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.
0.5N
If 0.5 N acts
on centre
then each
straw can
support
0.0277N of
weight
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
•
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