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The primary objective of this work is to provide connection-level force-deformation response appropriate for standard cold-formed steel (CFS) framed steel sheet sheathed shear walls under c...

Second-generation trapezoidal sheeting, characterised by longitudinal stiffeners in webs and flanges, is loaded near a support by a concentrated force and a bending moment. Currently, design codes predict related failure by: (a) determining the ultimate bending moment via the effective width approach or the Direct Strength Method (DSM); (b) finding the web crippling load via a curve-fitted formula; and (c) using an interaction rule to take into account the load combination. However, the effective width approach is quite complex to use for many longitudinal stiffeners, and the accuracy of the design codes is subject to improvement. Moreover, nowadays the DSM provides a consistent and well-established method to predict ultimate loads for cold-formed steel structures. Therefore, in this paper the application of the DSM for combined bending and web crippling of second-generation sheeting is investigated. First, to create a set of numerical experiments, an internationally representative set of second-generation trapezoidal sheeting types is found, and these types are used to design numerical three-point bending experiments with relevant span lengths and load bearing plate widths. Then, finite element models are developed and verified, and used to predict the buckling, yield, and ultimate loads for the set of numerical experiments. Additionally, all simulations are also carried out for pure bending, and (Interior One Flange) IOF and (Interior Two Flange) ITF web crippling cases. With the resulting data, an explicit DSM approach is developed, fitted to the data of the three-point bending simulations, which predicts the ultimate load for combined actions directly. Hereafter, also an interaction DSM approach is studied, which first predicts the ultimate bending moment by the DSM (by fitting the pure bending simulations), then the web crippling load by the DSM (by fitting either the IOF or ITF simulations), and then uses a classic interaction rule for the load combination. The explicit and implicit DSM approaches perform equally well, with a Coefficient of Variation (CoV) equal to 0.13. As most commercially available sheeting has been incorporated, and the DSM approaches allow for sections with an arbitrarily number of stiffeners in the web (different from the current design codes), it is recommended to include the DSM in future code revisions. The interaction DSM approach resembles the current design rules most and may therefore be preferred; however, the explicit approach is more direct and certainly deserves consideration too.

The objective of this work is to develop design guidance for existing hollow steel columns that are retrofitted by infilling concrete into the tubes. The primary challenge is the unknown effect of the existing preload on the steel columns prior to the concrete infill. Composite performance and buckling behaviour of circular hollow section (CHS) steel columns strengthened by infilling concrete under preload was experimentally and numerically investigated in this study. A total of 34 CHS steel columns were tested under pin-ended boundary conditions, and the overall buckling failure modes and corresponding ultimate buckling resistances were recorded. Prior to the member testing, material properties of the steel columns and the infilled concrete were attained. By means of the finite element (FE) software package ABAQUS, elaborate FE models for the CHS columns strengthened by infilling concrete were developed and validated against the obtained test results, which were further verified with other available test data. Using the validated FE models, systematic parametric studies were conducted to examine the influences of the major factors affecting the ultimate capacities of the CHS columns strengthened by infilling concrete, including preload ratios, steel and concrete strengths, steel ratios, initial global imperfections, eccentricity ratios and column slenderness ratios. The obtained test and numerical results were therefore utilised to develop design criteria for predicting the overall buckling resistance of CHS steel columns strengthened by infilling concrete. In view of the difficulty of determining the key parameters in practice and the uncertainty of the strengthening process, a new simplified design coefficient was proposed, taking into account the influence of the preload. It has been demonstrated that accurate and reasonable strength predictions can be provided by the proposed design method.

