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Wide Flange Steel I Beam: W8 × 21
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Glossary » Beams » Simply Supported » Uniformly Distributed Load » Four Equal Spans » Wide Flange Steel I Beam » W8 × 21
Wide Flange Steel I Beam | Single Span | Two Equal Spans | Three Equal Spans | Four Equal Spans

For a simply supported beam in four equal spans, we compute the displacement at the middle of the first and fourth spans, and the maximum normal stress stress_max occuring at the second and fourth supports of the beam.
The tabulated data listed in this page are calculated based on the area moment of inertia (Ixx = 75.3 in4) for the W8 × 21 Wide Flange Steel I Beam and the typical Young's modulus (E = 3.046 × 107 psi) of steels. Note that the typical yielding stress Yield of steels can range from 1.015 × 104 to 2.970 × 105 psi. The purpose of this page is to give a rough estimation of the load-bearing capacity of this particular beam, rather than a guideline for designing actual building structures. Please check your local building codes for regulatory requirements.

Note: The weight of the beam itself is not included in the calculation.
L = 3 ft
L = 5 ft
L = 10 ft
L = 15 ft
L = 20 ft
L = 25 ft
L = 30 ft
L = 40 ft
L = 50 ft
L = 60 ft
L = 70 ft
L = 80 ft
L = 90 ft
   
Steel I Beam: W8 × 21 (Wide Flange 8 inch tall × 21 lbf/ft)
L = 3.00 ft
P (lbf/ft) w_max (in) stress_max (psi)
21.0 8.07 × 10-6 13.4
30.0 1.15 × 10-5 19.1
40.0 1.54 × 10-5 25.4
50.0 1.92 × 10-5 31.8
60.0 2.31 × 10-5 38.2
70.0 2.69 × 10-5 44.5
80.0 3.08 × 10-5 50.9
90.0 3.46 × 10-5 57.2
100 3.84 × 10-5 63.6
200 7.69 × 10-5 127
300 1.15 × 10-4 191
400 1.54 × 10-4 254
500 1.92 × 10-4 318
600 2.31 × 10-4 382
700 2.69 × 10-4 445
800 3.08 × 10-4 509
900 3.46 × 10-4 572
1000 3.84 × 10-4 636
2000 7.69 × 10-4 1270
3000 0.00115 1910
4000 0.00154 2540
5000 0.00192 3180
6000 0.00231 3820
7000 0.00269 4450
8000 0.00308 5090
9000 0.00346 5720
1.00 × 104 0.00384 6360
2.00 × 104 0.00769 1.27 × 104
3.00 × 104 0.0115 1.91 × 104
4.00 × 104 0.0154 2.54 × 104
5.00 × 104 0.0192 3.18 × 104
6.00 × 104 0.0231 3.82 × 104
7.00 × 104 0.0269 4.45 × 104
8.00 × 104 0.0308 5.09 × 104
9.00 × 104 0.0346 5.72 × 104
1.00 × 105 0.0384 6.36 × 104
2.00 × 105 0.0769 1.27 × 105
3.00 × 105 0.115 1.91 × 105
4.00 × 105 0.154 2.54 × 105
4.67 × 105 0.180 2.97 × 105
Steel I Beam: W8 × 21 (Wide Flange 8 inch tall × 21 lbf/ft)
L = 5.00 ft
P (lbf/ft) w_max (in) stress_max (psi)
21.0 6.23 × 10-5 37.1
30.0 8.90 × 10-5 53.0
40.0 1.19 × 10-4 70.7
50.0 1.48 × 10-4 88.3
60.0 1.78 × 10-4 106
70.0 2.08 × 10-4 124
80.0 2.37 × 10-4 141
90.0 2.67 × 10-4 159
