Prefabricated Components for Building Storey Addition

When it comes to building storey addition involving prefabricated components, it is necessary to comprehensively control from five aspects: inspection, connection joints, structural integrity, seismic performance, and storey addition techniques to ensure safety and compliance.

1. Inspection of Prefabricated Components
The production quality of prefabricated columns, beams, and slabs must be strictly checked, with a focus on key parameters in the factory inspection reports: The thickness of the composite layer must meet design requirements to avoid affecting structural load-bearing capacity due to insufficient thickness; The quality of the rough surface directly affects the bonding performance between new and old concrete, ensuring the surface is free of laitance and loose layers; The keyway settings must comply with specifications to ensure efficient shear force transfer. For prestressed components, additional inspection of the integrity of the prestressed tendon anchorage zones is required, and verification of the completeness of tensioning process documentation is necessary to avoid structural damage caused by anchorage failure.

2. Evaluation of Connection Joints
Joints are weak points in prefabricated structures and require targeted inspection:

• Sleeve grouting connections: Use endoscopes to inspect the fullness of the grout, ensuring no voids or looseness inside the sleeves;
• Grouted splice connections: Verify the grouting quality in reserved holes to avoid splice failure due to inadequate grouting;
• Bolt connections: Check that the bolt grade meets design requirements, the tightening torque reaches the specified value, and anti-loosening measures (such as double nuts or spring washers) are taken.

3. Analysis of Structural Integrity
It is necessary to ensure that the structure forms an effective whole:

• Check that the post-pouring strips and ring beams are adequately provided to avoid sudden changes in structural stiffness due to storey addition;
• Evaluate the connection details between prefabricated slabs and supports to ensure effective transfer of horizontal forces (such as seismic actions);
• For prefabricated floor systems without cast-in-place layers, special attention must be paid to in-plane stiffness to avoid overall instability caused by insufficient stiffness.

4. Seismic Performance Evaluation
Seismic assessment should be conducted in accordance with the Technical Standard for Prefabricated Concrete Structures (GB/T51231):

• Consider the semi-rigid characteristics of connection joints and appropriately adjust the structural stiffness calculation model;
• For high-rise prefabricated buildings, elastic-plastic time-history analysis under rare earthquakes should be performed to verify the safety of the structure under extreme loads.

5. Suggestions for Storey Addition Techniques

• The storey addition part should preferably adopt the same prefabricated system as the lower structure to ensure consistent connection details and reduce stress concentrations;
• For cases where joint bearing capacity is insufficient, section enlargement or steel plate bonding reinforcement can be used to enhance the shear and bending capacity of the joints;
• Clearly define the lifting plan for prefabricated components, including lifting point locations, lifting sequence, and temporary support measures to ensure construction safety.

In addition, the production and application of prefabricated components should comply with the Evaluation Standard for Prefabricated Buildings (GB/T51129-2017) to ensure that material properties, processing accuracy, and installation quality meet national standards.