Prefabricated Panel Roof Structure

The prefabricated panel roof structure is a roof form created by directly covering prefabricated panels over the building construction. The following provides a detailed introduction from the aspects of structural characteristics, material composition, historical applications, and existing issues.

Structural Characteristics
The core feature of a prefabricated panel roof is its "non-integrality". After being prefabricated in factories, the panels are directly laid on the top of the building, forming a separate connection with the wall or beam structures. The panels are arranged horizontally side by side, and the gaps between them are filled with concrete or cement mortar. However, this connection method cannot form a continuous load-bearing structure, resulting in relatively weak overall integrity of the roof. Compared with cast-in-place concrete roofs, which form a rigid connection with the walls through a steel reinforcement framework, the joints of prefabricated panel roofs are prone to becoming stress concentration points and are susceptible to dislocation or fracture under seismic or external forces.

Material Composition
The main raw materials of prefabricated panels include rice stone (coarse aggregate), cement, sand, and steel reinforcement materials (coiled wire or cold-drawn wire). During production, the steel reinforcement framework is laid in the mold according to the designed spacing. Then, the mixed rice stone, cement, and sand are poured into the mold, compacted by vibration, and cured to form the panel. The role of the steel reinforcement is to enhance the flexural bearing capacity of the prefabricated panels and prevent cracking during transportation and installation. Depending on the purpose, the thickness of prefabricated panels usually ranges from 8 to 15 centimeters. Roof panels need to meet additional requirements such as waterproofing and thermal insulation, and may be equipped with waterproof layers or insulation materials.

Historical Applications
The prefabricated panel technology originated in the early 20th century. Due to its high industrial production efficiency and low cost, it was widely used in residential floor slabs and roof insulation layers. Among the residential buildings constructed in China before 1985, prefabricated panel structures accounted for more than 70%, especially in multi-story brick-concrete structures, where prefabricated panels were the mainstream choice for floor slabs and roof insulation layers. Its rapid construction characteristics met the demand for large-scale housing construction at that time. However, limited by technical standards, early prefabricated panels did not fully consider seismic design, and the density of steel reinforcement configuration and the strength of concrete were generally low.

Existing Issues
There are generally three major defects in existing prefabricated panel roofs:

1. Weak Seismic Performance: The non-integral structure makes the panels prone to relative displacement during earthquakes, leading to roof collapse;
2. Poor Sound and Thermal Insulation: The limited thickness of the prefabricated panels and the lack of a continuous insulation layer result in rapid heat absorption in summer and rapid heat dissipation in winter, and the gaps between the panels are prone to forming sound bridges;
3. Insufficient Durability: Early prefabricated panels had low cement grades and were prone to carbonation and steel reinforcement corrosion when exposed to the natural environment for a long time, leading to a decrease in structural bearing capacity.
   To address these issues, it is necessary to strengthen the connections between the panels (such as adding steel reinforcement anchors), add insulation layers, or reinforce the roof with cast-in-place concrete during renovation.