Journal of Structural Engineering

A section model test effectively assesses the aeroelastic behavior of long-span bridges in a wind-resistant design. The conventional approach uses springs to support a mass-calibrated physical section model scaled to the similarity principle. Modal damping can also be modeled using sticks soaked in oils. Although this procedure has been successfully applied to most bridges, it involves physical limitations in selecting the model scale and vibration frequencies. Also, certain degrees of time and effort are required for the calibration and modification of dynamic properties in order to achieve precision. This study proposes a new real-time aeroelastic hybrid simulation (RTAHS) approach that eliminates the potential drawbacks of the conventional spring-supported section model test. With this new approach, the aeroelastic force on the physical section model is directly measured using supporting load cells. The equation of motion is solved numerically, and linear electric motors impose the expected movement of the model in a real-time fashion. The hardware of the RTAHS consists of linear electric motors, motor drivers, sensors, and an Ethernet for Control Automation Technology (EtherCAT) based real-time motion controller. The hardware is controlled with three control loops, i.e., numerical integration, time-delay compensation, and PID control of the position. For this study, a series of comparative wind tunnel tests was used to demonstrate the validity of the proposed RTAHS concept.

In recent years, substantial efforts have been made to incorporate the nonlinear behavior of joints in frame analysis. In this regard, a well-established component-based model (CBM) is provided in EN 1993-1-8 to capture the nonlinear moment–rotation curve of steel beam-column joints. In this paper, to extend the design approach in EN 1993-1-8 to steel beam-to-reinforced concrete column (RCS) joints, a simple mechanical model is first developed to determine the moment resistance of RCS joints. The proposed model can predict two different failure modes of RCS joints and yields better accuracy and consistency compared to the current design method for such joints. After determining the joint moment resistance, an appropriate CBM is developed to simulate the nonlinear moment–rotation response of RCS joints. The proposed CBM can capture the moment–rotation behavior of RCS joints at elastic, transitional, and ultimate states. The initial rotational stiffness of RCS joints can be easily calculated based on the proposed CBM. This is particularly important in the frame analysis as the beam-column joint can be classified as a rigid, semirigid, or pinned joint based on the initial rotational stiffness. The derivations are discussed in detail, followed by verifications of the proposed CBM. Compared to the experimental results, the proposed CBM shows reasonable accuracy in predicting the moment–rotation behavior of RCS joints. Most importantly, the numerical procedure of the proposed CBM can be implemented by a spreadsheet method, which provides a simple and robust means for structural engineers to obtain the mechanical properties of RCS joints.

This paper presents shake table testing results of a scaled tower specimen equipped with a novel self-centering shear and moment dual-base mechanism system, termed the shear-controlling rocking isolation podium (SCRIP) system, for mitigating higher-mode effects in tall buildings. The scaled shake table specimen of the SCRIP system consists of a shear mechanism that controls base shear demands through the lateral response of a base podium supported by rocking columns below and friction braces in the periphery, in addition to a free-rocking mechanism above the base podium to limit the base overturning moment demands of the tower. Both mechanisms are designed to exhibit full self-centering capabilities. There were 220 shake table tests performed using two suites of ground motion (GM) excitations with increasing amplitudes from 50% to 150% in increments of 25%. The scaled SCRIP system was shown to reliably control both the peak base shear and overturning moment demands close to the design values even as the excitation amplitudes were increased. Seismic demands along the height of the tower above the SCRIP system were also well controlled. Negligible changes in the lateral resistance of the scaled SCRIP system were observed throughout the shaking table test program with no apparent damage or measured residual deformations. The bidirectional capability of the scaled SCRIP system was also experimentally demonstrated through GM excitations applied diagonally with respect to the system’s two principal horizontal directions. In addition, these results experimentally verified the concept of limiting both shear and overturning moment at the base of a slender structure to control the seismic demands and associated higher-mode effects along the height of the structure.

