1. BRIDGES CAD 449

2. Design It is the essence of engineering! “… the process of devising a system, component or process to meet desired needs. It is a decision-making process, in which the basic sciences, mathematics, and engineering sciences are applied to convert resources to meet a stated objective.” http://en.wikipedia.org/wiki/engineering_design

3. 10 steps of design and engineering 1.Identifying the Need 2.Defining the Problem 3.Conducting Research 4.Narrowing the Research 5.Analyzing set criteria 6.Finding alternative solutions 7.Analyzing possible solutions 8.Making a decision 9.Presenting the product 10.Communicating and selling the idea (http://en.wikipedia.org/wiki/Engineering_design)

4. Topics of Discussion: What is a Bridge? What is a Truss Bridge? –The components –Types of Truss Bridges The fundamental structural engineering concepts. The 4 key roles in the design construction process. How does construction quality affect the end performance of a structure?

5. What is a Bridge? A bridge, can be seen as today, as man made structure that is built to span a gorge, valley, road, railroad track, river, body of water, or any other physical obstacle, for the purpose of providing passage over the obstacle… (http://en.wikipedia.org/wiki/Engineering_design)

6. Swiss alps picture http://en.wikipedia.org/wiki/Image:Salginatobelbruecke_suedost_unten.jpg

7. Additional History Some of the first bridges where made by nature ex. Fallen tree over a stream of water Some civilizations that where big on bridges… 1. Romans 2. India 3. China

8. A Truss Bridge A structure composed of load carrying components, also called members, connected together to form a rigid framework. Most truss bridges are made up of interconnected triangles which make them very strong for their weight.

10. Components

11. Components Cont. Elevation View Isometric View

12. Two Common Connections 1.Pinned Connections: uses a single large metal pin to connect two or more members together much like a pin on a door hinge. 2.Gusset Plate Connections: More modern way members are connected by one or two heavy metal gusset plates.

13. Types of Truss Bridges

14. Types of Foundations Abutment: They support the bridge and hold back the soil behind them. Pier: Is used as a support as shown below.

15. Three Styles of Truss Bridges 1.Through Truss: When the deck is located at the level of the bottom cord. 2.Pony Truss: Similar to the Through Truss except it is not as tall. 3.Deck Truss: When the deck is located at the level of the at the level of the top chord.

18. Fundamental Concepts Force: Is simply a push or pull to an object. Force always has magnitude and direction (amount of weight & inward direction). Ex: A loaded truck crossing a bridge. Load: Is simply a force applied to a structure. Ex: weight of vehicles or pedestrians, weight of wind pushing on sides. Equilibrium: When a structure’s upward force equals the total downwards force. Reaction: Forces developed at the support (abutments & piers) of a structure to keep the structure at equilibrium. Tension & Compression: Are internal forces that make a member longer or shorter. Tension stretches a member and Compression pushes the member closer together. Strength: Is the largest internal force of a structure.

19. Examples Force Equilibrium Tension Compression

20. Overview: Students will use math and Science to implement engineering concepts in the design and construction of a model bridge from your own plans that will carry a maximum load while using as little wood as possible; stressing neatness, craftsmanship, and creativity. Materials: 1. Only solid untreated (no manufactured notches or holes), natural wood sticks may be used 2. Maximum number of sticks allowed is 10. Each piece of stick, can be cut to various sizes. 3. Only water soluble “green” type white glue must be used.

21. Rules For Bridge Size 1. Maximum horizontal length 20 inches 2. Maximum width 3 1/4 inches 3. Maximum height above top of roadway (superstructure) 7 inches 4. Maximum depth below top of roadway (substructure) 3 inches 5. Minimum horizontal length 10 inches 6. Must have 1”-2” of support system on either side.

22. AWARDS Awards are given in each of the following two categories:* 1.Strength to weight Ratio: Determined by dividing maximum load at failure by weight of bridge. Bridge with greatest load bearing capacity compared to its weight wins. Example: Maximum load = 220.0 pounds Bridge weight = 50.0 grams Ratio = 1997.8 * [220 pounds x 454g/pound)/50g] 2. Creativity: Finest workmanship, including neatness and innovation of design. *Although awards will be presented in two categories, bridges qualifying for MESA Regional finals will be determined by strength to Weight Ratio only. Safety: Appropriate safety measures will be used in testing.