CVE 312_Case Study

1 CVE 312 Structural Analysis I Case Study

2 I. Abstract In this essay, they contrasted the Pratt trust and the Howe trust, two well-known truss designs. A truss is a structure that provides support for things like roofs and bridges. A truss is a type of steel beam used to support a bridge. Engineers use tools like RISA to help collect all the data a truss can offer. RISA-3D is a thorough CAD-like drawing environment that makes even the most complex buildings easy to create. Information about axial forces, shear forces, and bending moments is collected with the use of RISA. Results from RISA-3D were quantified for the Pratt trust and the Howe trust. They chose the joint reactions, joint deflections, member forces, and member deflections as their outcomes. The output of those choices was a joint and member with the indicated loads from the Truss model. The objective is to determine which truss bridge design is more effective at dissipating the force of a load, the Howe truss, or the Pratt truss. II. Problem Statement To complete this task, a presupposed that the live load, or P, was 100 kips and the dead load, or P, was 15 kips. Additionally, a presumed that the members are constructed of steel with a yield stress of 45. (KSI). They choose to utilize a critical stress value of 24 for compression members (KSI). They then used RISA 3D to perform a structural analysis on each truss. They had to include a summary in their own words and writing. An illustration of the axial forces, a representation of the member forces and reactions, and the deflected form of each truss. The cross-sectional area of each member was then determined. A consideration of 1 (in 2 ) was the minimum value to be used. A displayed member forces, cross-sectional areas, length, and weight using the steel's 490 (lb./ft 3 ) density as a starting point was to be used. It was then necessary to

4 IV. Results and Discussion Pratt Truss Membe r Length (ft) Area (in^2) P(Natural force) (lbs.) Yield limit (KSI) Critical limit (KSI) P/A (lbs/in^2) Area (ft^2) Volume (ft^3) Density (lbs/ft^3) Weight (lbs) AB 20 18.5 445(C) 45 24 24 0.128 2.569 490 1259 AC 15 1 0 45 24 0 0.007 0.104 490 51 BC 25 12.5 556.25(T) 45 24 45 0.087 2.170 490 1063 CE 15 7.5 333.75(T) 45 24 45 0.052 0.781 490 383 BD 15 14 333.75(C) 45 24 24 0.097 1.458 490 714 DE 25 7.5 333.75(T) 45 24 45 0.052 1.302 490 638 CD 20 18.5 445(C) 45 24 24 0.128 2.569 490 1259 DF 15 22 534(C) 45 24 24 0.153 2.292 490 1123 EF 20 11 267(C) 45 24 24 0.076 1.528 490 749 EG 15 12 534(T) 45 24 45 0.083 1.250 490 613 FG 25 2.5 111.25(T) 45 24 45 0.017 0.434 490 213 FH 15 25 60.75(C) 45 24 2 0.174 2.604 490 1276 HG 20 7.5 178(C) 45 24 24 0.052 1.042 490 511 GI 15 12 534(T) 45 24 45 0.083 1.250 490 613 HJ 15 25 600.76(C) 45 24 24 0.174 2.604 490 1276 GJ 25 2.5 111.25(T) 45 24 45 0.017 0.434 490 213 IK 15 7.5 333.75(T) 45 24 45 0.052 0.781 490 383 JL 15 22 534(C) 45 24 24 0.153 2.292 490 1123 IJ 20 11 267(C) 45 24 24 0.076 1.528 490 749 IL 25 7.5 333.75(T) 45 24 45 0.052 1.302 490 638 KL 20 18.5 445(C) 45 24 24 0.128 2.569 490 1259 KM 15 1 0 45 24 0 0.007 0.104 490 51 LN 15 14 333.75(C) 45 24 24 0.097 1.358 490 665 KN 25 12.5 556.25(T) 45 24 45 0.087 2.170 490 1063 MN 20 18.5 445(C) 45 24 24 0.128 2.569 490 1259

5 Howe Truss

7 The total weight of the Pratt truss was 19,192 (lbs.) and the Howe truss was 16,418 (lbs.). The diagonal members are in tension, whilst the vertical members are in compression. As a result, the design can be simplified and more effectively by using less steel in the diagonal elements that are under tension. This has several benefits, including lowering the self-weight, lowering the cost of the structure due to more effective members, and making the structure easier to construct. The Howe Truss, whose diagonal members face the other way, is the closest relative of Pratt Trusses. The members exhibit an inverted compression/tension characteristic as a result. The Howe truss has no force on the center and the tension members are vertical instead. V. Conclusion Although both truss bridges significantly diffused the force more effectively than the beam bridge, the Pratt truss dissipated the load more effectively than the Howe truss. While Pratt truss uses diagonal beams that slope outward from the center of the bridge, here the structural diagonal beams slope toward the bridge center. With this method, the vertical web members of a Howe truss bridge are in tension while the diagonal elements are compressed. Additionally, the beam bridge deflected the most and held the least, whereas the Pratt truss deflected the least and held the most generally. This leads one to the conclusion that a structure is stronger and can support a greater weight if it is more rigid. Because of its stiff construction, the Pratt truss was able to distribute the load's force the most efficiently.

8 VI. Appendix Pratt Truss Figure 1- joint labels, member labels, and loads Figure 2- Axial force diagram Figure 3- Deflected shape

10