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During the past 10 years, many of the hydraulic structures on the Erie Barge Canal in upstate New York have undergone significant rehabilitation, first under the direction of the New York State Department of Transportation Waterways Maintenance and more recently under the direction of the New York State Thruway Authority (NYSTA). The required repairs are often quite extensive because of steel corrosion and damage from cycles of freezing and thawing. One of these historically significant facilities is the Court Street Dam on the Genesee River in Rochester, NY. In early 1996, the second phase of a three-phase rehabilitation program for this facility was completed. This phase included installation of precast-stay-in-place concrete panels and extensive sector-gate repairs.
The Court Street Dam functions as a water-control structure for the lower Genesee River to regulate water levels in the nearby Erie Barge Canal during navigation season and to furnish water for the Rochester Gas and Electric hydroelectric plant at the west end of the dam. Constructed in two phases in 1917 and 1926, the facility consists of four sector gates, separated by two concrete operating piers and a center mass-concrete pier and bounded by two concrete abutments (Figures 1 and 2). The sector gates are pie-shaped and hinged at their downstream end; they float up into position under hydraulic pressure. Through a series of interior valves and weir tubes located in the operating piers, the internal hydraulic pressures can be increased to lift the gates for water retention or can be decreased to lower the gates to release water downriver. This type of gate was first built in the Chicago area for a facility on the Chicago Drainage Canal at Lockport, IL. The original design has been credited to Mr. E.L. Cooley (Cooman 1927), and it is believed there are only a couple of other similar facilities in this country.
In 1993, Bergmann Associates, a 200-employee consulting engineering and architectural firm headquartered in Rochester, NY, was contracted by the NYSTA to provide additional in-depth inspections of all structural and mechanical components of the dam and to design, detail, and prepare construction documents. As Phase II of the overall rehabilitation of this facility, the work included extensive structural, mechanical, and safety repairs for each of the four sector gates, piers, abutments, and access bridges above the gates (Figure 3).
Although there were many unique aspects of the Phase II design and reconstruction for the Court Street Dam, this article will focus primarily on two of the more interesting components: the use of precast concrete panels to resurface pier and abutment wall surfaces and the structural repair of the sector gates themselves.
The use of precast concrete panels as a stay-in-place forming system and a very high-quality surface replacement option for lock and dam concrete structures has grown significantly in the 1990's, especially in New York State. The details of this system are described in Technical Report REMR-CS-41 (Miles 1993) for the Federal Lock at Troy, NY, and in Technical Report REMR-CS-49 (McDonald and Curtis 1995) for a wide variety of Civil Works applications. This system has now replaced the use of conventional cast-in-place concrete and shotcrete resurfacing for many waterways rehabilitation projects. Compared to cast-in-place concrete, precasting offers a number of advantages including minimal cracking, durability, improved abrasion and impact resistance, speed of construction, easier winter installation (limited heating), improved facility appearance, and reduced maintenance cost, all at a very similar initial cost.
Precast panels at the Court Street Dam were designed and detailed for the two operating piers, the center pier, and the west abutment. The panels extended from elevation 505 on the upstream faces of all units (about 2 to 3 ft below low-water levels) and from the sill slab on the downstream side of the center pier up to between 12 and 18 in. from the top of the unit, to allow for a new cast-in-place cap. There were a total of 36 panels at the four unit locations. The typical panels were 7 in. thick and were of variable surface dimensions, many of which were trapezoidal in configuration with widths up to 11 ft-10 in. and lengths up to 20 ft-8 in. See Figure 4 for a typical precast repair detail.
The typical panel installation required (a) a minimum removal of 12 in. of existing surface concrete (primarily using small impact hammers), (b) No. 6 reinforcement anchor dowels at a 2- to 4-ft spacing and a minimum 18-in. embedment, (c) a minimum of 5 in. of 4,000-psi infill concrete with 1/2-in.-maximum coarse aggregate, (d) she-bolt form anchors at a 4-ft-maximum spacing for construction phase tiebacks, and (e) completely sealed joints.
Specialty panels were provided for trash-gate recesses at the two operating piers, pier nosings, and a ladder recess at the west abutment. Additional special details included:
The panels were fabricated by Binghamton Precast and Supply in their Binghamton, NY, precast plant during the summer and fall of 1994. They were then shipped approximately 150 miles by truck to the project site as they were needed.
The general contractor, LeChase Construction, installed the panels for each concrete structure quickly and simply by means of a track-mounted crane located on the downstream concrete sill slab or rock riverbed. Work at each structure was performed during various cofferdaming phases from late 1994 through late 1995, with many of the panels being installed during the winter months.
