Structural renovation design of single-story and multi-story factory buildings?

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Sourced from the Internet for everyone to learn* Summary of use: This article combines engineering examples to make a relatively systematic summary of the renovation design of the original single- and multi-story factory buildings into multi-story commercial office buildings. It elaborates in detail the main force characteristics, design and calculation of the foundation and superstructure at each design stage, as well as the main technical issues in design and construction. 　　keywords: structural modification ； Pasted steel reinforcement method ； Pasted carbon fiber reinforcement method 1 Introduction In recent years, my country's construction has developed rapidly, and the contradiction between building occupation and insufficient land resources has become increasingly obvious. The renovation and utilization of old buildings has become a better solution at present. In the renovation and construction of old buildings, due to the influence of many factors such as the site, original building functions, increase in the number of floors, original structure, and new and old specifications, the design of the renovation project has increased vertical and horizontal effects, resulting in insufficient bearing capacity of the original structural members and uneven overall stiffness of the structure. At the same time, due to the difference in materials and strengths between the old and new components, the connection between the old and new components has become a key technology in engineering renovation. 　　 　　2 Project Overview This project is located in Luwan District, Shanghai. It is a machinery manufacturing plant. It was built in the mid-1980s. The original building has four units (hereinafter referred to as 1#, 2#, 3#, and 4#). Due to the needs of Party A, the four units are connected through corridors into a whole for commercial use. Buildings 2# and 3# will not change the use functions of the original buildings. The main reason is that the building functions of Buildings 1# and 4# have changed greatly, and their structures have also undergone major modifications accordingly. 　　Building #1 was originally a multi-story frame structure factory building (see Figure 1), with four floors on the ⑴~⑺ axis, and the floor heights from bottom to top are 8m, 5.6m, 5.1m, and 4.5m respectively. ； ⑺~ The ⑽ axis has three floors, with floor heights of 13.6m, 5.1m, and 4.5m respectively (one of the floors is equipped with a 10T crane at 8.9m). The original floor structure design live load is 12KN/m2. According to the functional needs of the building, an additional floor is added at the 4.0m elevation of the ⑴~⑺ axis, and one floor is added at the 2.95m and 8.0m elevation of the ⑺~⑽ axis. 　　 　　Building #4 was originally a single-story rack structure factory building (see Figure 2), with a building height of 20.4m and a net height of 18.4m. There is a 10T crane in the factory and two supports between the columns. According to the functional needs of the building, the original building is transformed into a five-story office building with floor heights of 2.8m, 4.3m, 4.2m, 4.2m, and 2.8m respectively. According to the original structural conditions, the current design considers breaking away from the original structure and building a new four-story frame structure within the original building. 　　 　　3. Basic structure reconstruction design. The original design of Building 1 uses a 450×450 pile foundation, which has a large design bearing capacity. After overall calculation, the structure with the newly added mezzanine can meet the existing specification requirements, and the foundation bearing capacity and settlement deformation can also meet the existing specification requirements. In addition, considering that there is an outdoor platform outside the (1~10) axis of Building 1# (the garage is under the platform), according to the requirements of the building, it is necessary to connect the platform to Building 1# (see Figure 1). During structural design, if the beams of the outdoor platform layer are directly connected to the columns at the (1~10) axis, it will have an impact on the overall structure of Building #1, and it will also be detrimental to the outdoor platform. In view of this, the structural design is to add an additional row of outdoor platform frame columns (standing on the original pile foundation bearing platform) at the (1~10) axis. After calculation, the original pile foundation has a large margin and has little impact on the original foundation. At the same time, the above contradiction is resolved. The original foundation of Building 4# uses a natural strip foundation. Since a new four-story frame structure is built in the original building, if a natural foundation is used, the foundation settlement cannot meet the requirements of the existing specifications and will have a great impact on the original foundation. According to the construction site and economic and technical conditions, the pile-raft composite foundation is now designed. The piles are static pressure anchor piles, and the reverse construction method is used during construction, that is, the construction of the anchor piles is carried out after the construction of the foundation raft and the upper two layers is completed. This can not only shorten the construction period, but also meet the structural design requirements, creating great economic benefits for the entire project. The raft of Building 4# is 500mm thick, the anchor piles are 250×250, and the pile length is 20m. Floor plan (see Figure 3). The internal four-story frame structure has a large bearing capacity, and is affected by the original building structural space at the edge. Therefore, the punching resistance of the columns at the edge of the raft cannot meet the requirements, so punching resistance steel bars for the raft were added in the design. 　　 　　