Study on the application of thin-walled large-tonnage stainless steel roof water tank in high-rise buildings?

In recent years, when some buildings are rebuilt in complete sets or adding stories, they often encounter the situation that the concrete water tank is too heavy for the building structure to bear, and the construction period is long, which affects the normal water supply. We encountered this problem when we added a high-rise residential building with 14 floor in combination with overhaul. When two roof concrete water tanks were demolished for subsequent construction, it was found that the concrete water tanks to be rebuilt weighed 30t, and the total weight reached more than 90 t after being filled with water, which was unbearable for the wall structure. Therefore, we designed two groups of cylindrical high-strength thin-walled stainless steel water tanks, with three in each group installed side by side. The water capacity of a single water tank is 12m3, but the weight of each water tank is only 1.5t, which effectively reduces the dead weight and solves this problem.

After two years of practical operation, the roof water tank is in good technical condition, which embodies the characteristics of convenient installation, cleanliness, convenient management and long service life. The number of water tanks can be flexibly switched during operation, which not only increases the safety and reliability of water supply, but also avoids secondary pollution of water quality, and has low cost. Compared with the concrete water tank with the same volume, it saves198,000 yuan. The design and application of ultra-thin large-tonnage stainless steel roof water tank are summarized as follows.

1 Selection of steel grade and requirements for strength, quality and physical and chemical stability of thin-walled stainless steel roof water tank.

Replacing traditional reinforced concrete water tanks with large-capacity thin-walled stainless steel roof water tanks, the first emphasis is light weight and high strength. Another key is to ensure that a water storage container itself does not pollute the water quality, and the steel grade must be hygienic and safe, and long-term operation is harmless to human health.

1. 1 Strength and quality of stainless steel water tank

Because the thickness of the stainless steel water tank group we designed is 0.8 mm ~ 1.0 mm, some people doubt whether it can meet the strength requirements after storing large-capacity liquid. Relevant technical data and design data show that although the material is thin, it has the characteristics of high strength, good toughness and good ductility. As long as we grasp the key points in production, it is beyond reproach to design and manufacture large-capacity stainless steel water storage containers.

Physical and chemical stability of 1.2 stainless steel

The stainless steel roof water tank of high-rise building, as a water storage container for hundreds of households, has a direct impact on people's health, so it is not suitable for oxidation and biochemistry in the long-term operation to avoid corrosion and the generation and precipitation of heavy metal chromium and nickel ions. For this reason, we designed and manufactured stainless steel of Japanese brand SUS304 (equivalent to domestic OCi 18Ni9 brand). According to the data of SUS304, this steel belongs to austenitic stainless acid-resistant steel, which has good corrosion resistance, metal calendering performance and corrosion resistance to strong oxidizing acids. It can be seen that this material can completely resist the action of low-concentration hydrochloric acid (HCl), hypochlorous acid (HClO), weakly oxidizing carbonic acid (H2CO3) and other acids in operation, thus ensuring that the water container will not pollute the water quality.

2 Design layout and hydraulic calculation basis of stainless steel water tank group

2. 1 Determine the arrangement of water tank group

Because the building is Z-shaped and there are many households, with an average of 23 households on each floor, the same pump group was used to supply water to two concrete roof water tanks at the same time before the building was rebuilt. Although the water level controller is installed in the No.2 water tank far away from the water supply pipeline of the pump house, the water inflow of the two water tanks is supplemented by the water level control floating valve, but due to the difference of water pressure, the water inflow is uneven, which often causes the ball valve lever to overflow out of control, and sometimes the water consumption of the two roof water tanks is quite different, which makes one of the water tanks cut off and affects the water consumption environment of residents. In view of this, combined with the storey-adding overhaul of the building to adapt to the roof plane of the building, we redesigned and arranged two groups of stainless steel roof water tanks, adopted parallel water tanks, and installed a circulating pipe between the two groups of water tanks (see figure 1), so that the water storage of the two groups of water tanks is complementary and the elevation is balanced, and the common stubborn disease, water cut-off and overflow accidents caused by the difference between the two groups of water tanks are eliminated.

2.2 Calculation of water storage capacity of stainless steel water tank group

2.2. 1 Calculate the total second flow of water supply in this building, and determine the domestic water storage volume of roof water tanks.

