SHEAR LAG OF STEEL BOX GIRDERS WITH LONGITUDINAL STIFFENERS BY TANPITCHA PUMPHAKA A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE (ENGINEERING AND TECHNOLOGY) SIRINDHORN INTERNATIONAL INSTITUTE OF TECHNOLOGY THAMMASAT UNIVERSITY ACADEMIC YEAR 2018 Ref. code: 25615922040208FTI