Journal of Structural Engineering

In this study, an experimental program on cold-formed stainless steel tubular sections with and without perforations under pure tension is presented. Nine cross section series made of ferritic, lean duplex, and austenitic stainless steel were included. The square and rectangular stainless steel tubes had a nominal outer dimension ranging from 20 to 80 mm and nominal wall thickness ranging from 1.5 to 4 mm, while the nominal diameters of circular tubes were 60.5 and 76.3 mm. Tensile coupon tests were performed to determine the mechanical properties, and 21 full cross section tensile tests were performed on 9 specimens with circular perforations and the rest without perforation. Tensile test results were discussed and further compared with the tensile strengths predicted by the prevalent design rules for stainless steel structures, such as the American Specification SEI/ASCE8, Australian/New Zealand Standards AS/NZS4673, and European Code EN1993-1-4. The comparisons reveal that the tensile strength predictions by these design rules are quite conservative and scattered for cold-formed stainless steel tubular sections with and without perforations.

The strength of longitudinally continuous stiffened steel plates, exhibiting column-like behavior under uniaxial compression, was investigated at ultimate as well as serviceability limit states. Compressive strengths were determined from nonlinear elastoplastic FE analysis, where both material and geometric nonlinearity were taken into account. In the parametric analysis, the reduced slenderness parameter ($R_R$) was varied from 0.4 to 1.4, and for each $R_R$, thick plates and high-performance steels (SBHS) were considered along with thin plates and ordinary steels. The probabilistic distribution of the strengths was obtained through Monte Carlo simulation, in association with a response surface method. The response surface function comprises three independent variables, upon which the uncertainties in estimating the compressive strength of a certain stiffened plate depend, i.e., the residual stress, the initial out-of-plane whole-plate deflection, and the initial out-of-plane local deflection. Comparing the ultimate strength with a 5% non-exceedance probability indicates that the AASHTO, Canadian Code, and Japanese specification provides significantly conservative design, specifically for $R_R>0.8$. Based on the obtained probabilistic information, partial safety factors for each $R_R$ were proposed, considering the mean value strengths as the nominal strengths, as an example.

The research presented in this paper aimed to investigate local buckling failure occurring adjacent to moment-resisting bolted connections in cold-formed steel back-to-back channel beams connected to a gusset plate through their webs. This failure is a result of a complex stress state originating from the transfer of both shear and bending moment through the web, combined with important shear lag effects. Experimentally validated finite-element models were used, accounting for material nonlinearity, geometric imperfections, and nonlinear bolt bearing behavior. The effects of the cross-sectional shape and thickness of the beam, the bolt group configuration, and the bolt group length were investigated. It was discovered that the detrimental effect of local buckling exponentially decreases when a longer bolt group length is used, when the load is introduced at the connection with a smaller eccentricity relative to the centroid, and when the thickness of the beam is increased. The results of the investigation were employed to develop a practical design equation with a wide range of applicability. Finally, a reliability analysis was performed within the framework of various standards.

The effectiveness of local (through-thickness) vibration testing, using a portable vibrator, is examined for determining damage locations and conditions within reinforced concrete (RC) bridge decks. The local vibration tests were conducted on deck specimens containing voids, for measuring resonant frequency during standing vibration. Wave propagation analyses based on a finite difference time domain (FDTD) method were then used to interpret the experimental results. It was shown that diffraction of waves around the void decreased the resonant frequency as the void size increased. As practical examples, local vibration tests were conducted on a deteriorated, decommissioned RC deck and bridge decks in service. The tests indicated that local resonant frequency was decreased by internal cracks within the deck. Resonant frequency distributions of the decks were also determined. The testing method is found to be applicable to detecting damage within actual bridge decks, even when the deck surfaces are covered with asphalt overlays and carbon fiber sheets. Moreover, periodic measurements could be used to evaluate the rate of deterioration of the bridge deck.

