A State-of-the-Art Review of Testing by Analysis in Cold-Formed Steel Design

New product development is crucial to allow innovation in the cold-formed steel structural industry. However, the required physical testing of new components and assemblies are often a cost barrier which prevents implementation and slows new product development. Testing by analysis can be a good alternative to physical testing as it reduces the expense and time for performing physical experiments, however, two considerations are necessary to ensure accurate results. First, it requires a rational engineering analysis to calculate the capacities and deformations of the system, and the requirements to produce accurate analyses must be explicitly stated. Second, it is necessary to understand if the software used is capable of correctly modeling the behavior of standard thin-walled and nonsymmetric structural members and systems. This study aims to evaluate existing design standards that include numerical test-based design for both cold-formed steel and other industries. Recommendations for the use of testing by analysis based on the design standards and recent research relevant to testing by analysis are presented. The results of this study will assist with determining recommended requirements for accurate design and testing by analysis.This paper is based in part upon work supported by the American Iron and Steel Institute through a fellowship. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of AISI

Experimental study on residual stresses in press-braked advanced high-strength cold-formed steel lipped angles by sectioning method

The rapid advancement of metallurgy during the past two decades has resulted in a new family of steel known as advanced high-strength steel (AHSS) that has a unique microstructure which enables unprecedented combinations of strength and ductility. The material properties and behavior of the AHSS structural members must be quantified to bring AHSS to the construction industry. This includes the residual stresses induced in the structural member due to the cold-forming process. The quantification of residual stresses, including the magnitude and distribution, is necessary to determine the impact of residual stress on the strength and stability of AHSS structural members. One method to measure residual stresses is the sectioning method, which is a destructive method where the cross-section is cut into strips and the measured change in strain after sectioning is converted to residual stress. Existing experimental studies quantified the residual stress of conventional cold-formed steel, but studies of residual stresses in high-strength cold-formed steel are limited. In this study, a series of residual stress experimental measurements of press-braked AHSS lipped angles using the sectioning method was conducted. The angles were formed from a 1.8-mm thick dual-phase steel sheet with a nominal yield strength of 580 MPa and a nominal ultimate strength of 980 MPa. The outer-to-outer lengths are 63.5-mm (2.5-inch) for the legs and 25.4-mm (1.0-inch) for the lips. Strains at the cross-section corners, legs, and lips on both inner and outer surfaces along the sheet coiling direction were measured by electrical strain gages and were used to calculate the residual stresses. The effect of the corner radius on the residual stresses was investigated, which included two inner corner radii (1.98-mm and 3.57-mm, or 5/64-inch and 9/64-inch). The results were compared to previous measurements of non-lipped press-braked AHSS angles.The authors would like to thank Prof. Benjamin Schafer at Department of Civil and Systems Engineering, Johns Hop- kins University and Prof. Zhanjie Li at College of Engineer- ing, SUNY Polytechnic Institute for their suggestions on the technical issue resolving and results demonstration of this experimental study

Calibration and validation of the hole-drilling method to measure residual stresses in advanced high-strength cold-formed steel members

Advanced high-strength steel (AHSS) has a unique microstructure which enables unprecedented combinations of strength and ductility. Quantification of residual stresses in AHSS sections is important to translate this newer material to the con- struction industry. Residual stresses are induced as a result of the cold-forming process where the distribution and magni- tude of residual stresses affect the strength and stability behavior of structural members. One method to measure residual stresses is the hole-drilling method, which is a semi-destructive method where the change of strain is measured locally before and after a small hole is drilled on a specimen. ASTM E837 recommends equations to calculate residual stress using calibration constants, which are derived from the assumption that the material is linear elastic over the range of residual stress magnitudes. However, AHSS materials have a significantly rounded stress-strain curve compared to conventional steel. Moreover, for a thin workpiece, through-hole drilling can be used to measure residual stresses, which assumes uni- form membrane stresses through the thickness of a specimen without flexural residual stresses. Currently there is a lack of existing studies to confirm if the suggested calibration constants are appropriate for AHSS members. A series of hole-drilling measurements to determine residual stresses in press-braked AHSS lipped angle members was conducted according to ASTM E837. A lipped angle was formed from a sheet of 1.8-mm thick dual-phase steel with a nominal yield stress of 580 MPa and a nominal ultimate strength of 980 MPa. Outer surface strains near the cross-section corners and on the flat regions along the sheet longitudinal and transverse directions were measured by electrical strain gauge rosettes. The distribution of residual stresses obtained from the hole-drilling method was compared with the residual stress measured by the sectioning method of identical AHSS angles. Recommendations for the use of the hole-drilling method and appropriate calibration constants to determine residual stress measurements in AHSS members is presented

