Directory of Researchers

NAGAO Takashi
Resaarch Center for Urban Safety and Security
Professor
Civil Engineering / Architecutre and planning / Building Engineering
Last Updated :2022/10/04

Researcher Profile and Settings

Affiliation

  • <Faculty / Graduate School / Others>

    Resaarch Center for Urban Safety and Security
  • <Related Faculty / Graduate School / Others>

    Faculty of Engineering / Department of Civil Engineering, Graduate School of Engineering / Department of Civil Engineering

Teaching

Research Activities

Research Areas

  • Social infrastructure (civil Engineering, architecture, disaster prevention) / Structural and seismic engineering

Published Papers

  • Christino Boyke, Afif Navir Refani, Takashi Nagao

    In Indonesia, infrastructure, such as port facilities, has been damaged by earthquakes. Therefore, evaluating rational earthquake ground motions (EGMs) for seismic design is necessary to mitigate earthquake disasters in the future. The EGMs in the Indonesian Seismic Code are stipulated based on the ASCE standards and not on site-specific ones. This study aims to propose site-specific EGMs for the seismic design of port facilities in Indonesia. The EGM records and ground data in Indonesia were used for analysis. The EGM incidents in the bedrock were evaluated with deconvolution analysis. The obtained EGMs were amplitude-adjusted to peak ground acceleration similar to that of the EGMs in the bedrock in the Indonesian Seismic Code. A seismic response analysis considering nonlinear soil characteristics was conducted, and 144 EGMs at port sites were obtained. Considering the variation in the obtained EGMs, we propose site-specific EGMs for the seismic design of port facilities. A comparison of the proposed EGMs with those in the design code reveals that the difference between them is significant.

    {MDPI} {AG}, 14 Feb. 2022, Applied Sciences, 12 (4), 1963 - 1963, English

    [Refereed]

    Scientific journal

  • Variation Evaluation of Path Characteristic and Site Amplification Factor of Earthquake Ground Motion at Four Sites in Central Japan

    Takashi Nagao

    The considered parameters in seismic design vary, with the Earthquake Ground Motion (EGM) having the largest variation. Since source characteristic, path characteristic, and Site Amplification Factor (SAF) influence the EGM, it is crucial to appropriately consider their variations. Source characteristic variations are mainly considered in a seismic hazard analysis, which is commonly used to evaluate variations in EGM. However, it is also important to evaluate variations in path characteristic and SAF with only a few studies having individually and quantitatively examined the variations of these two characteristics. In this study, based on strong-motion observation records obtained from four sites in central Japan, the three characteristics were extracted from seismograms using the concept of spectral inversion. After removing the source characteristic, the path characteristic and SAF were separated, and the variations in these two characteristics were quantified. To separate and obtain each characteristic from the observed record, one constraint condition must be imposed, whereas the variations in the constraint condition must be ignored. In that case, the variations in the constraint condition are included in the variations of the separated characteristics. In this study, this problem was solved by evaluating the variation in the constraint condition, which is the SAF at a hard rock site, by the use of the vertical array observation record at the site.

    Lead, EOS ASSOC, Oct. 2021, ENGINEERING TECHNOLOGY & APPLIED SCIENCE RESEARCH, 11 (5), 7658 - 7664, English

    [Refereed]

    Scientific journal

  • Evaluation Methods of Vertical Subgrade Reaction Modulus and Rotational Resistance Moment for Seismic Design of Embedded Foundations

    Takashi Nagao, Ryota Tsutaba

    In a seismic design of embedded foundations, the vertical Subgrade Reaction (SR) acting on a foundation bottom surface and the Rotational Resistance Moment (RRM) generated by the SR are calculated using an SR Modulus (SRM). The SRM and RRM depend on both ground rigidity and Foundation Width (FW). However, the SRM and RRM calculation methods adopted in design codes might not properly consider their FW dependency. In this study, SRM and RRM evaluation methods for embedded foundations subjected to a seismic load were examined by conducting a two-dimensional finite element analysis under the condition where ground rigidity and FW were changed considering the nonlinearity of the ground. The results show that when the seismic load is large and the nonlinearity of the ground appears, the SR distribution is different from the assumption in the design code. The FW dependency of the SRM was lower than the assumption of the design code. Furthermore, methods to calculate the SRM and RRM in accordance with the FW and ground rigidity are proposed.

    Lead, EOS ASSOC, Aug. 2021, ENGINEERING TECHNOLOGY & APPLIED SCIENCE RESEARCH, 11 (4), 7386 - 7392, English

    [Refereed]

    Scientific journal

  • T. Nagao

    Since an Earthquake Ground Motion (EGM) is amplified from the propagation through the ground, different models are required for each ground type in the seismic design of structures. While the shallow subsurface indicators are used for the classification of ground types, a deep subsurface has a significant impact on the amplification of the EGMs. This study discusses the maximum credible EGMs for seismic design reflecting seismic amplification due to deep subsurface. The design spectra, reflecting the site amplification factor of the target location, are presented by the calculation of the EGMs with the same source and path characteristics and different site amplification factors as recent major Japanese earthquake records have shown, from the perspective of establishing the maximum credible EGMs that may occur in the future at a target site. The present design spectra, which are based on the natural period of a shallow subsurface, are compared with those based on the site amplification factors, considering the effect of deep subsurfaces. Although there are almost no differences in the design spectra with the present design methods according to the surface ground type, the proposed method provides significantly different design spectra for each site amplification factor.

    Lead, Engineering, Technology & Applied Science Research, 11 Apr. 2021, Engineering, Technology & Applied Science Research, 11 (2), 6873 - 6881

    [Refereed]

    Scientific journal

  • Effect of Foundation Width on Subgrade Reaction Modulus

    Takashi Nagao

    Structures are subjected to vertical and horizontal loads. Vertical subgrade reaction acts on the foundation bottom surface, and in the case of an embedded structure, horizontal subgrade reaction acts on the embedded part. The subgrade reaction is obtained by multiplying the displacement of the foundation by the Subgrade Reaction Modulus (SRM). In practice, SRM is calculated using an equation that incorporates the negative power relationship of the Foundation Width (FW). If the structure is evaluated to be poorly seismic resistant, it is necessary to widen FW. However, when the FW is widened, the design value of SRM decreases. In this case, it is not possible to expect an increase in the subgrade reaction proportional to the increase of FW. Therefore, when the inertia force is very high, the FW has to be very wide. However, underestimating SRM can lead to structural overdesign. In this study, the relationship between SRM and FW, for a structure in which vertical and horizontal load act simultaneously, was analyzed. Compared with the design practice assumptions, the horizontal SRM was found to be highly dependent on FW while the vertical SRM was shown to be less dependent on FW.

