NUI Galway – UL Alliance First Annual ENGINEERING AND - ARAN ...

Seismic Design of Concentrically Braced Steel Frames and Dual Systems with
Vertical Irregularity
Suhaib Salawdeh 1 & Jamie Goggins 2
National University of Ireland - Galway
1 Suhaib.Salawdeh@nuigalway.ie 2 Jamie.Goggins@nuigalway.ie
Abstract
Analytical model of concentrically braced steel
frames (CBFs) with rectangular hollow section
bracings is studied and validated by experimental data
(pseudo dynamic cyclic tests for braces and shake table
tests for one-story one-bay CBF). Direct displacement
based design methodology is being developed for CBFs
and dual systems with vertical irregularities with many
different configurations and validated by non-linear
time history analysis (NLTHA).
1. Introduction
In any seismic area, every structure should be
designed to withstand the applied seismic forces in the
event of seismic activity to avoid both human and
economic losses. These seismic forces result directly
from the motion of the ground on which the structure
rests. All structures should be designed with an
adequate capacity to dissipate energy induced from this
ground motion without substantial reduction of its
overall resistance against horizontal and vertical
loading. The magnitude and distribution of lateral
forces and displacements resulting from ground motion
is influenced by the characteristics of the ground and
the properties of the structure. These lateral loadings
induced by the earthquake can be resisted by using
lateral resisting frames, walls or dual systems. This
research will concentrate in studying and developing a
design methodology for concentrically braced frames
and dual systems with vertical irregularity.
2. Concentrically braced frames (CBFs)
The study of the performance of CBFs is started by
studying the behaviour of the brace element, which is
the main element in this system that dissipates energy
during seismic actions. The brace element, which is
destined to carry reversal axial forces, may yield in
tension, buckle in compression or may fracture due to
the demand cycles it is expected to endure during
seismic actions. A robust numerical model for braces,
which are cold-formed square and rectangular structural
hollow sections, is developed by calibrating the
numerical model for braces with pseudo-dynamic cyclic
tests carried out by Goggins [1]. This work has been
submitted for publication in [2]. This numerical model
for the brace elements is then advanced for a singlestory
single-bay frame by comparing its performance
using shake table tests done by Goggins [1].
Preliminary findings are given in [3]. The validated
brace element model is then used to predict the
149
performance of multi-storey structures. Displacement
Based Design (DDBD) procedure [4] for CBFs is then
developed using the experimental data and non-linear
time history analysis.
3. Dual systems with vertical irregularity
Direct displacement based design methodology is
developed for dual systems with vertical irregularity.
Many configurations are studied, including a dual
system with CBF core and irregular steel moment
resisting frame that possess a vertical irregularity
associated with setbacks up the vertical axis of frame.
Another dual system is then investigated by using the
same irregular moment resisting frame but with a
concrete core. Furthermore, a dual system with a both
concrete core and irregular concrete frame is studied.
4. Conclusion
An analytical model for brace members by using
pseudo-dynamic cyclic tests is developed [2]. This
analytical model is advanced for single-degree-offreedom
CBFs by using shake table tests and NLTHA
then developing a DDBD design procedure [5]. DDBD
procedure is then developed for multi-degree of
freedom system CBFs and validating it using NLTHA.
In the second part of this research a DDBD
methodology is developed for dual systems with
vertical irregularity by using three different
configurations- CBF core and vertical irregular steel
moment resisting frame, a concrete core and vertical
irregular steel moment resisting frame, and a concrete
core and vertical irregular concrete moment resisting
frame.
Acknowledgement
The first author gratefully acknowledges the fellowship
provided by the COEI, NUI Galway.
References
[1] Goggins, J., Earthquake resistant hollow and filled steel braces.
2004, Trinity College, University of Dublin: Dublin.
[2] Salawdeh, S. and J. Goggins. Analytical model for the seismic
response of cold formed steel braces. in The 6th International
Conference on Thin Walled Structures. 2011. Timisoara, Romania.
[3] Salawdeh, S. and J. Goggins, Validation of a numerical model for
use in non-linear time history analysis of CBFs in The Eighth
International Conference on Structural Dynamics EURODYN2011.
2011: Leuven, Belgium.
[4] Priestley, M.J.N., G.M. Calvi, and M.J. Kowalsky, Displacement-
Based Seismic Design of Structures. 2007: , IUSS Press, Pavia, Italy.
[5] Goggins, J. and S. Salawdeh, Direct Displacement-Based Seismic
Design of Single Storey Concentrically Braced Frames, in 6th
European Conference on Steel and Composite Structures,
Eurosteel2011. 2011: Budapest, Hungary.