Cold-Formed Steel Strength Predictions for Torsion

Locally slender open cross-section members are susceptible to significant twisting and high warping torsion stresses. Torsion considerations are complicated by whether it is derived as a first-order effect from loading or a second-order effect from instability. Previous direct torsion experiments on lipped channels have shown significant inelastic reserve in limited cases. The current design for combined bending and torsion interaction has some limitations, including only considering the first yield in torsion and ignoring the cross-section slenderness in torsion. A parametric study is conducted to predict the torsion capacity in locally slender cross-sections. Shell finite element models of lipped Cee and Zee section members are validated with existing experiments on combined bending and torsion. The validated models are utilized for a parametric study with applied torsion on a range of cross-sections, steel grades, and members lengths to cover the range of practically expected torsional slenderness. A set of bimoment parameters, including yield bimoment, buckling bimoment, and plastic bimoment, are calculated and the ultimate bimoment is determined by performing shell finite element collapse analyses. A simple uniform equation is adopted to predict the bimoment capacity and two bimoment strength curves under torsion only are proposed for local and distortional buckling controlled cases respectively

Numerical study on residual stresses in press-braked advanced high-strength cold-formed steel angles by finite element simulation

Cold-formed steel is widely used in structural framing for its beneficial high strength-to-weight ratio, recyclability, and for convenient transportation and construction. The rapid advancement of metallurgy during the past two decades has resulted in a new family of steel known as advanced high-strength steel (AHSS) that has a unique microstructure which enables un- precedented combinations of strength and ductility. The material properties and behavior of the AHSS structural members must be quantified to bring AHSS to the construction industry. The cold-forming process, such as press-braking, induces residual stresses which affect the strength and stability behavior of the structural members. Existing numerical studies quan- tified the residual stress of conventional cold-formed steel, but studies of residual stresses in high-strength cold-formed steel are limited. This paper develops computational models to simulate the press-brake process of cold-formed AHSS sections and investigates their residual stress distribution through the simulation. The results are validated with recently conducted experimental studies. Numerical modeling of the press-braking process on AHSS angles by the finite element method was conducted. The model incorporated the residual stresses induced by coiling and uncoiling before the press-braking opera- tion was performed. Lipped angles were studied where the angles were press-braked from a 1.8-mm thick dual-phase steel sheet with a nominal yield strength of 580 MPa and a nominal ultimate strength of 980 MPa. Two different inner corner radii, 1.98-mm and 3.57-mm (5/64-inch and 9/64-inch), were investigated. Stresses at the cross-section corners, legs, and lips on both inner and outer surfaces along the sheet coiling direction were extracted from the analysis results. The stress data from the simulation was validated with its counterparts from a series of experimental measurements using the sectioning method, which are presented in a companion paper.The authors would like to thank Prof. Benjamin Schafer at Department of Civil and Systems Engineering, Johns Hop- kins University for his suggestions on the technical issue re- solving of this numerical study

Modeling of stress-strain relationship of advanced high-strength cold-formed steel at elevated temperature

