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. M

    Calculating Forces in Truss Members using Method of Section

    Homework Statement a) Find the reactions provided by the foundations at A and B. b) Use the method of Resolution at the Joints to calculate the forces in all the members. c) Which member will fail first and why ? Homework Equations ƩFx = 0 ƩFy = 0 ƩM = 0 The Attempt at a...
  2. L

    Analysing a 3D truss problem

    Homework Statement I am trying to analyse a 3D truss problem (attached). The idea is that when you pull with a force F in the direction of the arrows, the pin in the middle will be pressed downwards, decreasing the length of p2. In general the overall structure will be consistent of a series...
  3. S

    When using the method of sections to find a force in a truss, how to orient the cut?

    Homework Statement So, there is method of joints and method of sections to find the force of specific members of the trusses. They only give examples where the section was cut vertically or diagonally. Can it also be cut in a semi-circle? I tried it out and it didn't give the right answer...
  4. R

    Deployment of a Truss in Space

    I am having trouble getting started with this problem, any advice would be great. A truss is attached to a hinge point in space (zero gravity), it must deploy from the stowed postition and rotate 123°. Attached to the hinge are 4 torsion springs which have a spring constant of 50 (in-lb)/turn...
  5. J

    (Statics) Truss with no vertical members, will it work

    Homework Statement Supposed to support a 50 kN weight at a pin joint at the center of a void as cost effectively as possible using trusses (e.g., trusses and pin joints have costs) Homework Equations Basic sum of moments and sum of forces = 0 The Attempt at a Solution Why can't I...
  6. U

    Truss analysis- why does it not work in this case?

    Homework Statement Solve for the support reactions (at A and B) in the figure given. (the pink thing is a cable and there's an arbitrary weight hung at the end of the cable). Homework Equations sum of forces in y direction=0 sum of forces in x direction=0 Sum of moments =0 The...
  7. H

    Truss Analysis: Finding Forces in Marked Members - Homework Problem

    Homework Statement Here is a link to a picture of the problem http://img571.imageshack.us/img571/374/truss.jpg" I have to find the forces in the members marked with an x. 2. The attempt at a solution I found the support reactions, but I'm not sure if I need them. Should I try to find the...
  8. S

    Analysis Of Truss, Method Of Joints.

    Homework Statement Hi so I have the following truss: http://screencast.com/t/BIdagRt5abg and I need to calculate the forces in every member by method of joints The Attempt at a Solution So I got the Reaction forces: F(BG) = 25N and F(AC) = 35N Now I'm not exactually sure what to do...
  9. L

    Trouble Working Out Internal Forces in Truss - Need Help!

    hi all, im having trouble working out the internal forces in this question, i tried before and got stuck working out the forces at joint C. i have been to see my tutor however he is on holiday till after the deadline for this assignment. handy... i was working out the forces by the...
  10. S

    Forces in truss members greater than applied force?

    I've had to conduct an experiment with strain gauges attached to each member and when I've calculated the forces in the members I've come out with really large forces in comparison to the applied force.. how does this work out?
  11. D

    Solving a Truss Reaction Problem: Find Reactions & Moment

    I have a little bit of an issue. I am trying to find the reactions on this truss. I know there are x and y at the first and y at the 2nd on the truss. But when I create my moment, do it take the 2500 lb into effect for the rope across the top and side as well? or do i omit those? My...
  12. C

    Max compressive axial force in a bar in a truss

    I've attached the question. I'm not looking for solution just general guidance on how to tackle the question. Do I calculate the internal forces? Where do I put the live load, at node 3 or the midspan of 2 and 3?
  13. W

    Engineering Design: Truss Bridge Questions

    Hey. I am currently in an engineering class designing a truss bridge and had a couple questions. (Note all truss members are considered to be two-force members) 1) Suppose the truss is symmetric and a force is applied through the middle of it. Is it normal in industry for any individual...
  14. X

    Solving Truss Force Problems: Step-by-Step Guide and Example Calculation

    Homework Statement See attachment. Homework Equations Sum of Fx, Fy, and Moments=0 The Attempt at a Solution A and B are pins, so there is a x and y component at each of these points. Cable has same tension on either side, 1200. Take the moment at A to be zero...
  15. P

    Bridge truss Static Equilibrium

    Homework Statement A bridge truss extends x = 214 m across a river (Fig. P12.68) where θ = 35°. The structure is free to slide horizontally to permit thermal expansion. The structural components are connected by pin joints, and the masses of the bars are small compared with the mass of a 1270...
  16. H

    Pulley forces on truss crane problem.

