Glossary of Timber Bridge Terminology

AASHTO- The American Association of State Highway and Transportation Officials (AASHTO) is a respected nonprofit and nonpartisan organization that serves as a representative for highway and transportation departments. Its guidelines and specifications are the standard for defining loading requirements for highway (vehicular) bridges.

Abutment- The critical supporting structure at the end of a bridge that retains the roadway approach. ATS Builders' timber bridges include a timber abutment and wing wall as standard features.

ACQ (Alkaline Copper Quarternary)- An outdated pressure treatment no longer widely used. ATS Builders employs safer treatments such as Copper Azol (CA) to protect wood against decay and insects. CA contains copper and Azol, which are fungicides that effectively protect the lumber and are safe for hardware.

Bent- A supporting unit of a bridge consisting of two or more piles connected by a cap or another member. This connecting member evenly distributes superimposed loads on the bent. When combined with a system of diagonal or horizontal bracing attached to the piles, the entire construction efficiently transfers loads onto the foundation.

Bridge- A purpose-built structure that spans over ravines, waterways, highways, or wetlands to enable vehicular or pedestrian access.

Caisson- The commonly used term for a cylindrical casing that provides structural support for a piling.

Camber- The arch of a deck, sloping downward from the center toward the sides, or the arching of the deck upward measured at the centerline in inches per foot beam. It serves both aesthetic and structural purposes.

CCA (Chromate Copper Arsenate)- A water-based wood preservative containing arsenic, chromium, and copper. This treatment is used to protect against decay, insects, and increase the longevity of the timber used in our bridges.

Combination Design- A bridge design that combines pile supported sections with free span section(s) for enhanced structural stability.

Culvert- A pipe or concrete box structure that conveys flow from open channels, swales, or ditches under a roadway, driveway, fill soil, or surface structure. 

CuNap (Copper Napthenate)- An oil-based pressure treatment for wood that seals and protects against water damage, rotting, insects, and other dangers.

Dead Load-  The static load imposed by the weight of the materials that make up a given structure.

Deck- The horizontal riding surface of a bridge. All ATS Timber Vehicular Bridges include a structural deck and timber wear deck.

Deflection- The displacement of a structural member or system under load.

Diaphragm- The structural supporting member that is placed perpendicular to the main members of a bridge or building, providing lateral support and stability.

Elevation Difference- The height variance from one end of the bridge to the other. ATS seamlessly incorporates this feature into our designs.

Elevation View- The profile view of a bridge, typically depicted in shop drawings.

Filter Fabric- An erosion control method where fabric is wrapped around the timber abutment to prevent soil loss. This fabric allows water to pass through while preventing soil erosion. ATS utilizes this on all timber abutments.

Free Span- A bridge that is supported only at both ends of the embankment without a center pile. Ideal for crossing large areas where pile foundations are prohibited, such as road overpasses, environmentally restricted areas, and steep ravines.

Glue-Lam- An engineered timber product created by gluing together individual pieces of dimensional lumber. Glue-lam beams can span greater distances than sawn timber and are pound for pound stronger. This method is a more visually appealing way to span large distances compared to concrete and steel.

GVW- Gross Vehicle Weight refers to the total curb weight of the vehicle and payload. It indicates the maximum continuous load for vehicles crossing a bridge. ATS's Light Maintenance Capacity bridges are 5-ton GVW loading; Heavy Maintenance Capacity is rated for 10-ton GVW.

Guide Rail- A safety barrier mounted along the edge of a bridge or roadway to prevent vehicles from veering off the roadway.

Guide Rail Cap- The finishing timber piece that tops off a guide rail, providing a polished and secure railing.

Headwall- A crucial component placed at the end of a bridge, forming a large portion of the abutment. Headwalls serve to retain the road formation soil around and above the abutments and prevent erosion at the abutment.

HS20-44- A designation established by AASHTO. "HS" refers to the type of vehicles a bridge or highway can accommodate; "20" denotes the loading specification of the bridge; "44" indicates the year the specification was adopted. HS20-44 capacity ensures a bridge or highway can safely accommodate 3-4 axle vehicles, such as large semi-trucks and trailers. All ATS Timber Vehicular Bridges meet or exceed these AASHTO requirements. Additionally, ATS can design HS25-44 Timber Vehicular Bridges, which can accommodate a much higher continuous loading capacity.

KDAT (Kiln Dried After Treatment)- Wood that is dried in a kiln after pressure treatment. Kiln-drying the lumber after pressure treatment prevents substantial shrinkage, cupping, or warping. It also results in superior strength and stiffness.

Live Load- The variable load on a structure, such as moving traffic or pedestrians. It is usually expressed in pounds per square foot or kilonewtons per square meter.

Stringers, also known as joists, are essential supporting members that run lengthwise on a bridge, providing crucial structural integrity.

Wear deck, a second layer of wood planks on the bridge deck, provides a durable wear-surface that can be repaired or replaced without compromising the bridge's integrity, a standard feature on all ATS Timber Vehicular Bridges.

Wing walls are crucial in retaining the soil behind the abutment, ensuring stability and structural integrity.

Penta (Pentachlorophenol) is the predominant oil-based preservative utilized for pressure treating wood, providing unparalleled protection against decay and insect infestation.

Pile, whether constructed of long timber, concrete, or steel, serves as a foundational element driven or embedded into the ground to provide unwavering support for a structure.

Pile-supported bridge design employs evenly spaced piling driven into the ground as the primary support system for the structure, ensuring robust stability and longevity.

Piling Cap serves as the cornerstone of the support structure for weight displacement on a timber bridge, meticulously placed to fortify each bent and connect the stringers that reinforce the structure.

Plan View offers an all-encompassing aerial perspective of a bridge, typically depicted in shop drawings, providing a comprehensive view of the structure from above.

Retrofitting involves the meticulous modification of an existing structure to incorporate changes not initially available during the original construction, ensuring the structure's continued relevance and efficiency.

Refusal, a term used in pile driving, denotes the point when the piling resists further penetration into the ground despite the weight of heavy equipment, a testament to the strength and stability of the structure.

Rip rap, a layer of large stones or broken rock, is strategically placed on an embankment to provide unparalleled erosion control and protection, ensuring the structure's long-term stability and integrity.

Span, the horizontal distance between individual piling or the abutment and piling on a bridge, is a testament to the bridge's expansive reach and unwavering support.

Vehicular guardrail- A robust and customizable fence-like barrier designed to guide vehicular traffic and prevent accidental passage beyond the roadway. It can also serve as a decorative element tailored to the client's specifications.

Vibratory hammer- A specialized equipment that utilizes vibration and soil deformation to reduce inner stabilizing forces and facilitate the efficient driving of massive piles. The vibratory hammer's own weight and pre-tension are sufficient to quickly and effectively drive piles to refusal with minimal force.

X-bracing- Additional support for bridge piling, consisting of timbers placed in a "criss-cross" pattern to form an "X", providing strength and stability to the supporting piling.