Abstract: Seismic performance of steel moment-resisting frame structures is investigated considering nonlinear soil-structure interaction (SSI) effects. 10-, 15-, and 20-story planar building frames with aspect ratio of 3 are designed in accordance with current building codes. Inelastic seismic demands of the superstructure are considered using concentrated plasticity model. The raft foundation system is designed for different soil types. Beam-on-nonlinear Winkler foundation (BNWF) is used to represent dynamic impedance of the underlying soil. Two sets of pulse-like as well as no-pulse near-fault earthquakes are used as input ground motions. The results show that the reduction in drift demands due to nonlinear SSI is characterized by a more uniform distribution pattern along the height when compared to the fixed-base and linear SSI condition. It is also concluded that beneficial effects of nonlinear SSI on displacement demands is more significant in case of pulse-like ground motions and performance level of the steel moment-resisting frames can be enhanced.
Abstract: This study estimates the seismic demands of tall
buildings with central symmetric setbacks by using nonlinear time
history analysis. Three setback structures, all 60-story high with
setback in three levels, are used for evaluation. The effects of
irregularities occurred by setback are evaluated by determination of
global-drift, story-displacement and story drift. Story-displacement is
modified by roof displacement and first story displacement and story
drift is modified by global drift. All results are calculated at the
center of mass and in x and y direction. Also the absolute values of
these quantities are determined. The results show that increasing of
vertical irregularities increases the global drift of the structure and
enlarges the deformations in the height of the structure. It is also
observed that the effects of geometry irregularity in the seismic
deformations of setback structures are higher than those of mass
irregularity.
Abstract: When a building is located in an urban area, it is
exposed to a wind of different characteristics then wind over an open
terrain. This is development of turbulent wake region behind an
upstream building. The interaction with upstream building can
produce significant changes in the response of the tall building. Here,
in this paper, an attempt has been made to study wind induced
interference effects on tall building. In order to study wind induced
interference effect (IF) on Tall Building, initially a tall building
(which is termed as Principal Building now on wards) with square
plan shape has been considered with different Height to Width Ratio
and total drag force is obtained considering different terrain
conditions as well as different incident wind direction. Then total
drag force on Principal Building is obtained by considering adjacent
building which is termed as Interfering Building now on wards with
different terrain conditions and incident wind angle. To execute
study, Computational Fluid Dynamics (CFD) Code namely Fluent
and Gambit have been used.
Abstract: The advantage of using non-linear passive damping
system in vibration control of two adjacent structures is investigated
under their base excitation. The base excitation is El Centro
earthquake record acceleration. The damping system is considered as
an optimum and effective non-linear viscous damper that is
connected between two adjacent structures. A MATLAB program is
developed to produce the stiffness and damping matrices and to
determine a time history analysis of the dynamic motion of the
system. One structure is assumed to be flexible while the other has a
rule as laterally supporting structure with rigid frames. The response
of the structure has been calculated and the non-linear damping
coefficient is determined using optimum LQR algorithm in an
optimum vibration control system. The non-linear parameter of
damping system is estimated and it has shown a significant advantage
of application of this system device for vibration control of two
adjacent tall building.
Abstract: The differential column shortening in tall buildings can be reduced by improving material and structural characteristics of the structural systems. This paper proposes structural methods to reduce differential column shortening in reinforced concrete tall buildings; connecting columns with rigidly jointed horizontal members, using outriggers, and placing additional reinforcement at the columns. The rigidly connected horizontal members including outriggers reduce the differential shortening between adjacent vertical members. The axial stiffness of columns with greater shortening can be effectively increased by placing additional reinforcement at the columns, thus the differential column shortening can be reduced in the design stage. The optimum distribution of additional reinforcement can be determined by applying a gradient based optimization technique.
Abstract: Though nonlinear dynamic analysis using a specialized
hydro-code such as AUTODYN is accurate and useful tool for
progressive collapse assessment of a multi-story building subjected to
blast load, it takes too much time to be applied to a practical simulation
of progressive collapse of a tall building. In this paper, blast analysis of
a RC frame structure using a simplified model with Reinforcement
Contact technique provided in Ansys Workbench was introduced and
investigated on its accuracy. Even though the simplified model has a
fraction of elements of the detailed model, the simplified model with
this modeling technique shows similar structural behavior under the
blast load to the detailed model. The proposed modeling method can
be effectively applied to blast loading progressive collapse analysis of
a RC frame structure.