The objective of this paper is to investigate the moment-rotation behavior of floor-to-wall connections used in ledger-framed cold-formed steel building construction with full-scale experiments. Recently completed research employing full-scale shake table tests on a two-story ledger-framed cold-formed steel framed building utilizing oriented strand board (OSB) sheathed shear walls and floors exhibited beneficial lateral system response that exceeded predictions. One hypothesis is that the stiffness of the floor-to-wall connections, and the repetitive nature of this connection, provided beneficial semi-rigid frame response that augmented the designed shear walls. Monotonic and cyclic full-scale connections were tested and reported here to examine the connection strength and stiffness, so that this hypothesis may be explored further in the future. The test matrix is designed to evaluate the presence of OSB floor sheathing, applied moment/shear ratio of the joist, joist-to-ledger clip angle location (inside or outside of the joist section), presence of top and bottom screws connecting the joist and ledger flanges, and location of the joist relative to the studs. The results indicate how the connection details and loading conditions drive the moment-rotation response; in addition, several limit states not checked in current design were also observed. Current design for this connection assumes a pure shear condition governed by screw shear capacity. However, ledger-to-stud screw pull-out, ledger flange buckling, and stud web crippling limit states are all observed in the testing. Design methods to support strength predictions consistent with the observed limit states are developed and assessed. The testing provides needed characterization of cold-formed steel floor-to-wall performance and is augmented by improved design methods for this detail.

This work studied the cyclic shear performance of connectors used for sidelap and structural connectors in bare steel deck roof diaphragms. Typical bare steel deck roof diaphragms include t...

The objective of this paper is to propose relationships for the reduction in mechanical properties of cold-formed steels at elevated temperature. Predicting the degradation of strength and ...

Cold-formed steel (CFS) framed construction has been widely adopted and used toward a modern, lightweight, and cost-efficient engineering practice across the United States. The primary obje...

The objective of this work is to investigate the shear capacity of small end distance lap joints in sheet steel fastened with a single bolt. For bolted connections in shear, the current Ame...

Performance-based earthquake engineering (PBEE) provides a robust alternative to traditional earthquake design. PBEE enables engineers to estimate expected damage, repair costs, and economic losses due to downtime for a candidate design, potentially leading to novel new designs or retrofit solutions. With the increasing application of light-frame structural systems, such as cold-formed steel (CFS) panels, in residential and commercial construction, it is necessary to develop and employ fragility functions for these systems to enable PBEE. In this regard, a set of fragility functions was previously developed by researchers based on a series of monotonic and cyclic tests for CFS framed shear walls with wood structural panel sheathing, flat strap X-bracing, and steel sheet sheathing. Recently, the senior author has led in the development of a large database of CFS framed shear wall tests, including 617 monotonic and cyclic tests conducted in the last 20 years from 25 primary sources. Based on the wider database, the fragility functions for CFS framed shear walls are re-evaluated. The developed fragility functions provide updated knowledge for application of PBEE per the FEMA P-58 methodology and are recommended for future use.

The behaviour of stainless steel plate girders subjected to combined bending and shear was experimentally studied in this paper. Both tensile and compressive material properties of the two adopted stainless steel alloys, including austenitic grade EN 1.4301 and duplex grade EN 1.4462, were determined by standard coupon tests. The three-dimensional (3D) optical scanning technology was introduced to acquire an accurate distribution of initial geometric imperfections for each plate girder specimen. A total of six plate girders were fabricated by hot-rolled stainless steel plates, and were tested to failure under combined bending and shear. In-depth analyses of the critical buckling characteristics, the ultimate resistances and the collapse behaviour of the tested specimens were all presented. The obtained ultimate resistances were further employed to assess the existing moment and shear (M-V) interaction design methods in EN 1993-1-5, GB 50017-2017, ANSI/AISC 360-16 and SEI/ASCE 8-02, and the design proposal presented by Jáger et al. It has been found that most of the existing codified M-V interaction formulae can be applicable for both carbon steel and stainless steel plate girders, yet they lead to relatively conservative predictions for stainless steel plate girders, except that the design method in ANSI/AISC 360-16 provides apparently unsafe strength predictions.

This paper reports on experiments addressing the buckling and collapse behavior of common built-up cold-formed steel (CFS) columns. The built-up column consists of two individual CFS lipped channels placed back-to-back and connected at the web using two self-drilling screw fasteners at specified spacing along the column length. The experiments aim to quantify ultimate strength, composite action, member end fixity, and buckling interactions and collapse behavior for common built-up CFS members. The testing also explicitly explores the effect of sheathing, as typically employed in cold-formed steel framing, on the response. The experiments provide benchmarks for design that include specific considerations for both thin-walled buckling and fastener behavior. A total of 17 monotonic, concentric compression tests with a column length of 1.83 m (6 ft) are completed with an array of position transducers monitoring displacements at key locations. Tests are conducted with the built-up member seated in CFS tracks. Results indicate a large range of deformation behavior, with local-global interaction and flexural-torsional modes common in many of the unsheathed specimens. Columns sheathed with oriented strand board on both flanges behave as braced against global buckling in the plane of the wall, and local buckling induced failures prevail. The end condition for the tested built-up members seated in track is determined to be semi-rigid, but generally closer to fixed than pinned.

