Truss Factor of Safety and Characterization

1. Truss Factor of Safetyand Characterization Factor of Safety Member Cross-Sections Effecting Tensile and Compressive Strengths Characterizing Truss Members The truss bridge internal force calculations resulted in the stresses on each truss member. To find the Factor of Safety for each member, you need to understand how much a load a given member will support before failing. The students will use a tool to measure the failing point for different sized paper bars and tubes.The truss bridge internal force calculations resulted in the stresses on each truss member. To find the Factor of Safety for each member, you need to understand how much a load a given member will support before failing. The students will use a tool to measure the failing point for different sized paper bars and tubes.

2. Learning Objectives Calculate cross sectional area of a truss member Explain factors that affect the tensile and compressive strength of a truss member Explain the principle of the lever tool Experimentally determine the tensile and compressive strengths of truss members Graph and analyze the experimental data Calculate Factor of Safety for every truss member These learning objectives will be learned by completing the characterization of different sized truss bridge members.These learning objectives will be learned by completing the characterization of different sized truss bridge members.

3. Factor of Safety Design uncertainty Excessive loads: vehicles exceeding specifications, wind, snow, earthquakes, etc Construction: material variances, workmanship, etc Design Models: accuracy of design simulations These are some examples of things a designer must consider when designing a bridge. For example, even though a bridge may be posted with a 20 ton limit, the driver of a 30 ton truck may not heed the sign. And there will always be variances in building material strengths such as steel and concrete. Design modeling may have to make some assumptions. For our analysis, we will assume the bridge weight does not impact the loading and that every joint and beam is perfect.These are some examples of things a designer must consider when designing a bridge. For example, even though a bridge may be posted with a 20 ton limit, the driver of a 30 ton truck may not heed the sign. And there will always be variances in building material strengths such as steel and concrete. Design modeling may have to make some assumptions. For our analysis, we will assume the bridge weight does not impact the loading and that every joint and beam is perfect.

4. Factor of Safety Designers make a bridge stronger than design target Factor of Safety = Most codes require minimum Factor of Safety > 1.6