Details of a Researcher - Kohiyama, Masayuki

Papers - Kohiyama, Masayuki

Division display 21 - 40 of about 173 ／ All the affair displays >>

Detection method of unlearned pattern using support vector machine in damage classification based on deep neural network

Kohiyama M., Oka K., Yamashita T.

Structural Control and Health Monitoring (Wiley) 27 ( 8 ) 2020.08

Research paper (scientific journal), Joint Work, Lead author, Last author, Corresponding author, Accepted, ISSN 15452255

Deep neural networks (DNNs) are a powerful tool for structural health monitoring because they can automatically identify features that are useful for classifying and recognizing damage patterns of a target structure with high accuracy. However, it can misclassify input data of an unlearned damage pattern as any of the learned damage patterns. To address this shortcoming, this paper presents a method to detect unlearned damage patterns by using the collective decision of support vector machines (SVMs). SVMs are constructed using feature vectors from training data, which are stored in the output layer of a DNN. To validate the proposed method, we used two different datasets, one containing experimental data of a steel frame structure and the other containing simulated and experimental data of a wooden house. In both cases, it correctly identified data of both learned and unlearned damage patterns. The proposed method can enhance the effectiveness of structural health monitoring (SHM). In addition, because it does not employ SHM-specific characteristics, it can be used in various pattern recognition applications, such as image and audio processing.

Access to Document (DOI)

Seismic Response Control of an Instrument With Casters Using Computer Vision Based on Reinforced Learning of Dynamic Analysis Results Considering Friction

Kento WAKABAYASHI, Yosuke KAWANISHI, Masayuki KOHIYAMA, Ryo EGUCHI, and Masaki TAKAHASHI

Journal of Structural Engineering (Architectural Institute of Japan) 66B 305 - 314 2020.03

Research paper (scientific journal), Joint Work, Accepted, ISSN 0910-8033

We developed a computer vision system to control the seismic response of medical equipment with casters in a building subjected to earthquake excitation. The controller employs a neural network and the reinforced learning was conducted based on dynamic simulations of a controlled equipment under building floor motion. In the dynamic simulations, we used Open Dynamics Engine, which is a simulator library of three-dimensional rigid body dynamics, and we introduced a friction model to simulate the dynamic behavior of the casters. To validate the proposed system, we conducted shaking table tests and it was confirmed that the proposed control could successfully suppress the response of the equipment.

Semi-actively Implemented Non-linear Damping for Building Isolation Under Seismic Loadings

Zhu Y.P., Lang Z.Q., Kawanishi Y., Kohiyama M.

Frontiers in Built Environment (Frontiers) 6 2020.02

Research paper (scientific journal), Joint Work

It is well-known that semi-active solution can achieve building isolation with much less energy requirements than active solutions. Also, it has been shown in previous studies that compared to linear damping, non-linear damping performs better for building isolation under sinusoidal ground motions. The present study is concerned with the extension of the application of the semi-actively implemented non-linear damping to building isolation under seismic loadings. A two-degree-of-freedom (2-DOF) scaled building model is used for simulation studies. Experimental tests on a physical building model have been used to validate the effectiveness of the 2-DOF scaled building model in representing the behaviors of a physical building structure. The optimal design of the semi-actively implemented non-linear damping for building isolation under design seismic motions is then carried out using the 2-DOF scaled building model based on simulation studies. The results show that an optimal design of semi-actively implemented non-linear damping can improve the performance of building isolation under design seismic motions in terms of both absolute acceleration and inter-story drift.