After adding stories to the building, the water supply is divided into two vertical areas. The water tank on the roof of the upper district (3rd floor ~14th floor) supplies water from top to bottom, with 286 households, and the municipal pipe network in the lower district (basement ~ 2nd floor) supplies water directly. The water supply and drainage and toilet facilities of this high-rise residential building are relatively perfect, and the household water equivalent Ng is 6.0N.

Total water equivalent in upper area: n ∑ = ng× n

=6.0×286

= 17 16(N)

Total second current in the upper design area: qg = α× 0.2+kn ∑ (α is 1.02 and k is 0.004 5).

According to the nature of the building, QG =1.02× 0.2×1.716+0.0045× =16.17 (length/second).

Therefore, the required water supply is 16. 17L/s, that is, 58.2m3/h without adjusting the volume of the water storage tank. ..

Calculate the minimum storage volume Vt of the water tank:

Qgh is the design second flow, which is converted into the maximum demand of 58.2m3/h;

Qb is the output flow of the water pump (when the pump head is found in the Q ~ H characteristic curve) 23.8m3/h;

T is the duration of design second flow, calculated as 0.5h;

Tb is the shortest running time of the water pump, calculated as 0.25h h.

Vt=(Qgh-Qb)×T+Qb×Tb

Vt=(58.2-23.8)×0.5+23.8×0.25

= 23.2 cubic meters

According to the above calculation, the storage capacity Vt of roof water tank must be greater than 23.2m3 In order to ensure safe water supply, ensure the living water storage level and expand the hydraulic control and adjustment range, combined with practical experience, Vt should be set at 48m3.

2.2.2 Calculation of fire-fighting self-help water storage capacity

This building belongs to the second-class high-rise building, and there are fire hydrant fire fighting facilities indoors. The design flow of each system (50- 19 double-ended fire hydrant) is 8L/s ~ 10L/s, and now there are three systems, so the total amount of fire water supply is 30L/s, and the stainless steel water tank group on the roof should also meet the requirements of t = 10min initial storage of self-help fire water.

Its water storage capacity: VX = qgx× t initial.

=30× 10×60/ 1000

= 18 (m3)

According to the fire code, 18m3 can still be used when the indoor fire water consumption exceeds 25l/s and the calculated fire water storage capacity of the water tank exceeds 18m3. In practice, water is stored in two groups of six water tanks, and the roof water tank and the fire-fighting output pipe should be at a proper distance from the bottom of the water tank. In order to ensure the hardware reliability of fire-fighting facilities, we increase the water storage capacity of each water tank by 1m3, and then determine that the water storage capacity of fire-fighting self-help is 24m3.

2.3 Shape requirements for designing and manufacturing thin-walled stainless steel water tanks

After calculation, the total capacity of the roof water storage tanks of this building is 72m3 (48m3 for domestic use and 24m3 for fire protection), and six water tanks store water respectively, and the effective capacity of each water tank should be guaranteed at 12m3. In view of the fact that the water tanks are manufactured and processed in other provinces and cities, the total weight of the water tank group is only 3t, so the transportation is not difficult. However, the designed physical structure must meet the requirements of transportation, installation and management, otherwise it will bring trouble. Therefore, we design a single water tank as a cylinder with a diameter of 2.6m, a total height of 2.8m, a bottom of 0.05m and an upper manhole of 1.2m (see Figure 2). Out of consideration, although the transportation traveled long distances to the site for installation, it did not bring trouble to the future operation and management.

1 box 2 water inlet pipe 3 hydraulic control water inlet hole 4 fire hose

5 domestic water pipe 6 sewage pipe 7 manhole cover

8 lifting rings, 9 overflow pipes, 10 hydraulic steel bar.

3 effectiveness of thin-walled stainless steel roof water tank group

3. 1 Comparison of economic indicators

Compared with concrete structure water tanks and other types of water tanks, the current unit price of large-capacity water tanks is 2000 yuan /m3 ~ 2500 yuan /m3 for stainless steel water tanks and 2500 yuan /m3 ~ 3000 yuan /m3 for Jin Ao water tanks. If a single water tank with a storage capacity of 36m3 is 200,000 yuan/box (including building structure), the ordinary glass fiber reinforced plastic water tank designated by the relevant authorities is 6.5438+0.7 million yuan/box, while the cost of the two water tanks we choose is only 6.5438+0.96 million yuan, which obviously shows the price advantage of stainless steel water tanks.

