“Base material” is a generic industry term that refers to the element or substrate to be anchored to. Base materials include concrete, brick, concrete block (CMU) and structural tile, to name a few. The most common type of base material where adhesive and mechanical anchors are used is concrete.
Concrete – Concrete can be cast-in-place or precast concrete. Concrete has excellent compressive strength, but relatively low tensile strength. Cast-in-place (or sometimes called “poured in place”) concrete is placed in forms erected on the building site. Cast-in-place concrete can be either normal-weight or lightweight concrete. Lightweight concrete is often specified when it is desirable to reduce the weight of the building structure.
Lightweight concrete differs from normal-weight concrete by the weight of aggregate used in the mixture. Normal-weight concrete has a unit weight of approximately 150 pounds per cubic foot compared to approximately 115 pounds per cubic foot for lightweight concrete.
The type of aggregate used in concrete can affect the tension capacity of an adhesive anchor. Presently, the relationship between aggregate properties and anchor performance is not well understood. Test results should not be assumed to be representative of expected performance in all types of concrete aggregate.
Prefabricated concrete is also referred to as “precast concrete”. Precast concrete can be made at a prefabricating plant or site-cast in forms constructed on the job. Precast concrete members may be solid or may contain hollow cores. Many precast components have thinner cross sections than cast in place concrete. Precast concrete may use either normal or lightweight concrete. Reinforced concrete contains steel bars, cable, wire mesh or random glass bers. The addition of reinforcing material enables concrete to resist tensile stresses which lead to cracking.
The compressive strength of concrete can range from 2,000 psi to over 20,000 psi, depending on the mixture and how it is cured. Most concrete mixes are designed to obtain the desired properties within 28 days after being cast.
Concrete Masonry Units (CMU) – Block is typically formed with large hollow cores. Block with a minimum 75% solid cross section is called solid block even though it contains hollow cores. In many parts of the country building codes require steel reinforcing bars to be placed in the hollow cores, and the cores to be filled solid with grout.
In some areas of the eastern United States, past practice was to mix concrete with coal cinders to make cinder blocks. Although cinder blocks are no longer made, there are many existing buildings where they can be found. Cinder blocks require special attention as they soften with age.
Brick – Clay brick is formed solid or with hollow cores. The use of either type will vary in different parts of the United States. Brick can be difficult to drill and anchor into. Most brick is hard and brittle. Old, red clay brick is often very soft and is easily over-drilled. Either of these situations can cause problems in drilling and anchoring. The most common use of brick today is for building facades (curtain wall or brick veneer) and not for structural applications. Brick facade is attached to the structure by the use of brick ties spaced at intervals throughout the wall. In older buildings, multiple widths, or “wythes” of solid brick were used to form the structural walls. Three and four wythe walls were common wall thicknesses.
Clay Tile – Clay tile block is formed with hollow cores and narrow cavity wall cross sections. Clay tile is very brittle, making drilling difficult without breaking the block. Caution must be used in attempting to drill and fasten into clay tile.
Four different tension failure modes and three different shear failure modes are generally observed for post-installed anchors under tension loading.
|Steel Fracture Breakout Pullout (Mech. Anch.) Bond Failure (Adhesive Anch.)||Steel Fracture Breakout Pryout|
Breakout Failure – Breakout failure occurs when the base material ruptures, often producing a cone-shaped failure surface when anchors are located away from edges, or producing a spall when anchors are located near edges. Breakout failure can occur for both mechanical and adhesive anchors and is generally observed at shallower embedment depths, and for installations at less than critical spacings or edge distances.
Pullout Failure – Pullout failure occurs when a mechanical anchor pulls out of the drilled hole, leaving the base material otherwise largely intact.
Bond Failure – Bond failure occurs when an adhesive anchor pulls out of the drilled hole due to an adhesion failure at the adhesive-to-base-material interface, or when there is a cohesive failure within the adhesive itself. When bond failure occurs, a shallow cone-shaped breakout failure surface will often form near the base material surface. This breakout surface is not the primary failure mechanism.
Pryout Failure – Pryout failure occurs for shallowly embedded anchors when a base material failure surface is pried out “behind” the anchor, opposite the direction of the applied shear force.
Steel Fracture – Steel fracture occurs when anchor spacings, edge distances and embedment depths are great enough to prevent the base-material–related failure modes listed above and the steel strength of the mechanical anchor or adhesive anchor insert is the limiting strength.
