Experimental Study On Mechanical Properties Of New Joints Of Single-Layer Reticulated Shells With H-Shaped Steel Beam

Recently,owing advantages of spans,lightweight,good appearance,and cost,single-layer spherical reticulated structures with complex curved surfaces have been designed for different structural applications,including transportation,theatres,airports,museums,and so on.Most of those shell structures were designed using different sections of members,including circular tube members or rectangular tube members.The circular tube member is widely used in single-layer grid shell structures.However,the circular tube has sympatric inertia of moment while design requirements for members’out-of-plane and in-plane are different.In addition,traditional bolt-ball joints with circular tubes exhibit low bending stiffness and bearing capacity;thus,this joint is weak when subjected to out-of-plane bending moments.In the single-layer grid shells using the rectangular tube,bolts are used to connect the rectangular tubes with the hub in the centre which weakens the strength of these joints under out-of-plane and in-plane bending moments.Moreover,these joints suffered assembling bolts in the rectangular tube ends.In contrast,H-shaped beams present the advantages of strong and weak axes of inertia of moment which means reducing the structure’s material,weight,and cost.But,joints with H-shaped beams such as temcor joint of aluminium alloy only connect the upper and lower flanges of the H-shaped beam with the upper and lower gusset plates without connecting the web of the H-shaped beam;thus,a weak shear deformation can occur in this type of joint.Furthermore,beside challenges encountered during welding work on the site of welded hollow spherical joint with H-shaped beam,it suffers from welding H-shaped beam with curved end with the curved surface of the hollow spherical ball problems.Therefore,three types of joints using H-shaped beam（novel steel dovetail joint,novel steel dovetail joint with teeth pattern,and steel temcor joint）were proposed and investigated under Axial tensile loads,axial compressive loads,and bending moments in this study.And,single-layer spherical reticulated shells with H-shaped steel beams and rigid-and semi-rigid joints were analysed considering different design parameters.The main research contents are described as follows.Firstly,novel steel dovetail joint analysisTwo types of novel steel dovetail joints with teeth patterns（NDJGs）and without teeth patterns（NDJs）for single-layer grid shells are proposed and investigated.The design concept,design method,and FE modelling method are discussed.Experimental,numerical analysis and theoretical methods are adopted to explore the performance of the joint systems under axial tension and compression loads,and bending moments.The test results indicated that the novel steel dovetail specimens with and without teeth patterns exhibited different tensile bearing capacities:the specimens with teeth patterns generated twice the tensile load capacity of those without teeth patterns.This result can be attributed to the fact that the NDJGs specimens rely on the teeth patterns,edges of the hub keyway,and hub ring to bear the load,whereas NDJs specimens only rely on the edges of the hub keyway and hub rings.Further,the two types of specimens have the same failure modes when the beam-inserted end（tail）is pulled out of the hub keyway.In addition,shear failure occurs on the teeth patterns of the hub keyways and beam-inserted ends of the interlock of NDJGs specimens.Two FE models are established to verify the results of the tests,and the related equations are derived and calculated.The results obtained from the numerical analysis using the equations were compared with the test results.Based on the experimental and numerical results,both types of joints exhibit the same performance under compression loading,with three main failure modes:beam-throat failure,hub failure,and combined beam-throat and hub failure.Beam-throat failure occurs when the compressive bearing capacity of the hub is greater than that of the beam neck.The hub failure mode occurs when the compressive bearing capacity of the beam is higher than that of the hub,and the combined failure mode occurs when the compressive bearing capacities of the hub and beam-throat are similar.Finally,equations for calculating the examined joints and hubs’yield and ultimate bearing capacities are proposed and calculated.By comparing the numerical,theoretical,and corresponding experimental results,it is shown that the derived equations can be used to calculate the mechanical performance of the joints in this study.On the other hand,the specimens exhibited different bending moment-bearing capacities;the capacity of specimens with teeth patterns interlock type II（NDJGs）was255%of that of without teeth patterns interlock type I（NDJs）.All test specimens underwent a similar failure mode when the beam–tail pulled out the hub–keyway from the bottom with hub ring deformation.Based on the FE analysis and the parametric analysis results,it was found that the test bending moment was positively correlated to the height,ring thickness,and maximum thickness of the hub,whereas the hub diameter slightly influenced the bending capacities of these specimens.Finally,the rigidity values of the test specimens and their FE models were calculated according to Eurocode3 specifications,and related equations for analysing the yield bending capacity were derived.Secondly,steel temcor joint analysisExperimental,numerical,and theoretical methods were adopted to explore the behaviour of the steel temcor joint with an H-shaped beam of steel under axial tension and compression loads,and bending moments.In the axial tension and compression tests,three types of steel temcor joints（TC1,TC2,and TC3）were designed and tested considering the number of Huck bolts and the gusset plate thickness.According to the test results,the TC1 joint with only eight Huck bolts exhibited the lowest load-bearing capacity with main bolt shear failure under tension and compression loads.Moreover,the TC2 and TC3 joints exhibited high bearing capacities with bolt shear failure in the tension tests,while they generated the same bearing capacities with the main failure occurring in the H-shaped beam in the compressive tests.FE parametric analysis of the tested joints was conducted and verified by the test results,and the tension and compression theoretical solutions were derived.Moreover,twenty-two joints with a single Huck bolt connection were designed and tested to investigate the shear strength of Huck bolts.At the same time,three specimens of steel temcor joint（TC1,TC2,and TC3）were designed considering the number of Huck bolts,the thickness of the gusset plates,and material type.The experimental and numerical results indicated that the bending bearing capacity and the stiffness of the steel temcor joint were limited increased by increasing the gusset plate thickness and bolt number.However,when the thickness of gusset plates exceeded the thickness of the flanges of the H-shaped beam,the stiffness and bending bearing capacity stopped increasing.Moreover,the bending stiffness of steel temcor joints was higher than that of aluminium temcor joints by an average of 180%.The theoretical solution for bending bearing capacity of steel temcor joint was proposed,and their stiffness was calculated based on Eurocode 3.Thirdly,single-layer spherical reticulated shells with H-section steel beamFE models for single-layer spherical reticulated shells with H-section steel beam were established using 3D3S and Abaqus softwares.Shells’bearing capacity and failure modes were explored considering different design parameters,including shell span,rise/span ratio,joint’s semi-rigidity（rigid,NDJ,NDJG,and temcor joints）,initial imperfection,and material elastic and elastoplastic behaviours.Based on the analysis results,the average bearing capacity of shells with rigid and semi-rigid joints and spans,the impact of the rise/span factor(_/3),the impact of the initial imperfection,the stiffness reduction coefficients₀8)4)/4)2)4)（9）,and material elastoplastic/elasticity reduction₈)coefficient were calculated.Finally,the failure modes for those shells were determined.The global buckling failure was considered as the main failure for all shells except shells 90-6 with NDJ joint and 90-7 with NDJ joint and NDJG joint.Finally,a good agreement existed in the validation of the FE modelling and theoretical equations results against results of tension,compression,and bending moment tests.