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This paper introduces a methodology for developing collapse fragility curves for windstorms, with a focus on assessing collapse of electrical transmission towers for hurricane events. Incremental dynamic analysis (IDA) that incorporates the entire hurricane duration is adopted for collapse modeling. Fragility curves are cumulative distribution functions of a structural limit state such as collapse capacity, which is designated in this work as the intensity measure associated with the onset of collapse. A suite of selected hurricane wind records are used with IDA to propagate uncertainties from wind speeds, directions, and durations to collapse capacities. Compared with earthquake engineering methodologies, this work proposes appropriate approaches for scaling of wind records, fitting of IDA curves from simulation data, and parameter estimation of hurricane fragility curves. Fragility curves are appropriate for use both to quantify uncertainty in the context of performance-based wind design and for regional loss assessments. As inelastic deformations are allowed in performance-based wind design, it is useful to develop fragility curves based on nonlinear time history analysis for the entire windstorm duration, which has not been addressed in prior work. • Collapse fragility curves are developed for transmission towers under hurricanes. • Incremental dynamic analysis is used for the entire hurricane duration. • Uncertainties in hurricane wind speeds, directions, and durations are considered. • Fragility curves are developed for a region. [ABSTRACT FROM AUTHOR]

Abstract Design for Deconstruction (DfD) is a design approach that enables reuse of durable building components, including structural materials, across multiple building projects. An important DfD strategy is the use of pre-fabricated modular building assemblies and reversible connections, in contrast to cast-in-place composite systems that must be demolished at building end-of-life. In this paper we evaluate a novel DfD flooring system consisting of pre-cast concrete planks and clamped connections. Life cycle energy and environmental benefits of using this DfD system are evaluated using life cycle assessment (LCA) across four impact categories of interest to the building and construction sector including fossil fuel use, greenhouse gas emissions, respiratory effects, and photochemical smog formation. Eight different DfD building designs are tested for 0–3 reuses compared with a traditional structural design, with energy and environmental benefits accruing from substitution of avoided structural materials. Designs reflect expected loads and current code requirements, while the additional time required for deconstruction of DfD buildings is accounted for in the construction schedules. Monte Carlo simulation is used to generate 95% confidence intervals for the results. In general, DfD designs result in higher initial (original building) energy use and environmental impacts, but have statistically lower impacts than traditional designs if flooring planks are used at least once. Reusing planks three times as designed decreases impacts by a mean value of of 60–70%, depending on the building configuration and impact category. Energy use and environmental impacts from eventual recycling and/or disposal of the reusable components are significant, and emphasize the relative benefits of reuse over recycling. Highlights • Direct reuse of building materials is enabled by Design for Deconstruction (DfD). • DfD clamped precast composite flooring systems can replace cast-in-place decking. • Life cycle assessment reveals energy and environmental savings for DfD with reuse. • Actual disassembly and reuse practices depend on location and market forces. [ABSTRACT FROM AUTHOR]

The use of elastic analysis is prevalent in the design of building structures even under loading conditions where inelasticity would be expected. Accordingly, geometric and material properties used in the elastic analyses must be carefully selected to maintain accuracy. Steel-concrete composite columns experience different forms of inelasticity. Concrete cracking is the source of much of the inelasticity and occurs at relatively low levels of load, but partial yielding of the steel, slip between concrete and steel, and concrete crushing also contribute to losses in stiffness. In this paper, the behavior of composite columns is characterized at the cross section and member levels through comparisons between inelastic and elastic analyses. Then, through a broad parametric study, specific practical design recommendations are developed for the elastic flexural rigidity of composite columns for the determination of lateral drifts under service loads. The recommendations in this paper provide simple and robust values for the stiffness of composite columns to be used for drift computations involving lateral loads. [ABSTRACT FROM AUTHOR]