This study presents a design method for the seismic retrofit and rehabilitation of steel moment-resisting frames (MRFs) with composite steel–concrete beams using the minimal-disturbance arm damper (MDAD). The purpose is to enhance the seismic performance of this type of MRF by controlling both the overall structure deformation (roof and story drifts) and damage of individual members (local ductility). The MDAD imposes adequate strength and stiffness to limit the story drifts to the targeted values as well as redistributes the internal forces in order to delay beam yielding and fracture. The proposed design method for seismic retrofit and rehabilitation of MRFs integrates the member’s strength and ductility indices, such as the bending moment and plastic rotation, into the global frame response in terms of overall shear capacity and story drift through equations developed based on beam-column theory principles. The proposed design method aims to retrofit the structure to satisfy multiple performance objectives, such as (1) the delay of steel beam yielding, (2) the reduction of beam plastic rotation, (3) the control of strength reduction in postfracture behavior, and (4) the recovery of overall shear strength after frame rehabilitation. An experimental campaign was also conducted to evaluate the performance of both retrofitted and bare MRFs. The effectiveness of the proposed retrofit and rehabilitation procedure in limiting the story deformation and improving member ductility of the MRFs as well as its efficiency in recovering the overall strength capacity of heavily damaged framed structures was validated.

In this paper, four 1/2 scaled precast concrete (PC) beam-column subassemblages with high-performance connection were tested under push-down loading procedure to study the load-resisting mechanism of PC frames subjected to different column removal scenarios. The parameters investigated include the location of column removal and effective prestress in tendons. The test results indicated that the failure modes of unbonded post-tensioned precast concrete (PTPC) frames were different from that of RC frames: No cracks formed in the beams and wide opening formed near the beam to column interfaces. For specimens without overhanging beams, the failure of side column was eccentric compression failure. Moreover, the load-resisting mechanisms in PC frames were significantly different from that of RC frames: The compressive arch action (CAA) that developed in concrete during column removal was mainly due to actively applied precompressive stress in the concrete; CAA will not vanish when severe crush in concrete occurred. Thus, it may provide negative contribution for load resistance when the displacement exceeds one-beam depth; the tensile force that developed in the tendons could provide catenary action from the beginning of the test. Moreover, to deeper understand the behavior of tested specimens, numerical analyses were carried out. The effects of concrete strength, axial compression ratio at side columns, and loading approaches on the behavior of the subassemblages were also investigated based on validated numerical analyses.

Lip stiffened flanges in cold-formed steel compression members may undergo local or distortional buckling depending on the slenderness of the flange and rigidity of the lip. In distortional buckling, the flange-lip assembly moves perpendicular to the flange. The decrease in stiffness (or depth) of the lip increases the vulnerability of such elements to distortional buckling. In the limiting case of zero lip depth, the plate behaves as an unstiffened element. Hence the behavior of the unstiffened element may be intuitively understood as the limiting case of distortional buckling of lip stiffened element as the lip depth tends to zero. In this study, experimental and numerical results are used to show that both elastic buckling and ultimate strength behavior of a uniformly compressed unstiffened element may also be represented as distortional buckling of the lip stiffened element of zero lip depth. In addition to the effective width method, the modified direct strength method equation developed for distortional buckling is also shown to accurately estimate the ultimate strength of uniformly compressed unstiffened elements.

Seismic force resisting systems based on cross-laminated timber (CLT) shear walls have garnered considerable attention for in mid-rise construction around the world. The purpose of this study was to determine seismic performance factors for CLT shear wall systems in platform type construction. These factors, namely, the response modification factors, R, overstrength factor, ${\Omega }_{\mathrm{o}}$ and deflection amplification factor, ${\mathrm{C}}_{\mathrm{d}}$, have been developed in this study for CLT walls and proposed for inclusion in ASCE 7. The study follows the FEMA P695 methodology that incorporates testing, evaluating a design methodology, defining the design space representative of typical construction, and comprehensive performance evaluation. The testing phase of the project consisted of connector testing and CLT shear wall testing, all with nonproprietary generic connectors to facilitate building code recognition. The design methodology and archetype development process are also discussed in this paper. A total of nine index buildings were developed from which 72 archetypes were extracted for this study. The archetypes were designed based on the design methodology and assessed with nonlinear pushover analysis and incremental dynamic analysis. Based on the required collapse margin, an R factor of 3 is proposed for CLT shear wall systems with $2:1$ or mixed aspect ratio panels up to $4:1$, and an R factor of 4 is proposed for CLT shear wall systems made up of only $4:1$ aspect ratio panels.