    Lead, EOS ASSOC, Oct. 2020, ENGINEERING TECHNOLOGY & APPLIED SCIENCE RESEARCH, 10 (5), 6253 - 6258, English

    [Refereed]

    Scientific journal

  • Kenichiro MIYASHITA, Takashi NAGAO

    Japan Society of Civil Engineers, Sep. 2020, Journal of Japan Society of Civil Engineers, Ser. A1 (Structural Engineering & Earthquake Engineering (SE/EE)), 76 (4), I_596 - I_609

    [Refereed]

    Scientific journal

  • Source- and Site-Specific Earthquake Ground Motions Application of a State-of-the-Art Evaluation Method

    Takashi Nagao, Yasuhiro Fukushima

    Seismic codes stipulate earthquake ground motions by considering the seismicity and seismic amplification properties of the ground at the target site. However, the effects of source, path, and site amplification characteristics are not sufficiently anticipated in seismic codes. Regarding the source and path characteristics, earthquakes that have the strongest influence on the target site should be considered specifically, and, concerning seismic amplification, the effects of not only a shallow subsurface but also a deep subsurface should be considered. This article takes the design spectra of Japanese highway bridges as an object and compares them with the spectra produced by a ground motion prediction equation and the source- and site-specific spectra evaluated using a state-of-the-art method. The results show that the spectra differ greatly. In this way, the necessity of the application of a state-of-the-art technique in the evaluation of source, path, and site amplification characteristics is demonstrated.

    Lead, EOS ASSOC, Aug. 2020, ENGINEERING TECHNOLOGY & APPLIED SCIENCE RESEARCH, 10 (4), 5882 - 5888, English

    [Refereed]

    Scientific journal

  • State of Seismic Hazard Analysis: Reviewing the Needs after Mw 7.8 Gorkha, Nepal Earthquake

    T. N. Bhattarai, T. Nagao, T. N. Lohani

    Jul. 2020, Journal of Development Innovations, 4 (1), 48 - 63

    [Refereed]

    Scientific journal

  • An Experimental Study on the Way Bottom Widening of Pier Foundations Affects Seismic Resistance

    Takashi Nagao

    The resistance of a pier to horizontal loads, like seismic loads, is due to the flexural rigidity of its foundations and the horizontal subgrade reaction. In the event of a massive earthquake, the latter becomes very small because of the softening of the ground, while the structure may experience a large inertia force and lateral spreading pressure. Therefore, structures with high seismic resistance are required in areas with high seismicity. When a wide caisson is used as a pier foundation, a rotational resistance moment caused by the vertical subgrade reaction acting on the foundation bottom can be expected. Although this rotational resistance moment increases if the foundation is widened, in design practice the subgrade reaction coefficient is evaluated as being low under such circumstances. Therefore, even if the foundation is widened, the rotational resistance moment does not increase greatly. Rotational resistance commensurate with the increased construction cost due to foundation widening cannot be expected. In the present study, horizontal loading experiments were performed at one pier with a normal foundation and at one with widened at the bottom foundation, and the way that the widening affected the seismic performance was examined. The results show that compared with the normal foundation, the bottom-widened one experienced far less displacement and offered higher earthquake resistance.

    Lead, EOS ASSOC, Jun. 2020, ENGINEERING TECHNOLOGY & APPLIED SCIENCE RESEARCH, 10 (3), 5713 - 5718, English

    [Refereed]

    Scientific journal

  • Daisuke Shibata, Takashi Nagao

    International Information and Engineering Technology Association, 30 Apr. 2020, International Journal of Safety and Security Engineering, 10 (2), 209 - 218

    [Refereed]

    Scientific journal

  • Seismic Amplification by Deep Subsurface and Proposal of a New Proxy

    Nagao, Takashi

    Codes of practice and ground motion prediction equations involve ground structure proxies to account for seismic amplification. Although the ground consists of both shallow and deep subsurface, proxies are mainly related to the shallow subsurface as it is shallow subsurface information that is mostly available. However, as deep subsurface seismic amplification is not negligible, it may not be appropriate to use shallow subsurface proxies. In this study, the relationship between shallow and deep subsurface seismic amplification factors is discussed on the basis of S-wave velocity profile data from Japanese KiK-net strong-motion observation system stations. The correlation between typical proxies such as the average S-wave velocity of the top 30m of the ground surface and the seismic amplification factor was examined. Although there was a negative correlation between the two, the degree of the correlation was weak. A new proxy showing stronger correlations with the seismic amplification factor is proposed and its effectiveness is demonstrated.

    Lead, EOS ASSOC, Feb. 2020, ENGINEERING TECHNOLOGY & APPLIED SCIENCE RESEARCH, 10 (1), 5157 - 5163, English

    [Refereed]

    Scientific journal

  • Takashi Nagao, Panpan Lu

    © 2019 Elsevier Ltd Pile-supported wharves undergo lateral displacement as well as structural damage due to earthquakes. Therefore, residual displacement and structural safety assessment are necessary for earthquake-resistant design of pile-supported wharves. This study introduces a simplified reliability estimation method for pile-supported wharves, involving the residual displacement caused by earthquakes and the variation of earthquake ground motions. As the residual displacement of wharves is strongly affected by the deformation of subsoil caused by earthquakes, a soil-structure system finite element earthquake response analysis was performed. To reduce the computational load for the evaluation of a probability distribution of residual displacement, a first-order second-moment method estimating the probabilistic response of structures with a small number of trials was applied. Thefinite element analyses demonstrate that the summed squared Fourier amplitudes (SSFAs) of the input seismic motion for a cumulative probability frequency band better estimated the residual displacement. A simplified reliability estimation method utilizing three results of finite element analyses is proposed following the demonstration of its applicability.

    Lead, Feb. 2020, Soil Dynamics and Earthquake Engineering, 129

    [Refereed]

    Scientific journal

  • Experimental Study of the Lateral Spreading Pressure Acting on a Pile Foundation During Earthquakes

    Takashi Nagao, Daisuke Shibata

    In the seismic design of pile foundations, the safety of the pile is assessed by considering the inertial force during an earthquake and subgrade reaction as external forces against the pile. The amount of deformation of the pile must be limited to a small value to maintain the safety of the pile. In the event of a large earthquake, quay walls and seawalls are subjected to lateral spreading because of the influence of biased seaward earth pressure. The amount of lateral spreading is considerably larger than what can be expected in a typical pile seismic design and may reach several meters. In this study, loading experiments that reproduced lateral spreading were conducted to evaluate the lateral spreading pressure acting on a pile when considerably large lateral spreading occurred. The experiment results showed that lateral spreading pressure depended on the ratio of pile spacing to pile diameter while the peak value of lateral spreading pressure was larger than the one assumed in practical design.

    Lead, EOS ASSOC, Dec. 2019, ENGINEERING TECHNOLOGY & APPLIED SCIENCE RESEARCH, 9 (6), 5021 - 5028, English

    [Refereed]

    Scientific journal

  • Variation of Earthquake Ground Motions with Focus on Site Amplification Factors

    Fukushima Yasuhiro, Nagao Takashi

    Aug. 2019, ENGINEERING TECHNOLOGY & APPLIED SCIENCE RESEARCH, 9 (4), 4355 - 4360

    [Refereed]

  • FUKUSHIMA Yasuhiro, NAGAO Takashi

     In this study, by using simultaneous observation record at neighbouring earthquake ground motion observation stations, the variations of the site amplification factors was evaluated with IBR003 earthquake ground motion observation stations in Ibaraki prefecture. Furthermore, the earthquake ground motion considering the variation of the site amplification factors was calculated, and the relation between the variation of the site amplification factors and the variation of representative values of earthquake ground motion was discussed.

     As a result, the peak ground accelerations, peak ground velocities, and power spectrum intensity values of the earthquake ground motions considering the average site amplification factor are smaller than the average values of those of the earthquake ground motions.