    Hi for my design project at uni I am to design a truss crane to a certain spec. I can easily calculate the forces in a truss without the pulley systems. However when I have the pulleys I'm not sure how this affects the forces in the truss. I have the load attached via a 4 cable pulley at the...
  17. P

    Finding the force exerted on a truss

    Homework Statement Find the Force exerted on member ABCD by the pin at B in figure P4.162 (figure is attached) The Attempt at a Solution This is also attached. As you can see I solved for everything I could. If I could solve for just one more unknown, I could solve the problem. I just...
  18. C

    Triangle Cantilever Truss Design

    1. I am an architecture student and the assignment is to design a truss, set up the problem and solve it using graphic statics. I think I did it correctly using the graphical method but I am interested in solving it mathematically. Did I set the problem up correctly in my diagram and if so...
  19. C

    Cantilever Trianlge Truss Design

    1. I am an architecture student and the assignment is to design a truss, set up the problem and solve it using graphic statics. I think I did it correctly using the graphical method but I am interested in solving it mathematically. Did I set the problem up correctly in my diagram and if so...
  20. C

    Forces in Truss Members (Statics)

    Homework Statement See attachment. Edit: Point A is a pinned connection (has a reactionary force in X and Y direction). Point B is a roller connection (only has reactionary force in Y direction) Homework Equations Sum Fx=0 Sum Fy=0 Sum of Moments=0 The Attempt at a Solution...
  21. P

    Truss stress compressive/tensile stress

    Hi I have found out which truss member that have compressive stress, and which have tensile. Now I have to select the metal for each member, I know how to find it when it is simple tensile stress (Sigma=Force/Area) But I think there is another equation when it is compressive stress, or...
  22. N

    Truss Bridge Tension and Compressions

    Homework Statement Given the weight of a CL-625 design truck (625 kN) on a truss bridge of span 50m, divided into 8 sections (each 6.25 m) with a height of 6.25m making 45deg angles and a width of 6m, what are the tension and compression forces of the members? Homework Equations Mb =...
  23. B

    Solving the Truss Bridge Problem

    First time poster, long time reader... Consider the truss bridge as shown in the attached diagram (Each member is the same length) A force of 1000N is applied 3/4 of the way across the bridge. We get: R1 = 250 N R2 = 750 N Resolving from the left we get: T1 = 250 / sin 60 T1 sin 60...
  24. T

    Member forces of a simple Truss

    Homework Statement hi all, I've got a simple truss question. Which asks to solve for the member forces. I've learned the stuff in class, but from what I see here, I don't know which joint to start with. With the provided image below, can someone please direct me to which joint I should start...
  25. J

    Truss - find internal force in each member

    Homework Statement please see the image, I am supposed to find the internal force in each member of the truss and state if its in compression or tension Homework Equations The Attempt at a Solution here is what I have so far (all in kN)... My=40 up Gy=80 up Mx=0 from joint G...
  26. J

    Internal force, members of truss

    please see the attached image, I'm supposed to find the internal force in each member of the truss. I used moments to find My=40 and Gy=120, I then moved on to FBD of joint G where I found Fgh=30kN in tension, and Fga=50kN in compression, next I did joint A to find Fab=30kN in tension...
  27. S

    Understanding Truss Problems: Solving for Reaction Forces and Member Forces

    ok this is a basic truss problem and I have to solve every member in the truss(see picture) Basically I started off solving my reaction forces...For the bottom left Pin, i got 8kips goin left, and 9kips acting down...for the bottom right roller I got 9kips acting up. So after working my...
  28. A

    Forces on a truss (to calculate stress)

    Homework Statement A simple pin-connected truss is loaded and supported as shown in the figure. All members of the truss are aluminum pipes that have an outside diameter of 4 in and a wall thickness of .226. Determine the normal stress in each truss member. Homework Equations Normal...
  29. J

    Answer: Solve Truss Beam Analysis | Axial Force Determination

    Homework Statement The problem requires to determine which of the 2 bars has zero axial forces without any computation. Homework Equations The Attempt at a Solution I can't tell which bar has zero axial forces.
  30. J

    Strength of materials- simple truss problem

    Homework Statement The bars in the truss each have a cross sectional area of 1.2in^2. If the maximum axial stress in any bar is not to exceed 25ksi, determine the maximum magnitude of P of the loads that can be applied to the truss. Determine the elongation of each member. E=29,000 ksi...
  31. C

    Forces in a Truss: Solve for AB Force

    [PLAIN]http://img109.imageshack.us/img109/3825/truss3.jpg I am having some problems with this one. Can I section the truss through members AB, BE and EF to solve for the force in AB, thus disregarding the fixed connections at left? I suppose I could go join by join, but I would like to...
  32. C

    How Can You Solve for Force in Member GI of a Truss?

    Can anyone suggest the method to use for solving for the force in member GI in the attached diagram? Is there a way to section the truss?
  33. C

    Why is the sin(60) term doubled in the truss equilibrium equation?

    cannot understand something about this. here are the equations: -T1-T3-T2cos(60)=0 x direction 2T2sin(60)-981N=0 y directionI don't understand why the sin(60) term is doubled in the y direction equation. Can anyone explain?
  34. G

    Design of steel truss footbridge

    Hi, I have to design a steel structured truss footbridge. Im using beam anology to determine the correct member sizes. Having trouble determining the maximum design moment (M*) Here's what I have calculated thus far: Q=6kN/m G=1kN/m 50m long, 3m depth, 3.125m spacing Self Weight...
  35. G

    Design of individual members in a steel truss bridge?