Connections in mass timber structural systems transfer lateral forces from mass timber elements such as shear walls to floor diaphragms. Cross-laminated timber (CLT) is a prominent engineered mass timber material used to manufacture walls and floor assemblies. Fire performance research of CLT walls and floors has been abundant in recent years in an effort to develop an understanding of the performance of structural members under fire. Some fire-protected structural elements, including connections, may not be directly exposed to flames in a fire event but will experience elevated temperatures. There is limited research on elevated temperature performance of CLT connections, and consequently a lack of understanding of their fire performance in CLT structures. To aid in bridging this knowledge gap, in this study a series of cyclic shear tests were conducted on a CLT wall-to-floor bracket connection assembly to characterize thermal degradation according to a matrix of 28 exposure duration–temperature combinations. Two different methods were employed to develop force-displacement backbone models from the experimental hysteresis data. Models from both methods indicate an overall degradation of the connection performance in terms of load carrying capacity, elastic stiffness, ductility, and energy dissipation with increasing exposure to elevated temperatures.

The sliding hydromagnetic bearing is a low-friction isolator proposed in recent years. Its novelty lies in adaptive energy dissipation and alterable deflection constraint, which has been demonstrated by previous studies through pseudo-static tests and numerical simulations. In order to experimentally explore the effectiveness of the isolator for seismic mitigation of the base-isolated structure, a complete laboratory investigation by shaking table tests is carried out. Two sets of recorded three-dimensional and artificial one-dimensional horizontal earthquake ground accelerations pertaining to hard and soft soil sites are employed as the input to the table. The tests aim to explore the seismic mitigation of the base-isolated structure in terms of floor accelerations, interstory drifts, and horizontal torsions, as well as the seismic performance of the sliding hydromagnetic bearing in regard to oil leak prevention, deflection-resistance performance, and frictional behavior. The tests reveal that when subjected to far-field earthquake ground motions, the base-isolated structure with sliding hydromagnetic bearings exhibits a reasonable seismic mitigation of the floor accelerations and interstory drifts. In addition, it exhibits a satisfactory seismic mitigation of the horizontal torsions when subjected to either far-field or near-fault earthquake ground motions. It is also found that the workability of the sliding hydromagnetic bearing remains almost the same under different intensities of the considered earthquake ground motions. Furthermore, it is seen that the sliding hydromagnetic bearings exhibit a good oil leak prevention and deflection-resistance performance. The determined relationship between kinetic friction coefficient, bearing velocity, and axial compression in these tests reveals a similar finding in the previous pseudo-static test in that the sliding hydromagnetic bearing exhibits a shear thinning that becomes more remarkable under a larger axial compression and a higher sliding velocity.

The seismic performance of unanchored slender contents at various floor levels within a building has received little attention in the literature, despite earthquake reconnaissance reports routinely emphasizing the overturning of contents as a pervasive problem. This paper investigates the rocking response of building contents in a four-story concentrically braced frame building, focusing on how the variation in horizontal and vertical floor accelerations in the building affects the planar pure rocking demands (sliding and bouncing are not considered). A cascading dynamic analysis approach is taken whereby nonlinear response history analyses of a three-dimensional (3D) building model to a suite of ground motions provides the floor accelerations, which are in turn used to develop rocking spectra for assessing demands on unanchored building contents of various sizes and aspect ratios. The effect of the vertical floor excitation on the peak rocking response is found to be negligible for most practical purposes, especially for slender components. Consequently, rocking demands on an object are not affected by where it is placed on a specific floor. Rocking demands on an object increase at higher floors because horizontal floor accelerations are amplified with elevation, but the difference in rocking demands from one floor to the next are significantly more pronounced for stocky than for slender objects. Finally, the paper develops analytical fragility curves for rocking and overturning limit states using the normalized peak rotation angle as the demand parameter and a physically motivated floor intensity measure based on the peak floor velocity, block size, and slenderness.

Reinforced concrete (RC) U-shaped walls are a popular construction choice, commonly used to resist the lateral loads from wind and earthquakes. In many buildings, the center of stiffness of a floor is eccentric from the center of mass and the building will therefore undergo some twist. Often, U-shaped walls contribute significantly to the torsional stiffness of the building and the analysis of the structure therefore requires an estimate of the torsional stiffness. This research investigates the dependency of the torsional stiffness of U-shaped walls on the translational displacement demands using experimental evidence and advanced numerical models. The experimental results show that the torsional stiffness decreases with increasing translational displacement. Furthermore, the numerical and experimental results indicate that the torsional stiffness degrades at a similar rate as the translational stiffness of the walls. The rotational stiffness of the wall is smaller when it is centered than when it is subjected to a translation. This effect is attributed to the longitudinal stresses throughout the cross section that are already present due to the imposed flexural displacement. In particular, the compression zone resulting from the translational displacement imposed on the wall stiffens the wall with regard to the twisting. As a result, the effective torsional stiffness increases with increasing axial load ratio. Current codes do not provide reduction factors for the torsional stiffness, but the results show that the reduction factors for the shear stiffness can serve as estimate, albeit they do not capture the dependence on the axial load ratio.

