What is the approximate ratio of friction and anchoring force of a metric sleeve anchor in concrete

The Metric Sleeve Anchor is a fastener commonly used in concrete and masonry structures. It consists of a bolt body and an expansion sleeve. During installation, tightening the nut causes the sleeve to expand, creating friction and wedging forces with the base material, thereby achieving a secure anchor. Friction and anchoring forces work together to affect the bolt's load-bearing capacity and are a significant factor influencing structural safety.

The Role of Friction in Anchoring
Friction is the resistance generated by contact between the bolt and the concrete hole wall. As the expansion sleeve expands, friction is generated between the sleeve and the concrete hole wall. The magnitude of friction depends on the expansion pressure, the properties of the hole wall material, and the smoothness of the hole wall. Friction is the primary source of the Metric Sleeve Anchor's load-bearing capacity under low shear loads, preventing the bolt from slipping along the hole. Friction is positively correlated with bolt diameter, expansion length, and concrete strength.

Definition and Role of Anchoring Force
Anchoring force, also known as wedging force, is the axial resistance caused by the radial pressure exerted by the expansion sleeve on the hole wall. Anchoring force, achieved through the wedging action of the expansion sleeve, secures the bolt in the concrete and is the primary contributor to the bolt's pullout force. The magnitude of anchoring force is affected by bolt diameter, sleeve length, and concrete strength. High-strength concrete can withstand greater expansion pressure, thereby increasing anchoring force.

Ratio of Friction to Anchoring Force
In concrete, the friction and anchoring forces of a metric sleeve anchor typically contribute to the bolt's pullout load in a certain ratio. Professional experiments and engineering practice have shown that in standard concrete (strength grade C25/30), friction contributes approximately 20%-30% of the total bearing capacity, while anchoring force contributes approximately 70%-80%. Friction is generated immediately after installation, providing initial fixation. The anchoring force increases as the nut is tightened, providing long-term stable load-bearing capacity.

Factors Affecting the Ratio of Friction to Anchoring Force
Bolt diameter has a direct impact on the ratio of friction to anchoring force. Smaller diameter bolts have a slightly higher friction ratio and a relatively lower anchoring force ratio; larger diameter bolts have a higher anchoring force ratio and a lower contribution from friction. The longer the expansion sleeve, the greater the increase in anchoring force, and the correspondingly lower contribution of friction. The smoothness of the concrete hole wall significantly affects friction, with rough hole walls exhibiting higher friction and facilitating initial fixation.

Concrete strength is also a key factor. In low-strength concrete, the wedge force of the expansion sleeve is limited, reducing anchoring force and potentially increasing the contribution of friction. High-strength concrete allows for higher expansion pressures, increasing the contribution of anchoring force. Construction precision affects the effectiveness of friction, and excessively large hole diameters can reduce friction and overall bearing capacity.