3.2 Easy installation and switching to ensure safe and reliable water supply.

Stainless steel water tank is made in the factory, which is light in weight and easy to install. The design capacity this time is 12m3, and the bottom is polished by 0.05m, which means that the bottom plate can get enough bearing surface. During installation, cement mortar or fine stone concrete will be used as cushion to ensure the close contact between the plate and the supporting surface.

Because the water tanks are connected in parallel to supply water, the storage of domestic and fire water can be compatible with a water tank group. Once any water tank needs maintenance and cleaning, the other two water tanks still maintain water supply, and when fire fighting is needed, domestic water can also supplement fire fighting water, which increases the safety and reliability of water supply.

3.3 Reduce the chance of secondary pollution of water quality

In the design of water supply system, special attention should be paid to the phenomenon of "stagnant water" in fire water storage and the prevention of "stagnant water area" in and out of wet layer of water tank. The water supply pipe in the roof water tank is made into a siphon device, and the installation plane positions of the inlet and outlet pipes are intentionally staggered. At the same time, the pipeline into the tank is changed to UPVC pipe to prevent corrosion and pollution. The water tank group is also cylindrical and placed vertically, so even if there is heavy pollution, the sewage valve can be solved as soon as it is opened. Practice has proved that these measures are put in place, eliminating the phenomenon of "stagnant water" and "stagnant water area" and promoting the all-round flow of water in the tank. In addition, the inner wall of the stainless steel water tank is smooth and will not be attached with dirt and algae, thus eliminating another pollution link. Two years' operation shows that scaling (sand, clay, organic matter, etc. ) The bottom of the pool is obviously less than that of the concrete pool, the water quality is pure, and the residents respond well, which improves the water environment and plays a positive role in ensuring the health of the general public.

4 several problems that should be paid attention to

4. 1 Large-tonnage thin-walled stainless steel water tank must be carefully transported and installed.

Because the large-tonnage water tank is "bubble goods", more attention should be paid to avoiding collision and preventing weld deformation and cracking during transportation and hoisting. Gravitational percussion is strictly prohibited. If there is an error, it is difficult to repair it on the spot. Box pipe connection should be slowly tightened along the thread; In view of the thin wall of the box, the pipe wrench should not be forced too hard during construction; The water tank at the joint of the pipeline should be protected by lining reinforcement plate to improve the strength of the joint. The design of box width and height should consider the technical specifications allowed by automobile transportation such as roads, tunnels, bridges and culverts.

4.2 Lightning Protection Design and Calculation

Because stainless steel water tanks are in the highest and most prominent position in high-rise buildings, lightning protection facilities are mainly used to prevent direct lightning, and lightning protection devices combining lightning rods and lightning protection nets are adopted. The lightning protection belt can be laid along the upper edge of the water tank group and connected with the lightning protection belt of the building. Effective lightning rod devices are sensitive to direct lightning discharge and can safely introduce lightning symbols into the earth. The lightning rod can be installed in the center of the stainless steel water tank group, and the down lead is laid along the roof and wall of the building, which is directly and reliably connected with the lightning protection grounding device. The lightning rod has high design technical conditions, and the protection scope and manufacturing requirements are shown in Figure 3.

4.3 Anti-freezing and heat preservation measures for water tank group

The water consumption of high-rise residence is different from that of ordinary multi-storey residence, with many households, concentrated population and long daily water consumption cycle, so the water in the water tank keeps flowing all day. Even in the dead of winter, there is no ice. 1at the end of 990, Shanghai was suddenly hit by the once-in-a-century cold current. More than 90 pipeline freezing cracks occurred in more than 40 high-rise buildings under our management, all of which occurred in the fire pipeline system. The problem is "stagnant water". However, this time, the stainless steel water tank group did not take heat preservation measures. After two years of use, it has also passed the test of the lowest temperature of -8℃, and it is safe and sound. Considering the room, when we install it, the distance between the two water tanks is 20cm, which is convenient for the property management department to take anti-freezing and heat preservation measures again.

Managing and maintaining security issues

During the operation, it is found that it is ideal to use the liquid level controller to automatically control the water level, but the floating ball rope and the water tank wall are easy to wear, which affects the control effect. So when the rope passes through the tank wall, the middle should be protected by a protective cover. Due to the thin thickness of stainless steel water tank material, aluminum alloy ladders should be specially set up to facilitate the inspection and maintenance of managers. For the manhole protection cover at the top, it should be firmly fixed to facilitate opening and closing, so as to prevent it from being lost due to strong wind and other reasons.

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