1Introduction
In recent years, China's rapid development of construction, the building occupies the land and the lack of land resources of the contradiction is also becoming more and more obvious, the transformation and utilization of the old building has become a better way to solve the problem. In the renovation and construction of old buildings, due to the site, the original building function, the increase in the number of floors, the original structure and the old and new codes and many other factors, in the design of the renovation project, there is a vertical role and the horizontal role of the increase, resulting in the original structural components of the bearing capacity is insufficient and the overall rigidity of the structure of the uneven. At the same time, due to the difference in material and strength of the old and new components, the connection of the old and new components has become a key technology in the renovation project.
2 Project Overview
This project is located in Luwan District, Shanghai, for a machinery manufacturing plant, built in the mid-80's, the original building **** there are four monolithic (hereinafter referred to as 1 #, 2 #, 3 #, 4 #). Now, because of the needs of the party, the four monolithic through the corridor connected to a commercial use of the whole. 2 # and 3 # building does not change the use of the original building function, mainly 1 # and 4 # building building function change is bigger, its structure is also corresponding to do a big transformation.
1 # building was originally a multi-storey frame structure plant, of which (1) ~ (7) axis for the four-storey, floor height from bottom to top were 8m, 5.6m, 5.1m, 4.5m; (7) ~ (10) axis of the three-storey, the floor height were 13.6m, 5.1m, 4.5m (one of which is at 8.9m with a 10T cranes), the original floor structural design of the live load are 12KN/m2. According to the needs of the building function, in (1) ~ (7) axis 4.0m elevation at the addition of a floor, in (7) ~ (10) axis 2.95m, 8.0m at the addition of a floor.
4 # Building was originally a single-story rack structure plant, building height of 20.4m, net height of 18.4m, the plant is equipped with a 10T crane, there are two supports between the columns. Now according to the needs of the building function, the original building will be transformed into a five-story office building, the height of 2.8m, 4.3m, 4.2m, 4.2m, 2.8m. According to the original structural conditions, the current design is considered to be disconnected from the original structure, in the original building of a new four-floor frame structure.
3 Foundation structure renovation design
1 # Building original design using 450 × 450 pile foundation, design bearing capacity is larger, after the overall calculation, the new mezzanine layer after the structure can meet the existing specification requirements, foundation bearing capacity and settlement deformation can also meet the existing specification requirements. In addition, considering that an outdoor platform (garage under the platform) was originally set outside the (1~10) axis of the #1 building, it is necessary to connect the platform with the #1 building according to the requirements of the building. In the structural design, if the beam of the outdoor platform level is directly connected to the columns at the (1~10) axis, it will have an impact on the overall structure of the #1 building, and at the same time, it will be unfavorable to the outdoor platform. In view of this, the structural design is to add another row of outdoor platform frame columns at (1~10) axis (standing on the original pile foundation bearing platform). After calculation, the original pile foundation has a large surplus, the impact on the original foundation is very small, and at the same time solved the above contradiction.
The original foundation of the 4# building adopts natural bar foundation, due to the new four-story frame structure in the original building, if the natural foundation is used, the foundation settlement can not meet the requirements of the existing specification, and it will have a great impact on the original foundation. According to the construction site and economic and technical conditions, the design now uses pile raft composite foundation. The pile adopts static pressure anchor pile, and the construction adopts the inverse method of construction, that is to say, after the construction of the foundation raft and the upper two layers are completed, then the construction of the anchor pile is carried out. This can not only shorten the construction period, but also meet the structural design requirements, for the whole project to create a great economic benefits. 4 # building raft plate using 500mm thick, anchor piles using 250 × 250, pile length of 20m. plan layout. The internal four-story frame structure has a large bearing capacity, and at the edge of the original building structure space, therefore, the raft plate at the edge of the column impact cut is difficult to meet the requirements, in the design of the additional raft plate impact cut reinforcement.
4 superstructure renovation design
4.11 # Building structural reinforcement treatment
1 # Building was originally a mechanical processing plant, the original design for the frame structure, the floor live load are larger (12KN/m2). By the relevant testing unit identification, the original structure of the column concrete strength level of C18, the original structure in the design in accordance with the requirements of the 6-degree defense considerations. After the transformation shall be used as an office building, now according to the needs of the functional arrangement of the building, add a mezzanine, and at the same time in the 12m span shall not set up concrete columns. According to the existing functional arrangement of the building, the design of the current version of the PKPM March 2006 version of the software for the overall calculation, the calculation and analysis, the original structure of the displacement, the amount of reinforcement, stiffness and other parameters can meet the requirements of the existing transformation of the structure, but the original structure of the structure is designed in accordance with the requirements of the code at the time, failing to meet the requirements of the existing norms. There are two main aspects: first, the original columns have no hoop encryption area; second, there is no hoop encryption area at the top and bottom of the additional mezzanine. Now the design of the comprehensive economic and technical considerations, columns using external bonded steel reinforcement method. This can meet the structural requirements, but also to meet the requirements of economic savings.
In the 1 # building of the newly added mezzanine, due to the large span (12m), if the concrete structure, the beam section is very large (at least 1m high beams), the clear height of the building will have a great impact on the original concrete columns is also a great impact, and with the original concrete columns are difficult to connect (a large number of planting), the original structure of the integrity of the structure will be greatly affected. Now the design adopts the combination structure of steel beam and pressed steel plate - cast-in-place concrete floor slab, and the steel beam is connected with the original column by articulation. According to the existing specification, the concrete strength level must be higher than C20 (the original concrete is identified as C18) when connecting with the original concrete columns using rear anchors. In view of the actual situation, the steel beam and the original column connection with the addition of concrete bull legs, while in the bull legs and their upper and lower 800mm of reinforcing the use of adhesive steel, in order to enhance its seismic deformation capacity.
4.24 # Building structural reinforcement treatment
4 # Building due to the requirements of the building facade, the original structure for the row frame structure, the original design of the inter-column support on the building facade of the doors and windows have an impact. If the direct removal of inter-column support, the original structure becomes an unstable structural system. Now the design takes into account the original structure load reduction (crane canceled), the vertical load is mainly wind load and its own weight generated by the seismic effect, now the design will be used in the maintenance structure of the frame structure system, so that the original peripheral structure to form a frame rack system, which not only enables the original structure to form a stable system, but also enhances the seismic deformation of the peripheral structure capacity. The newly added frame structure in the interior is considered as a new building, and deformation joints are set up between the new part and the original structure. After using PKPM March 2006 version of the software to carry out the overall calculation, now the design of the frame structure can meet the requirements of the existing building structure code. Considering that the original structural design is only calculated according to the 6-degree fortification requirements, the original columns are reinforced by carbon fiber reinforcement method.
5 Conclusion
5.1 The design of the building reinforcement should be combined with the seismic identification of the building, seismic reinforcement, strength reinforcement, construction should be reinforced first after the addition of layers.
5.2 The structural reinforcement of the building should be combined with the use of the functional requirements of the building, comprehensively analyze the economy of various reinforcement methods, and then take the appropriate reinforcement methods.
5.3 When reinforcing the original building, the connection node treatment of different materials should be fully considered, and the appropriate structural treatment method should be calculated to ensure the safety of the whole structure.
5.4 Before reinforcing the original building, the stability and strength of the overall structure should be grasped from the perspective of structural concepts, and then the appropriate reinforcement methods should be adopted and structural software should be applied to analyze them, after which the appropriate treatments should be carried out.
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