Roscoe Bridge

Glossary of Terms

For a full glossary of terms, continue on to http://www.iowadot.gov/subcommittee/bridgeterms.aspx

Frequently Used Bridge Terms

AASHTO
The American Association of State Highway and Transportation Officials is a nonprofit, nonpartisan organization representing the five transportation modes of: air, highways, public transportation, rail, and water. AASHTO establishes the base standards by which bridges are designed, rated and inspected and is used throughout the United States and Puerto Rico.

Abutments
The support foundation structure for the bridge.

AISC
The American Institute of Steel Construction. This agency writes the design code used for bridge and steel building design and construction.

AISC Certification
The certification process involves an examination to evaluate a company’s quality management system rather than the specific product. Certification is one of the only ways a company can let you as the designer/contractor know that they are qualified and certified to provide good quality work.

Anchor Bolts
Bolts set in concrete abutments or piers. Used to secure bridge to foundations.

Beam Bridge
A bridge built of beams, either classified as a short-span or long-span beam bridge, which is supported on beams whose ends rest on piers or abutments.

Bearing Assembly
Device used to attach bridge to foundations. Several types are available, steel on steel, Teflon on stainless steel, and elastomeric. Combinations of the above types are also possible.

Bottom Chord
The bottom longitudinal structural member of a truss.

Cast-in-Place Abutment
A bridge support that holds the weight of the bridge (dead load) as well as the load-rating of the bridge (live load) by framing and pouring reinforced concrete with enough square footage to distribute the loads within the soil-bearing capacity (pounds per square foot – PSF) of the ground and prevent the bridge from settling over its life.

Camber
The arch found in bridges. Minimal arch, called dead load camber, is required on all bridges designated to be flat. This dead load camber is just enough camber to offset the deflection of the bridge due to its own weight. Arch beyond dead load camber is more for aesthetic reasons than structural value.

Clear Span
The unsupported length of a bridge. Typically measured from end of bridge to end of bridge.

Cover Plates
Plate steel welded to the supported beams to provide supplemental strength and/or cover expansion joints at abutments.

Deflection
The engineering term to indicate the distance that a bridge span will displace due to the application of a load. Maximum deflection of a simple span bridge will always occur at the center of the span. Deflection ratio is defined as a numerical value of length-of-bridge divided by the deflection of the bridge. Ratios of 400 to 800 are common.

Diagonal
The sloped web member of a truss, extending between the top and bottom chords.

Elevation Difference
The vertical height difference between two abutments or bridge bearing points.

Elevation View
Side view of bridge span on shop drawings

Floor Beam
Structural horizontal members connecting the bottom chords of a Half-Through Pony System and Full-Through Box System, or connecting the verticals in a Half-Through H-Section System.

Form Deck
A galvanized corrugated decking used specifically for accepting the placement of concrete or asphalt. In asphalt applications, the form deck is designed to support all deck dead and live loads. In concrete applications, reinforcing bars and concrete will support the deck dead and live loads, and the form deck will only support the weight of wet concrete and a small uniform construction load.

Half Through Systems
This type of bridge does not have any overhead lateral bracing system. Bracing of the top chord is accomplished by the stiffness of the U-frame.

Handrail
A longitudinal member attached to the inside truss, for use as an aid for pedestrians. Placement is normally dictated by the requirements in the American with Disabilities Act.

IronWoods®
The registered name of the premium naturally durable hardwood product. It is a very dense wood that does not require treatment. IronWoods® is comprised of hardwood species, such as Ipe.

Live Load
This is the term to indicate the carrying capacity of the bridge. It is to simulate the accumulation of pedestrians on the bridge. It is usually indicated as an uniform load specified in pounds per square food, such as 60psf, 85psf 100psf, etc.

Plan View
View of bridge from directly above the structure.

Perched Abutment
A bridge support that is installed on level ground that has a pounds per square foot (PSF) soil-bearing capacity capable of carrying the weight of the bridge (dead load) as well as the load-rating of the bridge (live load) without settling over the life of the bridge. A perched abutment is a simple method of supporting the bridge and can be constructed out of pre-cast concrete, wood, or steel, and sits on top of the ground.

Piled Abutment
A bridge support that holds the weight of the bridge (dead load) as well as the load-rating of the bridge (live load) by installing/driving steel, concrete or wood piling into the ground to 1) bedrock, or 2) a depth whereby the friction of the pile with the surrounding ground will not allow the bridge to settle.

Rolled Beam
The main structural support element of a beam bridge that is less than or equal to 120’ in clear span length. Rolled beams are processed in steel mils as standard W-beam shapes ranging from 4” (W4) through 44” (W44).

Safety Rails
Steel angle or tubing welded to the truss to deter objects from falling or small children from climbing through the truss. Safety rails may be either longitudinal or vertical pickets.

Skewed Ends
The condition where the bridge foundation and abutments are not perpendicular to the longitudinal center line of the bridge structure.

Sloped Ends
The end condition of a truss bridge where the end vertical slopes up from the abutment to the top chord. This condition is chosen for aesthetic reasons.

Specifications
A written document that explains aspects of the bridge structure to be purchased. Comprehensive, non-proprietary specifications are required to assure that the structure designed and manufactured meets all intended expectations of the customer.

Square Ends
The end condition of a truss bridge where the end vertical is plumb, that is the end is straight up and down.

Stringers
Structural members running the length of a truss bridge used to provide structural support of the wood or concrete deck.

Toe Plate
A plate located above deck level to protect golf carts, snowmobiles, and people from slipping off the bridge deck.

Top Chord
The top longitudinal structural member of a truss.

Top Chord Height
The distance from the top of deck (measured at its highest point) to the top of the top chord. Typically a minimum dimension of 42” is required for pedestrian traffic. Bicycle traffic usually requires a 54” dimension.

Truss
A framework of chords, verticals, and diagonals which give support to a trial-type. Found along either side of the deck.

Verticals
Structural members connecting the top and bottom chords of a truss. Usually they are at right angles to each of the chords.

W-Beam
Standard structural shape for bridge support beams that are manufactured in steel mills in 4” (W4) through 44” (W44) sizes.

Weathering Steel
Best-known under the trademark COR-TEN steel, is a group of steel alloys which were developed to obviate the need for painting, and form a stable rust-like appearance if exposed to the weather for several years.

Welded Plate Girder (WPG)
The main structural support element of a beam bridge that is greater than or equal to 120’ clear spans. The WPG is fabricated from plate and is comprised of a top flange, a WEB and a bottom flange. A typical WPG may be from 4’ to 8’ deep.