# What is Truss: Definition and 239 Discussions

A truss is an assembly of beams or other elements that creates a rigid structure.In engineering, a truss is a structure that "consists of two-force members only, where the members are organized so that the assemblage as a whole behaves as a single object". A "two-force member" is a structural component where force is applied to only two points. Although this rigorous definition allows the members to have any shape connected in any stable configuration, trusses typically comprise five or more triangular units constructed with straight members whose ends are connected at joints referred to as nodes.
In this typical context, external forces and reactions to those forces are considered to act only at the nodes and result in forces in the members that are either tensile or compressive. For straight members, moments (torques) are explicitly excluded because, and only because, all the joints in a truss are treated as revolutes, as is necessary for the links to be two-force members.
A planar truss is one where all members and nodes lie within a two-dimensional plane, while a space truss has members and nodes that extend into three dimensions. The top beams in a truss are called top chords and are typically in compression, the bottom beams are called bottom chords, and are typically in tension. The interior beams are called webs, and the areas inside the webs are called panels, or from graphic statics (see Cremona diagram) polygons.

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1. ### How to check the Stability of ANY Truss?

Dear experts, I´m searching for some method to determine whether any 2D or 3D truss is stable without solving complex matrix equations. I want to implement such method in a simple computer program to discard any a priori non-stable trusses for further analysis. Do you know any book or...
2. ### Engineering Understanding stress analysis of truss bridges

Hi im trying to understand truss bridges. Where would max stress be in single span truss bridge if it was evenly loaded across the bridge? I thought single span truss bridge, max stress would be in the ends of the bridge. it would act like a simple supported beam with max bending motion being...
3. ### Engineering Determining Force and Directions on Truss with Pulley

So far I have used methods of joints to determine the forces at point E, D, and C. However, there is also a pulley attached to point D and E which I included in the sum of forces, but I'm not sure if that's the correct way to apply them. Every force I've calculated so far has also been in...

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5. ### Engineering Using method of sections to solve for truss systems

Taking the moments about points A and C, why is a distance of 3 meters used in Fhc and Fhg? Isn’t it supposed to be 1.5 meters for both? I acknowledge that Fhc and Fhg have x and y components, but were we considering the horizontal or vertical component (or both components) of either Fhc and Fhg...
6. ### I Tension/compression in curved truss? (Diagram attached)

In the diagram, are the tension/compression labels in the correct position? The curve shown continues into a full circle, with the load pulling inwards from the cables shown
7. ### How to calculate the normal stress of a Howe reinforcement?

This is the structure I already made the calculation of all the bars T = tension and C = compression, these are the results. now I am asked to calculate the normal stress in all the bars but I don't understand where to start, could you tell me how? here is the diagram of the first node but I...
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### Steel Frame Design for Hanging Egg Chair: Calculating Weight Limitations

Hi, my name is Yuchen and I am a hobby-ist DIY engineer. I have designed a steel frame to hang an egg chair from. I am planning to have it welded but wasn't sure if it will be strong enough. I wanted to use 1/8 inch thick 2 inch by 2 inch square hot rolled carbon steel tube. I am planning to...
9. ### Truss behaviour, load-deformation curve

Hello everyone! I am analysing an 18 m per 1.2 m truss, simply supported, with 140x5 chords and 90x8 braces. I then loaded the superior nodes with 500 KN. The top nodes were also laterally constrained to prevent out-of-plane displacements. After imputing the structure in Abaqus (FEA software), I...
10. ### Engineering Truss problem with counter members

Since the question only asked for one member, I was trying to solve it using method of section. I cut in the middle of BD. I was unable to solve it because it has 4 unknown. Then I looked at the solution, it say that CD is zero force member. I don’t understand why CD is zero force member. Could...
11. ### Truss structure square problem

Here is the full question. I have already tried to answer the questions and have put a red dot next to the answers I think are right? Here is my working out to get the answers I had above Have I done this question right? Sadly I don't have the answers to check for myself here so I'm...
12. ### Heating an aluminum strut in a truss (Feyman Lectures of Physics 2.10)

A)W goes downward because before AB gets heat up the system was in equilibrium hen after getting heat up the Force that AB produce makes the roller moves to the right and that makes the whole system go down B)I don't know what it means I know that this can mean the forces that the member Ab is...
13. ### Forces in a Howe truss (2D) pinned at BOTH ends

Dear experts, How would I find the forces for the truss with both ends pinned? (Fig.1, bottom) I'm trying to determine the forces in all members of some trusses. I've successfully applied the method of sections to a Howe truss (top truss in Fig.1) and I' ve verified it by FEA with MecWay...
14. ### Best truss bridge design for this school project?

