Experimental Study On Mechanical Properties Of Single-Bolt And Multi-Bolt Connection With Slotted-in Steel Plate Of Glued Laminated Timber Structure

Wood is green and low-carbon,and fits with the carbon neutral concept in the 14th Five-Year Plan.Vigorous development of modern wood structures is required for the green transformation of the construction industry.Modern wood structure buildings have widely adopted metal connectors instead of wooden mortise and tenon connections,which have substantially improved the reliability and stability of the nodes.Bolted connection with slotted-in steel plate are more widely used in modern wood frame buildings because of their easy installation and non-exposed steel plates.However,there is a lack of systematic research on the mechanical model of such nodes and the effect of group bolts.To address this problem,this paper conducts a study on bolted connection with slotted-in steel plate of glued laminated timber structure.In the study of mechanical properties of single-bolt nodes,monotonic loading tests of 81 parallel to grained joint nodes were carried out in this paper,considering the influencing factors of bolt diameter,wood thickness and thickness-diameter ratio.The test phenomena and damage modes of the single-bolt connection nodes were studied,and mechanical performance parameters such as initial stiffness,yield load,peak load and ductility coefficient were obtained.The load-displacement relationship curves of the whole process were analyzed,and the mechanical model equation containing the descending section was proposed.In the study of the mechanical properties of multi-bolt nodes,monotonic loading tests of 72 parallel to grained joint nodes were carried out in this paper,considering the influencing factors such as the number of bolts,bolt diameters,and wood thickness.The damage modes and weak points of multi-bolt connection nodes were analyzed and evaluated.The correlation between the mechanical performance parameters of multibolt nodes and single-bolt nodes was studied in comparison.The results show that the improvement of mechanical properties of multi-bolt nodes relative to single-bolt nodes is not linearly superimposed,but there is a discount factor,which is related to the weakening of wood by bolt openings.The suggested value of the reduced factor of multi-bolt group factor was proposed in combination with the test results.Due to the large variability of wood,a probabilistic model was developed in this paper to describe the uncertainty of important mechanical property parameters(initial stiffness ke,yield load Py and peak load Pp)of the bolted connection with slotted-in steel plate.Eight distributions were fitted by frequency distribution histograms by using the data obtained from the tests.The optimal probability density functions of key mechanical performance parameters such as ke,Py and Pp were determined based on the fitted evaluation indexes.Finally,five nonlinear load-displacement curve mechanical models were analyzed to obtain the probability density functions of each parameter in the mechanical models,and their correlation and applicability were investigated.These works provided the theoretical basis for reliability studies in the future.In this paper,the single-bolt and multi-bolt connection with slotted-in steel plate of glued laminated timber structure were taken as the research objects,and their mechanical properties and internal relations were analyzed and evaluated.The mechanical model of single-bolt connection containing the descending section was proposed,and the recommended value of the reduced factor of multi-bolt group factor was given.Finally,the probability models of important mechanical parameters and different mechanical model parameters were established based on the probability statistical method,which provided a theoretical basis for reliability research.