Another very significant
problem with the use of crosstie reinforcement with 90° hooks embedded in the
concrete cover, is that during a violent earthquake the concrete cover is
lost due to spalling.
Premature crosstie failure
in laboratory experiments by Professor Shamin Sheik are shown in this
figure.Based on this evidence,
engineers on seismic code writing committees now require seismic hooks at
both ends of crossties and should also prohibit 90° hooks in concrete cover.