Bridge No: 0170003200200

Asset ID: 159

County: Abbeville

Facility Carried: S-1-32 (Old Calhoun Falls Highway/Old SC 7)

Feature Intersected: Shanklin Creek

Year Built: 1924

Main Structure Type: T Beam

Design: Continuous

Main Material: reinforced concrete

Railing Type: Concrete balustrades

Number of Main Spans: 5

Structure Length: 172 feet

Structure Width: 21 feet

Setting: The bridge carries a 2-lane road over a stream in a wooded rural setting.It is the westernmost of two 1924 bridges constructed when the state improved the road as SC 7 between Abbeville and Calhoun Falls in Abbeville County (see 0170003200400).The old highway retains its period geometry with an 18'-wide cartway and unimproved shoulders.

The custom design, 5 span, 172'-long T beam bridge consists of a three-span continuous main span with a maximum span length of 52' and a simply supported span at each end. There are three lines of beams, and all the beams are haunched with the greatest depth at the bearings. The beams are supported on concrete abutments and two-column bents.Those at the stream have partial web walls. The cantilevered deck sections are supported on brackets and are finished with standard-design concrete balustrades.End posts are inscribed with "1924," the date of construction.An asphalt overlay has been placed over the integral concrete deck.

The custom design T beam bridge was built in 1924 and stands as one of the earliest complete examples of the important bridge type. It is also a very early example of the continuous design. The reinforced concrete T beam bridge is believed to have been used by cities and counties in South Carolina prior to 1910. It is an adaptable bridge type as, in addition to custom designs, it could easily be standardized for relatively short span lengths. The fledgling state highway commission issued a set of standard plans for T beam bridges in 1917 (Standard Nos. S-201 to 204) with the earliest ones consisting of three or four lines of beams. The standards were updated for wider roadways in the late 1920s. The later examples usually consisted of four or more beams. Standard design T beam bridges became ubiquitous throughout the state during the 1930s and continued to be one of the Department’s workhorse standards through the 1950s. As common and important a feature of the early state highway system as the T beam bridge was starting immediately after World War I, no unaltered pre-1922 examples are known to exist. In 2012, the oldest complete example was the 1923 bridge over Coronaca Creek northeast of Greenwood in Greenwood County (2490003100100). The next oldest are two 1924 bridges on the original alignment of SR 7 between Calhoun Falls and Abbeville in Abbeville County (0170003200200 and 0170003200400). All three bridges are historically and significant within the statewide context as one of the most important technological building blocks of the state highway system (Criterion C).

This example is also technologically significant (Criterion C) as an early application of the principles of continuity to a beam bridge. Continuous designs have significant economic advantages because they use less material (smaller section beams) for a given span length than simple spans (those where the beams do not continue over the piers). A simple span must accommodate the entire load within the span, whereas the continuous span distributes loads from bearing to bearing over two or more spans. Continuous designs also allow for the reinforced concrete deck to be continuous over the interior substructure units, thus reducing the number of expansion joints, which are frequent sources of deterioration and high maintenance costs. Continuous beams are more complicated to design because of stress calculations are indeterminate, which made many bridge engineers reluctant to use them.