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Time Delay of Earthquake Excitation in High-Rise Building
Abstract
The nature of time delay of earthquake excitation in structures from the perspective of wave propagation is addressed, and then the time delay is used to modify conventional structural dynamics equation, which assumes implicitly the simultaneity of earthquake initial excitations at all degrees of freedom of a structure. A simple and practical method is then developed to compute structural responses considering the time delay effects of earthquake excitations in the structure. Through the computation of floor displacement and top floor maximum displacement according to current standards on seismic design of buildings, it was shown that conventional method neglecting the time delay effects of wave propagation in structures would not provide accurate structural responses, and should be modified. The introduction of the time delay effects of wave propagation in structures is thus of great importance for the safety of more and more supertall buildings to be constructed. The method proposed in the paper deals with this problem and provides a practical solution by incorporating time delay effects on analyzing structural responses for high-rise buildings subjected to earthquake excitations.
... The current research results on the wave passage effect are mainly focused on common large-span structures such as large-span bridges, large-span space structures, dams and underground pipelines [18][19][20][21] , and there have been few theoretical studies or shaking table tests on the influence of the wave passage effect on large-span high-rise buildings. By calculating the floor displacements and the top floor maximum displacements of high-rise buildings, Li et al. 22 showed that neglecting the wave passage effect will not provide an accurate structural response. To solve this problem, the traditional structural dynamics equations were modified using a time delay to incorporate the wave passage effect into the analysis of the structural response of high-rise buildings under seismic excitation. ...
This paper describes investigations in respect of the seismic performance of a large-span high-rise building in a mountainous area. The building consists of a 135 m high shear wall structure and a 174.5 m long steel truss structure, with dampers used to enhance the seismic performance. A 1/40 scale model of the prototype structure was designed, and shaking table tests was conducted. The experiments simulated the wave passage effect and slope amplification effect based on the building site and structural characteristics of the prototype structure. The seismic performance of the prototype structure was analyzed through the damage phenomenon, dynamic characteristics, and dynamic response of the model under earthquake effects. The results show that three seismic waves were delayed by about 0.4 s and amplified by about 1.6 times after passing through the steel frame with viscous dampers, which could effectively simulate the wave passage effect and slope amplification effect in the test. The maximum story drift ratios of the model shear wall structure and steel truss structure were 1/1258 and 1/455 for the SLE and 1/568 and 1/185 for the MCE. The damping devices played a key role in energy dissipation. As a result, this research provides a reference for the seismic design and shaking table testing of large-span high-rise buildings.
Two-dimensional continuous models have been used to investigate the effects of the propagation of seismic waves into buildings with shear walls at the ends and with a central core. Neglecting the soil-structure interaction, analytical solutions have been obtained for the displacement response to monochromatic SHwaves, propagating with finite phase velocities on the surface of the homogeneous half-space. Two-dimensional models were found to be more representative than the equivalent one-dimensional models of the response characteristics of such buildings. It will be shown that shear walls at the ends reduce the horizontal whipping of the building, that the central core does not reduce the torsional displacements, and that the core may allow too much horizontal whipping of the free ends of the building. It is suggested that the shear-resisting elements are more efficient if placed symmetrically and closer to the ends of long buildings.
This paper presents a discrete-time wave-propagation method to calculate the seismic response of multistory buildings, founded on layered soil media and subjected to vertically propagating shear waves. Buildings are modeled as an extension of the layered soil media by considering each story as another layer in the wave-propagation path. The seismic response is expressed in terms of wave travel times between the layers and wave reflection and transmission coefficients at layer interfaces. The method accounts for the filtering effects of the concentrated foundation and floor masses. Compared with commonly used vibration formulation, the wave-propagation formulation provides several advantages, including simplicity, improved accuracy, better representation of damping, the ability to incorporate the soil layers under the foundation, and providing better tools for identification and damage detection from seismic records. Examples are presented to show the versatility and the superiority of the method.
The majority of structural health monitoring methods are based on detecting changes in the modal properties, which are global characteristics of the structure, and are not sensitive to local damage. Wave travel times between selected sections of a structure, on the other hand, are local characteristics, and are potentially more sensitive to local damage. In this paper, a structural health monitoring method based on changes in wave travel times is explored using strong motion data from the Imperial Valley Earthquake of 1979 recorded in the former Imperial County Services (ICS) Building, severely damaged by this earthquake. Wave travel times are measured from impulse response functions computed from the recorded horizontal seismic response in three time windows—before, during, and after the largest amplitude response, as determined from previous studies of this building, based on analysis of novelties in the recorded response. The results suggest initial spatial distribution of stiffness consistent with the design characteristics, and reduction of stiffness following the major damage consistent with the spatial distribution of the observed damage. The travel times were also used to estimate the fundamental fixed-base frequency of the structure f1 (assuming the building deformed as a shear beam), and its changes during this earthquake. These estimates are consistent with previous estimates of the soil–structure system frequency, fsys, during the earthquakes (f1<fsys as expected from soil–structure interaction studies), and with other estimates of frequency (f1 from ETABS models, and fsys from ambient vibration tests, and “instantaneous” f1 from high-frequency pulse propagation).
Code for seismic design of buildings GB 50011-2001 " ,China architecture and building press Technical specification for concrete structures of tall building JGJ 3-2002
- China Committee
China Standards Committee.(2008), " Code for seismic design of buildings GB 50011-2001 ",China architecture and building press. China Standards Committee.(2002), " Technical specification for concrete structures of tall building JGJ 3-2002 ", China architecture and building press.
On the earthquake input model with multiple support excitations The 14th World Conference on Earthquake Engineerin Fundamentals of earthquake engineering
- D S Li
- H N Li
- S Y Xiao
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