Access to Document (DOI)

Detection of Unlearned-Damage-Pattern Data Based on k-Nearest Neighbors Algorithm and Welch’s t Test in Damage Classification Using Deep Neural Network

Masayuki KOHIYAMA, Motoki FUTEMMA, Kazuya OKA, and Takuzo YAMASHITA

Proceedings of the Ninth Japan Conference on Structural Safety and Reliability (The Society of Materials Science, Japan) 319 - 326 2019.10

Research paper (other academic), Joint Work, Accepted

Deep neural network has been applied to damage classification in structural health monitoring. However, it has a drawback that it classifies data of an unlearned pattern as any of learned patterns. We propose a method to detect unlearned-damage-pattern data based on k-nearest neighbors algorithm and Welch’s t test. As input data of neural network, we used acceleration records acquired in shaking table test using steel frame specimen, which is a 1/3-scale model of a four-story steel structure and imitates structural damage with relaxed braces. The records were divided into one-second-long samples and used for training and verifying neural network. We extracted feature data in an output layer of the network and clarified that the data do not follow to a Gaussian distribution. Therefore, Anomaly index based on k-nearest neighbors algorithm is introduced to measure the non-similarity to learned pattern data. Using data of shaking table test of a steel frame structure, we verified that unlearned-damage-pattern data can be detected by Welch's t test.

Haruka Yokoyama, Hajime Iwai, and Masayuki Kohiyama

Proceedings of the 29th European Safety and Reliability Conference, ESREL 2019 (Research Publishing, Singapore) 3217 - 3223 2019.09

Research paper (international conference proceedings), Joint Work, Accepted

We propose a quantitative phase model to predict element waves of adjacent element faults to simulate ground motion using the stochastic Green's function method. We paired seismic records under the specified conditions of near-identical magnitude and hypocenter depth. To model the acceleration waveform similarities of the seismic record pair, a relationship between the mean value of Fourier amplitudes and an absolute value of Fourier phase difference was represented using a beta distribution. We then derived a regression formula of beta-distribution shape parameters with respect to the distance between the two hypocenters of each pair. Based on the proposed model, a seismic wave was synthesized, along with a calculated RMS error in acceleration response spectra between the synthesized wave and the observed record of the 2016 Kumamoto earthquake. It was confirmed that the proposed model decreased the error successfully.

Access to Document (DOI)

Probability Distribution of Torsional Response Induced by Lateral Displacement and Inertial Force

Hiroki Yokoyama and Masayuki Kohiyama

Proceedings of the 29th European Safety and Reliability Conference, ESREL 2019 (Research Publishing, Singapore) 3224 - 3231 2019.09

Research paper (international conference proceedings), Joint Work, Accepted

In previous studies of torsional response, researchers considered that torsional vibration of building is caused by eccentric distribution of stiffness, damping, and mass of a structure, or spatially non-uniform ground motion input to a long or large base mat of a structure. However, we have discovered that the torque generated by horizontal displacement and perpendicular inertial force, which we call the Q–Delta effect, can cause torsional vibration. In order to investigate this effect, we considered a single finite-size mass-linear elastic shear and torsion spring model and derived the resonance condition with respect to a torsional response from the equation of motion. In this study, we discuss probability distribution of the induced torque and torsional displacement response to uncorrelated Gaussian white noise input ground acceleration in two translational directions. In the frequency domain, the power spectral density function of the torque induced by the Q–Delta effect is proportional to a convolution of two frequency response functions in two translational directions. In the time domain, the probability density function of the induced torque is the modified Bessel function of the second kind. Time-history response analysis was conducted to verify these theoretical results and to investigate the distribution of torsional response to Gaussian white noise input ground acceleration.

Access to Document (DOI)

Update of control parameters for semi-actively controlled base-isolated building to improve seismic performance

Masayuki Kohiyama, Masashi Omura, Masaki Takahashi, Osamu Yoshida, and Koichi Nakatsuka

Japan Architectural Review (Wiley) 2 ( 3 ) 226 - 237 2019.07

Research paper (scientific journal), Joint Work, Accepted, ISSN 2475-8876

The Sosokan building of Keio University located in Yokohama, Japan, is a base‐isolated building with a semi‐active control system. The semi‐active dampers’ damping coefficient is changed to best reproduce the optimal control force in linear‐quadratic‐gaussian control. However, the implemented control gain was calculated on the basis of the structural parameters applied at the design stage. In this study, we identified the building's actual structural parameters using observational records from the 2011 Tohoku earthquake. Using the updated structural model and 1000 simulated ground motions, we conducted a dynamic response analysis, which resulted in a fragility curve. Then, we evaluated the damage probability using the fragility curve and a seismic hazard curve. Finally, we determined the optimal control parameters to minimize the damage probability and used these parameters to implement the semi‐active control system.

