Sarah Mildred Long Bridge Replacement
Portsmouth, N.H., and Kittery, Maine
最佳项目，高速公路/桥梁和优点奖

Owners:Maine Dept. of Transportation; New Hampshire Dept. of Transportation
Lead Design Firms:Hardesty & Hanover; Figg Engineering
General Contractor:Cianbro Corp.
预制铸造和勃起工程：McNary Bergeron
工程支持：Structural Technologies
Subcontractors:Case Foundation (Drilled Shaft); Shaw Brothers Construction (Earthwork); Atlantic Coast Dismantling (Demolition); Panatrol (Automation & Controls)

Faced with the challenges of a fast-flowing tidal river in an area prone to harsh weather conditions, the $165.2-million Sarah Mildred Long Bridge replacement project team provided an updated link between Portsmouth, N.H., and Kittery, Maine, with a unique bridge that’s the first of its kind in the U.S. As the existing steel vertical-lift bridge approached the end of its life cycle, the design joint venture of Figg and Hardesty & Hanover, working in conjunction with contractor Cianbro Corp., devised an updated version of the design, incorporating the first use of precast concrete segmental towers on a vertical-lift bridge in the U.S., as well as other concrete elements that could be safely and efficiently fabricated off site.

这座2,800英尺长的替换桥梁既有车辆和铁路交通，因此在新范围内的坡度仅限于可以容纳火车的级别。由于船在Piscataqua河上定期通过，因此缅因州和新罕布什尔州的运输部门陷入了垂直的升级设计，该设计使大型船只在升起时可以通过。

该项目给Enr的法官留下了深刻的印象。新利luck一位法官说：“我认为这只是检查了所有框，与其他一些项目相比，它的规模范围很大，它只是掩盖了它们。”18luck官网“我的公司实际上竞标了该项目并丢失了该项目，但我仍然喜欢它的结果。”

Concrete Idea

Hardesty＆Hanover的首席运营官Mike Hawkins兼替代桥项目经理Mike Habins说，该团队很早就知道它希望最大程度地利用混凝土在桥上使用。他说：“首先，我们发现混凝土将有助于减少未来的维护需求并延长寿命。”

Initially, the team considered using cast-in-place concrete on the towers, but at roughly 60% design, an updated study showed that precast would be more cost effective. For Cianbro and its crews, precast would also make its field work faster, more efficient and safer, resulting in a shortened construction schedule, says Kaven Philbrook, senior project manager at Cianbro.

Philbrook credits much of the team’s ability to find creative solutions for the Sarah Mildred Long Bridge to the owners’ choice of a construction manager/general contractor delivery method. Cianbro was brought on the project in 2012 to help with early design concepts and to provide constructibility and budgetary input. The company was then contracted in 2014 for the construction portion of the work. “It functioned like a design-build procedure, but the designer reports to the owner, not the contractor,” he says.

The bridge consists of a concrete superstructure made up of 500 post-tensioned precast concrete segments resting on concrete piers. The bridge substructure and superstructure are supported by 29 10-ft-dia drilled shafts that extend roughly 60 ft, including a depth of up to 30 ft into bedrock. The steel lift span is supported by four towers made up of 22 post-tensioned precast segments each.

为了创建塔楼，该团队设计和安装了后张贴的预制混凝土Cofferdams。在现场，船员使用驳船安装的起重机将碎片提升到位。安装后，将Cofferdams脱水，然后填充钢筋和混凝土。所有88个塔节都在现场预制。

Offsite Work

Throughout design, the team worked to find additional opportunities where bridge components could be fabricated onshore or by offsite vendors. Components, such as the concrete segmental approaches and the steel twin box-girder lift span, were delivered from offsite fabricators. Structure depths were limited, and girders were provided as smaller field splices to allow them to be shipped to the site by rail, truck or barge.

Cianbro说，这些灵活的运输选项为内陆制造商打开了招标过程，并最终导致了更具竞争力的钢制制造商标。一旦在内陆设施完成了盒子的制造，将单个盒子运到现场附近的驳船上进行最终制造。在通道闭合期间，在驳船上竖立了300英尺乘50英尺的升降机跨度，以将其浮动。菲尔布鲁克（Philbrook）说18luck.cub，当比较制造成本时，多箱梁设计可节省约100万美元。

The post-tensioned concrete floor and roof slab of the bridge’s control room were also precast, then erected and cantilevered from one of the towers.

