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. A

    Calculating Support Forces and Stress in a Simple Truss Problem

    Homework Statement Hi guys, Below is a picture of what I am given. I need to calculate the support reaction forces and the stress in each truss. Having problems resolving the offset weight. Homework Equations All the supports are pin supports. Any ideas how to get started? The...
  2. C

    MATLAB Solving a Truss Problem with MATLAB: Equilibrium Equations and Results

    Ok, I've had a shot at this problem we've been given in MATLAB. Though I'm very new to physics forums. I've attached the actual problem and also a few of my equilibrium equations. I've written out the matrice in MATLAB but I'm guessing its incorrect as the answer I'm getting in Matlab...
  3. L

    Influence the overall strength of a truss bridge?

    Hi all, I've been looking at a few trusses lately and was wondering what the main factors are that influence the overall strength of a truss bridge? I have an idea that the more members taking loads, the stronger the truss, hence members should be at sharper angles. Of course i could be dead...
  4. H

    Simple truss question driving me crazy =/

    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...
  5. S

    Which truss structure is stronger in this jpg?

    All things considered equal, would one of these truss structures be stronger than the other? Consider all heights equal, load equal, arms dimensionally equal, etc.. Just going off the angle difference of the triangles. Oh... if there is a difference in strength, how can you calculate that? Is...
  6. M

    Truss Bridge Design and Analysis: Warren Truss with 20 Joints and 37 Members

    Truss urgent Help Homework Statement We must design a truss bridge that we will then build from spaghetti. The chosen design is a warren with vertical supports. It has 20 Joints and 37 members. (Bridge is 64.8cm long and 10.2cm high) Homework Equations I am trying to calculate the...
  7. Q

    How to Calculate Axial and Lateral Loads in a Truss System with a Pulley?

    Homework Statement http://g.imagehost.org/0110/nub.jpg Total tank weight (with liquid) is around 3.1kips Lateral load on wall is defined as 6kips[1-(Faxial/6kips)]^2 Faxial is defined as the axial force along a wall -- maximum allowable is 6kips Maximum allowable force in any truss member is...
  8. Z

    How Do You Calculate Forces in a Truss Without Given Angles?

    Hello, I have a test after 4 hours and I really need to know how to solve this :S I tried my best and threw 4 pages of scratch papers already ! Please help me... I know I am doing it wrong, I tried and tried but it did not work .. I am really frustrated I feel like I am going to fail the test...
  9. B

    Pratt Truss Analysis: Get Help From Experts

    Pratt Truss Analysis :( Homework Statement Hello, first post here. Been given an engineering assignment for school but not quite understanding how to answer all these questions. Homework Equations Was told to use Method of Joints for the reactions on left and right. And Method of Sections on...
  10. R

    Analyzing Forces in a Truss

    Homework Statement Determine the forces in each member of the truss shown. Also find the values for any reactant forces http://img201.imageshack.us/img201/6853/trussnu9.jpg Homework Equations Fx= 0 Fy= 0 The Attempt at a Solution I set θ in the corner of J1 tan θ=12/16 θ =...
  11. A

    Method of joints for a truss

    Hi there! Can anyone take me through the method of joints procedure for this truss? I am having trouble working out the reaction forces at the pin at joint A. Is there supposed to be a vertical component to the reaction force as well a a horizontal (seeing as it is a pin)? And if so where...
  12. H

    Complex scissors truss question

    Homework Statement The symmetrical scissors truss is supported at point A and D. The support at D is a rocker bearing and does not produce a horizontal reaction. A, B, C, D, E, & F are pin joints. The members of the truss are not joined to each other where they cross. At A, the angle...
  13. G

    Truss compression and tension forces help

    The space truss showin has compression and tension forces acting in the members as shown. Force F is 10kN, determine the three unknown forces (F1, F2 and F3). I know that it should be the summation of Fx, Fy and Fz, however for F1, there is no reaction force, so I don't know what to...
  14. P

    Shearing stress - timber truss

    Homework Statement member AD of the timber truss shown (attached) is framed into the 100 X 50 -mm bottom chord ABC as shown (attached - detailed view). determine the dimension 'a' that must be used if the average shearing stress parallel to the grain at the ends of the chord ABC is not to...
  15. T

    How Do You Calculate Forces in Truss Members IK, JL, and JM?