4 Superstructure Renovation Design 4.11# Building Structural Reinforcement Treatment Building #1 was originally a mechanical processing plant. The original design was a frame structure, and the live loads on the floor were relatively large (12KN/m2). After identification by the relevant testing unit, the column concrete strength grade of the original structure is C18, and the original structure was considered in accordance with the 6-degree fortification requirements in the design. After renovation, it must be used as an office building. Now according to the functional layout needs of the building, a mezzanine will be added. At the same time, no concrete columns shall be installed in the 12m span. Based on the functional layout of the existing building, the current design uses the March 2006 version of PKPM software for overall calculations. After calculation and analysis, the displacement, reinforcement amount, stiffness and other parameters of the original structure can meet the requirements of the existing reconstructed structure. However, the structure of the original structure was designed in accordance with the requirements of the regulations at that time and failed to meet the requirements of the existing regulations. There are mainly two aspects:: The first is the encrypted area of ​​the original column without stirrups. ； The second is that there are no stirrup dense areas above and below the additional mezzanine. The current design takes into account various economic and technical considerations, and the column adopts the externally bonded steel reinforcement method (see Figure 4). This can not only meet the structural requirements, but also meet the economical requirements. 　　In the newly added mezzanine of Building 1#, due to the large span (12m), as shown in Figure 1, if a concrete structure is used, the beam section will be very large (a beam of at least 1m high is required), which will have a great impact on the clear height of the building, and will also have a great impact on the original concrete columns. Moreover, it is difficult to connect with the original concrete columns (the number of planted bars is large), and the integrity of the original structure will be greatly affected. The current design adopts a composite structure of steel beams and profiled steel plates-cast-in-situ concrete floor slabs, and the steel beams are hingedly connected to the original columns. According to the existing specifications, when the post-anchored connection is used with the original concrete column, the concrete strength grade must be higher than C20 (the original concrete has been identified as C18). In view of this actual situation, additional concrete corbels were used to connect the steel beams to the original columns. At the same time, bonded steel was used to reinforce the corbels and their upper and lower 800mm to enhance their ability to resist seismic deformation (see Figure 5). 　　Corbel design is also a factor that cannot be ignored in the design of this project. In the design, considering that the horizontal force on the corbel is equivalent to the force on a cantilever member, the horizontal reinforcement at the corbel must be guaranteed to reach 23d (generally 15d). According to the actual conditions on the site, it is difficult to achieve 23 days of rebar planting. Taking into account various factors, we adopted the following treatment plan when designing this corbel.: On the one hand, for the crack control requirements of the corbels in the code, the following formula is used for calculation, which can meet the crack control requirements of the corbels in the code. At the same time, the local compressive stress caused by the vertical force is less than ； 　　On the other hand, regarding the reinforcement strength requirements of the corbels, considering that the planted reinforcement may not fully meet the expected design requirements, from a safety point of view, in the design, the longitudinal force of the corbels is completely borne by the pasted steel plates, and its calculation formula can still be calculated using the formula derived based on the moment balance condition, that is, after calculation, it can meet the structural calculation requirements. 　　4.2 Structural reinforcement of Building 4# Due to the requirements of the building facade, the original structure of Building 4# is a rack structure, and the original designed column supports have an impact on the doors and windows of the building facade. If the inter-column supports are directly removed, the original structure will become an unstable structural system. The current design takes into account that the load of the original structure is greatly reduced (the crane is eliminated), and the longitudinal load is mainly the wind load and the seismic effect caused by its own weight. The current design will adopt a frame structure system in the maintenance structure, so that the original peripheral structure forms a frame rack system. This can not only make the original structure form a stable system, but also enhance the seismic deformation resistance of the peripheral structure (see Figure 2). The newly added frame structure inside is considered as a new building, and deformation joints are set between the new part and the original structure. After overall calculation using the March 2006 version of PKPM software, the currently designed frame structure can meet the requirements of the existing building structure specifications. Considering that the original structural design was only calculated according to the 6-degree fortification requirements, the current design uses the carbon fiber reinforcement method to reinforce the original columns. 　　 　　5 Conclusion 5.1 The reinforcement design of the building should be combined with the seismic identification, seismic reinforcement and strength reinforcement of the building. During construction, reinforcement should be done first and then layers added. 　　5.2 Structural reinforcement of buildings should be combined with the functional requirements of the building, comprehensively analyze the economics of various reinforcement methods, and then adopt corresponding reinforcement methods. 　　5.3 When reinforcing the original building, the connection node processing of different materials should be fully considered, and appropriate structural processing methods should be used for calculations to ensure the safety of the entire structure. 　　5.4 Before strengthening the original building, the stability and strength of the overall structure should be understood from a structural concept perspective, and then corresponding reinforcement methods should be adopted and structural software should be used for analysis, and then corresponding processing should be carried out.