Brooklyn Bridge Park’s Squibb Bridge has 127 fewer years of existence than the borough’s iconic East River span, but the pedestrian crossing got lots of New York City attention since it was first opened in 2013 after being shut down twice—once for excessive “bounciness” and again due to rotting wood. Now its reconstruction, hopefully for good, is anything but a straightforward operation.

Even demolition work last month on the $6.5-million structure involved atypical obstacles—in this case, a pair of multistory residential buildings. “When the bridge was first built, the buildings on either side of it weren’t there,” says David Farnsworth, a principal and Americas tall buildings business leader at Arup, lead design firm on the new Squibb Bridge. “It was a big empty lot with plenty of staging space and plenty of access to get your cranes right up next to the bridge.”

但是，现在跨越桥梁的10层和六层建筑物需要工程团队，成为建筑经理的特纳建设，以适应更严格的宿舍，布鲁克林大桥公园公司的非营利组织建立的非营利组织总裁Eric Landa过去十年的85英亩公园。

“The span had to be picked up and turned on Furman Street at almost a right angle … in between these two buildings,” he says. The team had to remove the two largest spans, each 120 ft long, in a single October weekend, Farnsworth says. “That was tricky—trying to do all of this in a very short weekend in order to minimize impact on traffic in the neighborhood,” he says.

Builders also had to strengthen parts of the old bridge’s rotted timber with steel channels before removing two long chunks of the structure in single lifts. These were done by a large 63,000-lb-load-capacity mobile crane, using tensioned suspension cables and a custom spreader bar to ensure the unit pulled up both ends of each piece vertically.

The lift also faced complications from a design detail on the original bridge: a pin in a slotted hole that could not be disengaged, Farnsworth says. That forced the crane’s crew to pull not only on the weight of the bridge, but also against that connection’s resistance.

The team later deconstructed those spans on stands on Furman Street and used a smaller mobile crane to remove other approach spans.

Much of that exercise may be echoed when the team assembles and lifts the new 450-ft-long steel and wood-deck bridge into place early next year, says Alex Reddihough, Arup senior structural engineer. Crews will install five sections and set them on the original bridge piers, he says.

“Basically it will be the reverse of what we did [in October] because the weights are effectively the same,” he says.

在10月份在一个周末举行两个最大的桥接部分的删除。

Shaky History

由于一个非常规设计 - 一种与Brooklyn Heights Chanjion object的美学醒目的木结构，将Brooklyn Heights街道的美学醒目的木结构沿着越过Furman街的倾斜对齐。最初的400万美元的结构名为Edward Robinson Squibb，这是一个19世纪的药品巨头，附近有一个实验室的实验室，谁创立了被称为Bristol-Myers Squibb的公司 - 拥有另一个独特的功能：柔性黑色蝗虫木框架，旨在提供一个行人轻微反弹。

The bridge was open for more than a year when park corporation officials determined that it bounced far more than intended, Landau says. They closed the bridge and sued original designer HNTB for design flaws, later settling out of court for nearly $2 million. “The bridge is an example of a design risk that we took that didn’t work,” he says.

2015年，Park Corporation聘请了Arup设计了340万美元的修复，包括增加调谐质量阻尼器以减轻振动，并重新打开2017年的跨度，Landau说。但去年，检查员发现，过度的水分在黑色蝗虫木材中引起了先进的腐烂，迫使另一个闭合。

“We started working through our options,” Landau says. “You could either retrofit the bridge again, or you could decide to completely replace it.”

Parts of the old bridge’s rotted timber had to be strengthened with steel channels before long chunks were removed.

