Study On Global Stability Of Trapezoidal Section Simply Supported Space Truss

With the continuous development of steel structure,the structural forms of steel structure in engineering are also various.Compared with the traditional structural forms of gantry frame,mesh frame,tube truss and so on in architectural engineering,the trapezoidal section simply supported space truss studied in this thesis does not need to install lateral support between a single truss in engineering use,and can directly lay the roof plate between two trusses.It is a no-support space truss structure,and its joint forms can be articulated or rigid.The overall stability of the two joint forms needs to be studied and analyzed.In order to study the influence of slenderness ratioλ_yon the overall stability of trapezoidal section simply supported space truss,find the limit of strength failure and overall instability,and finally give the calculation formula of truss stable bearing capacity,this paper uses the finite element method to analyze and study the parameters of trusses with different spans.Firstly,the buckling analysis of the hinged truss with four spans of L=18m,30m,48m and 60m was carried out,and the boundary range between the overall instability and strength failure of the truss was determined,that is,when the slenderness ratioλ_y≤5.41,the failure mode of the truss was strength failure.Whenλ_y≥9.01,the failure mode of the truss is overall instability,while for the 5.41<λ_y<9.01 range,the structural failure mode may occur both strength failure and overall instability,and its failure mode is uncertain.Then,the influence of"X-shaped"and"V-shaped"inclined rod supports on the overall stability of the articulated truss was studied,and it was found that the two forms of inclined rod support greatly improved the lateral torsional stiffness and stable bearing capacity of the articulated truss.Compared with the case without inclined rod,the failure mode of the articulated truss after adding the oblique bar support all changed from overall instability to strength failure,and the stable bearing capacity of the truss was also increased by about25%～70%overall,which was significantly improved.Comparing the two forms of inclined bar support,it is found that there is no obvious difference in the lateral torsional stiffness and bearing capacity of the truss in the two cases,but the number of inclined rods supported by"X-shaped"oblique rod is twice that of"V-shaped",so it can be seen that the"V-shaped"inclined rod support is more economical and the effect is better.Then,the influence of slenderness ratioλ_yon the stability of rigid jointed truss is studied,and the value range of two failure modes is obtained,that is,when the slenderness ratioλ_y≥13.53,the failure mode of truss is global instability,and the stability plays a controlling role,while when the slenderness ratioλ_y≤10.94,the eigenvalue buckling of the structure has no global instability mode,and its mode is local rod buckling.Therefore,the overall instability of the structure no longer occurs.Finally,the stability coefficient of trusses is defined and calculated,and the calculation formula of the stability bearing capacity of trusses with simply supported trusses is given,and the applicability of the formula is verified.In addition,the trusses are simplified into simply supported beams and their strength is checked.The calculated values of the formulas are all smaller than the simulated values of the finite element,and the deviations are all within 10%.