Study On Flexural Performance Of Steel Reinforced Plywood-bolted Glued Laminated Timber Beams

Modern timber construction projects are developing towards large spans and high levels,and there is an increasing demand for large member glued timber beams,which usually need to be spliced or lengthened to meet structural requirements.In order to achieve the spanning of lengths of glued laminated timber beams,steel cleat-bolted connections have gained widespread attention as an important connection method.In a study of the flexural performance of glued laminated timber beams with steel plywood-bolted connections,it was found that there was a reduction in stiffness when 55%-70%of the ultimate load was reached.In order to solve this problem,a reinforcement method with steel reinforcement at the bottom of the timber beam is proposed to improve its stiffness and increase the load-bearing capacity for the application of the steel cleat-bolt jointing method in large-span glued laminated timber structures.This article is about the fabrication of 5 groups of 15 test beams:one group of pure wooden beams,one group of steel plywood-bolted glued wooden beams and three groups of steel reinforced steel plywood-bolted glued wooden beams,which were tested for flexural performance.Observe the force processes and damage phenomena of the specimens and investigate the effect of reinforcement rate on the damage pattern,flexural stiffness,ultimate load capacity and displacement ductility coefficient of the test beams.Numerical simulations of the test beam were also carried out using ANSYS finite elements,and the calculated results were compared with the test results for analysis.Research has been completed mainly in the following areas:(1)Five groups of test beams were subjected to flexural tests,the test process and damage phenomena were observed and recorded,and the test data were compiled.The ultimate load,load-displacement curve and load-strain curve are used to compare the damage mechanism,flexural stiffness,ultimate load capacity and displacement ductility coefficient of each group of test beams.The results show that the flexural capacity,overall bending stiffness and ductility coefficient of steel reinforced steel cleat-bolted glued timber beams are significantly improved by an average of 33.7%,23.1%and 16%compared to steel cleat-bolted glued timber beams.The reduction in stiffness at 55%-70%of the ultimate load of the steel cleatbolted test beams was significantly improved by the deployment of reinforcement in the tension zone of the steel cleat-bolted glulam beams.(2)Based on the analysis of the test results,the effect of reinforcement rate on the flexural performance of steel cleat-bolted glued laminated timber beams was revealed.The types of damage to steel reinforced plywood-bolted glulam beams can be classified as brittle damage in tension,ductile damage in tension and ductile damage in compression.When the reinforcement ratio<1.97%,the reinforced steel plywood-bolted glulam beams are brittle in tension,ductile in tension when the reinforcement ratio is between[1.97%,2.49%)and ductile in compression when the reinforcement ratio is≥2.49%.(3)The distribution of strain in the test beam section along the height direction is generally in accordance with the assumption of flat section.Through the test data and theoretical derivation,the calculation formula for the flexural load capacity of steel reinforced steel plywood-bolted glued laminated timber beams was derived and compared with the test results,the calculation error is within 5%.(4)Using ANSYS finite element software,finite element simulation models of each group of test beams were established to analyse the effect of reinforcement rate on the flexural performance of steel cleat-bolted glued laminated timber beams,and the mid-span vertical displacements under the same load were obtained,which were in good agreement with the test results.