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2023-07-313、Large-scale landscape-style independent column billboard foundation selection
In order to ensure that the foundation bearing capacity, foundation deformation and overall stability of large-scale landscape-style independent column billboards meet the requirements, the selection of foundation foundation needs to be based on site engineering geological data, surrounding environmental conditions of advertising facilities and the internal force value transmitted from the superstructure to the foundation. Factors such as quality and safety, construction schedule, construction convenience, and project cost are comprehensively considered for selection. The foundation of large-scale landscape-style independent column billboards is usually preferred to use the independent foundation under the reinforced concrete column. In order to prevent the upper structure from overturning, it is necessary to ensure sufficient foundation depth. If the bending moment value transmitted from the superstructure to the top of the foundation is large, and the shallow soil layer of the foundation has low bearing capacity and strong compressibility, the pile foundation should be selected. In addition, pile foundations can also be selected when large-scale excavation cannot be carried out due to site restrictions and the influence of the surrounding environment. Pile foundations can be divided into non-squeezing piles, partial soil-squeezing piles and soil-squeezing piles according to the pile-forming method; non-squeezing soil piles include dry-work method drilling (digging) hole filling piles and mud retaining method drilling (digging) hole filling piles, Part of the soil-squeezing piles include perforated cast-in-place piles, bored squeezed and expanded cast-in-place piles, etc., and soil-squeezed piles include driven (static pressure) prefabricated concrete pipe piles, closed steel pipe piles, etc. Due to the large buried depth of the pile foundation, the upper load can be directly transmitted to the deep rock (soil) layer, which is relatively easy to meet the anti-overturning requirements of the upper steel structure. When the groundwater level is relatively deep, manual excavation piles can be directly selected.
4、Points of design and construction of steel column feet
The internal force at the steel column foot of the large-scale landscape-style independent column billboard is relatively large. The design of the column foot can refer to the design of the column foot in Chapter 12, Section 7 of the “Steel Structure Design Standard” (GB5001-2017). The steel column foot can be divided into exposed type Plinths, recessed plinths, inserted plinths and encased plinths. When the billboard is 10-15m above the ground, due to the small height, the internal forces such as bending moment, shear force, and vertical pressure of the steel column foot are also small, and the exposed column foot can be used at this time. The design focus is on the calculation of the anchor bolts at the column foot, and it should be noted that the anchor bolts at the column foot are not suitable for bearing the horizontal shear force at the bottom of the column foot. The shear key bears, and the anchor bolts at the column foot should have sufficient depth. When the billboard is 16-25m above the ground, the internal force values such as bending moment, shear force, and vertical pressure of the steel column foot are also large due to the high height. If the billboard is asymmetrical in the plane, horizontal torque will also be generated. Should choose outsourcing type column base.
Engineering application examples
A large-scale landscape located at the entrance and exit of a certain expressway. The total height of the billboard is about 25.5m. After calculation and analysis, the main structure of the upper part of the billboard is controlled by the horizontal wind load, and the upper structure adopts a steel pipe independent column and a three-layer bolted ball space frame structure system. The steel grade of the steel pipe column is Q235B, the diameter of the steel pipe is 1800mm, and the wall thickness is 20mm. The inside of the steel pipe is poured with concrete within 1.500m above the ground. According to engineering geological data, the groundwater depth of the soil layer under the column is about 3.0m, and the pebble layer is -3.0~-6.5m below the existing surface, and its foundation bearing capacity fak=300kPa can be used as the foundation bearing layer, so the foundation chooses 8.0 m×8.0m×2.0m (length×width×thickness) raft-shaped foundation, the foundation depth is 3.5m (elevation -1.500~-3.500m); the steel column foot adopts outsourcing . This large-scale landscape-type independent column billboard has been built for several years, and its structure is safe and reliable, which can meet the requirements of use.
