Happiness for a bridge builder in a metropolitan area with chronic traffic congestion is a new bridge that will last a century, require no more than routine inspection during its lifetime, come at a reasonable cost and, during construction, allow residents near the jobsite to enjoy life without any major inconvenience and motorists to drive by as though nothing were happening.
This is not a dream scenario. All of the above are realistic expectations of the New York City Department of Transportation (NYCDOT) for its newest bridge in Brooklyn and its first federally funded design-build procurement. What’s more, the new Belt Parkway Bridge over Ocean Parkway in that heavily traveled part of the borough is to be completed in record time—290 consecutive days, starting March 1 of this year.
Eyes widened in disbelief when Paul Atkins, P.E., area manager of Granite Halmar Construction Co. Inc., Mt. Vernon, N.Y., told NYCDOT officials that his firm planned to complete the bridge in one construction season, an unusually short duration for a job of this magnitude. Although NYCDOT had set the duration of construction activities as a criterion for selection, most thought that this build pace was too good to be true. Upon careful review of the contractor’s proposal, NYCDOT felt this was the way to go. Furthermore, the general contractor is putting its reputation as well as its fiscal welfare on the line because they have agreed to a bonus/penalty of $85,000 a day based on beating or missing the completion deadline.
The design team led by Granite Halmar; Gannett Fleming Engineers and Architects P.C., New York; and precast concrete manufacturer The Fort Miller Co., Schuylerville, N.Y., is depending on the newest technologies, latest materials and good project management to meet the construction deadline. In concert with NYCDOT, they are blending their disciplines to provide several important quality improvements.
Stainless is powerful
Chris Sklavounakis, director of Design Build and Emergency Contracts for NYCDOT’s Division of Bridges, for example, was convinced from the start that only solid stainless steel reinforcing bar could provide the long-term durability and corrosion resistance needed for this bridge to provide safe service under an extremely heavy traffic load for 100 years or more. It will have to accommodate not only the current flow of 166,000 cars, trucks and buses daily, but also a significantly larger volume of traffic that will grow exponentially over the years.
The new bridge, like the one it replaces, will be exposed to the corrosive attack of a marine environment—the Atlantic Ocean a half mile away—and salt frequently spread on the roadway to melt snow and ice. Such attack could lead to expensive road repair and bridge deterioration. To sidetrack this potential problem, NYCDOT decided to use solid stainless steel reinforcement bar because of its inherent resistance to general corrosion.
No other rebar materials, clad or coated, were considered as options because they didn’t offer the long life demonstrated by stainless steel. Sklavounakis figured that the lower life-cycle costs for stainless steel rebar would more than justify the slightly higher initial cost of that material, compared with black carbon steel, which was used in the original bridge.
Subsequently, a decision was made to use UNS S31803 alloy, a duplex stainless steel known as Alloy 2205 by Carpenter Technology Corp., Reading, Pa., who was chosen to be the manufacturer. This alloy has excellent resistance to general rust corrosion. Key elements added to this steel to prevent corrosion are: chromium, molybdenum and nitrogen. Even pitting and crevice corrosion, which can occur in 18-8 type stainless, is unlikely in this alloy.
The specialty alloys producer has provided approximately 360,000 lb of No. 5 (5?8-in. or 16-mm diam.) and 40,000 lb of No. 7 (7?8-in. or 22-mm diam.) spiral ribbed Alloy 2205 rebar for use in the bridge superstructure. This is one of several projects in the New York City metropolitan area that have used solid stainless steel reinforcement bar from Carpenter.
Based on contract allocations, the NYCDOT planner was correct in her value/cost assumption. The overall bridge project itself, including the bridge, modification in interchange configuration, reconstruction of Ocean Parkway, extensive landscaping, design and supervision, is budgeted at $55 million. However, construction of the bridge alone will cost only $17.7 million.
Using Alloy 2205 stainless steel rebar instead of carbon steel rebar, she calculated, increases the cost of the bridge by approximately 1%. In exchange for that small investment, NYCDOT is getting a bridge designed to last more than twice the life of the 45-year-old bridge it is replacing.
During that time, the owner will save the cost of a replacement bridge halfway through the century, at a cost likely to be twice that of the current $17.7 million outlay. In addition, NYCDOT will save countless millions of dollars in maintenance that will not be required, while freeing itself from the aggravation of repeated traffic tie-ups and community turmoil that generally accompany such maintenance.
“This is a major artery through Brooklyn carrying very heavy traffic,” Sklavounakis said. “Our goal is to keep it moving. We cannot afford to replace the bridge every 30 or 40 years, nor did we want to spend city and federal funds on continual maintenance, causing disruption in the community every time work is required. It made good sense to spend a few extra dollars to put these problems behind us.”
