Dr. Arunachalam Rajaraman Profile

Dr. Arunachalam Rajaraman

Visiting Professor

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Publications (2)

Proceedings Article | 17 May 2005 Paper

Adaptive systems for truss and tower systems

T. Rengaraja, B. Nagabhushana Rao, A. Rajaraman

Proceedings Volume 5765, (2005) https://doi.org/10.1117/12.601551

KEYWORDS: Actuators, Control systems, Sensors, Telecommunications, Failure analysis, Earthquakes, Smart structures, Structural engineering, Structural design, Feedback control

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Truss and tower systems are widely used in variety of applications ranging from industrial structures to space stations. Such systems are normally designed for specified loads and by using respective codes. But in certain cases, they may be subjected to loads over the design values due to earthquakes of higher intensity, cyclones or even man-made disasters like terrorist attacks. Then a need arises to protect these systems, if they serve lifeline activities, through some inherent means; and this paper focuses attention on one such aspect. The objective is to provide a "smart control", which comes into effect only when the specified loads are exceeded by certain margins.[3] To demonstrate the introduction of smartness, a three-dimensional, three-panel tower system is chosen. Actuators, which activate corrective control to externally applied forces at the nodes of the truss, are provided on the members of the truss. The control forces within an active control system are typically generated through actuators based on feedback information from the measured response of the structure. The measured responses are monitored by sensors, which based on a pre-determined control algorithm, apply appropriate control signal for operation of the actuators. The generation of control forces requires external power leading to an active control system. Such a self correcting structure can be termed as smart or adaptive structure. This paper focuses on providing in-built smartness to handle both force and deformation when unanticipated loads up to 100 percent increase over a short duration act on these systems. Analysis is made for loads at the rate of 1.25,1.5,1.75 and 2 times the design load on the tower. For each of these loads, the example highlights how suitable control forces are generated and how the system under combined action of unanticipated and control forces balance in such a manner as to keep the structural integrity during short duration unanticipated loads.

Proceedings Article | 14 October 2003 Paper

Design smartness for tackling unanticipated loads

V. Badari Narayanan, C. Natarajan, Arunachalam Rajaraman

Proceedings Volume 5062, (2003) https://doi.org/10.1117/12.514756

KEYWORDS: Structural design, Failure analysis, Bridges, Statistical analysis, Radon, Structural engineering, Smart materials, Composites, Safety, Information operations

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With present day scenario on enviornment and living, unanticipated loads from natural and man-made causes are on the rise, defying any rationality or scientific reasoning for anticipation. This aspect, coupled with the interest in creating slender and sleek structural systems, has assumed greater significance in designing structures with 'smartness' -- either in-built or externally activated or through evolution to a different configuration -- for tackling loads which do not get bracketed in conventional or limit state approaches. The definition of smartness under these circumstances can be termed as the ability to carry unanticipated loads over and above the designed one. Although the design methodology is confined within the boundaries of codal and functional requirements, a "buffer" needs to be built in the design so that an extra reserve is available over and above that prescribed by normal approach. This might seem misleading and here only the present day computing methods provide the turn-around by shifting the paradigm from "design-for-requirement" to "requirement-from-designs," an Object Oriented Approach. Thus the focus on present paper is on choosing from different designs to satisfy "buffer requirements" to bring in "smartness" in the design choice. Reinforced concrete section under bending is the emphasis to highlight this aspect, even though the concept is expandable. For a given span, and design/ultimate moment, sections are chosen to provide buffer and compared with conventional designs. Nonlinear behavior is modeled so that failure state is kept as the endpoint. From the studies it is observed that for a given span, moment -- either ultimate or design state -- and given strengths, number of "smart designs" with buffer indications can be generated to satisfy different criteria. This is illustrated with some examples for a typical span and given external moment, modeling either a bridge section or part of a frame member. It was also observed from the studies that there is no unique design that satisfies all parameter simultaneously. A section that performs well in terms of cost and weight may yet fail in terms of buffer or utilization of steel upto its limit. Whereas a section that performs moderately in every one of the parameter may still be a better option. Depending upon the requirement, weightages for performance with respect to resisting moment, cost weight and additional buffer capacity must be specified. The section that best satisfies all the above criteria could be chosen as the ideal section. Section design done by varying other parameters such as grade of steel and concrete can also be studied. Strain hardening in steel can also be investigated to arrive at the greater carrying capacity of the sections. For example, it may even be possible for a structure to be designed purely for dead load and live load. But inherent smartness can be induced to take care of seismic loads either partly or even completely.

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