Bridge Building

Simplest bridge –a beam bridge The simplest of all bridges is called a beam bridge. This type of bridge is made up of beams that extend from one side of a gap to the other. Beams are anchored to solid ground at each end and carry the entire weight of the bridge deck and its loads. Because of this, long spans require very stiff and strong beams. The longer the span, the stronger and more rigid a beam needs to be to counteract the downward force it will experience.

Beam Bridge The simplest of all bridges is called a beam bridge. This type of bridge is made up of beams that extend from one side of a gap to the other. Beams are anchored to solid ground at each end and carry the entire weight of the bridge deck and its loads. Because of this, long spans require very stiff and strong beams. The longer the span, the stronger and more rigid a beam needs to be to counteract the downward force it will experience.

Why Truss Bridge I chose Truss Bridge instead of a simple Beam Bridge because supports called trusses can stiffen horizontal beams without greatly increasing weight. Trusses are made up of a series of triangles linked together. Engineers use triangles as opposed to other shapes because triangles are inherently strong. Unlike a rectangle, for example, a triangle cannot be deformed without changing the length of one of its sides or breaking one of its joints. When joined together, a series of alternating upright and upside-down triangles creates a rigid and lightweight beam.

The maximum Load I estimate the maximum load that the straws will with stand will be 1kg The truss bridge... consists of an assembly of triangles. Truss bridges are commonly made from a series of straight, steel bars.

Truss Bridge Truss Bridge: Forces Every bar in this cantilever bridge experiences either a pushing or pulling force. The bars rarely bend. This is why cantilever bridges can span farther than beam bridges. I will not include the Trusses at the bottom because this will not make it stand properly

Truss Bridge The more Triangles around the beam the more support will be given by the bridge. The longer the bridge the more likely it will bend The heavier the bridge the more likely it will bend. bending occurs when a straight material becomes curved; one side squeezes together in compression, and the other side stretches apart in tension

Bridge Design The bridge design I choose is a simple beam bridge with two sets of arches on each side., this then becomes a Truss Beam. The Truss bridge was characterized to support itself. I expect each straw to experience a force of under .5 N force. The bridge was constructed with 9 straws pined together for the base 2 straws cut at the bendy tip to make 1 arch so 8 straws for the arches. The one straw left wand the cut off tips were used to extend the bridge in length by inserting them into one another. If 0.5 N acts on centre then each straw can support 0.0277N of weight 0.5N

Calculation of Weight beam is a structural element that is capable of withstanding load primarily by resisting bending. The bending force induced into the material of the beam as a result of the external loads, own weight, span and external reactions to these loads is called a bending moment. The Truss Bridge will work the same way but the trusses are in shape of king post and their will aid the support of load. The support will be in form of compression and Tension.

king post (or crown post) extends vertically from a crossbeam to the apex of a triangular truss. The king post connects the apex of the truss with its base, holding up the tie beam at the base of the truss. King posts were used in roof construction in Medieval architecture in buildings such as parish churches and tithe barns, and also appear in Gothic Revival architecture and Queen Anne architecture. A similar structure may be used to construct a simple bridge.

The maximum load With 18 straws and having a beam and Trusses I think my bridge should be able to withstand more than 1kg

References http://www.technologystudent.com/struct1/model.html Teachers' Domain, Triangles: Designing a Straw Bridge, published January 22, 2004, http://www.teachersdomain.org/resource/phy03.sci.phys.mfe.zstrawbridge/ http://www.technologystudent.com/struct1/model.html http://www.pbs.org/wgbh/buildingbig/bridge/truss_forces.html