COMBINED TENSION AND SHEAR LOAD
Parabolic
Equations β NV
= β E N + βE V ≤ 1 . 0
Equations 318-14 Chapter 17 Provision Comments for PROFIS Engineering β NV
= β E N + βE V ≤ 1 . 0
R17 . 6 – Interaction of tensile and shear forces The shear-tension interaction expression has traditionally been expressed as
N ua
N n
E
+
where E varies from 1 to 2 . The current trilinear recommendation is a simplification of the expression where E = 5 / 3 . The limits were chosen to eliminate the requirement for computation of interaction effects where very small values of the second force are present . Any other interaction expression that is verified by test data , however , can be used to satisfy 17.3.1.3 .
V ua
V n
E
≤ 1.0
ACI 318-14 anchoring-to-concrete provisions default to what is known as a trilinear interaction equation , which is given in Eq . ( 17.6.3 ). PROFIS Engineering checks both Eq . ( 17.6.3 ) and the parabolic interaction equation given in the ACI 318-14 commentary R17.6 . The PROFIS Engineering report shows the most favorable results .
The failure mode for a given tension or shear load condition can be expressed as a ratio of factored load to design strength :
• Factored tension load / tension design strength = ( N ua / ϕN N
)
• Factored shear load / shear design strength = ( V ua
/ ϕVN )
The “ governing ” failure mode can be defined as the highest ( factored load / design strength ) ratio for the failure modes being considered . PROFIS Engineering defines the calculated results using the parabolic interaction equation via the parameter “ β NV
”.
Part 3 of the PROFIS Engineering report shows the ratio of factored tension load ( N ua
) to tension design strength ( ϕN N ) via the parameter β N
. For the example below , concrete breakout failure is the governing failure mode for tension because it has the highest utilization ( β N
= 51 %).
3 Tension load Load N ua
[ lb ]
Capacity ϕN n [ lb ]
Utilization
β N
= N ua / ϕN n
Status
Steel strength * 5,000 14,550 35 OK Bond strength ** 10,000 31,564 32 OK
Sustained tension load bond strength *
Concrete breakout Failure **
* highest loaded anchor ** Anchor group ( anchors in tension )
3,450 16,800 21 OK
10,000 19,971 51 OK
348 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-14 Provisions