What is a portal steel truss bridge

Referred to as a portal bridge, its legs and beams intersect perpendicularly 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 mostly used for bridges. As for the T-shaped rigid frame bridge (characteristically hinged in the middle of the span), and the continuous beam bridge with V-shaped two struts connected to the beam rigidly, the shape is similar to the multi-span portal bridge, but the internal force is distributed The law is different (see prestressed concrete bridge).

The portal bridge can be divided into:

①Single-span portal bridge. When made of steel, the legs and feet are permanently hinged to form a two-hinged door frame. When made of reinforced concrete, the legs can be hinged; they can also be consolidated with the foundation to form a fixed-end single-span portal bridge, which is mainly used in places with good geological conditions.

②Double cantilever single-span portal bridge. Extend both ends of the beam beyond the door leg, add a balance weight at the overhang end or set a pre-stressed tie rod between the overhang end and the leg to make the support section of the beam produce a larger negative bending moment to reduce the beam The positive bending moment in the middle of the span is correspondingly reduced in beam height, which is conducive to the construction of flyover bridges.

③Multi-span portal bridge. It is mostly used for bridges with small spans.

④ Three-span and two-leg portal bridge. This kind of bridge has abutments at both ends, and when prestressed concrete is used, the span can be made larger. 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.