Large-volume prefabricated prestressed reinforced concrete clearing pool construction Zhang Zhenyi 1 Zhao Yuhua 2, Ai Yong \ Fu Jinxiang 2 (1. Jinzhou City Water Supply Corporation, Jinzhou 121000, Liaoning; 2. Shenyang Institute of Civil Engineering and Architecture, Shenyang 110015, China) 500m3 prefabricated prestress Take the reinforced concrete clearing pool as an example to introduce its construction practices and experience: First, it is necessary to deal with the uniformity of the grounding endurance of the ground, otherwise it will cause tilting or overturning; second, it is necessary to close the reinforcing bars, and it is strictly forbidden to have the ribs and the half pass. The ribs are used to ensure the anti-leakage performance of the bottom of the pool; the third is to use the T-slotting formwork support method, and the through-screw method should not be used to prevent the vertical joints of the pool wall from leaking.
Fund Project: World Bank Loan Project (LoanNo.CHA-3781) The clear water pool is an important component of the water supply plant as a water storage and regulation structure. As the size of the water supply plant continues to grow, the volume of the clear water pool is also growing. The construction of the clear water pool is a technically strong and demanding hydraulic structure construction project. The number of clear water pools built at home and abroad is huge, and there are many cases of failures due to design errors and improper construction. The economic losses caused are serious. A large number of construction practices have shown that in addition to meeting the general technical requirements for civil construction, the construction of large-volume clear water tanks must pay special attention to the following technical requirements: First, the foundation foundation ground endurance should have higher uniformity due to the large volume clear water pool. The floor area is large, the uniformity of the foundation foundation resistance will cause tilting and even overturning; the second is to require high anti-leakage performance, which does not allow the water in the pool to leak or allow external sewage to infiltrate. This article only takes the two 3 500m3 prefabricated prestressed reinforced concrete clear water pools built by Jinzhou Water Supply Corporation (hereinafter referred to as the head office) in recent years as an example to introduce some practices and experiences of its construction for the peers.
1 Project Overview Jinzhou Dalinghe Water Source Project is a World Bank loan project with a water supply capacity of 200,000 m3/d. The water distribution plant has two clear water pools. The effective design volume of single tank is 3 500m3, round, the inner diameter of the tank is 30.5m. The ground type, the elevation of the inner bottom is 24 2m, the elevation of the outer ground is 245m. The bottom of the clear water pool is 200mm thick for C20S6 concrete, and the inner wall is 80 straight. The prefabricated solid concrete of the arc is composed of 43 prestressed steel bars. The top plate is a prefabricated beam-column structure. The pool is evenly supported by 52 columns. The inner wall of the pool is rigidly waterproofed with five layers of cement mortar, and the outer wall of the pool is made of 240mm brick insulation wall. This is a representative large-volume clear water pool, which is a typical hydraulic structure in civil structures.
2 Clear water pool construction 2.1 After foundation excavation of foundation treatment, it is found that the ground station has poor endurance uniformity and does not meet the design requirements. Through the technical calculation and economic analysis of several schemes, the deep excavation treatment measures were adopted. The depth of sand is 1500mm, the grain size of sand is medium and coarse sand, and it is divided into 6 layers. The thickness of each layer is controlled within 300mm. The rice is vibrated in sequence with a flat vibrator, and at the same time, sufficient water is accumulated to make the sand dense. After sandblasting, the endurance reached the design requirements.
2.2 Pool bottom plate construction After the foundation treatment, the inlet pipe, the outlet pipe, the drainage (overflow) pipe support pier and the C10 cushion are poured. After flattening, place the sample on the spot layer, tie the steel bar, support the mold, and then pour the C20S6 bottom plate.
The bottom plate is the foundation of the clear water pool and supports the weight of the entire clear water pool. At the same time, it is also the most critical structure for anti-leakage of the clear water pool, and the water pressure is the highest during use. Floor construction quality is the key to determining the quality of the entire clear water pool construction. Therefore, it is necessary to ensure the technical quality requirements of three aspects at the same time: one is the accuracy of the geometrical dimensions of the parts of the bottom plate to ensure the connection with the wall part; the second is the rigidity and strength of the bottom plate to meet the basic bearing requirements; Anti-leakage performance. In order to achieve the above three aspects of quality, F181 grade steel double control cold pull natural failure after a pre-stress this pool can be planted! In the process of roads, the following key links and processes that have the greatest impact on quality have been strictly controlled.
22.1 Reinforced clear pool bottom section as shown. There are 26 cup-shaped column bases at the bottom of the pool, and there are annular wall slots at the periphery. The structure and force of the bottom of the pool are relatively complicated, which makes the reinforcement also quite complicated. The cup-shaped foundation and the annular wall groove are independent reinforcements, and the bottom plate is a discontinuous double-layer reinforcement mesh. It is necessary to strictly control the fixing and support of the steel mesh, and at the same time, to ensure the leakage resistance of the bottom of the pool, it is strictly forbidden to have a permeable rib and a semi-passing rib. The method to avoid is to support the support under the support of the upper reinforcement mesh and the lower reinforcement mesh. All the steel bars must be tied at one time.
I* (the bottom section of the slab-finished plant plate bottom is shown as 2.2. The pouring bottom plate is to be poured in three times. The first time except the outer side of the wall (the middle virtual box 1) and the cup-shaped foundation (the middle virtual box 2), the rest The first casting is completed; the second time is to cast the cup-shaped foundation separately; the third time after the siding is assembled and potted, the outside of the siding groove is re-casted to ensure that the outer side of the siding and the siding are tightly combined to ensure the connection of the bottom wall of the slab Anti-leakage performance.
