Best Bridge Type: Cable Stayed Bridge

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Discussion Overview

The discussion revolves around the design and construction of a bridge for a homework assignment, specifically focusing on the cable-stayed bridge type. Participants explore various design considerations, materials, and structural efficiency while addressing the constraints of the project.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests building a cable-stayed bridge as it appears to be the lightest option based on theoretical considerations.
  • Another participant questions the rating criteria for the bridge and proposes that two cables with additional material for stiffness could support a significant weight.
  • A later reply clarifies that the bridge must simply hold the weight, with the materials specified as straws, masking tape, and string.
  • One participant argues that a cable-stayed bridge may require the deck as a compression anchor, which could complicate loading, and suggests a tied beam design with cables positioned below the deck for easier loading.
  • Another participant raises the need to consider the dimensions of the weights to be used and recommends a triangular or trapezoidal form for efficiency, while also suggesting listing potential failure modes before construction.
  • There is a discussion about the feasibility of anchor points that can handle tension from a string.
  • One participant advises considering how to secure the string to prevent slipping, emphasizing the learning experience from the design process.

Areas of Agreement / Disagreement

Participants express differing views on the optimal bridge design, with some supporting the cable-stayed bridge and others proposing alternative designs like tied beams. The discussion remains unresolved regarding the best approach to meet the assignment's criteria.

Contextual Notes

Participants have not fully defined the assumptions regarding material properties or the specific loading conditions, which may affect the design choices discussed.

nikirock021
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Homework Statement


In class we were asked to build a bridge with the length of 50 cm and the width of 20 cm, maximum weight is 50 g and the test is to place the bridge on two parallel chairs and then place a heavy object in the center. we can build any type of bridge. material: unknown. My question is that what would be the most efficient and easy to build bridge type that can cover all mentioned criteria?
if you have any advice on bridge making please share, it would be a great help. Thank you

2. relevant equations

the modulus equation?

3. attempt at solution

I was thinking of building a cable stayed bridge as it seems to be the lightest as per theory.
 
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What are the rating criteria?
Two cables with a tiny bit of additional material for stiffness would hold a large weight easily - do you need some deck, and does it have to be horizontal?
 
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mfb said:
What are the rating criteria?
Two cables with a tiny bit of additional material for stiffness would hold a large weight easily - do you need some deck, and does it have to be horizontal?
The criteria is simply that the bridge has to hold. The material has been updated straws, masking tape, and string
 
A cable-stayed bridge would need to use the deck as a compression anchor, and it would be difficult to load. A better solution is to use a tied beam with the cables going below the deck. Cables still need to be anchored to the deck, but it's easier to load. You need to know the dimensions of the weights to be used, but a triangular or trapezoidal form is closest to the bending moment diagram and should be the most 'efficient' Think about how to modify this two-dimensional shape so thet it doesn't buckle out of plane. Perhaps you should list all the possible failure modes before you start.
 
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Ah, good point. Do you get anchor points that can take tension from a string?
 
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Think of winding the string around something that won't slip. There are hazards in all designs but you will best learn from the experience itself.
 
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