    Japan Society of Civil Engineers, 2019, Journal of Japan Society of Civil Engineers, Ser. A1 (Structural Engineering & Earthquake Engineering (SE/EE)), 75 (4), I_763 - I_769, Japanese

    [Refereed]

  • A simple estimation method of the probability distribution of residual displacement and maximum bending moment for pile supported wharf by earthquake

    T. Nagao, P. Lu

    © 2019 Taylor & Francis Group, London. It is necessary to conduct two-dimensional nonlinear earthquake response analysis many times in order to evaluate probabilistic characteristic of residual deformations and maximum bending moment of a pile supported wharf by earthquake. This paper aims at proposing a simple estimation method for those parameters of pile supported wharf. Variations of input earthquake ground motion were evaluated based on the variations of site amplification factors. It was shown that the probability distributions of residual deformations and maximum bending moment of a pile supported wharf can be evaluated with enough accuracy by using the result of three earthquake response analyses.

    2019, Life-Cycle Analysis and Assessment in Civil Engineering: Towards an Integrated Vision - Proceedings of the 6th International Symposium on Life-Cycle Civil Engineering, IALCCE 2018, 2763 - 2768, English

    [Refereed]

    International conference proceedings

  • 震源のモデル化の違いによるスラブ内地震の予測地震動の比較

    福島康宏, NAGAO Takashi, 尾茂淳平, 末冨岩雄

    土木学会, 2018, 土木学会論文集A1(構造・地震工学), 74 (4), 1035 - 1044, Japanese

    [Refereed]

    Scientific journal

  • 控え直杭式矢板岸壁の簡易耐震性能照査法における控え杭のモデル化方法の改善

    宮下健一朗, NAGAO Takashi

    土木学会, 2018, 土木学会論文集A1(構造・地震工学), 74 (4), 686 - 698, Japanese

    [Refereed]

    Scientific journal

  • Daisuke Shibata, Takashi Nagao

    © 2018 WIT Press. An open-type wharf with a pneumatic caisson foundation has strong earthquake resistance because of its high rigidity. Construction of wharves with stronger seismic resistance and a larger planned depth is indispensable to accommodate ever-increasing larger vessels. Considering this trend and strong earthquake resistance, open-type wharves with a pneumatic caisson foundation will be widely applied in the future. Consequently, it is necessary to establish a practical design method of the wharf. Existing practical earthquake resistant design methods for an open-type wharf with a steel pipe pile foundation follow the below-mentioned procedure: (i) To calculate acceleration response spectra at the position of 1/β below the virtual ground surface by means of a one-dimensional earthquake response analysis of the ground. Here, the virtual ground surface means a 1/2 gradient face in between the slope and the seabed. β is a pile characteristic value; (ii) To calculate response acceleration corresponding to the natural period of the wharf. Here, the damping constant is 20%; (iii) To divide the response acceleration by gravity acceleration to obtain seismic coefficients; and (iv) To calculate inertial force using the seismic coefficients and verify the stability of the structure. To follow the design procedure described above may be appropriate. However, the difference in the rigidity of foundation between the two structural types should be considered. The authors conducted two-dimensional finite element earthquake response analyses, modelling both open-type wharves with pneumatic caissons and soil layers, and discussed their earthquake responses. As a result of this study, the earthquake response of the wharf with pneumatic caissons is different from that on a steel pipe pile foundation. The optimum evaluation positions of acceleration response spectra have proved to be foundation bottom levels, and the optimum damping constant for the evaluation of response acceleration to range from 5–20%.

    2018, WIT Transactions on the Built Environment, 180, 209 - 225, English

    [Refereed]

    International conference proceedings

  • A simple estimation method of the probability distribution of residual deformation of gravity type quay walls considering the variation of earthquake ground motion

    T. Hirai, T. Nagao

    © 2017 Taylor & Francis Group, London. It is necessary to conduct two-dimensional nonlinear earthquake response analysis many times in order to evaluate probabilistic characteristic of residual deformations of a gravity type quay wall. This paper aims at proposing a simple estimation method of effects of variation in earthquake ground motion on residual deformation of quay walls. Variations of input strong motions are considered as ones of site amplification factors and of site phase characteristics. As the result, the distribution of residual deformation of a quay wall is simply estimated with residual deformations by 3 earthquake response analyses.

    2017, Life-Cycle of Engineering Systems: Emphasis on Sustainable Civil Infrastructure - 5th International Symposium on Life-Cycle Engineering, IALCCE 2016, 485 - 491, English

    [Refereed]

    International conference proceedings

  • ODA Toshiya, NAGAO Takashi

     This study aims at proposing a simple evaluation method of seismic performance of pile pier supported wharf considering the effect of the ground deformation. The proposed method is based on a frame analysis referring the pile deformation evaluated by the two-dimensional earthquake response analysis. Estimated bending moment generated in piles by the proposed method was compared with that by the two-dimensional finite element earthquake response analysis and the applicability of the proposed method was discussed.

    Japan Society of Civil Engineers, 2017, Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering), 73 (2), I_414 - I_419, Japanese

    [Refereed]

  • NAGAO Takashi, SUETOMI Iwao, FUKUSHIMA Yasuhiro, IMAMURA Toshinari, KITAHARA Takeshi

     Although the performance-based design framework has been introduced to almost all the technical standards, the practical design follows all the specifications stated in the technical standards. Authors discussed the evaluation method of the design input earthquake ground motion considering source, path and site amplification characteristic of the site of interest in the performance-based design framework. The evaluated source and site specific earthquake ground motion, in this sample case where large earthquake is not expected and local site condition is very stiff, is shown to be smaller than those specified in the technical standards.

    Japan Society of Civil Engineers, 2017, Journal of Japan Society of Civil Engineers, Ser. A1 (Structural Engineering & Earthquake Engineering (SE/EE)), 73 (4), I_832 - I_840, Japanese

    [Refereed]

  • NAGAO Takashi, HAKODA Takahiro, ITO Yoshihiro, YAMADA Masayuki, NISHIBATA Kaoru, TSUDA Akira

     Generation of caves under pavements in the coastal area often causes serious accidents, however, those caves are not visible in general. Therefore, it is very important to establish an efficient method for the detection of caves under pavements. This paper aims at discussing the detection method of caves by use of microtremor. Microtremor observation was conducted at Sakaisenboku port where caves were generated. From the single point observation record of microtremor, both horizontal component and vertical component of microtremor were analyzed and it was found to be difficult to detect the caves by the single point observation record of microtremor. Next, array observation record of microtremor was analyzed using the spatial autocorrelation method. Phase velocity at the points with cave was found to be larger than that at the points without cave. As the results, maximum array radius for the detection of caves under pavements were found to be 3.6 meter in this study.

    Japan Society of Civil Engineers, 2017, Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering), 73 (2), I_450 - I_455, Japanese

    [Refereed]

  • LU Panpan, NAGAO Takashi

     It is necessary to conduct two-dimensional nonlinear earthquake response analysis many times in order to evaluate the seismic reliability of a pile supported wharf. This study aims at proposing a simple estimation method of the seismic reliability of a pile-supported wharf considering the variation of input seismic motion. The simple estimation method uses three results of two-dimensional nonlinear earthquake response analysis in order to evaluate the mean value and standard deviation of the residual displacement and the maximum bending moment of the wharf. It was shown that the method well evaluates the probability distribution of the residual displacement and the maximum bending moment of the wharf with enough accuracy.

