Contents
- Anchor Behavior - Failure Modes
- Anchor Fastening Design and Influencing Factors
- Influence of Edge Distance
- Influence of Anchor Spacing
- Anchor Loading
- Combined Loading
- Bending Moment
- Example of Application
1 Anchor Behavior - Failure Modes
There are several types of failure modes which are exhibited by anchors when they are loaded beyond their capacity: steel breakage, concrete cone failure, concrete splitting, edge failure, bond failure, or pullout (including slip or pull through). Anchors may fail by different modes depending on the concrete strength, depth of embedment, loading type, loading direction, edge distance or anchor spacing.  |  |  | | Concrete spall cone | Bond failure | Steel breakage |  |  |  | | Edge breakout | Concrete splitting | Pullout |
2 Anchor Fastening Design and Influencing Factors
There are several factors which directly affect the load carrying capacity of anchors; embedment depth, edge distances, spacing to adjacent anchors, and concrete strength. Testing is performed in different concrete strengths and embedments and values are presented in this Product Technical Guide for actual specific concrete compressive strengths and embedments. Ultimate and allowable loads for intermediate values of concrete strength and embedment can be calculated by linear interpolation. The other influencing factors are used to reduce the ultimate or allowable loads by using Eq. 1. | Frec = Fall * fR * fA | Eq. 1. |
| where: | Frec | = | the resulting recommended load after influencing factors have been applied to the allowable load | | | Fall | = | the tension or shear load value from the product data tables | | | Fr | = | the edge distance factor from the table for the appropriate anchor | | | fA | = | the spacing factor from the table for the appropriate anchor |
| If there is more than one edge or spacing influence, then a reduction factor is applied for each influencing condition, that is, fR1 * fR2 * . . . fRN fA1 * fA2 * . . . * fAn. |
2.1 Influence of Edge Distance
The distance from one or more edges must be considered in anchor design and appropriate adjustment factors applied as in Eq. 4.1.3.1. Testing has been performed and edge reductions generally determined for both the critical edge distance, ccr, and minimum edge distance, cmin. The critical edge distance is defined as the minimum distance from edge to obtain the full loading capacity of the anchor, and the minimum edge distance is defined as the minimum distance at which an anchor can be properly installed and the specified torque applied without failure. Reductions for edge distances between ccr and cmin may be calculated using linear interpolation. The product technical data presents the edge distance adjustment factors in three ways: by graph, by table and by equation. The adjustment factors for shear, fRV, and tension, fRN, are given separately where they are different. In the graphs (found in each anchor section) the edge distance is normalized by the embedment depth, either hef (actual), hmin (minimum) or hnom (nominal or standard) as given in the table at the top of the page titled "Anchor Spacing and Edge Distance Guidelines" for each anchor. Divide the edge distance, c, by the embedment depth. Move horizontally to the right to intersect the line for shear or tension. Then read down on the x-axis to obtain a corresponding edge adjustment factor, fRV or fRN, which is multiplied directly with the allowable load to calculate the recommended load. 
The load adjustment factor tables found in each anchor section provide an easy means of obtaining an adjustment factor if the edge distance is known. Find the edge distance in the left column titled "Edge Distance", and read across for the appropriate anchor diameter. Multiply the allowable load by the appropriate adjustment factor. Both the graphs and the tables are derived from the equations given at the bottom of the tables. Where there is more than one edge influencing the anchor, then each edge will contribute an adjustment factor and they are multiplied together. Where there are three edges, Fr = fR1 * fR2 * fR3. 2.2 Influence of Anchor Spacing
If the distance between two anchors is less than the critical spacing, scr, but greater than the minimum anchor spacing, smin, apart, then the load capacity of an individual anchor is reduced to account for the influence of the second anchor on the first. The critical spacing is the minimum spacing between two anchors to still attain the potential loading capacity of the anchors. The minimum spacing is that spacing which allows the anchor to be installed and torqued without premature failure. Adjustments for spacing between scr and smin may be calculated using linear interpolation. The adjustment factors are given in the product technical data in a manner similar to that for edge influences, except that the tension and shear reductions are the same for a given spacing. This is usually conservative for shear loading. The data is presented in graphs, tables and equations. The graphs found in each anchor section are normalized by dividing the spacing, s, by the embedment depth, hef or hnom as given in the table at the top of the page titled "Anchor Spacing and Edge Distance Guidelines" for each anchor. For a given anchor spacing, divide the spacing by the embedment depth. Using this value from the y-axis, move horizontally to the line labeled "Shear and Tension." From the intersection of these lines move down vertically to the x-axis and read the respective adjustment factor. Multiply this factor directly with the ultimate or allowable load from the load capacity tables. 
In using the "Reduction Factor" table format, find the actual or desired spacing in the left column. Move right to the column for the appropriate anchor diameter and read the adjustment factor. Multiply this factor by the ultimate or allowable load from the load capacity table. Both the graphs and the tables are derived from the equations given at the bottom of the tables. Where there is more than one influencing anchor, then each anchor spacing will contribute an adjustment factor and they are multiplied together. Where there are three anchor spacings, fA = fA1 * fA2 * fA3 3 Anchor Loading
| The type of anchor loads and their position play an important role in the selection of the proper anchor for an application. Both shear and tension values for various concrete strengths are provided in this manual. These must be carefully matched to the design requirements to develop a safe and serviceable connection. |  |
3.1 Combined Loading
A wide variety of interaction equations have been developed to represent the capacity of anchors loaded simultaneously in tension and shear. Where the capacity of the steel parts (threaded rod, bolts, etc.) controls, the usual interaction relationships used in the design of steel structures are valid, with due account given to secondary bending effects (see section 3.2). Test data for obliquely loaded anchors will typically include a mix of steel and concrete failures. As such, predictive relationships for interaction are typically based on a fairly wide data scatter. Two of the more common relationships in use, straight line and parabolic, take the form shown below: | 
A straight line assumption is nearly always conservative. Use of parabolic relationships should be supported by testing with oblique loading.
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3.2 Bending Moment Anchors subjected to ultimate shear loads will cause the base material (concrete, masonry) near the surface to crush or spall. This loss of bearing support in trun increases the secondary bending moment in the anchor body. In the absence of other guidance, the resultant reduced shear capacity of the anchor may be evaluated as follows:
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3.3 Prying Effect
When designing connections for tension loads, the effects of prying should be considered. See AISC Manual of Steel Construction (ASD Part 4 or LFRD Part 11) 4 Example of Application  | Anchor Selection: Building located in Seismic Zone must resist dynamic loads. The HSL or HVA is recommended for this fastening application. Preliminary Design: Anchor: HSL M16 Concrete: 4000 psi Allowable Working Loads Tension: 5790 lb Shear: 9645 LB |
| See HSL product pages for Loads and Influence Factors |
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