Uncracked Concrete

[Abigail Tyrie]

Tensionzone (cracked concrete) should not be equate with structural damage. The occurrence of this area is intended and intentional. Quantity and layout of reinforcement are designed in order to strict control of cracks width (usually at the level of wmax = 0,3 mm).

In practice, the issue can be more complicated. Complex structural systems with different load variants creates stress map for whole building. Analysis of this topic is a duty and responsibility of structural designer. He should define what type of concrete should be considered in fastenings calculations for selected area.

Concrete module of EasyFix software allows to take into account type of concrete. In general, cracked concrete area is more demanding, so the performance data of fasteners are reduced accordingly. User decides if counting process would be performed for cracked or uncracked concrete. The option can be found in Substrate tab. Depend on the choice, different range of the products is available.

In cracked concrete zone, following anchors can be successfully used: throughbolts R-HPTII-ZF/A4, R-HPTIII-ZP/A4, concrete screws R-HLX or bonded anchors: epoxy resin R-KEXII or hybrid resin R-KERII. Additionally, for uncracked concrete zone reliable will be throughbolts R-XPT, R-XPT-II-A4, R-XPTIII-HD as well as bonded anchor polyester resin R-KEMII.

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The difference between cracked an uncracked concrete is defined in BS EN 1992-4. Several of the design verifications requireed for concrte anchorage design depend on whether the concrete is defined as cracked or uncracked. This is not a simple case of checking onsite whether the concrete member is cracked or not. The definition of cracked or uncracked concrete is explained below.

To define a concrete member as uncracked the designer must be able to demonstrate with stress analysis that the concrete in the vicinity of the anchor will remain uncracked throughout the design life of the member in all anticipated loading conditions.

Modern construction schedules and conditions create a demand for solutions that can perform in a wide variety of environments. In the following post, Field Engineer Chris Johnson provides a rundown of different concrete and hole conditions for adhesive anchoring, the related design factors, and proper installation instructions and approved adhesive products for submerged anchorage.

Section 104.11 provides the design professional with two options for the substantiation of the acceptable performance of an Alternative Material: a. Research Reports. As described in the previous section (Design of Code Anchors), Research Reports are referenced as the primary source for the design and qualification of Alternative Materials. Research Reports for anchors are published by IAPMO UES or ICC-ES, both ANSI ISO 17065 accredited agencies. Publicly developed, majority-approved acceptance criteria are used to establish the test program and minimum performance requirements for an anchor type. Some Alternative Material anchor types have established acceptance criteria to which a product can be evaluated:

The design professional must consider additional factors that have the potential to result in concrete cracking in the region of anchorage. These factors include restrained shrinkage, temperature changes, soil pressure, and differential settlement. If no cracking is assumed in the region of the anchorage, the design professional should be able to justify that assumption.

Remember back to the days when you used allowable stress design for designing anchorage to concrete? Once you had your design loads, selecting an anchor was quick and easy. The 1997 UBC covered the anchorage to concrete in less than two pages, so the calculation was painless. Post-installed anchors were even easier, since allowable loads were tabulated and you just needed to apply a couple of edge distance and spacing reductions.

With the increasing demand for high-density housing and urban infill projects, designers are now faced with anchoring multi-story wood-framed shear walls to relatively thin elevated concrete slabs (typically referred to as podium slabs). Overturning tension anchorage forces at the ends of shear walls in these projects can routinely be in the 40 kip range and even get as high as 60 kips or more.

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One of the frequently asked questions that we usually receive from our customers is how to choose the right anchor that fits with a specific concrete category. Through this article, we shall understand together the main differences between cracked & non-cracked concrete, according to ETAG 001 of the European Organization for Technical Approvals (EOTA).

Cracked Concrete is the concrete that may experience cracking passing through the plane of the anchor at some time after installation of the system. Cracked concrete does not refer to the state of the concrete at the time of installation.

Non-Cracked Concrete is the concrete where the probability is acceptably low that either cracks will form after installation of anchors or the width of any existing cracks will increase significantly during the life of the anchors.

Non-cracked concrete may be assumed in special cases if in each case it is proved that under service conditions the anchor with its entire anchorage depth is located in non-cracked concrete (as shown on below figure).

To determine whether a specific anchor is suitable or not to be used with the specified concrete category you have, ETAG 001 has 12 options of required tests for assessing the admissible conditions of use that are based on the design methods mentioned in Annex C.

Anchors designed for cracked concrete automatically qualify for use in non-cracked concrete. Where cracked concrete is expected, anchors with Options 1 - 6 in their European Technical Approval (ETA) should be selected, whereas anchors qualified only in non-cracked concrete applications should be selected according to Options 7 - 12.

Red Head Trubolt+ seismic cracked and uncracked concrete wedge anchor are designed for use in solid concrete in a variety of environments. Tested under strict procedures and policies, each diameter and length has been approved for use in uncracked concrete, cracked concrete and seismic applications.

However, in practice, a slab is continuous over multiple supports. Over these supports, the tension zone is located at the top of the slab and in the compression zone at the base meaning the cracked condition will vary throughout a slab depending on the location of supports.

Concrete is likely to be cracked from a variety of causes including stress conditions inherent in the structure, those induced by characteristic permanent actions and characteristic variable actions, thermal movements, shrinkage and the restraint of deformation.

All of these factors make correct anchor specification a challenging process to ensure the anchor is designed for the conditions in which it will be used. It is therefore important to consult the relevant standards.

BS EN 1992-4:2018, the new Eurocode sub-standard for concrete anchors, states that uncracked concrete can only be assumed if it is proven that under the characteristic combination of loading at serviceability limit state, the fastener with its entire embedment depth is located in uncracked concrete.

Essentially, it cannot be assumed that concrete is uncracked in all cases. An assessment must be made of whether the concrete is cracked or uncracked for each anchor location. With masonry support, anchors are generally installed at the same level horizontally along the slab edge. Based on the theory above the opportunity arises for some of the anchors to be installed into cracked concrete, and some to be installed in uncracked concrete. Therefore, to avoid confusion and the potential for the incorrect anchor specification, a safe approach would be to assume that the concrete is cracked in all conditions over its service life.

Another relevant standard to the selection of anchors and cracked concrete is BS8539:2012, The Code of Practice for the selection and installation of post-installed anchors in concrete and masonry. This standard provides recommendations for the safe selection and installation of anchors for use in concrete and masonry. This again states that concrete should be assumed as cracked unless an exercise has been carried out to determine whether it is cracked or non-cracked.

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