    Japan Society of Civil Engineers, 2017, Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering), 73 (2), I_402 - I_407, Japanese

    [Refereed]

  • FUKUSHIMA Yasuhiro, GOTO Hiroyuki, NAGAO Takashi, OSHIGE Jumpei, SUETOMI Iwao

     The 2016 Kumamoto earthquake was occurred by the active fault which has been evaluated by the Headquarters for Earthquake Research Promotion. The magnitude of the main shock that caused severe damage on structures at Mashiki Town in Kumamoto Prefecture was MJMA 7.3, but, the magnitude of the Futagawa segment of Futagawa fault zone through the Mashiki Town has been evaluated as MJMA 7.0.
     In this study, estimated ground motion based on the information of the active fault was compared with the observed ground motion by the main shock at the KiK-net Mashiki site.
     In conclusion, the level of spectrum of estimated ground motion is close to the observation record, but it is lower than observation record at around 1 second period.

    Japan Society of Civil Engineers, 2017, Journal of Japan Society of Civil Engineers, Ser. A1 (Structural Engineering & Earthquake Engineering (SE/EE)), 73 (4), I_551 - I_557, Japanese

    [Refereed]

  • SHIBATA Daisuke, NAGAO Takashi

     It is necessary to evaluate seismic coefficients for open-type wharves against Level-one earthquake ground motions in the practical design, however, the evaluation method of those for open-type wharves with pneumatic caissons has not been established yet. In this study, two-dimensional earthquake response analyses on open-type wharves with pneumatic caissons were conducted for earthquake ground motions with different predominant frequencies. It was made clear that the evaluation method of seismic coefficients for open-type wharves with pneumatic caissons is different from that for open-type wharves with steel pile foundations. The optimum calculation positions of acceleration response spectra were found to be foundation bottom levels. The optimum damping constants for the calculation of maximum response acceleration were found to be in the range of 5% to 20%.

    Japan Society of Civil Engineers, 2017, Journal of Japan Society of Civil Engineers, Ser. A1 (Structural Engineering & Earthquake Engineering (SE/EE)), 73 (4), I_655 - I_671, Japanese

    [Refereed]

  • NAGAO Takashi, FUKUTA Ken, ITO Yoshihiro

     It is difficult to evaluate site amplification factor analytically because site amplification factor is affected by several factors such as three dimensional deep subsurface profile. Site amplification factors have been evaluated by spectral inversion using strong motion record in the previous study. Therefore, site amplification factor has not been evaluated precisely at sites without strong motion observation.
     This study aims at proposing a simple estimation method of site amplification factors by modifying the amplification factors assuming horizontally layered deep subsurface profile at the site of interest. Amplification factors at low frequencies and peak amplification factors were estimated both by the kriging method and regression equations in terms of peak frequencies of the amplification factors. Applicability of the proposed method was discussed.

    Japan Society of Civil Engineers, 2017, Journal of Japan Society of Civil Engineers, Ser. A1 (Structural Engineering & Earthquake Engineering (SE/EE)), 73 (4), I_148 - I_160, Japanese

    [Refereed]

  • Tara Nidhi Lohani, Takashi Nagao, Yasuhiro Fukushima

    © 2017 WIT Press. The 2016 Kumamoto Earthquake has caused vast building damages and human losses, although Japan is one of the world's well-prepared countries against earthquake disaster. The accelerometers set in Mashiki town area of Kumamoto prefecture rolled to the full scale measuring the seismic intensity as 7 in JMA scale of 7. In addition to such large shaking, there are opinions about the existence of three parallel fault lines beneath the town and the area lying on very soft volcanic soils regarding the vast damage of this particular area. In order to investigate the soil behaviour of this area, microtremor array studies were conducted starting from April 2016 to September 2016. Phase velocity obtained by spatial autocorrelation method was cross-checked with the borehole data available and was also found to be correlating well. Besides, the shear wave velocity distribution in the field was also consistent with the extent of damage observed after the earthquake.

    2017, International Journal of Safety and Security Engineering, 7 (4), 577 - 584, English

    [Refereed]

    Scientific journal

  • Evaluation of the Damage Level of Open-Type Wharf by Earthquake Focusing on the Natural Frequency

    NAGAO TAKASHI, ODA TOSHIYA

    2017, ICOSSAR2017, English

    [Refereed]

    International conference proceedings

  • NAGAO Takashi, LOHANI Tara Nidhi, FUKUSHIMA Yasuhiro, ITO Yoshihiro, HOKUGO Akihiko, OSHIGE Junpei

     The 2016 Kumamoto Earthquake caused severe damage on structures such as houses at Mashiki Town in Kumamoto Prefecture. Authors conducted microtremor observation at various sites in Mashiki Town in order to discuss the relationship between ground condition and damage level of structures. H/V spectra and phase velocities were evaluated from the microtremor records and average S-wave velocities were also evaluated from the phase velocities. It was found that both peak frequencies and average S-wave velocities are low at most of the sites where structures were severely damaged. Site amplification factors at some sites were evaluated from the aftershock records obtained during microtremor observation.

    Japan Society of Civil Engineers, 2017, Journal of Japan Society of Civil Engineers, Ser. A1 (Structural Engineering & Earthquake Engineering (SE/EE)), 73 (4), I_294 - I_309, Japanese

    [Refereed]

  • NAGAO Takashi, KAGAWA Yohei, YAMADA Masayuki, ITO Yoshihiro

     It is difficult to evaluate site amplification factor analytically because site amplification factor is affected by several factors such as three dimensional deep subsurface profile. Site amplification factors have been evaluated by spectral inversion using strong motion records in the previous study. Therfore, site amplification factor has not been evaluated precisely at

    Japan Society of Civil Engineers, 2016, EE)), 72 (4), I_317 - I_330, Japanese

    [Refereed]

    Scientific journal

  • NAGAO Takashi, ITO Yoshihiro, YAMADA Masayuki, MORITA Masahiro

     This study aims at discussing the S-wave velocity profile of the ground around Naha port. Both Ryukyu limestone layer and Shimajiri mudstone layer are deposited around the area. N-values obtained by the standard penetration test for Ryukyu limestone layer widely varies because of the variation of degree of consolidation of the layer. However, as the consolidation structur

    Japan Society of Civil Engineers, 2016, Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering), 72 (2), I_479 - I_484, Japanese

    [Refereed]

    Scientific journal

  • TERASHIMA Akihito, NAGAO Takashi, OOSAWA Fumitaka

     The present technical standard for pier design in Japan employs seismic coefficient method against level 1 earthquake; especially for aseismic reinforced facilities, it adopts dynamic nonlinear effective stress analysis against level 2 earthquake. The simple frame structure analysis for level 1 earthquake covers inertial force on superstructure of pier. However, it cannot

    Japan Society of Civil Engineers, 2016, Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering), 72 (2), I_473 - I_478, Japanese

    [Refereed]

    Scientific journal

  • NAGAO Takashi, KANO Takashi, ITO Yoshihiro, YAMADA Masayuki

     It is difficult to evaluate site amplification factor analytically because site amplification factor is affected by several factors such as three dimensional deep subsurface profile. Site amplification factors have been evaluated by spectral inversion using strong motion record in the previous study. Therfore, site amplification factor has not been evaluated precisely at