Abstract

The nonsymmetric sections commonly found in open-web steel joists present difficulties when evaluating eccentric loads applied to a single chord angle, which result in additional bending moments and torsion that are not typically considered in standard design practice. This study presents an experimental and computational approach towards qualifying the response of a steel joist with nonsymmetric sections and eccentric loading. An experiment was conducted in which a joist was subjected to uniform top-chord loading with an eccentric hanging load applied to one chord angle, while displacements and strains along the bottom chord were recorded. A second-order structural analysis with a novel beam-element formulation that considers nonsymmetric sections was able to accurately estimate the deflections and rotations of the joist bottom chord. Several alternative computational models were created to determine the effects of common design assumptions on the analysis output. It was found that model variations including using a first-order analysis, simplifying the hanging load condition, and using doubly-symmetric section behavior only resulted in changes to the applied torsion and corresponding rotations, which led to worse predictions of stresses and deflections on the chord angle. Detailed measurements of each cross-section geometry in the joist were obtained using a handheld three-dimensional laser scanner. Despite the significant changes in torsional cross-section properties, the computational model with measured cross-section properties resulted in minimal variations compared to the model with nominal section properties. The work presented herein provides insight into the torsional response of steel joists with eccentric loads.

Practical Applications

This paper demonstrates how a novel line element, which is available for use in MASTAN2, can account for nonsymmetric cross-section behavior resulting in a reasonable prediction of steel joists subjected to nonstandard loading, specifically eccentric loading to one bottom chord angle. The modeling approach was based on joist modeling recommendations from the Steel Joist Institute to align with existing design practices. The analysis results are shown to capture the movement of the overall joist as well as the twisting of the individual chord angle when eccentrically loaded. Therefore, the novel line element could be used to determine a conservative prediction for the maximum normal stress supported by a joist chord under torsion. Details are provided on how the stress values were determined as well as implications of modeling assumptions and analysis types through a series of alternative modeling and analysis approaches. These alternative analyses indicated that accurately defining the torsion on the cross-section is a key factor in properly distributing the supported moment between strong- and weak-axis bending. Future design provisions and recommendations will need to address the disconnect between the standard design assumption that angles have no warping stiffness and the fact that minimal warping stiffness causes significant theoretical local stress concentrations at connections and locations of applied loads.

A seismic retrofit method using external steel frames was studied for old RC buildings with nonseismic details. To verify the external retrofit method, 2-story frame specimens were tested under cyclic lateral loading. The test results indicated that the external steel frame successfully enhanced the stiffness and strength of deficient RC moment frames without deteriorating the deformation capacity. The energy-dissipation capacity was also improved by restraining early failure of the RC beam-column joints. The failure mode of the retrofitted frames was governed by the flexural mechanism of the first-story RC columns, with partial yielding of the upper structure. The RC columns were subjected to additional axial forces that were transferred from the external steel frame, in which the steel columns were not extended to the foundation. The strengths of retrofitted frames were evaluated by two approaches based on the frame plastic hinge mechanism: (1) the sum of the strengths of independent RC and steel moment frames, and (2) the strength assuming full composite section of concrete and steel members. On the basis of the test results, design considerations for the external steel frame-retrofitting method are recommended.

This study presents a new design of a wood–concrete connector that meets ductility and stiffness requirements in accordance with Eurocode 4. An analytical approach and a numerical model developed on Abaqus are proposed. The study is completed by experimental push-out tests and a specially made composite beam. Two types of timber concrete composite (TCC) are considered in this study. The first connector (stud connector), was applied in construction and its performance compared to that of a recently developed connector. The analytical calculation of stiffness was performed using the relevant standard. In addition, different connector configurations and spacing were tested in push-out and beam tests. The results showed that this new connector has interesting characteristics such as stiffness ($\mathrm{4,068.12}{\mathrm{kNm}}^2$) and maximum strength (24,70 kN) compared to existing connectors.

During an external detonation, blast-induced loads are initially exerted on the cladding system of a building. If properly designed, the dynamic reactions of the cladding to the supporting structure can be such that the consequences to the supporting structure are reduced, thereby avoiding extensive damage to the building frame. This behavior was examined in this study with a small-scale blast test on two specimens with different stiffness and strength characteristics. Specifically, two steel cladding types were tested, one comprising a solid plate and the other one a stiffened panel. The specimens of the two facade types were attached to girts of identical geometry, representing the supporting structure, and were exposed to the same blast load. Maximum and permanent displacements of the girts were measured as an index of the influence of the cladding types to the response of the supporting structure. Significantly lower displacements were exhibited in the girts of the solid plate in contrast to those of the stiffened panel, highlighting that the relatively lower flexure capacity of the solid plate compared with the flexure capacity of the stiffened panel was advantageous for the supporting structure. Furthermore, nonlinear transient finite-element analyses of the test were performed and compared well against the experimental data.

