Tests and mechanics model for concrete-filled SHS stub columns, columns and beam columns

A series of tests on concrete-filled SHS (Square Hollow Section) stub columns (twenty),rncolumns (eight) and beam-columns (twenty one) were carried out. The main parameters varied in therntests are (1) Confinement factor ( x) from 1.08 to 5.64, (2) concrete compression strength from 10.7MParnto 36.6MPa, (3) tube width to thickness ratio from 20.5 to 36.5. (4) load eccentricity (e) from 15 mm torn80 mm and (5) column slenderness ( l) from 45 to 75. A mechanics model is developed in this paperrnfor concrete-filled SHS stub columns, columns and beam-columns. A unified theory is described where arnconfinement factor ( x) is introduced to describe the composite action between the steel tube and filledrnconcrete. The predicted load versus axial strain relationship is in good agreement with stub column testrnresults. Simplified models are derived for section capacities and modulus in different stages of therncomposite sections. The predicted beam-column strength is compared with that of 331 beam-columnrntests with a wide range of parameters. A good agreement is obtained. The predicted load versus midspanrndeflection relationship for beam-columns is in good agreement with test results. A simplified modelrnis developed for calculating the member capacity of concrete-filled SHS columns. Comparisons are madernwith predicted columns strengths using the existing codes such as LRFD (AISC 1994), AIJ (1997), andrnEC4 (1996). Simplified interaction curves are derived for concrete-filled beam-columns.