Journal of Structural Engineering

This paper highlights the challenges before researchers who are working to understand the postbuckling mechanics of a stiffened web panel, design of transverse stiffener, mechanics of end panel, and the overall behavior of a plate girder subjected to shear, in general. It describes how the tension-field theories evolved to provide a solution to predict the postbuckling shear resistance and what the impact was of these theories on the design of different girder components. In addition, the paper describes how and why these theories failed to explain the rational mechanics involved in the postbuckling shear resistance. It also presents the alternative explanations provided by researchers who do not agree with the significance of tension-field action. From the analysis of these theories, their alternatives, and the latest research about other contributing factors to shear postbuckling mechanics, many future areas of research emerged. Many such important future areas of research are highlighted in this paper. This paper also underlines the need for an improvement in code provisions related to finite-element analyses.

The application of extreme loads, such as impact and blast, may lead to progressive collapse and the robustness of a structure must be considered in this context. Although extensive studies have been carried out in recent decades to investigate the load-resisting mechanism of RC frames to prevent progressive collapse, the effects of high-strength concrete (HSC) on progressive collapse resistance capacity remain unclear. Therefore, six tests of RC frames with different span-to-depth ratios and concrete strengths were conducted in present study. Among them, three are HSC frames and the others are normal-strength concrete (NSC) frames. It was found that the use of HSC could further enhance the compressive arch action (CAA) capacity, especially for frames with a low span-to-depth ratio. On the other hand, HSC can reduce the tensile catenary action (TCA) capacity at a large deformation stage, primarily because of the higher bond stress between concrete and rebar, leading to earlier fracture of the rebar. The analytical results from the model were compared with the test results. It was found that the refined CAA model could accurately predict the CAA capacity of NSC frames, but not of HSC frames. Moreover, using the existing model it is hard to accurately predict the CAA capacity of frames with relatively small span-to-depth ratios (less than 7).

Reliable analytical and empirical models of the force-deformation parameters used to characterize the nonlinear behavior of masonry panels are essential to simulating the seismic response of infilled reinforced concrete and steel frame systems. This paper presents the development of empirical equations to predict the backbone curve parameters of infill panels modeled using equivalent struts. For this purpose, a database of 264 infilled frame experiments is assembled from the existing literature. The experimental data from a subset of 113 specimens is used to calibrate the force-deformation parameters of the infill equivalent struts. Using the results from multivariate regression analyses, empirical equations are proposed for the backbone curve parameters that define the axial response of the infill struts. Discussions and recommendations for the cyclic degradation and pinching effect parameters are also presented.

This paper presents a reduced-order numerical modeling approach for the analysis of heat transfer in composite floor slabs with profiled steel decking exposed to fire effects. This approach represents the thick and thin portions of a composite slab with alternating strips of shell elements, using a layered thick-shell formulation that accounts for both in-plane and through-thickness heat transfer. To account for the tapered profile of the ribs, layered shell elements representing the thick portion of the slab adopt a linear reduction in the density of concrete within the depth in the rib. The specific heat of concrete in the rib is also proportionally reduced to indirectly consider the heat input through the web of the decking, because the reduced-order model considers thermal loading only on the upper and lower flanges of the decking. The optimal ratio of modified and actual specific heat of concrete in the rib is determined, depending on the ratio of the height of the upper continuous portion to the height of the rib. The reduced-order modeling approach is validated against experimental results.

This paper describes a reduced-order modeling approach for the thermal and structural analysis of fire effects on composite slabs with profiled steel decking. The reduced-order modeling approach, which uses alternating strips of layered shell elements to represent the thick and thin portions of the slab, allows both thermal and structural analyses to be performed using a single model. The modeling approach accounts for: (1) the trapezoidal profile of the concrete in the ribs; (2) the structural resistance provided by the steel decking, including the webs of the decking; and (3) the orthotropic behavior of the decking, which provides greater resistance along the ribs than transverse to the ribs. The modeling approach is validated against experimental data from one-way composite slabs tested under ambient-temperature, a one-way composite slab tested under fire conditions, and a two-way composite slab tested under fire conditions. Both implicit and explicit solution schemes are evaluated for the structural analysis, and the results show that it is feasible to scale down the hours-long fire duration to a simulation time of seconds in an explicit dynamic analysis, without adversely affecting the accuracy of the results. The steel decking contributes significantly to the structural resistance at an ambient temperature, but as expected, its contribution is found to decrease rapidly under fire exposure. The modeling approach can account for the location of reinforcing bars (i.e., at a specified depth in either the thick or thin portion of the slab), and it is found that reinforcement location can have a significant effect on the structural response, because heat transfer in the composite slab results in higher temperatures in the thin portions of the slab between the ribs.