The 360° standing seam roof system (360° SSRS) often suffers structural damage or even failure under wind uplift pressure with varied strength ratings. Under the action of wind uplift pressure, the prediction of 360° SSRS damage degree plays an important role in the risk assessment and postdisaster measures for buildings. In this work, a wind-uplift fragility assessment method is proposed to forecast the damage degree of 360° SSRS, which considers the multistage performance levels in the whole wind-induced failure process of 360° SSRS. First, a refined finite-element (FE) model, including roof panels, sliding support, and purlin, is established to analyze the wind-induced failure process of 360° SSRS. Meanwhile, the existing experimental results are used to verify the correctness of the FE model. Second, according to the whole wind-induced failure process of 360° SSRS, the failure process is qualitatively classified into three-stage performance levels (i.e., PL I, PL II, and PL III) and four damage states (i.e., slight damage, moderate damage, severe damage, and tripping failure). On this basis, the damage indicator, which is the node relative displacement of the female buckle, is defined to quantitatively derive the three-stage performance levels. Thirdly, the Latin hypercube sampling (LHS) technology in conjunction with derived multistage performance levels is employed to carry out the wind-uplift fragility assessment, which can reflect the probabilistic characterization between wind uplift pressure and damage state of 360° SSRS. Finally, the proposed method is applied to a 360° SSRS of an ultrahigh-voltage (UHV) converter station in actual engineering, in which wind tunnel tests are used to determine extreme wind pressure coefficients of 360° SSRS. The results demonstrate that the proposed method is feasible and suitable, and the obtained fragility curves can be applied as a reference for predicting wind-induced damage degree, failure probability, and wind-resistance capacity of 360° SSRS.

Recent studies have investigated the seismic response of controlled rocking masonry walls (CRMWs) that rely on gravity loads for self-centering and on supplemental energy dissipation (ED) devices to control the response (ED-CRMWs). However, such studies reported that limitations still exist due to ED devices being installed inside the wall, making repairs difficult or impossible following the yielding or fracturing of such devices. For these reasons, the current study develops a new system, namely, controlled rocking masonry walls with energy dissipation accessible in a steel base (EASt-CRMWs). In this system, walls are constructed upon a steel rocking base to allow for the installation of ED devices within the footprint of the wall. In addition, these ED devices are in the form of externally mounted cantilevered steel flexural yielding arms that can be easily replaced following a seismic event. To investigate the seismic response of the new system, the study reports the experimental results of six EASt-CRMWs tested under displacement-controlled quasistatic cyclic fully reversed loading. Various design parameters are investigated herein, including axial load, aspect ratio, vertical reinforcement, confinement technique, and size of the flexural arms. The experimental results are presented in terms of the force-displacement responses, residual drift ratios, and damage patterns, including the use of digital image correlation techniques. Using such results, iterative and simplified procedures are developed and validated to predict the monotonic force-displacement responses of the test walls. The experimental results show that the use of a steel rocking base considerably enhanced the seismic response of the walls by protecting their rocking toes at large drift ratios. Specifically, extremely low damage was observed at the end of the tests, where five walls reached drift ratios up to 4.0% with no strength degradation and with residual drifts of less than 0.1%. The vertical reinforcement and confinement properties of the rocking toes had almost no influence on the cyclic response of the test walls; however, the axial load, aspect ratio, and amount of ED altered their responses. The two prediction procedures were also able to simulate the monotonic responses of the walls at all displacement ranges. With these results, the current study demonstrates that the proposed EASt-CRMWs are expected to be a resilient system within the masonry construction practice by achieving low damage and rapid recovery following seismic events.

Precast concrete (PC) and composite structures have been widely used in large industrial buildings for constructability and cost efficiency. The PC beams and composite columns are preferrable for use as long-span beams and large-sized columns, respectively, to realize efficient steel-concrete composite construction. The present study developed seismic details of the PC beam-to-composite column joint. A cyclic loading test was performed on the beam-column joints to investigate the seismic performance. For the test parameters, the connection details and the plastic hinge relocation were considered. The test results showed that the load-carrying capacity and deformation capacity of the specimens satisfied the requirements for intermediate moment frames specified in AISC 341-16. Further, the load-carrying capacities predicted using the plastic hinge relocation concept and the effective tension force of the bottom reinforcement at the PC beam section agreed with the test results.

