Doctoral Dissertations

Ai-Shen Liu

Abstract

"It is well-known that the current AlSI Specification for the design of cold-formed steel structural members has been developed mainly for thin steel sections. In order to extend the applicability of the specification for the design of cold-formed steel members thicker than 1/4 in., both analytical and experimental investigations have recently been conducted with special emphases on the effects of cold work on the mechanical properties of corners and the strength of bolted connections.

For the effects of cold work, previous investigations have shown that the phenomena of strain hardening and strain aging are main factors which affect the mechanical properties of corners. The yield point and ultimate tensile strength of corners are larger than those in virgin steels, and the ductility of virgin steels will be decreased as a corner is formed. Mathematical corner models developed by other investigators for the prediction of tensile yield points of corners were studied in detail. It was found that the increase in yield point of corners is dependent upon the ratio of virgin ultimate tensile strength to virgin tensile yield point, the ratio of inside bend radius to the thickness of the corner, and the virgin tensile yield point.

In order to study the possible effects of thickness on the mechanical properties of corners, a total of one hundred corner tests have been conducted. The corner specimens used in the test program were cold-formed from 1/2 in. and 1 in. thick A36 and A588 steel plates with R/t ratios of 3, 5 and 6. On the basis of the test data obtained from the recent study and previous investigations, it was found that in addition to the above-mentioned three factors, the increase in yield point of corners also depends on the type of stress-strain curves of virgin steels, but is not directly affected by the thickness of corners. Consequently, modified equations were derived on the basis of a regression analysis which can be alternatively used for the determination of tensile yield point of corners, when the virgin steel has a sharp yielding type of stress-strain curve with a large plateau. In view of the fact that sharp yielding type of stress-strain curves is usually found for hot-rolled steels, and gradual yielding type of stress-strain curves is found for cold-reduced steels, the current AISI formulas can be used for cold-reduced steels and other steels having a sharp yielding type of stress-strain curve with a small plateau.

It has been realized that the AISC Specification is primarily developed for the design of thick, hot-rolled steel members. Studies of the strength of bolted connections made of thick, cold-formed steel members were, thus, conducted mainly by comparing the AISI and AISC Specifications. Other specifications, recommendations, and standards being used abroad and the research work carried out at other universities were also reviewed and considered. From a study of design criteria for bolted connections listed in various specifications, it was found that the main difference for the design of bolted connections made of thin and thick steels is the allowable bearing stress and the related, required edge distance in line of stress.

In order to study further the bearing capacity of bolted connections, a total of thirty single-shear and double-shear bolted connections were tested. The test specimens were fabricated from A36 and A570 steels with thicknesses of 11 ga., 3/16 in., and 1/4 in.

From a thorough analysis of the available results of connection tests, two modified design equations were derived for the determination of the minimum edge distance in line of stress and allowable bearing stress using ordinary bolts. These modified equations not only apply to steels with various ductilities, but also close the gap between the AISI and AISC Specifications for allowable bearing stress. These equations also provide a conservative basis for the design of bolted connections using high-strength bolts. For purposes of design, simplified equations were also developed and recommended for the minimum edge distance and allowable bearing stress.

With regard to other design requirements for bolted connections, such as allowable tension stress on net section and allowable shear stress on bolts, the current AISI design criteria can also be used for connections made of thick, cold-formed steel members "--Abstract, pages ii-iv.

Advisor(s)

Yu, Wei-wen, 1924-

Committee Member(s)

Best, John, 1925-2015
Senne, Joseph H.
Andrews, William A., 1922-2009
Hansen, Peter G., 1927-2010

Department(s)

Civil, Architectural and Environmental Engineering

Degree Name

Ph. D. in Civil Engineering

Sponsor(s)

American Iron and Steel Institute

Publisher

University of Missouri--Rolla

Publication Date

1974

Pagination

xxii, 274 pages

Note about bibliography

Includes bibliographical references (pages 119-124).

Rights

© 1974 Ai-Shen Liu, All rights reserved.

Document Type

Dissertation - Open Access

File Type

text

Language

English

Subject Headings

Steel, Structural
Steel -- Cold working
Strains and stresses

Thesis Number

T 3020

Print OCLC #

6012594

Electronic OCLC #

904158022

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