Research On Anti-seismic Behavior Of Unstiffened Overlapped Chs-joints In Truss Structure Of Steel Tubular

Truss structure of steel tubular, is also called steel truss structure, pipe truss orsteel tubular structure. It is a kind of steel structure form which consists of jointtubular section components. It is widely used in large span steel structure buildingsdue to its simple structure and beautiful modeling.Truss structure of steel tubular connected joints usually adopts unstiffenedtubular joint form.That is, we only weld the bracing member on the surface of thechord member without more stiffener unit needed. Besides, the independence of thejoints design decreases as well. So, in the perspective of the integrity of the structuresystem, unstiffened tubular joint is the key part of truss structure of steel tubular andthe part which can dissipate the energy that produced by the infrequent earthquakes.To appraise the seismic capacity of tube truss structure, we must know connectedjoints’ hysteretic behavior in the function of low cycle reciprocating load and exploreits damage mechanism under the effects of earthquakes.This paper systematically studied on hidden welds welded and non-weldedhysteretic behavior of unstiffened overlapped CHS（circular hollow sections）K-jointsand KK-joints. It is based on the Project of the National Nature Science Foundation ofChina-“Experimental research and numerical analysis on hysteretic behavior ofunstiffened overlapped CHS K-joints and KK-joints”(50968014).The main contentsand conclusions are as follows:Experimental research on hysteretic behavior of Unstiffened Overlapped CHSK-joints:Two specimen groups were designed according to Unstiffened OverlappedCHS K-joints hidden welds welded and non-welded. The groups are tested by thepseudo-static reciprocating loading test respectively. Through the analysis of the testdata, hysteretic curve of different welding forms of K-joints was acquired. What’smore,about bearing capacity, stiffness, ductility and energy dissipation of joints wasquantitative evaluated. By analyzing strain intensity distribution of joints domains, thejoint’s failure mechanism was revealed in reciprocating loads. The research resultshows：the bearing capacity slightly increased but ductility and energy dissipationreduced for hidden welds welded joint. The wall plastic yield failure mode of chordmember play the main control function in the failure modes of joints. However, thedamage of the joints caused by the bracing member’s axial bearing capacity is also notallowed to ignore. The maximum deformation of the joints happens in the saddlepoints and the deformation of bracing member is greater than that of chord member;The overlapped bracing member j tensile deformation is less than pressure. Thedeformation of the hidden welds welded joints is less than that of hidden weldsnon-welded. That is to say, hidden welds welded reduces the joint’s flexibility; Themore close the chord and bracing member diameter is,the smaller deformation of thejoint is.hidden welds welded and non-welded has no obvious effect on the stiffness ofjoints. Hidden welds non-welded is slightly lower than hidden welds welded on stiffness of joints; The yield displacement and limit displacement of hidden weldswelded joints is less than that of non-welded; The seismic performance of hiddenwelds non-welded joints is better; In the same displacement, hidden welds non-weldedjoints is better than hidden welds welded for energy dissipation capacity. With theincrease ofβ,τand ov%,the joint’s energy dissipation capacity increase as well.Numerical analysis on hysteretic behavior of unstiffened overlapped CHSK-joints by finite element method: Based on the experimental study, the test resultsand numerical mode of joints was evaluated and verified by finite element method.And then,influencing factors that was hysteretic behavior of unstiffened overlappedCHS K-joints to be studied systematically.The results show: joint’s energy dissipationperformance,hidden welds non-welded is superior to the welded. By using nonlinearfinite element method, the hysteretic behavior of joints can be predicted better. Thegreatest street mainly happens in the two bracing members overlap. So it is better totry to let the overlap smaller. Through the parameter analysis,we can see that theinfluence of τandγis more obvious thanβon the hysteretic behavior ofjoints,however,β，τandγhave not very significant influence on the bearingcapacity of the joints. With the change ofβ，τ，γ.YN is superior to the YH. Thegreater the value ofβ, the greater the ductility factor, and the better ductility jointsis. The bigger the thick chord diameter γ is,the smaller the ductility factor is,and thepoor joint ductility is;The thickness ratioτof bracing and chord member has notvery significant influence on the ductility coefficient.It shows thatτhas little influenceon the ductility of joints, and has no influence on the ductility of the joints especially.Numerical analysis on hysteretic behavior of unstiffened overlapped CHSKK-joints by finite element method: According to the KK-joints hidden welds weldedand non-welded.design two analysis models. Model1-there is clearance in the Xdirection, and in the Y direction, two bracing members overlap.Model2-there isclearance in the Y direction. In the X direction, two bracing