In recent years, there has been an increased interest in strengthening and repairing existing concrete structures, and this process requires a vast monetary investment. Therefore, today there is a need to find an appropriate and economical method to strengthen and to repair existing concrete structures. The purpose of this study is to perform experiments to understand the behavior of beams under flexure by attaching external clamps, which will behave like stirrups to improve their shear strength. This current paper reports on the study of 13 beams with differing levels of shear reinforcement deficiency. These beams were strengthened by external clamps and then experiments were performed on two groups in which the ratio of the shear span to the effective height of the beam is equal to 4.5 and 3.3 (M/Vd=a/d). Experimental results showed that this strengthening method is effective and the specimens' strength, rigidity and ductility were improved. Clamps controlled any shear cracks and they also helped to improve ductile flexural behavior of the members. © 2003 Elsevier Science Ltd. All rights reserved.