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Glossary » Beams » Simply Supported » Uniformly Distributed Load » Three Equal Spans » Wide Flange Steel I Beam » W21 × 73
Wide Flange Steel I Beam | Single Span | Two Equal Spans | Three Equal Spans | Four Equal Spans

For a simply supported beam in three equal spans, we compute the displacement at the middle of the first and the third spans, and the maximum normal stress stress_max occuring at the second and third supports of the beam.
The tabulated data listed in this page are calculated based on the area moment of inertia (Ixx = 1600 in4) for the W21 × 73 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
L = 100 ft
L = 125 ft
L = 150 ft
   
Steel I Beam: W21 × 73 (Wide Flange 21 inch tall × 73 lbf/ft)
L = 3.00 ft
P (lbf/ft) w_max (in) stress_max (psi)
73.0 1.43 × 10-6 5.23
80.0 1.56 × 10-6 5.73
90.0 1.76 × 10-6 6.45
100 1.95 × 10-6 7.17
200 3.91 × 10-6 14.3
300 5.86 × 10-6 21.5
400 7.81 × 10-6 28.7
500 9.77 × 10-6 35.8
600 1.17 × 10-5 43.0
700 1.37 × 10-5 50.2
800 1.56 × 10-5 57.3
900 1.76 × 10-5 64.5
1000 1.95 × 10-5 71.7
2000 3.91 × 10-5 143
3000 5.86 × 10-5 215
4000 7.81 × 10-5 287
5000 9.77 × 10-5 358
6000 1.17 × 10-4 430
7000 1.37 × 10-4 502
8000 1.56 × 10-4 573
9000 1.76 × 10-4 645
1.00 × 104 1.95 × 10-4 717
2.00 × 104 3.91 × 10-4 1430
3.00 × 104 5.86 × 10-4 2150
4.00 × 104 7.81 × 10-4 2870
5.00 × 104 9.77 × 10-4 3580
6.00 × 104 0.00117 4300
7.00 × 104 0.00137 5020
8.00 × 104 0.00156 5730
9.00 × 104 0.00176 6450
1.00 × 105 0.00195 7170
2.00 × 105 0.00391 1.43 × 104
3.00 × 105 0.00586 2.15 × 104
4.00 × 105 0.00781 2.87 × 104
5.00 × 105 0.00977 3.58 × 104
6.00 × 105 0.0117 4.30 × 104
7.00 × 105 0.0137 5.02 × 104
8.00 × 105 0.0156 5.73 × 104
9.00 × 105 0.0176 6.45 × 104
1.00 × 106 0.0195 7.17 × 104
2.00 × 106 0.0391 1.43 × 105
3.00 × 106 0.0586 2.15 × 105
4.00 × 106 0.0781 2.87 × 105
4.14 × 106 0.0809 2.97 × 105
Steel I Beam: W21 × 73 (Wide Flange 21 inch tall × 73 lbf/ft)
L = 5.00 ft
P (lbf/ft) w_max (in) stress_max (psi)
73.0 1.10 × 10-5 14.5
80.0 1.21 × 10-5 15.9
90.0 1.36 × 10-5 17.9
100 1.51 × 10-5 19.9
200 3.01 × 10-5 39.8
300 4.52 × 10-5 59.7
400 6.03 × 10-5 79.7
500 7.53 × 10-5 99.6
600 9.04 × 10-5 119
700 1.05 × 10-4 139
800 1.21 × 10-4 159
900 1.36 × 10-4 179
1000 1.51 × 10-4 199
2000 3.01 × 10-4 398
3000 4.52 × 10-4 597
4000 6.03 × 10-4 797
5000 7.53 × 10-4 996
6000 9.04 × 10-4 1190
7000 0.00105 1390
8000 0.00121 1590
9000 0.00136 1790
1.00 × 104 0.00151 1990
2.00 × 104 0.00301 3980
3.00 × 104 0.00452 5970
4.00 × 104 0.00603 7970
5.00 × 104 0.00753 9960
