regions are expected to sustain large-amplitude strain cyclic reversals before bar fracture occurs, in a mode of failure defining the collapse prevention limit state. To date, no successful large strain-amplitude cyclic loading testing has been reported on large-diameter reinforcing bars to observe the large-strain amplitude fatigue life of such bars, which often involves plastic bar buckling. This paper describes a test program designed to determine the plastic buckling/straightening fatigue life of ASTM A706 Grade 60 No. 18 bars ($Ø57\mathrm{mm}$) reinforcing bars subjected to cycles of reversed plastic strains. The design and implementation of the loading apparatus, critical for the gripping of the bars, the metallurgical characterization of the bars, and several key test results are discussed in the paper. Finally, the paper discusses a general unidimensional fatigue damage index precursor to bar fracture following a few plastic buckling and straightening cycles.

This paper investigates the progressive collapse behavior of composite beam-column connection subassembly under column removal scenarios. An analytical model is proposed based on the rigid-plastic assumptions, in which the plastic hinges and inelastic rotations are assumed to develop concentratedly at only the connection interfaces, whereas the remaining parts are rigid except for the axial shortening/lengthening deformation when subjected to compressive/tensile forces. The component-based joint model proposed by Eurocodes is utilized to approximate the axial and plastic moment resistances of composite beam-column connections. The method to determine the force-displacement relationship of each connection component is presented in detail, particularly for the concrete slab and profiled steel decking where the actual nonuniform stress distributions along the slab thickness and width are carefully considered. By comparing with the published test results of composite joints under respective hogging and sagging moment, the proposed rigid-plastic model is capable of predicting the progressive collapse behavior of composite beam-column connection subassembly with reasonable accuracy. Based on the verified model, a parametric study is conducted with focus on the effect of lateral restraint stiffness on the collapse-resisting capacity of composite beam-column connection subassembly under column removal scenarios.

Abstract

Protecting critical equipment in seismically excited buildings is essential to ensure functionality after an earthquake. Individual equipment or equipment sets can be seismically isolated from the building motion. Special isolators can be employed to mitigate the most severe accelerations that occur in the horizontal direction of a building. This paper presents the results of an investigation of the performance of an uncoupled bidirectional isolation system for horizontal isolation using a novel adaptive restoring force (ARF) device. The device changes the structural response transmitted to floor-mounted equipment by filtering the most intense portions of input floor acceleration histories to minimize the acceleration of the equipment and the stress demands imposed by the supporting structures. The ARF device utilizes restoring and damping elements to generate restoring forces that vary nonlinearly with displacement, resulting in a force–displacement curve with varying slopes and loading and unloading paths. The force–displacement relationship of the ARF device is characterized by high stiffness at small and large displacements, and low stiffness in between. A small-scale prototype was constructed to validate the ARF concept, and its force–displacement properties were observed for cyclic loading. A numerical model was developed that accurately predicted the relationship between the device force and displacement. The system’s performance was evaluated through numerical analysis of equipment installed on different levels of multistory buildings subjected to measured floor accelerations. The results showed that the horizontal isolation system effectively limited the transmission of the floor accelerations to the equipment. Furthermore, the results showed that the isolation system transformed the seismic acceleration profile from a high-amplitude and -frequency signal to one with a low quasi-constant amplitude and low frequency, acting as a low-pass filter under the most intense time window of the floor acceleration.

Practical Applications

Protecting critical equipment can be a significant concern for those who manage or work in facilities vulnerable to earthquakes. This study presents a new technology for horizontal seismic isolation of equipment, the adaptive restoring force device, that effectively minimizes the damaging effects of earthquakes on floor-mounted equipment in multistory buildings. The ARF device protects equipment by filtering out the most intense and destructive vibrations accompanying earthquakes, thus reducing accelerations on the equipment and its supporting structures. It transforms high-amplitude and -frequency vibrations to lower, more-constant levels. Unique to the ARF device is its adaptability to work effectively on any floor of a building, even on rooftops, while allowing considerable relative movement between the equipment and the floor. The results of this study are promising—equipment experienced reduced and nearly constant low-frequency accelerations during simulated seismic events. Although further research is required to address more complex problems, such as building torsion and vertical seismic effects, preliminary findings suggest that the ARF device offers a practical solution for preserving vital floor-mounted equipment in multistory buildings in earthquake-prone regions. This device can prove invaluable as a tangible solution for businesses, industries, and hospitals dependent on critical equipment.

