SEISMIC RESPONSE OF EQUIPMENT AND SERVICES IN INDUSTRIAL BUILDINGS

Abstract

In Industries, the cost of equipment is near about or greater than the cost of building itself. Hence earthquake resistant or safe design of equipment is as important as the safe seismic design of building. Ground response spectrum is used as the governing hazard parameter for seismic safety of building, similarly floor response spectrum is used for safety evaluation of equipment and their connection with floor. In case of services, the inter-storey drift is the key design parameter for seismic safety. Thermal power plants are unique and quite different structures than the normal buildings. Further, these contain drift sensitive services like heavy pipe lines, cladding, etc. and acceleration sensitive equipment and machines like low pressure and high pressure heaters, Turbo Generator, Deaerator, etc. which are critical during earthquake as damage to the these elements causes a significant loss. Variation of peak floor acceleration (PFA) along the height serves as an important parameter to measure the earthquake response of the structure for the design of secondary systems. Different codes like Eurocode 8, Indian draft code, SIA 261 consider the variation of maximum peak floor acceleration along the height as linear, which is valid only if the first mode of the structure is considered. Participation of higher modes can significantly change the variation of PFA with height. The floor response (de-coupled) approach is valid only in case of small equipment. In case of heavy machinery having significant weight in comparison with the building, the floor response approach does not provide a realistic estimation of the forces acting on the machines. However, these machines are generally rigid and their frequencies of vibration can be considered sufficiently different from the building frequencies of vibration. Hence a special form of coupled analysis is performed in the thermal power plants where the mass of the heavy equipment is included in the structure, and the response of the nodes at connections with equipment is used to estimate the forces in connections. In this project different codes provision for finding the forces in the secondary system is reviewed and some suggestions are made for the improvement of the existing code. A real under construction thermal power plant’s main power house building of NTPC Gadarwara is modelled in SAP 2000 software. Structual elements like beams, bracing, girder, slab, columns are modelled using proper finite elements iv tools (i.e. beam element, shell element) . Connection details like moment connection, shear connection are modelled as rigid and pinned connection. Preliminary analysis like modal analysis, p-delta analysis are done to check structure for any defects A site specific response spectrum is prepared for the given site by probability seismic hazard assessment by IIT Roorkee and for the same site specific response spectrum a set of seven spectrum compatible time history is generated and applied at the base of the structure. Finally the response of the deaerator is found out using the time history generated from the response spectrum. As the mode shape of the industrial building are complex and includes significant role of torsion also so to see the response of the structure the variation of Peak floor acceleration (PFA) along different column is studied. The effect of variation of response from the time histories generated from a single response spectrum is also studied.