6.00 × 104 0.00904 1.19 × 104
7.00 × 104 0.0105 1.39 × 104
8.00 × 104 0.0121 1.59 × 104
9.00 × 104 0.0136 1.79 × 104
1.00 × 105 0.0151 1.99 × 104
2.00 × 105 0.0301 3.98 × 104
3.00 × 105 0.0452 5.97 × 104
4.00 × 105 0.0603 7.97 × 104
5.00 × 105 0.0753 9.96 × 104
6.00 × 105 0.0904 1.19 × 105
7.00 × 105 0.105 1.39 × 105
8.00 × 105 0.121 1.59 × 105
9.00 × 105 0.136 1.79 × 105
1.00 × 106 0.151 1.99 × 105
1.49 × 106 0.225 2.97 × 105
Steel I Beam: W21 × 73 (Wide Flange 21 inch tall × 73 lbf/ft)
L = 10.0 ft
P (lbf/ft) w_max (in) stress_max (psi)
73.0 1.76 × 10-4 58.1
80.0 1.93 × 10-4 63.7
90.0 2.17 × 10-4 71.7
100 2.41 × 10-4 79.7
200 4.82 × 10-4 159
300 7.23 × 10-4 239
400 9.64 × 10-4 319
500 0.00121 398
600 0.00145 478
700 0.00169 558
800 0.00193 637
900 0.00217 717
1000 0.00241 797
2000 0.00482 1590
3000 0.00723 2390
4000 0.00964 3190
5000 0.0121 3980
6000 0.0145 4780
7000 0.0169 5580
8000 0.0193 6370
9000 0.0217 7170
1.00 × 104 0.0241 7970
2.00 × 104 0.0482 1.59 × 104
3.00 × 104 0.0723 2.39 × 104
4.00 × 104 0.0964 3.19 × 104
5.00 × 104 0.121 3.98 × 104
6.00 × 104 0.145 4.78 × 104
7.00 × 104 0.169 5.58 × 104
8.00 × 104 0.193 6.37 × 104
9.00 × 104 0.217 7.17 × 104
1.00 × 105 0.241 7.97 × 104
2.00 × 105 0.482 1.59 × 105
3.00 × 105 0.723 2.39 × 105
3.73 × 105 0.899 2.97 × 105
Steel I Beam: W21 × 73 (Wide Flange 21 inch tall × 73 lbf/ft)
L = 15.0 ft
P (lbf/ft) w_max (in) stress_max (psi)
73.0 8.91 × 10-4 131
80.0 9.77 × 10-4 143
90.0 0.00110 161
100 0.00122 179
200 0.00244 358
300 0.00366 538
400 0.00488 717
500 0.00610 896
600 0.00732 1080
700 0.00854 1250
800 0.00977 1430
900 0.0110 1610
1000 0.0122 1790
2000 0.0244 3580
3000 0.0366 5380
4000 0.0488 7170
5000 0.0610 8960
6000 0.0732 1.08 × 104
7000 0.0854 1.25 × 104
8000 0.0977 1.43 × 104
9000 0.110 1.61 × 104
1.00 × 104 0.122 1.79 × 104
2.00 × 104 0.244 3.58 × 104
3.00 × 104 0.366 5.38 × 104
4.00 × 104 0.488 7.17 × 104
5.00 × 104 0.610 8.96 × 104
6.00 × 104 0.732 1.08 × 105
7.00 × 104 0.854 1.25 × 105
8.00 × 104 0.977 1.43 × 105
9.00 × 104 1.10 1.61 × 105
1.00 × 105 1.22 1.79 × 105
1.66 × 105 2.02 2.97 × 105
Steel I Beam: W21 × 73 (Wide Flange 21 inch tall × 73 lbf/ft)
L = 20.0 ft
P (lbf/ft) w_max (in) stress_max (psi)
73.0 0.00282 233
80.0 0.00309 255
90.0 0.00347 287
100 0.00386 319
200 0.00772 637
300 0.0116 956
400 0.0154 1270
500 0.0193 1590
600 0.0231 1910
700 0.0270 2230
800 0.0309 2550
900 0.0347 2870
1000 0.0386 3190
2000 0.0772 6370
3000 0.116 9560
4000 0.154 1.27 × 104
5000 0.193 1.59 × 104
6000 0.231 1.91 × 104
7000 0.270 2.23 × 104
8000 0.309 2.55 × 104
9000 0.347 2.87 × 104
1.00 × 104 0.386 3.19 × 104
