2012 Competition Guide
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2012 Competition Guide
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Vertical Load Tests Competitor Preparation:
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Vertical Load Tests Video: VLoading.wmv, 4:39 min, 12.1 MB -----------------<0>-----------------
Again, while transporting the bridge between the various sites, it is possible that the fasteners may fall off or other damage occur. If this happens, the Marshal should notify the Head Judge at once. There is a penalty for falling fasteners. Again, care should be taken during transport and staging to ensure that the bridge is not 'preloaded' either by bouncing or other means that would remove as-built slack from the bridge. Marshals should make sure that no one leans or sits on a bridge. At the national competition, if such situations arise, the Head Judge will make the team disassemble their bridge and start over again, from the end of the rotation. There are safeguards put in place to ensure that the rebuild cannot improve on the original performance (but you can do worse!). So, don't mess with the bridge! At the load station, the Judge make sure that all team members have the required safety gear then will have the team position the bridge in the loading area, making sure that the 'A' and 'B' sides are correctly placed and the safety supports placed under the locations for the grating. On the subject of safety supports, it is vitally important that the supports be designed and constructed in such a way that they prevent grating from falling more than a few inches while still permitting the maximum allowed deflection. They should be placed so as to minimize the possibility of dumping the load off the side of the bridge if a unsymmetrical collapse occurs. At the National competition, stacked plastic buckets have been found to be effective. Some enterprising individuals have additionally built brackets that sit on top of the buckets and have a socket that will accept a piece of 6x6. They have small chunks of 6x6 in varying lengths on hand which they use to get support right up to the decking. There are other methods that work quite well also. Whatever you do, just be safe. Once the safety supports are in place, the Load Judge will carefully locate the decking on the bridge and have the team apply the preload. The sway targets and vertical deflection measuring devices are then installed and initial readings taken and recorded on the judging form for the load station. The Team Captain should be invited to verify the setup and initial readings. Once loading starts, it should be accomplished in a safe, smooth, and continuous manner as shown in the video. If loading manually, teams should not be allowed to stop the loading to look at gages or develop strategy. All teams should load in the same manner. Judges may stop loading for safety reasons or if the bridge exceeds sway or deflection limits. Concerning loading. At Nationals and most ASCE student conferences, loading is done manually by the team members. A few conference hosts over the years have devised ingenious 'automated' systems that can make the load test go very quickly and efficiently without requiring anyone to get close to the bridge. These systems take lots of time to devise, design, build, and test but feel free to take on the challenge if you wish. If you can come up with a relatively simple system that is easy to transport, please let the Rules Committee know. We'd like to consider such a device for the national competition. At the end of each load stage, the Judge will record the deflection readings and allow the Team Captain to verify them. After the last deflection reading, the team should unload the bridge safely and quickly. Note that the bridge does not pass the load test until it is fully unloaded. If it collapses at any time it will be penalized according to the rules. Note to Judges: There is no need for you to compute the deflection. This will be done at the scoring table by the spreadsheet. Just make sure that you include signs when you record the numbers. Another note to Judges: Don't ever let anyone stick their head or any other body part under the bridge to read gages or for any other reason. It's just not safe! Competitors must be encouraged to keep their feet from under the bridge as well. Sometimes these bridges come down very quickly and without warning. WARNING: At Nationals, if the measurement devices are compromised in anyway by anyone during load testing, then the bridge is disassembled and starts the entire competition sequence again. The reason for this is that the initial loading will take out any slack in the joints and reloading the bridge has the potential to result in smaller deflections than would have been seen in an uninterrupted first loading. So... DON'T TOUCH THE DEFLECTION DEVICES!!! When all is done and recorded, the Judge reviews the data form with the Team Captain. The Team Captain signs the form when all questions have been resolved and the forms given to the Marshal who accompanies the bridge to the next station. -----------------<0>----------------- Notes on Measuring Deflection There are many ways to measure vertical deflection. They range from simply using a yardstick to expensive digital devices. The rules do not specify a means for doing this. At a minimum the measurement system used should:
Click on the adjacent thumbnail to see some options used in the past. In at least one student conference, the real time deflection is often projected on a screen for all to see. This is fine, however, this information is not made public during the national competition--only the judges monitor the deflection at nationals. Team captains are required to verify the final deflection numbers but do not monitor deflection during loading. It should be noted that added expense does not equate to accuracy and precision. As shown in the video below, the device used at the 2011 ASCE Pacific Northwest Student Conference was simple to build, cheap (~$15.00 each, using materials laying around the shop) and as precise as any digital device. The repeatable multiple reader accuracy was 0.005" where as the electronic pots used at the national competition are only accurate to 0.007". Devise your own device and send us an image and description (ssbc.results@gmail.com) and we'll post it here. -----------------<0>----------------- Notes on Loading Methods Loading is typically done by manually stacking weights on the decking. This method is simple and the competitors love the drama associated with it. The method also has the potential for personal injury and damage to the floor if appropriate safety precautions are not taken. 'Automated' methods have been used at a few conferences over the years. All have proven to be very safe since they generally don't require anyone to be near the bridge when it is loaded. They also tend to be very quick, with the loading cycle taking just a few minutes once they are set up. The application of load is also very consistent for every bridge. The downside is that there is a lot more thought and effort by the host in the preparation for the event. They can also be more expensive depending on the design. Whatever method is used must abide by the following principles: The process must be:
------ Example of an 'Automated' Loading Device - 2011 ASCE Pacific Northwest Student Conference ------ In 2011 the crew at the University of Alaska Anchorage hosted the ASCE Pacific Northwest Student conference and used a pneumatic device to load the bridges vertically. The system allowed the bridge to be tested quickly and without anyone being nearby. The video below shows the system. It took about 15 minutes to set up and test a bridge once the bugs were ironed out of the procedure. The biggest complaint was the lack of drama. It seems that competitors like the drama which is associated with hand loading of the bridges. Advantages of this system include stationary weight (nothing to drop or damage the floor), consistent loading of the bridges (the load rate was identical for every bridge), the turn around time is very short. Also, they were able to borrow (instead of purchase) the weight as most fab shops have stock in 20 ft lengths. Disadvantages of the system include it is sway inhibiting, requires a bit more equipment (tanks, valves, tubing, rams, fabrication of crossheads, platforms, etc), and the lack of drama. They also successfully designed and used a deflection device which appears to be every much as accurate as electronic devices and it leaves a permanent record. Finally, 'ground mounted' garage parking lasers (purchased on sale for $13 at the local Fred Meyers--positioning lasers for automobiles in garages) were used with paper targets mounted at deck level on the bridge to measure sway and lateral deflection. These devices eliminate the swinging common with hanging plumb bobs and made determination of lateral deflection and sway very easy. If you have trouble with the video below, check it out on Youtube. The URL is: http://youtu.be/n4qcvL8eMCY
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