What Is a Screw Anchor?
A screw anchor is an anchoring component that utilizes screws for fastening and securing purposes. In construction, anchors are essential for attaching base materials to other materials or for connecting new materials to existing ones. There are primarily two types of anchors: pre-attached and post-attached, with post-attached anchors being specifically referred to as “post-attached anchors.”
Uses of Screw Anchors
Screw anchors are widely used in construction to attach metal components to concrete foundations and structures. Their applications range from installing handrails and column legs in parking garages to bicycle parking facilities, signs, solar panels, vending machines, and water pipes. They also play a crucial role in adding earthquake-resistant features to older buildings, installing protective railings on bridges and roads, fenders and vehicle stops in harbors, and tunnel lighting.
Principle of Screw Anchors
Screw anchors are installed by first fixing the anchor to the base material, then attaching other components to the anchor’s threaded portion. Unlike typical screws that rely on axial force for their anchoring strength, screw anchors generate a fixing force through shear stress between the base material and the anchor. This shear stress arises from the engagement of the screw’s threads with the base material, providing resistance against separation forces.
Other Information on Screw Anchors
1. Types of Anchors
Beyond screw anchors, the construction industry recognizes three major types of anchors: metallic, adhesive, and others. Metallic anchors, including metal diffusion anchors, secure themselves by expanding against the base material. Adhesive anchors are fixed in place by an adhesive agent cured within a pre-drilled hole in the base material.
2. Failure Modes of Post-installation Anchors
Post-installation anchors, including screw anchors, may fail in one of three modes: rupture of anchor reinforcement (yield failure of the anchor), cone failure (failure of the base metal), or anchor pullout. The mode of failure is determined by the weakest link in the anchoring system, whether it be the material strength of the anchor, the strength of the base metal, or the anchorage strength itself.