With the rapid promotion of prefabricated construction, the number of such projects is steadily increasing. To improve construction quality and standardization, the Ministry of Housing and Urban-Rural Development implemented three assembly-related standards on June 1, 2017: GB/T51231-2016 “Technical Standards for Prefabricated Concrete Buildings”, GB/T51233-2016 “Technical Standards for Prefabricated Wooden Structures”, and GB/T51232-2016 “Technical Standards for Prefabricated Steel Structures”.
In this article, we will highlight the key considerations when constructing prefabricated buildings based on these standards.
Concrete Structure
1. Storage
(1) Stacking floor slabs: The first layer of composite floor slabs should be placed on H-shaped steel beams, ensuring that the truss (including integrated decoration) is perpendicular to the steel. The steel should be positioned 500–800mm from the edge of the component. Four square timber blocks measuring 100mm × 100mm × 250mm should separate the layers. These blocks must be placed parallel to the steel at the four corners. The stacking should not exceed 8 layers or 1.5 meters in height.
(2) Wall panel storage: Wall panels should be stored in dedicated cube storage racks. For panels narrower than 4m, two 100mm × 100mm × 250mm square blocks should be placed underneath, one near each end, 30mm from the panel edge. For panels wider than 4m or with door openings, three square blocks are required: one at each end, 300mm from the edge, and one at the panel’s center of gravity.
(3) Stair storage: Stairs must be stored in designated, level areas. Four 100mm × 100mm × 500mm square blocks should be positioned at the second and third steps on both ends of folding stairs, 250mm away from the front and rear. The blocks should horizontally overlap on each stacked level. Storage height should not exceed 6 layers.
(4) Beam storage: The first layer of beams should rest on H-shaped steel, with the beam’s length perpendicular to the steel. Steel beams should be 500–800mm from the component edges. For long beams, an additional H-shaped steel support should be placed every 4m. No more than 2 layers should be stacked, separated by 100mm × 100mm × 500mm square timber blocks to ensure alignment with the H-beam below.
(5) Column storage: Columns are stacked similarly to beams. The first layer rests on H-shaped steel, perpendicular to the steel with 500–800mm clearance from edges. For long columns, an H-shaped steel support should be placed every 4m. Up to 3 layers can be stacked depending on length and weight. Layers are separated by 100mm × 100mm × 500mm square blocks aligned with the H-beam below.
2. Installation
(1) Before placing prefabricated components connected by grout with steel sleeves and overlapping steel grout anchors, verify the following: the specifications, positions, quantities, and depths of sleeves and reserved holes; the specifications, quantity, position, and length of connecting steel bars. Clean any debris inside sleeves or openings. Straighten any inclined steel bars. The offset of steel bars from the sleeve or hole centerline must not exceed 5mm.
(2) When applying grout at the base of multi-layer prefabricated shear walls, the grout thickness should not exceed 20mm.
(3) During grouting, ambient temperature should be above 5 ℃. If the curing temperature falls below 10 ℃, heating and protective measures must be implemented.
(4) When installing prefabricated bent components, the end length must meet design specifications. A grout or support pad should be placed between the end and the supporting component, with thickness not exceeding 20mm.
Steel Structure
1. Storage
Steel structures have low fire resistance and are highly sensitive to temperature changes. When heated between 100 ℃ and 250 ℃, tensile strength decreases while plasticity increases. Around 250 ℃, tensile strength slightly rises but plasticity continues to drop, causing a “blue brittleness phenomenon.” Above 250 ℃, steel experiences creep, and at 500 ℃, its strength is severely reduced, risking structural failure, economic loss, and safety hazards. Therefore, fire protection and insulation designs are critical, and environmental temperature must be considered during storage.
2. Installation
(1) Prefabricated steel structures can leverage information technology for full-process collaborative management covering safety, quality, technology, and construction progress. BIM technology allows for virtual construction of structural components, building parts, and equipment pipelines.
(2) When installing high-rise steel structures, the effects of vertical compression deformation must be addressed. Measures such as pre-adjusting installation elevations and installing connecting components should be applied based on structural characteristics and impact level.
(3) Prefabricated exterior wall panels must be permanently fixed after verifying axis alignment, elevation, and vertical arrangement. For double-layer wall panels in strip installations, joints between inner and outer panels should be staggered.
Wooden Structure
1. Storage
(1) Wooden components should be stored in well-ventilated warehouses or covered, ventilated outdoor areas. On-site, components should be sorted and stacked in installation order, within crane reach, and away from other construction activities.
(2) To prevent deformation during horizontal stacking, cushion blocks between layers must align vertically. The stacking height should be limited based on the bearing capacity of both components and cushion blocks.
(3) When stacking components on shelves, the shelf angle relative to the ground should exceed 80°.
(4) Curved components require appropriate protective measures based on their shapes during storage.
2. Installation
(1) When using temporary supports for installation, the support point on prefabricated columns or walls should be between 1/2 and 2/3 of the component’s height from the bottom.
(2) For vertical components, before installing base elements, ensure correct base elevation and apply moisture-proof measures such as pads. For upper layers, verify axis positions and elevation relative to installed components.
(3) For horizontal components, poles should be lifted at two points; longer components require multiple lift points. Monitor deformation and out-of-plane stability during lifting, especially for slender components.
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