Advanced Techniques in Prefabricated Concrete Structure Construction (Part III)

Chapter 2: Transportation and Site Inspection of Prefabricated Concrete Components (Part 2)

Content Summary

The transportation of prefabricated concrete components involves moving these elements from the manufacturing facility to the installation site. Ensuring both quality and safety during transportation is critical. The selection of transportation routes and equipment must meet specific requirements, and proper protective measures should be implemented to safeguard the components during transit.

Upon arrival at the site, all prefabricated components must be accompanied by a concealed acceptance form and a product qualification certificate. Both construction and supervision teams are responsible for conducting quality inspections on the incoming components. On-site stacking should be performed in dedicated yards, with components promptly lifted to their designated locations using tower cranes. Stacks should be organized according to component type, specifications, and lifting sequence, with adequate protective measures in place.

2.2 Inspection of Precast Concrete Components Upon Arrival

All prefabricated concrete components delivered to the site must come with a concealed acceptance form and a product qualification certificate. The construction and supervision teams must carry out thorough quality inspections, which include verifying certification documents, factory markings, appearance quality, and dimensional accuracy. It is essential to check that the component drawing numbers match the actual components, and to confirm the production date, model, manufacturer, and acceptance marks clearly displayed on the components.

1) Appearance Quality Inspection

The appearance of prefabricated components should be evaluated based on the type and severity of defects. These should comply with the classification criteria outlined in Table 2-1. Components exhibiting critical defects are not acceptable for use. For components with general defects, the production or construction unit must perform repairs following a technical plan approved by the supervision unit. Repaired components require full re-inspection, which involves visual checks and examination against the repair plan.

Table 2-1 Appearance Quality Defects of Prefabricated Components

2) Dimensional Deviation Inspection

Dimensional deviations of prefabricated components must comply with relevant national standards and design regulations. The following examples reflect control requirements applied in a certain region of China.

Inspection Quantity: For similar components, randomly inspect 5% of the batch entering on the same day, with a minimum of 5 pieces. If fewer than 5 pieces are delivered, inspect all.

Inspection Method: Use steel rulers, wires, measuring tapes, and feeler gauges to verify dimensions.

Table 2-2 Allowable Deviation and Inspection Methods for Prefabricated Wall Panel Components

Note: L is the length of the longer side of the component.

The allowable deviations for prefabricated columns and beams must follow the guidelines in Table 2-3.

Inspection Quantity and Method: Same as above.

Table 2-3 Allowable Deviations and Inspection Methods for Prefabricated Columns and Beams

Note: L refers to the component length.

Allowable deviations for prefabricated composite panels, balcony panels, air conditioning panels, and staircase components are provided in Table 2-4.

Inspection Quantity and Method: Same as above.

Table 2-4 Dimensional Deviations and Inspection Methods for Composite Panels, Balcony Panels, Air Conditioning Panels, and Staircase Components

Note: L is the component length.

Allowable deviations for embedded parts and reserved holes are listed in Table 2-5.

Inspection Quantity: Full inspection based on the number of randomly selected components.

Inspection Method: Use steel ruler, ruler, and feeler gauge.

Table 2-5 Allowable Deviations and Inspection Methods for Embedded Parts and Reserved Holes

The specifications and quantities of reserved steel bars must meet design requirements. Allowable deviations for position and size of reserved steel bars are detailed in Table 2-6.

Inspection Quantity: Full inspection based on the number of randomly selected components.

Inspection Method: Visual observation and steel ruler measurement.

Table 2-6 Allowable Deviations and Inspection Methods for Reserved Reinforcement Position and Size

Allowable deviations for prefabricated decorative panels (bricks) are provided in Table 2-7.

Inspection Quantity: Full inspection based on randomly selected components.

Inspection Method: Use steel ruler, ruler, and feeler gauge.

Table 2-7 Allowable Dimensional Deviations and Inspection Methods for Decorative Panels (Bricks)

Allowable deviations for prefabricated door and window frames are summarized in Table 2-8.

Inspection Quantity: Full inspection based on randomly selected components.

Inspection Method: Use steel ruler and ruler.

Table 2-8 Allowable Deviations and Inspection Methods for Prefabricated Door and Window Frames

2.3 On-site Stacking Requirements for Prefabricated Concrete Components

Prefabricated concrete components must be stacked in designated dedicated yards on-site. Upon arrival, components should be promptly lifted by tower cranes to these storage areas. Stacking must be organized by component type, specifications, and lifting sequence.

Storage areas should be within the reach of lifting machinery and avoid pedestrian pathways. Components are stacked following the lifting sequence, with each piece numbered accordingly. Components must not be placed directly on the ground, and anti-overturning measures are mandatory.

All prefabricated component yards should be separated from other equipment and material storage by a safe distance and ideally located around the building’s perimeter. Stacking areas must be flat, solid, with hardened surfaces and drainage facilities, and positioned as close to access roads as possible. When stacked on basement slabs, reinforcement measures are required.

The lifting zones must be fenced off and clearly marked with warning signs. Safe passageways for personnel should be established within the component yard. Embedded lifting parts should be positioned to avoid obstruction and to facilitate easy lifting.

Vertical components require downward buffer supports at the base, while horizontal components should be placed on wooden pads to ease lifting and protect them from damage.

Prefabricated exterior wall panels should be supported on stacking racks with adequate load capacity and rigidity. The outer surface of wall panels should not serve as a support surface. Weak parts must be protected. When panels are placed against each other, triangular channel steel brackets, meeting rigidity standards, should be used. These brackets should be balanced with the outer surface facing outward, inclined between 5° and 10°. Support points should be at the bottom ends of the panels, using flexible materials where appropriate. Temporary fixation after stacking is required.

Prefabricated interior wall panels, composite panels, columns, and beams should be stacked accordingly. Composite panels should not exceed six layers, with four evenly sized wooden blocks used as padding. The height of these blocks must exceed the exposed stirrups to prevent damage. Columns and beams should be stacked no more than two layers, with flat and vertically aligned support pads placed beneath and between layers on solid foundations. If stacking exceeds these limits, the bearing capacity of supports and foundations must be verified.

Figure 2-9 illustrates the on-site stacking method for prefabricated interior wall panels.

Balcony panels and stairs should be supported on four packs of yellow sand or wooden pads to level height differences and prevent tilting or sliding. Air conditioning panels should be placed horizontally to facilitate railing welding. Figure 2-10 shows the stacking method for air conditioning panels and stairs.

Stacking of irregular prefabricated components should follow the construction plan and site conditions. Irregular parapet wall components should be placed horizontally as individual pieces.

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