About new Haralson Mill Covered Bridge

This page was originally created by JReinhl who maintains a site on covered bridges of Ohio. He was nice enough to donate the page to Georgia.

About new Haralson Mill Covered Bridge in Rockdale County, Georgia, USA

(This information is excerpted from Rockdale County Transportation Improvement Program, a pamphlet available free from the Courthouse in Conyers, Georgia. Information in italics and brackets are from personal observation of the bridge.)

The covered wooden bridge replaces a historic ford which crossed Haralson Mill Road, formerly an unimproved dirt road on the north side of Rockdale County. The project site is immediately north of the Haralson Mill Historic District....[To find Haralson Mill Road, take Georgia highway 20 between Conyers and US highway 78. Turn EAST on Bethel Road and then north on Haralson Mill Road. Signs were erected pointing to the new covered bridge.]

Prestressed beams support the bridge. Additional diaphragms were added to distribute weight of walls

The Big Haynes Reservoir is supplied by two tributaries. One of the tributaries, Mill Rock Creek, was a ford crossing approximately 20 feet wide which crossed Haralson Mill Road. The existing stream crossing was only a few inches deep at times and easily fordable. Now, with the impoundment of the reservoir underway, it will eventually be under water. Since the ford crossing could be under ten to fifteen feet of water during certain times of the year, a bridge is preferred over a culvert due to the desire to minimize earth fills and retain mature hardwood growth in the area. Without this bridge, an area of land would be inaccessible with the road terminating on either side of the lake. This condition was not considered acceptable.

As part of the overall project improvements, the connecting roadway has been paved and upgraded to a 35 MPH design speed with a 20 MPH approach near the covered wooden bridge. Although the primary traffic on the bridge will be single-axle passenger vehicles, it has been constructed to accommodate multi-axle vehicles. However, as a secondary use, it will facilitate the movement of pedestrian traffic....

In selecting the type of bridge, Rockdale County considered the importance of historic preservation of the area, as well as the cost factor. The wooden bridge was chosen, as opposed to the conventional concrete and steel structures commonly seen throughout the state, due to it's historical significance. In order to retain the required attributes of the area, bridge designs from the early 1800's were considered.

The structure emulates a covered bridge design similar to the 1820's era Town Lattice Truss design patented by Connecticut architect Ithiel Town. The bridge consists of 3 fifty foot spans with solid concrete piers and spill-through abutments which have been encased with a granite veneer. [The Town lattice includes vertical posts very similar to the standard Town V bridges of Quebec. However, these are steel column supports with timber veneer! The substructure includes concrete abutments on 12 x 53 steel H piles, AASHTO Type II concrete beams, and intermediate concrete piers with granite veneer.]

The bridge superstructure is designed to utilize Georgia wood products and labor while still promoting new timber bridge technology. Moreover, the new bridge meets the American Association of State Highway and Transportation Officials (AASHTO) Standard Specifications, or more specifically, AASHTO Guide Specification HS20-44. All lumber is standard size (2" x 12" or smaller) Southern Pine treated with Chromated Copper Arsenate (CCA), a waterborne-based pressure-treated preservative, or Pentachlorophenol Type A (Penta), a heavy oil-based pressure-treated preservative. [The superstructure includes 109,000 board feet treated with CCA and 11,000 board feet treated with Penta.]

Faux Town Lattice design has no structural purpose. Roof is supported on steel columns with wood veneer

Preservative treatments were applied to the lumber to protect against living and non-living agents capable of degrading the wooden structure. Typical agents include heat, moisture, abrasion, ultraviolet light, decay fungi, bacteria, and insects.

The bridge decking is stress-laminated and was assembled off-site in twelve foot sections and transported to the job site. The innovative design of this deck type is unlike any method previously used in the State of Georgia. The deck is built with two inch lumber standing on edge and spanning perpendicular to the travel lanes for the complete width of the bridge (i.e., 37 feet). Each panel is assembled with high strength bolts torqued to 700 foot-pounds. The advantage to this installation and construction procedure is a high-strength stressed deck in a transverse spanned panel. This eliminates the problems associated with hydraulic jacked panels, on-site nail laminated panels, or prefabricated glue laminated panels.... [The bridge is wide enough to accommodate two travel lanes plus two sidewalks INSIDE the trusses.]

The superstructure is covered by a conventional roof/truss system. The exterior framing and lattice work are treated with pentachlorophenol. The roof is tongue and groove decking with dressed cedar shingles.

A fire control system has been added to the original design. The feed for this system is Rock Mill Creek which at times, will be inundated by the reservoir. During times that the reservoir is below normal elevations the ford crossing reverts to its natural state, a small spring fed creek. This creek, only inches deep and a few feet wide, is not sufficient to supply the fire system.

The system draw requires one hundred gallons a minute for approximately thirty minutes. The water source, for the system to be effective, must be a constant. A small dam to impound water from the creek has been incorporated into the design. The system will draw water from a submerged pump which is in a stand pipe near the creek. The stand pipe will be under the normal pool of the reservoir and will act as protection from debris for the pump.

As the system engages, a call is placed to a monitoring company. Once notified, they contact the Rockdale County Communications Department for Fire Department dispatch....

For further information regarding the Haralson Mill Covered Wooden Bridge, please call the Rockdale County Board of Commissioners at (770)929-4001 or the Department of Public Services and Engineering at (770)785-5919.

Back to the Rockdale County bridge.

Updated September 19, 2002. 14:40