Damage And Collapse Analysis Of Tall Building Structures Under Seismic Excitations

With the development of economy and science and technology, in recent twentyyears, a great number of tall building structures and super tall building structures havebeen built as the focus of the world in our country. These tall building structures havegreat social influence as the land marks of a city. However, most of these buildingsare located in seismic region, the loss of structural bearing capacity tends to causelocal collapse or overall collapse of the structure when strong earthquake occurs. Suchcollapse will result in great economic loss and casualties and has immeasurablenegative social impacts. Therefore, it is of significant theoretical and practical value tostudy the damage evolution and the collapse mechanism of tall building structuresunder severe earthquakes, and to improve structural seismic capability by takingeffective design methods and collapse resistance measurements.In this dissertation, the damage evolution and the collapse mechanism of themajor vertical bearing members (such as steel column, reinforced concrete shear walland reinforced concrete column), tall steel frame structure and tall steelframe-concrete tube hybrid structure under severe earthquake is addressed. Primaryresearch contents and achievements are summarized as follows:(1) Seismic damage analysis of the major vertical bearing members (such as steelcolumn, reinforced concrete shear wall and reinforced concrete column) of tallbuilding structures is conducted. A modified Krieg&Key constitutive model (K&Kmodel) with a consideration of the damage accumulation effect is proposed, based onthe K&K model considering the Bauschinger effect of steel material is developed byimporting the Bonora damage model. The results indicate that the vertical bearingcapacity of the steel column decrease significantly while considering the materialcumulative damage effect. The damage of steel column develops rapidly after thepeak acceleration appeared which also increases with the seismic intensity. With aconsideration of the degradation of strength and effects of negative stiffness, amodified Sina model of reinforced concrete shear wall on the basis of Sina hystereticmodel is introduced by importing the Fukuzawa algorithm criterion. The resultsindicate that the modified Sina model is well capable of simulating the mechanicalperformance of the reinforced concrete shear wall at different stages, such as concrete cracking, steel yielding, strength degrading and negative stiffness effects etc. Thedamage increase with loading amplitude and changes abruptly at the loading changepoint. By employing the refined analysis model, the damage model based on verticalresidual bearing capacity is established. The vulnerability curves with lognormaldistribution are constructed through incremental dynamic analysis for damageassessment. A seismic damage assessment method based on vulnerability curves isproposed for reinforced concrete columns. It is indicated that the recommendedmethod of damage assessment for reinforced concrete columns is simple in computingand effective in evaluating the damage level under different seismic intensity indices.(2) Seismic collapse analysis of tall steel frame considering damageaccumulation. On the basis of the explicit integration form of the central differencemethod and the modified K&K model is applied to the whole structure throughdefining a structural damage index for story level so as to study the rule of structurestrength and stiffness degradation due to earthquakes. Against the uncertainty ofstructure collapse, a numerical approach for simulating the collapse process of steelframe structure under the severe earthquake is proposed.The seismic response, failureultimate loading, failure path and the collapse process of a20stories benchmark steelframe structure under earthquake using this approach was studied, and the resultsdemonstrate that the damage accumulation effect considered in this numericalapproach works better at determining the failure ultimate loading of the tall steelframe. For the cases with unknown failure mode, of the structure, this approach canbetter simulate the failure path, the collapse process of structure and reveal thecollapse mechanism of structure to some extent.(3) Seismic collapse analysis of tall steel frame-concrete tube hybrid structurebased on equivalent stiffness. On the basis of the seismic hysteretic characteristics forthe structure, a damage model taking the equivalent stiffness of undamaged structureas an initial scalar is proposed. A story damage model is also established according tothe energy distribution on each story. Analysis on the damage evolution and collapseof the tall steel frame-concrete tube hybrid structure under severe earthquake isconducted. The results indicate that this damage model can effectively evaluate thedamage level of such structure, and the analysis model considering damageaccumulation effect, strength degrading and negative stiffness effects can effectivelysimulate the damage evolution and trace the route of collapse, i.e., the collapseprocess begins from the concrete tube, then, steel frame carries the majority of horizontal seismic force causing the ground floor columns gradually losing theirvertical bearing capacity, furthermore, the ground floor column will completely losetheir vertical bearing capacity when their bottom is seriously damaged and causes thewhole structure collapse.(4) The shaking table tests of the damage and failure process the scaled model isperformed. A three-story steel-concrete hybrid structure scaled model is designed andfabricated to analyse the damage evolution and failure process and to verify thedamage model based on the equivalent stiffness. The damage level evaluation of thescaled model is carried out using this damage model proving the damaged modelworks well in evaluating the residual stiffness and damage level after earthquake. Theresults indicate that the solid model with the consideration of bond slip effect andfiber model with the consideration of damage accumulation effect can effectivelysimulate the seismic response of the scaled model respectively. The simulatingprecision of solid model is slight better than that of fiber model, whereas, thecomputer efficiency of fiber model is far higher than that of solid model. The fibermodel combined with the modified K&K model and modified Faria model caneffectively simulate the damage evolution and dynamic responses of the scaled modelunder the earthquakes.