Planning the Future of North American Cold-Formed Steel Design Standards

Growth in cold-formed steel structures has long been tied to developing and advancing the engineering standards that govern their use in construction. The American Iron and Steel Institute (AISI) has taken a leadership role in this activity in North America since 1946. Conventional standards providing closed-formed solutions to member capacity, such as the recently completed suite of AISI Standards in 2015 and 2016. These standards have reached an impressive level of maturity given the complexity of designing entire (building) structural systems out of steel that is rarely greater than 2mm thick. However, the demands on the structural engineer designing cold-formed steel have evolved. System performance, resilience, and sustainability all present new challenges, while changing processes in construction and the integration of simulation tools in design alter engineering workflows and open up new opportunities. Cold-formed steel standards need to evolve to meet these demands and leverage new workflows. The Strategic Planning Committee of the AISI Standards Council facilitated a process that defined areas of focus (vision statements) for the AISI specification writing committees and then facilitated a process to generate prioritized issues for the subcommittees to address. Taken together the lists provide a snapshot of the needed work to evolve cold-formed steel standards, and in turn enable next-generation cold-formed steel structural systems. This paper provides a description of the strategic planning process and its significant outcomes, which will guide the efforts of AISI standards development over the next code development cycle and beyond

New ASCE Standards for Cold-formed Steel Deck Slabs

This paper presents highlights of the newly approved and printed ASCE Standard on the design and construction of composite floor deck slabs utilizing cold-formed steel. In 1992 four documents are being published including the following: • Standard for the Structural Design of Composite Slabs --ASCE3-92, • Standard Practice for Construction and Inspection of Composite Slabs -ASCE9-92, and • A separate commentary on each of the two above Standards. These above four documents stem from a previously published ASCE Standard entitled Specifications for the Design and Construction of Composite Slabs and the associated commentary thereon. The Steel Deck with Concrete Committee of the ASCE Standards Division Program has been the committee responsible for the development of these standards. The committee is continuing to work on a third standard on the diaphragm design of floor slabs utilizing cold-formed steel decking with concrete. The paper presents the results and highlights of the accepted two standards and will discuss the status and potential items for inclusion in the proposed new diaphragm standard. Also, the presentation will give summary highlights of the ASCE standards progress in the future development of the. standards program

Review of Testing by Analysis for Potential Implementation into AISI Standards

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. Although the computational capability for testing by analysis has been developed in recent years, the current US design code for cold-formed steel, AISI S100, lacks a standardized approach. This project 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, a survey for understanding the current commonly used software and software capabilities, and recent research relevant to testing by analysis are presented. The results of this report will assist with potential future codification of testing by analysis in the AISI standards

System-based reliability analysis of stainless steel frames subjected to gravity and wind loads

In the process of developing the next generation of design standards for steel structures, most relevant international structural codes including AISC 360, AISC 370, AS/NZS 4100 and Eurocode 3 already incorporate preliminary versions of system-based design-by-analysis approaches that allow a direct evaluation of the strength of steel and stainless steel structures from advanced numerical simulations. As a result, recent research works have focused on building rigorous structural reliability frameworks to investigate acceptable target reliability indices for structural systems and to develop new design methods in conjunction with adequate system safety factors and system resistance factors. Although design recommendations exist for the direct design of hot-rolled and cold-formed steel structures based on advanced finite element analysis, the extension of the method to other materials such as stainless steel is under development. This paper is part of a research effort to build a reliability framework for stainless steel structures subject to different load combinations and presents the results of system reliability calibrations carried out on six stainless steel portal frames subjected to combined gravity and wind loads. The study covers the most common stainless steel families and three international design frameworks (i.e., Eurocode, US and Australian frameworks). From the reliability calibrations derived, suitable system safety factors and system resistance factors are proposed for the direct design of stainless steel frames under combined gravity and wind loads using advanced numerical simulations.The project leading to this research has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under the Marie Sklodowska-Curie Grant Agreement No. 84239.Peer ReviewedPostprint (published version

