# How to calculate tension/compression in a truss bridge (diagram shown)?

• enosthapa
In summary, in a truss diagram, the forces like load and reaction force act on joints. However, in the case of a load being in the middle of two joints, the force can be split into two 5N forces at its ends. To find the forces on the members in this case, you can use the method of joints and treat the external load as a moment. It is recommended to start at the supports and work towards the center for easier analysis.
enosthapa
In general, in a truss diagram the forces like load, reaction force are act on joints but in this case the load is in the middle of two joints. How can I find forces on members in this case?

Since the force is in the center of the spar, you could split it into 2 5N forces at its ends...

Mech_Engineer said:
Since the force is in the center of the spar, you could split it into 2 5N forces at its ends...

Could you help me find out what force (tension/compression) do the truss members have please? I have done most of them but the middle section with "X" trusses are making it dificult to calculate the forces the carry...

I have done some calculations to find out the forces but i am confused with the middle section. Can someone tell me if figure 2 is correct or not?Thank you

Last edited:
You can just assume one or the other (tension or compresison) and if you guessed wrong, you will get a negative value.

enosthapa said:
In general, in a truss diagram the forces like load, reaction force are act on joints but in this case the load is in the middle of two joints. How can I find forces on members in this case?

Well, you can't use method of sections for the center... you'd have to use method of joints and treat that "external load" as a moment on the joint you're analyzing that's "connected" to the member that's loaded (as well as in force equilibrium)... seems as if the only two joints you'd concern yourself with with that center load are the ones to the left and right of it. at least that's how id attempt to do it. start at the supports and move your way towards the center.

## 1. How do you determine the forces acting on each member of a truss bridge?

The forces acting on each member of a truss bridge can be determined by using the method of joints. This involves breaking the truss down into individual joints and analyzing the equilibrium of forces at each joint. By applying the principles of statics, the forces in each member can be calculated.

## 2. What is the difference between tension and compression in a truss bridge?

Tension and compression are two types of forces that act on the members of a truss bridge. Tension is a pulling force, while compression is a pushing force. In a truss bridge, tension forces act to stretch the members, while compression forces act to compress them. Both tension and compression are necessary for the stability of a truss bridge.

## 3. How do you calculate the tension or compression in a specific member of a truss bridge?

To calculate the tension or compression in a specific member of a truss bridge, you first need to determine the forces acting on that member. This can be done by analyzing the equilibrium of forces at the joints connected to the member. Once the forces are known, the tension or compression in the member can be calculated using the equation F = A x σ, where F is the force, A is the cross-sectional area of the member, and σ is the stress acting on the member.

## 4. What factors can affect the tension and compression forces in a truss bridge?

The tension and compression forces in a truss bridge can be affected by several factors, including the weight of the bridge itself, the weight of any vehicles or other loads on the bridge, wind forces, and seismic forces. The design and material of the truss bridge also play a significant role in determining the tension and compression forces.

## 5. Why is it important to calculate the tension and compression forces in a truss bridge?

Calculating the tension and compression forces in a truss bridge is crucial for ensuring the safety and stability of the bridge. If the forces in a member are too high, it could lead to failure of the bridge. By accurately calculating the forces, engineers can design truss bridges that can withstand the expected loads and forces, ensuring the safety of the structure and the people using it.

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