AASHTO LRFD Bridge Design Specifications Quiz

AASHTO LRFD Bridge Design Specifications

• AASHTO LRFD Bridge Design Specifications are published by the American Association of State Highway and Transportation Officials.
• The 4th Edition was published in 2007 and uses SI units.

Definitions

• Bridge: a structure with an opening of at least 6100 mm that forms part of a highway or is located over or under a highway.
• Collapse: a major change in the geometry of the bridge rendering it unfit for use.
• Component: a discrete element of the bridge or a combination of elements requiring individual design consideration.
• Design: the proportioning and detailing of the components and connections of a bridge.
• Design Life: the period of time on which the statistical derivation of transient loads is based, which is 75 years for these specifications.

Key Concepts

• Ductility: the property of a component or connection that allows inelastic response.
• Engineer: the person responsible for the design of the bridge and/or review of design-related field submittals.
• Evaluation: the determination of the load-carrying capacity of an existing bridge.
• Extreme Event Limit States: limit states relating to events such as earthquakes, ice load, and vehicle and vessel collision, with return periods in excess of the design life of the bridge.
• Factored Load: the nominal loads multiplied by the appropriate load factors specified for the load combination under consideration.
• Factored Resistance: the nominal resistance multiplied by a resistance factor.

Bridge Types

• Fixed Bridge: a bridge with a fixed vehicular or navigational clearance.
• Movable Bridge: a bridge with a variable vehicular or navigational clearance.
• Multiple-Load-Path Structure: a structure capable of supporting the specified loads following loss of a main load-carrying component or connection.

Load and Resistance Factor Design (LRFD)

• LRFD: a reliability-based design methodology in which force effects caused by factored loads are not permitted to exceed the factored resistance of the components.
• Load Factor: a statistically-based multiplier applied to force effects accounting primarily for the variability of loads, the lack of accuracy in analysis, and the probability of simultaneous occurrence of different loads.
• Load Modifier: a factor accounting for ductility, redundancy, and the operational importance of the bridge.

Other Concepts

• Model: an idealization of a structure for the purpose of analysis.
• Owner: the person or agency having jurisdiction over the bridge.
• Regular Service: the condition excluding the presence of special permit vehicles, wind exceeding 90 km/h, and extreme events, including scour.
• Rehabilitation: a process in which the resistance of the bridge is either restored or increased.
• Resistance Factor: a statistically-based multiplier applied to nominal resistance accounting primarily for variability of material properties, structural dimensions, and workmanship, and uncertainty in the prediction of resistance.
• Service Life: the period of time that the bridge is expected to be in operation.
• Service Limit States: limit states relating to stress, deformation, and cracking under regular operating conditions.
• Strength Limit States: limit states relating to the maximum load-carrying capacity of the bridge.