1. Anchor
Channel Systems
2. HAC
Portfolio
3. HAC
Applications
5.1 BASE MATERIALS
5.1.2 CONCRETE
Cement is a binding agent which combines with water and
aggregates and hardens through the process of hydration to
form concrete. Portland cement is the most commonly used
cement and is available in several different types to meet
specific design requirements (ASTM C150).
Aggregate grading
specification Concrete unit weight
pcf
Normal-weight Fine: ASTM C33
Coarse: ASTM C33 145-155
Sand-lightweight Fine: ASTM C33
Coarse: ASTM C330 105-115
All-lightweight Fine: ASTM C330
Coarse: ASTM C330 85-110
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In view of the significantly lower strength of green concrete
(less than 28-day cure), it is recommended that cast-in anchor
channels not be loaded in concretes cured for less than 7 days,
unless site testing is performed to verify the fastening capacity. If
an anchor is installed in green concrete, but not loaded until the
concrete has achieved full cure, the capacity of the anchor can
be based on the strength of the concrete at the time of loading.
9. Special Anchor
Channel Design
10. Design
Software
11. Best
Practices
12. Instructions
for Use
13. Field Fixes
14. Design
Example
5.1.3 PRE-TENSIONED / PRE-STRESSED
CONCRETE 5.2 EVALUATION OF TEST DATA
Pretensioned concrete refers to concrete cast around
pretensioned steel tendons. 5.2.1 D
EVELOPING FASTENER PERFORMANCE
DATA
Cast-in anchor channel systems can be a solution for
pretensioned concrete, as it does not require drilling into the
concrete. AC232 does not provide provisions to account for
the influence of pre-tensioned cables on the anchor channel
concrete capacity.
Anchor channels installed near tendon(s) may induce additional
stresses in the concrete. Likewise, tendon(s) near anchor
channel(s) may impact the performance of the channel.
Conditions where anchor channels are installed near tendon(s)
shall be designed accordignly. Additional coordination with the
Engineer of Records (EOR), design engineer, and/or Pre-stressed
concrete engineer is required.
5.1.4 BONDED POST-TENSIONED CONCRETE
Post-tensioned concrete refers to a concrete member containing
steel tendons that are tensioned after casting the concrete.
As with the prestressed concrete case, anchor channels close
to post-tensioning strands should be designed accordingly and
additional coordination with the Engineer of Records (EOR),
design engineer, and/or post-tensioned concrete engineer is
required. AC232 does not provide provisions to account for
the influence of post-tensioned cables on the anchor channel
concrete capacity.
State-of-the-art anchor design uses what is known as the
Strength Design Method. By using the Strength Design Method,
nominal strengths are first calculated for all the possible anchor
failure modes. Subsequently, strength reduction factors are
applied to each nominal strength to obtain a design strength.
The controlling design strength is finally compared to a factored
load. The provisions of ACI 318-14 Chapter 17 are the basis used
for Strength Design.
Strength Design data for Hilti anchor channels in concrete
elements is derived from testing as per the provisions of
ICCES AC232.
Beginning with IBC 2003, the IBC Building Codes have adopted
the Strength Design Method for anchorage into concrete of both
cast-in-place and post-installed anchors.
Another anchor design method known as "Allowable Stress
Design" can be used as an alternative to the Strength Design
provisions. Section 2.2.2 provides detailed explanations to
analyze cast-in anchor channels via Allowable Stress Design.
Allowable Stress Design data for Hilti cast-in anchor channels is
derived from testing based on ICC-ES AC232.
Allowable loads are developed applying a statistical method
to the test data which relates the allowable working load to the
performance variability of the fastening.
5.1.5 ADMIXTURES
Chemical admixtures are ingredients added to the basic
components of concrete or mortar (cement, water, and
aggregates) immediately before or during mixing. Chemical
admixtures are used to enhance the properties of concrete
and mortar in the plastic and hardened state. These properties
may be modified to increase compressive and flexural strength,
decrease permeability and improve durability, inhibit corrosion,
reduce shrinkage, accelerate or retard initial set, increase slump
and working properties, increase cement efficiency, improve the
economy of the mixture, etc.
