Journal of Structural Engineering

Mass timber panel (MTP)-concrete composite floors are gaining increasing interest from builders and designers due to their optimized structural performance, light self-weight, and aesthetically exposed wood ceilings. Among various connecting techniques between timber and concrete, notched connections made by cutting grooves on timber and filling them with concrete are considered as one of the most structurally efficient and cost-saving connecting solutions. Numerous ways of making and reinforcing the notched connections, however, hinder the standardization and development of the design guidelines for this type of connection, which reduces the competitiveness of MTP-concrete composite floors. In this study, experiments were carried out to investigate the performance of MTP-concrete composite floors with different connection designs. Nine composite floor specimens with varying span, connection number, notch depth, concrete thickness, and loading direction were designed and tested under bending. The bending stiffness, load-carrying capacity, ductility, and failure mode of tested specimens were studied and discussed. Test results show that the connection number, notch depth, and concrete thickness affect the bending stiffness and strength of the floor positively, an increase in floor span impacts the floor performance negatively, whereas the effect of a limited number of self-tapping screws in the notch is negligible. The study also shows that MTP-concrete composite floors with high strength, high stiffness, and good ductility can be achieved through the optimized design of notched connections.

The punching shear failure of reinforced concrete flat plates has puzzled researchers for a long time due to the complexity of the punching shear mechanism and the difficulty of direct measurements of the internal failure mechanism. Measurements from previous punching shear tests cannot provide sufficient experimental evidence for revealing the failure mechanism. In this study, an industrial endoscope and specially designed strain measuring rods were installed inside small holes reserved in slabs around columns to track the occurrence and propagation of internal cracks of five isolated slab-column connections with different longitudinal reinforcement arrangements. The results indicated that critical shear cracks developed from internal diagonal cracks initiated at midheight of the slabs and unevenly distributed around the columns. The propagation of the internal diagonal cracks was independent of flexural cracks initiated at the slab tension faces but closely related to the unloading of radial strains of concrete at the slab compression faces. At the moment of punching failure, the critical shear cracks propagated from compression to tension zones, forming a punching failure cone. Moreover, the failure process was progressive, that is, the continuous weakening of the compression zone by the critical shear crack resulted in the shear splitting of the compression zone, which triggered the final failure of the connections. The experimental evidence obtained can provide a physical background and new ideas for modeling the punching shear mechanism of slab-column connections.

The friction behavior of mortar–polymer–steel debonding interfaces was experimentally investigated to support numerical simulation of buckling-restrained braces (BRBs). Characteristic contact and slip demands were developed using two-dimensional Abaqus models to inform a full-scale test program. A stabilized dynamic friction coefficient of 0.065 was observed for reciprocating two-way sliding at the reference bearing pressure (20 MPa), slip amplitude ($\pm 20\mathrm{mm}$), and velocity ($30\mathrm{mm}/\mathrm{s}$) but increased to 0.16 at low bearing pressures and reduced to 0.03 for quasi-static loading. A recurring 40% dynamic amplification was observed in each one-way sliding cycle, where contact was only applied in one direction of the reciprocating motion, replicating the actual condition of BRB wavecrests. A system wear effect was also observed where small patches of mortar were exposed and then resurfaced, increasing the smeared friction coefficient by up to 0.15. Finally, the compressible debonding gap closely matched the polymer thickness, excluding textile backing, if present. A nonlinear friction model dependent on pressure–velocity–distance was developed, and recommendations were made to improve common testing provisions.