An experimental investigation was conducted to assess the performance of a new buckling-restrained brace (BRB) system for retrofitting seismically deficient reinforced concrete frames. The BRB consists of a ductile inner steel core bar designed to yield in tension and compression without buckling while controlling the response to seismic forces. The core bar is contained within a tubular steel section, which in turn is housed in a larger tubular steel section infilled with mortar, providing lateral restraint against buckling. Self-consolidating mortar is used as filler material between the two tubular sections to increase the buckling resistance. The inner core bar is connected to innovative end units that allow extension and contraction during tension-compression cycles while providing lateral restraint against buckling. The new BRB system has been verified experimentally using two large-scale reinforced concrete frames, one of which was tested as a reference nonretrofitted frame and then repaired and retested three more times after BRB retrofits, while the other was retrofitted and tested, forming the fourth retrofitted frame test. Tests demonstrated substantial increases in the lateral load and energy dissipation capacities of retrofitted frames with satisfactory drift control. Three different types of steel bars with different strength and elongation characteristics were considered. Among the three, stainless steel provided the best strength, stiffness, and ductility enhancements.

This study presents the test results of three specimens of traditional Chinese timber frames (TCTFs) with two types of column heights and two types of vertical loads. The specimens were initially loaded to damage, then strengthened with different numbers of shape memory alloy (SMA) wires and retested. The lateral performance, such as failure modes, envelop curves, stiffness degradation, and energy consumption, was analyzed to evaluate the SMA strengthening effects. Results showed that the lateral bearing capacity, stiffness, and energy consumption of the strengthened specimens were evidently improved, and even exceeded the undamaged level when relatively larger displacements were imposed. An analytical model for frames jointed by semirigid mortise–tenon and hinged column-foot joints (SHFs) was proposed. Lateral load-displacement responses of both the strengthened and unstrengthened specimens were predicted by the model, and good consistency was obtained compared with the test results. The influence of column heights, vertical loads, strengthening degree, and frame spans on lateral behavior of TCTFs also were evaluated through both experiments and parametric studies. This work provides a valuable reference for the restoration of historic timber structures.

This paper studies the role of confining reinforcement on the compression behavior of axially loaded reinforced concrete (RC) columns at elevated temperatures. To demonstrate, experimental tests are conducted on 10 RC stub columns, each with a cross-sectional dimensions of $230\times 230\mathrm{mm}$ and a length of 860 mm. Two different concrete mixes (M30 and M50) exposed to varying combinations of two different heating durations (140 and 200 min) and two different volumes of confining reinforcement (0.25% and 2.14% by volume) are used in these tests. A length of approximately 500 mm at the middle of the column is heated for the desired duration and then loaded concentrically in compression until failure. The tests reveal that an increase in the amount of confining reinforcement significantly improves the axial load–carrying capacity of RC columns at elevated temperatures. These tests are also simulated using finite element (FE)–based heat transfer and stress analyses. The numerical simulations predict the time-temperature ($t\text{-}T$), axial load-deformation behavior, and the failure mode reasonably well. The numerical simulations are further used to understand the role of the confining reinforcement on the confinement pressure in the RC columns.

