In 1994, the Fort Worth Transportation Authority (the T) hired PB to carry out Program Management of its plan to link the cities of Fort Worth and Dallas with a commuter rail line. The T entered into an agreement with the Dallas Area Rapid Transit Authority (DART) to make the connection possible. This joint venture was given the name Trinity Railway Express (TRE). The T is responsible for the western half of the project in Tarrant County.

TRE acquired the existing right-of-way and track work of the Rock Island Line, a freight route ideally located in the commuter corridor between the two cities. At the west end, the alignment veered away from downtown Fort Worth, creating the need for approximately 3.2 km (2 miles) of new track to service the intermodal facility that was proposed for the city's convention center area (Figure 1) The intermodal transportation center (ITC) is planned to handle TRE and Amtrak trains, Greyhound buses, taxis, and the T urban bus service, and include a kiss-and-ride facility. Just 1.6 km (1 mile) further down the track is the terminal with park-and-ride capability.

Figure 1: Trinity Railway Express (TRE) Commuter Rail Corridor

Our Challenge Becomes Apparent

The alignment of the new track weathered significant changes. In fact, our environmental consultant worked with federal, state and local authorities from 1994 to 1998, during which time four alignments were examined and evaluated. In addition, there were environmental issues to handle because a large part of the property to be acquired was the site of former industrial facilities and rail sidings. The area also contained several warehouses of historical significance.

The third alignment, which passed through a warehouse known as the Tindall Storage Building, became unacceptable when that building became eligible for listing in The National Register of Historical Places as a result of an extensive effort during 1997 and 1998. This designation led to the development of the fourth and final alignment, which avoided the Tindall Building but intersected the adjoining Hunt and Hawes (a.k.a. Alarm Supply) Building.

The Alarm Supply Building was constructed in 1910 to serve as a warehouse for the local grocery firm of Hunt and Hawes. It later became one of the first warehouses rented by Montgomery Ward to facilitate its mail order business. The building ended its productive days being used by a company that marketed intruder alarm services until the T acquired the building.

A Finding of No Significant Impact (FONSI) dated December 1998 was issued for the rail alignment, with the final environmental assessment including the fourth alignment. The Memorandum of Agreement (MOA) attached to the FONSI required that the following measures be carried out:

• The building had to be documented by the T using the Historic American Building Survey/Historic America Engineering Record Level III quality documentation. (This refers to documentation required to be deposited in the Library of Congress for the Historic American Building Survey and the Historical American Engineering Record as defined by the National Park Service. Documentation Level III defines the level of data required to be provided.)
  
  
• The building had to be preserved in accordance with a preservation plan developed by the T in consultation with the Texas State Historical Preservation Office and representatives from the local historic preservation community. The preservation plan is intended to preserve the facade, windows, roof and portions of the interior floors of the building to the maximum extent feasible in order to provide the appearance of a complete building penetrated by a railroad tunnel structure. The Alarm Supply Building shared a common wall with the Tindall Building, so the preservation plan also had to consider and mitigate any effects that alterations to the Alarm Supply Building would have on the structural integrity of the adjacent National Register eligible Tindall Storage Building.

The challenge for the PB team was clear-design a tunnel through an old building without destroying its heritage and without disturbing the neighboring structures.

The T acquired the building in July, 1999. At that time, the schedule required the entire downtown intermodal infrastructure to be completed by July 1, 2001.

A Complex Solution is Engineered

The Alarm Supply Building is a 5-story structure with a footprint of roughly 29 m (96 feet) square. Its basic internal structure was provided by a series of 0.35 m (14 inch) square, solid timber columns on which cast iron collared caps carried the load from the incoming beams in two directions only. The beams were notched to match cleats on the collars. No rivets, bolts or pegs were used in the construction. Only the floor joists provided lateral stability.

The double track tunnel was designed to be 12 m (40 feet) wide skewed at 45 degrees to the building footprint and three stories high. Two systems had to be designed within the same very restricted working area because city building inspectors made it clear that the tunnel section was to be supported independently from the building (Figure 2). The MOA did not specify that the building should be occupied and the Federal Transit Administration funding mandated its use for intermodal transportation purposes only. Thus, it was possible to reduce the design live load to 9.07 kg/m² (20 pounds per square foot) if the upper floors were used only for maintenance and emergencies.

Under our direction, the design consultants developed several concepts, including both cast-in-place reinforced concrete and segmental structural steel trusses. Throughout the design and in keeping with the MOA, it was necessary for our managers to maintain contact with the local historical preservation organizations.

Figure 2: Alarm Supply Building showing the shored up north face.

The final design used two separate sets of drilled pier foundations for the tunnel and the building supports. Both superstructures are steel. The building support consisted of five internal truss portal frames with the trusses sitting at third floor level and I-beam portal frames at the north and south tunnel openings. In order to minimize disturbance of the building fabric, the trusses were assembled on site, with components handled through existing window openings.

We also constructed several enhancements related primarily to the possible transmission of locomotive vibrations through the support structure to the common wall with the Tundall Storage Building.

Harmony is Achieved

When the intermodal facility is completed, passengers on the station platform will have an uninterrupted view of this unique project element and will pass through it as they head east for Dallas. It is anticipated that the unique penetration of the Alarm Supply Building will become a signature facility, demonstrating the harmonizing of modern intermodal facilities with historic preservation in evolving urban environments.