他说，安装承载承重钢支撑的安装承载钢支撑件将花费400万美元，而添加原钢结构并增加新的钢结构将花费650万美元。根据Landau的说法，使用该设计的原始支持削减了大约200万美元的替换桥成本，同时保持了弗曼街的相同对准，长度和高度-6英尺高。

Landau说，Park Corporation选择了钢桥的确定性，有机会“逃离原有的跨度的挑战历史”。他说，改造也将保持黑色蝗虫木材，这可能会继续恶化，并且需要广泛的维护。“虽然不幸的是要彻底删除我们不仅建造的东西，但随后花费数百万美元试图修复......我们相信它既是公园和公众的最佳利益，”Landau补充道。

That’s also a common view among local residents, says Lara Birnback, executive director of the Brooklyn Heights Association, a neighborhood advocacy group.

“It was unfortunate. I’m sure that no one would have wanted it to happen this way,” she says. “But people in the community say they’re looking forward to the bridge and to a lasting solution.”

“People in the community say they’re looking forward to the bridge,” says Lara Birnback, executive director of the Brooklyn Heights Association.

Sturdier Design

The design for a new bridge had to match the allowable weight limits of the existing foundations and piers. That set the stage for steel, Arup’s Farnsworth says.

“The old timber bridge was quite light, and we certainly didn’t have a load allowance for a concrete or precast or prestressed concrete bridge,” he says. Overall, the bridge will use about 22,000 lb of steel, Arup’s Reddihough points out.

让皮尔斯还创建了“几何constraints” on how the bridge will connect to its supports, in part because the original structure used a catenary cable support system underneath. The new one will have trusses running along the deck’s underside, says Farnsworth. The design requires trusses that aren’t vertical; instead, they have a slope, some at angles of up to 30°, he says.

Farnsworth说，最小化重量的需要也导致了木甲板的使用。“我们只是没有具体甲板的基础能力，”他说。

该团队选择了热改性的白灰，这是一个木本公司已经拥有的长凳和“我们知道，喜欢”，Landau说。Reddihough说，第一结构的设计模仿特征的第一结构，包括常数ADA标准下降约4.9％。但它具有新的细节，如金属化，腐蚀保护完成。“我们想避免油漆和未来的维护。他说，很难在弗曼街的桥下起床。“我们整个指定了真正耐用的材料。”

Photo Courtesy Brooklyn Bridge Park Corp.

Working Ahead

Another design element was accounting for a more congested neighborhood, Farnsworth says. “We’re trying to minimize work in the field given ... space constraints and the activity,” he says. That led to a major focus on prefabrication and preassembly in the design, Farnsworth says. “We’re designing the bridge to basically be assembled as a full span on the ground,” he says.

Reddihough说，跨越普通的钢铁制剂已经开始。该团队于11月和12月对码头进行调整，包括拆除现有的轴承杯和基台，用新的支架和轴承代替它们。它还通过顶部表面上的纤维增强聚合物条带加强胶合的混凝土板，以适应新负载。

雷迪径表示，九个桥梁部分的第一个可能会抵达。“九个跨度将按顺序排列，”他补充道。它们包括两种主要的120英尺长的跨度，西侧五个30英尺长的方法跨度，两个跨度将最后的60英尺变成squibb公园。

A worker preps a support for Brooklyn’s Squibb footbridge. Photo By Tom Sawyer/ENR

The main spans will each arrive in three 40-ft sections, which the team will bolt together on site, he says. The team also will preassemble the wood decking on the ground, Reddihough says. That will allow each lift—using the same single crane and spreader bar system—to set in place a nearly complete section. “In this way we’re ensuring quality control,” he says.

Final tasks after the lift will entail adding handrails, lighting and mesh infill panels, Reddihough says. The team will also reinstall the mass tuned dampers. “We’ve saved those dampers in the demolition— they’re pretty expensive items—and we are going to be retuning them and reinstalling them on the new spans to assure that dynamic performance,” Reddihough says.

据Landau称，当新桥在明年夏天打开时，它应该在一个概念上关闭一个概念，这些概念在一个有许多独特的设计元素的公园内突然出现。

“Part of what makes Brooklyn Bridge Park so amazing is that everything we’ve done here from a design perspective is really different [than] parks around the country,” he says.