BergerWorld: 2nd Quarter 2008

Communities throughout the world are increasingly incorporating unique and innovative pedestrian bridges to herald their commitment to revitalization by creating aesthetically attractive landmarks. Such structures require engineers to approach projects like artists, taking on assignments with a more creative outlook and utilizing their skills to incorporate thoughtful designs that make a statement. Moreover, designers are once again paying close attention to the often immeasurable benefits pedestrian bridges bring to a community's residents and visitors, including creating inviting links to a city's vibrant downtown area or developing a signature focal point for a city center. The Berger Group is currently at the forefront of such efforts.

The Las Vegas Strip is a four-mile section of Las Vegas Boulevard where many of the world's largest hotels, casinos and resort properties are located. Because of Las Vegas' distinction as a renowned tourist attraction, the Strip serves nearly 200,000 pedestrians and more than 80,000 vehicles per day. In order to provide safer movement for pedestrians and relieve traffic congestion created from the mix of large numbers of pedestrians and vehicles, Clark County Public Works commissioned the Louis Berger Group, in collaboration with B/A, to design a set of three pedestrian bridges at the busy corner of the Strip and Spring Mountain Road: a west bridge from the Treasure Island Resort to the Fashion Show Mall, a north bridge from the mall to the Wynn Las Vegas Casino and an east bridge from the Wynn Casino to the Palazzo-Venetian Casino.

The Team worked with property owners to develop conceptual designs and establish touchdown locations agreeable to all property owners. Berger experts then prepared still and animated 3-D, computer-generated models for alternative bridge types; performed preliminary engineering to develop structure types and sizes; and evaluated alternative layouts, right-of-way needs, utility relocations, and pedestrian benefits and impacts.

The selected clear span plate girder bridges range from 135 to 165 feet in length, with widths of 16 feet. Tuned-mass dampers were included in each bridge to diminish any perception of vibration that might occur from synchronized pedestrian movement. Each bridge is equipped with two elevators and four escalators. The extensive use of glass, stainless steel and low-maintenance surfaces provide a modern look and high durability. Concrete tower structures were used to support steel bridge girders. Landings at each bridge were framed with steel beams and concrete slab on metal deck, providing efficient access to escalators and elevators leading to casinos, resorts and malls.

The completed bridges serve an estimated 150,000 pedestrians per day, offering safer routes to shopping, gaming and employment, as well as aesthetically pleasing sites to take in the outstanding views of the world-renowned Strip.

Approximately two million people live in the Portland metropolitan area, located near the confluence of the Willamette and Columbia Rivers. The city and region are noted for their strong commitment to land-use planning and public transit. TriMet, Portland's regional transit authority, retained B/A to provide project management and engineering services for the design of a $40 million, 1,600-foot light rail bridge and bicycle/pedestrian crossing over the Willamette River as a component of the proposed south/north light rail extension of the highly successful MAX light rail system.

B/A's duties included coordinating and directing a multidisciplinary team specializing in civil and structural engineering, architecture, geotechnics, hydraulics and environmental sciences. The Team explored potential bridge types, such as cable-stayed and arch bridges; established the location of the river crossing, as well as bridge touchdowns; and provided recommendations to mitigate highly sensitive environmental issues. In addition, B/A represented TriMet at public and agency review meetings and oversaw the preparation of a U.S. Coast Guard navigation permit.

The innovative final design features a single-tower, cable-stayed bridge with a contrasting steel truss superstructure. The unique scheme featured a symmetric S-curved alignment that accommodates tight site limitations. To meet the navigational clearance needs, the vertical profile rises from at-grade stations on each bank to 72 feet clear above dual shipping channels on each side of the tower located near the center of the river. A maximum grade of five percent was maintained in order to add a pedestrian/bicycle path on each side of the light-rail lines.