Floor systems are typically designed to satisfy tight deflection limits under out-of-plane loading. Although the use of concrete flat slabs is common in the built environment due to the ease of construction, the load-bearing performance is inefficient because the material is not optimally distributed within the cross section to take the bending caused by external loads. This typically results in significant oversizing. Floor slabs account for more than 50% of the material mass and associated emissions embodied in typical low-rise reinforced concrete buildings. In addition, the volume of carbon-intensive cement production has tripled in the last three decades. Therefore, lightweight floor systems that use minimum material resources causing low emissions can have a significant impact on reducing adverse environmental impacts of new constructions. Recent work has shown that rib-stiffened slabs offer significant potential for material savings compared with flat slabs. This work investigates adaptive rib-stiffened slabs equipped with an adaptive tensioning system. The adaptive tensioning system comprises cables embedded within the concrete rib through a duct that enables varying the cable tension as required to counteract the effect of different loading conditions without applying permanent prestress that might cause unwanted long-term effects including tension loss and amplified deflection. The cables are positioned following a profile so that the tension force is applied eccentrically to the neutral axis of the slab-ribs assembly. The resulting system of forces causes a bending moment that counteracts the effect of the external load. The rib placement is optimized through a greedy algorithm with a heuristic based on the direction of the principal stresses. The deflection of the slab is reduced by adjusting the cable tensile forces computed by a quasi-static controller. Benchmark studies comparing different cable profiles and active rib layouts are carried out to determine an efficient control configuration. A case study of an $8\times 8\text{-}\mathrm{m}$ adaptive rib-stiffened slab is implemented to evaluate material savings potential. Results show that the adaptive slab solution can achieve up to 67% of material savings compared with an equivalent passive flat slab.

This study presents an experimental investigation into the cyclic performance of a new tube-in-tube buckling restrained brace (BRB) configuration. In this study, reduced- and large-scale brace geometries are tested to quantify inelastic hysteretic response, understand core confinement parameters, and determine the influence of end connection constraints. A total of 11 reduced-scale brace specimens are cyclically tested, along with three large-scale braces representing two core geometries and two core constraint configurations. Results from the reduced- and large-scale brace testing suggest that the tube-in-tube BRB configurations are capable of achieving the required inelastic capacity for qualification in AISC 341-16 specifications. All scaled specimens survived cumulative inelastic demands that exceeded 240 times the yield displacement (with several surviving more than 400 times the yield displacement). Results indicate that tube-in-tube BRBs are capable of producing stable tension-compression hysteretic behavior during cyclic loading. Measured $\beta$ values for the large-scale Specimen G2 were lower than 1.06 for all deformation cycles at or below $9.2{\mathrm{\Delta }}_{\mathrm{by}}$, while measured $\beta$ values for the large-scale Specimen G3 were lower than 1.07 for all cycles at or below $3.6{\mathrm{\Delta }}_{\mathrm{by}}$. The peak $\beta$ value for Specimens G2 and G3 was 1.16 and occurred during the $15.3{\mathrm{\Delta }}_{\mathrm{by}}$ and $7.1{\mathrm{\Delta }}_{\mathrm{by}}$ cycles, respectively.

Cross-laminated timber (CLT) provides a solution for numerous structural applications, including entire seismic force resisting systems. The primary objective of the research presented herein was to develop a CLT shear wall system with hyperelastic elastomeric hold downs (HDs) that provide the required uplift resistance and deformability, so that the CLT panels develop coupled-panel rocking behavior, without strength and stiffness degradation in the HDs. Secondary objectives consisted of the mechanical characterization of the hyperelastic HD as a function of its geometry, and the determination of minimum edge and end distances to avoid brittle failure in the CLT, for development of capacity-based design procedures for this system. To achieve these objectives, the individual components (HDs, steel rods, spline joints, and CLT panels) were tested along with a total of 66 full-scale shear walls. The tests demonstrated that (1) the HDs remain elastic under rocking kinematics provided that the elastic limit of the steel rod is not exceeded, (2) sufficient CLT width can prevent undesired brittle CLT failure before steel yielding in the rods, and (3) the shear wall strength and stiffness is a function of HD size and the panel-to-panel shear connection properties. The hyperelastic HD assembly provides design engineers with a low-damage alternative to contemporary HD solutions for platform-type CLT shear walls.

