the characteristics of both the shape of the curves in
height above the ground, plus inch (13mm) for
these figures, and the deformation demand produced
each 10 feet (3.05m) of additional height.
by the design earthquake on the building, such that
the
expected
performance
at
the
estimated
(2) For higher or more flexible buildings, the
deformation level for the structure is acceptable.
gap or seismic joint between the structures should be
based on the sum of the deflections determined from
f.
Connectivity. It is essential to tie the various
the required (prescribed) lateral forces. If the design
structural elements together so that they act as a unit.
of the foundation is such that rotation is expected to
The connections between the elements are at least as
occur at the base due to rocking or due to settlement
important as the elements themselves. Prevention of
of
foundations,
this
additional
deflection
(as
collapse during a severe earthquake depends upon
determined by rational methods) will be included.
the inelastic energy-absorbing capacity of the
structure, and this capacity should be governed by
(3) In situations where it is impractical to
the elements rather than by their connections; in
provide adequate clearance, the consequences of
other words, connections should not be the weak link
potential damage due to hammering must be
in the structure. As a general guide, if no other
considered. If the floor levels of the two buildings
requirements are specified, connections should be
are approximately the same and the floor systems are
adequate to develop the useful strength of the
relatively robust (e.g., concrete beams and slabs), the
structural elements connected, regardless of the
resulting damage may be limited to local spalling
calculated stress due to the prescribed seismic forces.
that is readily repaired.
If the floor levels are
significantly offset and the bearing walls or columns
g.
Separation of Structures.
In past
of either building are vulnerable to hammering
earthquakes, the mutual hammering received by
action from the rigid floor systems of the other
buildings in close proximity to one another has
building, the potential damage is unacceptable. In
caused significant damage.
The simplest way to
such instances, either adequate clearance must be
prevent damage is to provide sufficient clearance so
provided, or the vulnerable structural components
that free motion of the two structures will result.
must be strengthened or provided with back-up
The motion to be provided for is produced partly by
elements to avoid the possibility of structural failure.
the deflections of the structures themselves, and
h.
Seismic Joints.
partly by the rocking or settling of foundations. The
Junctures between distinct
gap must equal the sum of the total deflections from
parts of buildings, such as the intersection of a wing
the base of the two buildings to the top of the lower
of a building with the main portion, are often
building.
designed with flexible joints that allow relative
movement.
When this is done, each part of the
(1) In the case of a normal building less than
building must be considered as a separate structure
80 feet in height using concrete or masonry shear
that has its own independent bracing system. The
criteria for separation of buildings in Paragraph a
walls, the gap shall be not less than the arbitrary rule
of 1 inch (25mm) for the first 20 feet (6.10m) of
above will apply to seismic joints for parts of
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