    Japan Society of Civil Engineers, 2016, EE)), 72 (4), I_188 - I_198, Japanese

    [Refereed]

    International conference proceedings

  • YAMADA Masayuki, ITO Yoshihiro, NAGAO Takashi, NOZU Atsushi, NAGASAKA Yosuke, OIWANE Hisashi

     In order to investigate the characteristics of site amplification factor around caldera, we evaluated site amplification factors based on earthquake recordings at two sites inside (the port in Satsuma-Iwojima Island) and outside (the airport) the Kikai Caldera. The result showed that there were the common peak frequency of 0.2-0.3Hz and this result suggests that there are

    Japan Society of Civil Engineers, 2016, EE)), 72 (4), I_691 - I_699, Japanese

    [Refereed]

    Scientific journal

  • DEGUCHI Takuma, NAGAO Takashi, YAMADA Masayuki, ITO Yoshihiro

     It is difficult to evaluate site amplification factor analytically because site amplification factor is affected by several factors such as three dimensional deep subsurface profile. Therefore, site amplification factors have been evaluated by spectral inversion using strong motion records and those at sites without strong motion observation records have not been evaluate

    Japan Society of Civil Engineers, 2016, EE)), 72 (4), I_199 - I_212, Japanese

    [Refereed]

    Scientific journal

  • NAGAO Takashi, FUKUTA Ken, ITO Yoshihiro, YAMADA Masayuki

     It is difficult to evaluate site amplification factor analytically because site amplification factor is affected by several factors such as three dimensional deep subsurface profile. Site amplification factors have been evaluated by spectral inversion using strong motion record in the previous study. Therefore, site amplification factor has not been evaluated precisely at

    Japan Society of Civil Engineers, 2016, Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering), 72 (2), I_485 - I_490, Japanese

    [Refereed]

    Scientific journal

  • ITO Yoshihiro, NAGAO Takashi, YAMADA Masayuki, MORITA Masahiro

     Tidal suction and consolidation settlement in the coastal area often result in the occurrence of cavities beneath the pavement around quay walls. As it is difficult to detect the cavities by eyesight, establishment of the method for the detection of cavities efficiently is strongly required. This study focuses the application of microtremor measurement to the detection of

    Japan Society of Civil Engineers, 2016, Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering), 72 (2), I_760 - I_765, Japanese

    [Refereed]

    Scientific journal

  • Evaluation method of the life-cycle cost of quay walls in view of earthquake resistance

    NAGAO Takashi, SONE A, NISHIMURA S

    2016, 16WCEE, English

    [Refereed]

    International conference proceedings

  • An efficient detection method of the peak frequency of microtremor HV spectral ratio using a low-pass filter

    YAMADA Masayuki, YAGi S, NAGAO Takashi, NOZU Atsushi, ITO Yoshihiro

    2016, 16WCEE, English

    [Refereed]

    International conference proceedings

  • NAGAO Takashi, KOMATSU Ayumi, ODA Toshiya

     Pile supported wharf is a framed structure which supports the superstructure of RC with a steel pipe pile. Design of pile supported wharf is conducted based on the assumption that load is not transmitted to the framed structure from the earth retaining because it is thought to be advantageous for the seismic performance of the wharf. However, validity of the assumption ha

    Japan Society of Civil Engineers, 2015, Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering), 71 (2), I_155 - I_160, Japanese

    [Refereed]

    Scientific journal

  • YAMADA Masayuki, ITO Yoshihiro, NOZU Atsushi, NAGAO Takashi

    sub>7.3 below the Tokyo capital region was verified in view of the seismic intensity published by the cabinet office, government of Japan. The validity of the proposed source model of the intra-plate earthquake below Aki-Nada sea was also verified in view of the seismic intensity observed during the 1905 and 1857 Geiyo earthquake.

    Japan Society of Civil Engineers, 2015, Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering), 71 (2), I_718 - I_723, Japanese

    [Refereed]

    Scientific journal

  • NAGAO Takashi, ODA Toshiya, KOMATSU Ayumi

     Pile supported wharf is a framed structure which supports the superstructure of RC with a steel pipe pile. Major damage mechanism of the wharf is the occurrence of the plastic hinge in the piles. As the close technical field survey is required for the evaluation of the damage level of the piles, it is difficult to judge the serviceability of the wharf just after the earth

    Japan Society of Civil Engineers, 2015, Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering), 71 (2), I_161 - I_166, Japanese

    [Refereed]

    Scientific journal

  • SHIOZAKI Yoshio, NAGAO Takashi, OZUTSUMI Osamu, MIYASHITA Kenichirou

     To simulate the local buckling of steel pipe piles on damaged open-type wharves, we revised model parameters in the two-dimensional effective stress analysis as follows : 1) The appropriate modeling of shear strength of soil around the piles; 2) Using the real yield strength of steel pipe piles, not a standard value. However, using the bi-linear beam element for piles wit

    Japan Society of Civil Engineers, 2015, EE)), 71 (4), I_537 - I_546, Japanese

    [Refereed]

    Scientific journal

  • ITO Yoshihiro, YAMADA Masayuki, OAKBE Noboru, NOZU Atsushi, NAGAO Takashi, TAKAHASHI Hiroaki, MIZUTANI Ryousuke

     Nozu et al. have been developing the SPGA model, which is suitable for the simulation of strong ground motions for subduction earthquakes. When the model is applied to a historical earthquake, it is desirable to construct an SPGA model which is consistent with seismic intensity data. In this study, as an example of the application of the SPGA model to a historical earthqu

    Japan Society of Civil Engineers, 2015, EE)), 71 (4), I_401 - I_407, Japanese

    [Refereed]

    Scientific journal

  • 防波堤の波浪及び津波に対する性能照査体系のあり方に関する一考察

    長尾 毅, 辻尾 大樹

    土木学会, 2014, 土木学会論文集B2(海岸工学), 70 (2), 1016 - 1020, Japanese

    [Refereed]

    Scientific journal

  • 地震ハザードを考慮した岸壁の耐震性能水準最適化に関する研究

    長尾 毅, 曽根 照人, 西村 壮介

    土木学会, 2014, 土木学会論文集A1(構造・地震工学), 70 (3), 418 - 434, Japanese

    [Refereed]

    Scientific journal

  • 桟橋の杭頭剛性と土留めとの境界条件が耐震性能に及ぼす影響に関する基礎的研究

    長尾 毅, 佐藤 俊

    土木学会, 2014, 土木学会論文集B3(海洋開発), 70 (2), 816 - 821, Japanese

    [Refereed]

    Scientific journal

  • 鬼首地域における地震動増幅の要因分析

    山田雅行, 長尾 毅, 野津 厚

    土木学会, 2014, 土木学会論文集A1(構造・地震工学), 70 (4), 33 - 43, Japanese

    [Refereed]

    Scientific journal

  • 深層地盤構造と常時微動の活用によるサイト増幅特性の評価に関する研究

    長尾 毅, 山田 雅行, 野津 厚

    土木学会, 2013, 土木学会論文集A1(構造・地震工学), 69 (4), 252 - 259, Japanese

    [Refereed]