An experimental test program was performed on grouted post-tensioned anchor rods to determine if anchors with high rod-to-duct area ratios could reanchor themselves upon fracture. Liftoff testing of the grouted anchors was also performed. Results of the study revealed the specimens were capable of reanchoring themselves over a short transfer length and possessed a significant amount residual bond strength following liftoff testing. A theoretical model was created to predict the transfer length phenomenon, which was founded on linear interference fit assumptions. The results between the physical tests and theoretical model demonstrated feasibility in the approach and assumptions.

Buckling-restrained braced frames (BRBFs) are attracting interest worldwide by virtue of their extraordinary response reduction performance. The system relies strongly on the energy dissipation of buckling-restrained braces (BRBs). Therefore, the surrounding members (beams, columns, or gusset plates) must sustain the force imposed by a BRB. Notably, beams are not designed primarily to support the axial force. The sections consequently tend to become deep and slender to enhance the flexural strength and stiffness effectively, thereby leading to local buckling, which lessens the reaction force to the BRB. Moreover, the instability is activated by the compressive axial force transferred from the BRB. However, beams in the BRBFs generally become composite beams through an assemblage with a concrete slab by stud shear connectors. The concrete slab shifts the neutral axis of the beam, which imposes more strain on the bottom flange. The BRB axial force and composite effect therefore influence the steel beam buckling behavior. Eventually, the beam might be subjected to instability at a smaller-than-expected deformation. However, the rotation capacity of the composite beam in BRBFs has not been clarified yet. To address this concern, this study established a finite-element analysis (FEA) model referring to a former specimen and an experiment scheme. Additionally, a parametric study of the influential factors was conducted using the experimentally validated FEA model. This study examined a proposed evaluation equation of an apparent axial force issued from the composite effect based on the obtained results. An earlier evaluation index established for bare steel beams was ultimately modified to include the axial force influence. Eventually, the results demonstrated that the structural performance can be assessed appropriately using the existing evaluation equations proposed using a steel frame subassembly.

The gust factor commonly is used in wind engineering community to convert mean wind speeds into gusty winds, which exhibit significant variability in real observations of typhoon winds. This study proposes a probabilistic gust factor model that accounts for uncertainties of wind speed statistics. The statistical characteristics of wind speed from nine typhoons, including the mean, standard deviation, skewness, kurtosis, power spectral density (PSD) parameter, peak factor, and gust factor, were examined. The effects of nonstationary characteristics in terms of time-varying mean wind speed and non-Gaussian attributes of fluctuating winds on the gust factor are discussed. These wind speed statistics were incorporated into a non-Gaussian moment-based translation model to perform the Monte Carlo simulation of peak factor and gust factor. The simulation results for different gust durations were juxtaposed with observations to substantiate the accuracy of the probabilistic model. Subsequently, a standardization framework for estimating site-specific probabilistic gust factor curves was developed. This approach was applied to determine the gust typhoon wind speed hazard curve at a real bridge site with flat open terrain. The present model enables the consideration of gust factor dispersion to achieve a probabilistic gust wind hazard curve and facilitate the development of performance-based wind engineering.

The sustainable development of the built environment is closely related to climate-neutral construction and minimum resources use. In this framework, deployable and reconfigurable building structures offer a promising solution while aiming at reduced self-weight with flexibility and structural efficiency. Nevertheless, commonly developed structural typologies often lead to increased structural weight, complexity, and energy-inefficient operation. The linkage-based systems considered in this work have minimum actuation components, are based on a modular design and the definition of a one-degree-of-freedom mechanism in each transformation step of a reconfiguration sequence from an initial to a target configuration. The effective crank–slider approach was applied on a class of planar eight-bar linkage aluminum structures of different typologies and geometrical characteristics of the members (i.e., simple and hybrid typologies), as well as of variable length. The considered planar structural mechanisms have an overall length of 12.0 m in their initial almost-flat configuration and a respective span of 6.0 m in their specific archlike target configurations. They are supported on a pivot joint on one end and a linear sliding block on the other end, which is associated to the external actuation. In addition, each intermediate joint is equipped with brakes. The simulation of the systems is based on kinematics and a comparative finite-element analysis. The study provides insight into the impact of various geometrical and typological aspects on the systems’ behavior. The experimental implementation of the kinematics approach on a small-scale prototype in different typologies demonstrates its feasibility and highlights practical implementation issues.

