HAC_Technical-Guide

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Cast-In Anchor Channel Product Guide, Edition 1 • 02/2019
1. Anchor
Channel Systems
2. HAC
Portfolio
3. HAC
Applications
4. Design
Introduction
5. Base material 6. Loading
7. Anchor Channel
Design Code
8. Reinforcing
Bar Anchorage
9. Special Anchor
Channel Design
10. Design
Software
11. Best
Practices
12. Instructions
for Use
13. Field Fixes
14. Design
Example
`8.1 Reinforcing Bar Theory
8.2 Development Length
of Straight Bars
8.3 Pullout Strength of Straight
Reinforcing Barsrs
8.4 Pull Out Strength of
Headed Bars In Tension
8.5 Pull Out Strength of
Standard Hooks
8.6 Rebar Lap Splices 8.7 Concrete Cover
8.6 REINFORCING BAR LAP
SPLICES
Behavior of lap splices
Opposed to development length where the length of the
reinforcing bar needed to transfer the stresses to the concrete is
calculated, lap splice calculates the lap length of the reinforcing
bar needed to transfer the stresses to another bar.
The mechanism of force-transfer in lap splicing is the force
in one reinforcing bar is transferred into the concrete, which
then is transferred to the adjacent reinforcing bar, or spliced
reinforcing bar. This behavior is shown in Figure 8.6.1.1 and
8.6.1.2. Although the term “lap splice” implies direct transfer of
stress from bar to bar, forces between bars are transferred via
struts and hoop stresses in the concrete.
The transfer of forces out of the reinforcing bar into the concrete
causes radially outward pressures on the concrete, as shown
in figure 8.6.1.3. This force transfer may create pressures that
result in splitting cracks on concrete between and along the
two reinforcing bar. When such cracks occur, the splice fails.
Therefore, transverse reinforcement can be supplemented to
delay the openings of the splitting cracks and improve the splice
capacity.
Figure 8.6.1.1 — Forces on bars at splice
Figure 8.6.1.2 — Compressive struts at splice.
Figure 8.6.1.3 - Radial forces on concrete and splitting stresses shown on
section through the splice.
Tension lap splices per ACI 318-14 25.5.2.1
Lap splices in tension in accordance to ACI 318-14 are classified
as a Class A or Class B splice. The lap splice length (ℓ
st
). is a
multiple of the tensile development length (ℓ
d
).
A class B splice taken as the greater of 1.3ℓ
d
and 12 in. is
required in all cases unless 1) the area of reinforcement is at
least twice that determined by analysis over the entire length
of the splice and 2) one-half or less of the total reinforcement
is spliced within the lap length. Where 1) and 2) are satisfied, a
Class A splice taken as the greater of 1.0ℓ
d
and 12 in. may be
used.
The transverse center-to-center spacing of spliced bars shall
not exceed the lesser of one-fifth the required splice length and
6 in. If individual bars are too widely spaced, an unreinforced
section is created causing potential cracks.
Table 8.6.1.1 (ACI 318-14 Table 25.5.2.1) — Lap splice
lengths of deformed bars and deformed wires in tension
As,provided/
As,required
[1]
over length of
splice
Maximum
percent of As
spliced within
required lap
Length
Splice type ℓ
st
≥ 2.0
50 Class A
Greater
of:
1.0ℓ
d
and
12 in.
100 Class B
Greater
of:
1.3ℓ
d
and
12 in.
< 2.0 All cases Class B
§ 25.5.1.2 For contact lap splices, minimum clear spacing
between the contact lap splice and adjacent splices or bars
shall be in accordance with the requirements for individual bars
in 25.2.1.
Figure 8.6.1.4 — Contact lap splice.
§ 25.5.1.3 For non-contact splices in flexural members, the
transverse center-to-center spacing of spliced bars shall not
exceed the lesser of one-fifth the required lap splice length and
6 in.
Figure 8.6.1.5 — Non-contact lap splice.
If individual bars in noncontact lap splices are too widely
spaced, an unreinforced section is created. Forcing a potential
crack to follow a zigzag line (5-to-1 slope) is considered a
minimum precaution. The 6 in. maximum spacing is added
because most research available on the lap splicing of deformed
bars was conducted with reinforcement within this spacing.
There is no difference in the performance of contact and
noncontact lap splices. Forces are transferred from one bar to
another via the concrete.
§ 25.5.1.4 Reduction of development length in accordance with
§ 25.4.10.1 is not permitted in calculating lap splice lengths.
Because the splice classifications already reflect excess
reinforcement, the development length, ℓ
d
, used to determine
the lap length should not include reduction factors for excess
reinforcement.
§ 25.5.2.2 If bars of different size are lap spliced in tension, ℓ
st
shall be the greater of ℓ
d
of the larger bar and ℓ
st
of the smaller
bar.