最大程度地利用水的工作的另一个主要原因是避免在快速流动的潮汐河上工作的挑战。水流可能达到4节，这条河是该国最快的河流之一。潮汐可能会在每日地表水位上产生多达10英尺的变化。菲尔布鲁克说：“我们只能在松弛的潮汐上安全地移动驳船，这是几个小时的窗户。”“我们安排了驳船的所有可交付成果，以击中这些松弛的潮流。如果您错过了一个，那么您要等六个小时才能完成下一个。”

为了进一步避免驳船工作，Cianbro使用了定制的模块化临时工作栈桥，以提供对距离和塔楼的访问。菲尔布鲁克说，该团队已经成功地在另一个桥梁项目上游使用了模块化栈桥，并将其存储在附近的设施中。该栈桥的一部分被纳入了Sarah Mildred Long Bridge Trestle中。他说，使用栈桥将混凝土和材料直接带到工作区域，从而极大地提高了该项目的生产力和安全性。

Although construction of the trestle took about 70,000 work hours, Philbrook says it still offered a significant cost savings. “We ran the numbers on barges and found that option was more expensive,” he says. “At the time, the Tappen Zee Bridge project was going and just about every barge around was taken. We saved millions of dollars, mostly in [avoiding] rental of barges.”

安全的水

660000工作小时的项目,Philbrook says the team’s strategies allowed more than 100,000 to be carried out off the water. Philbrook also notes that its strategies contributed to the team’s exceptional safety record, logging only one recordable injury and zero lost-time accidents. Fabrication carried out onshore or off site offered a more controlled environment, mitigating the potential hazards of working on or over the river. “We’re a 100% employee-owned company, and everyone has a stake in this,” he says. “We all want to do things safer and better.”

The bridge’s design also focused on improving future access on the bridge for maintenance work. The design team devised a unique hybrid tower drive mechanism that locates the main mechanism at the bottom of the tower rather than a more conventional placement at the top of the towers.

In another innovation, Hardesty & Hanover’s tower pier design included high-density absorbing rubber arch fenders that are directly attached to the bridge tower piers for added protection. The foundations are designed to withstand a 12,000-kip force or vessel load. By eliminating separate fenders, the design maintains the shipping channel width for shipping while reducing the required lift-span length.

A key advantage of the new bridge design is that it creates more clearance for ship traffic. The original bridge featured dual decks with a vehicular deck on top and a railroad deck below. The new bridge also features bi-level approaches, however it incorporates only one movable span with dual seating positions—one at the vehicle level and one at the rail level. Since the rail line only carries traffic twice per year, the span remains almost always at the higher resting position. With an average of 56 ft of vertical clearance in the resting position, the team estimates there will be 68% fewer bridge openings than with the original bridge. The design aims to significantly reduce the number of traffic delays due to stopped traffic on busy Route 1.

While the project finished on time in June 2018, the bridge opened to traffic seven months late. The project team declined to discuss reasons for the delay. After construction was completed, Cianbro sued the Maine and New Hampshire DOTs for more than $16 million, claiming design deficiencies resulted in increased costs and delays, according to press reports. Maine and New Hampshire were expected to pay Cianbro $5 million, according to media reports published in August.

Modern Design

By using mostly concrete, designers were able to give the completed bridge a uniquely modern look. The bridge theme “Sails to Submarines” was chosen to represent the history of the river and submarine construction at nearby Portsmouth Naval Shipyard. The vertical-lift towers were stained with a sweeping curve to represent sails. A sweeping curve was also designed in the concrete shape of the vehicular piers.

The exposed main counterweight sheave at the top of each tower references the sailing aesthetic of a mainsail halyard sheave atop sailboat masts. Local architectural elements inspired by lighthouses as well as textures and proportions drawn from local structures were utilized to articulate the scale of the towers. The team incorporated features of Maine lighthouses in the new bridge’s towers, including thin railing structures.

这座桥是用长而设计的,open spans, using 11 fewer piers than the old bridge. The new span layout not only enhances vistas for residents and motorists but also enables the new bridge to cross a neighboring Portsmouth street without a pier in the median.

缅因州DOT的首席工程师乔伊斯·泰勒（Joyce Taylor）说：“我们早期的口头禅是我们想要一座很好的桥梁。”“我们不一定要寻找一座签名桥，但我认为我们有一座签名，而是一个实用的桥梁。”

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