Ayhan Irfanoglu

Multi-Criteria Optimal Structural Design Under Uncertainty

A general framework for multi-criteria optimal design is presented which is well suited for performance-based design of structural systems operating in an uncertain dynamic environment. A decision theoretic approach is used which is based on aggregation of preference functions for the multiple, possibly conflicting, design criteria. This allows the designer to trade off these criteria in a controlled manner during the optimization. Reliability-based design criteria are used to maintain user-specified levels of structural safety by properly taking into account the uncertainties in the modeling and seismic loads that a structure may experience during its lifetime. Code-based requirements are also easily incorporated into this optimal design process. The methodology is demonstrated with a simple example involving the design of a three-story steel-frame building for which the ground motion uncertainty is characterized by a probabilistic response spectrum which is developed from available attenuation formulas and seismic hazard models.

The NEEShub Cyberinfrastructure for Earthquake Engineering

The US Network for Earthquake Engineering Simulation (NEES) operates a shared network of civil engineering experimental facilities aimed at facilitating research on mitigating earthquake damage and loss of life. The NEEShub gateway was created in response to the NEES communitys needs, combining data, simulation, and analysis functionality with collaboration tools.

Istanbul at the Threshold: An Evaluation of the Seismic Risk in Istanbul

There is no convincing evidence indicating that future ground motion in at least two-thirds of Istanbul, Turkey, shall be less demanding than the ground motions that devastated the city of Düzce, Turkey, in 1999. Comparison of vulnerability indices calibrated for Turkish construction indicates that the structures of the buildings in Istanbul are no better than the structures of buildings in Düzce. On the basis of these arguments, we project that a future earthquake near Istanbul may cause severe damage or collapse approximately quarter of a million buildings. Leaving the vulnerable buildings as they are and organizing for emergency response is not an option for Istanbul.

Measures of the Seismic Vulnerability of Reinforced Concrete Buildings in Haiti

Following the 12 January 2010 Haiti earthquake, teams of students and faculty members from the United States and Haiti surveyed 170 reinforced concrete (RC) buildings in Port-au-Prince and Léogâne. This paper summarizes the survey results and compares them with results from a similar survey done after the 1999 earthquakes near Düzce, Turkey. The survey results demonstrate that the frequency of damage in RC buildings was higher in Haiti than in Turkey. This increased level of damage is consistent with practical screening criteria based on cross-sectional areas of building columns and walls. Based on these criteria, 90% of the structures surveyed in Haiti would have been classified as seismically vulnerable before the earthquake. Damage was more frequent in structures with captive columns. A two-tiered screening process is suggested to rapidly assess the vulnerability of scores of poorly built low-rise RC buildings in future earthquakes.

Performance of School Buildings in Turkey During the 1999 Düzce and the 2003 Bingöl Earthquakes

Several school buildings were surveyed in the disaster areas of the Marmara (17 August 1999, Mw =7.4), Düzce (12 November 1999, Mw =7.2), and Bingöl (1 May 2003, Mw =6.4) earthquakes in Turkey. Among them, 21 reinforced concrete buildings were found to have an identical floor plan. Lateral load resisting structural system consisted of reinforced concrete frames (moment-resisting frame) in 16 of the buildings and structural concrete walls integrated with the moment-resisting frame (dual system) in the remaining five buildings. The number of stories above ground in these buildings ranged from two to four. These school buildings provide a nearly ideal test of the effect of a single important structural characteristic on the performance of buildings with structural designs that are uniform in all other respects. Our observation is that the presence of structural walls improves the behavior of reinforced concrete systems drastically.

A High-Quality High-Fidelity Visualization of the September 11 Attack on the World Trade Center

In this application paper, we describe the efforts of a multidisciplinary team toward producing a visualization of the September 11 attack on the North Tower of New Yorks World Trade Center. The visualization was designed to meet two requirements. First, the visualization had to depict the impact with high fidelity by closely following the laws of physics. Second, the visualization had to be eloquent to a nonexpert user. This was achieved by first designing and computing a finite-element analysis (FEA) simulation of the impact between the aircraft and the top 20 stories of the building and then by visualizing the FEA results with a state-of-the-art commercial animation system. The visualization was enabled by an automatic translator that converts the simulation data into an animation system 3D scene. We built upon a previously developed translator. The translator was substantially extended to enable and control visualization of fire and of disintegrating elements to better scale with the number of nodes and the number of states to handle beam elements with complex profiles and to handle smoothed particle hydrodynamics liquid representation. The resulting translator is a powerful automatic and scalable tool for high-quality visualization of FEA results.

Using Numerical Simulations and Engineering Reasoning under Uncertainty: Studying the Collapse of WTC-1

: A series of numerical aircraft crash simulations and thermal behavior analyses were made at Purdue University to study the response of the World Trade Center Tower 1 (WTC-1) on September 11, 2001. The process included accuracy verification for the computational tools using available experiment data. Numerical models for the Boeing 767–200ER aircraft and the structural system for the top 20 stories of WTC-1 were developed for the simulations. A second aircraft model, simpler yet comparable in effect, was developed and used for a parametric sensitivity analysis. Results from these simulations and published by other researchers indicate that while the observed impact damage to tower exterior framing can be estimated accurately, the unseen impact damage to the core structure of the tower could not be estimated with high confidence. Although the computational tools helped in developing an understanding as to what might have happened as the aircraft penetrated and disintegrated into the structure, they were not able to reduce the uncertainty in the core damage estimate. However, reflecting insight from the behavior of the Pentagon building under the impact loads it received on the same day and studying the effects of elevated temperature on mechanical properties of steel in light of experimental data, the uncertainty in the core structural damage estimate was found to be of negligible importance with regards to the ultimate fate of the tower. It is demonstrated that through use of numerical simulations and engineering reasoning, a dominant factor in the collapse of the tower could be proposed with confidence. It was the loss of fire-proofing in the tower core during aircraft impact that left the core vulnerable to ensuing thermal loads and resulted in the eventual collapse of the tower.

Evaluating the performance of distributed approaches for modal identification

In this paper two modal identification approaches appropriate for use in a distributed computing environment are applied to a full-scale, complex structure. The natural excitation technique (NExT) is used in conjunction with a condensed eigensystem realization algorithm (ERA), and the frequency domain decomposition with peak-picking (FDD-PP) are both applied to sensor data acquired from a 57.5-ft, 10 bay highway sign truss structure. Monte-Carlo simulations are performed on a numerical example to investigate the statistical properties and sensitivity to noise of the two distributed algorithms. Experimental results are provided and discussed.

Dominant Factor in the Collapse of WTC-1

The behavior of the World Trade Center Tower 1 on September 11, 2001 is studied in light of experimental data on the effect of elevated temperature on mechanical properties of structural steel. It is concluded that the damage inflicted by aircraft impact on the insulation of the core framing was the dominant factor in the collapse of the structure.

A Method for Extracting Building Empirical Capacity Curves from Earthquake Response Data

A method is presented for extracting empirical capacity curves from building earthquake response data. The method can be applied to buildings with acceleration response records from each floor to develop story empirical capacity curves assuming the building has flexible columns and rigid floors. The method can also be applied to buildings with acceleration response records from the roof and ground to develop a fundamental mode empirical capacity curve. The method relies on extracting the restoring force and relative displacement of the system by removing damping force, considered as equivalent viscous damping, from the inertial response, using a proposed viscous damping identification procedure. The method is demonstrated using data from a small-scale, three-story experimental model subjected to strong base motion.