Seismic design provisions for steel moment frame buildings have undergone substantial changes over the past half century. Despite the anticipated benefits of enforcing newer codes, it is not yet fully known how the evolution of seismic provisions has changed the risk associated with steel moment frame use. To address this shortcoming, a seismic loss assessment is performed for two-, four, and eight-story prototype steel moment frames designed using seismic provisions from three eras spanning the past half century. Frames of different vintages differ significantly in material properties, welding practices, connection types, seismic lateral force used for design, and panel zone design philosophy. High-fidelity models capable of explicitly capturing instabilities and fracture are employed to determine the effect of the differences in these designs. The simulation results show that although the collapse risk decreased as the codes evolved, the collapse probability of frames designed to the latest specifications still exceed the expected norms. Analysis of the four-story frames showed that the effect of brittle fracture in the welds of pre-Northridge connections on frame collapse capacity is modest. However, it is quite influential on economic and social losses for the level of seismic hazard considered. The assessment results are used to propose strategies for reducing the seismic losses of communities with steel buildings.

For better structural performance and constructability, a concrete-encased steel column that uses a steel cage prefabricated with bolt connections was developed. The steel cage consists of longitudinal steel angles and transverse steel plates. As a fundamental verification of the proposed column, an eccentric-axial-load test was performed on eight composite column specimens. Test parameters included column type (i.e., conventional concrete-encased steel column versus proposed column), shape and spacing of transverse plate, and axial load eccentricity. The test results showed that, owing to the high flexural stiffness of the steel angles placed at the corners of the cross section, the axial strength and ductility of the proposed column were greater than those of the conventional composite column using a wide flange steel section at the center of the cross section, particularly in the large eccentricity of axial load. Z-section plates and closely spaced flat plates used for transverse reinforcement provided better lateral confinement to the concrete, thereby increasing the load-carrying capacity of the proposed columns. In general, existing design methods safely predicted the axial-flexural capacities of the specimens. Nonlinear numerical analysis was performed to verify test results. The numerical analysis results agreed with the test results in terms of yield stiffness, peak strength, and postpeak strength degradation.

Contrary to the large dataset of test results exploring the monotonic bending response of steel tubes, the corresponding dataset of cyclic bending tests remains very small. Seven compact and semicompact S355J2H cold-formed circular-hollow sections with diameter to thickness ($D/t$) ratios between 20 to 60, representative of piles used in piers and wharves, were brought to failure in three-point cyclic bending tests. Digital image correlation was employed to estimate average cross-sectional curvatures, and hence the critical bending strains, during local buckling at the midspan plastic hinges. These estimates were compared against those from two simplified localized hinge models and differed by up to a factor of two. A parametric study was performed with a validated finite-element model to ascertain the suitability of proposed design equations at predicting critical strains in piles with $D/t$ from 20 to 60 under cyclic loading. Test and simulation data both show that critical buckling strains are lower under cyclic loading than under monotonic loading. This work can inform the future development of seismic design standards such as ASCE 61.

The innovative resilient slip friction joint (RSFJ) technology has recently been developed and introduced to the construction industry. This technology not only aims to provide life safety for the occupants, but also to reduce earthquake-induced damage so the building can be reoccupied after an earthquake with minimum business disruption. While the seismic behavior of the conventional timber structures may be acceptable, previous research showed they have significant shortcomings such as irrecoverable inelastic damage in the fasteners, high response accelerations, and possible residual displacements. This paper presents dynamic component test results on these joints to investigate their performance under rapid load cycles. In addition, experimental results related to full-scale bidirectional testing of a rocking laminated veneer lumber (LVL) panel with RSFJ hold-downs are presented. Furthermore, a progressive step-by-step analysis and preliminary design procedure for structures using this technology is proposed that is based on the use of force-based design principle. Accordingly, a numerical model for a 5-story timber structure was developed and then the proposed procedure was applied to the model to design the connectors. Then the model was subjected to nonlinear static pushover and nonlinear dynamic time–history simulations to investigate the seismic performance of the structure. Finally, the performance of the case study structure was compared with a similar structure with the RSFJs replaced with conventional friction dampers. The findings of this research demonstrate that the proposed system has the potential to be considered as an efficient resilient seismic solution for timber structures and the presented design procedure can potentially be used for preliminary design of buildings with RSFJs.