This paper reports on experiments addressing the buckling and collapse behavior of back-to-back lipped channel built-up cold-formed steel (CFS) columns assembled using 16 different CFS lipped channel sizes. The lipped channel sections are connected at the web using a pair of self-drilling screw fasteners at a specified spacing along the column length of 1.83 m (6 ft). These experiments aim to quantify the effect of two web fastener layouts on composite action for each section size, study member end fixity, observe buckling and collapse behavior, and provide benchmarks for design that includes specific considerations for thin-walled member buckling. A total of 32 monotonic, displacement-controlled, concentric compression tests are completed with up to 17 position transducers monitoring displacements at key locations. All tests are conducted with the built-up member seated in CFS tracks, as would be found in practice. Local–global interaction is shown to be a prevalent failure mode, and the stud-to-track end condition is determined to be semi-rigid, but generally closer to a fixed condition. End rigidities are estimated using a Southwell approach. Rational design approaches extending the application of the Direct Strength Method (DSM) and employing current state-of-the-art numerical modeling techniques are proposed and validated with test data. In addition, the development of definitive design recommendations that help reduce the complexity of fastener designs and incorporates the DSM framework when predicting built-up member strength is underway.

Transverse fillet welds in the lapped joints have been tested and the results compared against the predictions of the North American Specification for the Design of Cold-Formed Steel Structural Members, AISI S100, to address the strength discontinuity in the transverse fillet weld design method at the thickness of 2.54 mm (0.1 inches). The tests performed by the authors and those available in the literature, have not shown any significant discontinuity in the weld strength when the connected plates get thicker than 2.54 mm (0.1 inches). It has also shown that the current design method could be nonconservative for thin plates. Accordingly, potentials to improve strength predictions have been discussed and a modified design method is proposed. The proposed design method is in a good agreement with the experimental results and resolves the inconsistencies in the current design methods. Finally, a reliability analysis based on the available test results has been performed and resistance factors for the proposed design method are provided.

In this paper, the compound strip method is applied to the stability analysis of cold-formed steel built-up sections. A beam element with adjustable stiffness properties is adopted to represent the utilised fastener and the associated stiffnesses of the connection elements are incorporated in the global stiffness matrix of the built-up sections. The presented method allows for modelling arbitrarily-located discrete fasteners in the context of the semi-analytical finite strip method. The proposed numerical technique is verified against finite element solutions through various numerical examples and shown to be both accurate and versatile. Some typical and also complex built-up sections with various fastener configuration and end boundary conditions are analysed to evaluate the influence of fastener spacing. The extent of composite behaviour in built-up sections is determined by investigating the enhancement of buckling capacity and changes in the corresponding buckling modes. The simplicity of the proposed technique expedites extensive parametric studies of cold-formed built-up sections and facilitates the search for optimal placement of fasteners and choice of section geometry.

The objective of this paper is to advance the design of slender steel tubes by developing a practical approach for utilizing high-resolution measurements of geometric imperfections to estimate the buckling location and strength of such tubes in bending. This approach includes a novel measure of imperfection severity that is designed to be insensitive to noise. The ability of this measure to predict buckling behavior of slender tubes in bending is assessed through comparison with eight large-scale tests, and, for this set of data, the predictions are promising. This study is intended to be a starting point in the development of a simple, but accurate, design method to quantify the impact of imperfections on the buckling behavior of slender tubes.

