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f c i or f v -* (MPa)
60-80
80-100
100-120
>120
TABLE 2
RANGE OF TEST PARAMETERS FOR CONFINING STEEL
(Letters allude to references, given below)
300-500
c,e,f,l
c,e,l,q
b,c,d,e,g,j,q
b,e,g,h
500-700
f
o,p
o,p
h
700-900
d,f
k,q
dj,q,r
r
a. Ahmad and Shah (1982) b.AI-Hussainie/a/(1993)
d. Nagashima etal (1992)
e. Muguruma et al (1993)
g. Razvi and Saatciogiu (1994) h. Razvi and Saatciogiu (1996)
j Azizinammi and Kuska( 1993) LKimura etal (1996)
m.Tanakae/a/(1994)
n. Sugano(1996)
p. Galeota and Giammatteo (1996) q. Muguruma and Watanabe (1990)
900-1100
a
h
h
>1100
a,d,l,m
1
d,n
e t n
c.Bjerkeli etal (1990)
f. Cusson and Paultre (1993)
i. Sun etal (1996)
L Liet al (1994)
o. Bayrak and Sheikh (1996)
r. Nishiyama et al (1993)
It is clear from the above, that there are considerable gaps in testing results of relevance to seismic
response; which require attention prior to attempting to derive comprehensive design guidance. This is
further emphasized by the observation that some of the above tests were conducted under eccentric
axial load to represent combined axial-flexural testing. Notwithstanding other objectives that the
researchers may have had in mind, this type of testing is considered by the authors to be not strictly
relevant for seismic assessment purposes. There are several behavioral considerations supporting the
latter statement; amongst which is that levels of axial load at maximum moment are so high that the
mobilized confining stresses are rather unrealistic and unrepresentative of seismic response of
structures. A comprehensive testing program on beam-column members was recently completed at
imperial College (Elnashai et al [1998], Goodfellow [1998] and Elnashai and Goodfellow [2002]). The
testing range was concrete strength of 60 MPa to 130 MPa and steel yield strength of 500 MPa to 1300
MPa, with two stirrup spacing and two axial load levels under cyclic and monotonic transverse
loading, leading to 92 test specimens.
It was concluded (in the experimental studies above) that values of plastic hinge length and
displacement ductility of reinforced concrete members, constructed from concrete up to 130 MPa and
steel up to 1300 MPa, are on the whole similar and lower, respectively, than the normal material values
commonly expected. However, no indication was given that ductility-based seismic design cannot
make use of these materials that may be dictated on the project, by column size requirements and wind
vibration control It is clear though, that specific design guidance is needed and curbs on the level of
steel yield in particular should be imposed. This is confirmed by the low values of deformation-related
parameters obtained for the f c 130-f y !300 pairs. Until further work is undertaken, a limit of concrete
strength and steel yield for ductile seismic design may be set at f c =100 MPa, with f y =700 MPa. These
values started from the study reported above and therefore, are employed below. The study also gave
values of secant stiffness at yield and ultimate for displacement-based design purposes. Finally, it is
significantly concluded that the use of high strength confining hoops is not warranted, especially when
employing high strength concrete. This is attributed to the low levels of dilation generally observed for
high strength concrete. This is an important economic consideration in ductility-based design using
high strength materials.
There are very few studies on high strength materials at the structure level. The study by Kateinas
(1997) (summarized in Elnashai, 1998) was one of the first detailed analytical investigations into high
strength concrete buildings. It used the simplest approach possible for the analysis of a suite of