Post-tensioned timber (Pres-Lam) buildings have been constructed throughout the world, beginning in 2010. The technology, which originated from low-damage concrete building applications, relies on unbonded post-tensioning tendons to provide moment capacity to beam–column, wall–foundation, or column–foundation connections. Supplemental energy dissipation can be introduced by the inclusion of mild steel bars or replaceable damping devices when designing buildings for high-seismic-risk areas. Given the increasing demand for multistory timber buildings in high seismic zones, the Pres-Lam system is recognized worldwide as one of many efficient solutions for achieving seismic-resilient and sustainable structures. This paper presents an overview of the current state-of-the-art of the Pres-Lam system, including experimental campaigns, numerical and analytical modeling, and operating buildings as well as design procedures and design procurement.

The short-term flexural behavior of prestressed glulam beams reinforced with curved tendons was investigated via four-point bending of 12 glulam beams. These beams were equally divided into four groups of three identical specimens: one group of unreinforced beams, one group of prestressed beams reinforced with straight tendons, and two groups of prestressed beams reinforced with parabolic tendons. For the last two groups, the initial prestress force was applied in two levels. The results revealed that, in contrast to the failure mode of the unreinforced beams, the failure mode of the prestressed beams changed from brittle failure to ductile failure. The flexural capacity and the flexural stiffness of the prestressed glulam beams reinforced with straight tendons increased by 56.9% and 14.9%, respectively, compared with that of the unreinforced beams; for prestressed beams reinforced with parabolic tendons, the capacity and the stiffness increased by 54.4%–75.5% and 14.2%–15.5%, respectively. Based on the experimental results, a theoretical model for predicting the flexural stiffness and capacity of prestressed glulam beams was proposed. This model was validated with the test data.

The progressive collapse of building structures typically occurs when an abnormal loading condition causes a sudden loss in the structural capacity of one or more critical members, which leads to a chain reaction of failure and, ultimately, catastrophic collapse. This is the first of two independent papers involving a fundamental study of a numerical model for a progressive collapse-resistance design of a floor-to-floor joint in precast cross-wall structures This paper presents a finite-element (FE) model for the progressive analysis of a precast floor-to-floor system by considering a bar fracture and pull-out failure mode. The problem is studied using nonlinear dynamic finite-element simulations carried out following the Department of Defense (DoD) guidelines. The paper focuses on developing a model for a global analysis of precast structures when subject to increasing vertical loading and notional removal wall support. To this end, detailed three-dimensional (3D) finite-element models of the pull out behavior of a reinforcement bar in the keyway of precast concrete blocks to simulate pull-outs or a bar fracture failure mode were developed. The same modeling method was then used in the subsequent 3D nonlinear numerical analyses to simulate the ductility behavior of precast concrete floor joints in the absence of underlying wall supports. The objective of the present study is to identify modeling parameters affecting the behavior of the system and propose a model for a progressive analysis of a precast structure.

This paper presents the results of compartment fire experiments on four 12.8-m-long composite floor beams with various end support conditions. Specimens were constructed as partially composite beams, consisting of $\mathrm{W}18\times 35$ steel beams and 83-mm-thick lightweight concrete slabs cast on top of 76-mm-deep ribbed steel deck units. Test variables included two types of simple shear connections (shear-tab and welded-bolted double-angle connections) and the presence or absence of slab continuity over the girders. Each specimen was subjected to gravity loading using hydraulic actuators and 4,000-kW compartment fires produced using natural gas–fueled burners. This study evaluated the characteristics of the fire loading and thermal and structural responses of the specimens. The test results indicated that there were significant effects of thermal restraints on the behavior and failure modes of the specimens with simple shear connections. The specimens resisted gravity loads at large vertical displacements near midspan (approximately a ratio of span length over 20) under fire loading. However, various limit states and vulnerabilities to fires were observed, including local buckling of steel beams near supports, flexural failure (yielding of steel beams and concrete fracture near restrained end supports), and connection failure (weld shear or bolt shear) during heating and cooling, which could lead to partial or total collapse of the floor system.

During earthquakes, I-shaped beams (I-beams) in a braced structure are subjected to the flexural moment synchronized with reversed axial forces transmitted from buckling restrained braces. A prior study used the modified width–thickness ratio to evaluate the rotation capacity of I-beams that failed by local buckling under alternating axial force. Generally speaking, I-beams in braced frames are designed with larger sections to resist severe stress conditions. The buckling mode might thereby be switched to web-shear buckling, leading to inaccurate estimation of the rotation capacity when using existing equations. For this study, a classification index of buckling mode is constructed considering axial force and plate interactions. Moreover, a novel index and formulas are proposed for evaluating the rotation capacity of I-beams under alternating axial forces, including buckling-mode transition effects.

