Prefabricated Panels for the Roof of a Six-Story Building
Prefabricated panels for the roof of a six-story building are a structural form applied in construction in the form of factory-prefabricated cement components, possessing specific characteristics, a usage history, and governance methods, but also having certain issues.
Structural Characteristics
Prefabricated panels come in two types: solid and hollow. The hollow structure achieves lightweighting by reducing the concrete in non-load-bearing parts. The prefabricated hollow panels for the floors of brick-and-concrete structures are lightweight, soundproof, and material-saving. Compared to cast-in-place panels, they save approximately 40% of concrete and 50% of steel, as well as a large amount of formwork and labor, and are easy to install. However, their overall structural integrity is poor. They are assembled from individual prefabricated panels, with the horizontal and vertical joints filled with fine aggregate concrete or cement mortar, resulting in poor connection and seismic performance. Due to the gaps between the panels, improper construction handling can easily lead to floor cracking and water leakage during building settlement. Additionally, since the floor is constructed from multiple prefabricated panels, it is not advisable to randomly build partition walls on the floor, as this can cause floor collapse due to uneven stress distribution among the panels.
Usage History and Current Status
This building form originated in the early 20th century. Residential buildings constructed in China before 1985 mostly adopted this type of structure. Prefabricated panels almost 'dominated' low-rise residential buildings in the country at the end of the last century and are still commonly used in one- to three-story buildings in rural areas today. Existing prefabricated panel houses generally have issues such as weak seismic resistance, poor sound and heat insulation, and a service life of approximately 30 to 50 years. Some regions have already initiated demolition work. Since 2022, China has implemented a policy of renovating old residential areas, focusing on repairing and renovating prefabricated panel houses and only demolishing buildings that meet the criteria for dangerous houses.
Governance Methods
The fate of a house is never determined by its age but by a professional house safety appraisal report. House safety appraisals classify houses into four grades: A, B, C, and D. For six-story prefabricated panel houses appraised as Grade A or B with no major issues in the main structure, the most practical solution is the renovation of old residential areas. For those appraised as Grade C dangerous houses but still having repair potential, they enter the path of repair and reinforcement. As for expropriation and demolition, what truly determines whether a house can be demolished is not how old it is but whether there is a project in the vicinity.