Built with speed
Quality improvements and faster construction beneficial to the motoring public and the bottom line are conferred by Fort Miller, with its innovative precast concrete technology. Fort Miller, using its Inverset bridge system, makes precast, prestressed composite concrete and steel superstructure units away from the bridge site for easy installation when needed. In this case, they and New York City are reinforcing concrete sections with stainless steel bar for the first time.
For this project, the company has produced 51 precast bridge units, each consisting of two steel beams and a concrete bridge deck. The bridge decks are cast using a unique upside-down casting process that compresses the concrete and provides a highly durable, crack-resistant surface.
All of the bridge units are precast and pre-assembled at Fort Miller’s manufacturing plant in Schuylerville, about 200 miles north of the Belt Parkway bridge site in Brooklyn. Each Inverset unit is made of concrete produced in a state-of-the-art batch plant, then poured and cured under factory-controlled conditions. As the units are finished, they are set up in the same relative position to each other as they will be on the job site, for inspection by NYCDOT-Quality Assurance (QA). When the bridge site is ready, the precast bridge units can be transferred, like giant Legos, for installation as needed.
“This method of construction, compared with the conventional cast-in-place approach, will enable Granite Halmar to condense bridge construction time significantly,” explained John Gonyea, Fort Miller project manager and estimator. “Erecting the bridge components in a rural environment,” he noted, “remote from the busy jobsite, also minimizes the negative aspects of conventional construction.”
The technique of setting precast units in place at the jobsite will allow the contractor to avoid traffic tie-ups on the Belt Parkway bridge and below on Ocean Parkway. Use of precast components produced under roof in a controlled environment also will limit the contractor’s exposure to bad weather and its slowing effects on construction.
Also eliminated, or much reduced at the bridge site: the need to build forms for concrete pouring; water and wet burlap for curing concrete; concrete trucks; tractor trailers with reinforcement bar; excessive delivery equipment; machinery to finish the deck; conditions that can lead to accidents; and the dust, dirt and noise generated by the vehicles and equipment no longer needed.
Melting and rolling
Carpenter’s 2205 stainless bar has been used extensively to reinforce the modular precast concrete bridge decks, bridge parapet, the fascia barrier and median barrier. A liquid corrosion inhibitor was added to the concrete mix because it was specified by the Precast Concrete Construction Manual (PCCM). However, Carpenter suggested that such use was unnecessary since the stainless rebar itself is corrosion resistant.
Since the New York State Department of Transportation did not maintain a list of approved rolling mills for solid stainless steel reinforcement bar, and solid stainless steel reinforcement bar had not been used on NYCDOT bridge projects earlier, Muhammad Afzal, P.E., director of NYCDOT-QA, required that stainless steel lots designated for use on the bridge be evaluated to ascertain the quality and characteristics of the material as claimed by its producer, Carpenter Technology. Thus, NYCDOT-QA used Pennoni Associates, King of Prussia, Pa., to check every heat melted by Carpenter, observe the rolling of rebar and obtain and send rolled samples to the Materials Testing Lab Inc., New Hyde Park, N.Y., in contract with NYCDOT-QA, to measure mechanical properties.
To establish mechanical property requirements, NYCDOT referred to ASTM standard A955M. Three yield strength grades are available: 300, 420 and 520 MPa. The typical yield strength grade used for black carbon steel is 420 MPa. However, prior history with Carpenter Alloy 2205 stainless rebar has shown that it is capable of meeting the 520 MPa yield strength minimum with superior ductility. This is 25% higher than the typical strength required.
When Materials Testing Lab evaluated the mechanical properties of two samples of No. 5 bar size, it determined a yield strength of 580 MPa, compared with the 520 MPa minimum requirement. Ultimate tensile strength was 790 MPa, compared with the minimum requirement of 725 MPa.
Even at these high strength levels, samples had elongation of 30%, compared with the required 9% minimum, giving the alloy excellent bending characteristics. The high strength and elongation of Carpenter 2205 alloy results in superior fatigue resistance, important in withstanding stress cycling of the bridge under heavy truck traffic. Deformation spacing also met the ASTM requirement.
Carpenter melted and rolled the 2205 stainless rebar in its Reading mill. Thermo-mechanical processing heavy cross sections with spiral configuration is not easily accomplished because of the alloy’s high strength at elevated temperatures. The rolled product was shipped in 40-ft lengths to Talley Metals, a subsidiary in Hartsville, S.C., for acid cleaning and subsequent shipment to Denman & Davis, Clifton, N.J., metals distributor. That firm, in turn, sent the rebar to Fort Miller for storage, inspection by NYCDOT and fabrication.
Fort Miller cut the stainless rebar to various lengths from 5 to 40 ft, severely bent the ends and formed loops used to reinforce the edges of the decks and concrete closure pours. Fabricators were surprised at how easily they could bend the high-strength stainless on standard rebar equipment.
