Interactive Sample Project: Pedestrian Bridge

Step 14: Cost Analysis

Prices shown below are for one beam.

Section	Material	2 x 4	2 x 6	2 x 8	2 x 10
I-Beam	Southern Pine	$7.26	$11.40	$15.03	$19.18
I-Beam	Douglas Fir Larch	$8.02	$12.60	$16.61	$21.19
T-Beam	Southern Pine	$4.84	$7.60	$10.02	$12.79
T-Beam	Douglas Fir Larch	$5.35	$8.40	$11.07	$14.13
Rectangular Section	Southern Pine	$2.42	$3.80	$5.01	$6.39
Rectangular Section	Douglas Fir Larch	$2.67	$4.20	$5.54	$7.06

Comparative Cost Analysis

Design Values:

δ_o = L/500 = 0.192 in
Southern Pine S_req = 4.013 in³
Douglas Fir Larch S_req = 8.441 in³

The table below shows the calculated Section Modulus and Deflection along with Cost/beam for all of the possible design choice combinations. Not all of the possible combinations meet the design constraints. Your design must meet all constraints, and while minimizing cost.

		I-Beam			T-Beam			Rectangular Section
Material	Beam Size	S Modulus (in³)	Deflection δ (in)	Cost/beam ($)	S Modulus (in³)	Deflection δ (in)	Cost/beam ($)	S Modulus (in³)	Deflection δ (in)	Cost/beam ($)
Southern Pine	2 x 4	22.45	0.07065	7.26	7.583	0.2265	4.84	3.063	0.9617	2.42
	2 x 6	53.18	0.0228	11.40	16.19	0.07071	7.60	7.563	0.2478	3.80
	2 x 8	91.32	0.01101	15.03	26.45	0.03351	10.02	13.14	0.1082	5.01
	2 x 10	147.9	0.00569	19.18	41.29	0.01706	12.79	21.39	0.05209	6.39
Douglas Fir Larch	2 x 4	22.45	0.07065	8.02	7.583	0.2265	5.35	3.063	0.9617	2.67
	2 x 6	53.18	0.0228	12.60	16.19	0.07071	8.40	7.563	0.2478	4.20
	2 x 8	91.32	0.01101	16.61	26.45	0.03351	11.07	13.14	0.1082	5.54
	2 x 10	147.9	0.00569	21.19	41.29	0.01706	14.13	21.39	0.05209	7.06

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This material is based upon work supported by the National Science Foundation under Grant No. 0633602. Any opinions, findings and conclusions or recomendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation (NSF).

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