Rigid-frame bridge

The use of rigid-frame bridges began in Germany in the early twentieth century and quickly spread to the Americas. Emílio Henrique Baumgart and Arthur G. Hayden, in particular, gained notoriety for their use of concrete rigid frames in the early 1920s. At the time, reinforced concrete was commonly used in bridge design but the superstructure was designed with bearings on the substructure. Therefore, a much shallower cross section at mid-span can be used. Additional benefits are that less space is required for the approaches and structural details for where the deck bears on the abutments are not necessary. Engineers have also noted some disadvantages of rigid frame bridges. The placement of steel reinforcing bars (rebars) can be very difficult and the forming/placement of the concrete is complicated. Furthermore, rigid frames are statically indeterminate and the analysis is more challenging than that of simply supported structures. ==Types of rigid-frame bridge==

Single span Bridge over the West Branch North River, Adamsville MA.jpg|Single-Span Over River, United States A73 Bruecke CO1.jpg|Single Span Over Roadway, Germany Silta Kostianvirran yli.jpg|Single-Span in Shape of Arch, Finland Single span rigid-frame bridges are typically made of reinforced concrete and are commonly used on parkways and other roadways. This design is an efficient use of material as the cross section at mid-span is relatively narrow and the amount of concrete needed at the abutments is reduced. If steel is used, the economic advantage extends to spans of . Additionally, the effective length of each span is shortened compared to the spans of a bridge with vertical piers. However, this system is less commonly used in rigid frame bridges because the piers need to be approximately centered under the bridge. Often the bridges span over roadways or waterways and construction of piers in those cases can be costly and challenging. Batter-post Otamusjoen silta 2.JPG|Concrete Batter-Post Bridge, Finland 北橫 蘇樂橋.jpg|Steel Batter-Post Bridge, Japan or Taiwan Osaka-Bridge02.jpg|Batter-Post Bridge, Japan 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. This is particularly advantageous when the bridge crosses a river and constructing a foundation in the water is challenging. As a result, either the abutments have to be made larger or additional foundations must be placed next to the abutments. ==Recent advances==

In the past few years, most research on rigid frame bridges is related to retrofitting existing structures to meet new seismic specifications. This research often finds that the amount of reinforcing required at beam-to-column joints needs to be increased in concrete structures. In many bridges, the amount of steel required by the seismic code causes congestion at the joints. This is notable because it was already challenging to place standard reinforcing in a concrete rigid frame bridge. Prestressing the rebars is more difficult but was proven to still be feasible. Prestressed concrete is useful in bridge construction because it has higher tensile strength than traditional reinforced concrete, allowing for longer bridge spans. ==References==