22.3 Formwork and Support Wall The inner wall of the tank is a ring beam connected to the bottom of the tank at the bottom of the tank. It is required to be poured at the same time as the bottom plate. Therefore, the inner wall of the wall groove has high requirements on the formwork and support. The inner and outer annular formwork of the inner wall of the siding groove needs to be supported by the cantilever type outside the pool. It is preferable to use a template made of a medium plate or a thin plate lining the annular skeleton without using a standard steel template. The effect of the wood formwork is also not satisfactory, because the overall rigidity of the ring formwork is low, the cantilever support is difficult, and the mold is easy to run during the pouring process, which affects the geometrical dimensions of the cast body. The linen should be lined in the circular skeleton steel formwork to ensure the roughness of the surface of the groove wall and ensure the quality of the filling and internal waterproofing.
23.1 Cold drawing The outer wall of the clear water pool is 43 prestressed steel structures. Use steel bars. The designed cold drawing control stress is 450 MPa and the tensile rate is not more than 5.5%. The steel bars and steel bars, steel bars and screws are welded by flash butt welding before cold drawing.
Calculate, cold drawing control stress is 450MPa Calculated tensile force: =114.525kN23.2 Cold drawing equipment and load calculation The maximum tensile capacity of cold drawing equipment should be calculated as follows: S* winch tonnage, N; one equipment system resistance, the equipment system Calculated according to 19.6kN; K* pulley group labor saving coefficient, calculated by the following formula: * System pulley block working line number, the system is 9. The maximum tensile capacity of the cold drawing equipment system used in this construction is 182.7kN. The pulling speed should be calculated as follows: M reel speed, 7r/min. Calculate the cold drawing speed of the cold drawing equipment system used in this construction. v 2.4 Prefabricated siding assembly and filling. 24.1 Prefabricated assembly Prefabricated group The vertical order is carried out in the following order: the column is poured twice on the cup groove. The welded beam and column are connected to the steel beam beam. ※ The wall of the girder is welded to the wall of the wall. ※ The wall of the wall is sewed. After the upper side beam has reached a certain strength requirement in the cast-in-place concrete of the previous process, the 24.2 joint filling joint includes the vertical joint and the circumferential joint. Two technical improvements were made in this construction.
The first is to improve the support method of the vertical joint filling template. The conventional vertical seam joint template is supported as shown. However, according to the conventional practice, in the process of water seepage test in the clear water pool, it was found that water permeated around the screw to varying degrees. The reason was that during the pouring process, the screw was subjected to a large tensile force and deformation, and the screw was restored when the mold was removed, resulting in the screw and the screw.ç ¼ separation. Therefore, the screw penetrates the wall of the tank, and although a water stop ring is added to the screw, water seepage may occur.
After repeated research and experiments, the T-shaped support method was proposed, which fundamentally solved the problem of screw penetration and water seepage. This type of support is adopted for this construction, and the seepage prevention effect by the water seepage test is very good.
The second is to improve the waterproof method of the ring seam in the wall groove. The conventional inner wall groove is filled with linseed asphalt for waterproofing. The original clear water pools of the head office were constructed according to this method. After several years of use, it was found that there were different degrees of leakage at the seams. After the venting inspection, the main reason was that the asphalt aging and kenaf softening caused the filler to deform, and cracks and water leakage occurred. This construction has been replaced by a three-in-one cement filled ring seam. The clear water tank has been operated for 5 years without leakage of the ring gap.
25 prestressed steel bar electric heating tensioning pool has adopted the new technology of prestressed steel bar electric heating tension to achieve better results.
2.5.1 Calculation of electric heating tensile elongation Long value of electric heating tensile elongation can be calculated by the following formula: * tension control stress, MPa; total length of L steel bar before electric heating, m; elastic modulus of steel after Es electric heating, MPa. Calculate the electric heating tension of the steel bar used in this project. The length of the steel bar is 24.2. The electric heating temperature is calculated. When the steel bar is reached, the steel bar temperature can be calculated as follows: The electric heating temperature of the steel bar used in this project is calculated as 25.3 electric heating sheet. The selection of the drawing equipment is based on the theoretical calculation value of the electric heating temperature of the steel bar, considering the environmental temperature and other factors, and adopting a safety factor of 1.5 times. The electric heating tensioning equipment required for this construction is 65 kW, and two 35 kW DC welding machines are actually selected in parallel. Into the electric heating tension heating equipment. The heating time of each steel bar is about 15~18min, which satisfies the construction requirements.
25.4 Electrothermal tensioning process Controls the electric current during the electric heating tensioning process, and the insulation plate and the length of the wire between the fixture and the rib and the nut have a great influence on the electric heating tension effect. In the construction, a copper clamp with a large overcurrent area and a 3 mm thick bakelite insulation board with good insulation performance were used. To minimize the length of the wire, place the electric heating device on top of the clear pool.
In the process of electric heating tension, the level of steel bars should be strictly controlled. If the middle section of the steel bars is sag, it is difficult to level. In order to ensure the level of the steel bars, it is best to use the hanging bars to mark the exact position of each bar on the wall. In the electric heating tension process, it is necessary to closely cooperate with heating, tightening bolts and wooden hammers to strike the steel bars.
3 Conclusion Prefabricated prestressed reinforced concrete sluice pool saves materials, short construction period, low cost and convenient maintenance. It has been widely used in water supply projects in recent years. Mastering new construction techniques and methods is critical to ensuring the quality of the clear water tank construction. Only the head office has five 5 000 m3 prefabricated prestressed reinforced concrete clearing pools, but the construction quality has not been ideal because of the new construction techniques and methods. In the construction of 3500m3 clear water pool, the previous experience and lessons were carefully summarized, and the construction plan was put forward, which effectively solved many technical problems and obtained better construction results.
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