| Summary: | Concrete tilt-up panels are commonly used in constructing lower-rising buildings in
North America. Large window openings are sometimes required in the wall panels on the
whole side of tilt-up buildings. Subject to severe earthquake, such a tilt-up panel is
expected to experience inelastic deformation that has to be controlled. The relevant
clause 21.7.1.2 is presented in the draft 2004 Canadian concrete code CSA Standard
A23.3 regarding the displacement demand of concrete panel, which says: "Tilt-up Wall
Panels shall be designed to the requirements of Clause 23 except that the requirements of
Clause 21.7.2 shall apply to wall panels with openings when the maximum rotational
demand on any part of the panel exceeds 0.02 radians." The aim of this research is to
develop a simple method to estimate the inelastic displacement demand of tilt-up wall
panels with openings accounting for the influence of a flexible metal roof. The tilt-up
panel with openings is modeled as a static frame simply supported at the ground and the
roof is modeled as a simply-supported beam at the tilt-up walls. The first mode of the
wall is assumed to be dominant over all other modes, and the wall panel can be idealized
as a single degree of freedom system with equivalent stiffness and concentrated mass.
And also, the first mode of the roof is assumed to be dominant over all other modes, so
that the roof can be idealized as a single degree of freedom system with equivalent
stiffness and, concentrated mass. Hence, the lateral force resisting system in a typical tiltup
building is modeled as an idealized 2 degree of freedom system. The properties of
typical tilt-up panels and metal roofs commonly used in the lower mainland of British
Columbia are investigated, and the possible range of stiffness ratios and mass ratios
between wall panel and roof are presented. The range of the stiffness ratios and the mass
ratios is used in this research.
Program CANNY is used to perform simulations on computer with the idealized 2-DOF
system. Total five earthquake records are used as excitations to the testing system. Three
of them are modified to fit Vancouver acceleration spectrum of NBCC 2005, and two of
them come from City of Los Angeles and Seattle. A l l of them are modified so that the
earthquakes used in this research have a 2% probability of exceedance in 50 years.
The deformation of metal deck diaphragm developed by physical tests is studied. The
severe pinching of the testing deck after it yields is realized to be critical over all other
nonlinear dynamic responses. Heavy Pinching creates a small area enclosed by each
force-displacement cycle of deck, which indicates very limited energy dissipation by
deck yield. So, pinching of metal deck is the most important factor considered in the
selection of hysteresis model for the nonlinear metal roof.
The simulation starts with linear elastic 2-DOF system. The yield strength of wall or roof
used in the simulation of nonlinear 2-DOF system is determined by dividing the
maximum force of wall or roof in the corresponding linear system by the force reduction
factor (2 for concrete tilt-up panel). The simulations include 2 stages. During the first
stage of test, the various factors that may affect the dynamic response of system,
particularly the total elastoplastic displacement demand of tilt-up wall, are investigated.
The parameters that were investigated include the force reduction factor of wall, the
ductility of roof, the stiffness ratio of wall to roof, the mass ratio of roof to wall, the wall
stiffness, the earthquake record. The equal displacement principal is verified for the
current 2-DOF system by running simulations.
After first stage of simulations, an important discovery is presented, which is the roof
drift or the roof force is reduced proportional to the force reduction of tilt-up wall panels
due to the yield of wall panels. A simple formula is developed to estimate the maximum
inelastic wall displacement demand according to the above discovery and the equal
displacement principal. In the second stage of simulations, the formula is confirmed using
the inputs derived from practical wall and roof. The linear solution of the corresponding
2-DOF system is presented using spectral acceleration of Code NBCC and mode
extraction. The total elastic roof displacement and roof drift relative to wall with the
corresponding linear system are needed to estimate the inelastic wall displacement
demand in the nonlinear system. The thesis ends with summaries and conclusions of the
research and suggestion for further work. === Applied Science, Faculty of === Civil Engineering, Department of === Graduate
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