Prefabricated architectural design
History and current situation
Compared with the traditional cast-in-place shear wall structure, the assembled shear wall structure has two significant features: first, the cost increase is large, (when using prefabricated components, the weighted comprehensive unit price of various types of reinforced concrete components is about 3 times of the component ); Secondly, the structurability of the prefabricated component should be considered for the structural wall layout. Therefore, projects using prefabricated construction require structural professional intervention in advance during the design phase of the architectural plan, to analyze the implementability and economy of the architectural plan when using the prefabricated form, to avoid later program modifications and affect the project development schedule. The prefabricated shear wall structure should pay attention to the following points during the scheme design stage.
1. The applicable height of the structure, the maximum use height of the house with an integrated shear wall structure is lower than that of the cast-in-place shear wall structure. The specific comparison is shown in Table 1.1 .
Table 1.1 Maximum heights applicable for different types of shear wall structures ( m )
2. The plane shape of the structure should be simple and regular, and the distribution of mass, rigidity and bearing capacity should be uniform, and serious irregular plane layout should not be adopted. The vertical shape of the structure should be regular and uniform, to avoid excessive picking and receiving. The lateral rigidity of the structure should be large and small, and gradually change uniformly. The specific regular judgment shall be carried out in accordance with the provisions of GB50011 of “Code for Seismic Design of Buildings” .
3. The building adopts modular design, the basic modulus is 100mm ( 1M = 100mm ), and the expanded modulus should be 2M , 3M , 6M , 9M … The project should adopt a unified modulus, which can reduce the types of prefabricated components and effectively reduce construction costs.
4. Structure adoptability of prefabricated components. Focus on the following points:
a. Whether the length of the corner wall and the window wall meet the assembly type implementation.
b. When the depth of the concave in the plane is large, pay attention to whether the width of the notch meets the requirements of subsequent construction operations. See illustration a , b .
a-1 The length of the corner wall is too small (corner window)
a-2 The length of the wall between the windows is too small
b The net width of the plane notch is too small
5. The form of prefabricated components should be concise to facilitate cost control. Focus on the following points:
a. It is not advisable to use bay windows, and try to avoid the appearance of three-dimensional prefabricated components.
b. The outer wall should be flat.
a bay window
b The outer wall is not straight
Preliminary design of prefabricated building structure
According to the policy requirements, all projects that use prefabricated construction require special reports on industrialization implementation plans. The content of the report file is basically consistent with the depth of the preliminary design, so a good preliminary design can effectively improve the design cycle of subsequent construction drawings. The preliminary design stage of prefabricated buildings should focus on the following points.
1. Determine the number of cast-in-place floors at the bottom of the building. According to the relevant provisions in the “Technical Specification for Assembled Concrete Structure”:
a. The shear wall at the reinforced part of the bottom of the high-rise shear wall structure should use cast-in-place concrete.
b. For the structure with conversion layer, the cast-in-situ structure should be adopted for the frame support layer and the adjacent upper layer.
2. The section thickness of prefabricated wallboard should not be less than 200mm .
3. Split prefabricated components. The splicing parts on both sides of the wallboard should be set at the parts where the structure is less stressed; the vertical prefabricated members are preferably in the shape of a straight line, and it is not appropriate to use L -shaped, T -shaped, U -shaped and other three-dimensional components .
The core of construction industrialization is production industrialization, and the key to production industrialization is design standardization. The key to achieving standardization is reflected in the scientific disassembly of prefabricated components; therefore, the scientific disassembly of prefabricated components is the core work of prefabricated building structure design. The scientific disassembly of prefabricated components will have an impact on building functions, building elevations, structural stresses, bearing capacity of prefabricated components, and engineering cost.
4. Contents of preliminary design drawings for structural majors:
a. Description of structural design, including special assembly design.
b. Structural plan, there should be a floor plan and roof structure plan; prefabricated components should be marked with the number of prefabricated components, given the relationship between the number of prefabricated components and models, should include the weight of components
c. Details of typical connection nodes of prefabricated components.
d. Structural professional calculation book, including calculation of vertical component prefabrication rate (volume ratio), horizontal component prefabrication rate (area rate) calculation, etc.
5. Collaborative design of various majors. According to the technical points of different professions, analyze the factors that affect the construction cost, construction schedule and construction quality, adopt a scientific and effective technical combination, do a good collaborative design, and control the assembly rate.
6. Information design ( BIM ). The application of BIM in the entire industrial chain of prefabricated buildings can not only improve the refined management and intensive management of projects, but also improve the efficiency of resource use, reduce costs, and improve the quality of engineering design and construction; plus some cities have mandatory adoption of prefabricated buildings BIM requirements. Therefore, it is necessary to confirm whether BIM is adopted in the preliminary design stage of prefabricated buildings .
