7/28/2019 A Beam Design Aid for Structural Tubing

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A Beam Design Aid for Structural TubingFARUQ M. A . S IDDIQUI

Str uct ual tubing is used primarily by designers for pipe andequipment supports. Recently, tubes have also been usedin other major structures. Square and rectangular structural tubes have excellent resistance to lateral torsionalbuckhng depending on their lateral dimensions. They arealso pleasing aesthetically and assure cleanhness by eliminating dirt-collecting flange areas.

The 1978 AISC Specification^ has explicit provisions forthe use of square or rectangular tubes for beams . How ever,there are no beam design aids in the steel ma nuaP for tube s,other than section property information. Design aids areavailable however^ " in the form of "Beam Load Tables"showing allowable uniform loads for laterally supportedbeams. The author felt a design aid similar in scope andcontent to the "Allowable Stress Design Selection Table"in the Manual would be of use to the steel design professional. The accompanying tables would greatly facilitatethe selection of tubular flexural members designed on the

basis of allowable bending stresses in accordance with the1978 AISC Specification.

The design aid information available here is valid forlaterally supported tubular sections used as beams. It isassumed the loadingis apphe d in the plane of the minor axisand that the beam deflects vertically in the plane of bendingonly.

The lateral support requirement as given in Sect.1.5.1.4.1.6 for using fi, = 0.66 i^ is: "the laterally unsupported length of the compression flange of a bo^-shapedmember of rectangular cross section whose depth is notmore than six times the width {d < 6b ) and whose flange"thickness is not m ore than two times the web thickness(tf /44 X yi63 X yi65 x VA3 x '/24 X yi64 x Vi

3 X y,63 x 1/42 X y.62 X yn3 X ys4 X yi64 x '/45 X yi64 X y82 X y, 6

3 X yi64 X yi6

3 X yi62 x 1/43 x 1/44 X 3/, ,

4 x 1/42 X y,63 X yi63.5 X yi6

2 X y,63 X y 62 x 1/44 X yi6

3 x 1/43.5 X 1/4

2 X y,62 X yi63 X y,63 . 5 X y 63 X yi62 x 1/43 X 1/4

2 X y,63 X y,62 x 1/42.5 X 1/4

2 X yi62.5 X 2 .5 X y,6

2 x

2 x

2 x /4

2 X y,6

Wt., lb.

13.2515.6213.2516.9615.6221.6316.9621.63

11.9713.9111.9717.2717.2711.9713.9111.9717.2714.83

14.8314.83

10.7012.2112.2110.7012.2112.7012.7012.70

9.429.42

10.519.42

10.5110.51

8.1510.588.158.15

10.588.818.81

6.876.877.117.11

5.595.595.41

4.32

S^, in ?

7.407.367.267.036.786.756.656.13

6.025.985.975.945.895.815.655.365.355.34

5.274.79

4.764.604.524.494.113.903.723.48

3.703.623.393.30

3.233.02

2.752.662.622.452.392.352.10

1.931.731.471.35

1.241.140.766

0.668

F, = 46 ksiMr,, K-ft

18.7*18.618.317.817.117.116.815.5

15.215.11 5 . r15.014.914.714.313.513.513.5

13.312.1

12.011.611.411.310.49.889.428.81

9.379.178.588.36

8.187.65

6.966.736.636.206.055.955.32

4.884.383.723.42

3.142.881.94

1.69

Fy = 50 ksiM;,, K-ft

20.3*20.219.9*19.218.618.518.216.8

16.5*16.416.4*16.316.115.915.514.714.714.6

14.413.1

13.012.612.412.311.310.710.29.5

10.19.959.329.07

8.888.30

7.567.317.206.736.576.465.77

5.304.754.043.71

3.413.132.10

1.83

^Signifies capacity may have to be reduced (i.e. F^^ = 0.6 /\,) whenaxial loads are present to satisfy AISC1.5.1.4.1.4.

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