| Pultrusion profile node connection is a key factor that affects the structural performance of FRP.At present,the common connection methods include bolt connection,glue connection and hybrid connection.Hybrid connection has higher bearing capacity,better ductility,and greater stiffness.At present,most of the bolts used in the research on the hybrid connection are stainless steel bolts and titanium bolts.The full FRP structure with FRP bolt is more reliable in complex electromagnetic field and high corrosion environment.However,there are few studies on hybrid connection by FRP bolt,therefore,it is of great significance for engineering application to study reasonable hybrid connection mode by FRP bolt.This paper based on the national key R & D Program "Research on industrial standardized fiber reinforced composite pultruded profile components and new structure system"(2017YFC0703005).The mechanical properties of hybrid joints by FRP bolt were studied by experimental method.The research contents and achievements are as follows:The tensile tests of bolted,glued and glued bolted joints were carried out for the plates with the same structural parameters.The results show that the bolt has a strong restraint effect on the adhesive layer,the adhesive layer is peeling failure,the adhesive layer is shear failure,and the adhesive layer strength is fully utilized.The results show that the failure load of the adhesive layer of the composite joint is 97.6% higher than that of the adhesive joint.When the adhesive layer is damaged,the fiber on the surface of FRP plate is torn and damaged,and the bearing capacity of the joint is 12.7% lower than that of the bolt joint.Tensile tests were carried out on plates with the same structural parameters using stainless steel bolts,titanium bolts and FRP bolts.The test results show that stainless steel bolt and titanium bolt have strong resistance to the peeling force caused by eccentric bending moment because of the greater rigidity of bolt and gasket,and the adhesive layer failure load is 35% higher than that of FRP bolt;the connection bearing capacity of titanium bolt is 21% higher than that of FRP bolt and stainless steel bolt.24 single lap specimens of FRP bolt-concrete joint were designed to study the influence of geometric parameters such as bolt end distance,bolt edge distance,bolt number,lap length and plate thickness on the mechanical properties of FRP bolt-concrete joint.The test results show that the end distance has little effect on the failure load of the adhesive layer,but the bearing capacity of the connection increases by 5kn when the end distance increases by 0.5 times of the bolt diameter.With the increase of the end distance,the failure mode changes from shear failure to extrusion failure,and the ductility of the structure becomes better.However,when the end distance increases to 4 times of the bolt diameter,the screw shear failure occurs due to insufficient shear strength.The recommended end distance is 3 times of the diameter to 3.5 times of diameter.The edge distance has almost no effect on the failure load of the adhesive layer,but when the edge distance increases from 1.5 times the diameter to 2 times the diameter,the bearing capacity of the connection increases by 9%.When the edge distance increases from 2times the diameter to 2.5 times the diameter,the bearing capacity of the connection does not increase,so it is appropriate to control the bolt edge distance at 2 times the diameter.With the increase of two bolts,the damage load of adhesive layer will increase by 5kn and the connection bearing capacity will increase by 20 KN due to the increase of structural stiffness.However,increasing the number of bolts will lead to the decrease of longitudinal screw hole spacing,resulting in splitting failure between holes and the deterioration of structural ductility.When the lap length is 100 mm,the longitudinal screw hole spacing is too small,resulting in splitting failure between holes,and the ductility of the structure is poor.When the lap length is 200 mm,the longitudinal screw hole spacing is too large,and the strength of the middle plate can not be effectively used.It is recommended that the longitudinal screw hole spacing should be 5 times the bolt diameter to 9 times the bolt diameter.When the plate thickness increases from 4 mm to 6 mm,the adhesive layer failure load increases by 36.4%,the connection bearing capacity increases by 16%,and the failure mode changes from shear failure to bolt shear failure,but the structure becomes brittle failure.It is recommended that the ratio of bolt diameter to plate thickness be greater than 2 when FRP bolt and rubber bolt are used to make full use of the strength of the structure and FRP bolt degree.Through the experimental study,it can be seen that the failure modes of single lap tensile test are mainly shear failure,extrusion failure,splitting failure between holes and bolt shear failure;based on the structural resistance under different failure modes,the maximum tensile stress criterion is adopted,and the calculation formula of bearing capacity of FRP bolt and bolt is put forward according to the test data,and the reasonable bolt strength is given The layout suggestions are convenient for engineering application. |
