Design a Trussed Bridge to Measure Strength to weight ration - Essay Example

Design a Trussed Bridge to Measure Strength to weight ration In this design competition, two models of Warren truss (Bridge A and Bridge B) are presented. The aim of the competition is to provide an analytical approach to the bridge design by subjecting the prototypes to damaging failures. In the designs of Bridge A and bridge B, “scientific principles, mathematical tools, and engineering concepts” are considered. Experimental testing gave the results as follows; Bridge A with a mass of 0.

1892 Kg and 0.3m supports a mass of 25.251Kg, whereas Bridge B with a mass of 0.2003 Kg supported a mass of 5.729 Kg. 1. Introduction Bridges are solutions to complex puzzles. They help in overcoming common problems presented by rivers and lakes. Application of basic engineering principles results in the design of a model to mimic the actual bridge structures. The best bridge structure the one designed to be “most efficient, elegant, and safest” (Cronn-Mills 215). A truss is a common and basic design in bridge structures.

It is a compilation of straight members organized to transmit any load to entire structure (Zureick 51). The design used here in the Warren truss (Figure 1). Figure 1: Truss Bridge Geometry Materials Common truss bridges are from steel. However, in cases of minimal loads wooden truss bridges are used. When designing a bridge from any material, material stress is calculated. (Kappos 70). When the stress value is too high then the designer remains with only two options; increasing cross sectional area of the structure or redesign the geometry to allow even distribution of loads (Cronn-Mills 252).

Either of the choice has a negative impact on the structure. Increasing cross sectional area will increase the weight of the structure to the truss (Zureick 52). (Zureick 52). This might cause more geometrical problems leading to poor performance of the bridge structure (Jurado 103). On the other hand, redesigning the geometry introduces more connections, which increases the possible failure points (Zureick 52). Objectives The main objective of the bridge design task is to design a final prototype bridge structure that can support heavy loads before undergoing damaging failure.

Two structures are designed with the same material but in different ways. (i) Bridge A is designed with more triangle structures and a combination of both hollow cylindrical and rectangular members in the structure. (ii) Bridge B is designed with less triangular structures and larger cross section area than bridge B. It uses only the rectangular hollow members in the entire structure. Truss Loads There are three types of loads all bridges must withstand, the dead loads, live loads, and dynamic loads (Zureick 53).. (i) Dead Load The weight due to the bridge structure is the dead load.

It comprises of the weight of truss “members, gusset plates, and road deck” (Kappos 71). Dead loads will not change during the life span of the bridge. This load can be computed by computing the weight of one truss member. (ii) Live Load This is the weight due to things moving over the bridge. Live loads are temporarily on the bridge and changes from time to time (Zureick 53). (iii) Dynamic Load Temporary load tends to perturb the bridge structure for a short time. Such load includes wind load acting against the side faces of the truss (Jurado 111).

It results in the truss experiencing a drag force. 2. Methodology 2.1. Model Bridge designing Bridge A and bridge B are designed