EFFECT OF SHEAR WALLS ON THE BEHAVIOR OF REINFORCED CONCRETE BUILDINGS UNDER EARTHQUAKE LOADING A THESIS SUBMITTED TO THE GRADUATE SCHOOL OF NATURAL AND APPLIED SCIENCES OF MIDDLE EAST TECHNICAL UNIVERSITY BY HAKKI GÜRHAN ÇÖMLEKOĞLU IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN CIVIL ENGINEERING DECEMBER 2009