We report a procedure by which structural parameters and input ground motion are identified from measured responses only. We have assumed that the coda of the response time history represents the free vibration response of the structural system. Because the coda is not effected by the input ground motion, we can first identify such structural parameters as the masses, damping coefficients and spring constants from this part of the record. Input ground motion then is estimated from the full record and the identified parameters. The identification and estimation are made with the Kalman filter. To verify the effectiveness of this procedure, we have simulated the responses of a linear, three-degree-of-freedom system for different earthquake inputs and made estimations using the simulated responses as observed records. The estimated accelerograms, the identification of which usually more difficult than the identifications of velocitigrams and displacementgrams, are in good agreement with the recorded ones for the actual earthquakes.
We propose a dynamic analysismethod – a refined version of the DEM- that can simulate three-dimensional elastic, failure and collapse behaviors of structures. A structure is modeled as an assembly of rigid elements. Interaction between elements is modeled using multiple springs and multiple dashpots attached to surfaces of the elements. The elements are assumed to be rigid, but the method allows the simulation of structural deformation by permitting penetration between elements. There are two types of springs: one is a restoring spring to simulate elastic behavior before failure and the other is a contact spring for simulating contact and recontact between elements. A contact dashpot is also used to dissipate the energy of contact. Structural failure is modeled by replacing restoring springs with contact springs and dashpots. A method for determining spring constants is also proposed. The validity of the method is confirmed by the numerical simulation of masonry wall models. First, the elastic behavior induced by an impact force is calculated. It is found that the elastic behavior determined using the proposed method is in good agreement with that determined using the finite element method. Second, the seismic behaviors of masonry wall models with different laying patterns and a wall model with reinforcement are analyzed. It is found that the proposed method allows expression of the difference in behavior due to different laying patterns and reinforcement. The validity of the proposed method is thus confirmed. The proposed method is suitable for simulating seismic behavior of masonry structures.
On April 25, 2015, a M w 7.8 earthquake struck the Gorkha district of Kathmandu, Nepal. In Patan, vibrational characteristics of a 300-year-old two-story masonry building near Patan Durbar Square had been measured prior the Gorkha earthquake. In the inspection of the building after the Gorkha earthquake, several new cracks were found. The vibrational characteristics of the building were measured again, and it was found that the natural frequencies after the earthquake were smaller than those before the earthquake, indicating the reduction of the stiffness. Finite element models of the structure representing pre-and post-earthquake conditions are established so that the natural frequencies match the pre-and post-earthquake measurements and the structural damage is identified based on the stiffness reduction. Finally, the dynamic analysis of the finite element model of the building in the pre-earthquake condition using the observed ground motion record during the Gorkha earthquake as the input is conducted, and the structural response of the building during the Gorkha earthquake is discussed.
SUMMARYA new technique is presented with which to investigate slope stability during strong earthquake motion. This technique is based on a non-linear finite element method that uses a joint element to express non-linear behaviour and the progressive failure of a slope. Joint elements are arranged at every interface between soil elements. Accordingly, each soil element is allowed to move in directions parallel, perpendicular and rotational to neighbouring elements; consequently, they express the sliding and separation at any interface between the soil elements.The method was used to investigate the stability of an existing slope during strong earthquake motions. Preliminary static analyses were made, and their results were compared with results obtained with Janbu's method in order to check the validity of our proposed method.Thedynamicanalyses also took into account the material non-linearity of the soil. The process of progressive failure was examined for a slope whose material constants are known. The influence of input excitations on slope stability is discussed in detail. The method also has been used to assess the effectiveness of a countermeasure used to prevent slope failure.Numerous slope failures are reported after almost every major earthquake in Japan, and these failures have done a great deal of damage to both property and people.'-'The casualty rates are increasing in hilly suburban areas in which the population has increased very rapidly. Slope failures often are accompanied by failures in lifeline systems such as water and gas supplies. Also breakdowns in transportation due to these slope failures further delay relief and repair services. The effect of slope failures on daily life grows greater each year, and a rational method with which to make a dynamic estimate of slope stability during earthquakes is of increasing importance. At present the procedure most commonly used is the sliding circle method, which is based on the seismic coefficient method. After the Off-Izu Peninsula earthquake in 1974, in which more than twenty people were killed by slope failures: dynamic analyses were initiated that used numerical methods; 5-7 these, however, were limited to linear analyses. To estimate slope stability rationally, it is necessary to take into account the progressive failure process. This requires non-linear dynamic analysis to express both the shear failure of the soil and destructive non-linear phenomena such as sliding and cracking.We proposed a general method with which to analyse non-linear dynamic soil structure interaction problems that used the finite element methodsv9 in which joint elements" represent sliding and separation phenomena * Professor. t Associate Professor.
A new closed-open-loop optimal control algorithm is proposed that has been derived by minimizing the sum of the quadratic time-dependent performance index and the seismic energy input to the structural system. This new control law provides feasi ble control algorithms that can easily be implemented for applications to seismic-excited structures. We developed optimal control algorithms, taking into account the nonlinearity of the structural system for applying a control force to a structural system subjected to gen eral dynamic loads. The formulation of a predictive control law has been developed in which emphasis is placed on compensation for the time delay due to measurement process and the control action. These optimal algorithms are simple and reliable for on-line con trol operations and effective for a structural system with a base isolation mechanism. The control efficiency affected by two weighting matrices included in the performance index is investigated in detail. Numerical examples are worked out to demonstrate the control effi ciency of the proposed algorithms.
This study examines the effect of axial force fluctuation in supporting columns of a traditional wooden temple on the seismic response of the structure. The main structure and high wooden stage of the Kiyomizu Temple, a Japanese national treasure located in Kyoto, were reconstructed in 1633 following a fire. The temple was modeled numerically for three-dimensional inelastic earthquake response analysis. An inelastic vertical spring was set at the base of each column to represent uplift during an earthquake, coupled with a horizontal spring set to represent variable friction corresponding to the varying axial force of the column. The results reveal that axial force fluctuation has little effect on the maximum seismic response of the structure. However, this effect does influence the residual displacement of each column, particularly near the perimeter of the structure.
In the dislocation theory, focal parameters such as the fault area, dislocation, source-time function, rupture velocity, rise time, etc. are assumed in advance of calculation. But, in actual situations, these parameters are the results of fractures on the fault plane. To produce this physical condition in the analysis of the focal rupture mechanism, the process of successive rupture must be analyzed as a phenomenon of fracture caused by external forces on the fault plane. The finite element method is a promising tool for this type of analysis.In this report, only the stress drop and yielding stress values of the fault being considered are assumed. Parameters that are assumed to be controlling parameters in the dislocation theory are obtained by results of numerical computations using the proposed method. In our analysis, rupture begins at some point on the fault where mobilized shear stress reaches the yielding stress value, then the rupture is transmitted successively along the fault. The driving force of successive rupture is the released strain energy produced by the tectonic force applied laterally on the far field of the crust. The focal parameters obtained from simulations compare well with the empirical relationships of focal parameters determined from past seismic data. The analysis is two dimensional, with a thrust type fault plane being treated. Emphasis is on the approach rather than on results developed during application.
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