Cracked and Non-Cracked Concrete – Anchor Design Considerations
Whether concrete is cracked or non-cracked is an important consideration when selecting and designing anchors. Loads acting on a concrete structure can create areas of compression and tension, and tensile stresses can lead to cracking that affects the behaviour of an anchoring system.
For structural anchoring applications, the selected anchor must be suitable for the expected concrete condition and used within the scope of its relevant product approval.
Why concrete cracking matters for anchoring
Concrete performs very well under compression but has a relatively limited capacity to resist tensile stress. Where tensile forces occur, reinforcement is used to carry much of that tension, but small cracks can still develop in the surrounding concrete.
These cracks may be caused by structural loading, shrinkage, temperature changes, imposed deformation or other influences. They may also develop or change during the life of the structure.
An anchor installed in an area that can crack therefore needs to maintain its required performance as the condition of the concrete changes.
Pressure and tension zones in concrete
The stress distribution within a concrete element can create areas that are predominantly in compression and areas that are subjected to tension.
Compression zone
An area of the concrete element where compressive stresses dominate. Depending on the structural design, the concrete may remain non-cracked under the relevant loading conditions.
Tension zone
An area subjected to tensile stresses where cracking may occur. Anchors used in these areas must be suitable and approved for cracked concrete where required.
The actual stress condition should be determined as part of the structural design. Where the concrete condition cannot reliably be considered non-cracked, anchor selection and calculation should account for cracked concrete.
Learn more about tension and shear loads >
Anchoring in non-cracked concrete
Non-cracked concrete refers to concrete in which cracking is not expected at the position of the anchorage under the relevant design conditions.
A wider range of anchoring products may be suitable where non-cracked concrete can be established, but the selected anchor must still be used within the conditions stated in its technical documentation and relevant European Technical Assessment (ETA).
Factors such as concrete strength, anchor spacing, edge distance, embedment depth and applied loads remain important regardless of whether the concrete is cracked or non-cracked.
Anchoring in cracked concrete
Anchors installed in cracked concrete must be capable of maintaining their required performance when cracks develop or change around the anchorage.
Suitable solutions can include mechanical and chemical anchoring systems specifically assessed for use in cracked concrete. The appropriate system depends on the application, loading conditions, installation geometry and scope of the relevant approval.
An anchor that is suitable for non-cracked concrete should not automatically be assumed to be suitable for cracked concrete.
Learn more about mechanical and chemical anchors >
How cracking can affect anchor performance
A crack passing through or close to an anchor can change the way forces are transferred between the anchor and the surrounding concrete.
Depending on the anchor system, cracking may influence:
- Expansion and load transfer within the concrete
- Pull-out resistance
- Concrete cone resistance
- Anchor stiffness and displacement
- The interaction between anchors in a group
- The effect of edge distances and anchor spacing
This is why the concrete condition forms part of structural anchor design rather than being treated as a separate installation detail.
Common anchor failure modes
Anchor resistance is governed by more than the strength of the steel itself. Different failure modes need to be considered depending on the anchor, concrete condition, geometry and direction of loading.
Steel failure
Steel failure can occur when the forces acting on the anchorage exceed the resistance of the steel component. Anchor diameter, material and strength all influence this resistance.
Pull-out failure
Pull-out occurs when the anchor is extracted from the base material before the surrounding concrete reaches another governing failure mode. Anchor design, installation and embedment depth all influence pull-out resistance.
Concrete cone failure
Tension loading can cause a section of concrete around the anchor to break away in a cone-shaped failure. The available resistance can be influenced by embedment depth, anchor spacing, edge distances and concrete strength.
Concrete splitting
Splitting can occur when stresses generated by the anchorage exceed the ability of the concrete member to contain them. Small edge distances, restricted spacing, limited member dimensions and expansion forces can all contribute.
Concrete edge failure
Where shear is applied close to the edge of a concrete member, part of the concrete edge may break away. The distance from the anchor to the edge is therefore an important design parameter for shear-loaded anchors.
Anchor spacing and edge distances
Cracked concrete is only one of the conditions that can influence anchor resistance. Anchor spacing, edge distance, embedment depth and concrete-member thickness also affect how loads are transferred into the surrounding material.
Anchors installed close together can interact with one another, while anchors positioned close to an edge may have reduced concrete resistance.