Transportation industries have commonly used welded connections in the production of dynamic message signs (DMSs) for several years. Even though with numerous alternatives such as bolt/rivet connections, the majority of the clients prefer welded connections in DMSs. However, the structural behavior of DMSs with welded connections has not been rigorously examined through computational analysis to date. Therefore, this study was conducted with the aim of computationally investigating the ultimate strength of DMS with welded connections. To achieve this aim, a finite element (FE) model was generated to examine the ultimate strength of the welded DMS tested. The FE model created in ABAQUS software was validated utilizing the testing data and observed an error of 3.33% only for the ultimate strength. Design parameters of the validated FE model such as weld length and damage adjustment factors like tensile yield strength and shear yield strength of filler weld were tuned to identify their influence on the ultimate strength of welded DMS via multiple parametric simulations. The damage adjustment factors were found to be the most influential parameters affecting the ultimate strength of the welded DMS. The parametric simulation studies further revealed that the performance of welded DMS was able to be optimized to improve the ultimate strength of DMS up to 29.95% compared to that of tested DMS. A design equation generated in a statistical manner was also proposed incorporating the most influential parameters to predict the ultimate strength of welded DMS. The design equation showed an average error of 10.46% for the prediction of ultimate strength of welded DMS in comparison to the results of tested DMS.

A warping-inclusive kinematic coupling method to be used in finite-element analysis of members featuring wide-flange cross sections is proposed in this paper. This coupling method is used in mixed-dimension macromodels that combine continuum and beam-column elements to reduce the computational cost of purely continuum finite-element models. The proposed coupling method, utilizing either linear or nonlinear constraint equations, is implemented and validated in a commercial finite-element software; the source code is made publicly available. Case studies indicate that including warping in the coupling formulation is critical for components that may experience coupled local and lateral-torsional buckling. Also highlighted is the potential of macromodels to reduce the total degrees of freedom by up-to about 60%, and computational memory use by up to around 80%, while retaining solution fidelity for beam, column, and panel zone components in steel moment-resting frames. The case studies show that the linear constraint equation formulation may not be suitable for all problems; however, it may still yield acceptable results as long as the level of twisting is insignificant and lateral-torsional buckling is not critical.

Flexible civil structures are prone to aerodynamic instabilities, such as long-span bridges and high-rise buildings, and wind-induced vibration is harmful to structural life-span and users’ comfort. To address this issue, this study proposes a new aerodynamic countermeasure that is designed to improve the structural aerodynamic performance, i.e., adding a strip seam cover device (SSCD) on the surface of a structure, and the influence of the device on the aerostatic performance of the main structure is presented. Taking the box girder of long-span bridges, for example, the effectiveness and influence factors of the proposed device are investigated in detail. First, the proposed device is introduced and three aerostatic force coefficients are selected as the evaluation indices for the SSCD’s effectiveness. Second, the typical streamlined box-girder sectional model of bridges with and without the additional device is compared respectively based on the two-dimensional (2D) computational fluid dynamics (CFD) simulation technique. Results show the bridge girder’s pitch moment coefficients can be decreased efficiently. In addition, influences of gap distance (i.e., 30 cm, 60 cm, 90 cm, and 120 cm) between the device and the bridge girder, effective width (i.e., 50 cm, 60 cm, 90 cm, and 180 cm), and void ratio (i.e., $1:5$, $1:3$, $1:2$, $1:1$, $2:1$, and $5:1$) of seams are investigated based on wind tunnel tests. Results of the same cases based on the experiment and CFD simulation are very close, showing the accuracy of the simulation and experiment. Experimental results show that the gap distance is recommended to be 60 to 90 cm, the effective width is 90 cm, and the void ratio is recommended to be a value larger than $1:1$. In this case, the pitch moment value and the slope of the curve for the pitch moment coefficient versus wind attack angle are efficiently reduced, which is beneficial for improving the critical wind speed of aerostatic torsional divergence and aerostatic stability. The proposed device can be used to improve the aerostatic and aerodynamic performances of buildings, bridges, and some other structures; moreover, its potential application in the control of vortex-induced vibration is found preliminarily, which will be reported in further study.

