Critical Region for full length of short column (lc/hc<3)
Critical Region Prescriptive Confinement to clauses 220.127.116.11.2 (1) to (4), (10) and (11).
Critical Region prescriptive Confinement to dauses 18.104.22.168.2 (1) to (4), (10) and (11).
Reduced confinement away from plastic hinge zones. All column splices within this region.
Beam/Column Joint 'Special' Confinement to clauses 5,4,3,3 fl) to (3)
Figure 5.8 Typical column details - elevation where ®wd is (volume of confining hoopsf^Avolume of concrete core*/"^), bQ is the minimum dimension of concrete core and a is a confinement effectiveness factor, depending on concrete core dimensions, confinement spacing and the arrangement of hoops and ties. It is defined in Equations 5.16a to 5.16c and 5.17a to 5.17c of the code (EC8) for various cross sections.
In the critical region at the base of columns, a minimum value of of 0.08 is specified. However, for structures utilising low levels of ductility (q of 2 or less) and subject to relatively low compressive stresses (v^ 0.2), this requirement is waived and the normal EC2 provisions apply. In all other critical regions of columns the following applies:
• Minimum hoop and tie diameter is 6 mm.
• Maximum spacing of hoops and ties in the critical region is the least of:
• The maximum distance between restrained longitudinal bars should be 200 mm.
• Hoops must have 10 bar diameter anchorage length into the core of the column. Typical detailing requirements in critical regions of columns are illustrated in Figures 5.8 and 5.9.
The beam-column joints of frames represent a highly stressed region with quite complex reinforcement detailing. The design requirements in EC 8 are much more straightforward for DCM than for DCH.
In joints, no explicit calculation of shear resistance is required, provided the following rules are satisfied:
a. To ensure that there is adequate bond bettveen reinforcement and concrete, the diameter of the main beam bars passing through the joint must be limited as given earlier in Equations 5.12 and 5.13.
b. At least one intermediate column bar is provided between each of the corners of the columns.
c. oops ust continue unreduced through the joint fro the critical region of the column, or must meet the confinement requirements of Equation 5.14 if greater, unless the joint is confined on all four sides by beams. In this case, the hoop spacing may be doubled (but must not exceed 150 ).
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