Truss Bridge Tension and Compressions

Click For Summary

Homework Help Overview

The discussion revolves around analyzing the forces in a truss bridge subjected to a specific load, focusing on tension and compression in the members. The problem involves a CL-625 design truck and a truss configuration with defined dimensions and angles.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the application of equations related to tension and bending moments, with some questioning the appropriateness of the equations used. There is a mention of the need to find forces in each member and the placement of the load.

Discussion Status

Some participants have provided guidance on the distinction between trusses and beams, emphasizing the need to consider member forces rather than bending moments. There is an ongoing exploration of how to approach the problem, with multiple interpretations being discussed.

Contextual Notes

Participants note that the original poster's calculations seem low and express concern about the completeness of the approach, indicating that additional forces in diagonal and vertical members should be considered. There is also mention of specific equations and parameters that need to be addressed in the analysis.

noahsc
Messages
2
Reaction score
0

Homework Statement


Given the weight of a CL-625 design truck (625 kN) on a truss bridge of span 50m, divided into 8 sections (each 6.25 m) with a height of 6.25m making 45deg angles and a width of 6m, what are the tension and compression forces of the members?
pratt-1.jpg



Homework Equations



Mb = PL/4
T=M/H

The Attempt at a Solution


Using these equations, I got a total tension of 625kN.. I don't know if I'm using the equations wrong or I'm missing something completely, but that seems like a very small number.
 
Physics news on Phys.org
You are not using correct equations...Trusses are subjected primarily to tensile and compressive stresses in each member from member forces under the applied loads, whereas Beams are subject to bending stresses from bending moments under the applied loading. Two different processes. You need to find the force in each member...where is the load placed?
 
yeah I am going to restate the title.
this is only part of the problem. what i need to find is the area of the lower and upper chords with the equation T = phi*As*Fy with the Fy=350Mpa

So, what I have been instructed on doing is find the bending moment of the live load M=PL/4 and then find the tension using the moment arm of the height (or vertical truss)
 
noahsc said:
yeah I am going to restate the title.
this is only part of the problem. what i need to find is the area of the lower and upper chords with the equation T = phi*As*Fy with the Fy=350Mpa

So, what I have been instructed on doing is find the bending moment of the live load M=PL/4 and then find the tension using the moment arm of the height (or vertical truss)
Your answer for the top chord max force of 625 kN compression, and bottom chord max force of 625 kN tension appears correct, but generally, this is not the way to proceed. There are forces in the diagonal and vertical members also,,,,,forces in all members should be found using the trusss Method of Joints or Sections.
 

Similar threads

  • · Replies 2 ·
Replies
2
Views
7K
Replies
1
Views
2K
  • · Replies 2 ·
Replies
2
Views
3K
Replies
3
Views
7K
Replies
1
Views
2K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 8 ·
Replies
8
Views
2K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 1 ·
Replies
1
Views
3K
Replies
2
Views
6K