100 2.97 × 10-4 177
200 5.93 × 10-4 353
300 8.90 × 10-4 530
400 0.00119 707
500 0.00148 883
600 0.00178 1060
700 0.00208 1240
800 0.00237 1410
900 0.00267 1590
1000 0.00297 1770
2000 0.00593 3530
3000 0.00890 5300
4000 0.0119 7070
5000 0.0148 8830
6000 0.0178 1.06 × 104
7000 0.0208 1.24 × 104
8000 0.0237 1.41 × 104
9000 0.0267 1.59 × 104
1.00 × 104 0.0297 1.77 × 104
2.00 × 104 0.0593 3.53 × 104
3.00 × 104 0.0890 5.30 × 104
4.00 × 104 0.119 7.07 × 104
5.00 × 104 0.148 8.83 × 104
6.00 × 104 0.178 1.06 × 105
7.00 × 104 0.208 1.24 × 105
8.00 × 104 0.237 1.41 × 105
9.00 × 104 0.267 1.59 × 105
1.00 × 105 0.297 1.77 × 105
1.68 × 105 0.499 2.97 × 105
Steel I Beam: W8 × 21 (Wide Flange 8 inch tall × 21 lbf/ft)
L = 10.0 ft
P (lbf/ft) w_max (in) stress_max (psi)
21.0 9.97 × 10-4 148
30.0 0.00142 212
40.0 0.00190 283
50.0 0.00237 353
60.0 0.00285 424
70.0 0.00332 495
80.0 0.00380 565
90.0 0.00427 636
100 0.00475 707
200 0.00949 1410
300 0.0142 2120
400 0.0190 2830
500 0.0237 3530
600 0.0285 4240
700 0.0332 4950
800 0.0380 5650
900 0.0427 6360
1000 0.0475 7070
2000 0.0949 1.41 × 104
3000 0.142 2.12 × 104
4000 0.190 2.83 × 104
5000 0.237 3.53 × 104
6000 0.285 4.24 × 104
7000 0.332 4.95 × 104
8000 0.380 5.65 × 104
9000 0.427 6.36 × 104
1.00 × 104 0.475 7.07 × 104
2.00 × 104 0.949 1.41 × 105
3.00 × 104 1.42 2.12 × 105
4.00 × 104 1.90 2.83 × 105
4.20 × 104 2.00 2.97 × 105
Steel I Beam: W8 × 21 (Wide Flange 8 inch tall × 21 lbf/ft)
L = 15.0 ft
P (lbf/ft) w_max (in) stress_max (psi)
21.0 0.00505 334
30.0 0.00721 477
40.0 0.00961 636
50.0 0.0120 795
60.0 0.0144 954
70.0 0.0168 1110
80.0 0.0192 1270
90.0 0.0216 1430
100 0.0240 1590
200 0.0481 3180
300 0.0721 4770
400 0.0961 6360
500 0.120 7950
600 0.144 9540
700 0.168 1.11 × 104
800 0.192 1.27 × 104
900 0.216 1.43 × 104
1000 0.240 1.59 × 104
2000 0.481 3.18 × 104
3000 0.721 4.77 × 104
4000 0.961 6.36 × 104
5000 1.20 7.95 × 104
6000 1.44 9.54 × 104
7000 1.68 1.11 × 105
8000 1.92 1.27 × 105
9000 2.16 1.43 × 105
1.00 × 104 2.40 1.59 × 105
1.87 × 104 4.49 2.97 × 105
Steel I Beam: W8 × 21 (Wide Flange 8 inch tall × 21 lbf/ft)
L = 20.0 ft
P (lbf/ft) w_max (in) stress_max (psi)
21.0 0.0159 594
30.0 0.0228 848
40.0 0.0304 1130
50.0 0.0380 1410
60.0 0.0456 1700
70.0 0.0532 1980
80.0 0.0608 2260
90.0 0.0684 2540
100 0.0759 2830
200 0.152 5650
300 0.228 8480
400 0.304 1.13 × 104
500 0.380 1.41 × 104
600 0.456 1.70 × 104
700 0.532 1.98 × 104
800 0.608 2.26 × 104
900 0.684 2.54 × 104
1000 0.759 2.83 × 104
2000 1.52 5.65 × 104
3000 2.28 8.48 × 104
4000 3.04 1.13 × 105
5000 3.80 1.41 × 105
6000 4.56 1.70 × 105
7000 5.32 1.98 × 105
8000 6.08 2.26 × 105
9000 6.84 2.54 × 105
1.00 × 104 7.59 2.83 × 105
1.05 × 104 7.98 2.97 × 105