Access to Document (DOI)

Design Method of Inter-Story Tuned Mass Damper to Reduce Story Deformation and Its Verification Tests

Masayuki KOHIYAMA and Masashi OMURA

Journal of Structural Engineering (Architectural Institute of Japan) 65B 77 - 84 2019.03

Research paper (scientific journal), Joint Work, Accepted, ISSN 09108033

An inter-story tuned mass damper (ISTMD) is a variant form of a tuned mass damper, which is placed between consecutive floors to suppress the resonant response of a structure. We derived design parameters of an ISTMD under ground excitation that minimize story deformation on the basis of the fixed-points theory. Then, a shaking table tests were conducted to investigate the performance of an ISTMD with derived parameters. The result showed that the ISTMD worked well to suppress the response around the resonance point and it reduced the displacement and maximum acceleration responses more effectively than an ordinary damper when the El Centro wave was input to the specimen.

Torsional Response Induced by Lateral Displacement and Inertial Force

Masayuki Kohiyama and Hiroki Yokoyama

Frontier in Built Environment (Frontiers) 4 ( 38 ) 1 - 12 2018.07

Research paper (scientific journal), Joint Work, Accepted, ISSN 2297-3362

Eccentric distribution of stiffness, damping, and mass of a structure, and spatially non-uniform ground motion input to a long or large base mat of a structure are well-known causes of torsional response. We have discovered that the torque generated by horizontal displacement and perpendicular inertial force, which we call the Q-Δ effect, can be a cause of torsional response. We formulated the equation of motion of a single finite-size mass-linear elastic shear and torsion spring model and clarified the resonance condition of the torsional response to sinusoidal ground acceleration. Time-history response analysis verified that the torsional response forms beat and the maximum torsional response of the simulation result agrees with that theoretically predicted. Further time-history response analysis conducted of white noise ground acceleration showed that even one-directional white noise ground acceleration can induce torsional response in a linear elastic system without any structural eccentricity.

Access to Document (DOI)

Update of Control Parameters of Semi-Actively Controlled Base-Isolated Building

Kohiyama, M., Omura, M., Takahashi, M., Yoshida, O., and Nakatsuka, K.

Proc. 7th World Conference on Structural Control and Monitoring 351 - 359 2018.07

Research paper (international conference proceedings), Joint Work, Accepted

The Sosokan university building has base isolation and a semi-active control system. The semi-active dampers’ damping coefficient is changed so as to best reproduce the optimal control force in linear-quadratic-Gaussian control. However, the implemented control gain was calculated based on the structural parameters at the design stage. In this study, we identify the building’s actual structural parameters by using observation records of the 2011 Tohoku earthquake. Dynamic response analysis is conducted by using the updated structural model and 1000 simulated ground motions. Then, the damage probability is evaluated using a fragility curve derived from the result of dynamic response analysis as well as a seismic hazard curve. Finally, the optimal control parameters are obtained to minimize the damage probability, and these parameters are implemented in the semi-active control system.

Nonlinear damping based semi-active building isolation system

Carmen Ho, Yunpeng Zhu, Zi-Qiang Lang, Stephen A. Billings, Masayuki Kohiyama, and Shizuka Wakayama