As different types of hazards, including natural and man-made, can occur simultaneously, to implement an integrated and holistic risk management, a multi-hazard perspective on disaster risk management, including preparedness and planning, must be taken for a safer and more resilient society. Considering the emerging challenges that the COVID-19 pandemic has been introducing to regular hospital operations, there is a need to adapt emergency plans with the changing conditions, as well. Evacuation of patients with different mobility disabilities is a complicated process that needs planning, training, and efficient decision-making. These protocols need to be revisited for multi-hazard scenarios such as an ongoing disease outbreak during which additional infection control protocols might be in place to prevent transmission. Computational models can provide insights on optimal emergency evacuation strategies, such as the location of isolation units or alternative evacuation prioritization strategies. This study introduces a non-ICU patient classification framework developed based on available patient mobility data. An agent-based model was developed to simulate the evacuation of the emergency department at the Johns Hopkins Hospital during the COVID-19 pandemic due to a fire emergency. The results show a larger nursing team can reduce the median and upper bound of the 95% confidence interval of the evacuation time by 36% and 33%, respectively. A dedicated exit door for COVID-19 patients is relatively less effective in reducing the median time, while it can reduce the upper bound by more than 50%.

The objective of this paper is to present finite element modeling protocols and validation studies for the seismic response of a two-story cold-formed steel-framed building with oriented strand board sheathed shear walls. Recently, shake table testing of this building was completed by the authors. The building provides an archetype for modern details of cold-formed steel construction, and provides benchmarks for the seismic response of the building system, subsystem, and components. The seismic response of buildings framed from cold-formed steel has seen little study in comparison with efforts on isolated members and shear walls. Validated building-scale models are needed to expand our understanding of the seismic response of these systems. Finite element models corresponding to the archetype building during its various test phases are developed in OpenSees and detailed herein. For cold-formed steel framed buildings accurate seismic models require consideration of components beyond the isolated shear walls, e.g. the stiffness and capacity of the gravity framing is included in the model. Such decisions require model refinement beyond what is typically performed and details for completing this effort accurately and efficiently are described herein. In addition, nonstructural components, including exterior sheathing of the gravity framing, interior gypsum sheathing for the shear walls and gravity framing, and interior partition walls, are included in the building model based on nonlinear surrogate models that utilize experimental characterization of member-fastener-sheathing response. Comparisons between the developed models and testing for natural period, story drift, accelerations, and foundation hold-down forces validate the model. Performance of the tested archetype building is better than predicted by design or typical engineering assumptions. The model developed herein provides insights into how the building achieves its beneficial performance and will be used to further quantify the lateral resistance of each subsystem and the extent of their coupling. In addition, the protocols used to develop the model herein provide a first examination of the necessary modeling characteristics for wider archetype studies of cold-formed steel-framed buildings and the development and substantiation of seismic response modification coefficients.

The distinct spatial architecture of the apical actin cables (or actin cap) facilitates rapid biophysical signaling between extracellular mechanical stimuli and intracellular responses, including nuclear shaping, cytoskeletal remodeling, and the mechanotransduction of external forces into biochemical signals. These functions are abrogated in lamin A/C-deficient mouse embryonic fibroblasts that recapitulate the defective nuclear organization of laminopathies, featuring disruption of the actin cap. However, how nuclear lamin A/C mediates the ability of the actin cap to regulate nuclear morphology remains unclear. Here, we show that lamin A/C expressing cells can form an actin cap to resist nuclear deformation in response to physiological mechanical stresses. This study reveals how the nuclear lamin A/C-mediated formation of the perinuclear apical actin cables protects the nuclear structural integrity from extracellular physical disturbances. Our findings highlight the role of the physical interactions between the cytoskeletal network and the nucleus in cellular mechanical homeostasis.

The objective of this paper is to investigate the seismic time history response of single-story buildings with a wide range of wall and roof diaphragm periods and ductility. Current design specifications, e.g., ASCE 7-16, are transitioning from accounting for inelasticity in only the vertical lateral force resisting systems, i.e., the walls, to including inelasticity in the horizontal lateral force resisting system, i.e., the roof diaphragm. It is not clear if the wall and roof inelasticity can be considered independently, nor if they can utilize their own seismic response modification coefficients. More fundamentally, the basic manner in which stiffness, mass, and ductility of the wall and roof interact is not fully understood. Here, a single-story building is approximated with a reduced order mass-spring model and parameters are varied so that a wide range of wall periods, diaphragm periods, and wall and diaphragm inelasticity are explored. The model is imposed to vibration analyses, elastic time history analyses, and inelastic time history analyses. The results show clear regimes where the wall and diaphragms interact, and those where the response is largely independent. When inelasticity occurs the ductility demands can be significant for the building component, wall or diaphragm, that initiates the yielding, and greater than traditionally expected. The model results are compared to current and proposed provisions for predicting force and ductility demands and conclusions are drawn with respect to the accuracy of available methods.

