IN-26 Bridge

Information and Findings From DHPA Historic Bridge Survey

Statement of Significance

This bridge represents the IDH's revised standard and additionally-braced design for 150' Parkers with wide decks. The structure appears to retain its original members, including the metal guardrails. The concrete approach rails are replacements.

Architectural Description

The Indiana Department of Highways significantly modified its standard 150' Parker through-truss design in the late 1930s to accommodate roadways wider than 25'. The revised design reduced the number of panels, relied more heavily upon rolled I beams in the webbing and lower chord members, and stiffened the portal bracing.

The IDH used the revised design in this setting, although it retained its standard concrete substructure. Seven panels, demarked by differently-sloped top-chord segments, compose the single-span's riveted superstructure. The outer vertical consists of an I beam, and the others are made of laced channels. I beams also supply the outer and the center-panel diagonal and counter; laced channels compose the other diagonal. the lower chord consists of I beams, too, with holes to allow for drainage. Substantial portals and cross-frames, arched to allow for added roadway clearance, brace the trusses. The heavy I floor beams are riveted to the verticals at and above the lower chord and carry the 26' concrete roadway.

Other Information

The Yost Brothers of Decatur, Indiana, successfully bid $48,766.85 in April 1941 to replace a collapsed structure with a new one of state design to be seated upon concrete abutments. The Yosts completed the new bridge by the end of the year. The ISHC used a fourth-generation standard plan for this 150-ft., riveted, Parker through-truss span with a 26-ft. roadway bordered by 1-ft. 6-in. curbs. Standard #1522 appears to have essentially followed the earlier #1531 in all except the deck. Truss depth varied from 22 ft. at the portal to 29 ft. 8 in. at midspan. Each truss carried seven panels, the outer two at each end of 20 ft. and the inner three at 23 ft. 4 in. All top chord members are differently sloped, and only the central panel's is parallel with the lower chord. All were fabricated from a pair of 12-in. channels, the endposts at 35 lbs. and the others at 30 lbs. The lower chord's members consist of 10-in. rolled I-beams growing in weight from the ends (@54#) towards midspan (@77#). Most of the verticals were made of a pair of latticed 10-in. channels (@15.3#); the hip vertical of a 10-in. I-beam (@33#). To protect the quite-tall trusses against wind and vehicle-induced stress, substantial latticed struts and heavy upper sway framing buttressed the verticals above the 15 ft. of roadway clearance. The portals also relied on latticed sections. Even as they shifted between sections, the diagonals grew lighter toward midspan: in the second panel, a 10-in. rolled I-beam (@41#); in the third, a pair of 10-in. channels (@15.3#); in the fourth, a rolled 10-in. I-beam (21#). The ISHC required 36-in. I floor-beams, growing heavier toward midspan (150#>182#) and riveted to the verticals above the lower chord. Ten rows of 18-in. rolled I-beam stringers, also growing heavier toward midspan (47#>50#), were attached to the floor-beams' sides. Together, the floor-beams and the stringers carry the concrete deck. Tube-and-post guardrails lined the trusses, while coped concrete rails with bush-hammered panels marked the approaches.

The trusses of this example of an important fourth-generation ISHC standard plan for a moderately-long span remain intact, including their metal guardrails. The concrete deck and approach rails have been replaced.

The concrete approach rails are replacements.
1978: Bridge Seats, Approach Rails, Concrete Slab Deck Replaced, Paint

Bridge Considered Historic By Survey: Yes