Journal of Sound and Vibration (Fuji Technology Press) 424 302 - 317 2018.06

Research paper (scientific journal), Joint Work, Accepted, ISSN 0022460X

Many buildings in Japan currently have a base-isolation system with a low stiffness that is designed to shift the natural frequency of the building below the frequencies of the ground motion due to earthquakes. However, the ground motion observed during the 2011 Tohoku earthquake contained strong long-period waves that lasted for a record length of three minutes. To provide a novel and better solution against the long-period waves while maintaining the performance of the standard isolation range, the exploitation of the characteristics of nonlinear damping is proposed in this paper. This is motivated by previous studies of the authors, which have demonstrated that nonlinear damping can achieve desired performance over both low and high frequency regions and the optimal nonlinear damping force can be realized by closed loop controlled semi-active dampers. Simulation results have shown strong vibration isolation performance on a building model with identified parameters and have indicated that nonlinear damping can achieve low acceleration transmissibilities round the structural natural frequency as well as the higher ground motion frequencies that have been frequently observed during most earthquakes in Japan. In addition, physical building model based laboratory experiments are also conducted, The results demonstrate the advantages of the proposed nonlinear damping technologies over both traditional linear damping and more advanced Linear-Quadratic Gaussian (LQG) feedback control which have been used in practice to address building isolation system design and implementation problems. In comparison with the tuned-mass damper and other active control methods, the proposed solution offers a more pragmatic, low-cost, robust and effective alternative that can be readily installed into the base-isolation system of most buildings.

Access to Document (DOI)

Road Network Evaluation from the Viewpoint of Fire Extinguishing, Fire Spread, and Evacuation to Plan Improvement of District Seismic Safety

Yosuke KAWANISHI and Masayuki KOHIYAMA

Journal of Japan Association for Earthquake Engineering (Japan Association for Earthquake Engineering) 18 ( 2 ) 35 - 50 2018.05

Research paper (scientific journal), Joint Work, Accepted

Road blockage caused by collapsed buildings hinders evacuation, firefighting, and lifesaving activities. It also expands the damage of fire spreading. We propose a method to evaluate the disaster reduction performance of a district with three indices of fire extinguishing probability, ratio of non-burned buildings, and evacuation achievement rate. In the evaluation of these indices, we use the Monte Carlo method based on building collapse rate, fire outbreak probability, etc. As a result of evaluating the proposed indices for two virtual districts: one with latticed road and the other with the radial-ring road, we find that the proposed indices reflect the characteristics of the road network and can express the disaster reduction performance of the districts. In addition, they can facilitate the priority of seismic retrofitting plans considering the characteristics of the district.

Access to Document (DOI)

Evaluation of Torsional Vibration Due to Eccentrically-Located Mass and Planer Shape in Wooden Houses under Strong Ground Motion Based on Dynamic Analysis

Kazuya OKA and Masayuki KOHIYAMA

Journal of Structural Engineering (Architectural Institute of Japan) 64B 479 - 492 2018.03

Research paper (scientific journal), Joint Work, Accepted, ISSN 09108033

Time history response analysis was conducted to evaluate torsional response of wooden houses with eccentrically-located mass, such as balconies and solar power panels, under strong ground motion. Five kinds of two-story models were examined and the following findings were observed: (1) In the cases of models with a longer width in the east-west direction, a model with a living room on the first floor showed larger torsional response than that on the second floor because of difference in the amount of walls in the first story. (2) A model with a longer width in the north-south direction showed larger torsional response than that in the east-west direction because of larger eccentric distance. (3) A model with a double-height ceiling room had twice larger response than that without it. Thus, it is necessary to design houses with a double-height ceiling room with careful consideration of torsional response.

Seismic Fragility Function for Ceilings: A Formulation Using Upper Floor Response Acceleration

Kohiyama, M.

Proc. 12th International Conference on Structural Safety and Reliability (International Association for Structural Safety and Reliability) 1873 - 1881 2017.08

Research paper (conference, symposium, etc.), Single Work, Accepted

Contribution of Corporate Social Responsibility to Post-Disaster Life Recovery of Employees

Dan, M. and Kohiyama, M.