Cast steel energy dissipative components are increasingly being incorporated in structural systems in recent years. Cast steel yielding connectors (YC) demonstrate a stable symmetric hysteretic response with increased postyield stiffness at large deformations due to second-order geometric effects. In the present study, the seismic performance of a four-story steel structure equipped with cast steel YCs is investigated through pseudodynamic hybrid simulations using the University of Toronto 10-Element Hybrid Simulation Platform (UT10), where the structure is subjected to three maximum considered event (MCE)-level earthquakes. Four YCs in the seismic force–resisting system are represented physically, whereas the rest of the structure is modeled numerically. These experiments are performed as part of an initiative to produce a database of high-fidelity system-level benchmark test results and to critically study and improve existing numerical models, their calibration, and the loading protocols used in their calibrations. The experimental results can be used to study these aspects in the numerical models for YCs or systems with similar hysteretic characteristics. The hybrid simulations are followed by cyclic tests on two of the YCs to evaluate the remaining low-cycle fatigue life of the YCs and to provide information on the cumulative plastic ductility capacity of YCs.

This paper presents an analytical approach to predicting the shear strength of exterior beam-column joints without transverse reinforcement using a strut-and-tie model (STM). The proposed model contains a single diagonal strut with varied angle and width for modeling the shear behavior. Modeling analyses involve three approaches to determine the width and angle of the diagonal strut for the best prediction of experimental shear strength values. An experimental database of 25 exterior beam-column joints without transverse reinforcement and without confining out-of-plane members was developed to verify the accuracy of the model predictions. The presented analyses reveal that existing models may overestimate the shear strength of referenced joints and, therefore, highlight the need for a better fitting model. The discussions include a comparison of predicted joint shear strength values with existing experimental results using three different formulations. Moreover, the discussions examine existing code requirements and the reliability of the presented STM in comparison with code regulations. Concluding remarks supported by statistical measures highlight the fitness of the STM to safely predict the shear strength and identify the optimum approach to determining the model geometry.

This paper analyzes the influence of horizontal damped and undamped restraints in terms of the amplification of the response of rocking masonry walls subjected to seismic excitations. It also makes a practical contribution to the design of antiseismic devices conceived to control rocking motion, avoiding or at least limiting undesirable response amplifications that would lead to local or global failure. A horizontal restraint, simulating an elastoplastic steel tie-rod, was coupled with a damper, whose action is included in a proposed equation of motion. Parametric analyses were performed for three typical façades of masonry buildings, showing that, if the stiffness of tie-rod increases, the seismic vulnerability of a rocking façade is not necessarily reduced. Therefore, the calculation of rocking spectra is recommended in order to identify stiffness ranges in which amplification could occur. A simple method for calculating the design damping coefficient of a shock absorber is proposed and the consequent mitigation of vulnerability is demonstrated in various analysis configurations. Graphs plotting time-dependent ratios between the energy dissipated by the shock absorber and the seismic input energy are shown to be a useful tool for quantifying the effectiveness of the shock absorber itself in dissipating energy. The reduction of these time-dependent ratios occasionally observed for specific earthquake time ranges reveals that adverse frequencies are occasionally present in seismic excitation and allows for the identification of the optimal damping coefficient.

Current tall building design to ultimate wind loads is based on a linear elastic design framework. The adoption of a performance-based wind design framework for tall buildings explicitly requires evaluation of building performance under various levels of wind hazards, including inelastic response. This study presents a comprehensive characterization of inelastic response of tall buildings under simultaneous actions of both alongwind and crosswind loads using a fiber-based three-dimensional (3D) nonlinear finite-element (FE) model of a 60-story high-rise steel building. The statistics of inelastic responses in terms of building displacement, acceleration, interstory drift, and base bending moment and member forces are quantified through response history analysis at different wind speeds. The inelastic building responses under alongwind and crosswind loads acting separately are also calculated and compared. The inelastic response is also compared to the elastic response of the corresponding linear building model. The yielding causes building drift in the alongwind direction that leads to increasing time-varying mean displacement. The development of drift is affected by fluctuating alongwind and crosswind responses. The steady-state value of drift is determined by the mean load and second stiffness in the alongwind direction. On the other hand, the fluctuating alongwind and crosswind responses can be quantified regardless of the mean load and time-varying mean response. The yielding leads to a reduction of fluctuating responses due to additional hysteretic damping. The second-order P-Delta effect on both elastic and inelastic responses is also examined. Finally, the influence of material yield stress is investigated, and the inelastic response is discussed in nondimensional quantities. The results of this study reveal the importance of consideration of simultaneous actions of both alongwind and crosswind loads for inelastic response analysis. The inelastic crosswind response affects the alongwind inelastic response. It particularly results in increased time-varying mean alongwind displacement, which contributes to building collapse when the second-order P-Delta effect is considered.