Abstract: Current techniques for the rating of horizontally curved composite steel girder bridges often use approximate methods of linear elastic analysis based on the assessment of individual straight girders with altered properties to account for member curvature. This paper summarizes measured versus computed results from a field test with heavy live load conducted on a multi-span, horizontally curved composite steel I-girder bridge in Duluth, Minnesota. Eight 320 kN (72,000 lb) trucks were placed on the bridge in 43 static and 13 dynamic loading configurations, and the results were compared to those obtained from linear elastic grillage analyses. Stresses up to 75% of the girder yield stress were obtained in the bridge, whose design was controlled by strength, thus representing some of the largest stresses ever achieved in an instrumented curved steel girder bridge, and behavior is described in the girders, diaphragms, lateral wind bracing, deck, bearings, and fatigue details. Grillage analyses are developed and used to corroborate the results and assess the accuracy of these procedures for load rating of bridges. [Copyright &y& Elsevier]

Abstract: The 2005 AISC Specification for Structural Steel Buildings is the leading specification for composite construction in the US. However, these provisions do not provide a recommendation for computing the strength of headed steel stud anchors (traditionally used as shear connectors) under tension or combined tension and shear. Headed stud anchors are subjected to these types of forces in composite structures such as infill walls, composite coupling beams, the connection region of composite columns, or composite column bases. While the ACI 318-08 Building Code, the PCI Handbook, 6th edition, and CEB Design of Fastenings in Concrete include provisions for such conditions, those provisions are geared for more general anchorage conditions than are typically seen in composite construction. It would thus be beneficial to have design guidance specifically for the case of headed steel stud anchors subjected to tension or combined tension and shear in composite construction, evaluated within the context of the AISC and EC-4 Specifications. In this work, different strength equations to compute the nominal tensile strength of a headed stud are reviewed and compared to experimental results. The resulting recommendations seek to ensure a ductile failure in the steel shank instead of a brittle failure within the concrete. Several criteria are proposed to ensure that ductile failure controls in composite construction, and, different headed stud configurations and detailing reinforcement recommendations are proposed to improve the ductile behavior of headed stud anchors subjected to tension and combined tension and shear. [Copyright &y& Elsevier]

Abstract: The formula in the 2005 American Institute of Steel Construction Specification to compute the strength of headed steel stud anchors (shear connectors) in composite steel/concrete structures has been used in the United States since 1993, after being proposed based primarily on the results of push-out tests. In the past several decades, the range of members used in composite structures has increased significantly, as has the number of tests in the literature on the monotonic and cyclic behavior of headed studs in composite construction. This paper reviews 391 monotonic and cyclic tests from the literature on experiments of headed stud anchors and proposes formulas for the limit states of steel failure and concrete failure of headed stud anchors subjected to shear force without the use of a metal deck. Detailing provisions to prevent premature pryout failure are also discussed. This paper also reviews proposals from several authors and provides recommended shear strength values for the seismic behavior of headed studs. The limit state formulas are proposed within the context of the 2005 AISC Specification, and comparisons are made to the provisions in the ACI 318-08 Building Code, the PCI Handbook, 6th Edition, and Eurocode 4. The scope of this research includes composite beam–columns [typically concrete-encased steel shapes (SRCs) or concrete-filled steel tubes (CFTs)], concrete-encased and concrete-filled beams, boundary elements of composite wall systems, composite connections, composite column base conditions, and related forms of composite construction. [Copyright &y& Elsevier]

Abstract: This study investigates the implications of the use of alternative damage prediction methodologies to correlate ground shaking intensity to socio-economic losses in regional seismic loss analyses. In particular two methodologies are investigated: the over-damped Capacity Spectrum Method (CSM), and a modified version of a Parameterized Fragility Method (PFM) based on dynamic nonlinear analysis to reflect the generalized effects of degradation in hysteretic response. Investigations include comparisons of a variety of structural systems first assuming full hysteresis to minimize the discrepancies in modeling approaches, as well as parametric variations in ground motion intensity and degradation effects. The study culminates with an investigation of the influence of the application of each methodology on regional loss estimates, using a seismic risk analysis performed for the state of South Carolina as a case study, by comparing seismic loss estimates obtained using the over-damped CSM with estimates obtained by application of a modified PFM (MPFM). It is shown that the estimates obtained from the two methodologies are different, and that the over-damped CSM displays increased sensitivity to key analysis parameters relative to the MPFM method both in terms of displacement demands and estimated socio-economic losses. [Copyright &y& Elsevier]