Criteria are proposed for determining the stiffness and strength demands for the seismic design of pin-supported walls in low- and medium-rise reinforced-concrete moment frames. A plasticity ratio and a global stiffness ratio are introduced to evaluate the effect of pin-supported walls (PS walls) in mobilizing the seismic capacity of the moment frame. Incremental dynamic analyses of 4-, 8-, and 12-story prototype PS wall-moment frames of various global stiffness ratios show that a constant stiffness ratio of two can generally ensure the formation of a global plastic mechanism no matter if the moment frame is a strong column-weak beam one or not. By mobilizing more structural elements to resist the earthquake action, the PS walls also increase the earthquake-resisting strength of the structure. Higher mode vibrations have a major effect on the strength demand for PS walls. Simple criteria are also developed for estimating the strength demands for the purpose of preliminary design of PS walls. The same methods for determining the stiffness and strength demands for PS walls are also applicable to other strong spine systems.

This paper experimentally and analytically investigates the fire and postfire behavior of axially restrained high-strength steel columns. Tests on the buckling behavior during heating as well as the residual load-bearing capacity after heating are first conducted on the column specimens made of Grade Q550 steel with a yield strength of 730 MPa. A numerical model is established and validated against the test results, and parametric studies are conducted with influencing factors including the maximum temperature, load ratio, slenderness ratio, and steel grade. A simplified calculation method is proposed to determine the residual capacity of restrained high-strength steel columns. The experimental results show that restrained high-strength steel columns buckle at a low temperature of about 300°C. The postfire residual capacity and axial stiffness of the columns are significantly reduced to a level of 55% and 32% of its initial values, respectively, due to the presence of a residual bending deformation. The numerical results show that the residual strength decreases greatly if the maximum temperature of a column is higher than its buckling temperature. The axial stiffness ratio and slenderness ratio have a significant influence on the residual capacity of restrained high-strength steel columns at buckling temperatures, while the axial load ratio has a significant influence at critical temperatures. However, the steel grade has little influence on the residual capacity of restrained high-strength steel columns.

To investigate the influence of critical parameters on the progressive collapse resistance of reinforced concrete (RC)-flat plates, a set of finite-element modeling techniques was established. The modeling of bond-slip behavior between concrete and rebars was especially highlighted, which was found to have a significant impact on the performance of flat plates. Employing the modeling strategy, our previously tested $2\times 2\text{-}\mathrm{bay}$ flat plate substructure (S-1) and a similar specimen (ND) in the literature were simulated for model validation. Key structural behaviors, including tensile membrane and suspension actions in the large deformation stage, could be accurately replicated. Further, the validated S-1 model was used to conduct a series of parametric studies in which the influence of concrete strength, slab thickness, and reinforcement ratio on the collapse performance was examined. The results indicated that the concrete strength and the slab thickness only affected the slab flexural capacity with no impact on the load-carrying capacity after the initial flexural/shear failure. Moreover, the load-carrying capacity due to tensile membrane action was primarily governed by the reinforcement ratio. Further examination on the lateral stiffness suggested a lower bound ultimate flexural strength enhancement of 17%, due to the compressive membrane action, can be obtained.

This paper proposes a novel probabilistic approach to account for soil-structure interaction (SSI) in the seismic design of building structures. In this approach, an SSI response modification factor, $R_{\mathit{SSI}}$, is introduced to capture SSI effects on the seismic performance of structures. The proposed procedure quantifies $R_{\mathit{SSI}}$ such that the probability distribution of the collapse capacity of the structure designed to account for SSI concurs with that of the structure designed using the default fixed-base provisions. The proposed approach considers prevailing uncertainties in the properties of the soil-structure system and in the seismic loading. It is employed for special steel moment frame buildings with surface foundation. The results indicate that no reduction in the design base shear is advisable for structures located on moderately soft to firm soils with shear wave velocities above $150\mathrm{m}/\mathrm{s}$. This conclusion is at odds with the current prescription of SSI provisions of seismic design code, which allow some reduction in the design base shear for such buildings. A thorough assessment of the design base shears obtained through current codified SSI provisions reveals a nonuniform risk of collapse for different soil-structure systems. In comparison, the median $R_{\mathit{SSI}}$ values computed through the proposed approach lead to a uniform risk of collapse and can be considered for the seismic design of special steel moment frames.

