# Calculate Force Member in Truss

• lc99
In summary, the conversation discusses using the method of sections to calculate the members of a truss and determining if a specific member is a zero force member. It is confirmed that the method of sections is correct and it is stated that the member in question is not a zero force member due to the curved bottom chord not allowing for colinearity.
lc99

## The Attempt at a Solution

I just want to know if I am doing this right... So, my homework is to calculate the members of a truss. So, here i have a picture of a bridge (truss). I am suppose to calculate the member going from U3 to U4. Thus, I am going to cut the section off (the yellow highlighted part) and do a summation of moments about L3, so that i can solve for the member U3-U4.

Is this correct? Since with method of sections, i can just ignore the rest of the bridge and focus on the left side?

Also, is the member U6-L6 (vertical pillar) a zero force member? So that the member's force =0?

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lc99 said:

## Homework Statement

View attachment 223509

## The Attempt at a Solution

I just want to know if I am doing this right... So, my homework is to calculate the members of a truss. So, here i have a picture of a bridge (truss). I am suppose to calculate the member going from U3 to U4. Thus, I am going to cut the section off (the yellow highlighted part) and do a summation of moments about L3, so that i can solve for the member U3-U4.

Is this correct? Since with method of sections, i can just ignore the rest of the bridge and focus on the left side?

Also, is the member U6-L6 (vertical pillar) a zero force member? So that the member's force =0?
Yes your method of sections is correct . I assume you would already know all the applied loads and reaction load at pier 5.
Member U6L6 is not a zero force member because although no load Is applied to it, members L5L6 and L6L7 are not colinear, since the bottom chord is curved and not a straight line. Those members have to lie along a straight line in order for the vertical member to have no force in it.

CivilSigma
PhanthomJay said:
Yes your method of sections is correct . I assume you would already know all the applied loads and reaction load at pier 5.
Member U6L6 is not a zero force member because although no load Is applied to it, members L5L6 and L6L7 are not colinear, since the bottom chord is curved and not a straight line. Those members have to lie along a straight line in order for the vertical member to have no force in it.

thanks. i kinda doubt that it was a zero force member. I kinda didnt want to go through finding the joints around the vertical force member.

## 1. How do I calculate the force in a member of a truss?

The force in a member of a truss can be calculated using the method of joints or method of sections. The method of joints involves analyzing the forces at each joint in the truss, while the method of sections involves cutting the truss into smaller sections and analyzing the forces in each section. Both methods use equilibrium equations and the properties of the truss to determine the force in a specific member.

## 2. What information do I need to calculate the force in a member of a truss?

In order to calculate the force in a member of a truss, you will need to know the external forces acting on the truss (such as applied loads or reactions), the geometry of the truss (lengths of each member and angles between members), and the material properties of the truss (such as the modulus of elasticity and cross-sectional area of each member).

## 3. Can I use a computer program to calculate the force in a member of a truss?

Yes, there are many computer programs available that can analyze trusses and calculate the forces in each member. These programs use numerical methods to solve the equilibrium equations and can handle more complex truss structures than can be easily solved by hand. However, it is important to have a basic understanding of truss analysis in order to properly interpret and use the results from a computer program.

## 4. What is the maximum force that a member of a truss can withstand?

The maximum force that a member of a truss can withstand is determined by its material properties and cross-sectional area. This can be calculated using stress and strain equations, and is typically given in terms of a maximum stress or ultimate strength. It is important to ensure that the calculated force in a truss member does not exceed this maximum value, as the member could fail or deform under excessive forces.

## 5. How does the force in a member of a truss affect the overall stability of the structure?

The forces in the members of a truss are essential to maintaining the stability of the structure. If a member is experiencing excessive forces, it can lead to failure or collapse of the entire truss. Therefore, it is important to carefully analyze and design truss structures to ensure that the forces in each member are within safe limits and the overall structure remains stable.

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