    Hi, I have to design a steel structured truss footbridge. Im using beam anology to determine the correct member sizes. Having trouble determining the maximum design moment (M*) Here's what I have calculated thus far: Q=6kN/m G=1kN/m 50m long, 3m depth, 3.125m spacing Self Weight...
  36. X

    How are member forces calculated in a pin jointed truss structure?

    Hello all. I am give a pin jointed truss structure. (Look at attached jpeg image) I have a worked solution of: F2*4 + F1*3-Av*6=0 Av=1/6(3F1+4F2)=600kN Ch=F2=600kN Cv=Av-F1=200kN Member forces: S1=-5/4 Av = -750kN S2=-CH=-600kN S5=3/4 Av=450kN S3=-5/4 s4=250kN...
  37. I

    Finding Axial Forces in a Truss: A Guide to Solving for BC, BD, and BE

    Homework Statement The truss shown is part of an airplane’s internal structure. Determine the axial forces in members BC, BD, and BE. Homework Equations The Attempt at a Solution Ok I am trying to figure out how or where to divide this truss up and forces to draw when I do. I...
  38. A

    Solving a Truss Analysis Assignment - Choose the Suitable Beam

    hello guys i ahve assigment , this assigment talk about the truss analysis the assigment is 3 parts first part : analysis the framework & show the tension & compression , i used method if sections , i have done this part. second part : analysis by using STRAND7 & choose the suitable...
  39. R

    Finding reactions at points on truss

    I honestly don't know how to approach this problem. I am to find the reactions at C and E. Since E is a roller, it will have moment, but since C is a pin, it won't have moment? What exactly do I need to figure out before attempting to write the equations for the reactions? Do I need to find the...
  40. D

    Internal forces in a truss

    the queen posted truss in the picture consists of the beam ABCD, compression members BE CF amd the cable AEFD, a stress analysis under the uniform load q is required. outline an analysis procedure, state the effects you would ignore and why. i am not sure what i am meant to be doing here...
  41. jegues

    What is the correct FBD and equilibrium equations for a truss analysis?

    Homework Statement See figure Homework Equations \sum F_{x} = 0 \sum F_{y} = 0 \sum M = 0 The Attempt at a Solution See other figure. is the FBD for my truss correct?
  42. I

    How Do You Calculate Forces in a Pin-Jointed Truss?

    Hi all, been here several times and found good help for several questions, but this time I'm out of luck, so here I go. Homework Statement By taking a section through the pin-jointed frame as shown, and considering the quilibrium of the structure to either the left or right of the section...
  43. F

    Truss Analysis: Find Forces on Members

    Truss Analysis :( Homework Statement Find the force on each of the members and tell if it is tension of compression. Homework Equations M = fd \sumFx and Fy = 0 The Attempt at a Solution Well, my professor said to us that the first thing to do is to compute for the...
  44. S

    Analyzing a Truss with Excel: Solving the Matrix Problem

    Homework Statement I have a simple truss to analyze using excel. I have done this and know how to do it on pen and paper using one equation to eliminate variables in another until down the line an answer pops out and I go back in and solve for all the other variables. However, this...
  45. E

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

    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? Your help is really appreciated. Thank you for reading
  46. P

    Statics: bad solution to simple truss problem regarding determinancy

    Homework Statement The attached solution was given as an answer to a simple truss problem in my sophomore level Statics class. We were to solve for the forces in each member of the truss, using the method of sections for FE and BC, and by joints for the rest. The Hibbeler 12th edition we...
  47. E

    Arch Truss Bridge, Static Determinacy

    Homework Statement This is for a bridge design project. We went for an arch bridge over the roughly parabolic valley. The arch is parabolic and rises 1.3 meters above the deck of the bridge. The deck is divided in 20 sections and supported by both vertical and diagonal members (hollow...
  48. S

    Need help with finding forces in a truss

    Homework Statement http://itsyourpc.org/sue/files/statics.jpeg Homework Equations please show me the equations. The Attempt at a Solution I am having a very hard time with this.
  49. N

    Designing a truss (working stress method) Missing Info?

    Homework Statement "Design a bridge over a valley 300m wide. Road surface is supported by a truss underneath." My problem: With calculations Now calculation for buckling says i need to design the truss for compression such that I > (P. L^2) / (pi^2 x E ) or Pcr > P where I = reduction value...
  50. T

    Is the Kinematics of 3D Space Truss Affected by Closed Loops in the System?

    Hi, I am a PhD student in math and in my current research I'm faced with the problem of analyzing the rigidity of a structure of rigid beams in 3D, that is if the structure can move. In particular, something like this: http://img525.imageshack.us/img525/1545/98322092.th.jpg where all...
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