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# 311 Ch15

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### 311 Ch15

1. 1. <ul><li>VII.) Design of Compact Steel Beams </li></ul><ul><li>A.) Introduction </li></ul><ul><li> The allowable stress depends on how well the compression flange is supported out of plane. The distance between lateral supports is called the unbraced length. </li></ul>
2. 2. <ul><li>Compact means that the unbraced length (out of plane) is less than L c . </li></ul><ul><li> L c is the maximum length for which a given W-section can be considered Compact. (See AISC beam table) </li></ul>
3. 4. <ul><li>B.) Compact Beam Design Method </li></ul><ul><li>1.) Determine the location and magnitude </li></ul><ul><li>of the loads and draw a load diagram. </li></ul><ul><li>2.) Draw the shear and moment diagrams </li></ul><ul><li> to find the maximum shear and </li></ul><ul><li>moment in the beam. </li></ul>
4. 5. <ul><li>3.) Calculate the required section modulus: </li></ul><ul><li>S req’d = M = M , if L < L c </li></ul>  b,allow 0.66  y 4.) Select the lightest beam available with L c > L and S x > S req’d .
5. 6. <ul><li>a.) Enter AISC beam selection table </li></ul><ul><li> under the S x column. </li></ul><ul><li>b.) Find the lightest beam in bold </li></ul><ul><li> letters with S x > S req’d. The bold </li></ul><ul><li> letters indicate the lightest beam </li></ul><ul><li> available for a given range of S x. </li></ul>c.) Check the L c > L, if not, chose a heavier beam.
6. 7. <ul><li>5.) Add the moment due to the self-weight </li></ul><ul><li>of the selected beam to the maximum </li></ul><ul><li>moment and again check that </li></ul><ul><li> S x > S req’d. If not, repeat step 4. </li></ul><ul><li>6.) Check that  v = V < 0.4  y </li></ul>A Note: F y is the symbol for yield strength in the AISC handbook.