Summary:: In my course, we have to design a truss bridge (made out of balsa wood sticks) that can withstand the most weight compared to its mass. It’s our final, so very important haha. One of the rules is we can’t stack the wood right on top of each other to support it (just preventing us from...
15. ### Bridges: Exploring the Strength of Shapes - Arch vs Truss Design

So triangles are apparently triangles are the best shape to use in bridges... But why? I'm pretty sure that a circle or even an arch is stronger than a single triangle. So is it possible to combine circles or arches on a bridge like how a truss design combines triangles?
16. ### Engineering Question about Truss Analysis (Statics)

Hi, I am a civil engineering student currently taking Statics. We are doing truss analysis in the class right now; and I know that this joint is marked as correct. However, I don't see how this is even possible. I begin by considering this a concurrent 2D force system, Fy = 0 & Fx = 0. The...
17. ### Formation of an internally statically determinate truss

My professor taught me that a internally statically determinate truss is formed by having one basic truss - the triangular truss consisting of three joints and three members: and then repeatedly adding two members and a joint: So, it makes sense why this is a statically determinate truss...
18. ### MHB How to Conduct a Static Analysis of a Truss?

Below is a sketch of a truss in which external support reactions are given as R1 = 0 kN, R2 = 3.5 kN, R3 = 4.5 kN. Members (M) are labeled in boxes, joints labeled in circles, and forces R. Draw 2 Free body diagrams, one for each joints C and E. Define what direction represents a positive...
19. ### Calculating a force on a member (Statics)

I isolated the member ABC and drew the free body diagram: α is then calculated using inverse tan: Tan-1=(6.25+15)/50=23.03 Then force of member BD on the joint can be found by sum of all moments around point A. Then Ax is calculated which is equal to BD×Cos(α)=235.2×Cos(23.03) Ax=216.48...
20. ### Roof truss -- distributed load

Homework Statement Snow on a roof supported by the Howe truss of the figure can be approximated as a distributed load of 20 lb/ft (measured along the roof). Treat the distributed load as you would the weight of the members; that is, replace the total load on each of the upper members as a...
21. ### Statics - Compression and tension forces in a truss

Homework Statement I am trying to find the forces in KJ, CJ, and CD. Homework Equations ΣFx=0 The Attempt at a Solution I found the magnitude of KJ to be 26.8kN, which is correct (according to answers in the back of the book). I believe it is a compressive force. The book lists all 3 forces...
22. ### Statics - Support Reaction in Truss

Homework Statement I'm having a hard time finding the support reactions R_{fx} ; R_{fy} ; R_{kx} ; R_{ky} in this truss. 2. The attempt at a solution I got four equations using the equilibrium conditions (sum of forces along x and y ; sum of moments on F and on C) but the system doesn't...
23. ### Calculate Force Member in Truss

Homework Statement Homework EquationsThe 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...
24. ### Truss Method of Joints: Solving Unequal Member Forces

Homework Statement The load is known. Just 2 reactions needed to describe all external forces. Homework Equations method of joings The Attempt at a Solution I'm working on a pretty simple truss for work and want to check some of the elements for buckling. The strange thing is I am not...
25. ### Calculating truss shear and bending

Is it known how to do this? If so, how?
26. ### Finding Forces in Member AE & AB: Exam Follow-up

Homework Statement Determine all member forces and state if they are in tension or compression, in particular I am looking for member AE and AB[/B] Homework EquationsThe Attempt at a Solution Ok so we are supposed to redo the problems from our exam, only I can't figure out how to find the...
27. ### How to Obtain Reaction of Truss Pinned Connection A, B, and C?

Hey guys, Sorry for this newbie question, I would to ask how to I obtain the reaction of the pinned connection of A, B, and C (See attachment)? Do I really have to use Force-Method? I actually attempted to use Moment at different places and do simultaneously (Idk if it's the right thing to do)...
28. ### Determine the magnitudes and nature of forces in space truss

Homework Statement Homework Equations equivalent tension coefficient tDE= applied force/distance between points D and E = 17/SQRT(1[^2+2^2+4^2) = 3.7097 The component of the 17kN in the x-direction = Δx X tDE = -1...
29. ### Displacement in external redundant truss

Homework Statement In this question , the author doesn't stated which direction ( either horozintal support of the pinned E or the vertical support force at pinned E to be selected as redundant ) . So , I tried this problem by applying the vertical force support at E as redundant .Homework...
30. ### Solving an Internal Indeterminate Truss Problem

Homework Statement In this problem , it's a Internal Indeterminate truss . Homework EquationsThe Attempt at a Solution So , I remove one of the redundant member , AC and solve the problem . For the first part , I found the real force first . for the second part , I apply the virtual unit...
31. ### Statics: Method of Joints (Truss)

Can someone explain to me why that highlighted force is 0? Homework Equations ∑Fx = 0 The Attempt at a Solution I found FDC to be 780lb and I am still trying to solve for FDE
32. ### How Does FGF sin26.6 Generate Moment About Point D in Truss Analysis?

