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RE: Grade @ Anchor Bolts

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Title: RE: Grade @ Anchor Bolts

>Does the "chunk" behavior apply just to multiple anchor bolts connected to a
>single plate or would it also apply to anchor bolts each having its own
>individual plate (such as a plate washer) acting in group behavior?

It applies to both. The single plate spanning all anchor rods would probably represent the worst-case situation. For the case of rods with individual washers, it's similar but less drastic. Here's what I mean.

Start with a group of rods (without washers) placed so that the cones representing the pull-out failure for each rod in the concrete intersect. Now, add plate washers and gradually increase their size. As the size increases, the failure cones intersect more quickly (closer to the bottom of the embedments). The larger the plate, the less surface area you get on the intersecting cones. Eventually, the individual washers approach the case of a continuous single plate as their size is increased.

So really, the maximum cone pull-out strength is attained with the minimum plate washer size, which is no washer (i.e., just the head or nut). So then the question is, can the head or nut alone provide the necessary bearing area. Research (see Marsh and Burdette "Anchorage of Steel Building Components to Concrete" in the 1st Quarter 1985 AISC Engineering Journal) has shown that a head or nut is sufficient to develop the necessary anchorage.