Buckling-restrained brace frames (BRBFs) have been a popular seismic force-resisting system in the US since it was first introduced to the AISC Seismic Provisions and ASCE 7 in 2005. The steel core of a buckling-restrained brace (BRB) yields in tension and buckles plastically in a high-mode buckling pattern in compression under cyclic loading. Prequalification testing of BRBs in conformance with the AISC 341 requirements relies on a highly idealized loading protocol that is not representative of the expected response during an earthquake. Although testing has demonstrated that BRBs have excellent energy dissipation capacity, a low-cycle fatigue model will permit designers to evaluate the remaining life of BRBs after a seismic event. To develop and validate such model, 18 full-scale BRBs in groups of three different yielding strengths (1,110; 2,220; and 3,330 kN) were cyclically tested to fracture with the following loading conditions: (1) symmetric cycles with constant strain amplitudes ($\pm 0.25\%$ to $\pm 3\%$), (2) asymmetric cycles with constant strain amplitudes and non-zero-mean strains, (3) symmetric cycles with variable strain amplitudes, and (4) simulated earthquake responses. Two low-cycle fatigue models for BRBs (a standard model and an alternative model for ease of practical use) were developed based on 11 symmetric, constant-amplitude tests. An assessment procedure combining the proposed fatigue models, rainflow cycle counting method, and Miner’s damage index was proposed to predict the fatigue life of BRBs subjected to random cyclic loading histories, the accuracy of which was verified by the variable-amplitude test results.

Ultra high performance fiber reinforced cementitious composites (UHPFRCs) have demonstrated their outstanding efficiency as structural materials. Determination of the bending resistance of members combining UHPFRC with steel reinforcement bars (R-UHPFRC) using material properties obtained by material testing gives satisfactory results. However, the synergetic interaction between rebar and UHPFRC in the tensile action due to bending, especially under loading–unloading of the structure is not yet well understood. This paper compared methods of analytical inverse analyses, as well as finite-element modeling and nondestructive testing (NDT), for determining UHPFRC material properties based on plates and R-UHPFRC members’ test results. It was demonstrated that UHPFRC in the tensile zone of R-UHPFRC members can enter into compression during unloading, influencing the structural response under service loading.

The primary objective of this work is to provide connection-level force-deformation response appropriate for standard cold-formed steel (CFS) framed steel sheet sheathed shear walls under cyclic loads. Common CFS framing designs increasingly are exploring thicker framing options so that walls can meet gravity demands, overturning demands, and seismic overstrength requirements. For the seismic performance of self-drilling screw-fastened steel sheet sheathed shear walls, the cyclic nonlinear response of the screw-fastened connection is particularly important and should incorporate the impact of shear buckling of the steel sheet on the strength and ductility of the connection. Minimal cyclic connection-level shear test data exist, especially for combinations of screw-fastened thin steel sheet and thick framing steel. A unique lap shear test following current test standards was proposed to elucidate and characterize the cyclic screw-fastened connection behavior. An asymmetric cyclic loading protocol was selected with a small displacement applied in the direction that buckles the thin steel sheet, followed by progressively larger displacements in the opposite direction. A total of 93 tests were conducted, and characterization of the observed cyclic connection response with a multilinear backbone curve appropriate for use in models is provided. Connection strength is sensitive to whether the thin steel sheet ply is buckling away from or toward the fastener head in some test series. Performance of the screw shear strength as per the standard’s provisions is evaluated. The work is intended to provide critical missing information for CFS framed steel sheet sheathed shear walls for use in both simulation and design.

