Investigation On Seicmic Performance Of Steel Frames With Additional Stiffness Buckling-Restrained Braces

The interstory drift in soft floor will increase greatly than other story when traditional frames suffer earthquakes, then the collapese resistant capacity of structures becomes lower particularly with the effect of P-?. Accroding to this, a new structural system has been proposed in this paper——-additional stiffness buckling restrained braces frames, in which uniformity of interstory distribution can be controlled by additional stiffness. What's more, the tendon can be also regard as the 'fuse' of the low cyclic fatigue failure of buckling restrained braces, so the phenomenon of soft floor can be overcome by addtional stiffness buckling restrained braces. The feasibility of ASBRB with this type is demonstrated by quasi static test, as well as the siismic performence of ASBRB frames. The main works are as follows:(1) First, the mechanism of additional stiffness buckling restrained braces are analyzed. Then a specimen, which is light and assembled, is tested. After the pseudo static test, the influence of unequal lenghth(between the out tube and inner tube) and bolt slippage have been studied. Based on the bilinear elastic-plastic model, this paper compare the equivalent viscous damping ratio among BRB, SCBRB, ASBRB. A simplified beam-truss FE model based on opensees software can similate the behavior of ASBRB well.(2) A 9-story hinge-connected steel frame with BRBs and ASBRBs has been development based on American seismic specifications, with two configurations. The ASBRB is modeled with the combination of multi-materials and multi-elements. It can be found that the ASBRB is good for controlling the uniformity of interstory drifts distribution, according to the elastic-plastic time-history analysis of 20 design earthquakes. The best initiation displacement of ASBRB frame is the displacement of BRB corresponding to the median of interstory drifts in BRBF. In order to solve the problem such as the shear force increasement and story acceleration largen, the friction damper which is regard as fuses should be placed at joints.(3) The equivalent method transforming multi-degree of freedom system to single-degree of freedom system is established. An ASBRB single-degree of freedom system which contains P-? effect using Ibarra-Krawinkler model is proposed. Parameter study are conducted to evaluate the collapse-resistant capacity of the above system by the fill and hunt of collapse point based dichotomy. What's more, earthquake collapse capacity spectrum has been used to investigate the collapse-resistant capacity among different fundamental periods.(4) A 3-D numerical model based on 2007 E-Defense shaking table test is performed. Tthe low cycle fatigue failure of BRB is defined corresponding to 3% of the core. The difference of the distributions of story driftis between BRBF and ASBRBF is researched by IDA. The DCF factor for ASBRB frame is better than that of BRB. The earthquake response curve with different initial stiffnesses of various secondary structures demonstrates that ASBRBs can hold down the maximum story drift.