A major disadvantage of the existing joint shear strength models is that they cannot consider the shear-resistance mechanisms and various uncertainties comprehensively. In order to overcome this limitation, a probabilistic shear strength model of reinforced concrete (RC) exterior beam-column joints was proposed. A simplified deterministic shear strength model for RC exterior beam-column joints was derived first by considering the contributions of the diagonal strut mechanism and truss mechanism. Then the probabilistic shear strength model for RC exterior beam-column joints was developed by taking into account both aleatory and epistemic uncertainties. Furthermore, the posterior distributions of probabilistic model parameters were updated by means of the Bayesian theory and the Markov chain Monte Carlo method. Finally, the proposed model was verified by comparison with 135 sets of experimental data and existing shear strength models. The results show that the proposed model has satisfactory prediction accuracy and low dispersion, which not only calibrates the influencing parameters on the prediction accuracy of the existing models, but also provides a probabilistic method to calibrate the confidence interval of the existing models.

Recent research studies have investigated the use of high-strength materials in nuclear power plant structures to enhance the constructability of their massive squat RC shear walls. For example, high-strength reinforcement bars can significantly reduce the required steel areas, thus minimizing material/fabrication costs, reducing rebar congestion, facilitating concrete consolidation/placement, and simplifying quality control checks. High-strength concrete can also limit cracks and deflections because of its enhanced mechanical properties, including the elastic modulus and compression/tension strength. Despite the advantages of high-strength materials, the dynamic response of their squat nuclear shear walls has not yet been fully investigated when different design parameters are adopted. To address this, the current study focuses on developing fragility functions for squat RC shear walls with high-strength materials to evaluate their seismic response compared with their counterparts with normal-strength materials; the economic benefits of both material walls were also assessed. In this respect, a numerical model was developed and then validated using previous experimental programs that have been conducted on RC shear walls with different aspect ratios, vertical/horizontal web reinforcement ratios, yield/ultimate strengths of reinforcement, concrete compressive strengths, and axial load levels. Following the model development and validation, incremental dynamic analyses using 44 far-field ground motion records were performed to develop fragility functions for nine squat RC shear walls with normal- and high-strength materials at different damage states. These damage states were characterized by several performance indicators following relevant guidelines. The current study identified wall damage states based on (1) yielding of reinforcement bars, concrete crushing, shear failure, and reinforcement buckling/fracturing; and (2) crack widths (i.e., 0.5, 1.5, and 3 mm) calculated using the modified compression field theory. Several wall design parameters, including material strength, reinforcement spacing and axial load level, were investigated to quantify their influence on the seismic fragility of such squat RC walls. Finally, the economic benefits of using high-strength materials in nuclear power plants were evaluated by presenting direct comparisons between the walls in terms of their total rebar weights and the corresponding total construction costs. The results showed that the use of high-strength concrete and high-strength reinforcement with large spacing between the rebars can lead to early cracking of their walls, thus having a higher probability of exceedance values to damage relative to walls designed with normal-strength materials. The results demonstrate also that enhancements in seismic fragility coupled with low total construction costs can be attained by walls with normal-strength concrete and high-strength reinforcement. The current study facilitates the adoption of RC shear walls with high-strength materials in nuclear construction practice.

There is increasing interest in using cross-laminated timber (CLT) in buildings because of its high strength and stiffness. In Japan, structural design guidelines for CLT buildings were established in 2016 and construction of mid-rise buildings is increasing. Wide-panel walls can exceed widths of 10 m and integrate cut-outs for window and door openings. However, under lateral loads, corner cracks at the openings have been the most prevalent failure mechanism. To investigate the initiation and propagation of corner cracks, a series of bendings are undertaken on L- and T-shape specimens extracted from the CLT panels. In addition, three-point bending and shear tests are also carried out on beam sections extracted from the CLT panels. Three types of brittle failure were observed: bending failure of the beam or column, and rolling shear failure.