    Scientific journal

  • 汚濁防止膜の経過月数による強度劣化に関する実海域実験

    島田 伊浩, 新井 洋一, 長尾 毅, 三吉 正英, 山本 直文, 岡本 直, 石坂 修, 須藤 彰二

    土木学会, 2013, 土木学会論文集B3(海洋開発), 69 (2), 203 - 208, Japanese

    [Refereed]

    Scientific journal

  • 汚濁防止膜カーテン強度の経時劣化評価法に関する研究

    長尾 毅, 島田 伊浩, 三吉 正英, 小坂 康之, 力竹 正広, 東 博之

    土木学会, 2013, 土木学会論文集B3(海洋開発), 69 (2), 197 - 202, Japanese

    [Refereed]

    Scientific journal

  • ライフサイクルコスト最小化の観点による既設防波堤の最適な復旧水準に関する研究

    長尾 毅, 辻尾 大樹, 熊谷 健蔵

    土木学会, 2013, 土木学会論文集B3(海洋開発), 69 (2), 185 - 190, Japanese

    [Refereed]

    Scientific journal

  • ライフサイクルコスト最小化による防波堤の目標整備水準の検討

    長尾 毅, 辻尾 大樹, 熊谷 健蔵

    土木学会, 2013, 土木学会論文集B2(海岸工学), 69 (2), 951 - 955, Japanese

    [Refereed]

    Scientific journal

  • ニューマチックケーソン式横桟橋の耐震性能照査法に関する研究

    大石 雅彦, 長尾 毅, 大内 正敏, 佐藤 祐輔, 清宮 理

    土木学会, 2013, 土木学会論文集B3(海洋開発), 69 (2), 155 - 160, Japanese

    [Refereed]

    Scientific journal

  • HIRAI Toshiyuki, NAGAO Takashi

    It is necessary to conduct two-dimensional nonlinear earthquake response analysis many times in order to evaluate probabilistic characteristic of residual deformations of a quay wall. We aim at proposing a simple estimation method of effects of variation in earthquake ground motion on residual deformation of quay walls. Variations in input strong motions are considered as variations in site amplification factors and those in site phase characteristics. As the result, the distribution of residual deformation of a quay wall by 136 earthquake ground motions is simply estimated with residual deformations by 3 earthquake ground motions.

    Japan Society of Civil Engineers, 2012, PROCEEDINGS OF CIVIL ENGINEERING IN THE OCEAN, 68 (2), I_468 - I_473, Japanese

  • MIYASHITA Kenichirou, NAGAO Takashi

    Authors proposed the cross section setting method for the design of open type wharves by use of the optimization algorithm in the past research. However, past research was conducted only on the large impedance contrast ground condition. This study first discusses the applicability of the proposed method to the low impedance contrast ground condition. Next, we discussed the soil spring model to improve the accuracy of the proposed method for thick liquefaction soil layers.

    Japan Society of Civil Engineers, 2012, PROCEEDINGS OF CIVIL ENGINEERING IN THE OCEAN, 68 (2), I_348 - I_353, Japanese

  • NAGAO Takashi, KUWABARA Naonori

    We proposed a simple estimation method of the seismic performance of slope type revetment without liquefaction condition using one-dimensional earthquake analysis loading initial vertical stress of soil layers by elastic theory in the past study. Here,we propose a new simple evaluation method of seismic performance of slope-type revetment considering the influence of liquefachion. Calculation accuracy of the proposed method was discussed in comparison with the result of two-dimensional earthquake response analyses.

    Japan Society of Civil Engineers, 2012, PROCEEDINGS OF CIVIL ENGINEERING IN THE OCEAN, 68 (2), I_456 - I_461, Japanese

  • NAGAO Takashi, YAMADA Masayuki, NOZU Atsushi

     The peak information in microtremor H/V spectrum is often used in the evaluation of amplification characteristics of earthquake ground motion. Although characteristics of microtremor H/V spectrum can be generally explained by those of surface waves, the assumption that microtremor only consists of surface wave is hardly valid considering the fact that peak amplification is finite and often correlates with amplification characteristics of earthquake ground motion. This study presents a new in terpretation of wave components of microtremor H/V spectrum using medium response analysis. Mixture rates of surface wave and body wave that well explain microtremor H/V spectrum was studied.

    Japan Society of Civil Engineers, 2012, Journal of Japan Society of Civil Engineers, Ser. A1 (Structural Engineering & Earthquake Engineering (SE/EE)), 68 (1), 48 - 62, Japanese

  • NOZU Atsushi, YAMADA Masayuki, NAGAO Takashi, IRIKURA Kojiro

    Strong ground motions in the frequency range from 0.2 to 1 Hz observed at many sites along the coast of Miyagi through Ibaraki Prefecture during the 2011 off the Pacific coast of Tohoku earthquake are characterized by distinctive pulses. These strong motion pulses are similar to those from shallow crustal earthquakes in a sense that they appear in a frequency range of engineering importance. Because strong motion pulses from huge subduction earthquakes can also cause significant damage to structures, it is significantly important to consider the generation of such pulses in the strong motion prediction for huge subduction earthquakes, especially when the prediction is aimed at seismic design of structures. In this article, first, examples of strong motion pulses from huge subduction earthquakes are examined. Then, source models aiming at the reproduction of those pulses are compiled and the characteristics of SPGAs (Strong-motion Pulse Generation Areas) are investigated, with special attention to their relation to the size of the earthquakes.

    JAPAN ASSOCIATION FOR EARTHQUAKE ENGINEERING, 2012, Journal of Japan Association for Earthquake Engineering, 12, 4_209 - 4_228, Japanese

  • NAGAO Takashi, TSUJIO Daiki, KUMAGAI Kenzou, ISHIKAWA Masanori

    This study discusses the influence of various conditions on the target safety level of composite break-waters in view of life cycle cost. Target safety levels of two ports corresponding to minimum life cycle cost differ considerably although the influence of tail length parameter and damage loss cost were small. Wave breaking condition was the governing condition on target safety levels within the scope of this study.

    Japan Society of Civil Engineers, 2012, PROCEEDINGS OF CIVIL ENGINEERING IN THE OCEAN, 68 (2), I_294 - I_299, Japanese

  • Masumi Yamada, Masayuki Yamada, Koji Hada, Shiro Ohmi, Takashi Nagao

    SEISMOLOGICAL SOC AMER, Jul. 2010, SEISMOLOGICAL RESEARCH LETTERS, 81 (4), 597 - 604, English

    [Refereed]

    Scientific journal

  • NAGAO Tsuyoshi, TSUJIO Daiki, KUMAGAI Kenzou

    It is necessary to maintain wave dissipating blocks for the armor of breakwaters properly because settlement of blocks often causes large disaster. Therefore, clarification of correlation between block settlement and breakwater displacement is important for the establishment of effective maintenance strategy. Previous study discusses maintenance strategy of breakwaters armored with wave dissipating blocks on the assumption of uniform displacement of breakwaters, however, uneven displacement of breakwaters is observed in field. This study considers uneven displacement of breakwaters and discusses the maintenance criteria for the minimum repair cost during working life of breakwaters.

