RESEARCH ON THE DESIGN METHOD OF DOUBLE-LAYER SHOULDER BEAMS WITH DOUBLE-LIMB SIDE COLUMNS OF CONCRETE-FILLED STEEL TUBES

In order to study the design method of double shoulder beams with double-limb side columns, four finite element models of double shoulder beams with double-limb side columns were constructed. The finite element numerical simulation method was adopted. The height of upper shoulder beams, center distance of inner limbs of middle columns, height-span ratio of lower shoulder beams, height of inner limbs of middle columns and section height of inner limbs of middle columns were taken as parameters to determine the bearing capacity, failure mode and internal force distribution in double-layer shoulder beams of side column. The influence of the laws were studied. The results showed that:when the side webs of inner limbs yielded first, the elastic bearing capacity of the members was equaled the bearing capacity of the full section yield of the side webs of the inner limb; when the full section of side webs of outer limbs yielded first, the elastic bearing capacity of the members could be conservatively taken as the corresponding elastic bearing capacity when the internal and external shear forces of the shoulder beam were equal. The shear force calculation of the inner limb of the lower shoulder beam was the same as that of the single-layer shoulder beam; and the shear calculation formula of the main section of the lower shoulder beam in different conditions was given, and the critical value of the shear force on both sides of the lower shoulder beam was deduced, which was used to determine the yield order of the inner and outer sides of the lower shoulder beam. Combined with the characteristics of cross-section stress distribution, the design method of double-layer shoulder beams was proposed.