Structural Engineering and Bridge Design Lesson

Introduction

Many issues have to be considered for the design of a permanent structure. Structures are designed for function, visual appeal and aesthetics, load bearing, safety, longevity, resilience during weather extremes and earthquakes, and for a reasonable cost. The design and construction of structures is regulated through governing agencies. Types of permanent structures include buildings, skyscrapers, bridges, domes, dams, tunnels, viaducts, towers, etc.

Which of the following engineering and design considerations do all structures share?

Check all that are correct.

Loads

Forces

Materials

Shapes

Explore

Watch this video to learn about structural engineering.

The shape of a structure directly affects the ability to hold a load. To understand the rationale for the design of structures one must have a basic understanding of statics. Statics is the discipline of physical mechanics (physics) that deals with load analysis on systems that are stationary.

The goal in structural design is to maintain equilibrium within the structure so it does not collapse under loads. Opposing forces need to be balanced to achieve equilibrium. A pull by one member, element in a bridge structure, is balanced by an opposing push by another. This manages the loading to maintain a rigid and strong structure.

The trick for the engineer is not to “over design” the structure. The design should include a margin of safety; however, an overly designed structure will have greater complexity, materials, labor, and increased time for project completion. All of these will increase costs. Designing and constructing a safe structure at a reasonable cost is the goal of a structural engineer.

Basic shapes in construction are round and rectangular. These shapes alone are prone to failure with an applied force. With that realization, these basic shapes are modified for structural design. Rectangular shapes are made stronger through the use of cross pieces creating triangular shapes. Round structures are made stronger through a keystone to absorb the forces from each side of the arch, and abutments which absorb and support the load from the actual arch structure.

See the following videos to see how the forces act upon the shapes of and arch and cantilever (truss) bridges.

Challenge

Take Away

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