Bolted timber joints with corrugated versus flat steel plates and CFRP reinforcement

In this study, the mechanical behaviour of bolted timber joints with slotted-in steel plates was investigated experimentally, comparing flat plates with innovative corrugated plates, both with and without carbon fibre-reinforced polymer (CFRP) reinforcement. Thirty-two specimen sets (16 corrugated, 16 flat) were tested under monotonic loading parallel to the grain using an orthogonal design. Results showed that corrugated-plate joints exhibited distinct failure modes including shear, compression and transverse–longitudinal (TL) cleavage, with combined bolt yield deformations. Their load–displacement curves lacked a clear yield plateau, progressing through elastic, fracture-transition and failure stages. Corrugated configurations demonstrated superior stiffness and bearing capacity compared to flat-plate joints. U-shaped CFRP reinforcement significantly enhanced corrugated-plate joint performance, an effect absent in flat-plate joints. Theoretical analysis based on the Eurocode revealed that current formulas are applicable to flat-plate joints but overlook end-region mechanics in corrugated-plate joints. A simplified empirical method incorporating timber end characteristics and error analysis was proposed. However, mechanical aspects such as TL fracture effects require further investigation.