PROFIS ENGINEERING REPORT SHEAR LOAD
Concrete Breakout Failure Mode
Variables ψ c , V
Variables ACI 318-14 Chapter 17 Provision Comments for PROFIS Engineering
ψ c , V
17.5 . 2.7 For anchors located in a region of a concrete member where analysis indicates no cracking at service loads , the following modification factor shall be permitted :
ψ c , V
= 1.4
For anchors located in a region of a concrete member where analysis indicates cracking at service load levels , the following modification factors shall be permitted :
ψ c , V
= 1.0 for anchors in cracked concrete without supplementary reinforcement or with edge reinforcement smaller than a No . 4 bar ψ c , V
= 1.2 for anchors in cracked concrete with reinforcement of a No . 4 bar or greater between the anchor and the edge ψ c , V
= 1.4 for anchors in cracked concrete with reinforcement of a No . 4 bar or greater between the anchor and the edge , and with the reinforcement enclosed within stirrups spaced at not more than 4 in ψ c , V
, is a modification factor for cracked or uncracked concrete conditions . Concrete cracks when tensile stresses in the concrete imposed by loads or restraint conditions exceed its tensile strength . Concrete is typically assumed to crack under service load conditions . ACI 318 anchoring-to-concrete provisions assume cracked concrete as the baseline condition for designing cast-in-place and post-installed anchors , since cracks in the anchor vicinity can result in a reduced ultimate load capacity and increased displacement at ultimate load , compared to uncracked concrete conditions . Uncracked concrete conditions can be assumed if it can be shown that cracking of the concrete at service load levels will not occur over the anchor service life . PROFIS Engineering defaults to cracked concrete conditions , and the default ψ c , V
-value for this condition equals 1.0 . Uncracked concrete conditions are accounted for by increasing ψ c , V to a value of 1.4 .
When cracked concrete conditions are assumed , ACI 318 anchoring-to-concrete provisions also permit ψ c , V to be increased if supplementary edge reinforcement is present in the concrete member . If cracked concrete conditions exist , and existing reinforcement of # 4 bars or greater is present at the fixed edge where concrete breakout is being considered , ACI 318-14 Section 17.5.2.7 permits ψ c , V to be increased to a value of 1.2 . If cracked concrete conditions exist , and the existing edge reinforcement in a concrete member consists of # 4 bars or greater enclosed by a stirrup , Section 17.5.2.7 permits ψ c , V to be increased to a value of 1.4 . The figure below illustrates how ψ c , V can be assumed to equal 1.2 or 1.4 for cracked concrete conditions .
Use of additional , i . e . “ supplementary ” edge reinforcement for shear calculations permits an increased strength reduction factor ( ϕ-factor ) to be used when calculating design concrete breakout strength ( ϕV cb or ϕV cbg
).
Reference the Results section of the report for more information on the strength reduction factor ϕ concrete
.
178 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-14 Provisions