The main objective of this research is to experimentally characterize the performance of isolated single sheathing-to-framing fastener connections under cyclic load as utilized in emerging classes of cold-formed steel (CFS) framed steel sheet sheathed shear walls used for seismic lateral resistance. New shear wall variations include the use of steel sheet sheathing sandwiched between framing members (i.e., mid-ply) and the use of heavy hollow structural sections (HSS) chord members with the thin steel sheet sheathing attached by power actuated fasteners (PAF) to the HSS. The cyclic nonlinear response of the framing to steel sheet fastener connection is fundamental for simulating the seismic performance of steel sheet sheathed shear walls. Minimal cyclic fastener-level test data under shear exists for these new configurations. A unique lap shear test following AISI S905 was designed to study and characterize the cyclic fastener connection behavior. The specimens were loaded with an asymmetric cyclic loading protocol which intentionally buckles the thin sheet in the compression direction, and progressively increases in the tension direction. Sixty-three tests covering a wide range of framing thickness, sheet thickness, fastener type and size were completed. Each connection configuration is characterized with a multi-linear backbone curve ready for use in numerical shear wall models. The tested fastener configurations exhibit excellent performance as fastener tilting is largely or completely eliminated in these configurations, and connection degradation from buckling of the steel sheet is minimized. It is also shown that AISI S100 connection strength provisions are applicable to the tested connections.

Based on a shell finite element modeling protocol developed and verified by the first author in a previous study, a comprehensive investigation on stainless steel extended end-plate beam-to-column connections was carried out. A total of 180 connection configurations were numerically investigated, to establish a thorough understanding of the influence of a wide range of geometrical parameters on the behavior of this connection type commonly-used in earthquake-resistant steel structures. The initial stiffness; ultimate moment; rotation capacity; dissipative energy; ductility index; and failure patterns were compared and discussed. Furthermore, based on the data acquired from this parametric study, a simple analytical method, for predicting the moment-rotation (M-Φ) characteristics of stainless steel extended end-plate connections, was developed and validated. The results demonstrate that stainless steel extended end-plate connections can be designed to have substantial ductility and rotation capacity, more than satisfactory for beam-to-column joints of structures in seismic zones. In particular, connections with end-plate stiffeners displayed superior performance with enhanced ultimate moment and energy dissipation capacity. The recommended analytical method for M-Φ response of the joints is accurate, with an average error of less than 4% for the ultimate resistance and is robust as evidenced by its prediction of M-Φ response for models that were withheld from its initial calibration. The proposed equations provide, for the first time, a powerful analytical tool that can predict the complete moment-rotation curves of unstiffened and stiffened stainless steel extended end-plate joints, using easy-to-obtain geometric and material properties.

As a result of altered chemical composition, multiphase microstructures, and other micromechanical change, advanced high strength steel (AHSS) has three to five times the strength of conventional mild steels. Developed for automotive applications, AHSS has high potential for application in cold-formed steel construction. However, the material properties must be properly understood and quantified for application to structural design with economic efficiency. A series of tensile coupon tests were carried out to determine typical AHSS material properties. Existing stress-strain models, designed for steels with gradual strain hardening, were studied and recalibrated to the AHSS test data. No existing method provided an accurate fit for all cases. An updated two-stage plus linear stress-strain model, based on the Ramberg-Osgood expression, was developed. The predictive equations for the parameters required by the new model were provided based on the statistical analysis of AHSS test data. In addition, from the discussion of the new model, a novel proof stress was recommended to represent the yield strength of AHSS. Energy was used to compare the AHSS experimental stress-strain curves with conventional steel stress-strain models to examine the rationality of the proposed proof stress as the yield strength in design.