Longer, wider Belt
Corrosion of reinforcing steel has always been a major concern for aging infrastructure. The Belt Parkway bridge being replaced was a 45-year-old two-span structure with steel stringers and cast-in-place, reinforced concrete deck that was rapidly deteriorating. Corrosion had taken its toll, exposing abutments badly and diminishing deck capacity. Road plates had been installed on the roadway, and timber shoring was supporting the abutments that had lost their capacity. It was a classic case of Band-Aid repair and maintenance, with no alternative course of action available short of bridge replacement.
In addition to those challenging conditions, NYCDOT had to consider how it was going to demolish the old bridge and build the new one without disrupting the lives of thousands of neighbors who occupied and visited a large hospital and two schools fronting on the project limits. How, indeed, could the contractor manage, as he predicted, to keep the same six lanes of traffic moving through the construction area without any major delays? This was a major undertaking at a busy interchange involving two heavily traveled roadways carrying traffic in four directions.
The replacement bridge, to be installed quickly with modular pre-cast concrete units, will be longer than the old bridge. It will use three spans to better serve the traffic needs of the Ocean Parkway underneath, separating its mainline from its service roads and accommodating wide sidewalks and two malls. One of the malls will be landscaped and the other dedicated to pedestrians and bicycles.
The new bridge will have shoulders and will be widened from 117 ft to 133 ft. In addition to carrying three lanes each way, the added width allows for an acceleration and deceleration lane at the ends of the bridge to ease vehicle access and departure. The extra width also allows for the introduction of shoulder lanes, a feature that is now missing from the Belt Parkway.
Must be invisible
Fort Miller has produced, for pre-assembly on the grounds of its manufacturing plant, a large volume of precast reinforced concrete components including the 51 bridge units, eight pier caps, 530 sq meters of precast concrete T-Wall used to construct the abutments, 250 meters of bridge and approach barrier, and approximately 1,600 meters of highway barrier. Delivery of various components to the bridge site started in April of this year.
The three precast concrete spans are each 133 ft wide when assembled, generous enough to accommodate three lanes of traffic each way. Their lengths vary. Span one is 65 ft long; span two is 107 ft long; and span three is 49 ft long. Total deck surface is 29,000 sq ft.
Each of the three spans consists of 17 bridge units, with two Inverset beams and reinforced concrete deck that vary in width between 2.38 and 2.5 meters. The 51 bridge units are easily linked together and taken apart for delivery to and installation at the bridge site.
According to plan, all six lanes of traffic are to be open during rush hours, with limited lane closures during off-peak hours for timely bridge work. To maintain uninterrupted traffic flow, Granite Halmar installed a temporary bridge on the south side of the existing bridge. The traffic riding the northern portion of the bridge (westbound traffic) was diverted on the southern portion of the bridge (eastbound traffic) and the traffic that used to ride the southern portion was shifted onto the temporary bridge. This allowed the contractor to demolish the northern half of the old bridge.
In the space once occupied by the demolished half, the contractor was ready to set in place precast bridge units. In a joint effort between Granite Halmar and Fort Miller, the entire bridge superstructure was erected at the fabrication plant on temporary cap beams, steel diaphragms were pre-drilled and all fit-up issues were resolved. This investment mitigated field uncertainties, further limited the amount of work required at the site and reduced the project’s impact on the community and traveling motorists.
With heavy mobile cranes and large trucks, the precast bridge units were transported from the precast plant in Easton and moved into position at the bridge for installation. The deck sections were quickly and efficiently linked with small closure pours of concrete in holes and open edges provided in the cast structures. Construction crews worked multiple, extended shifts (with heaviest duty at night) to place and bind the sections together.
The north side of the bridge was erected in May. That effort consisted of setting 27 sections—nine pieces wide by three spans long. This construction phase actually took only a “couple of nights” in each of two weeks, reported Atkins. The two-week time frame was needed to comply with New York City restrictions on oversized trucks and travel.
With the north side of the new bridge set in place, its increased width allows for both the westbound and eastbound traffic in a temporary lane configuration. Then, the temporary bridge and the old bridge on the south side will be demolished.
In its place, the contractor in September will set the second half of the new bridge on the south side, again in a few nights in each of two weeks, also observing the same restrictions on heavy vehicular traffic. In this phase, 24 units—eight pieces wide by three spans long—will be installed. After the second construction phase is completed, the entire new bridge will be operating in its final design configuration.
Once the contractor starts installing the precast bridge units, the units go up so fast that most observers don’t realize what is happening. That’s why Fort Miller calls its precast technique “invisible construction.”
To build this bridge by conventional cast-in-place construction methods, in a similar phasing plan, Atkins estimated, would take a year rather than a few days. That, he added, would depend on the number of shifts per day and weekends worked—which are strategies that would adversely impact the community and violate NYCDOT’s desire and strict direction to protect residents and the traveling public from undue inconvenience.