Stefan Szyniszewski

Agent-Based Simulation of Building Evacuation after an Earthquake: Coupling Human Behavior with Structural Response

AbstractThe safety of building occupants during and immediately after disasters, such as a major earthquake, is highly dependent on the way in which people interact with the damaged physical environment. While there are extensive studies on evacuation from undamaged structures and on structural behavior under seismic and other hazards, research on the influence of building damage on human evacuation behavior is limited. This study presents a framework by which models for buildings and human behavior can be coupled to analyze the dynamic influences of building damage on the evacuation process. The framework combines nonlinear dynamic finite-element modeling of structures, probabilistic modeling of damage, and agent-based modeling of human occupants to investigate the behavior of people as they interact with each other and with their dynamically-deteriorating environment as they attempt to evacuate the building. A case study is presented for a typical three-story commercial office building subjected to the ...

Dynamic energy based method for progressive collapse analysis

Physics based collapse simulations of moment resisting steel frame buildings are presented with an emphasis on the development of energy flow relationships. It is proposed that energy flow during progressive collapse can be used in evaluation of moment resisting, steel frame building behavior and specifically, localized failure. If a collapsing structure is capable of attaining a stable energy state through absorption of gravitational energy, then collapse will be arrested. Otherwise, if a deficit in energy dissipation develops, the unabsorbed portion of released gravitational energy is converted into kinetic energy and collapse propagates from unstable state to unstable state until total failure occurs. The energy absorption of individual members provides very transparent information on structural behavior as opposed to oscillating internal dynamic forces in structural members. Therefore, critical energy absorption capacity is hereby proposed as a stable failure criterion in progressive collapse analysis. Energy flow quantification is shown to be readily available from the dynamic finite element simulations. The proposed dynamic, energy based approach to progressive collapse, provides insight and a simple yet robust analysis for producing structures capable of resisting abnormal loadings and/or unexpected hazards.

Probabilistic approach to progressive collapse prevention. Physics based Simulations

Physics based collapse simulations of moment resisting steel framed buildings are presented.Survival probability of a building occupant is proposed as a single scalar measure to quantify resistance to progressive collapse of a particular structure at hand. Practical procedure for the survival probability calculations by means of physics based simulations and theorem of total probability is shown in the paper. Simulations of structural response to the sudden removal of a key structural member have been carried out for a number of failure scenarios. Such analysis is at the forefront of civil engineering modeling because it involves material nonlinearities, large deflections, finite strains, and certainly requires dynamic analysis. Saving human lives in the case of abnormal loadings and/or unexpected hazards is equivalent to minimizing the area of collapsed floors. Such approach should also minimize the financial loss to a building owner.The area of collapsed floors can be extracted from the physics based simulations. It is proposed to quantify the goodness of design with the survival probability of a building occupant. Such single scalar measure provides an opportunity to employ optimization algorithms to produce the safest and the most economic structural design.

Effects of random imperfections on progressive collapse propagation

Progressive collapse is an increasing concern in the structural engineering community, especially after the collapse of the World Trade Centre Towers. While numerous papers have been published on the subject, the effects of random imperfections on failure paths have not yet been studied. The presented simulation study investigated the effects of random geometric imperfections on the formation of alternative paths after the removal of the first story column(s). Eccentricities and curvatures were introduced as independent random variables for each structural element. Gaussian distributions with means and standard deviations selected on the basis of a handbook of construction tolerances were applied to represent the real life imperfections. The selected, representative seismic building was repeatedly simulated under the same column(s) removal scenario with different imperfections randomly introduced in each simulation. The presented design exhibited competing failure modes. The dominant failure mode was observed in 80% of the simulations, while the secondary failure mode manifested itself in the remaining 20% of the simulations (the same column(s) removal scenario). The presented probabilistic study revealed that real-life imperfections may result in the alternate failure paths. Monte Carlo simulations shall be employed to detect such secondary load redistribution paths and/or collapse modes.

Damping of selectively bonded 3D woven lattice materials

The objective of this paper is to unveil a novel damping mechanism exhibited by 3D woven lattice materials (3DW), with emphasis on response to high-frequency excitations. Conventional bulk damping materials, such as rubber, exhibit relatively low stiffness, while stiff metals and ceramics typically have negligible damping. Here we demonstrate that high damping and structural stiffness can be simultaneously achieved in 3D woven lattice materials by brazing only select lattice joints, resulting in a load-bearing lattice frame intertwined with free, ‘floating’ lattice members to generate damping. The produced material samples are comparable to polymers in terms of damping coefficient, but are porous and have much higher maximum use temperature. We shed light on a novel damping mechanism enabled by an interplay between the forcing frequency imposed onto a load-bearing lattice frame and the motion of the embedded, free-moving lattice members. This novel class of damping metamaterials has potential use in a broad range of weight sensitive applications that require vibration attenuation at high frequencies.

Expected building damage using stratified systematic sampling of failure triggering events

Expected building damage is proposed as a measure of building performance against structural collapse. The proposed novel concept is illustrated with a case study of a typical steel framed building subjected to a bomb explosion and the resulting column removal. Stratified approach to systematic sampling was used to assign appropriate weights to sampled damage scenarios. Finally, an overall expected building damage resulting from randomly located explosions was analytically derived. The analytical expected damage gives a mean building failure as a function of the explosion reach. The presented expected damage is a scalar performance measure and thus it lends itself to a comparison of alternative designs. Expected damage function is a collapse signature of a given building that takes into account copiousness of explosion locations and feasible detonation magnitudes. Copyright

Dynamic Energy Balance Approach to Progressive Collapse Prevention

Physics based collapse simulations of moment resisting steel frame buildings are presented with an emphasis on the development of energy flow. It is proposed that energy flow during progressive collapse can be used in evaluation of moment resisting, steel frame building behavior and specifically, localized failure. If a collapsing structure is capable of attaining a stable energy state through absorption of gravitational energy, then collapse will be arrested. Otherwise, if a deficit in energy dissipation develops, the unabsorbed portion of released gravitational energy is converted into kinetic energy and collapse propagates from unstable state to unstable state until total failure occurs. The energy absorption of individual members provides very transparent information on structural behavior as opposed to oscillating internal dynamic forces in structural members. Therefore, critical energy absorption capacity is hereby proposed as a stable failure criterion in progressive collapse analysis. Energy flow quantification is shown to be readily available from the dynamic finite element simulations. The proposed dynamic, energy based approach to progressive collapse, provides insight and a simple yet robust analysis for producing structures capable of resisting abnormal loadings and/or unexpected hazards.