Wei-wen Yu

Cold-formed steel webs with openings: Summary report

Abstract Based on a 3-year study that focused on the behavior of cold-formed steel beams with web openings, researchers at the University of Missouri Rolla have developed simple, easy, to apply design recommendations. The design recommendations address the limit states of web buckling resulting from bending, shear, web crippling, combined bending and shear, and combined bending and web crippling. The recommendations were developed based on the results of experimental and analytical studies of C-section beams. The C-sections, which are commonly used for wall studs and floor joists, are manufactured with web openings. Common web opening sizes are 38 × 102 mm and 19 × 51 mm. All web openings are located at mid-depth of the web and spaced 61 cm on center along the length of the C-section.

Strain rate and aging effect on the mechanical properties of sheet steels

Abstract This study was primarily involved with the experimental determination of the dynamic mechanical properties of five different sheet steels. The nominal yield strengths of these five types of sheet steels ranged from 172 to 690 MPa (25–100 ksi) and the range of strain rates varied from 10 −4 to 1.0 mm/mm/s. All these five materials were studied in both longitudinal and transverse directions under various strain rates, and some materials were also tested under different strain rates and different amounts of prior cold stretching. In addition, two types of steels were tested to estimate the aging effect on the mechanical properties of sheet steels. The test results showed that the proportional limit, yield strength, and ultimate tensile strength increase with increasing strain rate. In general, the amount of increase was found to be dependent on the static yield stress of sheet steel, the amounts of prior cold stretching, and the strain rates used in the tests, and independent on the test directions (longitudinal or transverse), test types (tension or compression), and material aging conditions (aged or nonaged). General equations were also derived to predict the tensile and compressive yield stresses for strain rates ranging from 10 −4 to 10 2 mm/mm/s.

Local buckling flexural strength of webs with openings

Abstract One phase of an ongoing research study of the behaviour of web elements in flexural members is summarized. The unique aspect of this study is the focus on the influence of web openings on the structural behaviour. Flexure, shear, web crippling, and combinations thereof are being studied, this paper concentrates on the flexural behaviour. A test program, which concentrated on industry standard sections, was conducted. The results are presented, along with the correlation of tested moment capacity and computed moment capacity. The computed capacities were determined using recognized US design practices. Suggested refinements to the design practices are also discussed.

Recent research and developments in cold-formed steel framing

Recent research studies at the University of Missouri-Rolla (UMR) have focused on developing a better understanding of the behavior of cold-formed steel members and truss assemblies. This research was initiated by the more widespread use of cold-formed steel in the residential construction market, and the need to provide structurally reliable, as well as highly economical design solutions. Steel trusses are commonly assembled using C-shaped sections and self-drilling screws. Based on UMR findings, appropriate design recommendations have been proposed for the web and chord members of a truss. Also of concern is the introduction of large holes in the webs of floor joists. To assess the effect of the web opening, a multi-phased research effort has recently been concluded. This paper summarizes the UMR studies, and the suggested design recommendations.

Bending strength of hybrid cold-formed steel beams

For the purpose of determining the load-carrying capacity of cold-formed steel structural members, the effective width approach has been used. Since most studies were limited only to the structural members, which were assembled from the same material in a given section, this investigation was concentrated on a study of structural strength and behavior of hybrid cold-formed steel beams subjected dynamic loads. An investigation was also conducted to study the validity of effective design width formulas for the design of these specimens. The materials used in this study were 25 AK and 50 SK sheet steels. A total of 72 spot-welded closed-hat sections were tested under different strain rates. The results showed that the structural strengths including yield moment and ultimate moment of hybrid cold-formed steel beams increase with increasing strain rates. In the determination of the strength of hybrid sections, the effective cross-sectional area calculated on the basis of the dynamic yield stresses can be employed. A design procedure was also developed to compute the member strength of hybrid beams.

Local buckling behavior of stiffened curved elements

Abstract A series of stub column and beam tests has been performed to determine the initial buckling stress of stiffened curved elements. A semi-empirical expression has been developed for the elastic, local buckling of stiffened curved elements subject to uniform axial compression. For inelastic buckling, the tangent modulus approach is employed. Also, methods have been developed to predict the interaction between the local buckling of flat and curved elements and to predict local buckling of curved elements subject to bending. The predicted buckling loads, based on these expressions, are compared to the test data.

University of Missouri-Rolla research on cold-formed steel structures

Abstract During the past 27 years, numerous research projects have been conducted at the University of Missouri-Rolla (UMR) under the sponsorships of the American Iron and Steel Institute, National Science Foundation, American Society of Civil Engineers, Metal Building Manufacturers Association, Steel Deck Institute, Metal/Lath Steel Framing Association, Chromium Center, Nickel Development Institute, and several steel companies located in the USA, Canada, and South Africa. The purpose of these investigations has been to study the structural strength of cold-formed steel members, connections, and structural systems. Some of the research findings have been used in the development of the AISI Specification for the Design of Cold-Formed Steel Structural Members, the AISI Automotive Design Manual, and the ASCE Standard Specification for the Design of Cold-Formed Stainless Steel Structural Members. This paper reviews the research work and other related activities on cold formed steel structures conducted at UMR.

Serviceability limit state for cold-formed steel bolted connections

Publisher Summary This chapter investigates the tensile capacity, bearing capacity and the interaction of tension and bearing capacities of flat sheet cold-formed steel bolted connections. The influence of bolt hole deformation is also investigated. In the experimental investigation, single shear flat sheet connections are examined for single bolt and multiple bolt configurations. The intent of this investigation is to compare the current design equations for the nominal bearing and tensile capacities and to develop appropriate serviceability design criteria. The focus of this chapter is the development of a serviceability limit for the nominal bearing capacity of cold-formed steel flat sheet connections.

The structural behavior of homogeneous and hybrid stub columns under dynamic loading conditions

Abstract It has been recognized that the mechanical properties of sheet steels and the structural strength of cold-formed steel members can be influenced by strain rate. For studying the local and postbuckling behavior of the stiffened and unstiffened compression elements under dynamic loading condition, 97 stub columns which were assembled from the same material have been tested under different strain rates. In order to study the structural behavior of hybrid cold-formed stub columns, a total of 144 specimens were investigated. In addition, 52 drop silo tests of stub columns were conducted at General Motors Corporation (GM). The results showed that the strength of stub columns increases with increasing strain rate. The amount of increase was found to be dependent on the material yield strength, the type of steel, the stress–strain relationships, the width-to-thickness ratio and the type of compression element, and the strain rate used in the test.