Abstract: This paper presents an experimental study of the cyclic behavior of a composite structural system consisting of partially-restrained (PR) steel frames with reinforced concrete infill walls. The composite interaction is achieved through the use of the headed stud connectors along the steel frame–infill interfaces so that the two main components of the system share in the resistance of lateral shear and overturning moment. Having the relatively light steel frame constructed using PR connections maximizes the economy of the system, while still ensuring system integrity in the post-peak range of deformation. The one-bay, two-story test specimen was built at one-third scale. The study shows that this system has the potential to offer strength appropriate for resisting the forces from earthquakes and stiffness adequate for controlling drift for low- to moderate-rise buildings located in earthquake-prone regions. Redundancy is also exhibited in this system through alternate load paths occurring at different levels of loading, including shear stud–infill interaction, steel frame–infill strut interaction, and deformation of the steel frame. Improvement is needed for reducing the post-peak strength degradation observed in the present study. [Copyright &y& Elsevier]

This paper reports on the behavior of headed shear stud connectors for use in steel frames with partially restrained connections and reinforced concrete infill walls, attached compositely to the steel frame around the perimeter of each wall panel (S-RCW system), subjected to seismic loading. In infill walls, the shear connectors lie in the plane of the concrete panel, which results in different behavior from studs in composite beams, for which the majority of past research has been conducted. In particular, shear connectors in infill walls are subjected to axial tension and compression forces due to sidesway and overturning of the S-RCW system, are influenced by the parallel edges of the wall, and are subjected to cyclic forces.An experimental program was developed to quantify the strength and deformation capacities of shear studs for use in S-RCW infill systems addressing the above issues, and to verify existing AISC, PCI, ACI, and Japanese design equations. A modification of the classic push-out test setup was made to accommodate the application of cyclic shear loading and axial tensile loading. Two different steel reinforcement configurations were used, one providing little confining reinforcement around the shear studs, and the other utilizing a steel reinforcement cage to provide ample confinement to the shear stud. [Copyright &y& Elsevier]

The evolution of the shape of limit surfaces during plastic excursions is a key component of the inelastic response of structural members. However, stress-resultant-based computational plasticity formulations rarely account for any change in shape of the loading or ultimate strength surfaces. This research documents the evolution of the shape, size, and position of the loading and ultimate strength surfaces in stress-resultant space for wide-flange steel shapes subjected to cyclic proportional and nonproportional loading having a combination of axial force and either strong- or weak-axis flexure. The evolution is based on numerical integration of the cross-section stresses assuming a cyclic uniaxial stress–strain curve with a trilinear backbone that accounts for the Bauschinger effect. Surface evolution is investigated both with and without residual stresses. The results indicate that the evolution in shape of the loading surface, while relatively path-independent, is substantial, particularly at high levels of plastic excursion, where the loading surface essentially vanishes. The evolution in shape of the ultimate strength surface, in contrast, is mild. The research also documents the relative magnitudes of the components of cyclic plastic deformation. Recommendations are provided for the estimation of the direction of cyclic plastic flow through the calculation of gradients to the limit surfaces within the assumption of using an associated flow rule in stress-resultant space. [Copyright &y& Elsevier]

Research within the United States on seismic engineering of buildings using composite steel/concrete structural systems has increased dramatically in the past decade. This paper summarizes recent research on a number of these composite lateral resistance systems, including unbraced moment frames consisting of steel girders with concrete-filled steel tube (CFT) or steel reinforced concrete (SRC) columns; braced frames having concrete-filled steel tube columns; and a variety of composite and hybrid wall systems. The benefits of these structural systems relative to more common systems include their performance characteristics when subjected to service or ultimate loads, and their economy with respect both to material and construction. In addition, more in-depth research results will be presented on one of these composite systems, consisting of partially-restrained steel frames with composite reinforced concrete infill walls. The paper concludes with a summary of probable future design provisions for these composite systems. [Copyright &y& Elsevier]