2.00 × 104 0.772 6.37 × 104
3.00 × 104 1.16 9.56 × 104
4.00 × 104 1.54 1.27 × 105
5.00 × 104 1.93 1.59 × 105
6.00 × 104 2.31 1.91 × 105
7.00 × 104 2.70 2.23 × 105
8.00 × 104 3.09 2.55 × 105
9.00 × 104 3.47 2.87 × 105
9.32 × 104 3.60 2.97 × 105
Steel I Beam: W21 × 73 (Wide Flange 21 inch tall × 73 lbf/ft)
L = 25.0 ft
P (lbf/ft) w_max (in) stress_max (psi)
73.0 0.00688 363
80.0 0.00753 398
90.0 0.00848 448
100 0.00942 498
200 0.0188 996
300 0.0283 1490
400 0.0377 1990
500 0.0471 2490
600 0.0565 2990
700 0.0659 3480
800 0.0753 3980
900 0.0848 4480
1000 0.0942 4980
2000 0.188 9960
3000 0.283 1.49 × 104
4000 0.377 1.99 × 104
5000 0.471 2.49 × 104
6000 0.565 2.99 × 104
7000 0.659 3.48 × 104
8000 0.753 3.98 × 104
9000 0.848 4.48 × 104
1.00 × 104 0.942 4.98 × 104
2.00 × 104 1.88 9.96 × 104
3.00 × 104 2.83 1.49 × 105
4.00 × 104 3.77 1.99 × 105
5.00 × 104 4.71 2.49 × 105
5.97 × 104 5.62 2.97 × 105
Steel I Beam: W21 × 73 (Wide Flange 21 inch tall × 73 lbf/ft)
L = 30.0 ft
P (lbf/ft) w_max (in) stress_max (psi)
73.0 0.0143 523
80.0 0.0156 573
90.0 0.0176 645
100 0.0195 717
200 0.0391 1430
300 0.0586 2150
400 0.0781 2870
500 0.0977 3580
600 0.117 4300
700 0.137 5020
800 0.156 5730
900 0.176 6450
1000 0.195 7170
2000 0.391 1.43 × 104
3000 0.586 2.15 × 104
4000 0.781 2.87 × 104
5000 0.977 3.58 × 104
6000 1.17 4.30 × 104
7000 1.37 5.02 × 104
8000 1.56 5.73 × 104
9000 1.76 6.45 × 104
1.00 × 104 1.95 7.17 × 104
2.00 × 104 3.91 1.43 × 105
3.00 × 104 5.86 2.15 × 105
4.00 × 104 7.81 2.87 × 105
4.14 × 104 8.09 2.97 × 105
Steel I Beam: W21 × 73 (Wide Flange 21 inch tall × 73 lbf/ft)
L = 40.0 ft
P (lbf/ft) w_max (in) stress_max (psi)
73.0 0.0451 930
80.0 0.0494 1020
90.0 0.0556 1150
100 0.0617 1270
200 0.123 2550
300 0.185 3820
400 0.247 5100
500 0.309 6370
600 0.370 7650
700 0.432 8920
800 0.494 1.02 × 104
900 0.556 1.15 × 104
1000 0.617 1.27 × 104
2000 1.23 2.55 × 104
3000 1.85 3.82 × 104
4000 2.47 5.10 × 104
5000 3.09 6.37 × 104
6000 3.70 7.65 × 104
7000 4.32 8.92 × 104
8000 4.94 1.02 × 105
9000 5.56 1.15 × 105
1.00 × 104 6.17 1.27 × 105
2.00 × 104 12.3 2.55 × 105
2.33 × 104 14.4 2.97 × 105
Steel I Beam: W21 × 73 (Wide Flange 21 inch tall × 73 lbf/ft)
L = 50.0 ft
P (lbf/ft) w_max (in) stress_max (psi)
73.0 0.110 1450
80.0 0.121 1590
90.0 0.136 1790
100 0.151 1990
200 0.301 3980
300 0.452 5970
400 0.603 7970
500 0.753 9960
600 0.904 1.19 × 104
700 1.05 1.39 × 104
800 1.21 1.59 × 104
900 1.36 1.79 × 104
1000 1.51 1.99 × 104
2000 3.01 3.98 × 104
3000 4.52 5.97 × 104
4000 6.03 7.96 × 104
5000 7.53 9.96 × 104
6000 9.04 1.19 × 105
7000 10.5 1.39 × 105
8000 12.1 1.59 × 105