Journal of Disaster Research (Fuji Technology Press) 12 ( 4 ) 811 - 821 2017.08

Research paper (scientific journal), Joint Work, Accepted

Corporate social responsibility (CSR) is now considered to be one of the most important activities for companies as it greatly affects both companies and local communities. This study analyzes the effects of corporate social responsibility activities on the life recovery of employees. A questionnaire survey on the Great East Japan Earthquake Disaster in Iwaki City (Fukushima, Japan) was conducted. Iwaki City was among the areas most severely affected by the disaster. The effect of CSR activities on the life recovery of employees was analyzed by structural equation modeling. Life recovery largely depended on health and human relationships. CSR activities related to these two factors, such as work–life balance and local community activities, increased the life recovery of employees. Companies have large resources for improving local community resilience and local communities can recover from a disaster in a timely and effective manner when companies provide appropriate assistance. This study reveals how companies can contribute to the recovery of local communities through their CSR activities.

Access to Document (DOI)

Damage Probability Evaluation of a Large Span Steel Frame Based on Dynamic Analysis Considering Load Combination of Earthquake and Snow

Kenji YAMAZAKI and Masayuki KOHIYAMA

Journal of Structural Engineering (Architectural Institute of Japan) 63B 83 - 89 2017.03

Research paper (scientific journal), Joint Work, Accepted

Recently, disasters due to concomitant hazards of earthquake and snow have been increasing in Japan. When engineers verify the structural safety of buildings in a heavy-snow region by means of structural calculation, a coefficient value of 0.35 is used for snow weight under load combination with earthquake with reference to Building Standard Law of Japan. This paper investigates the necessity of load combination of moderate earthquake and moderate snow. The fragility surface of a large span steel frame under seismic excitation and snow load is developed based on dynamic analysis. Two kinds of damage-related responses, the maximum stress of members and the maximum response acceleration of ceilings are examined. With respect to the maximum stress, the evaluated fragility surface and joint hazard surface of earthquake and snow suggest that additional consideration is required for load combination of moderate earthquake and moderate snow.

Seismic Risk Assessment of Wooden Structures near Faults Considering the Locational Uncertainty of Source Area Using the Non-Uniform Slip Model

Seikai, M., Nakahara, S., and Kohiyama, M.

Proc. 16th World Conference on Earthquake Engineering 2017.01

Research paper (international conference proceedings), Joint Work, Accepted

Although the magnitudes of inland earthquakes are smaller than those of earthquakes in subduction zones, they have caused catastrophic disasters in the past. Seismic damage to structures strongly depends on the geometric relationship between a fault and the structure itself, especially near a fault. In recent years, the locations and activities of inland active faults have been identified in Japan. However, the position of a rupture-starting point and rupture extent are uncertain. Together with this uncertainty, we have to consider the difference in the seismic performances of structures, upon which the extent of damage also depends. In this study, seismic ground motions near a fault were simulated with consideration of the above-mentioned uncertainty, and the geometric distribution of the damage probability of wooden structures near a fault was investigated. The effect of seismic performance was also investigated. First, the ground motion with directivity on an engineering bedrock was simulated with a non-uniform slip model of an earthquake-source fault using the stochastic Green’s function. Element seismic waves overtook the phases of neighboring waves. Then, a rupture-starting point was decided stochastically and we assumed that the location of the earthquake-source fault followed a uniform distribution in the possible range. Ground motion on the surface was created by inputting the ground motion into a surface-layer model composed of loam using the one-dimensional equivalent linear analysis. If the maximum shear strain was over 5% in the response analysis result, we trimmed the input waves to maintain their reliability. Wooden structures were modeled considering the restoring force characteristics in accordance with the criteria of three seismic grades. Time-history response analysis was carried out by inputting the ground motion to the building model. Binomial discrimination as to whether or not damage occurred was conducted on the basis of the maximum story drift angle of the building models. Using the results of binomial discrimination, fragility curves assuming a lognormal distribution were constructed for each site using a maximum-likelihood method. Here the peak ground velocity was used as a ground-motion intensity parameter. A stochastic model of earthquake occurrence time was defined in consideration of the uncertainty of the earthquake scale, assuming a stochastic model for the variation of the slip quantity of the earthquake-source fault. We used a Brownian passage time distribution for making these models. Hazard curves of the ground motion were evaluated by this probability model. Finally, the earthquake damage probability of wooden structures was calculated for each site based on the fragility curve and the hazard curve mentioned above. As a result, the influence of the geometric relationship between a fault and the wooden structures and the seismic performance on the earthquake damage probability was obtained. The damage probability of wooden structures was significantly higher in the vicinity of the center of the possible range of the earthquake-source fault. In the vicinity of the fault, earthquake damage probability was reduced more effectively by changing the seismic grade from 1 to 2 than from 0 to 1.