A slab-column joint in a flat plate structure may exhibit upward or downward punching shear (UPS and DPS) failure when subjected to different abnormal loading conditions. This can cause distinct residual deformations of the slabs, which in turn influences the behavior of the consequent progressive collapse of the entire structure. This paper presents two experimental tests on two $2\times 2\text{-}\mathrm{bay}$, $1/3\text{-}\mathrm{scaled}$ flat plate substructure specimens. Both tests were conducted in two loading phases. In the first loading phase (LP-1), the interior column of specimens UPS-Sub and DPS-Sub was subjected to a gradually increased upward and downward concentrated load, respectively, until punching failure occurred at the interior slab–column joint. In the second loading phase (LP-2), an incremented downward uniformly distributed load was applied on the slab of both specimens up until the ultimate state just before a complete collapse of the slab. After LP-1, local and global damage patterns were observed respectively from UPS-Sub and DPS-Sub. The punching shear strength and the corresponding displacement of the interior joint in UPS-Sub were found to be 58.2% higher and 53.6% lower, respectively, than the corresponding ones in DPS-Sub. In LP-2, due to the upward residual deformation of the slab in UPS-Sub as a result of LP-1, its first peak load, vertical displacement, and horizontal displacement under compressive membrane action were, respectively, 8.4%, 91.1%, and 57.1% larger than those in DPS-Sub. On the other hand, the postpunching peak load of the two specimens under tensile membrane action were identical. To offer an in-depth understanding of the mechanical behavior that resulted from upward or download punching shear failure, the punching shear strengths of the interior slab–column joints and collapse resistance of the substructures were also analytically investigated.

This study estimated the wind gust factor and turbulence intensity for hurricane winds that are modeled as a nonstationary non-Gaussian process. The estimation considered the time-varying mean wind velocity, and the time–frequency decomposition using S-transform characterized the time-varying amplitude and frequency content of the fluctuating wind. Winds simulated by applying a newly developed algorithm were used to augment the sample size. Results indicate that the standardized power spectral density function of hurricane winds can be represented in terms of the reduced frequency but with time-varying mean wind velocity. The standardized fluctuating wind is only weakly non-Gaussian; the average skewness and kurtosis coefficients are not very sensitive to whether the 10-or 60-min time-varying mean wind speed is considered. The assessed relation between the gust factor and turbulence intensity indicates that such a relationship is influenced by whether the instantaneous aspect of the nonstationary process is considered. There is large uncertainty in the developed relationship. By removing samples associated with a low mean wind velocity, the largest value of the estimated gust factor decreases. The consideration of the non-Gaussian aspect of the fluctuating wind to estimate the gust factor could be important as turbulence intensity increases.

The paper presents a methodology for enumerating the dynamic response of one-way reinforced concrete (RC) structural elements subjected to combined blast and fragment loading, a scenario commonly associated with the detonation of cased explosive charges. The proposed methodology is motivated by the relatively few studies published in this area and the simplified design procedures that are currently used for addressing this problem. The formulated framework, in addition to the consideration of the blast and the fragment loading, also accounts for the damage incurred by the member due to the localized penetration caused by the impacting fragments. The fragment-induced damage is accounted for by considering a member having a reduced cross-sectional depth, i.e., a damaged member. Material nonlinearity and the strain rate–sensitive aspects of both concrete and steel are also considered. The dynamic structural response of the member was quantified by idealizing the member as an equivalent single-degree-of-freedom system. Finite-element (FE) simulations were conducted by the authors for assessing the efficacy of the adopted formulations. On the basis of the comparative assessment, the results of the FE simulations were found to match relatively well with the results of the proposed approach (relative difference being in the range of $8.95\%–12.67\%$). Additionally, the peak displacements for the cased explosive charges were noted to increase by approximately $31\%–123\%$ compared to bare (uncased) explosive charges of similar charge weights. While this observation underlines the severity of cased explosive charges, it also qualitatively highlights the damaging propensity of the striking fragments, a component that generally is not exclusively considered for design purposes.

