Study On Flexural Behavior Of Steel-Timber Composite Beams Connected With Grouted Shear Studs

Steel-timber composite(STC)structure has several advantages including green,low carbon,light self-weight and small seismic response.The STC beam is a key load bearing member in STC structures,and the traditional connection methods of STC beam mainly include screws and bolts.Previous research results showed that the above-mentioned doweltype shear connections have relatively limited shear bearing capacity and stiffness.Recently several scholars have studied the steel-timber joint connected by bolts in grout pockets(BGP),and the results showed that the initial stiffness,pre-peak stiffness and ultimate bearing capacity of the BGP connections were significantly higher than those of traditional dowel-type shear connections.However,the BGP connections require pre-drilling of holes in the flange of steel beams in practical application,which requires relatively high construction accuracy.In view of this,this paper proposes the use of studs in grout pockets(GSC)for the connection of steel beams to timber floor slabs,and investigates the flexural performance of steel-timber composite beams with GSC connections.The following are main works:Bending resistance test: The flexural performance of GSC-connected steel-timber composite beams was investigated by four-point bending tests with test parameters including stud diameter,stud arrangement,groove spacing and adding steel fiber in grouting material or not.The failure modes,load-deflection behavior,cross-sectional strain distribution at midspan and slip distribution at the interface of composite beam under different load levels were investigated so that the composite efficiency was evaluated overall.The results show that the GSC connected steel-timber composite beams have good flexural performance and ductile behavior.The coefficient of composite efficiency of the combined beams is basically over 0.8 before the serviceability limit state,and some of the specimens exhibited near full composite action at initial stage,indicating that the GSC connections can provide good interfacial shear resistance for STC beams.Finite element analysis: The finite element modelling was conducted based on ABAQUS.Parametric analysis was also carried out to study the effects of bevel angle of groove,width of CLT plane and different connection methods on the flexural stiffness and flexural load capacity of the composite beam.The results showed that the flexural load capacity of the composite beams decreased slightly as the bevel angle increased from 0° to30°,while the axial force of the studs at the same position increases gradually,which indicates that the GSC connections with studs play an effective role in resisting vertical lifting as well as resisting shear force.The GSC connections can significantly improve the flexural stiffness,combination efficiency and anti-slip performance of the composite beams,although the ultimate load capacity increased slightly compared with that of the composite beams with common screw connections.The ultimate load capacity and flexural stiffness of the composite beams increased linearly as the width of the CLT plane increased from 400 mm to 1200 mm.Theoretical analysis: The calculation models for timber-composite beams in Eurocode-"γ" method,combined with the "discounted stiffness method" and "ultimate equilibrium method" in steel-composite structure,were used to predict the flexural stiffness,flexural load capacity and mid-span deflection of STC beams in elastic phase.The results showed that theγ method can predict the flexural stiffness and flexural capacity of steel-timber composite beams more accurately.For the prediction of deflection of steel-timber composite beams,the equations used in this paper can predict the mid-span deflection of steel-timber composite beams in the elastic phase well with an error less than 10%.