The direct strength method (DSM) is a newly developed design method for cold-formed steel members due to its reliability and consistency. It has been well developed and incorporated in the North American Specification and the Australian/New Zealand Standard for the design of cold-formed steel members under compression, bending, and recently, in shear. To date, there are no DSM rules for the design of cold-formed members under localized loading resulting in the web-crippling phenomenon. Recent literature has attempted to propose the DSM design equations for four localized loading cases including the interior one-flange (IOF), end one-flange (EOF), interior two-flange (ITF), and end two-flange (ETF) loading cases specified in the design specifications/standards. However, these proposed DSM equations were calibrated differently depending on the types of loading cases and geometric shapes of the cross-sections by varying coefficients and exponents in the DSM equations. In this paper, consistent and simplified DSM equations previously proposed by the authors are explained and calibrated for use in the design specifications/standards. They include new plastic mechanism models developed for determining the yield load and also cover the design of sections in the inelastic reserve range as observed. Detailed explanations of the yield load ($P_y$) component and references to computing the buckling load ($P_{cr}$) component are given. A design example is also included.

Cross-laminated timber (CLT) is suitable for shear walls owing to its high in-plane stiffness. However, according to a series of shaking table tests on multistory CLT structures, premature connection damage always occurs in CLT shear walls under the applied loading scenarios representing moderate and major earthquakes. To mitigate the premature connection damage and improve the seismic resilience of CLT shear walls, a specific kind of posttensioned (PT) CLT shear wall is proposed herein, which is constructed by posttensioning CLT wall panels to the foundation with PT steel strands or bars. Previous studies on PT CLT shear walls with vertically continuous wall panels already exist. In this study, cyclic loading tests were conducted on three PT CLT shear wall specimens with different initial posttensioning forces. Floor diaphragms were included in these wall specimens and were structurally designed to mitigate the creep deformation of the CLT floor diaphragm subjected to perpendicular-to-grain compression. In addition, two conventional CLT shear walls with wall panels connected to the foundation using metal connections were also tested. The hysteretic behavior of the PT CLT shear walls was analyzed, and their lateral load–resisting performance was compared with that of the conventional CLT shear walls. Finally, fiber-based nonlinear finite-element models were developed within the Open System for Earthquake Engineering Simulation (OpenSees) framework to duplicate the lateral performance of PT CLT shear walls and conventional CLT shear walls. Results indicate that PT CLT shear walls exhibit excellent lateral performance with self-centering capability. After the entire loading process, almost no damage occurred in the PT CLT shear walls compared with the premature damage occurring in the metal connections of the conventional CLT shear walls. A friction coefficient of 0.32 is recommended for the contact interface between the CLT and steel foundation. Furthermore, for the PT CLT shear walls or conventional CLT shear walls, their analytical responses from numerical models agree well with the experimental responses, indicating the potential values of these fiber-based nonlinear models for engineering design.

This paper presents a low-damage solution for self-centering steel and composite beam-to-column connections, with the issue of beam-growth being particularly addressed by permitting the connections to rotate only about the top flange of the beam. Self-centering devices incorporating novel shape memory alloy (SMA) ring springs are the kernel components for the proposed connections. The fundamental working principle of the connections is depicted, followed by an experimental study on four proof-of-concept specimens, including three bare steel and one composite connections. The testing parameters are preload of web bolts, training of the SMA ring springs, and influence of the slab. Among other findings, it is shown that the damage to the concrete slab and the reinforcement are minimal for the composite connection. Stable flag-shaped hysteretic responses are typically exhibited, and good ductility, and energy dissipation performance are confirmed. The specimens can be generally classified as rigid and partial-strength connections. Slip-critical HS web bolts could provide an extra source of energy dissipation through friction. Applying training to the SMA outer rings further stabilizes the hysteretic behavior and mitigates the possible degradation. Based on the experimental observations, preliminary design recommendations are proposed, with the focus on the design of the SMA ring springs, web plate, cover plate, and other components of the device. Empirical design equations are also proposed for predicting the moment resistance of the connections, and the predicted values are shown to agree well with test results.

