Simple truss question driving me crazy =/

• hachi_roku
In summary, Hachi_roku suggests resolving the reaction forces in order, starting with A, then B, C, D, and finally E.

hachi_roku

simple truss question...driving me crazy! =/

Homework Statement

the question wants the forces in all the members of the truss. i have found that members bc and ef are zero force members...i cannot find the others. I am at a loss because I've tried all the methods i have been taught and the answers are not right. I NEED HELP!

The Attempt at a Solution

i have tried to take sum of forces in x prime (the AD axis), for members tbd and tcd...and also have tried doing tab and tda.

Attachments

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just in case you can't see the pic...the lengths from the pin to d is 16 ft, while the horizontal distance from the pin to d is 12 ft. the load at b is 2000 and the load at d is 3000. i have found a_y to be 3500 lbs

the angles between ab and ac is 30, while the angles between db and dc is 30

If you want to show the picture fast, you can upload it to picture-servers and post the link. Sometimes the approval can take a day.

> i have found that members bc and ef are zero force members
Very good!

> i have found a_y to be 3500 lbs
Very good. (note: in engineering/mechanics terms, the reaction at A is usually shown as Ra) Ay is understandable, you are probably doing a physics course.

> I've tried all the methods i have been taught and the answers are not right.
What methods have you been taught? Does 'triangle of forces' mean anything to you? How about 'summing forces in x and y'?
Can you post the calculations and the answer you've got using your method, and the answers given. Sometimes the answers are misprinted or mis-transcribed by the teacher or the student.

Hope to hear from you soon.

Hachi_roku, I have an idea. If the question really wants ALL of the forces in each member, start out by finding the reaction forces -of course. Then start by resolving the unknown forces in the pins A, B C, D... in that order. Surely every force in each member will become apparent.

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Hint:
with perfect symmetry of loading and geometry, you only have to work out half of the structure, for example ABCD. The other half (DEFG) can be replaced by a single horizontal reaction. Note, however, that the reaction at A has a vertical and horizontal component.
The horizontal reaction at D can easily be obtained by taking moments about A.

1. What is a simple truss?

A simple truss is a structural framework composed of straight, slender members connected at their ends by joints. It is used to support loads and distribute them evenly along its length.

2. How do you solve a simple truss question?

To solve a simple truss question, you need to draw a free body diagram and apply the equations of equilibrium. Then, use the method of joints or method of sections to determine the internal forces in each member.

3. What are the assumptions made in a simple truss analysis?

The main assumptions made in a simple truss analysis include: all members are connected by frictionless pins, all loads are applied only at the joints, and the truss is loaded in a plane.

4. What are the advantages of using a simple truss?

Simple trusses are lightweight, cost-effective, and easy to construct. They also have a high strength-to-weight ratio, making them ideal for supporting heavy loads.

5. Can a simple truss be used for all types of structures?

No, simple trusses are most suitable for structures with relatively short spans, such as roofs, bridges, and towers. For longer spans or more complex structures, other types of trusses may be more appropriate.