Structural Design of Prefabricated Slab Buildings

The structural design of prefabricated slab buildings requires comprehensive consideration of multiple factors to ensure structural safety, stability, and applicability. The specific design points are as follows:

I. Understanding the Limitations of Prefabricated Slabs
As a widely used building material in the early days, prefabricated slabs have lower load-bearing capacity and integrity compared to cast-in-place structures. During the design process, it is necessary to strictly evaluate the load-bearing limits of prefabricated slabs to avoid floor cracking or deformation caused by excessive local loads (such as the concentrated placement of large furniture and equipment). For example, in areas like kitchens and bathrooms where heavy objects may be placed, the specifications of prefabricated slabs need to be determined through load calculations, or local reinforcement measures should be adopted.

II. Strengthening the Structural Support System
To address the issue of insufficient integrity of prefabricated slabs, it is necessary to enhance stability by adding structural components. For large-span spaces (such as living rooms), steel beams or concrete crossbeams can be added below the floor slab to distribute the load to the surrounding load-bearing walls, reducing the stress on individual prefabricated slabs. For multi-story buildings, constructional columns should be set in the walls and form a 'weak frame' structure with ring beams to enhance seismic performance. For example, in the renovation of an old residential area, by adding H-shaped steel beams in the living room, the floor deflection was successfully controlled within the allowable range of the code.

III. Matching Seismic Fortification Intensity Requirements
The seismic fortification intensity directly affects the selection of floor slabs. In high-intensity areas of magnitude 7 and above, cast-in-place slabs must be used, as their continuity can effectively dissipate seismic energy. In low-intensity areas of magnitude 6 and below, for small-span buildings with two stories or less, high-quality prefabricated slabs can be used, but they must be equipped with reinforced concrete ring beams, and the spacing between ring beams should not be greater than 4 meters to restrain wall deformation. Some rural areas in Sichuan have significantly improved the seismic resistance of buildings through the 'prefabricated slab + double ring beam' design.

IV. Optimizing Room Span Design
Select the floor slab form according to the room function and span: For ordinary bedrooms within 3.6 meters, standard prefabricated slabs can be used, but the live load should be controlled not to exceed 2.0 kN/㎡. For living rooms/master bedrooms with a span of 3.6-4.8 meters, it is recommended to use cast-in-place slabs or thickened prefabricated slabs (with a thickness of ≥150 mm) and add constructional reinforcement. For large-span spaces above 4.8 meters, cast-in-place slabs must be used, and double-layer bidirectional steel bar meshes should be configured to meet the deflection (L/250) and crack width (≤0.3 mm) control requirements.

V. Strengthening Waterproofing and Damp-proofing Measures
The joints of prefabricated slabs are prone to becoming water infiltration channels and require special treatment: For wet areas such as bathrooms and balconies, the floor should adopt a composite waterproof layer of waterproof coatings (such as polyurethane) and waterproof membranes (such as SBS), and a drainage slope (≥1%) should be set. At the base of walls, a 200 mm high concrete counter-dam should be poured simultaneously with the floor slab to eliminate leakage paths. For indoor damp-proofing, the risk of condensation can be reduced by laying damp-proof membranes and selecting breathable building materials (such as aerated concrete blocks).