Influence of variability of material mechanical properties on seismic performance of steel and steel-concrete composite structures

Modern standards for constructions in seismic zones allow the construction of buildings able to dissipate the energy of the seismic input through an appropriate location of cyclic plastic deformations involving the largest possible number of structural elements, forming thus a global collapse mechanisms without failure and instability phenomena both at local and global level. The key instrument for this purpose is the capacity design approach, which requires an appropriate selection of the design forces and an accurate definition of structural details within the plastic hinges zones, prescribing at the same time the oversizing of non-dissipative elements that shall remain in the elastic field during the earthquake. However, the localization of plastic hinges and the development of the global collapse mechanism is strongly influenced by the mechanical properties of materials, which are characterized by an inherent randomness. This variability can alter the final structural behaviour not matching the expected performance. In the present paper, the influence of the variability of material mechanical properties on the structural behaviour of steel and steel/concrete composite buildings is analyzed, evaluating the efficiency of the capacity design approach as proposed by Eurocode 8 and the possibility of introducing an upper limitation to the nominal yielding strength adopted in the design

Reduced Order Models for Profiled Steel Diaphragm Panels

The objective of this paper is to provide progress on development and validation of reduced order models for the in plane strength and stiffness of profiled steel panels appropriate for use in structural models of an entire building. Profiled steel panels, i.e, metal deck, often serve as a key distribution element in building lateral force resisting systems. Acting largely as an in-plane shear diaphragm, metal deck as employed in walls, roofs, and floors plays a key role in creating and driving three-dimensional building response. As structural modeling evolves from two-dimensional frameworks to fully three-dimensional buildings, accurate and computationally efficient models of profiled steel panels are needed. Three-dimensional building response is increasingly required by ever-evolving structural standards, particularly in seismic design, and structural efficiency demands that the benefits of three-dimensional response be leveraged in design. Equivalent orthotropic plate models provide a potential reduced order model for profiled steel panels that is investigated in this paper. A recent proposal for the rigidities in such a model are assessed against shell finite element models of profiled steel panels. In addition, the impact of discrete connections and discrete panels, as occurs in an actual roof system, are assessed when applying these reduced order models. Extension of equivalent orthotropic plate models to elastic buckling and strength, in addition to stiffness, both represent work in progress, but initial results are provided. Examples show that equivalent orthotropic plate models must be used with care to yield useful results. This effort is an initial step in developing efficient whole building models that accurately incorporate the behavior of profiled steel panels as diaphragms

STANDARDS TO CONTROL FRACTURE IN STEEL BRIDGES THROUGH THE USE OF HIGH-TOUGHNESS STEEL AND RATIONAL INSPECTION INTERVALS

Non-redundant steel bridge systems have been used for major bridges in the United States since the late 1800’s. Designers recognized the inherent structural efficiency and economy associated with two-girder and truss systems. Unfortunately, early knowledge was limited regarding fatigue, fracture, and overall system behavior; subsequently, a small number of these structures experienced fatigue and fracture issues leading to the creation of the Fracture Control Plan (FCP). The FCP resulted in more stringent design, material, fabrication, and inspection requirements for non-redundant steel bridges; specifically, a 24 month hands-on inspection criteria for all fracture critical members was established. Significant advances have been made over the past 40 years since the original FCP was introduced. Developments in fracture mechanics, material and structural behavior, fatigue crack initiation and growth, and fabrication and inspection technologies now allow fracture to be addressed in a more integrated manner. Through these advances, it is now possible to create an integrated FCP, combining the intent of the original FCP with modern materials, design, fabrication, and inspection methodologies. The current study is focused on the development of new design standards which founded an integrated approach to prevent fracture in steel bridges through the use of high-toughness steel. The project is comprised of small-scale material testing, full-scale fracture testing of steel bridge axial and bending members, three-dimensional finite element modeling, and an analytical parametric study. Results from this research demonstrate large defects are well-tolerated by high-toughness steel. Further, rational inspection intervals were calculated to demonstrate how an integrated FCP will allow for a better allocation of owner resources while also leading to increased steel bridge safety

