On Saturday April 27th, 2019, the TCNJ steel bridge team competed in the Metropolitan Regional Student Steel Bridge Competition at the New Jersey Institute of Technology campus. The TCNJ team competed against nine other teams from the region in order to see which two teams would advance to the National Steel Bridge Competition.

After a long and hard day of competition, the TCNJ team placed 1st place in the Metropolitan Region! This marks the first time in TCNJ’s history that the steel bridge team took home the top prize. In addition to coming in 1st, the team placed first in Construction Speed, Construction Economy, and Lightness.

The team constructed the entire bridge in 9.65 minutes; however, with a couple of penalties, the final construction time ended up being 10.4 minutes. The measured weight of the bridge was 162.5 pounds; however, due to one penalty, the weight of the bridge used for scoring was 182.5 pounds. During the captain’s meeting before the competition began, Load Case 4 was announced to be the one out of the possible six load cases the bridge could be subjected to. This means that the lateral load was applied to the cantilever member at the east end of the bridge. As for the vertical load test, 1500 pounds was placed 14′-0″ from the cantilever end of the bridge, and 1000 pounds was placed 8′-4″ from the cantilever end of the bridge. The bridge experienced less than 1″ of sway during the lateral test and a total aggregate deflection of 3.14″ during the vertical load test. The Construction Economy Cost ended up being $6,496,000 while the Structural Efficiency Cost ended up being $20,517,500. The Overall Performance Cost for the TCNJ Steel Bridge Team is $27,013,500.

The overall cost was low enough for the team to move on to the National Student Steel Bridge Competition in Southern Illinois University, Carbondale campus! Moving forward, the team will check the members to ensure there is no damage, and work on stiffening the bridge in order to reduce the aggregate deflection.

Before the team headed to the Metropolitan Regional Steel Bridge Competition, the team painted the bridge and attached the official TCNJ logo to the West end of the bridge. This would help with the aesthetic look of the bridge as well as help the team to distinguish between the two stringers during the construction.

The South stringer was painted metallic gold while the North stringer was painted dark blue. The lateral bracing members were painted to match the side of the bridge they would be attached to.

After the bridge was completely painted, the team made final adjustments and continued to practice for the Metropolitan Regional Steel Bridge Competition. The final member sizes and the analysis results for the bridge are shown in the tables below.

Member Size	Dimensions
Top Stringer	1 1/2″ x 1/2″ x 1/16″
Bottom Stringer	1 1/2″ x 1″ x 1/16″
Diagonal Members	1 1/2″ x 1/2″ x 1/16″
Small Interior Members	1/2″ x 1/2″ x 1/16″
Lateral Bracing	1/2″ x 1/2″ x 1/16″
Footings	1″ x 1″ x 1/16″
Bolts	1/4″ x 3/8″

Analysis Type	Result
Weight	155 lbs
Max Aggregate Deflection	0.77 in
Max Lateral Deflection	0.14 in
Max Axial Stress	21.35 ksi
Approximate Construction Time	10 min

The team has been practicing assembling the bridge for the construction portion of the competition. The construction teams and techniques have been finalized with 2 builders on either side of the river that divides the course. A goal of 10 minutes has been set and accomplished throughout the early practices, and the team hopes to lower this construction time even more. Additionally, the bridge was weighed by using a scale under each footing and adding these values to calculate the total weight of the bridge. The current weight of the completely assembled bridge is 154 pounds. This puts the team in the desired weight bracket that will be used for scoring at the competition. The team’s practice course layout and weighing of the bridge can be seen in the picture below.

Now that the footings for each stringer were completely welded, the stringers could be hung up on the footings in order to check that the team exceeded the minimum clearance of 7.5″ and that the tops of the stringers remained in the range of 1′-7″ to 1′-11″. Once the stringers were placed in the footings, holes were drilled for connecting the stringers to the footings.

The spot where the top and bottom panels met for each stringer were clamped together and hangers were created out of scraps in order to make sure that the combined height of the panels remained uniform.

The clearance underneath the bridge and the height of the combined panels were checked against what was designed. The team then proceeded by determining the locations for the tabs that will connect the top and bottom panels together. Once the locations for the tabs were determined, the tabs were tack welded, checked, and then finish welded.

The holes for the tabs were then drilled out while the stringers were standing. Sleeves for the holes were placed and welded inside the panels to ensure that the tubing will not be crushed during the assembly of the bridge. In order to ensure that the top and bottom panels for the stringers line up perfectly during the assembly of the bridge, the team created guides for the panels to connect together easily.

The location of the guides were determined and then they were welded to the panels. The team then practiced assembling the stringers with the guides and made adjustments as needed.

Now that the top and bottom panels of the stringers were connected together, the team had to connect the two stringers together with lateral bracing. The team designed the lateral bracing in Visual Analysis under both possible load conditions. The lateral load for the competition can be placed approximately mid-span or on the cantilever end of the bridge.

The team then cut the tubing, tabs, and angles for the lateral bracing. A guide, with the designed 2′-8″ spacing, was created in order to keep the proper spacing of the stringers as the bracing was placed in. Each piece was checked to ensure they properly fit the 3′-6″ long constraint. The long diagonal pieces connecting the stringers and footings were further fabricated with telescoping connections to satisfy the member length constraint.

