REGRESSION MODELING OF BREAKOUT STRENGTH OF AN EXPANSION ANCHOR BOLT AS INFLUENCED BY CONCRETE AGGREGATES

Abstract

The frictional resistance of an expansion anchor bolt depends directly on the normal forces
generated by the anchor expansion mechanism around the anchorage zone of the concrete base material.
However, only the concrete aggregates around the anchorage zone have the direct shear contact with the anchor.
This study aims to develop a regression model that predicts the breakout strength of an expansion anchor in
plain concrete as influenced by the coarse aggregate size, coarse aggregate content, and fine aggregate content.
Crushed coarse aggregates of sizes 10mm, 12.5mm, 19mm, and 25mm were used. The coarse aggregate content
for each coarse aggregate size was 0.3452, 0.4046, 0.4462, and 0.4750, respectively. The fine aggregate content
for each coarse aggregate size was 0.4243, 0.3771, 0.3514, and 0.3341, respectively. A heavy duty type of an
expansion anchor bolt was used. There were five samples of base material specimens considered for each size
of coarse aggregate. Each specimen was tested first for its compressive strength to ensure that it will meet the
designed compressive strength and it will vary only at an acceptable deviation before the installation of the
expansion anchors. The installed anchor bolts were then tested for pull-out. Tests results showed that among
the parameters considered, coarse aggregate size is the most significant factor that could influence the breakout
strength of an expansion anchor and it is optimum at 19mm size. A polynomial regression model is
recommended to predict the concrete breakout strength of an expansion anchor bolt as influenced by the coarse
aggregate size.