What is Trusses: Definition and 54 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. 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. Vigardo

    Optimisation software for trusses (or frames)

    Dear experts, What software is available (free or not) to optimise the member cross-sections of trusses or frames? Which one is your favorite? Would any of them optimise the topology and geometry? Ideally, the global buckling of the whole structure as well as the buckling and strength of...
  3. T

    What do the numbers in the method of joints analysis for trusses represent?

    Hello all I am trying to analyse a truss using the method of joint process i.e I am trying to determine whether each member is in tension or compression. I have the following truss that I want to analyse using the method of sections. Just focusing on joint A, I have created a FDB and...
  4. S

    Why does ENGR Mechanics: Statics cover *hinged* trusses?

    Something that has always been off for me is the canonical pedagogical treatment of analysis of trusses in the course typically called "Engineering Mechanics: Statics". Certainly, every cantilever bridge I see has completely attached joints, although lately I have seen some airy, open...
  5. Francis Hannah

    How many Trusses act on this system?

    Is there only two trusses? As shown below:
  6. Vanessa Avila

    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
  7. F

    How Do You Calculate Forces in Truss Members?

    Homework Statement It's given that the applied force is 10kN at F and 25kN at E . I have trouble of finding the other real force in the member of the trusses . Homework EquationsThe Attempt at a Solution So , i start by drawing the FBD at F . I have 10kN point downwards , so the reaction is...
  8. F

    Why Is the Unit Load Not Considered When Moved to B in Truss Analysis?

    Homework Statement Pls refer to the second photo , the red line part ...I don't understand the meaning of when 1 unit load move at C , the unit load is inclusive in the right system... I can understand the FBG sin45 + 1 = RE Homework EquationsThe Attempt at a Solution When the in unit load move...
  9. C

    Moment about a point in trusses

    Homework Statement for moment about C, the author gave [-F_(FE)](5) +3.2(4) +6(5) = 0 i don't understand the working...Why there are moment 3.2(4) and also moment 6(5)? Homework EquationsThe Attempt at a Solution for moment 3.2(4) , it's centered at F, so ,it's not moment about C ,am i...
  10. Soumalya

    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...
  11. C

    Truss Forces: Calculating F(AD) and F(AB) for Resolution of Forces

    1.) from the calculation of F(AD), the force should point towards A,right? (red arrow) but, in the calculation of F(AB), the (1/sqrt rt2)(48.08) should be positive,right? (which is pointing towards LEFT)? 2. Homework Equations The Attempt at a Solution this involve the resolution of forces...
  12. K

    Designing bridge not perpendicular with ground

    I was wondering how to approach building a bridge which must lie across to points of differing points (one end is elevated 5 cm off the ground), meaning the bridge lies at an angle across a 35cm expanse. How would you calculate the forces exerted on each member if the bridge does not lie...
  13. Z

    Find Forces in Truss Bars BD, CD and CE

    1. Homework Statement How to find forces in bars BD CD and CE? Homework Equations Static[/B]The Attempt at a Solution Bd: -2.5 KN Cd: 0.866 KN Ce: 1.73 KN
  14. D

    Which members in the truss are zero force?

    Homework Statement Okay, I need help quick, exam in few hours, I won't be able to reply to this later. http://puu.sh/lQeXl/42907b0a12.jpg In my lectures notes this is given. In the example shown with it, the one on the right in particular. Look at Joint C, it is unloaded, it also has to...
  15. C

    Strength of Materials Stress Question

    Homework Statement Member AD of the timber truss (shown in attachment) is framed into the 100 x 150 mm bottom chord ABC as shown in the insert. Determine the dimension "a" that must be used if the average shearing stress parallel to the grain at the ends of chord ABC is not to exceed 2.25...
  16. thegreengineer

    Vector mechanics for engineers -- Confusion described below

    Homework Statement Look I have an exercise about trusses in vector mechanics. It's the following: https://scontent-lax3-1.xx.fbcdn.net/hphotos-xfp1/v/t1.0-9/12003339_1645511085733429_8210043018491702007_n.jpg?oh=4955534403fb6f3f5f9a40c9c0b8ecbc&oe=569761ED I have to determine the forces in...
  17. V

    Finding Forces in Truss Members for Solving Truss Problems

    Homework Statement Homework EquationsThe Attempt at a Solution First i Found the external forces. Ax =0 , Ay = 8Kn, Jy=8Kn and P = -16Kn Then i took moment about point G to eliminate FH and EG and so was able to find CH = 14.66Kn. I am kind of stuck on how to tackle the problem further...
  18. J-dizzal

    Finding Forces in Truss Members Using Method of Sections

    Homework Statement Determine the forces in members BC and CG. The forces are positive if in tension, negative if in compression. Homework Equations ΣF=0 ΣM=0 The Attempt at a Solution im not sure what I am doing wrong here, i think it might be my angle θ? I got 3.66N tension as my answer but...
  19. F