Many environments and materials can cause corrosion, including ocean salt air, fire-retardants, fumes, fertilizers, preservative-treated wood, de-icing salts, dissimilar metals and more. Metal fixtures, fasteners and anchors can corrode and lose load-carrying capacity when installed in corrosive environments or when installed in contact with corrosive materials.
The many variables present in a building environment make it impossible to accurately predict if, or when, corrosion will begin or reach a critical level. This relative uncertainty makes it crucial that specifiers and users are knowledgeable about the potential risks and select a product suitable for the intended use. It is also prudent that regular maintenance and periodic inspections are performed, especially for outdoor applications.
It is common to see some corrosion in outdoor applications. Even stainless steel can corrode. The presence of some corrosion does not mean that load capacity has been affected or that failure is imminent. If significant corrosion is apparent or suspected, then the fixtures, fasteners and connectors should be inspected by a qualified engineer or qualified inspector. Replacement of affected components may be appropriate.
Chemical Attack - Chemical attack occurs when the anchor material is not resistant to a substance with which it is in contact. Chemical-resistance information regarding anchoring adhesives is found in section V on this page.
Some wood-preservative chemicals and fire-retardant chemicals and retentions pose increased corrosion potential and are more corrosive to steel anchors and fasteners than others. Additional information on this subject is available at www.strongtie.com.
We have attempted to provide basic knowledge on the subject of corrosion here, but it is important to fully educate yourself by reviewing our technical bulletins on the topic (www.strongtie.com/info) and also by reviewing information, literature and evaluation reports published by others.
Galvanic Corrosion - Galvanic corrosion occurs when two electrochemically dissimilar metals contact each other in the presence of an electrolyte (such as water) that acts as a conductive path for metal ions to move from the more anodic to the more cathodic metal. In the galvanic couple, the more anodic metal will corrode preferentially. The Galvanic Series of Metals table provides a qualitative guide to the potential for two metals to interact galvanically. Metals in the same group (see table) have similar electrochemical potentials. The farther the metals are apart on the table, the greater the difference in electrochemical potential, and the more rapidly galvanic corrosion will occur. Corrosion also increases with increasing conductivity of the electrolyte.
Good detailing practice, including the following, can help reduce the possibility of galvanic corrosion of anchors:
|Corroded End (Anode)|
|Magnesium Magnesium alloys Zinc|
|Aluminum 1100 Cadmium Aluminum 2024-T4 Iron and Steel|
|Lead Tin Nickel (active) Inconel Ni-Cr alloy (active) Hastelloy alloy C (active)|
|Brasses Copper Cu-Ni alloys Monel|
|304 stainless steel (passive) 316 stainless steel (passive) Hasteloy alloy C (passive)|
|Silver Titanium Graphite Gold Platinum|
|Protected End (Cathode)|
Some hardened fasteners may experience premature failure if exposed to moisture as a result of hydrogen-assisted stress-corrosion cracking. These fasteners are recommended specifically for use in dry, interior locations.
|Corrosion Resistance Classification||Material or Coating|
|Mechanically galvanized (ASTM B695-Class 55)1|
|Hot-dip galvanized (ASTM A153-Class C)|
|Type 410 stainless steel with protective top coat|
|High||Type 302, 303 or 304 stainless steel|
|Type 316 stainless steel|
|Environment||Material To Be Fastened|
|Untreated Wood or Other Material||Preservative-Treated Wood||FRT Wood|
|SBX-DOT Zinc Borate||Chemical Retention ≤ AWPA, UC4A||Chemical Retention > AWPA, UC4A||ACZA||Other or Uncertain|
Expansion anchors that have been set to the required installation torque in concrete will experience a reduction in pre-tension (due to torque) within several hours. This is known as pre-load relaxation. The high compression stresses placed on the concrete cause it to deform which results in a relaxation of the pre-tension force in the anchor. Tension in this context refers to the internal stresses induced in the anchor as a result of applied torque and does not refer to anchor capacity. Historical data shows it is normal for the initial tension values to decrease by as much as 40–60% within the first few hours after installation. Retorquing the anchor to the initial installation torque is not recommended or necessary.