This paper presents a three-dimensional mixed beam element formulation for fully nonlinear distributed plasticity analysis of members composed of sections with no significant torsional warping such as steel angles and tees. This formulation is presented using a corotational total Lagrangian approach and implemented in the OpenSees corotational framework. In this context, a basic coordinate system is lined up with the element chord and translates and rotates as the element deforms. The element tangent stiffness matrix and resisting forces in the basic system are derived through linearization of the two-field Hellinger-Reissner variational principle. The displacement shape functions are cubic Hermitian functions for the transverse displacements and a linear shape function for the axial and torsional deformation. The generalized stress resultant shape functions are linear for moments and constant for axial force and torque with the P - δ effect considered, which are developed from equilibrium equations. The fiber section method with uniaxial constitutive laws is adopted to account for material nonlinearity. Since the degrees-of-freedom in the basic system are defined with respect to different reference points, all element responses are transformed to acting about the shear center before conducting the corotational transformation. The mixed element is validated through a number of experimental and numerical examples. • A mixed finite beam element for beams with no significant torsional warping is developed. • The corotational total Lagrangian method is used to model the axial-flexural-torsional interaction behavior. • This element is free of membrane locking. • This element can represent a nonlinear curvature field within the element. • Modeling of geometric and material nonlinearities is validated. [ABSTRACT FROM AUTHOR]

Tapered members produced by robotic fabrication techniques offer architectural and structural advantages and have the potential to become more prevalent than prismatic members. However, the conventional analysis and design methods based on simplified assumptions such as equivalent stiffness cannot be used to accurately evaluate a member's performance. To provide a reliable and practicable stability design method, a direct analysis method of tapered I sections is proposed. A mixed-field tapered beam-column element is derived for use within the modeling of structural frames. The effects of initial geometric imperfection and additional shear stress are directly considered in the element formulation. A polynomial describing the member's critical initial out-of-plumbness is adopted, and an arbitrarily located internal hinge is incorporated in the element to enhance the element's deformation capacity and capture the behaviors of the most critical section. Displacement and force interpolation matrices incorporating the shear deformation are utilized, and the Gauss quadrature method is employed to evaluate the element stiffness matrix. Finally, verification examples demonstrate that the proposed method can be used to accurately and efficiently evaluate the performance of tapered members, indicating that the element can be conveniently employed in member and frame analysis and design. • A tapered Timoshenko beam-column with internal degrees of freedom is proposed. • The effects of member initial imperfections and shear deformation is incorporated. • The effect of additional shear stress is considered through the section flexibility matrix. • The critical initial geometric imperfection function for tapered members is adopted. • One element per member direct analysis method is achieved. [ABSTRACT FROM AUTHOR]

Abstract This paper presents the results of pushout test of deconstructable clamping connectors which are utilized to connect precast concrete planks and steel beams in a deconstructable composite floor system. A specified turn-of-the-nut rotation was first established to ensure reliable pretension in the bolts. Nine specimens were then tested to study the effects of key parameters, including bolt diameter, reinforcement layout, loading protocol, use of shims and number of cast-in channels. It is shown that the clamping connectors have excellent slip capacity, ductility and energy dissipating capacity. The characteristics of the clamps are compared to steel stud anchors in terms of strength, stiffness and ultimate slip. Design recommendations are also provided to predict the slip and peak strengths of the clamps under monotonic and cyclic loading. Highlights • A deconstructable composite floor system utilizing clamping shear connectors is proposed. • Monotonic and cyclic pushout tests were conducted to study the behavior of the clamps. • Under monotonic loading, the M24 clamps retain approximately 80% of the peak strength at 127 mm (5 in.) slip. • The clamping connectors can withstand large slips with minimal damage. • Design equations are provided to predict the strength of the clamps. [ABSTRACT FROM AUTHOR]

