At prefabricated building construction sites, we often see this scene: a tower crane effortlessly lifts multi-ton prefabricated wall panels or staircases, placing the components precisely as if they were building blocks. Curiously, the hook doesn't engage rebar, nor does it wrap around cables, yet the concrete components are hoisted with rock-solid stability. The hero behind this is today's featured work: the precast concrete lifting anchor.

First, what is a precast concrete lifting anchor?

Simply put, a lifting anchor is a metal device (usually made of high-strength steel or stainless steel) embedded in a concrete structure. It's secured in place during concrete pouring. After the concrete sets, a threaded hole or eye appears on the anchor for attachment of lifting equipment. Its core purpose is to safely transmit lifting forces throughout the concrete structure.

II. Structural Composition: All three components are essential.

A typical lifting anchor consists of the anchor rod (head), the anchoring section (foot), and accessories:

Anchor Rod Head

Shape: Ring, hemisphere, tapered thread, or "harpoon" notch

Purpose: Quickly connects to the hook/chain and allows for oscillation within a 0–90° range to avoid additional bending moments

Anchoring Section

Forms: Short bar hook, disc, double-ended cone, spiral blade

Purpose: Converts axial tension into a localized combined compression-shear-friction force in the concrete through "shape-resistance," reducing peak pure tensile stresses

Accessories: Rubber locating plug: Ensures the anchor head is flush with the concrete surface

Rust-proof cap: Caps the anchor head after installation to prevent rust from spreading

Please note that a safe lifting system relies on the perfect combination of three essential elements:

The anchor itself: It must be made of high-strength material, properly designed, and free of manufacturing defects.

Concrete strength: The concrete must meet the design strength to provide sufficient compressive and bond strength.

Proper reinforcement arrangement: The surrounding reinforcement must be arranged strictly according to the design drawings.

So what is the workflow for precast concrete lifting anchors?

Positioning and embedding: Before pouring concrete, the lifting anchor is precisely fixed to the designated position on the formwork.

Pouring and curing: Concrete fills and envelops the anchor. During the curing and hardening process, it forms a strong bond with the anchor's surface texture (such as threads).

Connecting and lifting: After the concrete reaches full strength, the lifting bolts or shackles are screwed into the exposed threads of the anchor.

Force transmission: When the crane lifts, the tensile force is transmitted to the anchor through the bolts. The anchor converts the force into compression on the concrete through mechanical interlocking and bond strength. This force is further distributed by the surrounding reinforcement, ultimately allowing the entire component to be safely lifted.

In short, the precast concrete lifting anchor, though small, is the cornerstone of modern precast construction technology. Its ingenuity lies in adapting to and utilizing the fundamental properties of the material—using concrete to withstand its inherent compressive forces, while steel handles its inherent tensile forces. Consequently, it's considered a veritable "invisible hero" on construction sites.