Deep members can exist in different forms in concrete structures, such as coupling beams, short columns, pile caps, and corbels. Because they are typically prone to shear failure, accurate calculation of the shear behavior in these members is vital. The existing analysis procedures for deep members are either computationally expensive or limited to the calculation of shear strength for design purposes. There is a great need for reliable macromodeling analysis tools that can evaluate safety and performance of structures at the system level while considering the nonlinear shear behavior of deep members in detail. This paper presents a shear plastic hinge model developed based on the beam-arch action mechanism for nonlinear analysis of deep RC members. The contribution of web concrete and transverse reinforcement (i.e., beam action) to the shear response is considered based on the modified compression field theory, while the contribution of the inclined concrete compression chord (i.e., arch action) is taken into account using the compatibility condition for shear deformations. The model is capable of calculating the shear force and shear deformation at different stages of the response while considering important nonlinear material effects in RC and interactions between internal force components. Through a comprehensive verification and parametric study, it is demonstrated that the model is able to accurately compute the shear behavior in deep RC beams and columns with various design variables. Last, the effectiveness of the proposed model for system-level analysis of structures is evaluated by modeling a multistory RC shear wall with coupling beams. The analysis results show that shear deformations can have a great influence on the performance of the structure as a whole in addition to the behavior at the component level.

In Canada, southern Ontario is strongly affected by high-intensity thunderstorms, leading to catastrophic structural and economic losses. People in rural areas are more prone to those weather-related fatalities due to the lack of suitable storm shelters. This paper will build on previous research where three commonly used Bunkie shapes in Ontario, Canada, were tested experimentally at the Toronto Metropolitan University wind tunnel under boundary layer and downburst flows. This led to an aerodynamic database consisting of force and moment coefficients for the three shapes. In this paper, it is planned to couple the available aerodynamic database with the climate analysis in southern Ontario to quantify the actual forces and moments on low-rise Bunkie structures seen during normal wind and downburst flows. Subsequently, typical construction cross sections for low-rise wooden framed buildings were assumed, and the behavior of the Bunkie structures was assessed under both wind fields to evaluate their potential usage as storm shelters. This was achieved using finite-element modeling, and potential retrofitting solutions are suggested to stiffen the structures to resist high-intensity wind events.

Limited research exists on the deformation compatibility behavior of mass timber beam-to-column connections. Therefore, to investigate this behavior, large-scale experimental monotonic testing was performed on five different glue-laminated (glulam) beam-to-column connections. The purpose of this research was to create a better fundamental understanding of the deformation compatibility behavior of mass timber beam-to-column connections. Three connections were custom-designed connections, and two were pre-engineered connections. Specimens included the presence of cross-laminated timber (CLT) decking on the beam, as well as combined lateral and gravity loading. Monotonic tests pushed specimens to a target story drift of 7.2% at a rate of $0.51\mathrm{mm}/\mathrm{s}$. The data were analyzed, and the yield force, yield displacement, initial stiffness, secant stiffness, and connection classification (categorized as either rigid, semirigid, or flexible) were calculated for each connection. Per the connection classification methodology used, all connections were classified as flexible (simple) connections. However, the pre-engineered connections use substantially more screws and plates thereby increasing the cost and effort of installation. The results demonstrate that in some cases simple custom connections can have a larger yield force and initial stiffness than pre-engineered connections, and due to the reduction in number of screws, there was less damage within the connection at the completion of the test. The forces required to push connections to 2% drift all exceeded the lateral force capacity of the connections; however, all connections maintained load-carrying capacity throughout testing.

This study presents a novel type of self-centering energy-dissipative restrainers [i.e., SMA ring springs (SMARS) restrainer] incorporating shape memory alloy (SMA) ring springs as the core elements. Compared with conventional restraining solutions such as steel cables, the proposed device has unique advantages such as protective self-locking mechanism, large load resistance and energy dissipation, adjustable initial stiffness/yield strength, ease of installation, and no risk of anchorage premature failure. The study commences with a detailed introduction of the working mechanism of the SMARS restrainer, followed by a comprehensive experimental verification of the concept. Numerical studies are subsequently carried out to further interpret the test results and to reveal the influence of some important parameters. Stable flag-shaped hysteretic curves of both individual SMA ring spring and SMARS restrainer at room temperature were exhibited. An optional preload can be applied, leading to a yieldlike behavior. The preload could also promote large initial stiffness, better self-centering capability, and enhanced energy dissipation. The recovery rate (recovered-to-peak deformation ratio) and equivalent viscous damping ratio of the restrainer specimen with no preload were 90% and 3.6%–5.9%, respectively, and those of the specimen with preload increase to 98% and 5.7%–7.4%, respectively. The numerical study further confirms that the behavior of the SMARS restrainer is greatly affected by the friction condition and the preload applied to the SMA ring springs. Some preliminary design recommendations are subsequent provided. Potential practical applications, including isolation bearings, bridge restrainers, rocking columns/shear walls, and braces, are finally discussed.

