L36_Column design - fall 10

# L36_Column design - fall 10 - EAS 209-Fall 2010 Instructors...

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Unformatted text preview: EAS 209-Fall 2010 Instructors: Christine Human Lecture 36 Design of Columns under a Centric Load In practice the design of columns is based on empirical formulas. Today’s Lecture: • Consider design of steel, aluminum and wood columns Today’s Homework: 12/20/2010 1 Lecture 36 – Design of Columns Each point represents the measured stress at failure of a column buckling test specimen EAS 209-Fall 2010 Instructors: Christine Human Experimental data demonstrate that the mode of failure is highly dependent on slenderness ratio:- for short columns (small L e /r ) , σ cr is determined by the yield strength σ Y .- for long columns (large L e /r ) , σ cr follows Euler’s formula and depends upon E .- for intermediate columns , σ cr depends on both σ Y and E . Most design specifications follow this observation, and formulas are specified within a defined range of applicability. Specification for Structural Steel ( AISC)-2005 12/20/2010 2 Lecture 36 – Design of Columns EAS 209-Fall 2010 Instructors: Christine Human For AB use exponential expression to predict σ CR [ ] Y cr e Y σ σ σ σ ) / ( 658 . = where 2 2 ) / ( r L E e e π σ = For BC use an Euler-based relation ( 29 2 2 / 877 . 877 . r L E e e cr π σ σ = = At point B , Y e E r L σ 71 . 4 = and Y cr σ σ 39 . = To obtain σ all use a factor of safety of 1.67 12/20/2010 3 Lecture 36 – Design of Columns Most widely used formulas for steel columns under a centric load Allowable stress design For short and intermediate columns For long columns EAS 209-Fall 2010...
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L36_Column design - fall 10 - EAS 209-Fall 2010 Instructors...

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