Homework Statement For moment about D , how could the FGF sin26.6 generate moment about D ? Homework EquationsThe Attempt at a Solution FGF sin26.6 is located above point D , right ? How could FGF sin26.6 generate moment about D ?
33. ### Discover the Best Truss Design to Support Your Fascia | Expert Tips

Hey guys, from the figure, I was planning to put a truss (shaded in the figure) to support the fascia, due to the fascia being too high (3m) and it may be unstable, thus adding the additional truss support. But my question is how do I calculate if that shaded truss is enough to support the...
34. ### Efficient way to solve truss by hand

Homework Statement Hello. Given the statically determinate truss shown in the image, solve for all forces in the members, in terms of the load P. Homework Equations Equations of equilibrium. Node analysis. Section analysis. The Attempt at a Solution I was able to solve it by solving first...
35. ### Finding displacement at a point in truss

Homework Statement For the circled part , how to get the +1.33 , -1.67 , +1 ? What are they ? Are they the µ ? Homework EquationsThe Attempt at a Solution What is µ ? How to get the value ? It's not stated in my book though
36. ### Internal Forces in Truss: Solving for AB at Point A and Point B

Homework Statement For this problem , i found that the internal force AB at point A and point B pointed in the same direction ( as shown) in my working , so , how they cancel off each other ?Since they can't cancel off each other , so they are not stable , right ? The structure is statically...
37. ### Zero-force members prevent a truss from becoming a mechanism -- Why?

My professor explained to us that the purpose of a zero-force member in a truss is to increase the stability of the truss during construction, to provide added support if the loading is changed and to prevent the structure from becoming a mechanism. It is this latter point that I do not...
38. ### Understanding Plane Stress and Mohr's Circle in Truss Structures

Homework Statement [/B] For part b , i think one of the angle either $$\theta_s$$ or $$\theta_p$$ is wrong For the second question , what is plane stress ? Homework EquationsThe Attempt at a Solution [/B] 1.) Because in mohr's circle, the maximum shear stress on the vertical axis , for the...
39. ### Understanding Truss Mechanics: Why Use the Ratio 40/41 and Y Distance of 6.3?

Given the diagram in the file. I am trying to find the force for the member AB and I do not understand why they use the ratio 40/41 and why they are using 6.3 as the y distance because we have 9ft given and we use the ratio 4/5 instead of 40/41.
40. ### Solving Truss Equations: Find Force in Members EA, EF and EG

Homework Statement Find force in members EA, EF and EG given the loads shown. A and G are pinned supports. Homework Equations Three equations of equilibrium for sections (method of sections) 2 equations for any node (method of joints). I also used the dimensions to decompose member forces. The...
41. ### How Do X-Braces Affect Indeterminate Truss Analysis?

Homework Statement For a larger project we had to redesign a truss to prevent certain members going beyond yield stress. I've found that due to the nature of the reaction forces and the supports used, the only way to do this is to introduce an X-brace in the bay nearest the supports (as well...
42. ### How do I calculate the forces in a Truss?

Homework Statement Homework Equations The Attempt at a Solution I have spent the last 2 hours trying to figure out which part of the truss is compression or tension. Hopefully the second screenshot I took is correct. I tried figuring out the first few parts, just want to make sure that at...
43. ### Statics: Statically Indeterminate Unstable Plane Truss

Homework Statement The signboard truss is designed to support a horizontal wind load of 800 lb. If the resultant of this load passes through point C, calculate the forces in members BG and BF. [/B]Homework Equations For a solution using the method of sections for plane trusses,any three...
44. ### Understanding Truss Forces and Solving Equations for Homework Assignments

Homework Statement i don't understand the 8/BD = x/EB Can anyone explain about it? There's no point E in the diagram... Homework EquationsThe Attempt at a Solution
45. ### Simple truss question I can't seem to get right

Homework Statement ignore all the other writing! The Attempt at a Solution I can't tell where I'm making a mistake. Probably a massive oversight somewhere but I don't know where! First find the reaction forces at the pin and roller by treating everything as a rigid body. (I am now aware...
46. ### Horizontal Force in Bottom Member of a Truss

Hello, I've been studying for the FE, and this question in the Statics section of the review I am going through has really tripped me up for some reason. I understand Statics, and how to determine forces in X and Y directions, determining X and Y components using trig, etc, etc.. Maybe I am...
47. ### Having trouble calculating reaction forces for this truss.

Homework Statement Calculate reaction forces for truss. Truss is attached in picture. Homework Equations ΣFx=o ΣFy=0 ΣM about reaction point=0 The Attempt at a Solution attached in picture
48. ### Method of joints for bridge truss

Homework Statement Calculate the forces for each member. Homework Equations Sum of forces in x=0 Sum of forces in y=0 Sumof moments about D=0The Attempt at a Solution Work is on attached image of problem. I'm having trouble solving for support reactions. At D there is [/B] a hinge. At A...
49. ### Solving Simple Truss Problems: Identifying Compression & Tension

I wonder how to determine a member is in tension or compression without calculation. For the above video starting at 3:03, how to idenfify the last 2 members are in compression and tension respectively. Hope some more examples and diagrams to illustrate. Thanks a lot.
50. ### Understanding Truss Analysis: Investigating the Accuracy of a Bridge Design App

Hi, my high school students enjoy using the applet found here (http://pages.jh.edu/~virtlab/bridge/truss.htm) to design model (basswood) bridges for our annual regional contest. It seems to require firefox these days. Recently, some designs have been causing extremely large forces to be...