CFRP-Strengthening and Long-Term Performance of Fatigue Critical Welds of a Steel Box Girder

Abstract

Empa's research efforts in the 1990s provided evidence that a considerable increase of the fatigue strength of welded aluminum beams can be achieved by externally bonding pultruded carbon fiber reinforced polymer (CFRP) laminates using rubber-toughened epoxies over the fatigue-weak welding zone on their tensile flange. The reinforcing effect obtained is determined by the stiffness of the unidirectional CFRP laminate which has twice the elastic modulus of aluminum. One can therefore easily follow that an unstressed CFRP laminate reinforcement of welded beams made of steel will not lead to a substantial increase in fatigue strength of the steel structure. This consideration led to the idea of prestressing an external reinforcement of the welded zone. The present investigation describes experimental studies to identify the adhesive system suitable for achieving high creep and fatigue strength of the prestressed CFRP patch. Experimental results (Wöhler-fields) of shear-lap-specimens and welded steel beams reinforced with prestressed CFRP laminates are presented. The paper concludes by presenting a field application, the reinforcement of a steel pendulum by adhesively bonded prestressed CFRP laminates to the tensile flanges of the welded box girder. Inspections carried out periodically on this structure revealed neither prestress losses nor crack initiation after nine years of service.

Fatigue Behavior of Rotary Friction Welding of Acrylonitrile Butadiene Styrene and Polycarbonate Dissimilar Materials

“…It was found that the predicted fatigue life was consistent with the experimental result. Koller et al [ 17 ] identified an adhesive system suitable for achieving a high fatigue strength in a carbon-fiber-reinforced polymer patch. The results showed that the compressive nominal stress promoted the crack closure effect.…”

Viability of Utilizing CFRP Composites for Improving the Structural Behavior of Steel Beams

“…Few studies investigated the use of pre-stressed CFRP laminates to strengthen steel structures. It was noticed that the use of CFRP composites for retrofitting steel structures is not very popular [18,19].…”

Flexural Strength of Carbon Fiber Reinforced Polymer Repaired Cracked Rectangular Hollow Section Steel Beams

“…The defect of crack can also impair the bearing capacity and make the structures prone to brittle fracture. To restore the bearing capacity or retard crack propagation, CFRP plate was prestressed and patched to a steel pendulum with rectangular hollow section [13]. Scaled fatigue tests were conducted before the technique was applied to a site rehabilitation project.…”