The objective of this paper is to provide experimental results related to the elevated temperature performance of connections between cold-formed steel members and sheathing. Cold-formed steel building structures rely on sheathing for their mechanical benefits including bracing against member twist, global flexural and flexural-torsional buckling, and cross-section distortional buckling, as well as to supply lateral strength and energy dissipation in shear walls and diaphragms. Sheathing is also relied upon for non-structural benefits, including: fire, acoustic, and thermal performance. Predicting the degradation of the connection performance between cold-formed steel members and sheathing at elevated temperature is critical for any attempt to predict the structural performance of cold-formed steel buildings under fire demands. Steady-state connection tests were conducted under in-plane shear and pull-through at temperatures up to 400 °C for cold-formed steel members attached to gypsum board and oriented strand board. By combining the conducted tests with others in the literature retention factors for initial stiffness and ultimate strength of the connections are proposed.

The global growth of urbanization has caused an increase of wildfires that devastate communities at wildland-urban interfaces. Agent-based evacuation simulation can be a powerful tool for emergency decision-makers to estimate evacuation times during rapidly propagating wildfires. However, as these models increase in size and complexity for urban areas, computation costs rise significantly, making these models less suitable for emergency situations. Although advances in high-performance computing have partially addressed the long execution time associated with large-scale models, the overall computation costs are still high considering the required infrastructure and technical knowledge. Alternatively, we can simplify certain components of the models such that accuracy will not be compromised greatly while computation speed is increased significantly. The authors suggest using the bug navigation algorithms, popular in the field of robotics, for the navigation of pedestrians. In the interest of finding the best candidate bug algorithm, a performance evaluation framework is also introduced. To demonstrate applicability, the evacuation of the city of Iquique, Chile, is simulated using the proposed approach. The results show that the proposed model is successful in estimating the evacuee arrival times, while execution time is reduced by orders of magnitude without a need for powerful processing resources.

Built-up sections are increasingly used as structural elements in the cold-formed steel (CFS) industry. They are composed of two or more component sections connected by discrete fasteners, typically spaced evenly along the length and potentially with fastener groups at the ends. Conventionally, two singly symmetric C-sections are connected to form a doubly symmetric cross-section, and current design guidelines are limited to this particular application. As a means towards broadening the application of built-up CFS sections, the cross-sections in this study were composed of three or four lipped channel sections. The paper presents an experimental investigation of the strength and behaviour of built-up section columns of various lengths and cross-sectional shapes. As observed in the tests, singly-symmetric columns composed of three channel sections (3C) experienced either local, distortional and/or flexural-torsional buckling failure modes, while doubly-symmetric columns formed by four sections (4C) failed in local, distortional and/or flexural buckling modes. The current AISI Specification specifies the use of a modified slenderness ratio only for built-up sections composed of two sections connected back-to-back, whereas the design proposal in this paper recommends the use of an effective rigidity approach coupled with the Direct Strength Method for predicting the strengths of the test 3C and 4C built-up sections. This proposal also suggests a design procedure for the built-up sections experiencing flexural-torsional buckling, which is neither explicitly stipulated in current design standards nor in previous studies.

The objective of this paper is to present procedures for processing three-dimensional point clouds that are generated from laser-based scanning of a cold-formed steel member into useful measurements of cross-section dimensions and imperfections, as well as for use in finite element simulations of the as-measured geometry. The measurement data comes from a unique laser-based scanning platform developed by the authors. Multiple passes on the target cold-formed steel specimen using a line laser are registered with an iterative closest point algorithm to develop the initial three-dimensional point cloud. A novel feature recognition method is proposed to distinguish and extract geometric characteristics such as corners and flats in the targeted specimen. Three different applications are demonstrated herein for the three-dimensional point cloud: feature recognition for determination of nominal dimensions, deviation from nominal configuration for determination of simplified imperfection patterns, and re-mapping of the three-dimensional point cloud onto regularized grids appropriate for subsequent shell finite element modeling. The high fidelity of the measured data provides potential for new insights across all three application areas. Extensions of the algorithms to other cold-formed steel cross-sections, as well as built-up cold-formed steel cross-sections, are currently being pursued.