K. Sathish Kumar

DYNAMIC RESPONSE EVALUATION OF A FRAMED TYPE TURBO-GENERATOR FOUNDATION INCORPORATING DYNAMIC MODULUS AND OPERATING SPEED VARIATIONS

Framed type foundation structures supporting turbo-generator machinery in a power plant have stringent vibration limits to ensure proper functioning of turbine generators without any breakdown. Current dynamic analysis methodology for such dynamically sensitive structures involves modal synthesis considering a single value of operating speed for the machinery and a uniform dynamic modulus for the frame material, which cannot be realized in site conditions. Such variations in the dynamic modulus across the whole structure and running speed of the machinery during normal operation have a profound impact on its dynamic performance which may result in alarmingly increasing amplitudes leading to subsequent breakdown of the machinery. A new methodology is outlined that combines the effects of the two variations by way of considering an enhanced range of speeds on either side of the operating speed for the modal synthesis process. This study shows the effects of variations in the dynamic modulus and operating speed on the peak dynamic response of a typical framed turbo-generator foundation structure. The modal synthesis process adopted in the study includes the significant modes in the sub-resonant range and a band of modes around the operating speed to obtain the peak response of the framed structure.

Seismic Vulnerability Assessment of Open Ground Storey Buildings

Open Ground Storey (OGS) in multistoried buildings is meant for a parking space within a building plan. These buildings have reduced stiffness at the ground storey due to absence of in-fill walls. The abrupt change in the stiffness of the open ground storey compared to the stories at the top result in huge seismic displacement demand, to be borne by the ground storey itself. Conflict demand between seismic safety and functional requirement, and moreover huge number of OGS buildings in urban areas in India, necessitates the seismic vulnerability assessment of OGS buildings. In the present paper, a simplified procedure to assess the level of severity of OGS building is developed using plastic hinge concept. The simplified procedure is validated with the shake table experiment conducted on three-storey model OGS building. The simplified procedure will help to identify the urgency for repair and rehabilitation of OGS buildings.

Semi-active Control of Structures Using Magnetorheological Elastomer-Based Seismic Isolators and Sliding Mode Control

Control of structures against the earthquake forces had been a keen topic of interest in research for past decades. Isolator being one such system which works passively to decouple the structure from the earthquake forces has many disadvantages such as large displacements, poor adaptability to varying ground conditions. Recently, magnetorheological (MR) elastomer-based base isolation systems have been actively studied as an alternative smart base isolation systems because MR elastomers are capable of adjusting their modulus or stiffness depending on the magnitude of the applied magnetic field. In this paper, MR elastomer-based isolators have been used to semi-actively control the structure subjected to earthquake excitation. Sliding mode control algorithm has been investigated and used effectively to control the structure semi-actively.

Seismic Response Measurement of an Under‐Water Model Through High Speed Camera and Feature Tracking

Shake table testing is a viable validation tool for bench-marking the analytically computed seismic response of under-water structural models with fluid–structure interaction effects. Conventional displacement sensors like LVDTs (linearly variable differential transformer) cannot be used for under-water response measurements as they require a stationary platform near the measurement point as a reference. This rather limiting application of LVDTs in several situations warrants the use of high speed camera as a potential measurement tool. This article presents the vision based displacement measurement of an under-water model tested on a shake table. High speed video camera is used to record the motion during shaking. The video images are processed using a special motion tracking algorithm and displacements are measured. The sloshing effect of water on the test model and their free vibration at the end of the shaking are studied to calculate natural frequency and damping. Vital information on the allowable under-water motion of the test model is obtained and discussed.

Seismic performance of polymer modified concretes in flexure-modelling

Considerable research has been carried out in the recent years in the development of models to simulate the inelastic responses of reinforced concrete elements. The enhancement of ductility and the post-peak behaviour are of special interest for the seismic design of structures. Polymer modified fibre concretes are found to be ideal for seismic application with its inherent structural characteristics. An experimental investigation has been undertaken to understand the flexural behaviour of the polymer-modified fibre concrete modified with natural rubber latex. The results are compared with the response of normal strength concrete beam. Analytical modelling of the beams were carried out in a user friendly finite element software to accurately predict the monotonic behaviour of the beams which is considered to be the envelope of cyclic curve. The strains developed were found and are compared with the theoretical results.