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Waffle slabs are preferred for spans greater than 40 feet (12 m), because, for a given mass of concrete, they are much stronger than flat slabs, flat slabs with drop panels, two-way slabs, one-way slabs, and one-way joist slabs. [2] Section of a waffle slab including beam, ribs, and column head
Compared to traditional solid slabs, the reduced self-weight of biaxial slabs allows for longer spans and/or reduced deck thickness. The overall mass of concrete can be reduced by 35–50% depending on the design, [ 1 ] as a consequence of reduced slab mass, as well as lower requirements for vertical structure and foundations.
A grid deck uses beams and diaphragms as the supporting structure. The supporting system of a grid deck is analyzed using a grillage analysis. A slab deck is one where the deck is analyzed as a plate. If the slab has a stiffness that is different in two directions (at right angles), then the deck is known and analyzed as an orthotropic deck.
In engineering, span is the distance between two adjacent structural supports (e.g., two piers) of a structural member (e.g., a beam). Span is measured in the horizontal direction either between the faces of the supports (clear span) or between the centers of the bearing surfaces (effective span): [1] A span can be closed by a solid beam or by ...
The same structural effects are also true of the concrete slab in a composite girder bridge, but the steel orthotropic deck is considerably lighter, and therefore allows longer span bridges to be more efficiently designed. Resistance to use of an orthotropic deck relates mainly to its cost of fabrication, due to the amount of welding involved.
Decks can also be covered by a canopy or pergola to control sunlight. Deck designs can be found in numerous books, do-it-yourself magazines, and websites, and from the USDA. [8] Typical construction is either of a post and beam architecture, or a cantilever construction. The post-and-beam construction relies on posts anchored to piers in the ...
The concrete elements may be reinforced or prestressed. Such modern bridges include girder , plate girder , and box girder bridges, all types of beam bridges. Types of construction could include having many beams side by side with a deck across the top of them, to a main beam either side supporting a deck between them.
Batter-post rigid frame bridges are defined by their supports that run from the deck to the abutments at an angle. This design supports the deck in a similar way to v-shaped piers but differs in how the foundations must be built. The piers bear on or next to the abutments, eliminating the need for foundations directly beneath the bridge.