ACI 318-14, Section R17.2.1: The impact of the Inclusion or Exclusion of Anchor Reinforcement 1

[jochav52802]

ACI 318-14, Section R17.2.1 states:

"When the strength of an anchor group is governed by breakage of the concrete, the behavior is brittle and there is limited redistribution of the forces between the highly stressed and less stressed anchors. In this case, the theory of elasticity is required to be used, assuming the attachment that distributes loads to the anchors is sufficiently stiff. The forces in the anchors are considered to be proportional to the external load and its distance from the neutral axis of the anchor group."

My question is whether or not a "sufficiently stiff" "attachment" needs to be used to ensure proportional load distribution among the anchors when anchor reinforcement is used instead of the concrete's break-out capacity?

I've got a few cases where my base plates will need to be excessively thick in order to meet the rigid base plate requirement of R17.2.1 and was hoping that using anchor reinforcement would eliminate this requirement since the reinforcement offers a ductile load path. However, I'm hesitant to go that way since the anchor reinforcement still involves the brittle concrete break-out cone, in that the reinforcement must overlap each side of the cone to sufficiently to develop the reinforcement. Not sure if this involvement of the break-out cone still requires a rigid base plate to be designed.

Any help or thoughts are appreciated!

Thank you!

 

[HTURKAK]

Pls read again Section R17.2.1 . Incase of failure mode is breakage of the concrete, In order to determine the forces , THE ASSUMPTION ( the attachment that distributes loads to the anchors is sufficiently stiff ) IS MADE so ( the forces in the anchors are considered to be proportional to the external load and its distance from the neutral axis of the anchor group ).

In your specific case , I assume tension failure of Concrete is critical ..that is , you checked and find that pull-out failure of concrete is critical and you provided tension reinforcement as per code . If this is case, you do not need to check the base plate thickness in order to find the individual forces in the anchors.

The base plate thickness should be determined looking to the governing design loading combination ( e.g. axial compression, axial tension, small ecc., large ecc., and for shear) .

I will suggest you to look ;

i= Anchorage Design for Petrochemical Facilities-ASCE Committee and,

ii = AISC Design Guide 1 ,Base Plate and Anchor Rod Design .

If you have a specific question, pls provide more details to get specific responds..