    Japan Society of Civil Engineers, 2010, PROCEEDINGS OF THE JAPANESE CONFERENCE ON COASTAL ENGINEERING, 66 (1), 836 - 840, English

  • Atsushi Nozu, Takashi Nagao, Masayuki Yamada

    The strong motion simulation technique using site-dependent amplification and phase characteristics was originally proposed by Kowada et al. and its applicability has been extensively studied by the authors. One disadvantage of the method, however, was that it cannot generate a ground motion that satisfies causality conditions, meaning a ground motion with zero amplitude at the beginning of the time history. In this article, the authors revise the method by introducing a smoothing technique in the procedure to generate Green's functions. It was confirmed that the revised method can generate causal ground motions, which are in agreement with the observed ground motions during the 2003 Tokachi-oki earthquake.

    2009, Doboku Gakkai Ronbunshuu A, 65 (3), 808 - 813

    [Refereed]

    Scientific journal

  • SHIOZAKI Yoshio, NAGAO Takashi, OZUTSUMI Osamu, MIYASHITA Kenichiro

    This paper explores the possibility of improving the accuracy for the 2-dimentional effective analysis code FLIP for open-type wharves on vertical piles. We picked up the T-wharves damaged by the 1995 Hyogoken Nambu earthquake as study subject. In the past studies the agreement between the damage and simulation result was fairly good, but the problem that the buckling positions of the steel pipe piles were different was left. To simulate the buckling positions we revised model parameters as follows: 1) The appropriate modeling of shear strength of soil around the piles; 2) Using the constitutive law of the steady state of sandy soil to solve the shear locking under the earth-retaining section; 3) Using the real yield strength of steel pipe piles, not a standard value.

    Japan Society of Civil Engineers, 2009, PROCEEDINGS OF THE JSCE EARTHQUAKE ENGINEERING SYMPOSIUM, 65 (1), 881 - 891

  • Nagao Takashi

    This study aims at discussing the efficient evaluation method of failure probability of breakwaters in view of cumulative sliding displacement by Monte Carlo simulation. The target problem is different from many other problems because failure probability is judged by the cumulative displacement during the design working life of breakwaters. The fact that failure probability shall be evaluated by the repetitive actions of waves makes the adoption of variance reduction techniques difficult. The proposed method evaluates the cumulative probability distribution of sliding displacement for one year by importance sampling method and calculates failure probability for design working life by using the cumulative probability distribution.

    Japan Society of Civil Engineers, 2009, Kozo Kogaku Ronbunshu. A (Journal of Structural Engineering. A), 55, 236 - 248

  • Nagao Takashi, Miyashita Kenichirou

    The standard earthquake resistant design method of quay wall against a level-one earthquake ground motion is a pseudo-static method and is not necessarily in harmony with the failure mechanism of quay walls. Therefore, authors proposed a frame model for the evaluation of the seismic performance of sheet pile quay wall with vertical pile anchorage in the previous study. This study aims at improving the frame model proposed in the previous study for the precise reproduction of the deformation of quay wall. Major improvement was made on the evaluation of soil reaction spring model for the deformation of sheet pile and the model for the calculation of residual deformation of soil layers beneath the sheet pile.

    Japan Society of Civil Engineers, 2009, Kozo Kogaku Ronbunshu. A (Journal of Structural Engineering. A), 55, 421 - 434

  • Nagao Takashi, Ozaki Ryuzo

    This study discusses the life cycle cost for sheet pile quay walls considering the progress of corrosion. It is necessary to calculate the failure probabilities according to the decrease of section modulus by corrosion for the evaluation of life cycle cost. The condition that the section modulus becomes initial value after the restoration work makes the evaluation of life cycle cost difficult. We proposed the simple evaluation method of life cycle cost and showed that the proposed method well evaluates the failure probability corresponding to the minimum life cycle cost. We also compared the failure probability for minimum life cycle cost with that for minimum expected total cost.

    Japan Society of Civil Engineers, 2009, Kozo Kogaku Ronbunshu. A (Journal of Structural Engineering. A), 55, 249 - 260

  • Design method for caisson-type breakwaters covered with wave-dissipating blocks considering LCC during execution

    Takeshi Yoshioka, Takashi Nagao

    TAYLOR & FRANCIS LTD, 2007, APPLICATIONS OF STATISICS AND PROBABILITY IN CIVIL ENGINEERING, 289 - 290, English

    International conference proceedings

  • Katsuaki Konno, Takahiro Suzuki, Yasuhiro Kamata, Takashi Nagao

    First, Average S-wave velocity in the uppermost 30 m (Vs30) obtained from PS-logging data and site amplification factors for peak acceleration and velocity derived from strong motion records are compared at the dense strong-motion network sites in Yokohama (Y-NET). Next, a simple method for estimating Vs30 is examined at Y-NET sites. This method involves placing 3 sensors in the shape of the letter 'L' for simultaneous microtremor observation. Finally, a method to estimate peak ground acceleration and velocity using Vs30 is proposed and its applicability is investigated.

    2007, Doboku Gakkai Ronbunshuu A, 63 (4), 639 - 654

    [Refereed]

    Scientific journal

  • Calderas Atsushi Nozu, Masayuki Yamada, Takashi Nagao

    Strong motion simulation technique using site-dependent amplification and phase characteristics, whose applicability is already shown for short-period ground motions, is applied to basin-induced surface waves with periods of several seconds. First, empirical site amplification factors are estimated for strong-motion sites in Kyushu region, Japan, including sites in calderas. Then, the tequenique is applied to simulate ground motions from the Kagoshimaken-Hokuseibu earthquake of March, 1997, with special reference to predominant basin-induced surface waves in the calderas at preriods of several seconds. The good agreement between the synthetic and the observed ground motions indicates the applicability of the method to ground motions with periods of several seconds.

    2006, Doboku Gakkai Ronbunshuu A, 62 (4), 891 - 905

    [Refereed]

    Scientific journal

  • Nagao Takashi, Kikuchi Yoshiaki

    現在,構造物の性能設計に関する取り組みが各方面で行われている.また,政府調達協定やTBT 協定などを背景に,ISO 規格などの国際規格との整合性・調和性が今後は強く求められるため,国際標準と調和的な設計体系の確立が早急に必要となっている.このため本稿では,港湾構造物の設計法の改定に向けた取り組みを紹介する.

    The Japanese Geotechnical Society, 2004, Proceedings of the Japan National Conference on Geotechnical Engineering, 39, 25 - 26

  • NAGAO Takashi

    This paper presents the flexural design way of breakwaters by means of reliability based design method. By using the probability distributions of design parameters such as wave force, deadweight, material strength and so on, distribution of safety indices against ultimate flexural failure of breakwaters designed with conventional design method has been clarified. Target safety level has been determined in terms of comparison of life cost of breakwaters for external safety and internal safety. Code calibration has been carried out and safety factors for level 1 reliability design method have been proposed.

    Japan Society of Civil Engineers, 21 Jan. 2002, Doboku Gakkai Ronbunshu, 696, 173 - 184, Japanese

  • 長尾 毅, 宮下 健一朗

    The inertia force acting on open-type wharves on vertical piles changes according to the natural period of the wharves. The natural period also changes according to the section modulus of the piles. This means that an iterative calculation is needed in the design of the wharves and an effective method is desirable to reduce the number of iteration.
    In this study, we conducted the optimal design of the wharves using the conjugate gradient method. It was shown that the number of iteration can be reduced focusing on the shape of the response acceleration spectrum.

