Timber Bridge Construction Terminology & Construction Glossary

AASHTO

Definition: The American Association of State Highway and Transportation Officials. This nonprofit, nonpartisan agency writes the code that governs highway design. It covers all bridges from county roads to interstate bridges. Its guidelines provide important information about the load capacity and usage requirements of vehicular bridges in the 50 states, the District of Columbia, and Puerto Rico.

ACQ

Definition: (Alkaline Copper Quarternary) – a water-based wood preservative used by Bridge Builders to prevent lumber decay from fungi and insects.

Camber

Definition: the arch of a surface, sloping downward from the center toward the sides.

CCA

Definition: (Chromated Copper Arsenate) – a chemical wood preservative containing chromium, copper and arsenic. CCA is used in pressure treated wood to protect wood from rotting due to insects and microbial agents and increase the longevity of your bridge.

CuNap

Definition: (Copper Napthenate) – a historically proven, oil-based preservative treatment for wood products. It is basically the reaction product of a copper compound with napthenic acid. CuNap seals and protects against water damage, rotting, insects and many other dangers.

Dead load

Definition: the static load imposed by the weight of the materials that make up a given structure

Clearspan

Definition: a bridge that is supported only on both ends of an embankment and not in the center section with a pile.

Glulam

Definition: a stress-rated engineered wood product comprised of wood laminations, or “lams.” Special bonding techniques using strong, waterproof adhesives allow individual lumber pieces to be joined end-to-end to span long distances without intermediate columns. Glulam beams are much stronger than sawn lumber. The laminating process allows timbers to be produced in a variety of shapes from straight beams to graceful, curved arches. Glulam timber is a more attractive way to span long distances compared with concrete or steel.

GVWR

Definition: (gross vehicle weight rating) – the maximum allowable total weight of a road vehicle or trailer when loaded – i.e., including the weight of the vehicle itself plus fuel, passengers, cargo, and trailer tongue weight. GVWR expresses the maximum continuous load for vehicles traversing a bridge.

HS20-44

Definition: a designation established by AASHTO. “HS” refers to the type of vehicles a bridge or highway can accommodate; “20” refers to the loading specification of the bridge; “44” indicates the year the specification was adopted. HS20-44 capacity means that the bridge or highway is able to safely accommodate 3-4 axle vehicles, such as a large semi-truck and trailer. All Bridge Builder Timber Vehicular Bridges meet these AASHTO requirements. Bridge Builders can also design HS25-44 Timber Vehicular Bridges, which are able to accommodate a much higher continuous loading capacity.

KDAT

Definition: Wood that is dried in a kiln after pressure treatment to control the rate of drying so that stresses that might otherwise result in splitting, warping, or twisting are minimized.

Live Load

Definition: a moving, variable load on a structure (e.g. a bridge) such as moving traffic or pedestrians, usually expressed in terms of pounds per square foot.

Penta

Definition: (Pentachlorophenol) – the most commonly used oil based preservative used to pressure treat and wood and guard against decay and word-boring insects. In the non-pressure process method pentachlorophenol is applied by spraying, brushing, dipping or soaking.

Bridge Builders constructed nine (9) AASHTO rated bridges for our planned residential community, The Bluffs on Cape Fear, located in Wilmington, North Carolina. The bridges were designed and constructed using highway rated treated timbers and serve as a wetlands crossing on the subdivision roads. The total design-build contract amount was in excess of $2m dollars.

The professionalism exhibited by Bridge Builders was exceptional during the entire process from design development through construction. The field crews were led by a very experienced project manager whose attention to detail was first rate. They worked well with all of the other contractors on our site during construction of the roads, infrastructure, and bridges. They met all of our scheduled milestones during the course of the project.

Overall, we were pleased with the quality of construction and the end product and would recommend Bridge Builders for future work.

Jay Stillwell
Member/Manager
River Bluff Holdings II, LLC