Simple Truss

4 Key excerpts on "Simple Truss"

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  eBook - PDF

  Foundations and Applications of Engineering Mechanics

  • H. D. Ram, A. K. Chauhan(Authors)
  • 2015(Publication Date)
  • Cambridge University Press

    (Publisher)

  4 TRUSS 4.1 Introduction Truss is a structure made of straight mechanical members to support or transfer the loads to other bodies, e.g., structures used for supporting the power transmission lines, TV towers and the bridges. Structures which support the roof of sheds at railway stations, food grain stores the common examples of the application of truss. The truss is a very common structure in the engineering applications. Figure 4.1 shows a Simple Truss. AB, BC, AC, etc., are called members of the truss. The members are joined to form a rigid structure. A, B, C, D, etc., are called joints. These members are joined together at the joints by bolts, rivets or welds. Figure 4.1 The truss supports the loads at joints and transfers them to the support. In the Figure 4.1, the supports are at A and E. These supports are either pin connected or roller. The trusses are classified in different ways and in different groups in order to understand the procedure and simplification of analysis. 4.2 Construction of truss Truss is made of straight members joined at the ends. Members may be joined by rivets or bolts or welded, but they are assumed to be joined by smooth pins. This is the idealization of the joints. It simplifies the analysis of truss. 208 | Foundations and Applications of Engineering Mechanics 4.3 Dimensionality of truss The trusses are classified in two groups on the basis of dimensionality. These are: (a) Two-dimensional or plane truss (b) Three-dimensional or space truss 4.3.1 Plane Truss: If the center lines of all the members of the truss lie in a plane, the truss is called plane truss. It is also called two-dimensional truss. 4.3.2 Space Truss: If the center lines of all the members of the truss do not lie in a plane, the truss is called space truss or three-dimensional truss. 4.4 Rigidity of truss Consider a triangular structure of three members ABC as shown in Figure 4.2a. Figure 4.2a The members AB, BC and CA are rigid and pin connected at the ends.

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  Engineering Mechanics: Statics

  Modeling and Analyzing Systems in Equilibrium

  • Sheri D. Sheppard, Thalia Anagnos, Sarah L. Billington(Authors)
  • 2017(Publication Date)
  • Wiley

    (Publisher)

  For example, the truss shown in Figure 8. 1.1 carries the weight of the roof to the walls, and the truss in Figure 8.1.2 carries the weight of a bridge roadway to the vertical supports. For a system to be classified as a truss, it must: 1. Consist exclusively of straight members joined at their ends to form a rigid frame. 2. Have joints that can be represented as pin connections, even though the actual joints may consist of welds, rivets, large bolts, or pins (often in conjunction with a gusset plate). We idealize these joints into the representation shown in Figure 8.1.3—that of a simple pin connec- tion. In this idealized joint, the pin fits smoothly into holes at the ends of the straight members and is therefore capable of transferring gusset plate idealized as Figure 8.1.3 A connection in a truss, idealized as a pin connection. Thalia Anagnos Figure 8.1.2 (a) An example of a truss bridge; (b) Schematic of a truss bridge; (c) Free-body diagram and analysis of truss support forces. A B C D E Deck Stringer Floor beam (b) W/2 A B C Bridgetruss D E W W W W/2 F Ax =0 F Ay =2.0W F Ey =2.0W (c) John Bishaw/EyeEm (a) 462 CH 8 MEMBER LOADS IN TRUSSES forces between members but not capable of transferring moments. Furthermore, the centerline of each straight member is assumed to intersect the center axis of the pin (Figure 8.1.4). 3. Carry external forces (and no moment), exclusively at the pin joints. This requirement is not as restrictive as it might first appear. For example, in Figure 8.1.1b, the roof force is transferred to purlins, then to the truss, and finally to the walls. In Figure 8.1.2b, the weight of the roadway is transferred to the stringers and floor beams, then to the trusses, and finally to the vertical supports. As a consequence of these three requirements, the members that make up a truss behave as two-force members.

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  Engineering Mechanics

  Problems and Solutions

  • Arshad Noor Siddiquee, Zahid A. Khan, Pankul Goel(Authors)
  • 2018(Publication Date)
  • Cambridge University Press

    (Publisher)

  Chapter 6 Analysis of Trusses 6.1 Introduction Engineering structures are built by joining large number of members to support heavy loads. These are broadly classified as truss, frame and machine, depending upon loading conditions and applications. Truss is built up by joining various prismatic bars at different joints. The members may be of different cross-sections like angle section, channel section or circular section, etc. Trusses are called economic structure as these can support heavy load over the large span. The examples of trusses are mobile or electrical transmissions towers, bridges and roof truss, supporting roof of buildings and workshops, etc. 6.2 Classification of Trusses Trusses are broadly classified in two categories: a. Depending upon joining of members in planes: Two-Dimensional Truss: This type of truss is also called plane truss as its all members lie in one plane. Thus, it can be considered as a structure of coplanar members. Bridges and roof trusses are examples of this type of truss. Three-Dimensional Truss: This type of truss is also called space truss and its all members lie in different planes. It is a structure which consists of collection of non-coplanar mem-bers. Mobile or electrical transmission towers are examples of this type of truss. b. Depending upon quantity of members and joints: Perfect Truss: This type of truss does not change its shape under external loading. It utilizes the optimum numbers of members and joints. It is considered as just rigid truss because removal of any member can cause failure of the truss. 246 Engineering Mechanics Mathematically the condition for a perfect truss is m = (2 j − 3) Consider Fig. 6.1 where m = 9 and j = 6 (2 j − 3) = (2 × 6 − 3) = 9 As equality exist between ‘ m ’ and ‘(2 j − 3)’ it called perfect truss. Imperfect Truss: This type of truss does not retain its shape under external loading due to joining of fewer members as compare to perfect truss.

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  Architectural Structures

  Visualizing Load Flow Geometrically

  • Edmond Saliklis(Author)
  • 2022(Publication Date)
  • Routledge

    (Publisher)

  4 Trusses

  DOI: 10.4324/9781003180913-4

  Two-dimensional trusses are defined as planar structures made up of individual straight elements, known as “bars”. Trusses are an unusual subset of structures in that they ultimately act as a beam, spanning long distances, yet the individual elements of the truss are assumed to never bend. It is important to understand that even though the overall structure bends like a beam and becomes concave up typically for gravity loads, the individual bars themselves remain straight and unbent. There are some idealized, mathematical assumptions about classical trusses:

  • The individual bar elements are assumed to be “hinged” at their ends, i.e. they cannot transfer bending to the subsequent member. This connection at the ends of truss elements is completely analogous to the “internal hinge” previously shown in Figure 2.23 of Chapter 2 .
  • The individual bar elements are assumed to be weightless, i.e. they do not bend at all due to their lack of self-weight.
  • Any loads applied to the truss may only be applied at the connecting points linking the bars together. These connecting points are called “nodes”. Loads may only be applied to the nodes of a truss, never to the bars directly. The reader can imagine that if loads were applied to the bars themselves, those bars would bend, which would violate the fundamental idealization of “no individual bars bend”.
  • The individual bars experience only pure tension, or pure compression, no twisting, no bending. This is the hallmark of the truss’ efficiency; namely carrying load solely through tension and compression, as opposed to bending. This is a very efficient means of load flow, notice how open and airy the trusses of Figure 4.1

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