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The ductility of beam sections in some existing earthquake
resistant R.C. building may be insufficient due to
insufficient compression stell , poor concrete quality ,
large stirrup spacing and inappropriate reiforcing bar details
. In the study , curvature ductility of beam sections was
evaluated analyticaly , and it is found that ： (1) a
ductility factor of 7 is required for R.C. sections with f''
c=210kg/cm2 and Fy=2800kg/cm2 , (2) concrete strength has
significant effect on curvature ductility and less effect
on flexural strength , (3) the regulations on tensile and
compressive steel of ACI Code are too brief to assure
sufficient ductility . In addition to analytical
investigation , 9 full scale beam tests were carried out
to study the effect of concrete cover confinement on the
ductility of R.C. beams . It is found from the tests that
：(1) confine mechanism A was able to confine concrete cover
when stirrup spacing was not too large , (2) confine
mechanism B was able to confine concrete cover effectively ,
(3) bond strength could be problem when concrete strength is
too low .
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