Section 3: Historic Highway Bridges in Texas
Anchor: #i1003166Overview
The Environmental Affairs Division (ENV), in cooperation with the State Historic Preservation Officer (SHPO), has inventoried and evaluated bridges potentially eligible for the National Register of Historic Places (NRHP), including metal truss, masonry, and concrete bridges, and reached an agreement as to which of those structures are significant—that is, they are eligible for inclusion in the NRHP. A list of those historically significant bridges may be obtained from the district environmental coordinator or ENV. The list may not be comprehensive.
Anchor: #i1003178Steel Truss Bridges
Currently, steel trusses are the predominant historic highway bridge type in Texas. The two most common types of trusses are the through truss and pony truss. Truss bridges were constructed mainly from the 1880s through the 1940s and vary greatly in their general condition, load carrying capacity, width, vertical clearance, and safety features. This variation dictates that an engineering and economic feasibility study by the HBT, as described in Chapter 4, Section 2 of this document, be performed as early as possible to determine if the particular bridge is a viable candidate for continued vehicular service or whether an alternative use should be sought.
While both through and pony truss bridges have been successfully moved and preserved, pony trusses generally are moved more easily due to their shorter span lengths, lower profiles, and absence of cross bracing between the top chords of the trusses. Pony trusses up to 90 feet long have been successfully transported without disassembly. The particular type, length, weight, condition, route, and distance to new locations are critical factors to consider in any preservation effort.
Anchor: #i1003196Concrete Bridges
Concrete Arch Bridges. Concrete arch bridges consist of either single or multiple arches supported by abutments and intermediate piers. Typical arch shapes include the high, round semicircular arch and the low, flat, elliptical arch. Concrete arch bridges are well suited for short and long spans where the foundations are solid. The arch can be constructed of plain or reinforced concrete. Concrete arch bridges may be closed- or open-spandrel structures. They are typically used in situations where the design and aesthetics of the bridge are particularly important, such as an entry bridge to a city or park. Concrete arch bridges were built from about 1905 through the 1940s.
Concrete Slab Bridges. Reinforced concrete slab bridges can be composed of single or multiple spans. Slab bridges can be used for short spans where headroom is limited. This was a common bridge type in the 1930 − 40s.
Concrete Girder Bridges. Though similar in appearance to a slab bridge, the concrete girder span is distinguished by a series of longitudinal beams on its underside. The girders can be an integral part of the slab or they can be cast separately. Cross beams are sometimes placed between the girders to provide extra support. The concrete girder bridge was one of the most popular types used for highway bridges in the 1930 − 40s.
All Concrete Bridge Types. All of these concrete bridge types may possess decorative concrete railings, which add to their historic significance. Other engineering qualities such as unusual length or design in response to difficult crossing situations also contribute to an individual bridge’s significance. Relocation of these structures is practically impossible due to their type of construction.
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Some masonry or masonry-element bridges may also be historic. Typically, masonry-element bridges are concrete slabs with masonry substructure elements such as piers, abutments, or wingwalls. They may also feature masonry guard walls or curbs. Some of these bridges are significant for their unique design, materials, and workmanship, which follow the principles of “rustic” design. They are historically significant because of their construction by circa 1930s Works Progress Administration (WPA), Civilian Conservation Corps (CCC), or other such federal work-relief agencies. Work-relief agencies maximized labor-intensive construction methods, bought locally-available stone, and hired local laborers in an effort to reduce unemployment during the Great Depression of the 1930s. Relocation of these structures is practically impossible due to their type of construction.
Anchor: #i1003231Suspension Bridges
Few suspension bridges remain in Texas. These bridges are significant because of their rarity, historical importance, and engineering features. Most suspension bridges were built from the 1870s through the 1930s. Due to their uniqueness, suspension bridges often receive special consideration or preservation as may be directed by the Texas Legislature or other policy-making body. Due to the engineering difficulties and high cost of relocation, preservation in place may be the only feasible alternative.