Aerated Concrete Extra workable concrete that is protected against freeze-thaw damage. Aeration is achieved by mixing the concrete with air-entraining additives.
Allowable Load The maximum static load that should be applied on an anchor.
ANSI American National Standards Institute Admixture – An ingredient added to the core ingredients of concrete to change its properties. Examples include water repellent, coloring, and agents to retard or hasten setting time.
Aggregate A granular material that is used with a cementing medium to form a hydraulic cement concrete or mortar. Examples include sand, gravel and crushed stone.
Aggregate, Lightweight – An aggregate with a dray, loose weight maximum of 70 lbs per cubic foot (pcf).
Base Material The material that an anchor and load are being applied to. Common base materials include concrete, substrates that have the properties of concrete, brick, tile and stone.
Brick A solid masonry unit of clay or shale, formed into a rectangular prism while plastic and burned or fired in a kiln that may have cores or cells comprising of less than 25 % of the cross sectional area.
Cast-In-Place Anchor An anchor that is cast directly into cement rather than drilled in after the concrete is set.
Combined Load A load that apply stress with the properties of both tension and shear loads.
Concrete A mixture of portland cement and any other hydraulic cement, fine aggregate, course aggregate and water. The approximate weight of cement is 150 pcf.
Concrete Block A hollow concrete masonry unit (CMU) made from portland cement, water and aggregates.
Concrete Brick A solid concrete masonry unit (CMU) made from portland cement, water and aggregates.
Concrete Compressive Strength (f’C)
The pounds per square inch that categorize a base material’s compressive load carrying capacity.
Concrete Masonry Unit (CMU)
The term to describe either a solid or hollow masonry unit.
Core Drill The term used to describe the process of using a special drill attachment to create a smooth hole in any base material.
Creep Movement under a sustained load over time.
Drop-In Anchor An anchor that is dropped, rather than set, into concrete. Drop-in anchors are internally threaded to accept a bolt or threaded rod.
Edge Distance
Edge Distance (C) – The distance between the centerline of an anchor and the free edge of the base material.
Critical Edge Distance (Ccr) – The minimum distance at which the allowable load capacity for an anchor holds true.
Minimum Edge Distance (Cmin) – The minimum distance from the free edge of the base material that anchors are tested.
Embedment Depth The distance from the surface of the base material to the installed end of the anchor.
Embedment depth is determined prior to installation of the anchor.
Expansion Anchor A category of mechanical anchors that is placed into the base material. The anchor expands inside the base material during installation and engages the sides of the base material in order to create shear and/or tension resistance.
Expansion Joint A control joint in the concrete designed to allow for concrete movement.
Friction Anchor A category of anchors that creates friction within the base material. The friction created determines load resistance.
Green Concrete Concrete before it is completely set.
Grout A mixture of cementitous material and aggregate that has enough water added to make give it pouring consistency. The addition of water does not segregate the constituents.
Grouted Masonry Masonry in which the hollow core is completely filled with grout.
Grouted Anchor An anchor that is held in the base material with grout.
Lightweight Concrete Concrete, not exceeding a weight of 115 pcf, that is composed of a light weight aggregate.
LVDT, Linear Variable Displacement Transducer
A device that creates fine movements to displace an anchor under a test load.
Masonry Base materials bonded with mortar to form a structure.
Mercaptan A curing agent used in epoxy.
Mortar The mixture of aggregates used to bond masonry units.
Oblique Load Same as combination load. A load that applies stress with the properties of both tension and shear loads.
Portland Cement Hydraulic cement consisting of finely pulverized compounds of silica, lime, and alumina.
Post-Tension A method of pre-stressing in which tendons are tensioned after concrete has hardened.
Precast Concrete Concrete that is made off site or on site, but that is first formed and then moved into its final place within the structure.
Prestressed Concrete Structural concrete in which internal stresses have been introduced to reduce potential tensile stresses in concrete resulting from loads.
Pretensioning A method of pre-stressing in which tendons are tensioned before concrete is placed.
Rebar Reinforcing steel that is deformed and whose surface contains ridges that give it better gripping within concrete or adhesive material.
Reinforced Masonry Masonry units that are bonded to reinforcing steel with mortar or grout.
Set Time The amount of time it takes for an adhesive anchor to reach its maximum load strength.
Shear Cone An anchor failure in which the concrete fracture appears in a cone shape. Shear cone failure is usually the result of a tension load.
Shear Load A load applied perpendicular to the axis of an anchor.
Shotcrete (Gunite) Pneumatically projected concrete or mortar.
Sleeve Anchor A stud type anchor with a full-length expansion mechanism made from a sheet of metal.
Slump A measure of consistency of concrete according to a strict standard ASTM C143 procedure. Slump is the sag or a truncated cone shape of free standing concrete.
Smooth Dowel Steel with a smooth surface that is used to tie new concrete to an existing slab.
Spacing
Spacing (S) – The distance between the centerline of one anchor to the centerline of another.
Critical Spacing (SCR) – The minimum space allowed between two anchors for load capacity to hold true.
Minimum Spacing (SMIN) – The minimum spacing at which anchors are tested for recognition.
Tendon A steel element used to pre-stress concrete.
Tension Load The load applied parallel to the axis of anchor.
