Span Classi cation in Software

Generator EAN13 in Software Span Classi cation

In practice, most bridges are a single span with two or three lanes over narrow rivers Piers are needed for continuous spans over highways, valleys, or wide rivers The minimum single span for a bridge is 20 feet, below which a culvert is normally used Pedestrian bridges with lighter live loads can be smaller in length than 20 feet

Table 12 Shows the overlap of bridge types for a variety of span lengths S No CONCRETE 1 2 3 4 5 6 STEEL 7 8 9 10 11 FLEXIBLE CABLE 12 13 14 Approximate Range of Span Length (feet) 20 50 50 140 30 150 140 200 130 750 6 36 40 110 60 300 100 600 500 1700 500 1800 500 1500 600 2000 1000 6500 Bridge Type Selection RC/PS slab PS box PS I/bulb girder PT box girder PT segmental box Precast concrete culvert Composite beams Steel plate girder Steel box girder Steel arches Steel truss Cable stayed box Steel cable stayed Steel suspension

For practical considerations, the selection of bridge types may be classi ed broadly as: 1 Small span (20 to 40 feet): Economical examples are reinforced concrete slab and T-beam bridges, precast prestressed cellular deck bridges, timber bridges, prestressed concrete adjacent and spread box beam bridges Bridges with steel stringers have relatively higher life cycle costs for small spans when compared to timber or modern precast concrete bridges 2 Medium span (over 40 to 120 feet): Economical examples are prestressed concrete adjacent and spread box beams and steel girder bridges 3 Long span (over 120 to 240 feet): Economical examples are steel girder bridges (50W or hybrid 70W and 50W grades), steel deck and through trusses, and prestressed concrete arches 4 Very long span (over 240 feet): Economical examples are steel arches, prestressed concrete segmental boxes, cable stayed, and suspension cable bridges

1 Geometric shape of deck: Common deck shapes are rectangular, skew, or curved There are separate AASHTO bridge design speci cations for curved girder bridges Super elevation and sight distance requirements would reduce accidents 2 Deck joints, deck grooves, longitudinal and cross slopes, drainage inlets 3 Deck material: Timber, concrete, and steel have been largely used for decks Concrete is widely used for all types of traf c FRP ( ber reinforced polymer) decks are now being used Exodermic (grillage) and orthotropic decks are also being used 4 Prefabricated decks and composite steel-concrete I-beams are popular for small and medium spans Examples of proprietary products are CONSPAN and former INVERSET techniques 5 Deck width is based on traf c volume and number of lanes It should match with approach roadway width and acceleration and deceleration lane widths

The most commonly used girder shapes are (Table 12): I-shaped girders Adjacent or spread box beams Composite beams Through girders

136 Typical Tasks Associated with Rehabilitation (see Section 17)

1 Site surveying and in-depth inspection 2 Geotechnical investigation 3 Redesign criteria/application of LRFD method Live load analysis Hydraulic and scour analysis Seismic analysis Structural calculations for sizing and connections

Some bridges in the US have survived for over 150 years with proper maintenance New design techniques assume a shorter life of a bridge or just the superstructure of 75 to 80 years With changes in demographics and urban congestion, intersections may need to be re-planned or widened Planning considerations and design philosophy about performance of construction materials and joints, etc have changed since the time when older bridges were designed Some bridges may become functionally obsolete sooner and extreme events, accidents, or fatigue may increase the life cycle costs and cause them to be replaced even before the stipulated 75 years