Corrosion-induced concrete cracking significantly weakens the integrity, serviceability and durability of reinforced concrete (RC) structures. Existing reliability analysis of corrosion-induced concrete cracking often considers the corrosion of reinforcement as a uniform process, in favor of implementing the analytical formulation of corrosion rust progression. However, corrosion distribution in RC structures is seldom uniform around the steel reinforcement, hence the corrosion-induced pressure. Thus, considering the nonuniform corrosion process in the reliability analysis becomes important. This paper develops a time-dependent reliability methodology, combining mesoscale heterogeneous fracture modeling and a state-of-the-art machine learning algorithm, to assess the serviceability of the RC structures subjected to nonuniform development of corrosion. The effects of critical crack width, corrosion nonuniformity, chloride content, temperature, and relative humidity on the failure probability are investigated. The worked example demonstrates the importance of considering the nonuniformity of the corrosion product distribution, which provides reliable evaluation of the remaining safe life of RC structures compared with the use of a uniform corrosion model. The developed unified assessing methodology for corrosion of RC structures can serve as a useful tool for engineers, designers, and asset managers for their decision making with regard to repair and maintenance of corrosion-affected RC structures.

The objective of this work is to investigate the strength of bolted lap shear connections with advanced high-strength steel (AHSS) sheets and the effects of steel ductility on bolted connection behavior. An experimental study on AHSS bolted lap shear connections has been conducted, involving six different steel sheets that have nominal yield stress ranging from 340 to 1,200 MPa and ductility ranging from 3% to 20% in elongation. Four limit states are investigated: bearing, tilting/bearing, net section, and end tear-out. The connection strengths obtained from the tests are compared with strength predictions from relevant design specifications (AISI S100, AS/NZS 4600, EN-1993-1-3) and proposals in the literature. Connections with specific low-ductility AHSS sheets cannot reach full design strengths. Extending the strength reduction factor in the current AISI S100 specification to AHSS sheets is found to provide an adequate correction. Based on the test data, two new continuous strength reduction factors are proposed, one based on ductility as measured by ultimate elongation and a second utilizing true fracture strain as the ductility measure.

The interface force condition on the cross section of parallel steel wire strands is an important basis for studying the longitudinal friction and slip behavior of wires. In this study, force-chain superposition was proposed to solve the transmission and distribution of transverse forces between parallel wires. The calculation rules for the basic parameters in the solution were determined, and a wire-drawing experiment was designed to verify their applicability. A two-dimensional discrete model corresponding to the cable cross section was established. According to the source and characteristics of the transverse load, the force system is decomposed into two directions to form two force chain analysis paths so that the model assumptions can be applied properly. A recursive algorithm was proposed to solve the two force chains, and symmetry conditions were applied at the coupling position to make the system self-consistent. The normal forces acting on the interface points were obtained by superimposing the results onto the two force chains and were verified against finite element analysis (FEA) results. A long-span cable-stayed bridge was considered as an example to investigate the interface force condition of its cables, based on which the approximate development length of the broken wires and the interface extrusion force of the multilayered beam model were established. The results indicate that the slight twisting of the parallel wire strands under the action of a large cable force provides 85% of the total interface forces, and the normal force is significantly concentrated in the central area of the cross section. The approximate development length of the central wire is only 25.9% of that of the outermost wire, and the minimum slip friction force between the layers accounts for only 21.2% of the maximum value for the multilayered beam model, confirming that the interface force condition has a significant impact on the longitudinal friction and slip behavior of cable wires.

The concept of generalized plasticity theory provides an appealing approach to developing efficient finite element models that can improve computational performance and allow flexibility in customizing plastic response. In this work, we revisit its application in developing frame elements and reformulate a concentrated plasticity frame element to allow its axial force to interact with its end moments (N-M interaction). The proposed element formulation relies on the physical implication of axial plasticity and updates its definition accordingly. Inasmuch, a single axial plasticity history can participate in plasticity evolution and N-M interaction at both ends. The new formulation also redefines the hardening rules to recover desired hardening behavior, which is not available in the previous formulation. In terms of numerical performance, the new formulation removes the potential bifurcation issue when both ends experience identical pure axial plasticity history. The proposed frame element is a high-performing alternative to simulate zero-length plastic hinge frame members that are frequently used in simulations in seismic engineering.