Highlights • A new descriptor's been proposed for seismic performance of ductile moment frames. • New seismic demand models and collapse fragility relations are obtained for frames. • The new collapse fragility relations are compared with the traditional approaches. • The developed techniques help achieve reliable prediction of structural collapse. Abstract In assessing the likelihood of structural collapse under strong earthquake motions, uncertainties in structural properties and ground motions can be incorporated by use of a probabilistic analysis framework in conjunction with analysis methods such as incremental dynamic analysis (IDA). Maximum inter-story drift ratio (IDR) is typically selected as the key descriptor to characterize the global behavior of structural system in such a probabilistic assessment. The structural collapse capacity is often defined in terms of a threshold value of IDR or a reduced slope of the IDA curve between a selected seismic intensity measure and the corresponding IDR. However, collapse assessment approaches based on IDR may not accurately represent the overall structural collapse behavior due to redistribution and variation of local damage within the structure. Moreover, results of collapse predictions are found to be sensitive to variability in such drift measures, and assumed threshold values used in the collapse criterion. Recently, an energy-based seismic collapse criterion has been developed to describe collapse in terms of dynamic instability of the whole structural system caused by gravity loads. Using the energy-based collapse criterion, this paper proposes a more effective sidesway collapse risk assessment approach of ductile planar frames subjected to horizontal seismic loadings based on a new key descriptor of structural performance. The key descriptor, designated as the equivalent-velocity ratio, is related to the ratio of the energy dissipated through structural degradation to the seismic input energy. Using the equivalent-velocity ratio, a probabilistic collapse assessment method is developed for systematic treatment of uncertainties in the ground motions. [ABSTRACT FROM AUTHOR]

The prediction of collapse of structures has gained growing attention recently, as it is important to be able to predict and model structural collapse due to extreme loads. A lack of accurate, pragmatic, and validated structural collapse models currently limits the capabilities for predicting collapse due to possible extreme loads. This research compares three finite element deletion strategies that account implicitly for fracture under monotonic loading to be used as predictive tools for collapse modeling of steel structures. The first strategy employs a Void Growth Model (VGM) to simulate the initiation of softening and the Hillerborg model for modeling of material softening, followed by an element deletion strategy that is developed in this framework. The second strategy adds a Bao-Wierzbicki model to the VGM strategy (VGM-BW) in order to account more directly for fracture initiation in lower and negative triaxiality regions. The third strategy is a constant critical strain (CS) approach that does not include softening but instead deletes an element when it achieves a peak equivalent plastic strain. The parameters of the VGM strategy were calibrated to a comprehensive set of experimental test results of circumferentially notched tensile (CNT) coupon specimens, the Bao-Wierzbicki parameters in VGM-BW strategy were determined analytically through tensile coupon (TC) specimens, and the CS approach used a constant value for equivalent plastic strain at softening initiation. These strategies were then validated through comparison with experimental test results of specimens commonly used for material characterization of steel. The results establish the accuracy and effectiveness of the VGM strategy for high-fidelity parametric simulation capabilities for collapse of steel structures and provide recommendations for where additional experimental research is needed to validate regions of low and negative triaxiality. [ABSTRACT FROM AUTHOR]

One of the most common approaches to assess the collapse capacity of structures under earthquakes is incremental dynamic analysis (IDA), which tracks relationship between a structural damage measure and a ground motion intensity measure by so-called IDA curves. This IDA approach often uses collapse criteria given in terms of a large value of the maximum inter-story drift ratio, plastic hinge formations at structural components, or flattening of the IDA curve. However, these collapse criteria may not accurately represent the overall collapse behavior of structural systems due to redistribution and variation of damage within the structure. Moreover, collapse predictions by these subjective collapse limit-states are found to be sensitive to the assumed threshold values and to the characteristics of IDA curves. For more accurate assessment of collapse capacity and the likelihood of the collapse, this paper proposes a new collapse criterion that describes dynamic instability of frame structures in terms of the balance between the energies from the applied gravity loads and input ground motions. The collapse criterion is developed for planar frames under horizontally applied earthquakes and then tested using computational models of collapse behavior of ductile steel frame structures, which are validated by experiments reported in the literature. The collapse prediction results by the developed collapse criterion and existing criteria are compared in order to investigate sensitivity of the prediction results with respect to threshold values used by existing approaches. The results show that the proposed energy-based seismic collapse criterion is a more reliable option for assessing structural collapse of planar frames. The energy-based criterion can represent global dynamic instability of structural system more effectively by using aggregated quantities of energy responses of structural components instead of using assumed threshold values for structural responses such as story drifts. [ABSTRACT FROM AUTHOR]

