GP Tubular Conveyor Bridge

This design was entered for the 1980 Prize Bridge Competition, sponsored by the American Institute of Steel Construction.......:

AMERICAN INSTITUTE of STEEL CONSTRUCTION
1980 Prize Bridge Competition
Special Purpose Category
Tubular Conveyor Bridge

As part of the renovation of the wood chip handling and storage system at Georgia Pacific Corporation's paper mill in Toledo, Oregon, a 1641 foot long, 70 foot vertical clearance utility bridge was constructed over Depoe Slough, a tributary of the Yaquina River. The bridge consists of nine structural steel support towers and eight spans of 12 foot diameter, thin wall structural steel tube ranging in individual lengths from 167 to 263 feet. The tubular enclosure houses a 48" wide belt conveyor, a 500,000 pound per hour high pressure steam line, water lines, electrical conduit and a walkway. The walkway enables mill personnel to move unrestricted between both sides of the mill which is divided by the slough.

The spans and support towers of the bridge were shop assembled in the Portland, Oregon area to their full length and height respectively and then shipped to the site, approximately 300 waterway miles away, by oceangoing barge. Once at the site, the precisely manufactured, modular components were completely assembled by a single, high capacity crane in one month.

Among the more notable characteristics and unique features of the bridge are:

1. The sitting of the bridge called for high clearance, short and long spans since the bridge crosses the tidal slough, a navigation channel, an island, a lumber storage yard and a creek in its direct route from one side of the mill to the other. The inherent strength of the steel tubular spans provided the capability to span the needed distances, and the flexibility to allow a variety of erection loads to be applied during transport and construction.
2. The direct, straight line routing of the bridge, which replaced an older obsolete suspension bridge, allowed for an increase in energy efficiency on a unit for unit bases in excess of 1400%.
3. The steel tube provides a total environmental barrier to prevent wood chips, grease droppings, condensate water and other environmentally deleterious agents from migrating into the river or onto the land areas under the bridge. The steel shell also provides shelter for workmen and mill personnel during maintenance operations or while transiting form one side of the mill to the other.
4. The circular cross section of the bridge lended itself quite readily to the fitting of aerodynamically tested, wind induced, vibration spoilers. The Oregon coastal location is subject to hurricane force winds and, together with the required lengths of the spans, produced a situation that called for attention to aerodynamic considerations. The spirally wound "strakes" or fins which project form the surface of the tubular shell are designed, and wind tunnel tested, to allow the bridge to sustain winds in excess of 100 miles per hour.
5. The lightweight design of the structural steel tube enabled shop assembly of the gallery, ease of transport and relative ease of erection. These features all combined to enable construction costs to be maintained below budget and the bridge an internal components to be placed in operation ahead of schedule. From bridge design to start-up encompassed a period of only 16 months.

The photos attest to the relative simplicity of design, yet attention to detail, that this bridge provides. The clean, uncluttered appearance of the structure is an indirect result of considerable devotion to utilitarian, environmental, economic and aesthetic concerns.