This research investigated the mechanical characteristics of cross-laminated timber (CLT) connections fastened with structural wood screws, also known as self-tapping screws (STS). The CLT connection assemblies were toe-screwed (TS) at 45° and cyclically tested in tension and in-plane shear to evaluate the failure modes and applicability as seismic connections in CLT shear walls. The connection assemblies were representative of full-scale CLT shear walls connected to CLT floors as often seen in platform construction. Toe-screwed CLT connections exhibited screw fracture, head pull-through, and pinched hysteresis loops. Mechanical connection properties and backbone curves were extracted for comparison with design estimates. A head pull-through design method was developed, which predicted peak strength within 5% of test results. Connection parameters for ASCE/SEI 41 idealized-component curves were presented for use in performance-based design nonlinear-static pushover analysis. Combining the presented ASCE/SEI 41 parameters with the proposed design method and test results provides a simple and reasonably accurate nonlinear toe-screwed connection response curve. Partially threaded washer-headed screws were found to be superior to fully threaded screws in seismic applications due to their 15 times greater ultimate deformation capacity, substantially greater energy dissipation, similar peak strength, and similar elastic stiffness. However, the yield strength of partially threaded STS was found to be 48% of the yield strength of fully threaded STS.

Hollow structural sections (HSS) are used as columns in frame systems because of their ability to efficiently resist multiaxial loads. While the majority of previous studies of special moment frames (SMFs) focused on wide flange columns, HSS columns can provide a means of increasing the versatility of SMFs. In order to fully explore the use of HSS columns in SMFs, the collapse behavior of HSS columns subject to combined axial and lateral loading is computationally studied. Seventeen different HSS profiles are selected to cover a wide range of local and global slenderness ratios, including width-to-thickness ratio ($b/t$), depth-to-thickness ratio ($h/t$), and the global slenderness ratio about the weak axis ($L/r_y$). Detailed finite element studies show that the behavior of HSS columns is highly dependent on the local slenderness ratios and the level of initial applied axial load ($P/P_y$). A regression analysis is performed leading to a proposed design aid for HSS columns in SMFs along with updated highly ductile local slenderness limits. The proposed highly ductile limits suggest that the current AISC limits for HSS columns are conservative when considering the width-to-thickness ratio and potentially unconservative when considering the depth-to-thickness ratio.

Closed-form equations for the initial thermal postbuckling response of axially restrained elastic columns with six well-known sets of rotational and lateral end restraints are presented. These equations, which are consistent with the conventional beam-column (Euler–Bernoulli) theory, are based on the assumption that the column axial force remains constant at the buckling level in the postbuckling phase, i.e., the (additional) thermal axial extension because of the increased temperature above the buckling temperature is converted into the column’s lateral deflection via the bowing effect. The equations consider the effects of partial axial restraints as well as the degradation of elastic material properties with rising temperatures. To evaluate their accuracy, the postbuckling response predicted by these approximate equations is compared to the exact (elastica) solutions available in the literature and to the finite-element solutions. The results of these validation studies indicate that these relatively simple closed-form equations can predict, with a high degree of accuracy, the initial thermal postbuckling response of axially restrained columns with the various rotational and lateral end restraints considered in this paper.

This paper introduces an innovative structural system consisting of four-sided hyperbolic-paraboloid (hypar) roof umbrellas as hard countermeasures against nearshore hazards. The umbrellas line the coast and remain upright during normal operation, providing shade and shelter along the waterfront while not limiting access to the shore. A hinge at the hypar-column interface permits tilting to form a physical barrier against surge-induced coastal inundation. Analytical equations based on idealized boundary conditions are formulated in the hydrostatic regime. The equations provide insight into optimal geometric parameters and are used to validate a decoupled numerical scheme constituting smoothed particle hydrodynamics (SPH) and the finite element method (FEM). All numerical reactions concur with the analytical solutions for water inundation matching the total deployed height. A proof-of-concept study was employed to successfully illustrate the applicability of deployable hypar umbrellas as coastal armor from a structural engineering perspective. This work ultimately demonstrates the feasibility of decoupled SPH-FEM methods in modeling fluid-structure interaction involving hypar forms, while establishing a foundation for their analysis and design for coastal hazard adaptation.