Nonstructural damage to the cladding and façades systems caused by excessive wind pressure and debris impact is the primary damage to urban high/midrise buildings after hurricanes. This paper focuses on the assessment of damage to urban buildings envelopes due to windborne debris while leaving the wind pressure-induced damage outside the scope. The existing building envelope damage assessment models for urban high/mid-rise buildings often neglect the geometry of building clusters or simply assume a homogeneous configuration, which can introduce errors and uncertainties for urban building clusters with varying geometries and layouts. In this context, this paper proposes a new fragility modeling approach for urban buildings envelopes, which explicitly considers geometric configurations of urban buildings, to improve the accuracy of risk assessment for urban buildings. To develop such a fragility model, first, a physical model of debris impact on building envelopes is established, considering the configuration of the surrounding buildings. Then the fragility function is rigorously formulated by propagating the uncertainties from hurricane wind hazard, local urban wind field, the resistance of the envelope component, as well as debris size, location and generation. Reduced-order modeling and Monte Carlo simulation are employed to construct fragility surfaces. An illustrative example is presented to validate the proposed physical model of debris impact and demonstrate the implementation of the proposed fragility modeling approach.

The frequency domain decomposition method (FDD) is a commonly used method to identify structural modal parameters and analyze the structural dynamic performance. Although FDD has a high identification accuracy in natural frequencies and mode shapes, damping ratios cannot be identified accurately. The logarithmic decay method to identify the damping ratio in FDD needs the transformation from a narrow frequency band to the time domain, which leads to the loss of the corresponding mode outside the narrow band and add other modes in the narrow band. In this paper, an iterative frequency domain decomposition method (iFDD) is proposed to identify the structural damping ratio in frequency domain. Firstly, the natural frequencies and mode shapes are obtained by the FDD method, and the damping ratios during this identification process are assumed to be unknowns. Then, the natural frequencies, mode shapes, and unknowns are substituted into the output power spectrum formula to construct nonlinear equations. The damping ratios are obtained by solving the equations using iterative optimization methods. Finally, a numerical example and benchmark model are employed to validate the effectiveness of the proposed method. The results showed that the proposed iFDD method can identify the damping ratio precisely in the frequency domain, which is better than the traditional FDD performance.

This paper investigates the feasibility of employing timber pegged joints in modern seismic-resistant structures or for retrofitting existing structures. The behavior of timber pegged connections has been investigated for about twenty years, but seismic design aspects are not treated in existing standards. In the framework of the force-based design approach, this paper analyzes and defines seismic design aspects and rules for timber pegged connections that are easy-to-use in engineering practice. A large database (more than 350 test results) has been elaborated and the data processed with the purpose of (1) analyzing the effectiveness of the European Yield Model for evaluating the maximum strength of the connection, accounting for the particular embedding behavior due to the presence of timber peg; (2) assessing and defining the capacity design rules to design the dissipative regions (i.e., overstrength factor); and (3) defining the available ductility of the connection with identification of ductility class intervals. The obtained results proved that timber pegged joints have a good potential to be used in seismic-resistant structures. In fact, data processing identified a suitable value for the overstrength factor (useful to project the joint with the capacity design) similar to that used for steel-dowelled connections, and defined a likelihood range of ductility classes. Finally, it is highlighted that the European Yield Model can be a practical tool to calculate connection strength, provided that some modifications are included to consider peg behavior.

The ASCE 7-16 standard and its previous editions specify wind speeds for structural design that increase monotonically above the Earth’s surface up to heights between 200 and 400 m, above which they are considered constant. This model was proposed in the 1960s and based on research completed up to that time. Subsequent research has shown that the model is inadequate and may result in the significant underestimation of wind loads in the higher elevations of supertall and megatall structures. For this reason, a new model for the vertical variation of wind speeds and associated velocity pressure exposure coefficients, $K_z$, was developed for inclusion in the ASCE 7-22 standard. The purpose of this paper is to present and explain the logic of the new model based on physics-based meteorological research.