Abstract: Research has been conducted to better understand the effect of fillers in bolted steel connections. In a companion paper, the results of sixteen experiments on bolted steel slip-critical connections with fillers are presented along with proposed design recommendations. In this paper, detailed behavior of the specimens is documented through an examination of deformation and strain response. Additionally, mechanisms are proposed that clarify key aspects of the behavior of bolted connections with fillers, including prediction of slip and shear strengths. A stochastic analysis, using order statistics, is employed to quantify the detrimental effects of multiple possible slip surfaces on expected slip strength. The use of multiple plies and the effects of developing the filler plate are investigated with respect both to the experimental results and the proposed behavioral mechanisms. The results indicate that the use of multiple plies exacerbates the detrimental effects on slip strength and, to a lesser extent, on shear strength. Furthermore, filler development reduces and in many cases eliminates the reduction in slip and shear strengths. [Copyright &y& Elsevier]

Abstract: This paper reports the results of sixteen experiments of bolted slip-critical connections with fillers. Fifteen of the connections used oversized holes and one connection used standard holes. Such connections with oversized holes are commonly fabricated for use with structures such as long-span trusses, since the use of oversized holes allows erection in-place rather than first assessing fit-up on the ground. Filler plates are used to connect members of different depths or widths. The sixteen experiments reported herein highlight the behavior of bolted steel connections with oversized holes in which fillers are included and are undeveloped, partially developed, or fully developed. Both single-ply and multi-ply fillers are investigated, as are welded developed fillers, and specimens fabricated using either turn-of-the-nut or tension control bolts to pretension the connection. The results augmented with previous literature document the slip and shear strengths of these connections, propose formulas for assessing these strengths for the different conditions investigated, and provide recommendations for design of these types of connections. [Copyright &y& Elsevier]

Abstract: This paper examines the structural behavior of bridge timber piles under eccentric compression loading. Samples of the piles were retrieved from a recently collapsed bridge and experimentally tested under compression and combined compression and flexure. The experimental timber pile response was used to calibrate a numerical model of full timber piles of a prototype bridge, including material and geometric nonlinearity as well as soil–structure interaction. The numerical results illustrated that the pile strength was significantly reduced under eccentric load compared to concentric load. Therefore, it was concluded that the effect of compression–flexure interaction on bridge timber piles must be checked during bridge design and/or rating, especially in the case of simply supported superstructures where loading on one span may lead to eccentric loading on a timber pile group. [Copyright &y& Elsevier]

This paper presents a finite element-based model for direct simulation of cyclic fracture in steel components and connections with application to predicting failure and collapse of steel structures. The formulation couples a plasticity model for large deformations that captures plastic work stagnation and the Bauschinger effect with a two-stage damage model to simulate fracture initiation, propagation, and failure through an element deletion strategy. The model includes the non-proportional loading and load-history effects in the fracture initiation and propagation process. Fracture initiation and propagation is controlled using new fracture initiation strain and fracture energy surfaces with stress triaxiality and Lode angle dependance that can represent different fracture behaviors. Model calibration is discussed for common grades of structural steel, weldments and bolts using typical material tests. The model capabilities are validated against experiments including ancillary material tests, components, and subassemblies of steel structures that experienced fracture subjected to monotonic and cyclic loading. A culminating validation is conducted on a four-story steel frame structure tested to collapse. The proposed model provides a robust and valuable tool for stability analysis and simulations of damage and collapse triggered by fracture in components and connections of three-dimensional steel structures subjected to extreme loads. [Display omitted] • A two-stage damage model is coupled to a plasticity model for large deformations to simulate damage that leads to fracture. • Cyclic fracture model includes non-proportional loading and load history effects on damage accumulation. • New fracture energy and fracture initiation strain surfaces are proposed to control the material stress response softening. • Stress triaxiality and Lode angle dependance implemented through a function that can represent a large family of surfaces. • Validation against experiments highligths the model's robustness in the analysis of steel structures including fracture. [ABSTRACT FROM AUTHOR]