Experimental results provided in the related literature are used in the present study to develop a method for estimating the shear strength of circular concrete-filled steel tubes (CFSTs). This study benefits from using the findings of a significant number of experimental specimens with high diversity in terms of experimental details such as geometric dimensions, material specifications, test setups, as well as axial load. Within this method, the shear strength of the CFST member is considered to be the sum of the shear strength of the steel tube and that of the concrete core. The parameters supposed to affect the shear strength of the concrete include confinement factor, shear span ratio, and axial load ratio. A comparison between the results of the proposed method and other analytical ones also reveals that the proposed equation has a generally higher accuracy, and its estimates are in more agreement with experimental values than the results of other methods.

Concrete cover spalling induced by steel corrosion is generally assumed to be the limit state of concrete structures when considering their structural safety. A new method for testing the resisting bending moment in a spalling concrete block is proposed in this paper. Spalling experiments were conducted on six beams after being subjected to simultaneous sustained loads and accelerated corrosion, and the resisting bending moments in the spalling concrete block were measured. Two spalling mode types were identified, and the spalling bending moment was found to be negatively related to the crack widths. Based on the experimental results, an analytical model was preliminarily established to determine the resisting bending moment in a spalling concrete block of corroded beams, and the results indicate that the predictions from the analytical model exhibit reasonable agreement with the experimental data. According to the experimental results and analytical model, a criterion for predicting concrete cover spalling is proposed.

Wind tunnel pressure tests on flat-roof buildings were carried out for three kinds of length-width ratio models in three types of terrain. Based on the fitted generalized force spectrum, the analytical expression of equivalent static wind load (ESWL) on plate-like flat roofs was derived using the inertial force method, which is expressed as a function of the structural reduced frequency. The results show that wind directions along the short building side and the long building side are the two most unfavorable wind directions in the view of nodal displacement and member stress; terrain type has important effects on the coefficient of ESWL, increasing the turbulence intensity enlarges the coefficient of ESWL, and it decreases with increases in the reduced frequency. The nodal displacement and member stress calculated by the proposed analytical formula agree well with the actual peak response in two unfavorable wind directions, and the response agreement in the wind direction along the building long side is poor using the gust loading factor method.

Wind load is one of the main concerns for engineers in the design of tall buildings. In contrast to seismic demand, the wind load spectrum has more energy at lower frequencies, which is why taller buildings that have less frequency are more sensitive to wind load. Equivalent static wind load (ESWL) is the primary method to calculate the mean wind load and fluctuation effect due to wind turbulence-structure interaction, called the gust effect. The most accepted way to calculate the effect is the gust load factor (GLF) approach, which is widely adopted by current codes and standards. With further improvements, the base moment gust load factor (MGLF) method enhances the GLF method and eliminates its disadvantages. This paper discusses all aspects of defining wind load and studies the effect of certain parameters on the calculation. This paper focuses on calculating the along-wind force and how the gust effect changes by following the procedure in the relevant ASCE standard and comparing the approaches and results side by side.

The shear capacity of reinforced concrete knee joints in closing and opening actions are determined in this paper using the framework of the softened strut-and-tie model. The proposed model considers the closing and opening actions separately and takes into account the differences in joint behavior to accurately predict the joint capacity in closing and opening actions. The proposed model satisfies force equilibrium, strain compatibility, and the constitutive relationship of the cracked concrete. The predicted shear capacity values in both actions are compared with the experimental results of 59 knee joint specimens reported by various researchers. The gathered dataset consists of specimens with a wide range of geometric and reinforcement variations. The comparison showed an excellent correlation between the predicted shear capacity values and the available experimental results in both closing and opening actions of knee joints.

