Truss Design Project Essay -- Engineering

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... ... 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.