Steel I Beam: W8 × 21 (Wide Flange 8 inch tall × 21 lbf/ft)
L = 25.0 ft
P (lbf/ft) w_max (in) stress_max (psi)
21.0 0.0389 927
30.0 0.0556 1320
40.0 0.0742 1770
50.0 0.0927 2210
60.0 0.111 2650
70.0 0.130 3090
80.0 0.148 3530
90.0 0.167 3970
100 0.185 4420
200 0.371 8830
300 0.556 1.32 × 104
400 0.742 1.77 × 104
500 0.927 2.21 × 104
600 1.11 2.65 × 104
700 1.30 3.09 × 104
800 1.48 3.53 × 104
900 1.67 3.97 × 104
1000 1.85 4.42 × 104
2000 3.71 8.83 × 104
3000 5.56 1.32 × 105
4000 7.42 1.77 × 105
4470 8.28 1.97 × 105
Steel I Beam: W8 × 21 (Wide Flange 8 inch tall × 21 lbf/ft)
L = 30.0 ft
P (lbf/ft) w_max (in) stress_max (psi)
21.0 0.0807 1340
30.0 0.115 1910
40.0 0.154 2540
50.0 0.192 3180
60.0 0.231 3820
70.0 0.269 4450
80.0 0.308 5090
90.0 0.346 5720
100 0.384 6360
200 0.769 1.27 × 104
300 1.15 1.91 × 104
400 1.54 2.54 × 104
500 1.92 3.18 × 104
600 2.31 3.82 × 104
700 2.69 4.45 × 104
800 3.08 5.09 × 104
900 3.46 5.72 × 104
1000 3.84 6.36 × 104
2000 7.69 1.27 × 105
2150 8.28 1.37 × 105
Steel I Beam: W8 × 21 (Wide Flange 8 inch tall × 21 lbf/ft)
L = 40.0 ft
P (lbf/ft) w_max (in) stress_max (psi)
21.0 0.255 2370
30.0 0.365 3390
40.0 0.486 4520
50.0 0.608 5650
60.0 0.729 6780
70.0 0.851 7910
80.0 0.972 9040
90.0 1.09 1.02 × 104
100 1.22 1.13 × 104
200 2.43 2.26 × 104
300 3.65 3.39 × 104
400 4.86 4.52 × 104
500 6.08 5.65 × 104
600 7.29 6.78 × 104
681 8.28 7.70 × 104
Steel I Beam: W8 × 21 (Wide Flange 8 inch tall × 21 lbf/ft)
L = 50.0 ft
P (lbf/ft) w_max (in) stress_max (psi)
21.0 0.623 3710
30.0 0.890 5300
40.0 1.19 7070
50.0 1.48 8830
60.0 1.78 1.06 × 104
70.0 2.08 1.24 × 104
80.0 2.37 1.41 × 104
90.0 2.67 1.59 × 104
100 2.97 1.77 × 104
200 5.93 3.53 × 104
279 8.28 4.93 × 104
Steel I Beam: W8 × 21 (Wide Flange 8 inch tall × 21 lbf/ft)
L = 60.0 ft
P (lbf/ft) w_max (in) stress_max (psi)
21.0 1.29 5340
30.0 1.85 7630
40.0 2.46 1.02 × 104
50.0 3.08 1.27 × 104
60.0 3.69 1.53 × 104
70.0 4.31 1.78 × 104
80.0 4.92 2.04 × 104
90.0 5.54 2.29 × 104
100 6.15 2.54 × 104
135 8.28 3.42 × 104
Steel I Beam: W8 × 21 (Wide Flange 8 inch tall × 21 lbf/ft)
L = 70.0 ft
P (lbf/ft) w_max (in) stress_max (psi)
21.0 2.39 7270
30.0 3.42 1.04 × 104
40.0 4.56 1.38 × 104
50.0 5.70 1.73 × 104
60.0 6.84 2.08 × 104
70.0 7.98 2.42 × 104
72.7 8.28 2.52 × 104
Steel I Beam: W8 × 21 (Wide Flange 8 inch tall × 21 lbf/ft)
L = 80.0 ft
P (lbf/ft) w_max (in) stress_max (psi)
21.0 4.08 9500
30.0 5.83 1.36 × 104
40.0 7.78 1.81 × 104
42.6 8.28 1.93 × 104
Steel I Beam: W8 × 21 (Wide Flange 8 inch tall × 21 lbf/ft)
L = 90.0 ft
P (lbf/ft) w_max (in) stress_max (psi)
21.0 6.54 1.20 × 104
26.6 8.28 1.52 × 104
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