Analysis of design method of assembled building structure?

This paper focuses on the analysis of the implementation methods of prefabricated buildings in the process of structural design, hoping to promote the process of structural design standardization of prefabricated buildings in China and promote the realization of various benefits.

1 Present situation of prefabricated building structure design

1. 1 A residential project, shear wall structure, prefabrication rate of 20%, prefabricated components: floor, air conditioning board, parapet, and stairs with more than two floors. Design basis of this project: Technical Specification for Assembled Concrete Structures (JJ1-2014); Technical standard for prefabricated concrete buildings (gbt51231-20163); Grouting sleeve for steel bar connection (JG/T398-2012); Technical Specification for Reinforced Welded Mesh Concrete Structures (JJ114-2014). The standard atlas adopted in this project: Connection Node Structure of Assembled Concrete Structure (G 310-1~ 2); Truss reinforced concrete composite slab (15G366-1); Precast reinforced concrete slab stairs (15G367-1); Precast reinforced concrete balcony slab, air conditioning slab and parapet (15G368- 1). Design live load of this project: construction concentrated load:1.0kn; ; Checking calculation in construction stage (dynamic coefficient): demoulding, overturning, transportation and hoisting:1.5; Checking calculation in construction stage (demoulding adsorption force): 1.5kN/m2. Connection mode: the upper and lower steel bars of the floor are anchored into the cast-in-place beam and connected with the wall; The upper and lower steel bars on the air conditioning board are anchored into the cast-in-place floor slab for connection; The stair tread plate is simply connected with the embedded steel bar of the cast-in-place ladder beam through the reserved hole; The horizontal reinforcement of parapet is anchored in the cast-in-place concrete member.

1.2 A residential project adopts integral shear wall structure, and the prefabrication rate is 40%. Precast components are: internal and external wallboard, floor slab, balcony, bay window, air conditioning board and stairs. Design method: PKPM calculation software is adopted, and the overall calculation is based on the principle of equivalent cast-in-place; Some members on the same floor are prefabricated and cast-in-place, and the seismic force of cast-in-place members is amplified 1. 1 times (the bending moment and shear force of cast-in-place wall limb are multiplied by1.1); The joint part needs to be inspected; Various working conditions (such as formwork removal, transportation and hoisting) have been added to prefabricated components.

2 prefabricated buildings and traditional buildings

Differences in structural design process. Through the above engineering design projects, it is not difficult to see that in the process of structural design, prefabricated buildings are different from traditional buildings, and designers need to consider more and deeper.

2. 1 How to consider the participation of prefabricated components in the overall calculation?

Traditional buildings are cast-in-place, so all the components are built into the model in the process of structural design, and the overall calculation can be done. How to consider the overall calculation of prefabricated components in prefabricated buildings is a difficult point in the structural design of prefabricated buildings. The overall calculation of the aforementioned project is based on the principle of equivalent cast-in-place; Some members of the same floor are prefabricated and cast-in-place, and the seismic force of cast-in-place members is amplified 1. 1 times (the bending moment and shear force of cast-in-place wall limb are multiplied by 1. 1). Based on this calculation principle, the connection between precast members and between precast members and cast-in-place members must be reliably guaranteed.

2.2 Various working conditions (such as formwork removal, transportation and hoisting) have been added to prefabricated members.

In the design of traditional architecture, only the feasibility of construction can be considered. All aspects should be considered in the design of prefabricated buildings, that is, in-depth design on the basis of conventional design. At present, the deepening design is mostly carried out by prefabricated component manufacturers, which requires cross-disciplinary process coordination and collision inspection, and also needs feedback to structural design. The design unit should combine the deepening design, construction technology, prefabrication, transportation and installation to carry out structural design, which undoubtedly increases the design difficulty and requires designers to have a deep understanding of the whole construction process of prefabricated buildings.

2.3 Assembled buildings need bim technology system.

From the beginning of design, to deepening design, to process coordination and collision inspection, to prefabrication and installation, and then to project construction, prefabricated buildings need to be seamlessly connected in the whole cycle, and refined integrated design is needed to ensure the smooth implementation of the project. To achieve this requirement, BIM technology must be applied. The model based on the relevant information of construction projects provides a basis for designers and engineers, including construction and operation units, to work together. After information integration, the design, construction, operation, maintenance and other stages are executed at the same time by using the same platform with its characteristics of consistency, visibility, coordination, simulation and optimization, thus ensuring the smooth completion of prefabricated buildings.

3. The implementation content of prefabricated building structure design

3. 1 calculation flow of assembled building structure

Combined with the structural design part of an assembled building project, taking PKPM structural design software as an example, its concrete implementation is as follows: firstly, PKPM modeling is consistent with the traditional method, then PKPM-PC software is imported, then the prefabrication rate of the project is determined, the process principle is determined, the initial design and optimization of the assembly scheme are carried out, then the assembled whole calculation is carried out to generate the construction drawing, and finally the design is deepened.

