In today's rapidly developing industrialized construction and large-scale infrastructure projects, the application of heavy precast components (such as prestressed double-T slabs, ultra-large span beams, giant wall panels, and nuclear power modules) has become commonplace. They have brought a leap in construction efficiency and a high degree of control over project quality. However, every movement of these behemoths—especially during hoisting—affects the safety of the entire project.

The hoisting anchoring system is the most critical link in this safety chain. Improper selection can lead to component damage and project delays, or even catastrophic accidents. So, faced with a dazzling array of anchoring products on the market and complex working conditions, how can we make a scientific, safe, and economical choice?

Before making a selection, we must be the ones who know the component best. Key information includes:

1. Component weight and center of gravity: This is the most crucial data. Not only must the total weight be known, but the location of the center of gravity must also be clearly defined through the design drawings to ensure balanced stress during hoisting and prevent overturning.

2. Concrete strength: The load-bearing capacity of the anchoring system is directly related to the strength of the concrete. The early strength (release strength) and design strength of the component at the time of hoisting must be clearly defined.

3. Component size and shape: Is it a slender beam, a wide slab, or an irregularly shaped component? This determines the possibilities and number of hoisting points.

4. Reinforcement distribution: The anchors must coexist harmoniously with the internal reinforcement mesh of the component to avoid conflict. Detailed reinforcement layout drawings are essential.

Common hoisting and anchoring methods include the following:

(I) Anchoring with Embedded Parts

Embedded parts are one of the commonly used anchoring methods in the hoisting of precast components. The material properties and construction calculations of embedded parts should comply with the provisions of current national standards. During the production of precast components, anchors should be accurately embedded according to design requirements to ensure that their position and quantity meet the hoisting needs. The bearing capacity of embedded parts needs to be strictly calculated to meet the stress requirements under various working conditions during hoisting. For example, when tower cranes, temporary supports, and other equipment are attached to precast components, embedded parts must be set according to stress calculations.

(II) Anchoring with Through-Wall Bolts

For some precast wall components, through-wall bolts can be used for anchoring. During the production of precast components, through-wall holes should be reserved, and relevant reinforcement measures should be designed at this location. The hole diameter and position of the through-wall bolts should be strictly set according to design requirements to ensure the reliability of the anchoring.

(III) Anchoring with Embedded Nuts or Bolts

Embedded nuts or bolts are another commonly used anchoring method. The advantages of this method are convenient lifting and the ability to select the appropriate method based on the corresponding product standards. During the prefabrication of components, embedded nuts or bolts are pre-embedded inside the components, ensuring accurate positioning. During lifting, a special lifting tool connected to the lifting equipment works in conjunction with the embedded nuts or bolts to achieve stable lifting of the components.

Matching component information with anchorage type requires a systematic evaluation of the following five points:

1. Bearing Capacity and Safety Factor

* Absolute Red Line: The rated working load of the anchorage system must be greater than the weight of the component it supports.

* Dynamic Effects: The dynamic factor during lifting (typically 1.5 to 2.5, or even higher) must be considered in calculating the design load.

* Safety Factor: Select certified products with a high safety factor (typically ≥4:1 or 5:1). Never use substandard or counterfeit products.

2. Failure Mode – Concrete is Key

An excellent anchorage system is designed so that the yielding of the steel (lifting rod or anchorage) precedes the failure of the concrete. This means that in the event of overload, you will see a "warning" of steel deformation and elongation, rather than the brittle failure of sudden concrete collapse. Therefore, concrete cone failure calculations must be performed.

3. Number and Layout of Lifting Points

* Basic Principle: Ensure smooth lifting of the component and uniform stress distribution at each lifting point.

* Quantity: Depending on the weight and shape of the component, typically 2, 4, or more lifting points are required.

* Arrangement:The line connecting the lifting points should pass through the component's center of gravity, and the angle between the line and the horizontal plane (sling angle) should generally not be less than 60°. The smaller the angle, the greater the stress on the lifting point.

4. Ease of Installation and Repeatability:

* Disposable vs. Reusable: Embedded anchors are usually disposable, while some specialized lifting tools are reusable, requiring a cost-benefit analysis.

* Installation Speed:In large projects, rapid anchoring significantly improves efficiency.

5. Long-Term Impact on Components:

* Exposed: Embedded internal threaded sleeves can be capped after lifting, having no impact on the building's aesthetics. Exposed anchors may require later cutting, increasing procedures and costs.

* Impact on Structural Performance: Embedded anchors should not weaken critical sections of the component or interfere with prestressing tendons.

Selecting a hoisting and anchoring system for heavy precast components is not a simple matter of "whichever looks best," but a rigorous and systematic engineering decision-making process. It requires us to start with the characteristics of the components, deeply understand the principles of various anchoring methods, and make a comprehensive judgment based on the principles of safety, economy, and efficiency.

Remember, the hoisting and anchoring system is the lifeline connecting the "stationary" and the "moving." Investing extra effort in it is adding the strongest insurance to the smooth progress of the entire project and the safety of everyone involved.