Assessment of the Effect of Size of Diaphragm Discontinuity (Opening) on the Rigidity of Diaphragm and Distribution of Lateral Load to the Lateral Load Resisting Element
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Date
2013-07
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Addis Ababa University
Abstract
Earthquake - resistant structures are provided with lateral and vertical seismic force –
resisting systems capable of transmitting inertial forces from the location of masses
throughout the structure to the foundations. Floor and roof diaphragms play a key role in
distributing earthquake-induced loads to the lateral load resisting systems. Continuity and
regular transitions are essential requirements to achieve adequate load paths. Floor
diaphragm that has a large opening is likely to be inefficient in distributing seismic loads to
the vertical elements.
Design codes like UBC-97 specify that diaphragms having cut out or open areas greater than
50 percent of the gross enclosed area of the diaphragm are affected by diaphragm
discontinuity[11]. However, there are different cases where this provision can be
unsuccessful. In order to investigate the effect of diaphragm discontinuity on the response of
a structure, different parametric studies have been carried out. In the parametric studies,
story height, shear wall width, number of stories, number of bays, shape of diaphragm
opening, diaphragm opening size, span length and opening location in stories are taken as
parameters.
The study proceeded by assessing the effect of diaphragm discontinuity/opening on response
of a structure like diaphragm rigidity, story drift, distribution of lateral load to lateral force
resisting element and natural vibration period for each parametric study listed above. The
study has shown that the rigidity of a slab does not only depend on the opening size, but
rather depend on the stiffness of vertical elements, number of stories, aspect ratio of the slab
dimension and shape of diaphragm opening.
Master’s Thesis Effect of Diaphragm Discontinuity
Structural Engineering iv AAU
The investigation has shown that the code provision relating diaphragm rigidity to opening
size is not always satisfied.
Key words: diaphragm discontinuity, opening, diaphragm rigidity, actual diaphragm
stiffness, rigid diaphragm, flexible diaphragm, stiffness, story drift, lateral force distribution,
period
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Keywords
diaphragm discontinuity; opening, diaphragm rigidity; actual diaphragm stiffness; rigid diaphragm; flexible diaphragm; stiffness; story drift; lateral force distribution; period