DESIGN SPECIFICATIONS FOR HIGHWAY BRIDGES - IISEE

10.6 Structural Details for Improving Ductility Performance
(1) Lapping of axial reinforcement
In order to ensure the lateral strength of a pier specified in Section 10.2, lappings of
axial reinforcements shall not generally be placed within the plastic zone, when
generation of plastic deformation of the pier is expected in the verification of its seismic
performance.
(2) Arrangement of lateral hoop ties and cross ties
1) To prevent buckling of axial reinforcement and for the restraint of internal
concrete, hoop ties and cross ties shall be arranged in an appropriate manner
having suitable spacings, when generation of plastic deformation of the pier is
expected in the verification of its seismic performance.
2) Hoop ties shall be deformed bars of at least 13mm diameter, and the spacings shall
not generally be greater than 150mm in the plastic zone. However, in the case of
adopting different spacings in the middle section of the pier, the spacings shall not
be altered abruptly.
3) Hoop ties shall generally be arranged so as to enclose the axial reinforcement, and
the ends of hoop ties with the hooks described below shall normally be fixed into
the concrete inside a pier. Lap joints without hooks shall not be generally adopted.
When right angle hooks are used, measures shall be taken to prevent the hooks
from becoming ineffective, even if the cover concrete spalls. In addition, lappings of
hoop ties shall be placed in a zigzag pattern along the pier height. Straight length
of a hoop tie between two bending ends at the hooks shall be longer than the
values provided below. Internal radius of bending of a hook shall be at least 2.5
times the hoop tie diameter. Here, internal radius of bending refers to the inside
radius of a bent reinforcing bar. Provisions for the straight length of a hoop tie are
as follows:
i) Semi-circular hook: 8 times the diameter of a hoop tie or 120mm whichever is the
greater.
ii) Acute angle hook: 10 times the diameter of the hoop tie
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