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Steel Beams Design Problem 1 - Design a steel beam:
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Design the lightest W-shape to carry a uniformly distributed dead load of 2 kips/ft and a live load of 4 kips/ft.
The beam is simply supported and the compression flange has a lateral support only at the supports.
Use Cb = 1.0 and Fy = 50 ksi.
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1. From the steel beams submenu open the shears and moments submenu, BeamsShearsMoments.aspx.
From the shears and moments submenu open the Simple Beam Uniform Load Shear and Moment Calculation, 1SBUDL.aspx.
Input the "Title" of the calculation, the "Designer/Checker" information.
For the calculation the LRFD factored distributed load, w = 1.2WD + 1.6WL = 1.2(2) + 1.6(4) = 8.8 kips/ft.
Enter the variables click on the "Calculate" button and read the results. The shear is 132 kips and the moment is 990 kips-ft.
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2. Next, from the steel beams submenu open the 50 ksi I shapes Lp and Lr values table, AISC_IShapes_LpLr_50ksi.pdf.
From this table look at the available W shapes with the moment ranges that cover the required moment. Use a beam with Lr slightly more than Lb and the moment at Lr slightly less than the required moment.
Try a W24 x 146 beam.
From the steel beams submenu open the W-Shapes-US tables, CIBeamMoment.aspx.
Input the "Title" of the calculation, the "Designer/Checker" information.
Next, navigate to the steel sections submenu and open the W-Shapes-US tables, WShapeTables.pdf.
Look up the additional required variables for the beam, Zx and rts and enter all of the variables in the Beam Calculation, CIBeamMoment.aspx.
Click on the "Calculate" button and read the results.
The maximum moment of the beam is 1,068.432 kips-ft.
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3. If you closed the shear and moment calculation for a simple beam with a uniform load, go through step 1 above to open the Simple Beam Uniform Load Shear and Moment Calculation, 1SBUDL.aspx.
Otherwise going back to the calculation, input the "Title" of the calculation, the "Designer/Checker" information.
For the calculation the new LRFD factored distributed load will incorporate the weight of the beam in the dead load, w = 1.2WD + 1.6WL = 1.2(2.146) + 1.6(4) = 8.975 kips/ft.
Enter the variables click on the "Calculate" button and read the results.
The shear is 134.625 kips and the moment is 1,009.688 kips-ft which is less than the maximum moment of the beam, 1,068.432 kips-ft.
Use a W24 x 146.
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4. Summary
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The lightest W section is a W24 x 146, with a maximum moment 1,068.432 kips-ft at L = 30 ft.
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