A total of 3,625 sq ft of panels were installed for the structures at Court Street Dam with an average bid price of $42.40/sq ft and a low bid price of $25/sq ft for the panels alone. However, the average bid price for the panels installed at the Court Street Dam is not as low as for other recent New York State canal projects, in large part because of the lack of repetition of the panel dimensions and low total quantity needed for this project.
As a result of over 70 years of use and constant wear from water and ice forces, the four steel sector-type tainter gates at the Court Street Dam had suffered extensive deterioration. Based on previous biennial inspection data and in-depth hands-on inspection, including exterior, interior, and underwater, the various structural elements of the gate were evaluated, and repairs were developed for necessary rehabilitation. See Figure 6 for a typical pier and gate cross section.
The primary gate repairs provided under the Phase II repair contract included the following:
The various gate repairs required each gate to be individually cofferdamed with steel sheet piling and shoring members and to be jacked up onto temporary shores. Only then could each gate be taken out of service, dewatered, and thoroughly cleaned. Cleaning of the gate structures required the removal of extensive silt and zebra mussel buildup caused in part by the partially failed original seal systems.
The original top seal system at each gate consisted of a two-piece section of conveyor belting in the form of a tee that was originally considered experimental. Those seals had a tendency to be forced out of the tee-shape by water and ice pressure. The result was substantial leakage, especially near the bottom of the top plate. The original front seal system consisted of a bent plate that was connected to the fixed concrete sill and closed against the front skin plate of the sector gate by water pressure. The original gates had no side seal system, which meant the gate maintenance staff was forced to plug spaces with rope, sand bags, and gravel during gate dewatering operations.
The new seal systems installed under the Phase II rehabilitation contract consisted of new rubber sections as shown in Figure 7. The new top seals consist of a rubber J section connected to an 8- by 6-in. steel angle that extends inside the gate end frames. They seal against the steel seal plates cast into the piers and abutments by means of interior water pressure.
The new front seals consist of a rubber J section connected to a 1/2-in. bent plate connected to existing breast wall steel sections. They seal against the steel front skin plates of the sector gates by means of the upstream water pressure. Both the top and front seal J-sections have a 0.03-in. thickness of fluorocarbon film on the bearing surfaces for improved durability.
The new side seals consist of a rectangular rubber section that is bolted to bent steel plates which in turn are bolted and welded to the pier and abutment faces. These seals function only when the gate is raised on its prop systems and dewatered. Only then does the upstream water pressure force this seal section against the curved front skin plates to seal off the end joints. The side seals were detailed to make them more resistant to impact damage from floating logs, a common hazard at the dam.
These new seal systems are similar to those used on another tainter-gate dam located farther down the Genesee River. They have functioned well at that site for over 10 years and have been functioning well for approximately 1 year at the Court Street Dam. The approximate bid cost for the new top, front, and side seals was $155,000 for the four sector gates.
A significant portion of the repair cost for the gates consisted of the localized steel replacement and patching, the blast cleaning and containment systems, and the new vinyl paint systems. Framing members within each of the gate trusses or diagonal bracing were replaced where there was an estimated 25 percent or greater loss of total section.
The top skin plates were severely pitted from corrosion as the result of frequent wetting and drying cycles. This deterioration necessitated the replacement of the total plates for Gates No. 1 and 3 and frequent small patches installed on the interior for Gate No. 2. Also, original rivets were replaced with new 3/4-in. high-strength bolts throughout the skin-plated areas where there was a loss of section of the rivet head of 50 percent or greater. As a result, over 15,000 rivets were replaced on the four gates.
Many of the miscellaneous metal items were also replaced in the gates including the fine and coarse trash racks and guides, the access ladders, the bearing plates at each truss support pad, the stop angles, and various valves.
The paint system used for coating the four gates was specified as a three-coat black vinyl system with a minimum total dry film thickness of 7.5 mils. This is the typical paint system used successfully by the NYSTA for all of its waterway structures. A special three-coat system with a copper epoxy top coat (18 mils total minimum dry film thickness) was used on the trash racks and guides as a trial usage to discourage zebra mussel encrustation at the pier inlet areas. It is too early to evaluate the success of this antifouling paint system at the dam.
The Phase II rehabilitation of the Court Street Dam was recently completed at an approximate total cost of $5.0 million. For more information, contact William R. Miles at 716-232-5135.
Cooman, C.C. (1927). "110-Foot Sector Gate Dam at Court Street, Rochester, N.Y.," Cornell Civil Engineer XXXV (6).
Miles, W.R. (1993). "Comparison of Cast-in-Place Concrete Versus Precast Concrete Stay-in-Place Forming Systems for Lock Wall Rehabilitation," Technical Report REMR-CS-41, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS.
McDonald, J.E., and Curtis, N.F. (1995). "Applications of Precast Concrete in Repair and Replacement of Civil Works Structures," Technical Report REMR-CS-49, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS.
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