Owing to the natural defects of wood, structural timber is currently used with
conservative safety factors. This study investigates the use of Carbon Fiber Reinforced Polymer
(CFRP) for improving the strength of structural timber. Four flexural test stages were carried
out, the modes of failure of the three specimens in each stage were studied to determine and
strengthen the suspected weak zone which caused the failure. It was found that the tensioned
fibers of ordinary timber girders normally fail first especially at the sections containing knots.
Using a strip of CFRP to strengthen tensioned fibers is a well known technology, but it will not
prevent a premature failure due to horizontal shear. A strength increase of 56% was reached by
the adaption of shear connectors in the form of screws. After treating tensile and shearing
strengths, still testing specimens showed failure at the compressed fibers. By enhancing the
compressed fibers with a steel strip, the prototype girders showed a remarkable increase in
flexural strength of about 175% compared with the ordinary wooden girders having the same
dimensions.