Summary
We have designed a truss to support a point load, placed at 190mm from the edge of a 450mm gap. The vertical face of the trusses is modelled on the already established ‘K’ truss design, but the overall shape of the structure is our own. There are three ‘K’ units on each truss. The two vertical faces are held together at the top by another truss-like design. We modelled this on the ‘N’ truss.
The truss is constructed from hot-dog sticks, glue and bolts.
Introduction
The task was to construct a truss out of 48 hot-dog sticks and 30 bolts to support as large a point load as possible. It was to span a gap of 450mm and to support a load placed at 190mm from the end. The truss may have a maximum depth beneath the supports of 130mm, and the loading rod placed not more than 110mm beneath the supports. Member ends must be bolted and the forces within the members calculable.
Project Objectives
• Maximise the load capacity of the truss
• Achieve an even distribution of force to each member
• Construct the truss carefully for maximum quality
• Design a truss which did not fail from flexural-torsional buckling.
Development of the Model
We began by researching established truss designs, such as the Bailey bridge, Baltimore bridge and the N truss. We realised that although each type of truss was useful for its own purpose, none of the bridges was intended for supporting a point load. However, we compared the designs by calculating the distribution of forces in the members. This gave some guidance to the development of the model.
We researched the ‘K’ truss, which is composed of many repeated ‘K’ units, in either direction. This design gives the most even distribution of force to the members, which satisfies o...
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... to the members; reinforcing material glued to compression members; holes drilled towards the middle of tension members to give extra support; the rounded shape of the top and bottom of the trusses for improved weight distribution; and the ‘N’ truss design on the top and bottom to prevent flexural-torsional buckling.
Drawings are over the page
Conclusions
• The K-truss is the most effective means of distributing a point load amongst members, under determinate conditions.
• Increasing the concavity/ angle of the outer members of the truss lessens the forces in the members.
• Reversing the direction of the K’s at the position of the point load helps to lessen the force in the corresponding vertical members.
• It is desirable to have as many K’s in the truss as possible. The solution is maximised so that all 30 bolts are used, giving a good amount of K joints.
...Modelling: Rigging Patterns - The Carracks and Caravels." Jan's Sites: Navigation. N.p., 8 Mar. 2012. Web. 24 Nov. 2013.
Bridge efficiency is important as it helps reduce cost of building while maximizing the strength of the bridge. Many things can influence the bridge’s strength and weight, but the two main things that can cause a bridge to be a failure or success is the design of the bridge and construction of its joints. In order to build a potent balsa truss bridge, it is crucial to know how the layout of members and style of gluing can help increase or decrease strength.
A connecting rod subjected to an axial load F may buckle with x-axis as neutral axis in the plane of motion of the connecting rod, {or} y-axis is a neutral axis. The connecting rod is considered like both ends hinged for buckling about x axis and both ends fixed for buckling about y-axis. A connecting rod should be equally strong in buckling about either axis [8].
According to Suspension bridges: Concepts and various innovative techniques of structural evaluation, “During the past 200 years, suspension bridges have been at the forefront in all aspects of structural engineering” (“Suspension”). This statement shows that suspension bridges have been used for over 200 years, and that people are still using them today because they are structurally better bridges. This paper shows four arguments on the advantages of suspension bridges, and why you should use one when building a bridge. When deciding on building a suspension bridge, it has many advantages such as; its lightness, ability to span over a long distance, easy construction, cost effective, easy to maintain, less risk
The failure mode in Case 2 is similar to that in Case 1, but the buckling load was increased in Case 2 to reach 51% of the total applied loads rather than 44% in the previous case. The end braces at the top of girder helped to resist and minimize the lateral moment of the webs, Figs 18-19. As a result, the load buckling increased (capacity) and the bending and buckling displacement decreased (0.021", 0.1"), as shown in Figs 16-17.
The first is for control of buckling in the main girders during construction. The wet concrete imposes significant bending of the bare steel girders and the compression flange needs to be restrained against buckling. The second function is that bracing can be used to distribute the vertical bending effects between the main girders, and to ensure that lateral effects such as wind loading and collision loading are shared between all the girders. The third function is dimensional control, as a result of unequal loading, the horizontal distance between the flanges of adjacent girders will vary if not constrained. Bracing was placed at every transverse stiffener location for both girder sizes. 4 x 4 x ½ inch angles were used for bracing elements (Figure
Mr. John Roebling who had built numerous smaller suspension bridges was commissioned to design the new bridge. Mr. Roebling knew he needed an innovate design to deal with the unique challenges of this project. So he designed the first suspension bridge that used steel cables instead of iron, had an open truss deck structure, and it was the first bridge to use caissons to anchor the structure. This creative design represented the new industrial age an...
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Strain in the Euler-Bernoulli beam analysis is expressed in terms of the deflection of a “neutral surface”. Under transverse loading, one of the beam surfaces shortens while the other elongates. Therefore, a neutral surface that undergoes no axial strain is established at the centroid (or centroid of an “equivalent” section in the instance that the beam is a composite of different materials) between the surface undergoing axial compression and the surface undergoing axial elongation.
Another theory that has been suggested has come from Dr, Joseph West from the Indiana State University. He suggests that three round wooden beams to each
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Fanella, D. (2011). Reinforced concrete structures: analysis and design / David A. Fanella. New York: McGraw-Hill, c2011.
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