Relation Between CSR Activities and the Resilience of Local Communities in Iwaki City after the 2011 Tohoku Earthquake

Dan, M., Kohiyama, M., and Kiremidjian, A. S.

Proc. 16th World Conference on Earthquake Engineering 2017.01

Research paper (international conference proceedings), Joint Work, Accepted

The concept of resilience is widely used in the disaster management field. In the earthquake-engineering field, many studies have investigated the structural performance of buildings and seismic resilience in terms of performance-based earthquake engineering. However, there are a limited number of studies on the social aspects of resilience. This study focuses on social activities by private companies. A company’s social activity is termed as its Corporate Social Responsibility (CSR). Further, this study also focuses on the relationships between the resilience of a community and the companies’ CSR activities in a local area.
We conducted two questionnaire surveys for citizens and companies in Iwaki City, which suffered from the 2011 Tohoku earthquake. We hypothesized that social activities by companies would improve the resilience of the local community. In the questionnaire surveys, we set two types of respondents as follows: CSR staff of companies and citizens in the local areas. Using the questionnaire responses of the CSR staff, we analyzed characteristics of CSR activities using principal component analysis. Subsequently, using the local citizens’ responses, we compared the differences in their life recovery in terms of economic circumstances and social aspects.

Experimental Study of the Effectiveness of Semi-Actively Implemented Power-Law Damping on Suppressing the Seismic Response of a Base-Isolated Building

Dan, M., Omura, M., Nakamichi, F., Kohiyama, M., and Lang, Z.-Q.

Proc. 6th European Conference on Structural Control (European Association for the Control of Structures) 2016.07

Research paper (international conference proceedings), Joint Work

This study focuses on verifying the effectiveness of the nonlinear power-law damping system on reduction of the vibration of base-isolated buildings with semi-actively implemented dampers over the ranges of resonance frequencies without causing detrimental effects over other frequency ranges. To verify the effectiveness of the proposed power-law damping system, shaking-table tests on a small-scale two-story physical building model are conducted. Random ground motions are used as the input excitations. The physical building model is equipped with a semi-active oil damper whose damping coefficient can be varied over four different values. This provides an effective mechanism for semi-actively implementing the power-law damping system. The shaking-table tests have demonstrated the effectiveness and robustness of the power-law damping and indicated that this can be a more practical solution to improving the performance of building base-isolation systems.

Shaking Table Tests of Cooperative Control between an Active Mass Damper for a Building and Semi-Active Damper for a Base-Isolated Floor Using a Small-Scale Specimen

Nakamichi, F. and Kohiyama, M.

Proc. 6th European Conference on Structural Control (European Association for the Control of Structures) 2016.07

Research paper (international conference proceedings), Joint Work

To reduce the amount of earthquake damage, the effectiveness of cooperative control between two controllers (one for the building and another for the equipment) was verified using a shaking table test. We employed a Kalman filter and the linear quadratic Gaussian strategy to minimise the amount of damage under strong ground motions, and the two controllers share the quantities of the state variables of the building and equipment. A three-storey specimen, which comprise a building (the main system) with an active mass damper and a base-isolated floor (a subsystem) with a semi-active oil damper, represents a 15-storey building of a data centre on a real scale. As a result of the shaking table test, we confirmed that implementing cooperative control reduced the relative displacement between the main system and subsystem without increasing absolute acceleration.

　 Previous page - Next page 　