Natural Seismic Protection Properties of Historical 'Walled Obelisk' Structure in Istanbul: Modeling-Numerical Approach

The “Walled Obelisk” is a 32.77-meter high, 2x2 meter mean square, rough-cut limestone monument that is becoming thinner to the four-sided hill. This monument is in a very sensitive seismic region of the World-Istanbul and remains intact from the time of its construction (approximately tenth century) to the present despite all seismic activity during that time. The current study extracts and investigates a mathematical model of the monument, which reveals that support of the structure incorporates a “natural seismic isolator” that demonstrates behavior similar to current used lead-core rubber-bearings isolator (LRB). The total height of the “natural seismic isolator” is 3.44 m. and consists of three–steps of rough-cut limestone and a massive marble stone that forms four sliding surfaces bonded with Horasan mortar. The components of the “natural seismic isolator” form four sliding surfaces and appear to function similar to LRB’s combined layers of steel plates and hard rubber. The massive marble stone appears to function like the lead cylinder core of the LRB. The “natural seismic isolator” demonstrates fully plastic behavior and differs from the LRB by maintaining the monument’s upper part in equilibrium during earthquake excitation, which also varies near zero equilibrium. During this study’s comparison of the isolator’s use of the expression, “similar” is frequent used in this meaning, and the comparison uses a fixed base model of the monument that cannot reciprocate during recovery from earthquakes over the 1000-year history. The proposed model of “natural seismic isolation” from historical experience (for this monument, 1000 years), suggests that the easily constructed natural isolator requires no special maintenance, and is suitable for modern structures in seismic regions.