What is Rigid Frame Bridge?

Portal frame bridge is abbreviated as portal bridge, and its legs and beams intersect vertically to form a portal frame

The bending moment of the leg will increase as the stiffness ratio of the leg to the beam increases Portal bridges made of steel or reinforced concrete are mainly used for bridges As for the T-shaped rigid frame bridge (characteristically hinged in the middle of the span), and the continuous girder bridge with two V-shaped struts and girders rigidly connected with the legs, the shape is similar to the multi-span frame bridge, but the internal force is distributed according to the law is different (see prestressed concrete bridge)

Portal bridges can be divided into: Single-span portal bridges When made of steel, the legs and feet are always hinged to form a double-hinged door frame (Figure a) When made of reinforced concrete, the legs can be hinged, can also be consolidated with the foundation to form a fixed-end single-span portal bridge (Figure b), which is mainly used in places with good geological conditions Double Cantilever Single-Span Gantry

Extend both ends of the beam past the door leg, add a balance weight to the end of the overhang (Figure c), or place a prestressed brace between the end of the overhang and the legs (Figure d), which can make the support section of the girder larger To reduce the positive bending moment of the girder in the middle of the span, the height of the girder is correspondingly reduced, which is conducive to the construction of the elevated bridge

Multi-span portal bridge (Figure e) Mainly used for bridges with small spans Three-span portal bridge with two arms (figure f) This type of bridge has abutments at both ends and when prestressed concrete is used the span can be extended By For example, the highway bridge built by the United States on the Houston Waterway in 1981 has a span of 114.3 + 228.7 + 114.3 meters

The rigid truss legs of the sloping leg rigid truss bridge are inclined and the axis of the two legs and one half of the girder is approximately bowed (Figure g)

In this way, the bending moment of the legs and beam is significantly smaller than that of the frame of the same span The axial pressure has increased Compared with platform arch bridges, this type of bridge does not require an arch structure superior and has a smaller number of components; when the bridge deck is narrow (such as a single track railway bridge) and the span is large, its inclined legs can be placed on the lateral side of the bridge to ensure the lateral stability of the bridge

Famous prestressed concrete inclined leg rigid frame bridges include: German Federal Railway Horem Bridge (1953, leg hinge span 85.5 meters), China Handan (Dan) Chang (zhi) Railway Zhuozhang River Bridge ( 1981, hinged span standing 82.0 meters), the Saint-Michel French road bridge (in 1957, the span based on the distance to the center of the piers was 1 × 60 + 5 × 65.2 meters ) and so on

Famous steel sloping leg rigid frame bridges include:

Luxembourg Alzette Road Bridge (1965, hinge span 234.1 meters), Yugoslavia Neretva Railway Bridge (1966, 100 meters), France Martigues Road Bridge (1972, 210 meters), Italian Sfalasha (376 meters ) meters) highway bridge (1972, 376 meters) and China’s Ankang Hanjiang railway bridge (1982, 176 meters, see color image), etc.

Ankang Han River Bridge, a steel sloping leg rigid frame railway bridge with a hinge span of 176 meters, completed in 1982

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