An experimental investigation of 12 screw-fastened back-to-back built-up aluminum alloy slender columns under axial compression is presented, complemented by a numerical finite element study comprising 246 results. Using a laser scanner, the geometric imperfections were measured. In the numerical study, the effect of the modified slenderness, number of screws, and section thickness were investigated. Axial strengths obtained from the tests and finite element (FE) were used to assess guidance given in the Aluminum Design Manual (ADM 2020), Eurocode9 (CEN 2007), Australian/New Zealand Standards (AS/NZS 2018), and American Iron and Steel Institute (AISI 2016) standards. The ADM 2020 and CEN 2007 were found to be conservative by 30%. However, AISI 2016 and AS/NZS 2018 were found to be more accurate relative to the test and FE analysis results and shown to be conservative by 5%.

The progressive collapse of the World Trade Center showed the devastating consequences of pancake-type collapses, triggering significant research on failed-floor impacts for different forms of construction. In current high-rise construction, concrete flat slabs supported on columns are used widely, and, in this case, the fall of the slab could be prevented depending on the detailing and the horizontal propagation of the collapse from one support to adjacent supports. The activation and interaction of different phenomena during horizontal propagation governed by the slab–column response was investigated in this study for cases of flat slabs with and without integrity reinforcement. This paper focuses on slabs without punching reinforcement which are more critical. A slab system analytical model is presented based on a column removal scenario considering the dynamic response of the column–slab connections before and after punching including membrane effects. The model was verified using finite-element models with solid elements at the connections. The results highlighted the key role of integrity reinforcement in preventing slabs from falling by means of activating tensile membrane action concentrated around the columns.

Concrete-filled double-skin tubular (CFDST) columns have high fire resistance, and are widely used in the construction of electrical towers and bridges. However, previous research showed that the buckling of steel tubes can be significant in noncircular CFDST for nonuniform confinement or a large width-to-thickness ratio. The authors proposed a novel stiffened thin-walled CFDST column with steel strips welded on both inner tube and outer tube to form several closed cavities to fully utilize material strength. This paper presents an experimental study on the axial compressive behavior of this new type of stiffened thin-walled CFDST column; tests were conducted on six thin-walled CFDST columns and two steel tubes. The test results confirm that the stiffened CFDST columns have higher strength and better deformation capacity than the control columns. Moreover, the finite element (FE) model was developed to simulate the interaction between steel tubes and concrete. The average error of the FE analysis when predicting the column bearing capacity was 1.3% compared with experimental results. Finally, a strength design formula was proposed to predict the compressive strength of the stiffened thin-walled square CFDST column, which is recommended for design purposes.

In this paper, a total of 254 results comprising 30 shear tests and 224 finite element (FE) analysis results are reported. Simply supported test specimens of cold-formed steel (CFS) channels with aspect ratios of 1.0 and 1.5 were tested. For comparison, specimens with unstiffened web holes and plain webs were also tested. A nonlinear elastoplastic FE model was then developed and validated against the experimental results. Using the validated FE model, a parametric study was conducted to investigate the effect of various influential parameters on the shear capacity of such CFS channels. The test results show that for a channel with edge-stiffened web holes, the shear capacity increased by 14.5% on average when compared with that of a channel with unstiffened web holes. The test and FE results were compared against the design predictions. Upon comparison, it was found that the design rules of CFS channels with unstiffened web holes in accordance with the AISI and AS/NZS can be unconservative by 7% while calculating the shear capacity of CFS channels with edge-stiffened web holes. Therefore, a suitable design formula in the form of a shear capacity reduction factor was proposed for CFS channels with edge-stiffened web holes.

