PSWC Conference
The conference was held at the University of Southern California (USC) on April 4-6, 2013.
The final design can be seen in the picture above.
Our design, did not receive a rank at conference due to a disqualification. The top bearing surface was a combined total of 4 ½ inches too short and resulted in the disqualification of the bridge. Since the bridge was disqualified, it was unable to be loaded and receive an official score.
Our team wanted to measure deflections with the construction time we had at the conference to calculate a score for the bridge. We completed lateral load testing to ensure the deflections were acceptable to continue testing and then used a pallet jack with concrete cinders blocks to impart the approximate load to measure deflections. The pallet jack with a load of 1500lbs was placed on to the bridge and deflections were measured at the center and at the end of the cantilever. Then the pallet jack was loaded with a load of 1000lbs and placed on the edge of the cantilever and deflections were measured again at the center and at the end of the cantilever. Since the load at the center (1500lb load) causes the bridge to have a positive moment and the cantilever load (1000lb load) causes the bridge to have a negative moment, the first data set was subtracted from the second data set to get our total deflection.
Figure 21Picture of Bridge Being Loading
Figure 21 above shows the weight being loaded onto the bridge with a pallet jack to prevent the load from falling off in case the bridge was to fail. After the center was tested the pallet was loaded with 1000lbs and placed on the edge of the cantilever and deflections were measured again. Since the load at the center (1500lb load) causes the bridge to have a positive moment and the cantilever load (1000lb load) causes the bridge to have a negative moment, super position was used to get our total deflection. The deflections were measured with deflection gages that were attached to the bottom chord of the bridge. Figure 22 below shows how the gages were setup to measure deflection.
Figure 22 Picture of Deflection Gage Attached to Bridge
As seen in Figure 22 above, when the weight is applied the pin at the top is pushed down and the amount is measured. Super position was used to determine total deflection since we could only load the bridge at one location at a time. The deflections were input into the ASCE Conference Scoresheet and were used to calculate a total deflection of 0.493 inches.
With a total aggregate deflection of 0.493 inches, total weight of 256 lbs. and a total build time of 26 minutes and 18 seconds; our overall cost came out to be $13,943,000. The stiffness of 0.493 inches would have gotten us 5th in deflections among the other bridges at PSWC. The total penalized weight of 256 lbs., would have ranked our bridge 7th in lightness among the other bridges at PSWC. The total penalized time of 26 minutes and 18 seconds would have given our bridge 10th place in construction time among the other bridges at PSWC. The only other part of our bridge to incurred penalties was during the construction phase where 3 bolts were drop and one bridge member stepped over the boundary lines. After the bridge was constructed, the team was allowed a final inspection and incurred another penalty as a loose bolt needed to be tightened on the bridge. Because of these 3 penalties, our build time increased from 23 minutes and 22 seconds to 26 minutes and 18 seconds. The overall bridge cost of $13,943,000 would have earned us 10th place at PSWC.