Collapse in steel structures is often controlled by loss of load carrying capacity of steel columns due to interactive buckling, which involves interactions between local and global (i.e., lateral and lateral torsional) buckling. Commonly used concentrated plastic hinge or fiber-based elements do not simulate the physics of this response, potentially leading to inaccuracy in performance assessment. A nonlinear fiber-beam-column element [termed the Torsion Fiber Element (TFE)] to simulate monotonic interactive buckling in steel beam-columns is presented. The element, implemented in the OpenSees platform, incorporates St. Venant as well as warping torsion through enrichment of strain interpolation functions, in addition to axial and flexural deformation modes. Local buckling is represented through a softening multiaxial constitutive relationship. The efficacy of this approach is examined by comparing its results against those obtained from continuum finite element simulations as well as experimental data on beam-columns subjected to monotonic loading. The comparisons indicate that the element can functionally represent the physics underlying interactive buckling, resulting in effective prediction of the overall monotonic load-deformation response, as well as internal deformation and stress fields. Limitations of the element in its current form are summarized, along with prospective improvements.

New building code changes enable mass timber panels (MTP), including cross-laminated timber (CLT), to be used in moderate and tall buildings as a floor system, usually with a concrete topping. A floor system of CLT composite with a reinforced concrete topping slab can provide increased stiffness and strength, making the system more advantageous. Present connection methods used to produce composite action within timber-concrete composites (TCC) have limitations when considering constructability or performance. This study presents experimental results from four (4) shear connectors for CLT-concrete composite floor systems, including three developed for this study. The connectors included self-tapping screws (STS) at 45-degrees, a modified lag screw with an integral plate washer that bears on the CLT surface at installation, a steel angle anchored only at the end of the span, and an inverted-T steel section with stem perforations. Different tests were performed on the different connectors including individual fastener tests, push-off group tests, and full-scale one-way bending tests. The push-off group tests showed that the proposed washer-screw exhibited higher stiffness and strength than a conventional STS. The full-scale one-way bending testing showed that the STS specimen exhibited the lowest strength of the alternatives. The inverted-T section exhibited the highest stiffness, while the other three connections had similar stiffness to the STS.

An innovative self-centering modular steel structure (SC-MSS) connection is proposed in this research, which adopts a plug-in integration technology to permit efficient construction and reliable structural continuity, introduces diagonal self-centering (SC) haunch braces installed near the connection core serving as a pleasing approach to achieve seismic improvement, safety, and recoverability purposes. In order to evaluate the seismic performance of the SC-MSS connection system, quasi-static cyclic loading tests were conducted on two SC haunch braces and three SC-MSS connections with different braces. Representative test phenomena and failure modes of the specimens were recorded during the tests, the discussion and the comparison of the primary seismic behavior indicators of the three specimens, including hysteretic responses, energy dissipation, residual deformation, and strain features, were provided. The results demonstrate that the SC haunch braces present sufficient mechanical stability and excellent self-centering behavior as expected, and all the SC-MSS connections show satisfactory development potential of bearing capacity, stable energy dissipation, and self-centering capacity. The prepressed force and post-activation stiffness of the haunch brace can impact the strength, deformation behavior, and plastic development of the connection to varying degrees. As for the resistance of tenons in the connector and the control effect of the haunch braces, they can protect the key areas of the connection by concentrating the main damage on the beam. Moreover, the SC haunch braces are able to maintain a coordinated deformation with the modules, and they can continuously provide reliable and effective restoring forces for minimizing the residual deformation of the system.