    [PLEASE HELP!] Forces in members of a truss Homework Statement A barrel vault truss is loaded as shown. Knowing that the length of the bottom chords DF, FH, ..., and QS is 3 ft, determine the force is members IK, JL, and JM. http://img68.imageshack.us/img68/4817/fyjfhjfgjhfghgx8.jpg...
  16. C

    Calculating Forces in Roof Truss Members for Basic Roof Truss Experiment

    Im doing this problem as a part of the experiment for a Basic Roof Truss. I first started off measuring the deflection for each member of the roof truss (member dismantled from the roof structure) by applying certain amounts of weights. Next I put all the members up into a roof structure as...
  17. I

    Truss Analysis and Method of Sections

    Hello all, first post. I have a mechanics test coming up and a the lecturer gave a very strong hint that a question like this with a scissor truss will be on the exam so how would you go about solving a question like this (finding force in all members). I worked out the reaction forces as...
  18. K

    Find Reactions of 4000lb Crate in Truss Figure 1

    Homework Statement A 4000lb uniformly weighted crate is attached by light inextensible cables to the trus show below. Simply determine the reaction at A and E of the truss show below Figure 1 attachment Homework Equations I used the Moment arm equation of M = F*Distance The Attempt...
  19. S

    Force in each member of truss

    Homework Statement Determine the force in each member of the truss shown. Homework Equations \SigmaFx = 0 \SigmaFy = 0 \SigmaM = 0 The Attempt at a Solution I divided up the truss into different systems, the whole truss, and then a system for each pin. I must be doing something...
  20. C

    Truss Structure Dilemma: Determining Compression and Tension Forces

    Homework Statement I spent a few hours trying out this question, so I probably need help. This is a seven pin-jointed structure mounted on the wall, with the following information given: 1) S1 and S2 are wall supports, but S2 is assumed to have no friction with the wall i.e. no vertical...
  21. M

    Statics: pratt truss calculation check

    Homework Statement please find it attached as pdf. Homework Equations joint method was conducted. The Attempt at a Solution please find it attached. i spent so much time on this and i took statics like 1.5 years ago. can you help me find my mistake? i can't seem to find why...
  22. D

    Pratt vs Howe Truss Bridge Building: Deciding for Physics Class

    Homework Statement Hi, I have to build a Popsicle Stick bridge for Physics class. I really don't have much knowledge on bridges as most of this was to be researched. I did a lot of research but I'm having trouble deciding between these two trusses. Restrictions/Requirements: Length: 55 cm...
  23. V

    Analyzing Member Forces in a Truss

    Homework Statement Determine all the member forces in the truss shown below, and identify tension/compression for each member. I know there was more to what I was supposed to put here, but I really only have a terminology question. I know that I have to determine all of the reactions...
  24. S

    How Do You Resolve Forces in a Statically Determinate Truss?

    Homework Statement Help required please. Method to be used is resolution of forces. thanks, sharifullah. Homework Equations The Attempt at a Solution
  25. P

    Solving Truss Calculations: How to Find the Forces

    I mainly am having trouble accurately calculating the force on members in a truss. The reason being is sort of common, my teacher skimmed through the lecture on these calculations, and left the entire class in a fog. I've made my best attempts at researching on the Internet, but so far no real...
  26. A

    Truss and Suspension bridge.