The dynamic effect of structures under column removal scenarios is investigated by conducting comparative experiments on two identical steel frames with concrete slabs. One frame suffers from a static edge-column loss, while the other is subjected to a dynamic column loss that is simulated by imposing an impact on a three-hinged column. The vertical deflections at the column-removal location of the two frames are reported and compared. The stress measurements at key locations of the frame in the static test are also presented. Numerical models are created and validated against experimental results. To quantify the dynamic effect of structures under a sudden edge-column loss, a dynamic amplification factor (DAF) is analytically determined based on the principle of energy conservation and is verified against validated numerical analyses. Parametric studies are also conducted on DAFs for various deflections and stiffness ratios. The experimental results suggest that the two orthogonal steel beams intersecting at the column-removal location deform linearly. The double-span beam after column loss suffers more external loads than the cantilever beam perpendicular to it. The positive yield lines diagonally distribute at the slab bottom, extending from the column-removal location to the corners of the slab. It is found that, owing to the dynamic effect, the ultimate bearing capacity of the frame in the test decreases by approximately 25.6% under a sudden edge-column loss scenario. The discrepancies between the dynamic and static deflections are intensified when the initially imposed gravity loads increase. The DAF at the ultimate limit state of composite frame structures due to a sudden edge-column loss can range from 1.15 to 1.4. Ignoring the enhancement of membrane and catenary action to the resistance can result in an underestimation of the dynamic effect of frames at large deflections. The method for calculating DAFs proposed by Department of Defense is not conservative in practical safety design since a monotonously decreasing value is designated.

Twelve concrete prisms pretensioned with 2,400-MPa strands were fabricated to investigate the effects of initial prestress ($f_{pi}$), concrete compressive strength at prestress release ($f_{ci}^{\prime }$), and the spacing of the lateral confining reinforcement ($S$) on the transfer length. Test results showed that the transfer length increased with an increase in $f_{pi}$ and with decreases in $f_{ci}^{\prime }$ and confinement level. A theoretical model incorporating rigid–linear local bond-slip relationships was developed and validated by its reasonable predictions of the distributions of the measured concrete strains in the transfer region. Based on the theoretical model, predictive formulas of transfer length were derived for both conventional and high-strength strands.

A numerical simulator that very closely resembles the experimental tornado simulator facility called VorTECH at Texas Tech University (TTU) is modeled using three-dimensional simulation. Details of an efficient, simplified computational fluid dynamics (CFD) model without vanes are presented. The pressure field is compared with experimental observations with an emphasis on the vortex breakdown, touchdown, and post-touchdown phase of a tornado. The simulation results indicate that the time-averaged radial ground pressure profile follows a similar trend with the experiment in terms of pressure field distribution. The tornado vortex core is found to be in a transient state in both space and time. The flow at higher swirl ratios has also been observed to lead to greater unsteadiness in flow. Moreover, the effect of roughness on the critical touchdown swirl ratio was also investigated, and increasing roughness length was found to increase the critical touchdown swirl ratio and vice-versa.

The strength of cold-formed steel beams with stiffened flanges may be controlled by distortional buckling. Buckling stress prediction methods have been developed for flanges under uniform compression. However, channel sections are commonly used where bending occurs about the minor axis with flanges under a stress gradient, such that the edges that are in compression and the flanges may experience distortional buckling. Current design specifications do not explicitly address this failure mode, which could lead to unsafe designs. This paper presents and verifies an analytical approach for distortional buckling stress prediction for flanges under a stress gradient. The approach is consistent with the design method used for flanges under uniform compression in the American Iron and Steel Institute (AISI) specification for the design of cold-formed steel members. This consistency facilitates a straightforward incorporation into the design specification.