Abstract

Since the Ronan Point collapse in the UK in 1968, the progressive collapse analysis of residential buildings has gradually drawn the attention of civil engineers and the scientific community. Recent advances in computer science and the development of new numerical methodologies allow us to perform high-fidelity collapse simulations. This paper assesses different scenarios that could have hypothetically caused the collapse of the Champlain Tower South Condo in Surfside, Florida, in 2021, one of the most catastrophic progressive collapse events that has ever occurred. The collapse analysis was performed using the latest developments in the Applied Element Method (AEM). A high-fidelity numerical model of the building was developed according to the actual structural drawings. Several different collapse hypotheses were examined, considering both column failures and degradation scenarios. The analyses showed that the failure of deep beams at the pool deck level, directly connected to the perimeter columns of the building, could have led to the columns’ failure and subsequent collapse of the eastern wing of the building. The simulated scenario highlights the different stages of the collapse sequence and appears to be consistent with what can be observed in the footage of the actual collapse. To improve the performance of the structure against progressive collapse, two modifications to the original design of the building were introduced. From the analyses, it was found that disconnecting the pool deck beam from the perimeter columns could have been effective in preventing the local collapse of the pool deck slab from propagating to the rest of the building. Moreover, these analyses indicate that enhancing the torsional strength and stiffness of the core could have prevented the collapse of the eastern part of the building, given the assumptions and initiation scenarios considered.

Practical Applications

Building catastrophic collapses can cause significant lives and economic losses. Poor design and maintenance, in combination with aging, will more likely increase, in the next years, the number of buildings potentially vulnerable to the risk of collapse, due to either seismic, accidental, or degradation actions. This research focuses on the analysis of the Champlain Tower South condo collapse, which occurred in Surfside, Florida, in 2021. Different hypothetical collapse scenarios were simulated, comparing the analysis results with the actual evidence of the collapse. The analyses have shown that the degradation of the pool deck slab, due to corrosion, may have contributed to the collapse of the building. Finally, two different minor revisions of the original design of the building were analyzed to reduce the risk of failure and understand how the collapse of similar residential buildings could be prevented.

Composite shear walls are widely used to resist the lateral load in high rise-buildings nowadays; however, prior experimental tests have shown high damages and residual drifts at the plastic zone region. At present time, designing resilient buildings with low or no damage is one of main goal in performance-based seismic design of structures. In current research, a new design of an innovative low damage self-centering composite steel plate shear wall (SC-C-SPSW) equipped with unbonded posttension tendons (UPTs) is proposed to control the damage and the residual drift under seismic loading. To this end, five specimens including two composite steel plate shear walls (C-SPSW) and three SC-C-SPSWs were tested under gravity and reverse cyclic loading. The SC-C-SPSWs were detached using a pair of steel plates placed symmetrically under the wall boundary elements in order to form the bottom gaps with the foundation. The gap length, steel plate dimensions, and the initial prestressing on UPTs were considered as experimental parameters in this study. The construction details and the seismic performance including failure modes, damage progression, hysteretic response, and energy dissipation are presented in detail. The experimental results indicated that SC-C-SPSWs have excellent behavior in term of lateral strength and ductility and experienced low damage levels in comparison with C-SPSWs. The SC-C-SPSW walls experienced a large lateral displacement before initiation of the strength degradation, and the residual drifts were much smaller in comparison with C-SPSWs.

In this paper, the optimum outrigger locations of the outrigger-braced structure are studied by considering the influence of the core-wall width and structural asymmetry. The axial forces in the columns are taken as unknowns, and the compatibility equations of the columns’ axial deformation are formulated in terms of the axial forces. Then, the equations governing the optimum locations of the outriggers are formulated to minimize the top drift of the core wall. After that, the parametric analysis on the optimum locations of outriggers, drift-reduction efficiency, and moment-reduction efficiency in the base of the core wall are conducted numerically. The influences of different structural parameters on the optimum locations of outriggers, drift-reduction efficiency, and moment-reduction efficiency in the base of the core wall are all discussed. The change of optimum outrigger locations with the increase of $\omega$ is obviously when $r=2$ or $\eta =0$. For the structure with a larger core-wall width, a smaller number of outriggers can be adopted regarding the drift or moment-reduction efficiency. For instance, the drift or moment-reduction efficiency of the structure with one outrigger when $\eta =0.5$ is close to the drift or moment-reduction efficiency of the structure with two outriggers when $\eta =0.25$. Some results are presented for reference in the preliminary structural design of asymmetrical outrigger-braced structures with limited core width.