MULTI-SCALE COMPUTATIONAL SIMULATION OF PROGRESSIVE COLLAPSE OF STEEL FRAMES

[yanburak]

MULTI-SCALE COMPUTATIONAL SIMULATION OF PROGRESSIVE COLLAPSE OF STEEL FRAMES

ABSTRACT
Progressive building collapse occurs when failure of a structural component leads to the
failure and collapse of surrounding members, possibly promoting additional collapse.
Global system collapse will occur if the damaged system is unable to reach a new static
equilibrium configuration. The objective of this research is to identify and investigate
important issues related to collapse of seismically designed steel building systems using
multi-scale computational models.
Coupled multi-scale finite element simulations are first carried out to investigate the
collapse response of moment resisting steel frame sub-assemblages. Simulation results
suggest that for collapse resistant construction, designers should strive to use a larger
number of smaller beam members rather than concentrate resistance in a few larger
members and should specify ASTM A-992 steel rather than specifying generic steels.
Improved behavior can also be achieved by increasing the shear tab thickness or directly
welding the beam web to the column.
Using information gleaned from the sub-assemblage simulations, computationally
efficient structural scale models for progressive collapse analysis of seismically designed
steel frames systems are developed. The models are calibrated and utilized within the
context of the alternate path method to study the collapse resistance of multistory steel
moment and braced frame building systems. A new analysis technique termed
“pushdown analysis” is proposed and used to investigate collapse modes, failure loads
and robustness of seismically designed frames. The collapse and pushdown analyses
show that systems designed for high seismic risk are less vulnerable to gravity-induced
progressive collapse and more robust than those designed for moderate seismic risk.
Motivated by a number of deficiencies in existing ductile fracture models for steel, a new
micro-mechanical constitutive model is proposed. Damage mechanics principles are used
and a scalar damage variable is introduced to represent micro-structural evolution related
to micro-void nucleation, growth and coalescence during the ductile fracture process in
steels. Numerical implementation and parametric studies are presented and discussed.
Calibration and validation studies show that the proposed model can successfully
represent ductile fracture of steels.
Although the system studies in this dissertation focused primarily on in-plane collapse
response, the models and simulation methodologies developed herein can be extended in
future work to address the collapse resistance of three-dimensional models.

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