An analytical procedure was developed to predict the compression membrane behavior of laterally restrained reinforced concrete members subject to extreme loads, such as those generated by the loss of bearing elements or during the application of excessive lateral loadings (e.g., explosions and impact). The procedure is based on the simplifying assumption that flexure and arching calculations can be uncoupled and that beam growth due to flexure after cracking can be approximated using rigid body rotation of beam half-segments. A lumped inelasticity flexure analysis is first performed to determine the degree of contact between the beam end and lateral support. The arching contribution to load capacity is computed by considering equilibrium of the contact zone arising from the projection of the beam into a partially rigid support. The total compression membrane strength is taken as the superposition of flexure and arching strength components. The methodology can handle supports with both rigid and nonrigid lateral restraint and varying degrees of rotational fixity. The numerical procedure has been verified extensively against the results of laterally restrained beam-column assembly and slab tests reported in the literature. The methodology can be used to model arching action under quasi-static conditions, or for inelastic dynamic analysis of structures subjected to blast and impact, provided high strain rate material properties are incorporated.

This paper investigates the seismic demand on acceleration-sensitive nonstructural components in buildings equipped with fluid viscous dampers. Nonlinear dynamic response analyses were conducted on three steel moment-resisting archetype frames of different heights, and incorporating linear and nonlinear viscously damped braces. The FEMA P695 far-field ground motion records set scaled to various intensities were used as seismic input. The main variables investigated in the parametric study included three different target supplemental damping levels, two different distributions of damper properties along the frames’ height, and six different nonlinear damper velocity exponents. The numerical results indicate that the inclusion of fluid viscous dampers generally improves the seismic response of the archetype frames. However, the seismic demand on acceleration-sensitive nonstructural components varies significantly depending on the properties of the dampers. For some combinations of dampers’ properties, the peak floor horizontal accelerations and floor spectral absolute accelerations in certain nonstructural period ranges can exceed that of the control frames without fluid viscous dampers. These results highlight the limitations of the peak floor acceleration as an engineering demand parameter for acceleration-sensitive nonstructural components.

Due to the large number of bridges that will need upgrade, retrofit, or replacement in coming years, there is an increasing need for seismic bridge design techniques that are compatible with accelerated bridge construction (ABC). This study examines one promising column design strategy, the hybrid sliding–rocking (HSR) system, which incorporates precast segmental columns with unbonded post-tensioning, and both rocking and sliding joints. The goal of the study is to evaluate damage states and identify repair strategies for these columns through integrated experimental testing and expert panel solicitation. The expert panel methods use two different established group solicitation techniques to identify seismic repair objectives for bridges and to propose repair strategies for HSR columns that are consistent with these objectives. In parallel, a series of large-scale pseudo-static cyclic tests at the Texas A&M University Center for Infrastructure Renewal are carried out on a HSR column. The column is then repaired, based on the guidance of the expert panel, and tested again. The results show that the column experiences limited damage, consisting of spalling of concrete near the rocking joints, and up to 4% drift (consistent with hazard levels with return periods greater than 4,500 years). This damage can be repaired with grout and a carbon fiber reinforced polymer jacket. Most of the residual drift can be recovered by recentering sliding joints. The panel found that the HSR columns were less damageable than conventional columns and promising for application in high seismicity areas. The damage states and repair strategies identified will facilitate future performance-based engineering assessments of the new HSR columns.

This paper examines the mean wind profiles of tropical cyclones (TCs) toward 1,000-m height with a low-level jet (LLJ) feature over the Southeast China Sea based on the newly released fifth-generation atmospheric reanalysis (ERA5) from the European Center for Medium-range Weather Forecast (ECMWF). The local TC track distributions and the statistical wind-pressure relationship in ERA5 are verified against observations. A mesoscale simulation study of Typhoon Chan-hom provides a basis for close comparison of the LLJ wind features (i.e., jet height and strength) between ERA5 data and simulated results. The composite mean TC wind profiles classified by mean boundary layer wind speed groups ($30–50\mathrm{m}/\mathrm{s}$) are produced based on an ERA5 reanalysis data set, and presented in four quadrants with respect to the storm center. The axially asymmetric properties of composite wind speed profiles are revealed in four quadrants. The composite mean wind speed profiles up to a 1,000-m height including LLJ are then characterized by fitting them to the three wind profile models, i.e., the power-law, the log-law, and the combined power-logarithmic models, for the wind-resistant structural design of supertall buildings. The main contribution of this paper is to propose a quadrant-dependent TC wind profile model considering LLJ features for determining design wind loads on supertall buildings in typhoon-prone coastal areas of China.

