Houston, we have a solution!

The city of Houston, Texas is getting a much needed new bridge to replace an existing structure, addressing a transportation problem that will only grow in the coming years – and mageba is supplying the bridge’s expansion joints, with a newly developed solution that will optimize their maintenance

Although less than forty years old, the Sam Houston Tollway Bridge over the Houston Ship Channel – one of the busiest waterways in the United States – has been determined to be unfit to meet the challenges of growing traffic in the coming years, and construction has already started on a replacement structure. The new cable-stayed bridge, with four lanes and a generous hard shoulder on each of its twin superstructures, will be far better able to accommodate the 60,000 vehicles that currently cross the existing structure each day – with enough extra capacity to handle the enormous increase expected in coming decades, with daily traffic of approximately 158,000 vehicles expected by 2035. The southbound structure is set for completion in 2021, with the existing bridge then to be demolished and the northbound structure built in its place. The main spans, with a length of 1,320 feet, will be the sixth longest in the United States, and the project’s cost of approximately USD 1 billion is being financed by toll revenues.

One of the project’s biggest challenges is posed by the need to minimize impacts on shipping traffic on the channel below, which must cease while construction work is progressing overhead. The various stakeholders involved agreed to limit shipping closures to two three-hour closures during the daytime, with a five-hour gap between closures, in any 24-hour period. At night, crews can close the channel for nine hours, with a 48-hour period between closures. The construction contract allows for 42 closures for each new structure and 33 for demolition of the existing bridge, with a bonus payment for each closure not used and a penalty payment for each additional closure required.

A smaller but still significant challenge was posed by the specification for the new cantilever finger expansion joints at each end of each structure. This required the joints to be designed to accommodate 16.5 inches (420 mm) of movement – a very large movement capacity for a finger joint of the cantilever type, in which the steel fingers do not receive sliding support at their free ends. The solution proposed by mageba, consisting of specially detailed TENSA®FINGER (type RSFD) cantilever finger expansion joints, additionally addresses the challenges arising when finger plates require to be temporarily removed or permanently replaced – with steel anchorages to which the finger plates are bolted, with the nuts held in nut-locking tubes, as opposed to having the finger plates anchored directly into the main concrete structure as originally anticipated. As a result, although the bridge replacement project will inevitably have some impact on traffic during the construction phase, future impacts during the structure’s service life will be minimized – at least insofar as they might relate to maintenance of its expansion joints.

Bridge designer: Figg Bridge Group
Bridge owner: Harris County Toll Road Authority
Bridge contractor: Ship Channel Constructors (a Traylor Bros. / Zachry Construction Corp. joint venture)

Image © shipchannelbridge.org

Rendering of the Sam Houston Tollway Ship Channel Bridge, currently being constructed in Texas, USA

Project-specific 3D drawing detail of the required TENSA®FINGER expansion joints – of type RSFD, with cantilever (not sliding) steel fingers forming the driving surface

TENSA®FINGER RSFD finger-type joints have proven their worth on many bridges around the world – including, for example, the Audubon Bridge over the Mississippi River in Louisiana, USA

The scope of the supply contract also includes sliding cover plates for the barriers at each end of each expansion joint