The Elwha River Bridge was constructed in 1913 in Port Angeles, Washington. In 2007, the 94-year-old bridge was closed for demolition and replacement due to concerns regarding its structure after the I-35W Mississippi River Bridge collapse in Minnesota. Clallam County selected B/A to design a structure to replace the bridge.

B/A's initial field work included hydraulics studies and geotechnical investigations. Following analyses of a variety of alternatives, including three bridge replacement alternatives and three alternatives for providing pedestrian access across the river valley, the Team also prepared cost estimates, construction schedules, demolition plans for the existing structure and environmental assessments. Finally, B/A assisted in obtaining permits and providing documentation in support of a NEPA categorical exclusion and a State Environmental Protection Agency determination of non-significance.

The preferred replacement bridge consists of a three-span, post-tensioned concrete box girder bridge. A walkway will be suspended from the bridge soffit to provide pedestrian and cyclist access to the Olympic Discovery Trail without blocking drivers' views of the scenic river valley. To minimize environmental impacts, the bridge will be constructed using the balanced cantilever method, utilizing two cantilever arms extending from opposite sides of the Elwha River and meeting at the center. Construction is slated to be completed in June of 2009.

Crossing the majestic Ohio River at its headwaters, the West End Bridge frames the Pittsburgh Skyline and serves as the city's portal to the river. While a prominent riverfront landmark, the existing bridge lacks sufficient pedestrian access and connection to the riverfront trail network and waterfront. In an effort to create a connection between the bridge and water, the Riverlife Task Force challenged architects and engineers to "envision a new pedestrian crossing, anchored to the existing West End Bridge, creating new connections to the bridge and water."

A&W, in cooperation with Endres Ware Architects Engineers, recently won the design competition sponsored by the Riverlife Task Force for the new West End Pedestrian Bridge. The jury described the winning design as "an elegant solution that is structurally viable and that respects and enhances the West End Bridge while incorporating multiple new access routes and providing opportunities for lingering and strolling, giving people in Pittsburgh access to the water and to the views of the city and the rivers in a way that has never before been possible."

A&W is currently providing a number of services for the signature project, including structural and civil engineering, cost estimates and constructability reviews. The completed structure will be suspended from the existing West End Bridge, requiring A&W's expert analysis of the existing cable truss arch bridge.

A&W is evaluating a pedestrian crossing over Kenilworth Avenue, two Metro Rail lines and six sets of CSX Transportation tracks in Washington, D.C. The new bridge will carry pedestrians from the proposed Parkside Development, a multi-use community providing retail and housing in a rapidly growing area of the city, to the Minnesota Avenue Metro Station.

Because the site is highly constrained, severe limitations regarding available bridge options exist, including maintaining vertical clearances above the rail lines and the roadway while passing under high voltage electrical distribution lines above. These constraints have led to the exploration of several innovative aesthetic, economical, functional and buildable solutions, including cable-stayed, suspension, extradosed, truss and tubular bridge forms. A&W's study will conclude with the selection of a single alternative for the final design.

The D.C. Department of Transportation selected A&W to design a pedestrian bridge spanning CSX Transportation tracks and linking the Metropolitan Branch Trail with the Rhode Island Avenue Metro Station.

A&W prepared several alternatives before the D.C. Commission of Fine Arts selected a truss bridge. Because the structure is expected to become a prominent new feature of the landscape, aesthetics are a design priority, and various alternatives for viewing platforms and ramping configurations are currently being considered in order to optimize the bridge's visual impact.

Tukwila, Washington, lies in the heart of Puget Sound, 12 miles south of downtown Seattle, B/A was recently commssioned by the city to prepare the planning and design for the south 180^th Street grade separtion, which required a pedestrian brdige linking to the area's popular Interurban Trail, a 14-mile recreational trail for pedestrian and cyclists offering views of Mount Rainier annd the Kent Valley countryside. In addition to conceptual planning and designs, B/A also provided environmental studies; final designs, plans and specifications; and cost estimates for the award-winning project.