Abstract
The composite unbonded bracing is a member that consists of a core steel bracing (made of a built-up square hollow section) which is encased firstly by an unbending material in order to re-duce bond-stresses, and after by reinforced concrete. The main role of the use of reinforced concrete is to prevent an overall buckling in the core steel bracing. The role of the unbending material is to make independent both the core steel bracing and the RC part when axial loads are applied, due to that RC can not work for this type of loading. For tension and compression loading conditions, their corresponding stiffness and strength are in-tended to be same. Experiments on 16 specimens were performed to make clear the effects of the following parameters under cyclic axial loading; For the core steel 1. Slenderness ratio Bracings with medium range slenderness ratio (40-80) were mainly studied in these ex-periments. 2. Width to thickness ratio of the square hollow section. For the encased reiforced concrete 1. Quantity of axial reinforcing bars 2. Quantity of hoops 3. Strength of concrete 4. Thickness of concrete cover From these experiments, it can be confirmed that a properly designed composite unbonded bracing has a large ductility in an elasto-plastic range under axial cyclic loading.