    Can you check my solution for this trusses problem

    < Mentor Note -- thread moved to HH from the technical physics forums, so no HH Template is shown > I didn't attend the lecture in which the professor explained trusses so I don't really know. Am I doing something wrong so far? is the force DE 0? because if go at the point C and calculate CD...
  20. S

    [Trusses] Problem finding forces in members

    Can anyone please explain where does 5/sqrt29 and 3/sqrt34 come from? I already got BC/know how to find BC, but in my own method, I tried to use moment about A or B, knowing that there is HGx, HGy & HCy, HCx -- there are way too many unknowns @ H. So, looking at this, I'm wondering where does...
  21. D

    Solving trusses with the Direct Stiffness Method

    I'm creating a computer implementation to solve planar trusses. And I'm not sure how to check if the truss is solvable or not. Can you help me with that? In my implementation, the trusses are created randomly (needs to be this way), so i get a lot of unstable or indeterminate trusses. I want...
  22. P

    Truss Analysis: Find Reaction Forces with Explanation

    Hi, I'm new on this website and it seems great :p So, I'm struggling with something really simple... trusses analysis. I'm struggling with moments etc , I've just drawn an example linked in this post , could you try to find the reaction forces (roller pin etc) with some explanation ? Thanks
  23. K

    Solving Truss Structures: Troubleshooting and Equilibrium Equations

    Homework Statement I'm having trouble with this structure, but I think I finally figured it out. I'm hoping to get a confirmation or a push in the right direction if I'm wrong. I'm trying to solve the truss in terms of the weight at the end. Homework Equations Standard equilibrium...
  24. P

    Need help on some questions - Moments, Bearings & Trusses

    Need help on some questions -- Moments, Bearings & Trusses Hi guys, just have some general queries on a couple of problems : 1) http://i1097.photobucket.com/albums/g357/princejan7/reactiondirection_zps85d28093.png They got the moment of the force BC about A by splitting into components...
  25. J

    Castigliano's Theorem for Trusses

    Can we get the rotation(Slope) of a TRUSS member, let's say a warren truss using Castigliano's Theorem? Thanks.
  26. W

    What causes the change in direction of CD in a truss free body diagram?

    I missed a class and now I am having some trouble understanding what's going on. I am trying to solve for the components of forces in the truss and whether they exert a compression force or a tensile force. I have attached an image taken from my book and the free body diagrams provided by the...
  27. B

    Plane Trusses Finite Elements 2 - Assembled Matrix

    Folks, I am having difficulty understanding how this global matrix is assembled with the naming convention used as shown in attached. The numbers in the corners such as 1(1,2) etc in figure 4.6.3 (b) denote the global and element numbers respectively. Can anyone shed light on how this...
  28. B

    Transformation between Global and Local Coordinates for Uniform Bar Elements

    Folks, The element equations for a uniform bar element with constant EA according to the attachment is given as ##\displaystyle \frac{E_a A_e}{h_e}\begin{bmatrix} 1 &0 &-1 &0 \\0 &0 &0 &0 \\-1 &0 &1 &0 \\ 0 &0 &0 &0 \end{bmatrix}\begin{Bmatrix} u^e_1\\v^e_1 \\u^e_2...
  29. D

    Statics Forces Problem (Trusses)

    Homework Statement I was doing a problem with my friend (the image that is attached to this) and when looking up a solution online... It said that the forces at reaction supports B and C are 5 kN in the y direction... Homework Equations The Attempt at a Solution We thought...
  30. G

    Method of Pins- Trusses (conceptual)

    Homework Statement I am designing a bridge that looks like this: http://imgur.com/zFsW7 and using the method of joints to find the tension in each pin. The bridge has to hold 10,000 lbs on each pin, and we have to find the maximum tension in each member (so tension of each member when...
  31. T

    Load on Bridge Trusses for Intro to Engineering

    Homework Statement Calculate the load on each member Homework Equations \sum \tau=0 -because it isn't rotating. \sum F =0 - because it isn't moving. \tau = Fd\sin \theta - to take the torque at any point The Attempt at a Solution I can calculate the torques at each point. I...
  32. J

    Solving Truss Problems: Need Help!

    Need help with trusses! Hey guys So I'm trying to solve this truss problem and get all the reactions of the trusses I've done it so many times but my equations never work out and I get crazy answers :\ I've found the reactions at A and B Ax=-50kN Ay=72kN By=128kN My answers for...
  33. B

    Statics in traingles, or trusses

    Hi there, I have been given the questions below as part of some revision before we begin mechanics next term. I have looked back through my notes and I seem to be missing the notes on calculating the forces. So far I know XZ = 9.49m ZY = 4.24 Angle x = 18.4 Angle y = 45 Angle Z =...
  34. G

    Why do trusses, beams, and frames have unique force systems?

    What makes the three mechanical objects Truss members, beams, and frames having different characteristics related to force systems. Example truss members only exhibit tension and compressional forces, that's different from others.
  35. M

    How Is the Right Triangle Used in Truss Force Calculations?