This paper presents experimental investigations on the thermal response and structural behavior of a full-scale, 2-story, steel-framed building exposed to traveling fire. In this test protocol, the fuel bed consisted of $6.6\text{-}{\mathrm{m}}^3$ pine cribs and then ignited from one end. Thermal and structural responses of the steel-framed building were measured throughout the fire, from which unsteady spreading and burnout rates of the fire could be obtained. Multiple temperature peaks and drastic temperature gradients were observed as flames spread across the compartment, which, led the structural members to become successively displaced due to the short period of thermal action at peak temperature in one location. Fracturing of connecting bolts was observed, indicating these connections should be further strengthened in practical design. As a main failure mode, local deformation of the beam lower flange and web adjacent to beam-to-column joints was also found. The test results invalidated the homogeneous temperature assumption and provided important data for performance-based structural fire design in such large compartment fire scenarios.

The new ASCE 7-16 Chapter 6 offers a comprehensive and practical methodology for the design of structures for tsunami loads and effects. While it provides prescriptive tsunami loading and design requirements, Chapter 6 also allows for the use of performance-based nonlinear analysis tools. However, the specifics of load application protocol and system and component evaluation for such a nonlinear approach are not provided. This paper presents a procedure for performing nonlinear static pushover analysis for tsunami loading within the framework of the ASCE 7-16 standard. Through this approach, the user can both estimate the effective systemic lateral load-resisting capacity of a building and the local component demand. This enables the identification of deficiencies in structural elements with respect to the ASCE 7-16 standard acceptance criteria. To demonstrate the procedure, a prototypical reinforced concrete multistory building exposed to high tsunami hazard on the US Northwest Pacific Coast is assessed. This is a building with sufficient height to provide last-resort refuge for people having insufficient time to evacuate outside the inundation zone. The results of the nonlinear static pushover analyses show that the structural system has sufficient lateral strength to resist ASCE 7-16 prescribed tsunami loads, but fails the checks for component-based loading, with the exterior ground-story columns observed to fail in flexure and shear. The example demonstrates that use of the tsunami nonlinear static analysis procedure allows the identification of structural deficiencies such that a targeted strengthening of the building can be conducted (i.e., flexural and shear strengthening of the seaward and inland columns for the case study building presented), leading to significantly reduced costs.

Due to the increasing tendency to construct taller and more slender buildings, the need to address aerodynamic and induced dynamic forces (inertial forces) under both service and strength-level wind loads has become more important. Currently, application of performance-based wind design (PBWD) to reduce induced dynamic forces applied through the acceptance of inelastic deformation is permitted as an alternative design approach, in which wind load can be reduced with respect to the yield strength and ductility of the structure. However, reduced wind load smaller than aerodynamic forces may not ensure proper inelastic wind design. The results of this study indicate that to avoid huge ductility demand due to damage accumulation, the yield strength for structural systems with zero-to-modest post-yield stiffness must be larger than the aerodynamic forces. Moreover, due to uncertainty in the number of occurrences of peak aerodynamic loads applied to a structure during a wind event, it would be advisable for systems with large post-yield stiffness to consider upper limits of aerodynamic forces.

Composite timber steel encased columns comprising low-grade coniferous softwood radiata pine (Pinus radiata) (MGP10 grade) and Douglas fir (Pseudotsuga menziesii) (F7 grade) with encased steel bars (yield strength of 300–660 MPa) were fabricated and tested under concentric and eccentric loads. The timber lamellae and encased steel bars were bonded together with a two-component epoxy adhesive and mechanical fasteners to achieve a composite member that combines the lightweight and ductile behavior of timber in compression with the high strength of steel bars. The structural performance of the columns was evaluated with respect to control bare timber samples. The test results revealed that stiffness and load-carrying capacity of the stocky composite columns (slenderness ratio ${\mathrm{\rho }}_{\mathrm{c}}\text{S}<10$, per AS1720.1) were significantly increased (over 100% in some cases) by the encased steel bars. The hybridization of timber columns with steel bars was also effective in reducing the variance in the load-carrying capacity. An analytical model based on a simplified bilinear elastoplastic relationship and principles of structural mechanics was proposed to estimate the stiffness and load-carrying capacity of the composite columns under axial compression and bending moment.