members overlap. designfour kinds of combined forms specimen according to the orders of different bracingmember overlap for each model.For each CHS KK-joint,using nonlinear finite elementmethod,Hysteretic energy numerical models were created.bearingcapacity,deformation ability and energy dissipation capacity etc was evaluated. hiddenwelds welded and non-welded to influence discipline of the KK-joints’ seismicperformance was revealed.The results prove that influence to the bearing capacity ofKK-joints is not very significant on hidden welds welded and non-welded. Thedeformation and the energy dissipation performance of hidden welds non-welded issuperior to hidden welds welded. Because of three dimensional effect of unstiffenedoverlapped CHS KK-joints, the stiffness degradation trend of different forms of modetends to be the same.analysis the two models, find the deformation ability of model2is superior to model1,and this explain the seismic performance of model2is superiorto model1.The analysis of the influence of hidden welds welded and non-welded on theultimate bearing capacity of steel tubular truss structure: In two cases of hidden weldswelded and non-welded,the ultimate bearing capacity of the truss structure of steel tubular with K-joints was analyzed.explore the failure mechanism of the YHT andYNT.The analysis results show that,in the tubular truss plastic development process,the bearing capacity of the YHT is slightly higher than YNT and the gap is aboutwithin20%. Along with the joints eccentric distance increases, the bearing capacity ofYNT relatively decline more.To China’s steel structures design codes,it isn’tconsidered the scope of the eccentric impact,should be distinguished according tohidden welds welded and non-welded of joints.That is,the YNT scope of the eccentricimpact shall be more strict. With the increase of βandτvalues,the bearing capacityof the whole truss is enhanced and hidden welds welded and non-welded follow thesame change trend. In the aspect of tubular truss structure damage model, mainlyexists joints local damage and overall instability destruction two failure models. Thetruss bracing member instability has “surprise”, which brings about serious damage toa structure. So, the actual structure should be controlled in the bracing memberslenderness ratios so as to avoid the whole bracing member instability.Tubular trussstructure beam element can be used instead of shell element to simplify calculation ofanalysis model and satisfy the need of project precision.Analysis of seismic behavior and simplified calculation on steel tubular trussstructure felling to the ground: define a steel tubular truss structure felling to theground as a basic example, use nonlinear finite element method,select beam elementand bar element and establish steel truss rigid model, semi-rigid model and hingedmodel. Through the time history analysis method, select different seismic waves andconduct comparative analysis of the seismic response with different analysis models.Moreover, through the vibration mode decomposition method, some variableparameter was analyzed about the seismic behavior of the truss structure felling to theground. The analysis results show that the deflection change of floor truss structure isdifferent, to different calculation models. semi-rigid model has the smallest deflectionreaction and rigid model is the second and the maximum deflection reaction is hingedmodel. In the tubular truss calculation, if hinged model is adopted, the results tend tobe conservative. What’s more,there is unsafe factors if semi-rigid model is used.However, rigid model is reasonable analysis models. Tubular truss structure stiffnessof the joint domains has important influence on the whole deflection of the truss buthas a little influence on the axial force of components. The big bending momenthappens in under-chord member which contacts with the ground. Furthermore, thebending moment of under-chord member is bigger than that of up-chord member. Thekey parameters that influence the dynamic characteristic of steel tubular truss structureis the depth-span ratio(H/L) and section wide high ratio(W/H) and hinged spacing(S).Of all the key parameters, the depth-span ratio has the most significant influence onthe steel tubular truss arch dynamic response. Therefore, design the floor steel tubulartruss structure.the depth-span ratio in the range of1/32to1/8,the wide high ratio inthe range of within1/1.2and hinged space beyond4meters, but hinged spacingshouldn’t be too big. Within this reasonable range, the introduction of horizontalseismic impact factor k, and the analysis of a single parameter.the results show:siteclassification and seismic fortification intensity significant impact on k,the earthquake grouping is impact smaller.Therefore, site classification, seismicfortification intensity as the two variable parameters,the floor-truss structure ofseismic analysis,the values of k was get on the top chord member, bottom chordmember and bracing member in different site classification and seismic fortificationintensity.It is reasonable to choose the values in those scale and these provideconceptual design for truss structure with references.Finally, on the basis of the studies above, the paper discusses the problems thatexist in the field and required further research.