IMPROVEMENT OF PUNCHING STRENGTH OF FLAT PLATES BY USING CARBON FIBER REINFORCED POLYMER (CFRP) DOWELS A THESIS SUBMITTED TO THE GRADUATE SCHOOL OF NATURAL AND APPLIED SCIENCES OF MIDDLE EAST TECHNICAL UNIVERSITY BY HAKAN ERDOĞAN IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN CIVIL ENGINEERING DECEMBER 2010