Study On Seismic Performance With Buckling Restrained Braces Monolithic Jacket Plus-story Frame Structure

The layer-adding transformation of the existing buildings has become one of the hotissues in civil engineering sector. The main layer-adding forms include direct, separating,unitary, cooperating with seismic reduction and isolation forms and so on. The unitarystructure-spanning-structure means the new added stories are held together with theexisting buildings by level fulcrums, which are able to take full advantage of the seismicpotential of the existing buildings, have a low cost, reduce the slenderness ratio of theunderlying column, adjust the vertical stiffness of the structure-spanning-structure, andincrease the unitary seismic behavior of the building. However, according to someearthquake disaster information and previous researches, in the earthquake fortificationareas, the biggest drawback of this form exists in the joints, which may crack or be nolonger work if encountered strong or rare earthquake, then the underlying column of thenew added structure will lose supports and become instability. The Buckling-RestrainedBrace (BRB) is recommended to be set in the unitary structure-spanning-structure toprevent the deadly destruction for the building and the huge life and property losses forpeople.The Buckling-Restrained Brace (BRB) is a new kind of energy dissipation andseismic reduction members. It can be in elastic stage under the frequent earthquake andnot premature buckling under the rare earthquake because of the constraint units being setto prevent the overall instability, which not only can maintain its stiffness and stability,but also protect the main structure by hysteretic energy dissipation of seismic energy ofthe steel core material. Therefore, BRB has more superiority of seismic than generalsupports.The article establishes the finite element analysis model by ANSYS, makes modalanalysis and time-history analysis under the frequent and rare earthquake of the unitarystructure-spanning-structure with BRB or not. Setting the storey drift as index tocomparatively analysis the changes of seismic behavior of the structure, the mainconclusions are as follows:(1)The natural vibration period of the unitary structure-spanning-structure with BRB is about5%shorter.(2) Under the frequent earthquake, the storey drift of each layer of the framestructure reduces after being set the BRB; however, the reduction is not obvious, atabout10%.(3) Under the rare earthquake, the storey drift of the unitarystructure-spanning-structure without BRB is beyond the provision of limit of theelastoplastic storey drift in the standard, which is1/50, however, it meets therequirement after being set the BRB and the reduction rate is up to60%.