Proportion of Prefabricated Components in Buildings

The proportion of prefabricated components in buildings is usually reflected through the assembly rate, with specific requirements varying by region and structural type.

Calculation of the Assembly Rate in National Standards: According to the national standard GB/T 51129-2017 'Evaluation Standard for Prefabricated Buildings', the assembly rate refers to the comprehensive proportion of prefabricated components used in the main structure above the outdoor ground level of a single building, as well as in the enclosure walls, interior partition walls, decoration, and equipment pipelines. The calculation formula is: $P=(Q1+Q2+Q3)/(100-Q4)×100%$. Here, $P$ represents the assembly rate, $Q1$ is the actual score for the main structure indicator, $Q2$ is the actual score for the enclosure wall and interior partition wall indicators, $Q3$ is the actual score for the decoration and equipment pipeline indicators, and $Q4$ is the total score of missing evaluation items in the evaluation project.

Specific Requirements in Different Regions:

• Hainan Province: The assembly rate of prefabricated buildings should not be less than 50%. When the application proportion of prefabricated components in the vertical members of the main structure is not less than 35%, a Level III evaluation for prefabricated buildings can be conducted. This means that in Hainan Province, to achieve a Level III evaluation for prefabricated buildings, not only must the overall assembly rate meet the requirements, but there is also a clear lower limit for the prefabrication proportion of vertical members in the main structure.
• Shanghai: The prefabrication rate of a single building can be calculated using the 'volume proportion method' and the 'weight coefficient method'. The formula for the 'volume proportion method' is: Prefabrication rate of a single building = $\sum$ (volume of prefabricated components × component correction coefficient) / total volume of components × 100%. In this formula, 'components' include exterior enclosure walls (load-bearing and non-load-bearing), interior load-bearing walls, beams, columns/diagonal braces, floor slabs, stairs, balconies, air conditioning panels, etc. (excluding non-load-bearing interior partition walls). This calculation method places more emphasis on the proportion of prefabricated components in the building volume and distinguishes between different components.

Selection of Prefabricated Components and Their Contribution to the Assembly Rate: The design process for prefabricated buildings is divided into three stages: schematic design, preliminary design, and construction drawing design. The order of selecting prefabricated components should consider the proportion of components, manufacturing and construction techniques, and installation characteristics. Generally, beams, composite slabs, and prefabricated non-load-bearing exterior enclosure walls contribute the most to the assembly rate. During the design process, priority can be given to the prefabrication of these components.