In this paper, the ultimate shear capacity of the 3-bolt cold-formed steel clip-angle between the cold-formed steel (CFS) beam and column is evaluated through 54 laboratory tests. A series of experiments were conducted by varying (1) thickness, and (2) aspect ratio ($L/D$) of clip-angles for different depths ($D$) and widths ($A$). The experimental program consists of three phases of tests: (1) Phase-I: direct shear load tests on clip-angle attached to a CFS column through 4.6-grade bolts; (2) Phase-II: CFS column replaced with a hot-rolled steel (HRS) column, since the CFS column experienced bearing failure in Phase-I; and (3) Phase-III: 10.9-grade bolts used instead of 4.6, as the 4.6-grade bolts subjected to bolt shear failure in Phase-II. Failure modes observed in the test specimens are (1) shear local buckling of clip-angle; (2) column bearing failure; (3) bolt shear failure; and (4) tear failure in clip-angle. Design shear equations from the literature, for the bolted clip-angle, were found to be inefficient for the high-grade steel ($f_y=375\mathrm{MPa}$ to 550 MPa), and conservative for the commonly available low-grade steel ($f_y=275\mathrm{MPa}$). Hence a new shear strength equation is suggested for the clip-angle from the collated data of the present study and past research work. A comparative study between 2-bolt and 3-bolt clip-angle configurations was conducted to evaluate the increase in shear strength. Reliability studies were conducted, and corresponding resistance and safety factors were suggested for the design shear strength calculation corresponding to load and resistance factor design (LRFD), limit state design (LSD), and allowable strength design (ASD) methods.

Experimental data is imperative to characterize the behavior of materials used in structural analysis models. The aim of this data paper is to establish a database of material-scale uniaxial experiments, primarily conducted at EPFL, to assist with simulating the monotonic and cyclic behavior of structural steel materials and components. The proposed database consists of stress-strain data from test specimens subjected to tensile straining or to one of nine cyclic load protocols consistent with earthquake loading. The database includes 353 experiments on test specimens fabricated from 11 steel materials from around the world and an iron-based shape memory alloy; the database will evolve as additional tests are conducted. A downsampling method is developed that ensures a difference in strain energy of less than 0.5% between the original and downsampled data while reducing the number of datapoints by 89 times, on average. Results for S355 steels, constituting 57% of the database, are quantitatively validated by comparing the average measured initial yield stress and elastic modulus with prior work. The initial yield stress for S355 steels is found to be between 305 and 430 MPa and the elastic modulus between 190 and 230 GPa; these results are consistent with prior values. Finally, examples illustrate how the database can be used to calibrate constitutive models used in nonlinear finite element analysis.

The random decrement method (RDM) is often used in the experimental modal identification of existing structures. The aim of this study was to improve the applicability of RDM in the identification of multimodal structural damping, taking into account the reduced quality of the random decrement (RD) signature. This goal was achieved by introducing a new approach (Approach 2) to the classic RDM procedure based on linear regression fitting of the extreme values of the RD signature within its limited range in which the stability of this signature is not less than an acceptable threshold level. To quantify the quality of the RD signature, the concept of a stability ratio of the RD signature is introduced. In a case study analyzed in this paper, it was determined that the required value of the stability ratio is at least 92%. The effectiveness of Approach 2 was compared with the classic approach, Approach 1, based on the least-squares curve fitting technique. For this purpose, experimental modal identification of a 292-m steel cable-stayed bridge excited by daily traffic flow was carried out. The results showed improved accuracy of modal damping estimation using Approach 2 for all 11 identified bridge modes, from approximately 1% to 26%, depending on the mode number. To ensure the effectiveness of the RDM analysis, it was recommended to set the parameters of the filtration process, the number of time segments included in the RD signature averaging process, and the triggering level of these time segments. The present study can be applied to the performance of similar modal analyses of complex engineering structures, the response of which is represented by multimode vibrations.

Long-cantilever transmission towers are drawing more and more attention in ultrahigh-voltage (UHV) transmission projects. To meet the requirements of high-voltage safety clearance, the structural characteristics of long-cantilever transmission towers are significantly different from traditional ones. Aiming to ensure the safety of long-cantilever transmission towers during service, this paper investigates their static and dynamic characteristics under various extreme loading conditions based on full-scale tests and numerical simulation. With the strain data tested in seven typical cases, the bending moments and axial forces of the main members were back-calculated and the initial imperfections were calculated based on these results. Using a stochastic subspace identification algorithm, the evolution of the modal parameters during the full-scale test was revealed. The damage position of the main members was identified according to the mode shape changes, and the dynamic collapse process was analyzed via the measured dynamic responses and recorded videos. Numerical simulation was conducted in ANSYS using the calculated initial imperfections, and the results were in good agreement with the full-scale test. The results show that torsion action was not dominant for this tower and the failure mode was still the bending failure at the tower body. The proposed imperfection quantification method makes up for the deficiency of the empirical values, and using experimental results to guide numerical simulation proves practical. The modal parameters vary greatly under different loading conditions, which can be attributed to the damage after each loading case.