CAE303Classnote_on_tension

CAE303Classnote_on_tension - 1 CLASS NOTES ON Design of...

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1 CLASS NOTES ON Design of Steel Structures Design of Tension Members (As a supplement to the References) By Jay Shen (P.D., PE, SE) Illinois Institute of Technology 09/06/2007 STEEL DESIGN/ TENSION FALL 2007_ J.SHEN
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2 DESIGN OF TENSION MEMBERS References: (1) Textbook: Chapter 7; and (2) AISC-Manuel/Part 16: ANSI/AISC 360-05 Specification Chapters B and D; 1. INTRODUCTION ¾ Tension members are those structure components that primarily carry tension load. ¾ Tension members can be found in many structures, such as: STEEL DESIGN/ TENSION FALL 2007_ J.SHEN
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3 ¾ Tension members can be divided into the following categories: Rolled shapes and built-up sections Pin connected members and eye bars Tie bars and rods Cables Typical cross sections of tension member are listed as follows: ¾ Possible failure modes (strength Limit States) in tension members when a steel member is subjected to a tension force. It behaves elastically until reaching one of the Limit States (or called Failure Modes). The main Limit States of failure of tension members are: 1. Yielding of Gross Area; 2. Fracture of Effective net area; 3. Block shear failure; and in a some cases, 4. Failure of connection elements Design of a tension member is to identify the controlling failure mode. (The limit state with the smallest capacity), and to select the section or connection to ensure the safety. 2. GENERAL DESIGN PROCESS IN LRFD/ASD FOR TENSION MEMBERS A general design criterion: N N r Limit Required Strength Design limit RR Demand / Load Capacity / Resis tan ce (1) STEEL DESIGN/ TENSION FALL 2007_ J.SHEN
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4 Where, R r = Required Strength due to loads, which will be decided by structural analysis. R Limit = Design Limit that can be tolerated by the structural member, specified in the specification. Note that both the Required strength and Design Limit consist of number of uncertainties, such variations in loads and material properties. There are two approaches, Load and Resistance Factor Design (LRFD) and Allowable Stress Design (ASD) , for steel design. They are different mainly in ways how the uncertainties are considered. Load and Resistance Factor Design (LRFD): For LRFD, Equation (1) becomes u RR n ≤ φ ( B 3 - 1 ) R u = Required Strength (LRFD) due to loads, i.e., = Factored load effects on the member force (tension). Due to various load combination. Subscript “i” refers to the type of loads, (Dead Load, Live Load, etc.). ii Ru Q i γ = Load factor to consider load variation during the service of the structure. Its value varies with the load combination and is defined by codes, as shown in ASCE 7-05 Chapter 2. . φ R n = Design Strength. R n = Nominal resistance of a given limit state, based on specified material strength and member size, specified Chapters B through K in ANSI/AISC 360-05 φ = Resistance factor associated with the limit state to account for uncertainties in the determination of R n In design, R n might be represented by the nature of the load, such as axial force (P n ), bending moment (M n ), shear force (V n ). Similarly, R u , the Required Strength (LRFD), might be represented by P u
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CAE303Classnote_on_tension - 1 CLASS NOTES ON Design of...

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