Deck level construction was implemented in order to minimize heavy equipment on the island and to preserve the sensitive environment surrounding the project. This one Volvo backhoe, shown working on the pile driving, was the one heavy machine used.
Pirates once hid on Bald Head Island, the state’s southern-most barrier island — technically part of the larger Smith Island — accessible only by a 20-minute ferry ride across the Cape Fear River from Southport, N.C. Now renowned as one of the country’s favorite car-free destinations for tourists and millionaires, it’s a privately owned haven of vacation rentals and 1,200 private residences along 14 mi. of beach and 12,000 acres of maritime forest, tidal creeks and rolling dunes, located 65 mi. north of Myrtle Beach.
Although no bridge connects it to the mainland, a new bridge will soon span portions of the island itself. York Bridge Concepts Inc., (YBC) the nation’s largest on-site timber vehicular bridge builder, based in Lutz, Fla., is expected to complete construction of a 520-ft. (158 m) timber bridge in early March 2012.
The main purpose of the bridge is to provide a convenient path from the harbor to the residential area, allowing pedestrians to bypass the commercial corridor and service traffic. By separating golf cart and pedestrian traffic from the commercial-utilities corridor, the direct route will reduce congestion and increase safety.
The two-way bridge connecting home sites to Harbour Village is part of a joint infrastructure improvement project by the Village of Bald Head Island and Bald Head Island Limited LLC, and includes improvements to roadways.
A properly maintained timber bridge can last more than 50 years. In addition to durability, this bridge will offer aesthetic appeal that correlates with the ambiance of the quiet, picturesque island that once played a role in two American wars and now serves as a vacation getaway where the only traffic is electric cart, bicycle or foot.
YBC’s belief that every bridge should be a signature piece and add value and interest to a project makes their custom-designed pedestrian bridge an appropriate choice for Bald Head Island.
“York Bridge Concepts is taking every step necessary to preserve the beauty and natural ecology of Bald Head Island,” stated James York, company president. “The bridge will complement and emphasize the natural beauty of the marshlands and the island.”
Because the bridge crosses an environmentally sensitive marshland, it incorporates an arch from end to end. The bridge rises from the ends to the middle approximately 5 ft. (1.5 m) and features a radius that was meticulously followed in the field to achieve the beautiful arching profile. At its highest point in the center, the bridge is approximately 11 ft. (3.3 m) high.
To take advantage of spectacular views, YBC’s design team created a low-profile 24-in. (61 cm) guiderail for the cart section and a 42-in. (107 cm) timber rail with stainless steel wire cable handrails for the pedestrian walkway. The two-way traffic bridge features a 5-ton (4.5 t) gross capacity.
Of the island’s 12,000 acres, 10,000 (80 percent) will remain undeveloped and under the protection of an island conservancy. To address the environmental concerns of Bald Head Island, YBC implemented deck level construction, which eliminates the need for heavy equipment on the ground and minimizes potential damage to the environmentally sensitive marshlands. According to Jim Henry, director of planning and construction for BHI, they used only a Volvo back hoe.
Deck-level construction, also referred to as top-down construction, is building from a platform or, in this case, from the bridge itself.
“As much work as possible is done from the bridge, literally reducing the footprint of building the bridge,” Henry said.
YBC’s building techniques will reduce the need for additional construction or bridge replacement which decreases the risk of damage to the environment and reduces the cost of bridge maintenance.
The Long View
Work began on December 15, 2011, after considerable delay. YBC has had the contract since 2006.
“This project has literally been almost 10 years in the making, with our first contact being in 2005,” Henry stated. “Because Bald Head Island has had to deal with so many factors like state agencies, coastal permits and other environmental considerations, building something as major as a 520-foot bridge is a big deal. Once we had all of our approvals and permits (in 2008), the economy took a downturn. With a slight uplift in the economy, we were finally (in 2011) ready to have York Bridge Concepts build our one-of-a-kind timber bridge.”
One complication resulting from the delay impacted the budget.
“YBC met the foreseen budget set in 2006,” Henry said, “but because the wetlands had expanded over time, we were faced with about 25 percent in overages due to the bridge being lengthened by 40 feet and the piling having to be driven deeper.”
Unusual site conditions prompted extensive coordination. Arrangements had to be made to use barges to transport materials to the Island and accommodations had to be made for foot and cart traffic between the storage area and the bridge access point.
Deliveries included nine trucks of treated lumber and six pallets of galvanized steel. All the lumber is either CCA- or ACQ-treated, and either rough-sawn or smooth four-sided southern yellow pine. Bolts were galvanized or painted black. Wire for the pedestrian rails is stainless steel. Each truck gross was approximately 80,000 lbs. (36,287 kg), with payload (lumber and timbers) about 47,000 to 48,000 lbs. (21,318 to 21,772 kg).
YBC indicated that reparations were routine: “just the standard of access” to both sides, controlling the elevation hub near each end of the bridge and center markers of the bridge path. There were a few surprises along the way, however. As they started work on the bridge, utility lines necessitated use of longer pilings. YBC had to splice the piling to a refusal depth lower than anticipated, Henry explained.
YBC drove all the pile foundations as the bridge was constructed, 10 ft. (3 m) of span at a time. The deck level process uses a vibratory hammer to drive the piles to refusal. Some pile foundation locations did not achieve refusal and the splicing process was utilized for greater depth of the foundations. For every 10-ft. span, the process entailed driving the foundations, installing the cap, installing the stringers and blocking, installing the decking and fastening it down. This process is repeated 52 times until the end of the bridge is achieved. Once the entire bridge is decked from end to end, the finish work starts, which consists of the pedestrian area and guide rails.
Fortunately, the crew has approximately 30 years of experience and an efficient system. This three-man team consists of the working foreman, master carpenter/lead man and carpenter. Working an average nine-hour day has helped keep this three-month project on schedule.
“I am extremely impressed with the professionalism and craftsmanship from the York Bridge Concepts crew,” Henry reported. “Visitors and residents often comment on how quickly and precisely their high-quality work is done.”
The bridge is the talk of the town, Henry concluded, “The bridge is a major deal on the island. It is absolutely beautiful and will be a huge community asset.”