Explore anchor spacing, edge distance and installation conditions >
Special consideration for hollow-core slabs
Hollow-core slabs require particular care because the available concrete thickness can be limited by the internal voids and reinforcement layout.
Anchor position, drilling depth and installation method should therefore be checked carefully against the slab construction, anchor approval and any requirements provided by the slab manufacturer.
Anchors should not be selected for hollow-core slabs solely on the basis of their performance in solid concrete.
Selecting anchors for cracked concrete
For structural applications, the relevant product documentation should clearly confirm whether the anchor is suitable for cracked concrete and under which conditions it can be used.
When selecting an anchor, check factors including:
- Whether cracked concrete is included in the approval
- Permitted concrete strength classes
- Anchor diameter and effective embedment depth
- Tension, shear and combined loading
- Minimum edge distances and anchor spacing
- Concrete-member thickness
- Fire or seismic requirements where applicable
- Installation instructions and drill-hole preparation
Approval for cracked concrete should not automatically be interpreted as approval for seismic loading. Where seismic performance is required, the selected anchor must have the appropriate assessment for that application.
Calculate anchors in cracked and non-cracked concrete
For structural fastenings in concrete, the concrete condition should be assessed together with the applied loads, anchor geometry, spacing, edge distances and embedment depth.
The Fabory Anchor Calculator helps you design post-installed anchors for structural use in concrete in accordance with EN 1992-4.
Use the calculator to:
- Calculate for cracked and non-cracked concrete
- Assess tension, shear and combined loading
- Consider anchor spacing and edge distances
- Evaluate different anchor configurations
- Assess fire and seismic design conditions where applicable
- Generate calculation reports for project documentation
Use the Fabory Anchor Calculator >
Cracked concrete, EN 1992-4 and ETA documentation
For post-installed structural fastenings in concrete in Europe, EN 1992-4 provides the design framework used together with product-specific performance data from the relevant European Technical Assessment (ETA).
The ETA defines the conditions under which the anchor has been assessed, which can include concrete strength, cracked or non-cracked concrete, anchor dimensions, installation requirements and other application parameters.
Structural anchor selection should therefore be based on both the design requirements and the scope of the approval for the specific product.
Explore more anchoring guidance
Continue exploring Fabory's technical anchoring guidance:
- Types of anchors >
- Understanding anchor loads >
- Anchoring base materials >
- Anchoring conditions >
- Practical anchor design >
- Explore all anchoring technical guidance >
Need help with an anchoring application?
Selecting anchors for cracked concrete can become complex when structural loads, multiple anchors, restricted edge distances or additional fire or seismic requirements are involved. Fabory's technical specialists can help you assess the application requirements and identify a suitable anchoring solution.
Contact our technical specialists >
Frequently asked questions about cracked concrete and anchors
Find answers to common questions about cracked concrete, tension zones and structural anchor selection.
What is cracked concrete?
Cracked concrete is concrete in which tensile stresses can cause cracks to develop at the position of the anchorage. Cracking may result from structural loading, shrinkage, temperature changes, imposed deformation or other influences and can affect the behaviour of an anchor.
What is the difference between cracked and non-cracked concrete?
Non-cracked concrete is concrete in which cracking is not expected at the anchor location under the relevant design conditions. Cracked concrete is subjected to conditions in which cracks may develop or change, so anchors used there must be suitable and approved for those conditions where required.
Can any concrete anchor be used in cracked concrete?
No. An anchor should only be used in cracked concrete where the relevant product documentation and approval confirm that it is suitable for those conditions. An anchor approved only for non-cracked concrete should not automatically be used in cracked concrete.
Is an anchor approved for cracked concrete also suitable for seismic applications?
Not necessarily. Suitability for cracked concrete and seismic performance are separate design considerations. Where seismic resistance is required, the selected anchor must have the appropriate assessment or approval for the required seismic application.
How do I calculate anchors in cracked concrete?
Structural anchors in cracked concrete should be designed using the applicable design method together with the product-specific performance data and conditions in the relevant approval. For post-installed fastenings in concrete in Europe, EN 1992-4 provides the design framework used alongside the relevant ETA.
The Fabory Anchor Calculator supports the design of post-installed anchors in both cracked and non-cracked concrete in accordance with EN 1992-4.