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Szuladzinski G.,Analytical Service Pty Ltd. | Szamboti A.,Aerospace Industry Performing Structural and Thermal Analyses and Design | Johns R.,Langara College
International Journal of Protective Structures | Year: 2013

This article elaborates on variables associated with the collapse of the North Tower of the World Trade Center. The previously published quantifications of inertia, column capacity, and the assumptions related to the beginning of downward motion, are examined and corrected. The reasons for false conclusions reached in several previous analyses are presented.


Szuladzinski G.,Analytical Service Pty Ltd.
International Journal of Protective Structures | Year: 2014

In the analyses of the WTC collapse carried out so far the kinetic energy of fuel of the impacting aircraft was accounted for, but the chemical energy content was not. This paper addresses the problem by means of analysis as well as well as Finite Element simulation. The effect of fuel detonation is evaluated with only 10% of fuel acting in this manner. The fuel in the model was distributed in the impact area according to what is known from the official reports. The extensive damage resulting from this, as demonstrated below, appears to be a strong contributing factor to what happened afterwards. The attention of the reader was drawn to the fact that at present the official reports are unable to explain the mechanism of collapse, when attributing those to the fires burning after the impact.


Szuladzinski G.,Analytical Service Pty Ltd
International Journal of Protective Structures | Year: 2012

The objective of this work is to create a set of engineering formulas approximating structure response to a loss of one of supporting columns. Those expressions are created for the beam mode, arching mode, and the cable mode of a beam losing the column support. The correction coefficients are derived on the basis of experimental results. To assess the design load for an isolated beam subjected to a test, it is proposed to use the safety factor as a guide, the factor that can easily be calculated for any real project. The response to dynamic column removal is quantified and the Dynamic Factor is determined. This is helpful in the initial assessment of RC elements. The proposed column failure mechanism has two phases; the first one can be slow, but the second is usually fast, because of the altered configuration. The energy criterion presented provides another check of the capacity of a beam to withstand a column removal.


Szuladzinski G.,Analytical Service Pty Ltd
International Journal of Structural Engineering | Year: 2012

The circumstances leading to the collapse of the WTC Towers were described in numerous publications before but quantification of possible mechanisms published so far remains very limited. The basic observation is that columns of a 110-story building were weakened, over a relatively short segment of an upper part of the structure, to a degree where they were unable to support the building above them. As the upper part began to descend, successive buckling of columns caused flattening of the stories below. The process was presumably driven by the action of gravity until a complete destruction of the building. This article concentrates on progressive collapse of the core of the building. Several mechanisms are considered and quantified, to assess whether they offered a plausible explanation. One of the criteria used was whether the potential energy available was sufficient to cause the demolition in the assumed manner. The calculated duration of the event versus the available observation is regarded as the main criterion to qualify the postulated collapse mode. The details presented here are in reference to the North Tower. Some relationships presented here are also useful for a progressive collapse analysis of reinforced concrete structures. Copyright © 2012 Inderscience Enterprises Ltd.


Szuladzinski G.,Analytical Service Pty Ltd
International Journal of Protective Structures | Year: 2012

Over the last few decades multistory buildings have been designed using gradually stronger and stronger concrete. The obvious advantage of increasing the material strength is the ability of the designer to reduce section area of some members without sacrificing strength. This paper takes a broader view in that it examines a number of mechanical characteristics of a structural member that had been thinned-down because of stronger concrete. Apart from nominal strength there is the elementary quantity of elongation at failure, which limits the deflection that can be attained. Other properties of concern are: Natural frequency, deflection under static and dynamic lateral loading, dynamic bending moment response under lateral loading and, above all, the amount of energy absorbed prior to the beginning of failure. The importance of the latter comes from the fact that when some elements are subjected to extreme loads, they are certain to fail, but the amount of energy absorbed by their destruction may be decisive for the survival or collapse of the entire structure. A distinction is made between prescribed lateral loading and a prescribed pressure applied. The paper uses simplified methods of comparison, which makes it possible to reach clear conclusions related to the advantages and disadvantages of employing high-strength concrete.


Szuladzinski G.,Analytical Service Pty Ltd.
Journal of Engineering Mechanics | Year: 2014

When a dynamic point load is applied laterally to a beam, the deflection gradually spreads over time until the entire beam length is affected. The determination of the early stages of response presents substantial mathematical difficulties. The normal-mode superposition is made awkward by the fact that the number of modal components necessary to get a reasonably accurate answer increases as the time interval of interest decreases. This paper presents a different solution based on a dominating flexural wave, which allows one to formulate compact and transparent expressions. © 2014 American Society of Civil Engineers.

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