Calculating the Tensile and Compressive Strength of Bridge Members EGN1006

What have we done so far? Measured the WEIGHT, W, of a bucket necessary to either rip or compress a bridge member. Measured the distance,L 2, the weight, W, is from the point of rotation of our testing apparatus. Measured the distance,L 1, the Tension, T, is from the point of rotation of our testing apparatus. The same is true for the Compression, C 1.

Next step: Calculating “T” and “C” To measure the Tensile and Compressive strength we MUST use the lever equation.

Calculating Strength in EXCEL Use formulas, copying techniques, and ABSOLUTE addressing. YOU WILL DO THIS THREE TIMES!

Tensile v.s. Width Using your tensile strength data and your width, make a TENSILE (y-axis) vs. Width (x-axis) scatter plot. Perform a linear regression on the plot and record your equation.

Compressive Strength vs. Length: 6x10 & 10x10 Using your Compressive strength data and your length, make a Compressive (y-axis) vs. length (x-axis) scatter plot. Perform a polynomial regression(3 rd order) on the plot and record your equation.

Calculating the “ACTUAL” tensile and compressive strengths The lengths and widths you used during testing are not necessarily the actual widths and lengths on the bridge. But you now know the MATHEMATICAL MODEL that tells us how the tensile strength behaves as a function of width and how the compressive strength behaves as a function of length.

Method 1 : Reading the value off the graph Not exactly accurate if the graph doesn’t have a well defined scale

Method 2: Using the equation of fit Measure the actual WIDTH of the bar on the bridge, then insert that width for “x” in your equation. Then solve for “actual” tensile strength. The same is true for compression strength. Measure the exact LENGTH of the tube then insert that length into the appropriate equation (6x10 or 10x10) to solve for the “actual” compressive strength.