9000 13.6 1.79 × 105
1.00 × 104 15.1 1.99 × 105
1.49 × 104 22.5 2.97 × 105
Steel I Beam: W21 × 73 (Wide Flange 21 inch tall × 73 lbf/ft)
L = 60.0 ft
P (lbf/ft) w_max (in) stress_max (psi)
73.0 0.228 2090
80.0 0.250 2290
90.0 0.281 2580
100 0.312 2870
200 0.625 5730
300 0.937 8600
400 1.25 1.15 × 104
500 1.56 1.43 × 104
600 1.87 1.72 × 104
700 2.19 2.01 × 104
800 2.50 2.29 × 104
900 2.81 2.58 × 104
1000 3.12 2.87 × 104
2000 6.25 5.73 × 104
3000 9.37 8.60 × 104
4000 12.5 1.15 × 105
5000 15.6 1.43 × 105
6000 18.7 1.72 × 105
6800 21.2 1.95 × 105
Steel I Beam: W21 × 73 (Wide Flange 21 inch tall × 73 lbf/ft)
L = 70.0 ft
P (lbf/ft) w_max (in) stress_max (psi)
73.0 0.423 2850
80.0 0.463 3120
90.0 0.521 3510
100 0.579 3900
200 1.16 7810
300 1.74 1.17 × 104
400 2.32 1.56 × 104
500 2.89 1.95 × 104
600 3.47 2.34 × 104
700 4.05 2.73 × 104
800 4.63 3.12 × 104
900 5.21 3.51 × 104
1000 5.79 3.90 × 104
2000 11.6 7.81 × 104
3000 17.4 1.17 × 105
3670 21.2 1.43 × 105
Steel I Beam: W21 × 73 (Wide Flange 21 inch tall × 73 lbf/ft)
L = 80.0 ft
P (lbf/ft) w_max (in) stress_max (psi)
73.0 0.721 3720
80.0 0.790 4080
90.0 0.889 4590
100 0.988 5100
200 1.98 1.02 × 104
300 2.96 1.53 × 104
400 3.95 2.04 × 104
500 4.94 2.55 × 104
600 5.93 3.06 × 104
700 6.91 3.57 × 104
800 7.90 4.08 × 104
900 8.89 4.59 × 104
1000 9.88 5.10 × 104
2000 19.8 1.02 × 105
2150 21.2 1.10 × 105
Steel I Beam: W21 × 73 (Wide Flange 21 inch tall × 73 lbf/ft)
L = 90.0 ft
P (lbf/ft) w_max (in) stress_max (psi)
73.0 1.15 4710
80.0 1.27 5160
90.0 1.42 5810
100 1.58 6450
200 3.16 1.29 × 104
300 4.75 1.94 × 104
400 6.33 2.58 × 104
500 7.91 3.23 × 104
600 9.49 3.87 × 104
700 11.1 4.52 × 104
800 12.7 5.16 × 104
900 14.2 5.81 × 104
1000 15.8 6.45 × 104
1340 21.2 8.66 × 104
Steel I Beam: W21 × 73 (Wide Flange 21 inch tall × 73 lbf/ft)
L = 100 ft
P (lbf/ft) w_max (in) stress_max (psi)
73.0 1.76 5810
80.0 1.93 6370
90.0 2.17 7170
100 2.41 7970
200 4.82 1.59 × 104
300 7.23 2.39 × 104
400 9.64 3.19 × 104
500 12.1 3.98 × 104
600 14.5 4.78 × 104
700 16.9 5.58 × 104
800 19.3 6.37 × 104
881 21.2 7.02 × 104
Steel I Beam: W21 × 73 (Wide Flange 21 inch tall × 73 lbf/ft)
L = 125 ft
P (lbf/ft) w_max (in) stress_max (psi)
73.0 4.30 9090
80.0 4.71 9960
90.0 5.30 1.12 × 104
100 5.89 1.24 × 104
200 11.8 2.49 × 104
300 17.7 3.73 × 104
361 21.2 4.49 × 104
Steel I Beam: W21 × 73 (Wide Flange 21 inch tall × 73 lbf/ft)
L = 150 ft
P (lbf/ft) w_max (in) stress_max (psi)
73.0 8.91 1.31 × 104
80.0 9.77 1.43 × 104
90.0 11.0 1.61 × 104
100 12.2 1.79 × 104
174 21.2 3.12 × 104
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