Torque The measure of the force applied to a member to produce rotational motion usually measured in foot-pounds. Torque is determined by multiplying the applied force by the distance from the pivot point to the point where the force is applied.
Ultimate Load A load that when applied to an anchor will result in failure.
Undercut Anchor Anchor that develops its load capacity by expanding into a void created by a secondary drilling operation or the anchor itself.
Unreinforced Masonry (URM) Masonry units that do not contain reinforcing steel.
Wedge Anchor A stud type anchor with a limited length expansion mechanism and cone that creates and initial friction fit and then is seated when the cone is drawn inside the expansion mechanism.
Wythe A continuous vertical section of masonry one unit in thickness.
Concrete Anchors and Fasteners
General: Anchors and fasteners are available in a wide variety of types and sizes. The type and size needed for a particular application depends on a variety of factors including load level, direction of load (tension, shear, or a combination of the two). Other factors are environment (shock and/or vibration) and characteristics of the material into which the fastener is to be imbedded (new concrete, old concrete, concrete or cinder block, plaster, dry wall, etc.)
Fastening Is when a fixture needs to be connected to another, but subject to minimal amount of stress for example, hanging a small picture, towel rack or mirror.
Anchoring Is when a fixture needs to be connected to another, but subjected to appreciable stress and vibration - for example, steel beam to concrete or guard rail to concrete.
Determining Correct Fastener:
The following questions must be answered before a correct fastener can be selected.
1. What is the base material and its density?
There are two types of base material;
Hollow Core Drywall, plaster board. sheet rock, particle board, wafer board, plywood, plaster and lath, tile, glass, metal, fiber-glass, plastic and concrete block.
A. Drywall: A low density material formed between sheets of paper and used primarily for covering studded walls and ceilings. Exhibits relatively low pull-out resistance.
B. Plaster and Lath: Thin wooden strips (lath) were nailed to the studs or ceiling beams and low density plaster was applied over them. Exhibits relatively good pull-out resistance.
C. Hollow Core: Concrete Block: Commonly used in basements and commercial properties. Exhibits relatively high pull-out depending on compression strength of the block,
Solid Core Concrete, brick and mortar, stone, solid cinder block and wood.
A. Solid Concrete: Exhibits the highest pull-out resistance, but requires a suitable carbide bit than meets ANSI standards.
B. Stone: Since there are a large variety and different types, first identify the hardness and characteristics. Match up with the type of anchor needed
.
C. Brick or Mortar: like stone, it will vary from hard (brittle) to soft. In hard brick anchors with low-impact and/or low- torque are recommended. In soft brick, a draw-up anchor is recommended, i.e. sleeve anchor, machine screw anchor.
There are three degrees of density and strength of base materials; Low Density - weak resistance to stress, i.e. drywall and cinder block. Medium Density - moderate resistance to stress, i.e. plaster, tile fiber board and particle board. High Density - significant resistance i.e. concrete, concrete block, stone.
Resistance to stress will vary within density and thickness of the base material. Age and manufacturing standards for material will result in different failure points for each anchor.
2. What is the thickness of base material?
How thick the base material is, will help identify the type of anchor as well as the
embedment allowable.
For Hollow Core base material it is critical to have the right length anchor so as to be able to secure tightly. For Solid Core base material the embedment of anchor can not be closer than five (5) anchor diameters, because it’s an unsupported edge and holding values will be affected.
3. What is the size and weight of the fixture to be fastened?
If a fixture weighting 100 pounds needs to be fastened/anchored and the safe working load of the anchor selected is 50 pounds, at least 2 anchors will be needed to safely secure the fixture. Additional anchors may be warranted; not because of weight, but because of the bulkiness or size of fixture. When in doubt, always use more anchors.
4. What is the location of the fixture to be fastened?
Will the fixture be outside and subjected to the elements, inside, on a wall, suspended from a ceiling or fastened to a floor. Will the fixture be close to an unsupported edge? The distance between anchors is critical. If installed to close to each other, the interaction of forces between fasteners will reduce the holding power of the anchor in the base material. As a general rule, the anchor & fastener industry has established the following minimum spacing standards: Ten (10) anchor diameters between anchors, five (5) anchor diameters from the edge.
5. What kind of stresses may be on fixture once fastened?
The type and size of anchor or fastener suitable for a specific application depends
in part on the type and level of stress imposed on it. Five stress factors, illustrated below, should be considered.
Tension:
Where a force acts in line with a Fastener, tending to pull it out. Ceiling mounted fasteners, as shown are subjected to tension. But so sometimes are fasteners that are mounted on walls and floors
Shear:
Where a force acts at right angles to a fastener, tending to shear it off. Wall mounted fasteners, as shown are subjected to shear stress. But so sometimes are fasteners that are mounted on ceilings and floors.
Impact:
Occasional or repetitive impacts subject fasteners to stress over and above that resulting from normal tension and shear forces. The railing at right would undergo such impact loads.
Vibration:
Over time vibration will stress fasteners and the base material; Vibration stress can be induced by near by heavy machinery, railroad, automobiles or truck traffic and wind.
Combination:
In some cases, fasteners are subjected to two or more of the forgoing stresses. The example at the right fasteners supporting drapery rods. The fasteners are in both tension and shear as well as vibration and shock stress.
