- #1
Alpha[X]²
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How will I calculate the forces involved in a truss and suspension bridge, my teacher did not explain this fully and I'm confused as hell.
How Do You Calculate Forces in Truss and Suspension Bridges?
- Thread starter Alpha[X]²
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- Bridge Suspension Truss
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Discussion Overview
The discussion revolves around calculating forces in truss and suspension bridges, focusing on the application of equilibrium equations, support reactions, and methods for analyzing forces in truss members. Participants express confusion and seek clarification on specific calculations and methodologies.
Discussion Character
- Exploratory
- Technical explanation
- Debate/contested
- Mathematical reasoning
Main Points Raised
- One participant expresses confusion about calculating forces in truss and suspension bridges, indicating a lack of explanation from their teacher.
- Another participant suggests that the geometry and applied loads are crucial for calculations and recommends posting a diagram for clarity.
- A participant provides a specific example of a 100-meter bridge with trusses at a 60-degree angle and a total weight of 20,000 N.
- Discussion includes the importance of calculating support reactions as a first step before analyzing forces in truss elements.
- Participants mention analyzing nodes separately to determine forces, starting with nodes having only two unknown forces.
- There is a question about how specific calculations were derived, particularly regarding the numbers representing forces in the truss members.
- Some participants discuss the use of matrix methods for solving forces, with one suggesting Cramer's method for simultaneous equations.
- Disagreement arises regarding the correctness of calculated forces, with different values reported for the same truss elements.
- Clarification is sought on the shape of the triangles in the truss and the implications for calculations.
Areas of Agreement / Disagreement
Participants express varying levels of understanding and agreement on the methods for calculating forces, with some asserting that the calculations are correct while others challenge them. The discussion remains unresolved regarding the accuracy of specific force values and the methods used.
Contextual Notes
Limitations include a lack of detailed diagrams, assumptions about the geometry of the truss, and varying interpretations of the calculations presented. The discussion also reflects different approaches to solving the problem, including matrix methods and equilibrium equations.
Who May Find This Useful
This discussion may be useful for students and practitioners interested in structural engineering, particularly those seeking to understand the analysis of forces in truss and suspension bridges.
- #2
radou
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Alpha[X]²;1286900 said:
Depends on the geometry and the loads applied to your bridge. If would be great if you posted a pic.
Basically, all you have to do is apply the equations of equilibrium to your system. I can't be any more specific with the given data.
- #3
Alpha[X]²
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Erm, let's just say a 100 metre bridge with trusses with an angle of 60 degress. The bridge weights 20 000 N.
- #4
Pyrrhus
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Well, a picture and your attempt will be a good start.
- #5
Alpha[X]²
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I don't have anything because I don't know how to calculate the forces.
- #6
radou
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Do you know how to calculate the support reactions? Your bridge must have some supports. Did your teacher explain this? It's the first step.
- #7
radou
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Well, after calculating the support reactions, you can calculate the force in every truss element by analyzing every node separately. Start with the node(s) where you have only two (out of three) unknown forces.
- #8
Alpha[X]²
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How did it come up with those calculations though?
- #9
radou
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Alpha[X]²;1288812 said:
Which calculations? Do you mean, the calculation of the reaction forces at the supports?
- #10
Alpha[X]²
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Yes, the numbers on the members in the diagram.
- #11
radou
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Alpha[X]²;1288819 said:
I assume the numbers represent the forces in the members, and the colors represent compression/tension. As I said, you can calculate every force by looking at every node separately. Imagine you "cut out" the leftmost node. You have two unknown and forces and one familiar force. Set up two equations of equilibrium, one for the "y-direction", and one for the "x-direction". You can calculate the forces in the members from these equations.
- #12
Alpha[X]²
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But, that looks like an equilateral triangle, why is there different calculations?
- #13
Alpha[X]²
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Also, I the program used a matrix to solve the forces, what would the matrix calculation formula be?
- #14
radou
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What matrix are you talking about?
The calculations seem wrong. For example, I got ~28.87 for the leftmost blue truss element.
The calculations seem wrong. For example, I got ~28.87 for the leftmost blue truss element.
- #15
AlephZero
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The triangles are not equilateral in the drawing.
The answers are correct (to 2sf) for the shape as it is drawn. I get 30.05 for the force in the leftmost blue truss.
The answers are correct (to 2sf) for the shape as it is drawn. I get 30.05 for the force in the leftmost blue truss.
- #16
radou
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AlephZero said:
Of course, for some reason, I totally ignored the mesh.
Alpha[X]^2, sorry for causing eventual confusion.
- #17
dfx
- 59
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Read up on "pin-jointed analysis of trusses". The "matrix" is probably just Cramer's method to solve simultaneous equations for the member forces.
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