3.2 Basic requirements of structural designers

Through the calculation content of structural calculation software, we can know that designers need to have the basic knowledge of prefabricated buildings. In traditional design, designers can design by mastering design specifications, atlas and basic construction conditions. However, in the structural design of prefabricated buildings, designers must first master the specifications, atlas and standards related to prefabricated buildings. These aspects include design content, connection nodes, structural requirements, etc., which are different from traditional design and need to be re-studied and skillfully used. Secondly, we should understand the content of deepening design, which requires designers to understand the processing technology and installation requirements of prefabricated components in prefabricated buildings, as well as the construction methods of prefabricated buildings. On this basis, we can accurately grasp the requirements of deepening design and correctly carry out the structural design of construction technology, prefabrication, transportation and installation.

3.3 Mastery and application of BIM technology

Designers should have a deep understanding of BIM technology. BIM technology began to develop in China in recent years, but it has not yet formed a scale in traditional design units, and it has only been applied in a few design institutes and a few engineering projects, and some projects only stay in the surface application fields such as mold turnover and collision inspection. Deepen the design part, such as steel bar end adjustment, pre-embedded reservation of plumbing pipes, embedded parts arrangement, installation simulation, collision inspection, construction hoisting, center of gravity inspection, etc. The application of BIM technology can solve this kind of assembly problem well. For prefabricated buildings, the application of BIM technology is extremely important because of the improvement of construction accuracy. The later construction simulation, construction organization and engineering calculation can all be carried out on the platform of BIM data set.

3.4 Prefabricated building structure design content

The design part of precast concrete structure should have special structural description, which should be combined with the general description of the main structure, and the drawings of precast members should be combined with the construction drawings of the main structure. The concentrated load of construction and the load value of checking calculation in construction stage must be clearly given. The design drawings need to include the following contents: 1. The general description of precast concrete structure design is the guiding document of the whole project and the guiding description of the processing and installation of precast members. Second, the plan of prefabricated components, expressing the distribution position, plate name and weight of prefabricated panels. 3. Cross-sectional view, which refers to the cross-sectional view of the wall in various parts of the building related to prefabricated components, and expresses the relative relationship between prefabricated components and the main structure. Fourthly, the distribution map of floor embedded parts shows the position of metal parts that need to be embedded in advance before prefabricated components are assembled. 5. Detailed drawings of prefabricated components, drawings used by component factories to produce prefabricated components, indicating the overall dimensions of components, reinforcement information, positioning and quantity of related connectors and metal embedded parts, etc. Sixth, the node diagram, which expresses the node structure between prefabricated components and the connection between prefabricated components and cast-in-place components. Seventh, the processing diagram of metal parts expresses the processing diagram of all metal parts used in PC production and construction.

3.5 Requirements of Prefabricated Building Structure Design for Prefabricated Component Factory and Construction Unit

At present, the real industrialization and standardization of prefabricated buildings have not been formed, and the structural design of prefabricated buildings is influenced by the technological processes of different prefabricated components manufacturers and the construction schemes formulated by different construction units. Therefore, in the structural design part, it is necessary to increase the requirements for precast component factories and construction units. For example, the processing unit of prefabricated components should prepare the production and processing scheme according to the structural design regulations and the requirements of the construction unit. Before all components are processed, they must be verified with relevant disciplines (architecture, structure, water supply and drainage, electrical) before processing. The general contractor shall formulate a special construction plan before the construction of the assembled concrete structure. The construction scheme should be planned and formulated in combination with the structural deepening design, the checking calculation of the whole process of component production, transportation and installation, the construction lifting and the checking calculation of the supporting system. It should include the scheme of component installation and node construction, quality management and safety measures of component installation, etc. , and should fully reflect the characteristics of prefabricated structure construction and the special requirements of technological process. Engineering construction general contracting enterprises must carry out technical training and post technical assessment for construction management personnel and operators in key processes such as hoisting and positioning of prefabricated members and connection of longitudinal steel bars, and construction personnel should strictly implement post operation standards; Construction management personnel should check and accept each working procedure and make construction records truthfully; Engineering supervision units, construction contractors, prefabrication units and deepening design units, as well as other product suppliers related to the project, shall strictly implement these provisions in the engineering design.

4 conclusion

Prefabricated buildings are not a new thing, and great progress has been made in all countries. However, the early brick-concrete structure in China used prefabricated panels, but the connection mode was not good and the seismic performance was poor, so it was changed to cast-in-place structure in the later stage. Until recent years, prefabricated buildings have become popular, which is a great change for designers and even the whole construction industry.

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