    How will I calculate the forces involved in a truss and suspension bridge, my teacher did not explain this fully and I'm confused as hell.
  27. B

    Forces on a Truss Homework: Find Tension/Compression

    Homework Statement Ok, you'll have to wait for my picture. Basically we are doing trusses, and I'm not sure where I'm going wrong here. We are to find the tension/compression in each member(line) of the truss. Ok, from my picture. F1 is directly at B(in neg y direction), and is...
  28. S

    Analyzing Truss w/ Counters: Find Force in Green & Pink Members

    How would you begin to analyze a truss of this style? The picture I posted is the situation given. Say you want the force in the green member and the pink members given loads 1,2,3. If the pink members can only act in tension, where you begin? For those who may not know, the support on the...
  29. U

    How to Identify Zero Force Members in a Truss Problem?

    I need to find all the zero force members, and solve for the other members. I am at school right now but I can definantly tell AB and AC are zero force members. When I get home I will see what else I can come up with. Also I cannot remember how to get the angled trusses :grumpy: Also All 3...
  30. V

    Truss Analysis: Solving for Zero Force Members using Method of Joints

    Hi Guys, I am having trouble determining the zero force members in the truss below. I am planing to use the method of joints to solve for the forces in the beams. So if I knew the zero force members it would be easy.
  31. J

    Understanding Torque Truss Problems: Examining Question 3.22 with Diagram

    Okay, I have uploaded the question to imageshack because it would be to difficult to understand the question without the diagram. Basically, I've done a lot of work on it and know I'm on the right track. If someone could point out where I have made a mechanical error it would be greatly...
  32. S

    Max Load Calculation for Truss with 10ft Span

    fig 6-12) Members AB and BC can support a max compressive force of 800 lb. and members AD,DC and BD can support a max tensile force of 1500 lb. If a=10 ft determine the greatest load "P" the truss can support. My dear friends! the above truss question has become a headache for me. I...
  33. B

    Why Can't I Achieve Equilibrium in My Truss Analysis Problem?

    Hello, I'm having trouble with a truss analysis problem. We are supposed to use the method of joints & the method of sections. We have to find all the external reaction forces and internal member forces. The method of joints is not problem, and I THINK I'm doing the method of sections...
  34. P

    Truss Problem 6.30: Urgent Help with Stress Calculation | 1020 Steel

    truss problem, urgent help! Hey guys i need help with setting up this truss problem 6.30 which can be seen here, http://www.mustangmods.com/data/16002/study1.jpg I know the stress in bc is 10.4ksi (tension) and that the safety facotr for it from 1020 steel is 4.038, I just need help...
  35. M

    Gees, Feeling Stupid? Need Help with Truss Forces? Let's Get Started!

    Gday guys, Im having trouble finding the forces in this truss. I feel really stupid, I should be able to do this. Can you guys give me a hand starting off? Cheers. :blushing:
  36. L

    Solving Statics Truss Problems: Plotting Force in Member BC & Angle ø Range

    The question is stated below. I found out an answer but it doesn't seems to be correct to me. I made a few sketches to clear things up a bit, sorry for bad quality, too much compression. The simple truss of Prob. 4/2 is modified as shown in the figure, in that the angle of the support surface...
  37. O

    Truss - how are forced transfered

    I'm having problems with truss. Is there like a simulation or animation which shows me how the forces are being transfered. I need to mentally visualize what's going on before i start to calculate. I'm doing really bad.. need help~ i'm going over truss by cutting and by piece or frame ..
  38. exequor

    What are the forces and connections in this roof truss?

    The diagram for this quesion is at http://www.drewtemp.com/helios/physics.gif The first thing that i did was that i made the free body diagram. From my knowledge i would say that AB and BC are in compression and AC is in tension (i think that is correct). Now the question asked to take...
  39. exequor

    How Do Forces Affect Tension and Compression in a Roof Truss?

    The diagram for this quesion is at http://www.drewtemp.com/helios/physics.gif The first thing that i did was that i made the free body diagram. From my knowledge i would say that AB and BC are in compression and AC is in tension (i think that is correct). Now the question asked to take...
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