Truss Definition and 18 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.

View More On
  1. Tapias5000

    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...
  2. S

    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...
  3. bardia sepehrnia

    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...
  4. A

    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...
  5. jacobthejones

    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...
  6. R

    Truss Problem

    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 Equations The 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...
  7. A

    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...
  8. A

    Truss in 2D

    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...
  9. kostoglotov

    How can I solve this indeterminate truss bay?

    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...
  10. N

    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...
  11. C

    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...
  12. W

    Method of Joints

    Homework Statement Determine the axial forces in the members of the truss and indicate whether they are in tension or compression. Homework Equations Fx = 0 Fy = 0 Mp = 0 The Attempt at a Solution I attempted to find the reactions at the supports first. So: Fx = 0 = Bx + 800cos(250)N Fy...
  13. A

    Reaction Forces on members

    Homework Statement I am given the forces on picture and I´m asked to find the reactions on both supports. I see they are pin supports so they ask me for 4 unknowns. Homework Equations Sum of forces in both directions equal to zero Sum of torques wrt a convenient point equal to zero THREE...
  14. EdajMay

    Truss Analysis : Method of Joints only (Picture provided)

    Hello, In my statics course, we had to design a bridge, and now, I have to calculate the internal forces in every member of the truss. At first, I have found Ay and Oy with the moment of force, but then, I am stuck since the truss is not perfectly aligned. Sadly, I can't use the method of...
  15. thegreengineer

    Vector mechanics for engineers -- Confusion described below

    Homework Statement Look I have an exercise about trusses in vector mechanics. It's the following: I have to determine the forces in...
  16. C

    Does Angling a pin support on a truss change anything?

    Homework Statement If you had a simple 2D truss with a pin and a roller support, would making the pin on a 30 degree incline change the supporting reactions? Homework Equations The Attempt at a Solution Can't see why since it still supports a horizontal and vertical, don't know hwy the angle...
  17. C

    Simple Statics Question: Truss Structure

    Homework Statement Homework Equations ∑M = 0, ∑Fx = 0, ∑FY = 0 The Attempt at a Solution If so, If so, I will be using the method of sections to cut along the red line as indicated in the picture. This gives me 3 equations of equilibrium as shown above. However, before solving these...
  18. T

    Truss problem

    Homework Statement I've solved all but one force. I can't seen to get the force within element D-C. All relevant variables are shown on the pics attached i.e loads, supports, dimensions etc... Homework Equations Sum of forces in x=0, sum of forces in y=0, sum of moments=0 on Here are links...