NEGATIVE SHEAR LAG IN FRAMED-TUBE BUILDINGS

Occurrence of negative shear lag in framed-tube buildings under latera l loading is reported in the literature, but explanation of its origin and comprehensive studies of it are lacking. The present paper separa tes column axial-force distribution in a story into two modes; one con tributing to the positive shear lag and the other to the negative shea r lag. The net shear lag, positive or negative, is the resultant of th e axial-force distributions in these modes. Further, an analogy betwee n shear-lag behavior of a uniform box girder and uniform framed-tube b uilding is established by interpreting structural parameters occurring in the closed-form solution of a box girder in terms of those of the framed-tube building. Adequacy of the proposed analogy is demonstrated . Structural parameters governing the shear-lag behavior are identifie d, and their effect and of different loading types is studied.