Web Crippling of Cold Formed Steel Members

A new design expression for web crippling of cold formed steel members has been developed. An extensive statistical analysis was performed using published test data from Canada, the United States, Sweden and France to develop new expressions for the web crippling strength of cold formed steel members under four different loading cases, i.e. (1) end one-flange loading (EOF), (2) interior one-flange loading (lOF), (3) end two-flange loading (ETF) and (4) interior two-flange loading (lTF). I-sections made of two channels connected back-to-back, Z-sections, channels and multiple web sections (decks) were considered. Comparisons were made with the web crippling expressions presented in the Canadian Standard for the design of cold formed steel structural members, CAN/CSA-S136-M89 (from here on referred to as S136) and with the 1991 LRFD edition of the American Iron and Steel Institute Specification (from here on referred to as AlSI). The web crippling strength depends primarily on the web thickness (t), the yield strength (Fy), the inside bend radius (r), the bearing length of the load (n), the flat dimension of the web measured in the plane of the web (h) and the angle between the plane of web and the plane of the bearing surface (θ). The definition of web depth, h, in both current design standards in Canada (SI36) and the United States (AlSI) was incorporated in the development of the new expressions. The new developed expression is nondimensional, therefore any consistent units of measurement can be used such as imperial or SI. Certain unnecessary complexities which now exist in both design standards have been removed to simplify the web crippling expressions. Eight simplified new expressions have been \u27developed and one particular expression is recommended for design, which has already been adopted by the 1994 edition of S136

Illustrative examples based on the ASCE standard specification for the design of cold-formed stainless steel structural members

PREFACE During the past four years, two methods were developed for the design of stainless steel structural members at the University of Missouri-Rolla with consultation of Professor T. V. Galambos at the University of Minnesota. One of the methods is based on the load and resistance factor design (LRFD) and the other is based on the allowable stress design (ASD). Both design methods are now included in the new ASCE Standard 8-90, Specification for the Design of Cold-Formed Stainless Steel Structural Members. At the September 21, 1990 meeting of the Control Group of the ASCE Stainless Steel Cold-Formed Section Standards Committee held in Washington, D.C., the urgent need for design examples using the new ASCE Standard was discussed at length. The University of Missouri-Rolla was asked to submit a proposal for preparation of such illustrative examples beginning October 1, 1990. During the period from October 1990 through December 1991, a total of 27 illustrative problems have been prepared as included herein. Most of the given data used for these examples are similar to those used in the 1986 edition of the AISI Cold-Formed Steel Manual except that for each problem, two examples are illustrated by using LRFD and ASD methods. The research work reported herein was conducted in the department of Civil Engineering at the University of Missouri-Rolla with the consulting work provided by Dr. Shin-Hua Lin and Professor T. V. Galambos. The financial assistance provided by the Nickel Development Institute and the Chromium Centre is gratefully acknowledged. Appreciation is also expressed to Dr. W. K. Armitage, Mr. J. P. Schade, Professor P. Van der Merwe and Professor G. J. Van den Berg for their technical review and suggested revisions

Reuse of Steel in the Construction Industry: Challenges and Opportunities

The construction industry plays a critical role in tackling the challenges of climate change, carbon emissions, and resource consumption. To achieve a low-emission built environment, urgent action is required to reduce the carbon emissions associated with steel production and construction processes. Reusing structural steel elements could make a significant impact in this direction, but there are five key challenges to overcome: limited material availability, maximizing different reusable materials from demolition, lack of adequate design rules and standards, high upfront costs and overlooked carbon impact of the demolition prior to construction, and the need to engage and coordinate the complete construction ecosystem. This article described these barriers and proposed solutions to them by leveraging the digital technologies and artificial intelligence. The proposed solutions aim to promote reuse practices, facilitate the development of certification and regulation for reuse, and minimize the environmental impact of steel construction. The solutions explored here can also be extended to other construction materials