ASTM concrete type
Values for the ultimate strength of fasteners in concrete are
traditionally given in relation to the 28-day uniaxial compressive
strength of the concrete (actual, not specified). Concrete that
has cured for less than 28 days is referred to as green concrete.
Aggregate type, cement replacements such as fly ash, and
admixtures can affect the capacity of some fasteners, and this
may not be reflected in the concrete strength as measured in a
standard uniaxial compression test. In general, Hilti data reflects
testing with common aggregates and cement types in plain,
unreinforced concrete. In questionable cases, consult with Hilti
Technical Services.
8. Reinforcing
Bar Anchorage
The aggregates used in concrete consist of both fine aggregate
(usually sand) and coarse aggregate graded by particle size.
Different types of aggregates can be used to obtain concrete
with specific characteristics. Normal-weight concrete is generally
made from crushed stone or gravel, while lightweight concrete is
obtained using expanded clay, shale, slate, or blast-furnace slag.
Lightweight concrete is used when it is desirable to reduce the
dead load on a structure or to achieve a superior fire rating for a
floor structure. When thermal insulating properties are a prime
consideration, lightweight aggregates are manufactured from
perlite, vermiculite, blast-furnace slag, clay or shale. Finally, sand
lightweight concrete is obtained using lightweight aggregate and
natural sand. In general, all concretes with a unit weight between
85 and 115 pcf are considered to be structural lightweight
concretes. The ASTM specifications related to concrete type and
weight can be summarized as follows:
The effect of aggregate mechanical properties on anchor
performance is less well understood. In general, harder/ denser
aggregates (i.e. granite) tend to result in higher concrete cone
breakout loads, whereas lightweight aggregates produce lower
tension and shear capacities. Concrete is typically assumed to
crack under normal service load conditions or, more specifically,
when tensile stresses imposed by loads or restraint conditions
exceed its tensile strength. Crack width and distribution are
generally controlled through the use of reinforcement. With
consideration for the protection of the reinforcing steel, crack
widths, per ACI 318, are assumed to be less than approximately
0.012 in (0.3 mm). Under seismic loading, flexural crack widths
corresponding to the onset of reinforcing yield are assumed to
be approximately 1-1/2 x static crack width = 0.02” (0.5 mm).
Both ACI 318 and the International Building Code conservatively
assume cracked concrete as the baseline condition for the
design of cast-in-place and post-installed anchors since the
existence of cracks in the vicinity of the anchor can result in a
reduced ultimate load capacity and increased displacement
at ultimate load compared to uncracked concrete conditions.
Design for uncracked concrete conditions is permitted by the
model Building Codes only for cases where it can be shown that
cracking of the concrete at service load levels will not occur over
the anchor service life. For cases involving design for seismic
actions, cast-in anchor channels must be demonstrated as
being suitable for use in cracked concrete as well as for seismic
loading.
7. Anchor Channel
Design Code
Concrete is a synthetic stone consisting of a mixture of cement,
aggregates, and water. In many cases, special additives are
used to influence or change certain properties. Concrete has
a relatively high compressive strength compared to its tensile
strength. Thus, steel reinforcing bars are frequently cast in
concrete to carry tensile forces, and this combination is referred
to as reinforced concrete.
6. Loading
The wide variety of building materials used today provides
different anchoring conditions for anchors. There is hardly a
base material in or to which a fastening cannot be made with a
Hilti product. However, the properties of the base material play
a decisive role when selecting a suitable fastener/anchor and
determining the load it can hold. It is the responsibility of the
designer to carefully match the type of fastener with the base
material to obtain the desired results.
5. Base material
5.1.1 BASE MATERIALS FOR FASTENING
4. Design
Introduction
Testing of post-installed anchors is performed in concrete
without admixtures. Designers should take into consideration the
effects produced by admixtures on concrete when considering
the use of post-installed anchors.
Cast-In Anchor Channel Product Guide, Edition 1 • 02/2019
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