# more bridges

This is a continuation of the story about Bridges. Here are many more interesting examples of bridges

• Lujiazui Circular Pedestrian bridge Shanghai, China – the pedestrian bridge allows commuters to avoid the busy traffic by providing a clean and convenient platform for foot transport. The bridge also connects malls and cafés to transit stations and office buildings.

Four kinds of bridges

• arch – One of the oldest types of bridges, arch bridges have great natural strength. Instead of pushing straight down, the weight of an arch bridge is carried outward along the curve of the arch to the supports at each end.
• beam – In its most basic form, a beam bridge consists of a horizontal beam that is supported at each end by piers. The weight of the beam pushes straight down on the piers.
• suspension – a suspension bridge suspends the roadway from huge main cables, which extend from one end of the bridge to the other. These cables rest atop high towers and are secured at each end by anchorages.
• cable-stayed – In cable-stayed bridges, the cables are attached to the towers, which alone bear the load.

A bridge not far enough
Building a Temporary Bridge from Cardboard (video 3:50) – build a cardboard bridge for temporary use, in this case crossing a “kiddy pool of doom.” Check to see whether his bridge carries him safely, or whether he takes a plunge.

• Ask – What is the distance to cross? How much weight does the bridge need to support? What materials are available?
• Imagine – What are some types of bridge designs to consider? Which ones might work? How is the modeling software used to help determine the design?
• Plan, Create – Once the basic design and materials are selected, how is the bridge constructed?
• Improve – How could the bridge be improved knowing what he knows now?

That’s engineering

• structural analysis – the determination of the effects of loads on physical structures and their components. Structures subject to this type of analysis must withstand loads, such as buildings, bridges, vehicles, machinery, furniture, attire, soil strata, prostheses and biological tissue. Structural analysis incorporates the fields of applied mechanics, materials science and applied mathematics to compute a structure’s deformations, internal forces, stresses, support reactions, accelerations, and stability. The results of the analysis are used to verify a structure’s fitness for use, often saving physical tests. Structural analysis is a key part of the engineering design of structures.

Engineering ideas

• load, compression, tension, power law, modeling, destructive testing, deformation, internal force, stress, strain, equilibrium, support reaction, acceleration, stability

Do it
Here are some challenges for you to work on…

• Build a suspension bridge inspired by spider webs that spans 10 inches and can hold at least 15 pennies.
• Build a Bridge – Four open spans need bridges. You’ve just been put in charge of deciding which type of bridge is best for each of those four spans. Are you up to the task?
• Bridge designer – design trusses. Trusses are composed of straight members connected at their ends by hinged connections to form a stable configuration. When loads are applied to a truss only at the joints, forces are transmitted only in the direction of each of its members. That is, the members experience tension or compression forces, but not bending forces. Trusses have a high strength to weight ratio and consequently are used in many structures, from bridges, to roof supports, to space stations. requires Java, advanced design activity
• West Point Bridge Designer 2013 – introduction to engineering through an authentic, hands-on design experience. This software provides you with the tools to model, test, and optimize a steel highway bridge, based on realistic specifications, constraints, and performance criteria. Software is used with a competition and can be downloaded.
• File folder bridge – design and construction of a simple A-truss structure, based on a well-known 19th century railroad bridge. This project requires the application of geometry, algebra, and some basic trigonometry. Thus it is intended primarily for high school students.