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Unformatted text preview: SHEAR DESIGN IN AASHTO LRFD CODE By Gustavo Parra Department of Civil & Environmental Engineering University of Michigan Presentation Outline • Introduction on shear design methods in AASHTO LRFD Code • Sectional Models Mechanisms contributing to shear strength in concrete members Simplified Sectional Method General Sectional Method Overview of Modified Compression Field Theory Application of General Procedure MDOT Workshop 2003 Presentation Outline (cont.) • StrutandTie Method Modeling Strength of struts, ties and nodes Reinforcement detailing requirements Example MDOT Workshop 2003 Shear Design Methods in AASHTO LRFD Code • Sectional Methods (Section 5.8.3) Applicable when assumption of plane section remaining plane after loading is reasonable Typically used in bridge girders, slabs, and other slender concrete members of bridge structures Not good for deep members MDOT Workshop 2003 Shear Design Methods in AASHTO LRFD Code • StrutandTie Method (Section 5.6.3) Can be used for the design of full structures, members or regions of structural members Typically used in design of members where assumption of plane sections remaining plane after loading is not reasonable Can be used to design slender members MDOT Workshop 2003 Sectional Methods (Section 5.8.3) • Used when assumption of plane sections remaining plane after loading is reasonable. Typically applicable to design of concrete slender members MDOT Workshop 2003 Nominal and Factored Shear Resistance MDOT Workshop 2003 p s c n V V V V + + ≤ p v v c n V d b f' .25 V + ≤ • Nominal shear resistance (Section 5.8.3.3), V n , accounts for contributions from “concrete”, “steel” and prestressing steel • Factored Shear Resistance • Upper limit for Nominal Shear Resistance Concrete) t Lightweigh vs. (Normal 0.7 or 0.9 V V V u r n = ≥ = φ φ “Concrete” Contribution to Shear Strength, V c • Accounts for aggregate interlock, dowel action and shear carried in the compression zone of the member • In AASHTO LRFD Sectional Method, V c is estimated based on the ability of diagonally cracked concrete to resist tensile stresses in between cracks MDOT Workshop 2003 ksi) in (f' d b f' .0316 V c v v c c β = ¡ β is a factor that depends on amount of tension carried by the concrete in between cracks Truss Mechanism in Cracked Concrete Member MDOT Workshop 2003 (from Collins and Mitchell 1997) “Steel” Contribution to Shear Strength, V s MDOT Workshop 2003 s cot d f A V v y v s θ = For steel transverse reinforcement oriented at an angle other than 90 with respect to the member axis: s sin ) cot (cot d f A V v y v s α α + θ = How Do We Determine...
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This note was uploaded on 05/01/2010 for the course CEE 615 taught by Professor Parra during the Winter '09 term at University of MichiganDearborn.
 Winter '09
 parra

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