• Two FE deletion strategies that account for fracture are compared and validated. • Specific parameters' influence on performance of FE deletion strategies is discussed. • FE deletion strategies that account for triaxiality have greatest degree of accuracy. Collapse prediction of steel structures should incorporate a finite element model that accounts for ductile fracture through material separation in critical structural members. Finite element deletion approaches have been used successfully in the past to account for fracture in steel members. However, the current common approach in collapse modeling of steel structures, a constant critical strain strategy (CS), typically requires recalibration when used with different structural configurations due to the fact that it does not account for triaxiality, which is a primary parameter in ductile fracture. To better predict structural response of steel structures undergoing collapse, it is important to study the effect of triaxiality on fracture in steel structures. A new finite element deletion approach that accounts for triaxiality was previously proposed, calibrated, and validated in small steel specimens for use in predicting collapse of steel structures. In this approach, fracture initiation is modeled using Void Growth Model (VGM) and the subsequent softening of the material to element deletion is modeled by a Hillerborg model. This paper describes the change of triaxiality, equivalent plastic strain, and other parameters during the duration of the loading, influencing the strategies implemented and provides explanation for the performance shown. In addition, the paper examines the effect of triaxiality on accurately predicting fracture in steel structures through comparison of VGM to CS strategy with validation in simulations of full-scale structural steel connection and frame tests without recalibration. The VGM strategy provided an accurate prediction based on calibration to test results that are most widely available for different types of structural steels, while CS strategy frequently provided less accurate results. The VGM strategy thus allows for an accurate collapse modeling of steel structures for use by researchers, code developers, and practitioners who address collapse of steel structures. [ABSTRACT FROM AUTHOR]

A barrier to the development of the offshore wind resource along the U.S. Atlantic coast is a lack of quantitative measures of the risk to offshore wind turbines (OWTs) from hurricanes. The research presented in this paper quantifies the risk of failure of OWTs to hurricane-induced wind and waves by developing and implementing a risk assessment framework that is adapted from a well-established framework in performance-based earthquake engineering. Both frameworks involve the convolution of hazard intensity measures (IMs) with engineering demand parameters (EDPs) and damage measures (DMs) to estimate probabilities of damage or failure. The adapted framework in this study is implemented and applied to a hypothetical scenario wherein portions of nine existing Wind Farm Areas (WFAs), spanning the U.S. Atlantic coast, are populated with ∼7000 5 MW OWTs supported by monopiles. The IMs of wind and wave are calculated with a catalog representing 100,000 years of simulated hurricane activity for the Atlantic basin, the EDPs are calculated with 24 1-h time history simulations, and a fragility function for DM is estimated by combining variability observed in over one hundred flexural tests of hollow circular tubes found in the literature. The results of the study are that, for hurricane-induced wind and wave, the mean lifetime (i.e., 20-year) probability of structural failure of the tower or monopile of OWTs installed within the nine WFAs along the U.S. Atlantic coast ranges between 7.3 × 10 −10 and 3.4 × 10 −4 for a functional yaw control system and between 1.5 × 10 −7 and 1.6 × 10 −3 for a non-functional yaw control system. [ABSTRACT FROM AUTHOR]

This paper studies the mechanical behavior of the circular concrete filled steel tubes (CCFTs) under axial tension. A group of three CCFTs with different steel ratios and in-filled concrete diameters are tested and compared with hollow steel tubes (HTs). Based on the experimental results in the present and previous studies, three key issues of CCFTs under tension, i.e. the confining-strengthening effect , the confining-stiffening effect , and the tension-stiffening effect , are studied at both the stress-resultant level (i.e., force-displacement relationship) and stress levels (i.e., stress-strain relationship). Due to the tendency of the shrinking and slipping of the steel tube in relation to the infilled concrete, the confining contact stress and bonding shear stress, in the vertical and tangential direction respectively, are distributed in the interface between the steel and concrete, which results in the confining and bonding effect of the CCFTs. At the stress-resultant level, the test results demonstrate that the strength and stiffness of CCFTs are average 10% and 29% larger than those of HTs, respectively. The strength increase is contributed by the confining-strengthening effect, and the stiffness enhancement is a combined result of the confining-stiffening and tension-stiffening effects. At the stress-strain level, the measured strains show that the steel tube of the CCFT is in the state of the bi-axial tensile stress state because of the difference of the Poisson's ratio between steel tube and infilled concrete, which contributes to the confining-strengthening and confining-stiffening effects of the CCFTs. In addition, a fractal cracking phenomenon of the core concrete of tensile CCFTs is observed and discussed. [ABSTRACT FROM AUTHOR]