This research proposes an innovative method utilizing power-actuated fasteners (PAFs) for the shear connection joining cold-formed steel (CFS) plates to hot-rolled steel (HRS) plates. An experimental program comprising 66 single-lap-joint shear strength tests was conducted to investigate the behavior of the connectors and connections under quasi-static monotonic loading. The parameters studied were the thickness of the CFS sheet, the strength of the base material (i.e., HRS), the diameter of the fastener, and the manufacturers of the fasteners. Fasteners from two different companies, Hilti and Ramset, were used in the program to ensure diversity. Three failure modes were captured including (1) bearing of CFS sheet, (2) shear fracture of the fastener, and (3) pullout by shear from the HRS sheet. The test results are compared with the predictions of the equations the Australian/New Zealand Standard for cold-formed steel structures or the North American Specification for cold-formed steel structural members. It is revealed that the equation for the bearing capacity results in unconservative predictions for the specimens tested. Meanwhile, the predictions of shear fracture and pullout by shear underestimate the actual strength of the connections.

The constitutive model of concrete is the key basis for nonlinear analysis of concrete structures under disastrous dynamic actions, e.g., earthquakes. The material parameters of the constitutive model of concrete are essentially probabilistically dependent. However, in practice, it is mostly assumed that these parameters are either independent or perfectly dependent. In the present paper, the quantification of probabilistic dependence configurations between random material parameters and their effects on stochastic structural responses are investigated. Based on the ample amount of data from tested complete curves of compressive stress-strain relationships of concrete with different strength grades, the parameters in the damage constitutive model of concrete are samplewise identified. Further, the probabilistic dependence configurations are studied based on copula theory, which is also considered as a data-mining tool. The complete constitutive curves of concrete are generated according to the obtained dependence configurations and marginal distributions. Then, combined with the probability density evolution method, the stochastic response analysis of concrete structures is carried out. The analysis results show that the dependence among the strength, peak strain, and the parameter of the descendent segment cannot be ignored. Due to the constraint of dependence configurations, the distribution characteristics of the generated point set are substantially consistent with the tested results, and the generated complete stress-strain curves agree well with the tested curves at both the level of sample and the level of second-order moments. In addition, no abnormal complete stress-strain curves, e.g., those with low strength and sharp descendent segment, which are unlikely to occur in the test, are generated. The dependence configuration of the parameters of concrete has considerable effects on the response and reliability of concrete structures, and may even lead to the change of overall structural failure mode. Consequently, ignoring the probabilistic dependence of material parameters may yield misleading results for decision making. Problems to be further studied are also discussed.

A common structural design challenge arises when a new structure is built adjacent to an existing structure with a lower roof. Retrofitting the existing building for the now expected leeward snowdrift is typically difficult and expensive. Hence, a mitigation strategy that prevents the formation of a leeward drift atop the existing roof is desirable. Herein, one such mitigation strategy, specifically a wall at the interface between the new and existing structures, is considered, and the minimum wall height needed to capture the blowing snow from the new building roof will be determined.

The purpose of the presented research is to evaluate the potential future manufacturing of hot-rolled asymmetric I-beams (AIBs) for construction in building floor systems. This technical note presents some of the primary manufacturing and structural challenges. A feasibility study is conducted to numerically evaluate the potential impact of AIBs. The first part of the study investigates composite behavior of AIBs in the final constructed state. As expected, an increase in flexural strength was observed, along with a decrease in deflections. Both are clear advantages of AIBs. The second portion of the feasibility study focuses on the noncomposite section behavior during construction. Stability concerns are present for unbraced lengths typically seen during construction. The primary finding was the benefit of reducing the thickness versus reducing the width of the top flange. Future AIB dimensions should consider thin top flanges with sufficient width to maintain adequate lateral-torsional buckling and local buckling strength. The latter portion of this technical note presents future direction of the research to comprehensively understand the behavior of hot-rolled AIBs. The focus is on extensive numerical simulation studies validated through full-scale laboratory experiments. The experiments are to be conducted on proof-of-concept AIBs produced by Nucor steel. The validated numerical modeling approaches will then be utilized for larger parametric studies to develop cross-section proportional limits (e.g., width-to-thickness ratios). These limits will be used to establish specific AIB cross-section dimensions.