Ductility and robustness are two of the most important structural properties for the design of a building against extreme load cases, such as earthquakes and column loss scenarios. Various guidelines are based on the premise that an adequate amount of ductility is available and that structural robustness is attained. In this article, the outline of an experimental and analytical investigation related to the flexural behavior of a specific type of shallow (slim) floor beam, commonly known as Deltabeam, is presented. In order to determine the ductility and the robustness of the system, six full-scale composite beams with different geometry details were investigated under a three-point loading setup, up to large deflections. Tests showed that the ability of the concrete section, enclosing the steel beam, to withstand large strains without strength reduction strongly affected the ductility and robustness of the tested beams, which were thus far defined only by the class of their compressed steel components. The proper detailing of the reinforcement and the lateral protection provided by the stirrups were proven to be particularly important for the behavior of this type of beams when subjected to large deformations.

A novel welded demountable shear connector for sustainable steel-concrete composite structures is proposed. The proposed connector consists of a grout-filled steel tube bolted to a compatible partially threaded stud, which is welded on a steel section. This connector allows for an easy deconstruction at the end of the service life of a building, promoting the reuse of both the concrete slabs and the steel sections. This paper presents the experimental evaluation of the structural behavior of the proposed connector using a horizontal pushout test arrangement. The effects of various parameters, including the tube thickness, the presence of grout infill, and the concrete slab compressive strength, were assessed. A nonlinear finite element model was also calibrated against the experimental results, and the validated numerical model was used to extend the validity of the experimental results and to perform further parametric studies. The experimental and numerical results show that the tested connectors have similar stiffness, but higher shear resistance and slip capacity compared with traditional welded shear studs and can be classified as ductile according to Eurocode 4.

This study presented an experimental and analytical investigation on the seismic behavior of a reinforced concrete (RC) interior joint with corroded reinforcements. A total of eight RC interior joints with similar reinforcing detailing were tested and subjected to lateral cyclic loading. The variables studied in this research were the corrosion level of reinforcements in terms of mass loss and the column axial force ratio. The cyclic performance of all the joints including crack pattern, lateral loading capacity, energy dissipation, and lateral displacement decomposition were examined. The corroded joint constitutive model was calibrated and validated using the finite-element method. An analytical strut-and-tie model (STM) was developed for explaining the internal force flow and further parametric investigations. Results indicated that corrosion of reinforcements had a substantial effect on the strength and lateral drift capacity of the joints. In addition, based on the STM model, the axial force ratio exceeding 0.3 and longitudinal reinforcement corrosion level around 6–10% were detrimental toward joint behavior and can contribute to joint shear failure.

It is generally taken as a given that there is no reasonable design concept that could have prevented the collapse of the Twin Towers, once it was initiated, from progressing all the way down to the ground. This view is rooted in the idea that the force generated during the inevitable impact between what may be called the intact upper section (IUS) and the intact lower section (ILS)—meaning the building sections above and below the initially lost columns, respectively—will exceed by at least one order of magnitude the capacity of the latter. On closer inspection, this turns out to be only partially correct—it is correct with regard to the topmost floor plate of the ILS but not with regard to the columns below this floor plate. This paper shows that if the ILS in the Twin Towers had been topped by a stronger-than-ordinary floor plate allowing the columns below to respond properly, rather than be bypassed, these columns—and with them the ILS—would likely have survived. The paper subsequently proposes a building design concept consisting in the insertion of strengthened floor plates in intervals of 10–20 stories.