When structures give support, they either experience a pull (tension) or push (compression). Structures under tension such as ropes or cables are made from material that can stretch a little. These structures are usually thin and rope-like. Structures under compression, such as elephant legs and columns, are made with firm material and tend to be thick.

Load distribution is a very important aspect of structures. Load refers to the forces to which a support is subjected, for example, a person walking over a bridge or a spider walking across its web. Structures such as bridges and spider webs are designed to most efficiently distribute this force across their entire length and width.

• Wooden Frames (2 m x 2 m x 0.5 m)
• Bundles of polyester twine (around 10 m each)
• Nails
• Bolts
• Washers
• Wingnuts

• 4 2x4's, 2 m in length
• 4 2x6's, 2 m in length
• 4 2x4's, 0.5 m in length

The 2 m 2x4's form the top of the structure. Nail 2 2x4's parallel to the 2x6's (at the opposite ends of the 0.5 m 2x4's). You now have two structure ends, 2 untouched 2 m 2x4's and 2 untouched 2 m 2x6's.

The remaining wood can be nailed on to form a square frame. Alternatively, the structure can be made more manageable in terms of storage and transportation if you drill holes at the sites you would have used nails and place bolts and wingnuts here. (The bolts can be removed and the structure dismantled when you move or store the structure.)

Making the Spider Webs
This project can best be done with a large group, such as at a camp or at school. The large group should divide up into teams, and each team will design a spider web. Each team is allowed 5 bundles of string; however, should all teams be successful, the team to use the fewest bundles of string is the winner. (Note that the twine cannot be cut). This may best be introduced by giving each team five hundred imaginary dollars and charging one hundred dollars for each bundle of string.

You can also try this project at home and make a spider web with some friends or with your parents.

1. Break into teams (as many as you have wooden frames for). Within each team, discuss a design and a plan of approach for building which will include each member of the team. Design principles to be considered include minimizing time, cost, and materials.
2. Once a design is complete, each team should construct its web, following the design plan.
3. Once construction is complete, teams take turns testing their web. Testing involves simultaneously sitting on the web. The structure is successful if it is able to hold the weight of the team without breaking. Should a tiebreaker be necessary, teams may test the web a second time with the added weight of a student from another team.
4. Evaluate the success/failure of your structure and identify modifications to improve it. How did the limited time and materials affect your success in making your product, the spider web?

Civil engineers design structures like bridges, dams, and towers. Famous structures like the Golden Gate Bridge, the Hoover Dam, and the CN tower were all built by civil engineers.

Structures are also found in nature. Spiders making webs can be thought of as civil engineers, as can birds building nests and beavers building dams.