Shear capacities of the columns were assessed using Priestley's model [1995]. (Eqn. 2). The design of the OMRF
using higher strength concrete allowed the use of smaller column utilising the concrete’s favourable load
carrying capacity. Although the reduction in size reduced the shear strength of the HSC columns, a higher
concrete strength compensated for that reduction. The sections that needed attention were on the lower levels
which contained low yield lateral reinforcement. These sections displayed a low curvature ductility capacity, and
the values of shear strength and flexural shear strength were close. According to Priestley’s model, no shear
failure would be expected, although the calculations are based on nominal values.
Eqns. 3, 4 and 5 were used to assess the Beam-column joints in the frame assuming the concrete strength within
the joint is equal to the column strength. For frame No.1 (concrete strength of 50MPa in the joint), the required
amount of horizontal shear reinforcement within an interior beam-column joint to resist the maximum shear
force is equal to 4272 mm2. According to the ACI318, the total horizontal reinforcement required is equal to
1831 mm2. For Frame 2 (Concrete strength of 100 MPa) these values are 3891 and 2870 respectively. As
mentioned earlier ACI formula gives incorrect results for high strength concrete joints.
Bond transfer within the beam-column joints were assessed using Eqn. 6 suggested by Fujii et al. [1995] and NZ
code [1995]. For OMRF with 50MPa joints the maximum bar sizes are 46mm according to Fujii et al. formula
and 21mm with NZ formula. For OMRF with 100MPa joints these diameters are 56 and 23mm respectively. As
seen the two methods give significantly different allowable bar diameters. However, larger bar diameters are
allowed in HSC joints.
CONCLUDING REMARKS
With increasing concrete compressive strength, the section sizes and reinforcement ratios in columns can be
effectively reduced. This changes the balance of beam and column flexural capacities, which in turn may change
the response from extensive beam hinging to extensive column hinging. Column hinging is prevalent and greater
detailing may be needed in such potential plastic hinge regions. However, frames with HSC columns, in this case
study, performed well in satisfying ductility demands. Although the column sizes were reduced, the maximum
displacements were slightly reduced due to higher elastic modulus in HSC and slightly lower earthquake loads.
There are other benefits in using high strength concrete such as improved shear capacity of columns, stronger
beam-column joints, larger bar diameters allowed within a joint to transfer bond and higher rotational ductilities
in flexural members. High strength concrete can be an attractive option to reduce the member sizes in secondary
Shear capacities of the columns were assessed using Priestley's model [1995]. (Eqn. 2). The design of the OMRF
using higher strength concrete allowed the use of smaller column utilising the concrete’s favourable load
carrying capacity. Although the reduction in size reduced the shear strength of the HSC columns, a higher
concrete strength compensated for that reduction. The sections that needed attention were on the lower levels
which contained low yield lateral reinforcement. These sections displayed a low curvature ductility capacity, and
the values of shear strength and flexural shear strength were close. According to Priestley’s model, no shear
failure would be expected, although the calculations are based on nominal values.
Eqns. 3, 4 and 5 were used to assess the Beam-column joints in the frame assuming the concrete strength within
the joint is equal to the column strength. For frame No.1 (concrete strength of 50MPa in the joint), the required
amount of horizontal shear reinforcement within an interior beam-column joint to resist the maximum shear
force is equal to 4272 mm2. According to the ACI318, the total horizontal reinforcement required is equal to
1831 mm2. For Frame 2 (Concrete strength of 100 MPa) these values are 3891 and 2870 respectively. As
mentioned earlier ACI formula gives incorrect results for high strength concrete joints.
Bond transfer within the beam-column joints were assessed using Eqn. 6 suggested by Fujii et al. [1995] and NZ
code [1995]. For OMRF with 50MPa joints the maximum bar sizes are 46mm according to Fujii et al. formula
and 21mm with NZ formula. For OMRF with 100MPa joints these diameters are 56 and 23mm respectively. As
seen the two methods give significantly different allowable bar diameters. However, larger bar diameters are
allowed in HSC joints.
CONCLUDING REMARKS
With increasing concrete compressive strength, the section sizes and reinforcement ratios in columns can be
effectively reduced. This changes the balance of beam and column flexural capacities, which in turn may change
the response from extensive beam hinging to extensive column hinging. Column hinging is prevalent and greater
detailing may be needed in such potential plastic hinge regions. However, frames with HSC columns, in this case
study, performed well in satisfying ductility demands. Although the column sizes were reduced, the maximum
displacements were slightly reduced due to higher elastic modulus in HSC and slightly lower earthquake loads.
There are other benefits in using high strength concrete such as improved shear capacity of columns, stronger
beam-column joints, larger bar diameters allowed within a joint to transfer bond and higher rotational ductilities
in flexural members. High strength concrete can be an attractive option to reduce the member sizes in secondary
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