Chimney reinforcement

Chimney structure overview and working status

 The 60m chimney project of a company in Chongqing was built and put into use in 1986. The main body of the chimney is 60m high, the outside diameter of the chimney is 5.52m at the elevation of ± 0.5m, and the outer diameter is 5.02m at 10m above the ground. 2.5%. The entire chimney structure is divided into a foundation part, a 10m high concrete base part and a 50m high brickwork simplified part. The design drawings show that the chimney foundation is an independent concrete foundation with an outer diameter of 8.2m and a height of 3.0m. Under the C13 concrete foundation is a matte concrete cushion with a height of about 6m, and the foundation bearing layer is mudstone. The base part is simplified as a cast-in-place reinforced concrete structure with a wall thickness of 300mm. The upper chimney is divided into lining and outer wall. The outer wall is made of MU10 brick and M5 mixed mortar. The thickness of each section is 490mm in 10-30m section, 370mm in 30-50m section and 240mm in 50-60m section. A 6 @ 252 circumferential steel bar is added in the horizontal gray joint of the masonry. The steel bar is densified within 500mm of each section of the variable cross-section, and the spacing is 2 bricks. The chimney is lined with MU7.5 bricks and 1: 1: 4 mixed mortar, with a thickness of 120mm.

 Around 1988, a reinforced concrete semicircular environmental observation platform was added at 13.8m from the chimney ground. The observation port was set at the 15.0m elevation of the chimney. The platform was cast-in-place concrete cantilevered slab structure, supporting The end of the seat is made by pouring concrete into the brick masonry, and the platform is 0.93m wide. It is led by the concrete stairs from the roof of the fan house near the chimney.

Chimney crack inspection

(1) The cracks in the chimney body are severe, mainly vertical cracks, 2 in total. Both of these cracks penetrated into the interior of the masonry, and the bricks were all cracked.

(2) There are a lot of cracks along the barrel at the junction of the environmental protection observation platform and the barrel. There are cracks at the joint of concrete and brick at the root of the platform. Some bricks are broken, and the width of the crack is about 0.1 ~ 0.6mm.

(3) The lining bricks of the chimney are damaged. Because of the inconvenience of entering the chimney, the location of the damage is unknown.

(4) The structure of the concrete at the bottom of the chimney is intact, and no undesirable phenomena such as cracks are found.

Analysis of the causes of cracks

(1)The effect of temperature changes.

(2)Damage to the chimney lining (cracks or damage caused by poor masonry quality).

(3)The effects of smoke corrosion.

(4)Add the environmental protection observation platform and its deformation effect

(5)The effect of different coefficients of linear expansion.

Reinforcement plan

Use unidirectional carbon fiber fabric as the main material for reinforcement. Carbon fiber has the characteristics of high strength, light weight, easy construction, high construction efficiency, high temperature resistance and corrosion resistance. Reinforcement with it can improve the bearing capacity and ductility of structures and components, which is of great significance for seismic reinforcement.

The reinforcement of this project started construction in early March 2001, and the reinforcement was completed at the end of March with a construction period of 20 days. The reinforcement plan is as follows.

Since the chimney cracks in this project are up to 20m long, the mortar masonry structure part of the chimney is grouted with epoxy mortar before reinforcement. Then, a 250mm wide carbon fiber cloth was vertically and vertically glued along the chimney from the top to the bottom of the concrete base (8m in height), evenly spaced in the circumferential direction, a total of 6 longitudinal carbon fiber cloths. After that, from the bottom of the concrete base and the elevation of 8m, a 250mm wide circumferential carbon fiber cloth was pasted at a distance of 2.0m (center-to-center distance) up to the chimney at a distance of 36m. Finally, from the top of the chimney at 36m, a circular carbon fiber cloth with a width of 250m is pasted every 3.0m (center distance), and it sticks to the top of the chimney.

Conclusion

Brick chimney crack reinforcement usually adopts the outsourcing reinforced concrete method, but this method is greatly affected by production and climatic conditions, the construction is difficult, and the construction period is long. They are also reinforced with steel structures or prestressed bars, but their corrosion resistance is poor. The chimney was reinforced at the end of March 2001 with a construction period of 20 days. The reinforcement has been used for more than 1 year, and the cracks have not expanded, and the reinforcement effect is good. The chimney reinforcement uses the carbon fiber method, which has a short construction period, high reliability, and low difficulty. The reinforcement cost is equivalent to other reinforcement methods, and it is a fast and new method.