Recent material advances in the steel manufacturing processes have led to materials with greatly enhanced capabilities at competitive cost. New grades of cold-formed steels, referred to as Advanced High-Strength Steels (AHSS), have been developed with yield strengths up to 1200 MPa and ultimate strengths up to 1900 MPa. However, the behavior of these novel materials must be understood and characterized under extreme environments which may arise in structural applications, including high temperatures resulting from fire. In most current design codes, including the American Iron and Steel Institute standard, Eurocode and the Australian Standard, the properties of high strength cold-formed steel subjected to fire conditions are limited or non-existent. A series of steady-state coupon tensile tests for two families of AHSS with nominal yield strength of 340 MPa, 700 MPa, 1030 MPa and 1200 MPa at various uniform temperature stages from ambient to 700 C were carried out. A new constitutive model was proposed based on the characteristics of AHSS stress-strain curves from the tests, and a good agreement between the test data and the model was achieved. In addition, existing stress-strain models from previous studies were investigated to represent the material properties of AHSS at elevated temperatures and compared with the updated model. The fittings of the multiple material models for various families and grades of AHSS were evaluated. The data generated by this research addresses fire safety design and will be essential in supporting the adoption of these next generation steels in future infrastructure

Structural Analysis in Virtual Reality for Education with BMLY

Virtual reality (VR) is an engaging and immersive medium for interacting with a digital environment. The educational benefits of implementing virtual reality into learning modules has recently been explored. This work presents a process for creating a virtual reality learning module on beam bending and a preliminary study on its effectiveness. In this work, virtual reality and structural analysis are combined to create an interactive virtual experiment on a steel beam. A VR user can select the location of a gravity load along the member and increase its magnitude while following the deformation and stresses in real time. The VR environment is implemented using the open source three.js library. The results of a survey to assess student interaction and evaluation of the developed learning module is presented.The authors would like to acknowledge the support of The University of Sydney for the time in the Immersive Learning Laboratory which facilitated this work

Structural Behavior Of Advanced High Strength Steel: Ductility, Connections, Members

This paper summarizes recently completed experimental and numerical research on the structural behavior of advanced high strength steel (AHSS) structural components conducted at the authors’ institutions. For material ductility, tensile coupon tests were completed to establish a database of the stress-strain curves for these new materials and also to develop quantifications of their ductility. The research on connections focuses on the strength of four cold-formed steel (CFS) connection limit states: tension rupture, bearing, tilting/bearing, and end tear-out. The relationship between connection strengths and material ductility is investigated to further the understanding of ductility demand in CFS connections. Research on AHSS structural members includes columns in pure compression and beam in major axis bending. Analysis of the member experiment and finite element simulation results lead to proposed improvements for the Direct Strength Method (DSM) in members with high slenderness and/or high mode interaction potential. Overall, the study reported in this paper improves the understanding of ductility’s influence in structural connection design and extends the applicability of the current CFS buckling design method for high slenderness members, all of which make necessary preparations for introducing this new type of high-strength steel, AHSS, into cold-formed steel design specifications and more broadly in building construction.This paper is based in part upon work supported by the U.S. National Science Foundation under Grant No. 1760953. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation

Evidence for widespread hydrated minerals on asteroid (101955) Bennu

Early spectral data from the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) mission reveal evidence for abundant hydrated minerals on the surface of near-Earth asteroid (101955) Bennu in the form of a near-infrared absorption near 2.7 µm and thermal infrared spectral features that are most similar to those of aqueously altered CM-type carbonaceous chondrites. We observe these spectral features across the surface of Bennu, and there is no evidence of substantial rotational variability at the spatial scales of tens to hundreds of metres observed to date. In the visible and near-infrared (0.4 to 2.4 µm) Bennu’s spectrum appears featureless and with a blue (negative) slope, confirming previous ground-based observations. Bennu may represent a class of objects that could have brought volatiles and organic chemistry to Earth

QCD and strongly coupled gauge theories : challenges and perspectives

We highlight the progress, current status, and open challenges of QCD-driven physics, in theory and in experiment. We discuss how the strong interaction is intimately connected to a broad sweep of physical problems, in settings ranging from astrophysics and cosmology to strongly coupled, complex systems in particle and condensed-matter physics, as well as to searches for physics beyond the Standard Model. We also discuss how success in describing the strong interaction impacts other fields, and, in turn, how such subjects can impact studies of the strong interaction. In the course of the work we offer a perspective on the many research streams which flow into and out of QCD, as well as a vision for future developments.Peer reviewe