Structural risk assessment against fire requires robust material models that take into account the uncertainty in material behavior over a range of elevated temperatures. Such probabilistic material models can directly inform performance-based design procedures for building fire safety. The objective of this research is to quantify uncertainties in retained strengths of steel and concrete when exposed to fire. First, hundreds of experimental data points covering a temperature range of 20°C–1,000°C are collected from literature. Then, different distribution candidates and modeling approaches are used with the collected data to identify probabilistic models for temperature dependents strength of steel and concrete. The proposed models are continuous probability distribution functions, with simple mathematical representations that are easy enough to arrange into systematic code for implementation in analytical and computational frameworks. Additionally, the proposed stochastic functions consider continuity in reliability appraisals during transition from room temperature to elevated temperatures. These models are applied to probabilistic evaluations of structural performance of three steel and two concrete columns, and the influence of the model choice is compared using fragility curves. Finally, the proposed probabilistic models, developed using different approaches, led to close results when characterizing the performance of structural members.

The structural fire engineering community has been slowly evolving over the past few decades. While we continue to favor a classical stand toward evaluating fire resistance of structures through fire experimentations, a movement toward developing numerical assessment tools is on the rise. A close examination of notable works shows that the majority of these tools continue to have limited scalability, lack standardization, and thorough validation. Perhaps two of the main challenges of adopting such tools can be summed by their need for collecting true representation of response parameters (e.g., temperature-dependent material properties, etc.), and necessity to carry out resource-intensive two-stage thermo-structural analysis. In order to overcome such challenges, and in pursuit of modernizing fire resistance evaluation, this paper introduces a new generation of fire-based evaluation tools that capitalize on perception rather than imitation. More specifically, this paper explores how automation and cognition (A&C), realized through machine learning (ML), can be applied to comprehend structural behavior under fire conditions. To achieve this goal, genetic programing (GP) and computer vision (CV) are used to assess fire response of structural members. The outcome of this study demonstrates that A&C can accurately evaluate fire resistance and identify damage/spalling magnitude in reinforced concrete (RC) structures; thus, paving the way to realize autonomous fire-based evaluation and inspection.

In the present study, effects of panel shapes on wind-induced vibrations of solar wing system under various wind environments were investigated through conducting a series of wind tunnel tests. A scaled solar wing system with solar panels connected by cables was manufactured. Vertical displacements of four panels were measured using laser displacement sensors. The tests showed that the largest mean displacements occurred in low-turbulence flow for wind directions 40°–60°. For fluctuating displacement, boundary-layer and grid-generated flows showed buffeting vibration for all wind directions, but the values were much larger in boundary-layer flows. When the wind direction was greater than 40°, characteristic vibrations were found for low-turbulence flow, showing limited and instability vibration for a specific panel shape and wind direction. Mean and fluctuating displacements were highly dependent on panel shapes and wind environments.

An experimental study was conducted to investigate the mechanical behavior and residual capacity of concrete-filled steel tubular (CFST) columns subjected to a post-earthquake fire. Nine circular cantilever CFST columns, including two control specimens, were tested to investigate their post-earthquake fire resistance time. The residual seismic behavior and load carrying capacity of an additional four columns were also studied following post-earthquake fire. All specimens were first subjected to a reversed cyclic or simulated earthquake loading (to induce initial seismic damage) and were then heated to obtain the fire resistance time or were subjected to additional cyclic reversed loading after a post-earthquake fire. The experimental results indicate that the CFST columns generally performed well after a post-earthquake fire. Specimens with high compressive strength concrete exhibited longer post-earthquake fire resistance times, whereas the increase in tube wall thickness only had a marginal effect on improving post-earthquake fire resistance. More importantly, the presence of residual lateral drift at the end of the earthquake loading had a much more significant effect on the post-earthquake fire performance than specimens without residual deformation. Finally, it is recommended that the failure criterion for fire loading should possibly take into consideration lateral deformation limits during fire testing.

