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Balsa wood is a kind of wood that grows naturally in the humid rain forests of Central and South America. Due to its lightness and flexibility, balsa wood is often used for educational purposes, like building bridges.
Over centuries, bridges are structures to built to span obstacles, and to provide passages to over the obstacle. That's why people see bridges are built over the rivers, valleys, or roads. Building bridges are not easy as they looked, different designs vary according to different situations, structure materials, geographic terrain, or loading weights. Thus, building bridges are tough for engineering.

To experience a tip of the iceberg, our physics class required us to build a bridge by using balsa wood.

Restrictions:
Restricting the maximum mass of the bridge;
Restricting the minimum span;
Restricting the minimum length of the bridge and the inner roadway;
Restricting the elements' width and thickness

Testing:
By hanging gradual heavier weights under the bridge until the bridge breaks;
By using a mechanical testing device that pushes down on the bridge with increasing force until the bridge breaks

By looking up the information online,I found out there are basically 4 kinds of balsa wood bridges.

1. Beam Bridge
Beam bridge is the simplest form for bridge spans supported by abutments at the ends. Beam bridge are not limited to a single span. It is supposed to viaducts using continuous spans over the piers. Beam bridge can be classified as Short Beam bridge and Long Beam bridge. According to the experiment, a short beam bridge can contain 95 lbs but a long beam bridge can just contain 25 lbs (and also easily broken).

2. Arch Bridge
An arch is a structure that spans a space and supports structure and weigh on it. It can span a large area by resolving forces into compressive stresses and in turn eliminating tensile stresses. An arch bridge is a bridge with abutments at each ends shaped as a curve arch. Arch bridges work by transferring the weight of the bridge and its loads partially into a horizontal thrust restrained by the abutments at either side. According to the experiment, a arch bridge can contain 100lbs.

3. Truss Bridge
Truss bridges are one of the oldest types of modern bridges. A truss bridge is a bridge whose load-bearing superstructure is composed of a truss, a structure of connected elements forming triangular units. The connected elements may be stressed tension, compression , or sometimes both in response to dynamic loads. Truss bridges can also span a longer distances. According to the experiment, a truss bridge can contain 32lbs.

4. Suspension Bridge

This type of bridge has cables suspended towers, plus vertical suspender cables that carry the weight of the deck below, upon which traffic crosses. This arrangement allows the deck to be level or to arc upward for additional clearance. A suspension bridge is a type of bridge in which he deck is hung below suspension cables on vertical suspenders. According to the experiment, a suspension bridge can contain 32lbs.

By comparison, I found out that the arch bridge is the most strongest bridge among all. Arch is bendable so that it can separate the forces which apply on it into the other sides, which means arch can contain the heaviest weight. Also, triangle is also the most stable graph among all. Every leg of the triangle only faces one angle, and the length of the legs decide the degree of the angles. Think about it, any graphs that have more than three legs face more than two angles. So if just one leg decides the angles which are more than two, it can only decide the sum degree of the two angles, thus the graph is easy to transform or twist, and it is not as stable as triangular.
Therefore, I decide to combine arch and triangular. Making a fundamental arch bridge and support it with little triangular stripes. I bought two kinds of balsa woods: relatively hard wood and relatively soft wood. I am going to use the hard wood as triangular stents and soft wood as arch surface.

A system of particles is in static equilibrium when all the particles of the system are at rest and the total force on each particle is permanently zero. The necessary and suff icient conditions for a particle to be in mechanical equilibrium is that the net force acting upon the particle is zero.
The necessary conditions for mechanical equilibrium for a system for particles are:
1.The vector sum of all external forces is zero;
2. The sum of the moments of all external forces about any line is zero.
When coplanar forces is in balance, we can separate the force into two directions---X direction and Y direction.
ΣFx= 0 and ΣFy = 0 ＜＝＞is in balance

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Balsa wood is a kind of wood that grows naturally in the humid rain forests of Central and South America. Due to its lightness and flexibility, balsa wood is often used for educational...

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1. Who is your favorite soccer/football player?

2. What is your favorite animal and why?

3. What is your money called?

4. What is your favorite color and why?

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Unit 3: Cultural Partnerships Project Rubric  

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Start thinking of the criteria for each of the five phases.

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Unit 3: Cultural Partnerships Project Rubric  

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Winners at a bridge building competition

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Learning by practice is always the best, says civil engineering professor Amr ElRagaby. That's what makes a contest to design and build a model bridge from popsicle sticks a valuable experience for his students.

"They can understand the principles, but when they have a chance to apply the theories, they learn something they will never forget," he says.

Students of his third-year class in Finite Element for Analysis and Design will test the load-bearing capacity of their structures Wednesday, and invite the campus community to watch. The competition measures their skills in analyzing, designing and constructing truss bridges built only with craft sticks, toothpicks, and glue. Each bridge will measure 750 mm and will be subjected to a load test until it collapses.

"Failure is the ultimate goal, because only then can we know the ultimate limits of their strengths and flexibility," says Dr. ElRagaby.

The competition offers cash prizes in three categories:

highest ratio of load borne to structure mass and deformation;

most accurate prediction of maximum load; and

most creative and innovative design.

The testing is open for public viewing and begins at 10 a.m. on Wednesday, July 31, in the Industrial Courtyard, Centre for Engineering Innovation.

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Model competition to test engineering students' bridge-building skills

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The public is invited to watch engineering students test the strength of their model bridges on Wednesday.

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He's an American who teaches 4th grade at Shekou International School in Shenzhen, China.