    Hi, I have a, I believe simple, problem. I am studying for a Statics final and while doing problems with a Truss I came to a problem that I did not know how to solve. It is already solved for me, but I do not get how. The truss has a force coming out from the side but instead of an angle there...
  36. S

    What are the force components for each member in the loaded truss?

    Homework Statement I need help with trusses. Determine the force in members: (a)AD, (b)CD, (c)AB, (d)BC, (e)BD of the loaded truss. (Note: compression forces must be negative.) Homework Equations ? The Attempt at a Solution I found the components of AB and BC since upward...
  37. Femme_physics

    In trusses, does the number of screws on a joint matter?

    we're going to start trusses soon (statics) and I want to know if I should pay attention to several screws on a joint...for instance, I attached a question and in the drawing I see sometimes 2 and sometimes 3 screws on a joint...is it relevant, or should I treat them as though they were one screw?
  38. M

    Timber Roof Trusses: Supporting Domestic Residences

    Dear all, Situation: plumber has drilled a 32mm hole through a 9"x2" timber joist. This is being used to support a second floor domestic residence. ive been told the hole is central with in the section (ie: 9" thus 4.5" to centre) but its only 30mm from the nail plate. Will this...
  39. P

    How Do You Solve for Unknown Forces in a Truss System Using the Point Method?

    Homework Statement Below is a truss system, use the point method to solve for all forces within the trusses. http://tinypic.com/view.php?pic=25i2dma&s=3 my question, If I take pin F then I have 4 trusses, 2 of them known(FE, FD) and 2 unknowns(GF, CF). exactly what should I do with truss...
  40. jegues

    Analyzing Force Members and Trusses: Calculating Equilibrium and Moments

    Homework Statement See Figure Homework Equations \sum F_{x} = 0 \sum F_{y} = 0 \sum M = 0 The Attempt at a Solution See Figure I'm fairly certain the force I drew at point D isn't at a 90 degree angle, but if its not I can't find the perpendicular distance for the...
  41. N

    A few questions about a problem involving Trusses

    Hi! I'm really having a problem understanding this part of statics so please help! In this picture, http://i312.photobucket.com/albums/ll323/IAmMaxwellEdison/Members.jpg, what are the zero force members and how do I identify them? I'm pretty sure that GH, CF, and CD are zero-force members...
  42. N

    A few questions about a problem involving Trusses

    Hi! I'm really having a problem understanding this part of statics so please help! In this picture, http://i312.photobucket.com/albums/ll323/IAmMaxwellEdison/Members.jpg, what are the zero force members and how do I identify them? I'm pretty sure that GH, CF, and CD are zero-force members...
  43. S

    How Accurate Is the Analytical Method for Calculating Truss Forces?

    Hi. The question is attached as well as my attempt at the answer, which I'm pretty sure is at least partially wrong. I have'ne included my calculations at point B as I have uploaded the limit of 3 files but I got BC=18.30kN (compression) Any help would be great thanks.
  44. K

    Determine Zero Force for trusses

    Homework Statement http://img43.imageshack.us/img43/4355/97240590.png Homework Equations * If only two members meet in an unloaded joint, both are zero-force members. * If three members meet in an unloaded joint of which two are in a direct line with one another, then the third...
  45. C

    Frame Works Trusses Homework: Determine Forces in Trusses

    Homework Statement I need to verify a couple of unknown forces in a truss, attached image (all individual trusses are 300mm in length) Homework Equations Determine the forces in trusses shown. The Attempt at a Solution This is a lab and I've used a telescopic gauge with a...
  46. J

    Solving Truss Loads: Moment, Trusses & Reactions

    Homework Statement http://i277.photobucket.com/albums/kk63/sarcasticlil123/truss.jpg Homework Equations p1=800#, p2= 600# and a=8, determine a reaction load The Attempt at a Solution sum Ma=0=-4.5p1-6p2+12.5cy I am generally lost, this isn't homework its practice for the final...
  47. S

    Problems involving trusses using method of joints

    While solving for problems involving trusses using method of joints, how do i know which member is in compression and which is in tension? any help would be appreciated, this stuff's been bugging me for quite some time thanks and god bless
  48. L

    Pin joint Trusses and Equilibrium

    I have a general question about solving these types of problems. I had two different problems for calculating the tensions and compressions of a pin-jointed truss. both problems were of a trapezoidal shape with 5 pins in total. in one problem, a weight was applied to the center truss on...
  49. J

    Solve Force in Member HE: Trusses Homework

    Homework Statement Determine the force in member HE for the truss in the figure. All members are length 0.8m except GH. The Attempt at a Solution I solved for the reaction forces at G and got Gx = 1039 N , Gy = -1200 N, A = 1800 N. My professor said to then draw a FBD of G and solve for...
  50. M

    Trusses Assignment: Help Needed for Sources and Calculation

    Homework Statement I'm currently doing a assignment about trusses, it's all about the theory, concept, animation and calculation. However, I'm lack of sources for doing this assignment. So, can anyone please kindly recommend some useful links to me? Thank you... : )