1. Anchor
Channel Systems
2. HAC
Portfolio
3. HAC
Applications
Overcoming the Limitations of the Concrete Edge Breakout
Strength
Anchor Channels with Welded Reinforcing Bars
5. Base material
6. Loading
Welding reinforcing bars to an anchor channel changes the
behavior of the anchor channel in tension and combined tension
and shear. When tension forces are applied to the anchor
channel, the concrete above the reinforcing bars fails and
reduce the concrete cone resistance of the anchor channel.
Also, due to the large cracks in front of the anchor channel
in case of shear loading, the interaction with concrete cone
failure is negatively influenced. These effects are even more
pronounced in lightweight concrete structures. Therefore,
the negative effect of the welded reinforcing bars should be
considered in the design of these types of anchor channels.
8. Reinforcing
Bar Anchorage
9. Special Anchor
Channel Design
10. Design
Software
HAC EDGE
Utilizing the basic principles of reinforced concrete structures
has lead Hilti to develop a new anchor channel system that
copes with the curtain wall market needs. Rather than relying on
the relatively low tensile capacity of the concrete for the failure
mode “concrete edge breakout”, HAC EDGE brings superior
concrete edge performance by optimizing the load transfer for
small edge distances, thin concrete members, low concrete
compressive strengths, and lightweight concrete.
The first loading stage of HAC EDGE is equal to the one of
standard anchor channels and anchor channels with welded
reinforcing bars (1). After shear loads are applied to the anchor
channel, the loads are first transferred from the channel profile
towards the free edge of the concrete. The EDGE plate which
is held back by the welded reinforcing bars confines the edge,
allowing for the formation of compression struts (2). The shear
load is transferred back to the reinforcing bars. The ultimate
resistance of the system is reached after the reinforcing bars are
fully activated (3).
The EDGE plate is not structurally connected to the anchor
channel. This allows decoupling of the shear and tension load
transfer mechanism. The concrete cone resistance of the anchor
channel can be conservatively calculated according to AC232.
In analogy to standard anchor channels, the shear loads are
transferred into the concrete via the channel profile (1). The
failure also occurs in front of the channel profile (2). However,
compared to standard anchor channels the shear loads are
redistributed to the reinforcing bars. The higher ultimate
resistance of the system is reached only with increased
deformations and large cracks in front of the channel (3).
11. Best
Practices
12. Instructions
for Use
13. Field Fixes
14. Design
Example
channel. Moreover, depending on the geometry of the concrete
member and location of the anchor channel, HAC EDGE can
outperform standard anchor channels without reinforcing bars
up to a factor of 5.
Additional Benefits of HAC EDGE
In addition to the high concrete edge breakout in shear
performance, HAC EDGE comes with the specified/ordered
edge distance to reduce errors in placement, and provide a
safer and quicker installation. This goes in hand with Hilti’s
mission of building a better future. HAC EDGE reduces the
probability of installing the product at the wrong edge distance.
The edge distance is the most sensitive variable that has the
highest impact on the concrete edge breakout strength in shear.
Moreover, the installation of the anchor channel is simplified as
the product can easily be secured to the formwork by nailing
or screwing the EDGE plate to it. Moreover, HAC EDGE brings
overall material savings as it allows the use of smaller facade
brackets. The superior concrete shear performance for small
edge distances allows the curtain wall bracket to be concealed
by the stool trim or gypsum wall, if they are at least 4”-5” away
from the edge of the building. This eliminates the need of
so-called pockets, bringing substantial savings
For small edge distances HAC EDGE provides more than 2
times the capacity of traditional top of slab anchor channels
where the reinforcing bars are welded to the back of the
To overcome the limitations of the relatively low concrete edge
breakout strength close to an edge, often anchor channels with
reinforcing bars structurally welded to the back of the channel
are used.
7. Anchor Channel
Design Code
In curtain wall applications, the design of the anchor channel
typically takes place at one of the last stages of the building
design. Oftentimes, the design of the anchorage comes as
an afterthought. By the time the anchor channel is sized, the
variables that can significantly influence the performance of the
anchor channel have been defined. The edge distance is the
variable that has the largest impact on concrete edge breakout
failure. However, even this variable may have already been
defined leaving designers with minimal options. Typically, the
edge distance can only be varied in a very narrow band due to
the size of the bracket.
4. Design
Introduction
Anchor channel with anchors and welded reinforcing bar
Figure 9.6.1.4 — Welded rebar channel — Behavior of anchor channels with reinforcing bars loaded in shear (left). Shear load vs displacement curve (right).
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Anchor channel with anchors and rebar edge confinement
plate (EDGE Plate)
Figure 9.6.1.5 — HAC EDGE Behavior of HAC EDGE loaded in shear (left). Shear load vs displacement curve (right).
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