This paper presents the results of an experimental study into the behavior of perforated (containing openings) unreinforced masonry (URM) walls subjected to cyclic in-plane lateral loading. Damage to perforated URM walls during previous earthquakes has revealed that the in-plane response is mainly influenced by the pier and spandrel geometry, as well as the level of axial compressive stress on the walls due to gravity loading. The study focused on masonry typologies representative of historical URM buildings in the Australian context. To investigate this behavior, eight full-scale URM walls with semicircular arched openings, double wythe thickness, and materials representing masonry construction from the mid-19th to mid-20th century were constructed for pseudostatic cyclic in-plane testing. The experimental program considered varying spandrel depths and pier widths and the imposed vertical loading on the piers was also varied to observe the lateral load capacity and the variation of pier-spandrel failure modes. The test results showed that the in-plane capacity and the failure modes were significantly affected by changes of wall geometry and the imposed vertical precompression loading. Predictions of wall strengths, in-plane stiffnesses, and failure modes according to ASCE guidelines show that the guidelines agree well with the test observations.

Accurate prediction of progressive damage and failure of structural steels is a nontrivial issue in practical design and assessment of steel structural buildings. It appears far more important in the fracture-oriented scenarios under extreme environmental actions or accidental overloading conditions because, in these cases, the ultimate strength of steel structures is directly governed by material failure. However, previous studies on ductile fracture of structural steels were relatively limited, especially for high-strength steels (HSSs) like Q690D steel. In this paper, an enhanced fracture model based on the voids growth model (VGM) is proposed. The normalized maximum shear stress is introduced to make it capable of capturing ductile fracture at low and moderate stress triaxialities. To calibrate and verify the newly proposed model, a series of tensile tests of smooth and notched round bar specimens and shear specimens with different shear angles were carried out by using Q690D steel. Bridgeman’s theory was applied to identify the postnecking constitutive relationship with the help of a three-dimensional digital image correlation (3D-DIC) system. The good agreements between numerical simulations and experimental results finally verified the applicability and reliability of the enhanced model in ductile fracture prediction.

This paper presents a quasi-steady technique that combines aerodynamic force coefficients from straight-line wind tunnel tests with empirically developed tornado wind speed profiles to estimate the time history of aerodynamic loads on lattice structures. The methodology is specifically useful for large and geometrically complex structures that could not be modeled with reasonable scales in the limited number of tornado simulation facilities across the world. For this purpose, the experimentally developed tornado wind speed profiles were extracted from a laboratory tornado wind field and aerodynamic force coefficients of different segments of a lattice tower structure were assessed for various wind directions in a wind tunnel. The proposed method was then used to calculate the wind forces in the time domain on the model lattice tower for different orientation angles with respect to the tornado’s mean path based on the empirical tornado wind speed profiles and the measured aerodynamic force coefficient of each tower segment, where the wind field at the tower location was updated at each time step as the tornado went past the tower. A tornado laboratory simulation test was conducted to measure the wind loads on a scaled model of a lattice tower subject to a translating tornado for the purpose of validation of the proposed method. The moving average of the horizontal wind force on the lattice tower model that was calculated with this method compared very well with that measured in a laboratory tornado simulator, which paves the way for the use of straight-line wind tunnels to assess tornado-induced loads on a lattice structure and possibly other similar structures.

Elastic buckling of steel plate shear walls (SPSWs) vertically stiffened by either flat-bar or closed-section stiffeners is studied first to determine the required bending stiffness on stiffeners. The torsional stiffness of the stiffener is found to increase the buckling stress and reduce the required bending stiffness. The proposed equation for the elastic threshold stiffness is related to the increment of the elastic buckling stress of stiffened SPSWs over that of unstiffened SPSWs. Comparisons with previous research on stiffened plates are presented. For moderately thick and stocky plates, elastic-plastic buckling stress is used to define the threshold stiffness. It is found that the threshold stiffness based on elastic-plastic buckling stress is less than that based on elastic buckling stress. Replacing the elastic buckling coefficients with elastic-plastic buckling coefficients, the proposed equation gives good predictions for elastic-plastic threshold stiffness. The findings of this study may be helpful in understanding the real demand on stiffeners in stiffened SPSWs.