Abstract: In this work, experiments on composite connections consisting of steel girders framing into concrete-filled steel tube (CFST) beam-columns conducted in recent years were investigated and the test results were compared with the calculation results of the AIJ specification, the calculation method proposed by Fukumoto and Morita, and the calculation method verified by Nishiyama et al. Through data analysis, the study confirmed the applicability of each of the three methods. The ultimate shear strength calculation results of Fukumoto and Nishiyama were found to be more accurate and reliable than AIJ specification procedure, and the shear yield strength calculation results of the two methods were also shown to be appropriate. Through a parametric analysis, this study confirmed that the three methods have a broad applicability for joints of various axial compression ratios, connection formations and column cross sections. The analysis results suggested that the applicable steel tensile strength and concrete compression strength for the AIJ specification should not exceed 450MPa and 70MPa, respectively, and the applicable ratio of steel tensile yield strength to concrete compression strength should not exceed 8 for the AIJ procedure to yield accurate results. This paper also provides proposed amendments to these procedures for joints having special connection details. [Copyright &y& Elsevier]

Abstract: Seismic isolation is a well-accepted bridge design philosophy for providing earthquake resistance, but the design complexity and higher cost of construction can make this approach relatively less attractive in regions of moderate seismic hazard or with the potential for large earthquakes only at long recurrence intervals. Quasi-isolation is an innovative, yet economical and pragmatic, design philosophy that employs typical bridge bearings as fuses to ensure predictable seismic structural response. This paper presents computational models for evaluating quasi-isolated bridge systems, where certain bearing components can slide and limit the forces transferred between the superstructure and substructure. Nonlinear elements have been formulated to capture the local bi-directional stick–slip behaviors in the bridge bearings and the bilinear (and eventual fracture) behavior of steel retainers that limit transverse bearing movement. A bridge prototype is described, with the anticipated nonlinear behaviors in the structural components defined and implemented in a finite element model of the global structure. Static and dynamic pushover analyses are performed in both longitudinal and transverse directions to demonstrate limit states and progression of damage in the bridge structure. Results indicate that the abutment backwalls provide significant force capacity in the longitudinal direction. In the transverse direction, the force capacities of the retainers and fixed bearings have a significant influence on global bridge behavior and therefore should be appropriately proportioned to allow for effective quasi-isolation of such bridge structures. [Copyright &y& Elsevier]

Cladding details that span the building envelope are particularly susceptible to forming thermal bridges, where heat is transferred between interior and exterior, resulting in loss of energy. Steel buildings are particularly susceptible to forming thermal bridges due to the relatively high thermal conductivity of steel compared to that of other structural materials. To mitigate these thermal bridges, thermal breaks may be inserted in the cladding detail connection to the building interior, and have demonstrated promise in previous thermal modeling studies, with up to 65% reduction in thermal bridging. This paper summarizes recent work on the design, validation, and implementation of thermal break strategies that maintain structural integrity. Fiber-reinforced polymer (FRP) shims were used to provide thermal breaks in steel connections of cladding details. Partial replacement of steel structural members with FRP members was also explored. Shims were the focus of the work due to ease of installation, cross-section availability, and thermal performance. While several cladding details were examined in this research, this paper summarizes the cyclic performance of roof posts (under axial and cyclic lateral loads) and canopy beams (under cyclic lateral loads only), representing their anticipated performance during earthquakes and wind events. While roof posts and canopy beams exist in a range of applications in building construction, structural archetypes selected for this work represent lightly-loaded examples that are common in the field. The impact of adding FRP shims at the bolted base plate connection to the building interior is discussed. Recommendations for design and future research are also presented. [Display omitted] • Fiber reinforced polymer (FRP) shims are thermally and structurally viable as structural steel connection thermal breaks • It is possible to design for FRP shims in axially- and laterally-loaded cantilever base plate connections • FRP shims do not negatively impact the performance of lightly-loaded steel cantilevers [ABSTRACT FROM AUTHOR]