The strength design data for adhesive anchors in this catalog are based on installations into concrete that is at least 21 days old. Anchors may be installed in concrete less than 21 days old, provided a reduction factor is applied to bond strength:
|Products||Concrete Age When Installed||Concrete Age When Loaded||Bond Strength Factor|
|14 days||21 days||1.0|
|7 days||21 days||1.0|
The performance data for adhesive anchors are based upon anchor tests in which holes were drilled with carbide-tipped drill bits of the same diameter listed in the product’s load table. Additional static tension tests were conducted to qualify anchors installed with SET, SET-XP®, ET-HP® and AT adhesives for installation in holes with diameters larger than those listed in the load tables. The tables indicate the acceptable range of drilled hole sizes and the corresponding tension-load reduction factor (if any). The same conclusions also apply to the published shear load values. Drilled holes outside of the accepted range shown in the charts are not recommended.
|Insert Diameter (in.)||Acceptable Hole Diameter Range (in.)||Acceptable Load Reduction Factor|
|3/8||1/2 - 3/4||1.0|
|1/2||5/8 - 1 5/16||1.0|
|5/8||3/4 - 1 1/8||1.0|
|3/4||7/8 - 1 5/16||1.0|
|7/8||1 - 1 1/2||1.0|
|1||1 1/8 - 1 11/16||1.0|
|1 1/8||1 1/4 - 1 7/8||1.0|
|1 1/4||1 3/8 - 2 1/16||1.0|
|1 3/8||1 1/2- 2 1/4||1.0|
|Insert Diameter (in.)||Acceptable Hole Diameter Range (in.)||Acceptable Load Reduction Factor|
|1/2||5/8 - 3/4||1.0|
|5/8||3/4 - 15/16||1.0|
|3/4||7/8 - 1 1/8||1.0|
|7/8||1 - 1 5/16||1.0|
|1||1 1/8 - 1 1/2||1.0|
|1 1/4||1 3/8 - 1 7/8||1.0|
|Insert Diameter (in.)||Acceptable Hole Diameter Range (in.)||Acceptable Load Reduction Factor|
|3/8||7/16 - 1/2||1.0|
|1/2||9/16 - 5/8||1.0|
|5/8||11/16 - 3/4||1.0|
|3/4||13/16 - 7/8||1.0|
|1||1 1/16 - 1 1/8||.75 for 1 1/8 only|
The performance data for adhesive anchors are based upon anchor tests in which holes were drilled with carbide-tipped drill bits. Additional static tension tests were conducted to qualify anchors installed with SET and AT anchoring adhesives for installation in holes drilled with diamond-core bits. In these tests, the diameter of the diamond-core bit matched the diameter of the carbide-tipped drill bit recommended in the product’s load table. The test results showed that no reduction of the published allowable tension load for SET and AT anchoring adhesives is necessary for this condition. The same conclusions also apply to the published allowable shear loads.
SET-XP, ET-HP and AT-XP: The performance data for adhesive anchors using SET-XP, ET-HP and AT-XP adhesives are based upon tests according to ICC-ES AC308. This criteria requires adhesive anchors that are to be installed in outdoor environments to be tested in water-saturated concrete holes that have been cleaned with less than the amount of hole cleaning recommended by the manufacturer. A product’s sensitivity to this installation condition is considered in determining the product’s “Anchor Category” (strength reduction factor). SET-XP, ET-HP and AT-XP may be installed in dry or water-saturated concrete.
SET, EDOT and AT: The performance data for adhesive anchors using SET, EDOT and AT adhesives are based upon tests in which anchors are installed in dry holes. Additional static tension tests were conducted for some products in damp holes, water-filled holes and submerged holes. The test results show that no reduction of the published allowable tension load is necessary for SET, EDOT and AT adhesives in damp holes, or for SET and AT adhesives in water-filled holes. For SET and AT adhesives in submerged holes, the test results show that a reduction factor of 0.60 is applicable. The same conclusions also apply to the published allowable shear load values.
The performance of all adhesive anchors is affected by elevated base material temperature. The in-service temperature sensitivity table provided for each adhesive provides the information necessary to apply the appropriate load adjustment factor to either the allowable tension based on bond strength or allowable shear based on concrete edge distance for a given base material temperature. While there is no commonly used method to determine the exact load-adjustment factor, there are a few guidelines to keep in mind when designing an anchor that will be subject to elevated base-material temperature. In any case, the final decision must be made by a qualified design professional using sound engineering judgment:
Creep is the slow, continuous deformation of a material under constant stress. Creep occurs in many construction materials, including concrete and steel when the stress is great enough. The creep characteristics of adhesives are product-dependent. Adhesive anchors that are not creep-resistant can pull out slowly over time when sustained tensile loads are applied.