Construction drawing design of prefabricated building structure
The construction drawing design of prefabricated building structure should include the following aspects.
1. General description of structural design, which should have special instructions for assembled structural design.
2. Structural layout drawing. There should be a floor plan and reinforcement drawing of each layer structure; prefabricated components should be marked with prefabricated component numbers; cast-in-place wall limb numbers, cast-in-place node numbers, etc.
3. Detailed drawings and processing drawings of prefabricated components. Component details should include:
a. The template drawing of the component shall indicate the size of the template, the location and size of the reserved hole and the embedded parts, the number of the embedded parts, the necessary elevation, etc.
b. Reinforcement diagram of the component: the longitudinal section indicates the form of the reinforcement, the diameter and spacing of the stirrups. When the reinforcement is complex, the non-prestressed reinforcement should be drawn separately; the transverse section should indicate the cross-sectional size, reinforcement specifications, location, number, etc.
c. The content that needs supplementary explanation.
4. The design and construction of the connection nodes of the horizontal and vertical joints of prefabricated wall panels are the key points and difficulties of the assembled structure. The performance of the connection nodes is the key to ensuring the performance of the assembled structure. The completion of the connection node of the assembled structure at the construction site is the most prone to quality problems, and the construction quality of the connection node is the core of the construction quality of the entire structure. Node design should focus on the following points:
a. Sleeve connection is the most criticized quality defect of the assembled structure. The design document should specifically indicate the material properties of the rebar connection sleeve and the grouting material, and the relevant testing and inspection requirements.
b. prefabricated wall panel vertical seams, give priority to connection section length is not greater than 600mm connection node (according to “Evaluation Standard fabricated building” is not larger than the length of the cast node 600mm , the node may be included in precast concrete cast Volume ), The prefabricated component horizontal tendons and cast-in-situ node level should be selected to facilitate the lifting of the components and to facilitate the on-site reinforcement lashing. The “one” shape connection node steel bar arrangement structure is shown in Figure 3.1 . For other types of connection nodes, please refer to COSCO “Handbook of Standard Nodes for Assembled Building Structures”.
Figure 3.1 “One” shape connection node reinforcement arrangement structure
c. Leakage prevention of the outer seam joint seam. The anti-leakage structure of the “one” shape connection node is shown in Figure 3.2 . For the other types of connection nodes, please refer to COSCO “Handbook of Standard Nodes for Assembled Building Structures”.
Figure 3.2 Leak-proof structure of “one” connection nodes
Deepening the design of prefabricated components
The deepening design of prefabricated components should take into account the actual processing of the project, lifting, transportation, stacking, etc. The key tasks are as follows:
1. Deepen the design calculations, which should include the unfavorable combination of the load specified in the design documents and the unfavorable combination of loading under various working conditions such as stacking, demoulding, transportation, and lifting.
2. The deepening drawing should correctly reflect the reserved holes and embedded pipelines, embedded parts, etc. required by the professions of architecture, equipment, electrical, etc., and the design and adjustment of conflicts for the embedded pre-embedded should be coordinated with each profession.
3. The deepening drawing of prefabricated components shall take into account the embedded parts needed for the construction and hoisting of prefabricated components ( temporary support required for wall panels as shown in Figure 4.1 ).
(Left) Temporary support layout of external wall panels
(Right) Temporary support layout of inner wall panels
Figure 4.1 Layout of temporary support of wall panels
4. The deepening design of prefabricated components should be considered with the general unit package to consider the pre-embedded issues required for scaffolding and tower crane installation. The vertical wall member adopts the assembled construction of the shear wall structure . The integrated climbing frame should be used . The integrated climbing frame can effectively solve the problem of the balcony picking frame and realize the construction of the external wall interpenetrating.
The in-depth design work of prefabricated components is the key link to ensure the implementation of the project. This work not only involves the study of architectural plans and the cooperation of various professional construction drawings, but also needs to cooperate closely with the component production unit and the construction and installation unit to fully study the details of the project implementation process. . Multi-professional collaboration and multi-unit collaboration are the guarantee for the unification of technical and economical aspects of prefabricated buildings.
At present, China’s construction industrialization is relatively backward, and the industrial chain is not very perfect, and further support and promotion are needed. As the leader in the development of prefabricated buildings, the design industry needs to keep pace with the times, keep pace with the development of the times, and continue to make breakthroughs and innovations in order to truly play a positive role in promoting the development of China’s overall construction industry.
Source: PKPM Construction Force Technology, Ocean Design Exchange