Urban bridge engineering formwork supports are mainly used for the support of cast-in-place structures and temporary structures, such as formwork supports for cast-in-place reinforced concrete cover beams, cast-in-place reinforced concrete slab beams, and cast-in-place reinforced concrete box beams. Temporary support for steel-concrete composite beams, etc.
Generally divided into three situations:
1. Full-covered supports with small support spacing
The cast-in-place concrete structure has a small construction height and the foundation is The processing is simple. If the site conditions permit, the construction of full-covered supports is fast, low-cost, and economical and reasonable. Full-covered brackets are commonly known as Mantanghong brackets. In the construction of bridge cast-in-situ concrete beams, under normal circumstances, the surface load is below 50kN/m2, the vertical and horizontal spacing of the brackets are less than 2m, and the load-bearing capacity of a single column is 20-50kN between.
2. Door opening brackets with larger support spacing
Urban bridges use brackets with higher support heights, brackets with larger bearing capacity, and door openings with larger support spacing due to traffic needs. Brackets usually come in two ways. --Use small brackets and small spacing to form group columns. The other uses brackets or steel pipe columns with larger load-bearing capacity.
3. Independent temporary supports to bear concentrated loads
Nowadays, many parts across rivers and railways also use steel-concrete composite beam structures, with high erection heights, mostly using the 65-type Military piers or Type 83 light military piers. When restricted by the construction site, steel pipe columns with a diameter of more than 1Om can also be used as temporary support for construction.
IV. Selection of support beams
In the construction of cast-in-situ concrete beams, the support distance between the full-scale brackets and the columns is small, and the setting of the longitudinal and horizontal beams can generally use no. 12 or below. Word steel, channel steel, or square wood can meet the strength and stiffness requirements. Square steel is light in weight and high in stiffness, and is currently being used gradually. The support spacing of door opening brackets is relatively large, and the load-bearing beams must not only meet the load-bearing capacity requirements, but also the stiffness requirements. Generally, I-beams above No. 40 or matching truss beams are used. The doorway-type support system with large support spacing not only has high requirements on the bearing capacity, stiffness, and stability of the supports, but also strictly controls the deflection value of the load-bearing beams, requiring the load-bearing beams to have strong resistance to deformation.
5. Templates and Basics
1. Various formworks are widely used in the concrete process, including wooden formwork, combined steel formwork, bakelite formwork, steel frame wood formwork, bamboo surface bakelite formwork, phenolic-coated bakelite membrane board, all-steel large formwork, etc.
2. The foundation of the all-over support is mostly treated with lime fly ash stabilized gravel. Generally, a thickness of about 300mm can meet the usage requirements. When the support spacing of the brackets is greater than 4m, foundation design should be carried out, and concrete or reinforced concrete foundations should be used. Independent foundations with large bearing capacity must be designed with foundation bearing capacity, and reinforced concrete enlarged foundations or pile foundations must be used.