How to calculate bridge deformation based on "design"?

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Homework Help Overview

The discussion revolves around calculating the maximum load a bridge can support before deforming or collapsing, specifically focusing on different bridge designs made from balsa wood. Participants are exploring concepts such as stress and ultimate tensile strength in relation to various bridge designs, including truss, suspension, and arch structures.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants are questioning how to calculate ultimate tensile strength and stress for different bridge designs. There is a focus on whether existing material properties can be applied to the structural designs of bridges. Some participants express uncertainty about the applicability of tensile strength concepts to complex structures rather than just materials.

Discussion Status

The discussion is ongoing, with participants sharing their backgrounds and the limitations of their current resources. Some guidance has been offered regarding the complexities of testing materials versus structures, and the importance of understanding material properties in the context of design.

Contextual Notes

Participants note that their physics textbooks do not adequately cover the engineering aspects of bridge design, leading to a search for additional resources and equations. There is an acknowledgment of the challenges posed by testing complex structures like bridges compared to simpler material samples.

David Goldman
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Homework Statement


I'm not sure if this belongs here, sorry if it does not. I am trying to find the most amount of mass a bridge can hold before deforming/collapsing. I was trying to factor stress/ultimate tensile strength into it in a way. Is there a way I can calculate ultimate tensile strength and/or stress if I'm creating different designs of bridges using balsa wood? I'm trying to find if a certain design of bridge (truss, suspension, arch, etc.) affects how much load it can carry or how much load a bridge design can carry before collapsing.

Homework Equations



Unknown

The Attempt at a Solution


Nothing so far
 
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Purpose: I want to find the amount of stress or ultimate tensile strength of different designs of bridges.
 
David Goldman said:

Homework Statement


I'm not sure if this belongs here, sorry if it does not. I am trying to find the most amount of mass a bridge can hold before deforming/collapsing. I was trying to factor stress/ultimate tensile strength into it in a way. Is there a way I can calculate ultimate tensile strength and/or stress if I'm creating different designs of bridges using balsa wood? I'm trying to find if a certain design of bridge (truss, suspension, arch, etc.) affects how much load it can carry or how much load a bridge design can carry before collapsing.

Homework Equations



Unknown

The Attempt at a Solution


Nothing so far
Welcome to the PF.

What reading have you been doing about this so far? What grade/year are you in school? Since this is for schoolwork, does your textbook go over this at all? :smile:
 
I have been reading about tensile strength , however, I noticed it was only for materials, not based on different designs. I am currently in my senior year of high school. This is not really explained in my physics textbook as it pertains more to engineering. I read about stress, strain, and tensile strength, and I noticed that they only apply to materials? I wanted to see if I could calculate the stress, strain, or tensile strength based on different designs of bridges of the same material (balsa wood) instead of measuring how many weights each design could hold until it collapses. Sadly, I could not find much on this or the equations needed to calculate the, if available. Thanks for the response!
 
David Goldman said:
I have been reading about tensile strength , however, I noticed it was only for materials, not based on different designs. I am currently in my senior year of high school. This is not really explained in my physics textbook as it pertains more to engineering. I read about stress, strain, and tensile strength, and I noticed that they only apply to materials? I wanted to see if I could calculate the stress, strain, or tensile strength based on different designs of bridges of the same material (balsa wood) instead of measuring how many weights each design could hold until it collapses. Sadly, I could not find much on this or the equations needed to calculate the, if available. Thanks for the response!

It's much cheaper (not to mention safer) to test materials in a lab to find out what their ultimate tensile strength is, or their stress v. strain charactertistics.

Doing such testing using complex structures, like bridges for instance, introduces too many unknowns into the process of measuring things like tensile strength. The pieces tested in a strength lab use a simple geometry and have standardized dimensions for things like length, diameter, etc., which makes calculations very simple and reduces the possibility of making errors. By testing only a single piece, it is clear when failure occurs, which may not be so apparent in a complex structure like a bridge.

This article discusses tensile tests and how many engineering materials are tested:

https://en.wikipedia.org/wiki/Tensile_testing

The information derived from such tests is then used to design a particular structure, say a bridge or a skyscraper.

A further word. The strength characteristics of materials like balsa wood are dependent on several factors which may not be present in metals. The direction of the grain relative to the application of the load, the moisture content, and the species of wood all factor into what strength characteristics you will obtain. Metals don't have these limitations.
 
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