YNJ Rail is the last remaining car float operation in the metropolitan Outside New York area. This shortline rail- road operates between Jersey City, NNJ and , NY moving freight across New the Box York Harbor, and is one of four remaining car float operations in the United States. The transfer bridge concept originated in the mid 1800s with highlighting the out-of-the- a between Havre de Grace and Perryville, ordinary within the realm of MD for the Camden & Amboy Railroad and structural engineering the , Wilmington and Railroad. Rail cars were transported across the Figure 1. NY Harbor Circa 1928. river by moving them from land to a by means of a transfer bridge. The rail cars are then car float. This mooring connection can impose unloaded at a similar facility across the waterway. significant loads onto the bridge structure, even In the late 1800s, was a major though fender systems® and mooring dolphins manufacturing and industrial center requiring may be used. These loads include the propulsion massive transfer of raw materials and finished from the tug as well as wind loads, causing goods. The base of the industry was on a moment at the end of the bridge. Island, requiring materials to be moved by water In Figure 2, a typical arrangement between the between New York and , or through car float and the transfer bridge, along with the Copyrightthe only land route capacity for elevation adjustments, is shown for a across the Spuyten mechanically driven structure. This structure uses Duyvil (northern tip hydraulic cylinders suspended from a gantry to Car Float and Transfer Bridges of NYC), which was raise and lower both the bridge and the apron. controlled by Cornelius In older designs, the bridge and apron utilized Vanderbilt’s New York counterweights to balance the dead load of the By Peter Davis Central Railroad. All other railroads terminated structure. The reality of these structures is that the along the New Jersey side of the , dead load represents approximately 20% of the and goods were moved either by lighter (small total load on the structure. For this new transfer barge) or car float. At the pinnacle of this period, bridge, the cost of the counterweight system was over 6000 freight cars per day were transported not justified compared to increasing the hydraulic across the rivermagazine by car float. cylinder size. S TSuper R Storm SandyU caused C severe damageT to UAnother R design utilizesE a pontoon (floating both the Jersey City and Brooklyn transfer bridge structure) to support the bridge. This system facilities. A temporary pontoon structure was constructed in Jersey City while a new permanent bridge is designed.

Peter Davis, a licensed mechanical Transfer Bridges engineer, has 39 years of experience in the inspection, design and The structure that allowed rail cars to be loaded construction of heavy infrastructure onto car floats is the float or transfer bridge. The including locks, dams and movable transfer bridge is unique in that it must function bridges. He can be reached at as a movable bridge for the purpose of allowing [email protected]. adjustment between the top of rail elevation on land and on the car float. In , the typical tidal fluctuation is up to10 feet. As this relative elevation change is due to tide and car float freeboard changes, the bridge must adjust to provide the connection between car float and land. This elevation adjustment typically occurs over the 30 minute load/unload cycle. While both rail and highway movable bridges are opened to allow marine traffic to pass, they do not operate under live loads as do transfer bridges. Transfer bridge live loads include locomotives and rail cars that vary in weight due to their changing cargo. Today rail car loads can be in excess of 286 kips. In addition to operating under live load, these bridges provide a mooring connection to the Figure 2. Transfer bridge arrangement.

10 October 2014 STRUCTURE magazine Are you measuring tension forces at

Figure 3. Toggle bars connecting the car float to the Figure 5. Heel bearing. dizzying heights? transfer bridge. relies on the pontoon to adjust the bridge rotate as the freight cars are moved on and off. No Problem with Polytec elevation based upon tidal variation, but does It is common for the operators to develop a ® not compensate for the car float freeboard loading/unloading sequence that accounts for (loaded/unloaded). The size of the pontoon the shifting load conditions. is based upon the dead load of the bridge A key feature of these bridges is that com- and the expected change in freeboard of ponents of all loads are transmitted to the the car float. A simple calculation is used to substructure through the hinge pin arrange- Figure 4 determine the volume of water that must be ment ( Copyright). The hinge pin is a critical displaced to compensate for the changes in element of the entire system. These loads car float loads. The volume of the pontoon is include: live load, dead load, traction/brak- then sized appropriately. The railroad opera- ing loads, mooring loads (tug boat loads and visit www.STRUCTUREmag.orgADVERTISEMENT–For Information, Advertiser tor must adjust the elevation between the car moments from wind load on the car float), float and bridge by loading the bridge (usu- as well as seismic loads. Due to the operation ally with a locomotive) such that the toggle of these structures, the seismic loads tend to bars can be engaged. This approach requires govern. It is not uncommon for hinge pins to substantial operator skill and can limit the see loads ranging from 300 to 700 kips in the speed of loading and unloading operations. longitudinal direction, 180 to 800 kips in the Based upon the range of tidal variation, the vertical direction, and up to 230 kips trans- length of the bridge and apron are adjusted such versely.magazine The original design was a simple pin that the maximum angular changeS between T the Rand clevis arrangement.U C For the loadsT of today’sU R E land, bridge, apron and car float do not exceed freight cars, the hinge pin assembly becomes the allowable for the rail cars (prevent bottom- extremely large. In order to resolve the loads in ing). Most freight cars do not pose a limitation compliance with AREMA design standards, a compared with hopper cars which dump the different approach was taken. A saddle design cargo through the bottom. The length of the (heel bearing) was developed, both simplifying bridge and apron determines the maximum the construction and improving the reliability positive and negative angles that will occur of the hinge over time (Figure 5). The trans- over the operating range of the bridge and car verse loads are resolved using a mechanical float. Transfer bridges generally range from 80 device which is a movable key located in the to 150 feet in length. In order to compensate center of the pier. An added design challenge RSV-150 for the angular changes of the rail during tidal includes regular submergence of the hinge pin Laser-based vibration measure- extremes, the bridge shown is articulated. The arrangement. The selection of materials for this articulated design allows the apron to make a component is critical to provide the capacity, ment allows you to calculate hard connection with the car float utilizing a but also to provide reliable operation over an tension forces on stay cables toggle bar arrangement (Figure 3). The toggle extended period (30 years). very rapidly and very bars are critical to maintain top of rail alignment These “workhorse” bridges truly provide a precisely. You’ll also need between the bridge and car float. These toggle unique challenge for engineers to showcase less effort and save nerves, bars resist large loads, as the car float tends to their skills.▪ time and money.

Learn more: www.polytec.com/rsv

Figure 4. Hinge pin arrangement connecting the transfer bridge to the abutment.

STRUCTURE magazine11 October 2014

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