Going forward, the team will test the bridge, paint the bridge, weigh the bridge, practice assembling the bridge for competition, and optimize as needed.

The remaining T-slot connections for the bottom part of both the North and South stringers were successfully cut out on the water jet machine. These connections were cut out of 1″ thick A36 steel plate to match the 1″ wide rectangular tubing for the bottom panels of the bridge. These T-slot connections were then tack welded onto the previously tacked bottom panel members on both the North and South stringers.

The T-slots were carefully lined up with the ends of the member, clamped down, and then tack welded. The panels were put together on the welding table before and during the tacking of the connections to ensure that the alignment of the members and the connections were accurate.

Once all of the bottom T-slot connections were tacked onto the North and South stringers, the team assembled the stringers on the ground to check if the tops of the stringers were completely straight with the now attached bottom panels. This was accomplished with a laser light.

Once the stringers were completely tacked together, the footings could be tacked and finish welded in order to hang up the bridge and drill the holes for connecting the top and bottom panels together. The footings for the bridge consist of a base plate, straight bar, two diagonal pieces (in order to help counteract moment during loading of the bridge at competition), and two yokes for the members to sit in.

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Going forward, the team needs to hang each stringer on the footings in order to check for a uniform clearance underneath the bridge, place and tack the tabs for connecting the top and bottom panels of the stringers together, and work on the lateral bracing to connect the two stringers together.

All of the T-slot connections for the top stringers have been successfully cut out on the water jet machine. Each connection will be secured with a bolt in order to satisfy the rules set out by the AISC.

A Metal Inert Gas (MIG) welding machine was used to tack weld the previously cut members together in order to form the panels of the bridge. The team utilized fixtures in order to quickly and accurately weld members and connections together.

Once all of the panels were tack welded, the team assembled the North top stringer in order to check the layout and length.

Going forward, the team will cut out and tack weld the remaining T-slot connections for the bottom stringers, and tack weld the footings.

The TCNJ Steel Bridge Team has been well underway with the fabrication of their bridge! The material was donated by Penn Steel Fabrication Inc. located in Bristol, PA. Once the material came in, the team cleaned the tubing and pipe before they could begin cutting the material down to their proper lengths.

The material was then cut down to the part dimensions from our created shop drawings using a horizontal metal bandsaw, milling machines, and water jet machine.

All of our pieces that had a smaller angle or that had to be cut down to true length were done so on the Bridgeport milling machine. These lengths were determined from our created shop drawings.

Our more angular pieces in all of the panels for the bridge were cut on the water jet machine from our CAD drawing files. Cutting the parts this way saved time since they did not have to be milled. Additionally, our cuts were more accurate using this machine which decreased the error that could have been caused by manually cutting the angles.

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Once the team had all of the parts cut down properly, we were able to see the basic layout of our panels to be used during the competition.

The next step in the fabrication process is to cut out our T-slot connections on the water jet machine.

After selecting the optimal bridge design, the team made final adjustments to the design  trying to reduce the weight as much as possible as well as editing dimensions of members to allow for easier fabrication. This finalized bridge design was modeled in Visual Analysis, and then each member was modeled in drafting software. The team modeled each member in 3D, and this allowed the bridge to be thoroughly checked for any possible dimension errors. The top chord of the truss will be 1.5″x0.5″x0.063″ rectangular pipe, and the bottom chord will be 1.5×1″x.0063″ rectangular pipe. The diagonal connecting members will be made of 1.5″x0.5″x0.063″ rectangular pipe. The shop drawings were made, and the team is ready to fabricate over the coming months. Additionally, the team is finalizing the design of lateral bracing, footings and connections.

In order to select the most optimal design out of the five alternatives, the team decided to create a weighted decision matrix using the criteria most important to the competition scoring. The five alternative designs can be found in Update 4. The team’s decision matrix is shown below.

The criteria was listed in ordered of importance and the weight assigned to each criteria was based upon the number of criteria important to the final decision. The most important criteria (the weight of the bridge) was assigned the heaviest weight, the second most important criteria (max vertical deflection) was assigned the next heaviest weight, and this trend continued until the least important criteria (sustainability)  was assigned a weight of 1. The alternative designs were ranked on a scale of 1 to 5, 1 being the worst and 5 being the best, for each criteria. These ranked values for each alternative were then multiplied by the weight and added together in order to determine the maximum value. It was found that Alternative Design 5 had the highest combined values; therefore, going forward, this design will be the main focus of the team’s optimization efforts. Alternative Design 5 is shown below. 

Our team has created five alternative designs. Each alternative is a unique design drawn in Visual Analysis by each team member. The goal is to have a light weight bridge with a low number of connections and members, low deflection and a yield stress close to 72 KSI. We intend on using ASTM A513 steel, which has a yield strength of 72 KSI. The five designs can be seen below with pro’s and con’s listed. Also, provided is a table with an overall analysis. We will be focusing on optimizing design 4 and 5.