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6 Analysis of Rigid truck loading, and the average depth of the deck is usually as little as 1/25 of the span. Far-reaching advantages can be gained from shallow bridge floors, particularly in flat country where headroom is limited. The rigid frame concrete bridge lowers the overpass roadway or raises the underpass road way. Consequently, substantial reductions are obtained in volume of embankment fill or excavation, and in area of land required for the ap proaches; often the drainage of underpasses can also be simplified. The ultimate cost of rigid frame concrete bridges is low. It includes the three major items: first cost, maintenance, and replacement charges. Compared with simple spans, maintenance expense is smaller since the various details where the deck bears on the abutments are eliminated. Rigid frame concrete bridges will have a practically unlimited length of serviceable life; the annual charge for replacement is therefore un usually small. Rigid frame concrete bridges may be widened with but slight altera tions of the existing structure. The widening operation need not inter fere with normal traffic. Traffic moves with the greatest safety both on and under rigid frame concrete bridges. There are no structural parts projecting above the roadway or track bed ; and the bridge deck can span farther without aid of intermediate columns. The waterway passage per foot of span length is greater under a rigid frame concrete bridge than under an ordinary deck structure without intermediate columns. The expression of the continuity in the external aspects of the rigid frame concrete bridge has given rise to a new and stimulating bridge architecture of pleasing, aesthetic appearance. Rigid frame concrete bridges with solid decks are economical up to span lengths of about 70 feet for heavy highway loading. For long spans, the ribbed deck construction is preferred on account of its lightness. Rigid frame concrete bridges with spans up to 175 ft. 0 in. liave been built in the United States. SECTION II—ESTIMATING THE FRAME DIMENSIONS Two analyses of the forces and moments are usually needed for designs of rigid frame bridges. The first analysis should consume a minimum of time as its object is merely to determine the approximate frame dimen sions. A more detailed analysis is needed to check the stresses in the final structure. The first approximate analysis may often be omitted and replaced by empirical rules derived from similar structures formerly analyzed. It Generated on 2015-11-26 09:25 GMT / http://hdl.handle.net/2027/coo.31924003881277 Public Domain, Google-digitized / http://www.hathitrust.org/access_use#pd-google

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6 Analysis of Rigid

truck loading, and the average depth of the deck is usually as little as

1/25 of the span.

Far-reaching advantages can be gained from shallow bridge floors,particularly in flat country where headroom is limited. The rigid frameconcrete bridge lowers the overpass roadway or raises the underpass roadway. Consequently, substantial reductions are obtained in volume of

embankment fill or excavation, and in area of land required for the approaches; often the drainage of underpasses can also be simplified.

The ultimate cost of rigid frame concrete bridges is low. It includesthe three major items: first cost, maintenance, and replacement charges.

Compared with simple spans, maintenance expense is smaller since thevarious details where the deck bears on the abutments are eliminated.Rigid frame concrete bridges will have a practically unlimited lengthof serviceable life; the annual charge for replacement is therefore un

usually small.

Rigid frame concrete bridges may be widened with but slight alterations of the existing structure. The widening operation need not interfere with normal traffic.

Traffic moves with the greatest safety both on and under rigid frameconcrete bridges. There are no structural parts projecting above theroadway or track bed ; and the bridge deck can span farther without aidof intermediate columns.

The waterway passage per foot of span length is greater under a rigidframe concrete bridge than under an ordinary deck structure withoutintermediate columns.

The expression of the continuity in the external aspects of the rigidframe concrete bridge has given rise to a new and stimulating bridgearchitecture of pleasing, aesthetic appearance.

Rigid frame concrete bridges with solid decks are economical up tospan lengths of about 70 feet for heavy highway loading. For long spans,the ribbed deck construction is preferred on account of its lightness.

Rigid frame concrete bridges with spans up to 175 ft. 0 in. liave beenbuilt in the United States.

SECTION II—ESTIMATING THE FRAMEDIMENSIONS

Two analyses of the forces and moments are usually needed for designsof rigid frame bridges. The first analysis should consume a minimum oftime as its object is merely to determine the approximate frame dimensions. A more detailed analysis is needed to check the stresses in thefinal structure.

The first approximate analysis may often be omitted and replaced byempirical rules derived from similar structures formerly analyzed. It

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