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CONCLUSIONS
In this paper, the seismic performance and cost effectiveness of high rise high strength RC buildings
were discussed. Based on the analyses performed, the following conclusions are supported by the
results:
• Contrary to some of the studies performed on columns subjected to pure axial load, the optimum
concrete strength that will give the most economical structure is not necessarily the highest
concrete strength available. The concrete strength that can reduce the cost of the steel component,
while at the same time limit the cost of the concrete component, will result in the most cost
effective structure.
• In the light of the common practice of using high strength concrete only in the columns of the
structure, it was shown that the use of high strength concrete in the beams and slabs, where they
are less effective, can still furnish substantial cost savings.
• Under static loading, the high strength concrete structures have stable load-displacement curves.
The shape of the curve is similar to that of normal strength concrete structures. For this type of
loading, inelasticity developed mostly in the beams. The columns appear to be well protected from
hinging by capacity design regulations.
• The level of overstrength in high strength concrete structures, calculated based on the static
pushover analysis, is less than that of the normal strength structure. In the normal strength
structure, the additional steel reinforcement required to resist high axial loads provide extra lateral
load capacity, thus increasing overstrength.
• At the global level, based on the three response parameters (top displacement, base shear and
maximum interstorey drift ratio) examined, the performance of the high strength concrete
structures compares favourably with that of the equivalent normal strength concrete structure.
• The selection of the grade of steel to use with the high strength concrete is very important. Results
from the dynamic analysis indicate that using normal grade steel for concrete strengths of up to 80
MPa is adequate. Beyond 80 MPa, the use of normal grade steel with high strength concrete
resulted in significantly more hinging in the columns. The use of high yield steel in beams and
normal grade steel in the columns should also be avoided.
• The maximum curvature ductility demand at the design and twice the design earthquake is 3.73
and 7.15, respectively. These are well within the achievable ductility capacity of seismically
designed and detailed members. Moreover, the use of high yield steel with high strength concrete
significantly reduced the ductility demand on the members to about 1.63 and 3.83.
• The calculated behaviour factors suggest that the SOMPa concrete is the optimum concrete strength
for the given structural configuration, in terms of energy dissipation capacity. In general, the higher
strength concrete structures have a larger behaviour factor compared to the normal strength
structure.