Because of the creep phenomenon, it is important for Designers to consider the nature of the applied tension loads and to determine whether the tension loads will be continuously applied to the anchor over the long term. If this is the case, a product that is suitable for resisting sustained loads over the long term must be selected.
All Simpson Strong-Tie® anchoring adhesives (SET-XP, SET, ET-HP, EDOT, AT-XP and AT) have been qualified for resisting long-term loads through ICC-ES AC58 or ICC-ES AC308 “creep tests” in which an anchor is loaded and monitored for movement over time. According to AC58 and AC308, anchors that pass the creep test are determined to be suitable for resisting long-term tensile loads.
Samples of Simpson Strong-Tie® anchoring adhesives were immersed in the chemicals shown below until they exhibited minimal weight change (indicating saturation) or for a maximum of three months. The samples were then tested according to ASTM D 543 Standard Practices for Evaluating the Resistance of Plastics to Chemical Changes, Procedures I & II, and either ASTM D 790 Standard Test Method for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials or ASTM D 695 Standard Test Method for Compressive Properties of Rigid Plastics. In cases where mild chemicals were evaluated, the exposure was accelerated per ASTM D 3045 Standard Practice for Heat Aging of Plastics Without Load.
Samples showing no visible damage and demonstrating statistically equivalent strength and elastic modulus as compared to control samples were classified as “Resistant” (R). These adhesives are considered suitable for continuous exposure to the identified chemical when used as a part of an adhesive anchor assembly.
Samples exhibiting slight damage, such as swelling or crazing, or not demonstrating both statistically equivalent strength and elastic modulus as compared to control samples were classified as “Non-Resistant” (NR). These adhesives are considered suitable for periodic exposure to the identified chemical if the chemical will be diluted and washed away from the adhesive anchor assembly after exposure, or if only emergency contact with the chemical is expected and subsequent replacement of the anchor would be undertaken. Some manufacturers refer to this as “limited resistance” or “partial resistance” in their literature.
Samples that were completely destroyed by the chemical, or that demonstrated a significant loss in strength after exposure were classified as “Failed” (F). These adhesives are considered unsuitable for exposure to the identified chemical.
Note: In most actual service conditions, the majority of the anchoring adhesive is not exposed to the chemical and thus some period of time is required for the chemical to saturate the entire adhesive. An adhesive anchor would be expected to maintain bond strength and creep resistance until a significant portion of the adhesive is saturated.
|Aluminum Ammonium Sulfate (Ammonium Alum)||10%||R||R||R||R||R|
|Aluminum Potassium Sulfate (Potassium Alum)||10%||R||R||R||R||R|
|Aluminum Sulfate (Alum)||15%||R||R||R||R||R|
|Ammonium Hydroxide (Ammonia)||28%||NR||R||NR||R||R|
|Aviation Fuel (JP5)||100%||R||R||R||--||--|
|Brake Fluid (DOT3)||100%||R||NR||F||--||--|
|Calcium Hypochlorite (Chlorinated Lime)||15%||R||R||R||R||R|
|Calcium Oxide (Lime)||5%||R||R||R||R||R|
|Detergent (ASTM D543)||100%||R||R||R||--||--|
|Iron (II) Chloride (Ferrous Chloride)||15%||R||R||R||R||R|
|Iron (III) Chloride (Ferric Chloride)||15%||R||R||R||R||NR|
|Iron (III) Sulfate (Ferric Sulfate)||10%||R||R||F||--||--|
|Methyl Ethyl Ketone||100%||NR||F||F||--||--|
|Methyl Isobutyl Ketone||100%||NR||NR||NR||--||--|
|Mixture of Amines1||100%||R||F||F||--||--|
|Mixture of Aromatics2||100%||NR||NR||R||--||--|
|Motor Oil (5W30)||100%||R||R||R||--||--|
|Seawater (ASTM D1141)||100%||R||R||R||--||--|
|Soap (ASTM D543)||100%||R||R||R||--||--|
|Sodium Hexafluorosilicate (Sodium Silicon Fluoride)||5%||R||R||R||R||R|
|Sodium Hypochlorite (Bleach)||25%||R||R||R||R||R|
|Sodium Phosphate (Trisodium Phosphate)||10%||R||R||R||R||R|