KEC Conference Seismic Strengthening of Intze Type RC Elevated Water Tank by Jacketing: A Pushover Approach Hariram Rimal Department of Earthquake Enginering IOE Thapathali Campus Kathmandu, Nepal [email protected]Abstract— Earthquake is one of the natural calamities that produces the vibration to the ground which cause to produce most destructive forces on earth, and have potential to cause damage to lives and lifeline facilities. Elevated storage reservoir need to be functional even after the major earthquake event. During past earthquakes elevated storage tank experience damage or collapse all over the world. This paper presents nonlinear static analysis (Pushover Analysis) to evaluate seismic demand for 600 m3 capacity of intze type elevated water tank at zone V, soil type III in reservoir full, reservoir 60% full and reservoir empty condition. This gives the plastic hinge formation and plots the total base shear verses top displacement curve, which is known as ‘capacity curve’ of the structure. The analysis is performed using CSI SAP2000 V17 software package to evaluate base shear demand and performance point. The initial structure consisting of inadequate frame staging system and study is focused on column jacketing and braces replacement technique of retrofit and then base shears, fundamental time periods and performance points are compared. Final structure after retrofit is safe in major seismic event as it have performance point base shear greater than design base shear and all the column and braces hinges are at Immediate Occupancy (IO) performance level at Design Base Earthquake (DBE). Keywords— Column Jacketing, Capacity Curve, Performance Point, Pushover analysis, DBE, Intze type Elevated water tank. 1. INTRODUCTION Earthquake is known to produce one of the most destructive forces on earth. It cause damage to man- made structures, like Buildings, Chimneys, Towers and Public Infrastructures like, Bridge, Roads, Dams and Irrigation structures, Water supply and Sewerage systems, Telecommunications systems, Power Plants Industries, Life line systems etc. The earthquakes are also known to cause landslides, liquefaction, slope-instability and damage to earth and rack structures. The earthquake causes loss of life and property and shakes the moral of people. Elevated storage reservoir is the very important component of water distribution system for any country therefore it is necessary to remain function even after the major earthquake event. Elevated reservoirs are constructed in order to distribute water in the gravity flow in the distribution network. Typically Department of Water Supply and Sewerage (DWSS) and other water distribution agencies construct the Intze type RC reservoir as the RC elevated water reservoir in Nepal. Intze type RC water tank are quite susceptible to seismic forces due to their basic configuration consisting of large mass concentrated at the top with relatively slender supporting system. The poor seismic performance of many elevated water tanks was observed during past major earthquakes due to the inappropriate structural design of framing system and joints, low overall strength and ductility. Present study is primarily focused on understanding seismic behavior and performance characteristic of elevated water tank using a non-linear static analysis approach: a pushover approach. Study assumes all the components above the staging like top ring beam, tank wall, bottom ring beam, conical wall, top and bottom spherical domes are intact and the vulnerable part is the staging. And hence the focus of study is towards the seismic strengthening of the staging i.e. columns and braces using RC jacketing. Three cases; reservoir full case, half full case and empty case are modeled in SAP 2000 v17 and analyzed. 2. METHODOLOGY In the present study, two cases were separately analyzed one is the structure before retrofitted and another is the structure after retrofitted with column and braces jacketing. For each cases; three conditions i.e. reservoir full, partially full and empty were analyzed in SAP 2000 v17 software. Hydrodynamic forces exerted by liquid on tank wall shall be considered in the analysis in addition to hydrostatic forces. These hydrodynamic forces are evaluated with the help of spring mass model of tanks. 2.1 Spring Mass Model for Seismic Analysis: When a tank containing liquid vibrates, the liquid exerts impulsive and convective hydrodynamic pressure on the tank wall and the tank base in addition to the hydrostatic pressure. In order to include the effect of hydrodynamic pressure in the analysis, tank can be idealized by an equivalent spring mass model, which includes the effect of tank KEC Conference 2021, April 18, 2021 “3 rd International Conference On Engineering And Technology” Kantipur Engineering College, Dhapakhel, Lalitpur, Nepal ISBN 978-9937-0-9019-3 2021 148
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KEC Conference
Seismic Strengthening of Intze Type RC Elevated Water Tank by Jacketing: A
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