    Japan Society of Civil Engineers, 2008, 海洋開発論文集, 24, 195 - 200, Japanese

  • 長尾 毅, 尾崎 竜三

    Technical standards for port and harbor facilities were revised in 2007 and the deformation of quay-wall during earthquake became the controlled object in seismic safety verification. As an introduction to the establishment of the method for the determination of the allowable deformation for gravity type and sheet pile type quay-wall, this paper shows the statistical analysis on correlation between deformation of quay-wall during earthquake and its damage.
    Firstly, we gathered the damage data from the report of past several earthquakes and closely examined the collected data set. Secondly, we surveyed the correlation among the parameters focusing on the failure loss cost and recovery days. Finally, we conducted the multiple regression analyses and proposed the regression equations for the failure loss cost and recovery days according to the deformation of the quay-walls and other design conditions.

    Japan Society of Civil Engineers, 2008, 海洋開発論文集, 24, 213 - 218, Japanese

  • 宮下 健一朗, 長尾 毅

    Earthquake resistant design of quay wall is carried out by using quasi-static method especially for Level-one earthquake ground motion. The method is easy to be implemented, however, residual deformation of quay walls cannot be evaluated precisely by the conventional design method. Therefore, it is very important to establish the method to control the residual deformation of quay walls without much calculation load for practical design.
    In this study, we identified the parameter that affects the residual deformation by the parametric study using two-dimensional earthquake response analyses. As the result of the analysis, we found that the distance from sheet pile to anchorage is the governing parameter. We also proposed the method to evaluate the residual deformation of sheet pile quay walls with vertical pile anchorage in accordance with the change in the distance from sheet pile to anchorage.

    Japan Society of Civil Engineers, 2007, 海洋開発論文集, 23, 841 - 846, Japanese

  • NOZU Atsushi, NAGAO Takashi, YAMADA Masayuki

    Site amplification factors were evaluated for strong-motion sites in Japan by using the spectral inversion technique. The seimic moment calculated from the source spectra, which were obtained through the analysis, agrees well with that of the CMT solution of the F-net, indicating the validity of the newly-introduced criteria to determine the reference site. Because the site amplification factors obtained in this study include the effects of later phases, they are suitable to be used for simulating strong ground motions by Kowada's method. Strong ground motions from the 1995 Hyogo-ken Nanbu, the 1968 Tokachi-oki and the 2003 Tokachi-oki eathquakes were simutated by the method to confirm the usefulness of the site amplification factors obtained in this study.

    JAPAN ASSOCIATION FOR EARTHQUAKE ENGINEERING, 2007, Journal of JAEE, 7 (2), 215 - 234

  • 長尾 毅, 野津 厚, 山田 雅行

    This paper aims at presenting the examples of the level-one ground motions for port and harbour facilities. Authors proposed a new framework for seismic hazard analysis considering source, path and site amplification effects especially due to the deep subsurface profile. Level-one ground motions as time histories were calculated for 23 ports by this method. It is shown that PGA and PGV for each port differ a lot although regional seismic coefficient is classified into only 5 categories in the current design method. Authors also evaluated the difference of earthquake response of gravity type quay walls

    Japan Society of Civil Engineers, 2005, 海洋開発論文集, 21, 767 - 772, Japanese

  • 長尾 毅, 山田 雅行, 野津 厚

    Seismic fragility is influenced not only by subsurface profiles above engineering bedrock but also by deep subsurface profiles below engineering bedrock. We aim at presenting the method of seismic zoning in view of deep subsurface profile by use of both microtremor and strong motion record. The method employs the horizontal-to-vertical spectral ratios of microtremor to classify the deep subsurface structures and site amplification factor by the spectral inversion of strong motion. We showed an example of seisimic zoning for Mikawa port by the proposed method. It was also shown that frequency characteristic of site amplification factors and horizontal-to-vertical spectral ratios were in good agreement.

    Japan Society of Civil Engineers, 2005, 海洋開発論文集, 21, 951 - 956, Japanese

  • 長尾 毅, 山田 雅行, 野津 厚

    This paper aims at presenting the level-one ground motion for port facilities in Kanto region. Authors proposed a new framework for seismic hazard analysis considering source, path and site amplification effects especially due to the deep subsurface structure. Seismic hazard by the proposed method is obtained as time histories of seismic motions and therefore it can be used directly for dynamic analysis. Difference of earthquake response of quay walls by ground motion of present design method and that of proposed method is discussed.

    Japan Society of Civil Engineers, 2004, 海洋開発論文集, 20, 137 - 142, Japanese

  • 尾崎 竜三, 長尾 毅

    Seismic stability, which is on sliding and overturning, is verified for a design of a caisson type breakwater if necessary. Static method is used in the practical design, which doesn't take the dynamic response of the breakwater into account. In this study, based on the framework of the performance based earthquake resistant design for caisson type breakwaters, the procedure for the case of applying the friction increasing mat is presented. Firstly, the necessity of earthquake resistant design is judged by the schematic chart. Secondly, dimension of the breakwater for the evaluation of earthquake resistant performance is calculated by the proposed method. Finally, earthquake resistant performance is checked by the methodology based on single degree of freedom system.

    Japan Society of Civil Engineers, 2004, 海洋開発論文集, 20, 155 - 160, Japanese

  • NAGAO Takashi

    This paper presents the design way of breakwaters to evaluate the safety against sliding, overturning, and foundation failure through the reliability based design method. By using the probability distributions of design parameters such as wave force, deadweight, coefficient of friction and so on, distribution of safety indices of breakwaters designed with conventional design method has been clarified. Target safety indices have been determined in two ways; (1) mean value of safety indices with reliability based design method and that with conventional design method are to conform to each other, (2) 5th percentile value of safety indices with reliability based design method and that with conventional design method are to conform to each other. Code calibration has been carried out for each way, and safety factors for level 1 reliability design method and target safety indices for level 2 design method have been proposed.

    Japan Society of Civil Engineers, 2001, Doboku Gakkai Ronbunshu, 2001 (689), 173 - 182, Japanese

  • christino boyke, Takashi Nagao

    Jul. 2022, Applied Sciences

    [Refereed]

    Scientific journal

MISC

  • 福島 康宏, 長尾 毅

    神戸大学都市安全研究センター, Mar. 2018, 神戸大学都市安全研究センター研究報告, (22), 26 - 44, Japanese

  • 柴田 大介, 長尾 毅

    神戸大学都市安全研究センター, Mar. 2017, 神戸大学都市安全研究センター研究報告, (21), 91 - 98, Japanese

  • ニューマチックケーソンの桟橋基礎への適用 (特集 最近のケーソン工法)

    長尾 毅, 大石 雅彦

    総合土木研究所, May 2015, 基礎工 = The foundation engineering & equipment, monthly : 土木・建築基礎工事と機材の専門誌, 43 (5), 32 - 35, Japanese

  • Estimation of Subsurface Structures Using Microtremor Data at the Port and Airport in Satsuma-Iwojima Island

    山田 雅行, 伊藤 佳洋, 長尾 毅

    物理探査学会, 2015, 公益社団法人物理探査学会学術講演会講演論文集 = Proceedings of the SEGJ Conference, 133, 125 - 128, Japanese

  • Before and after the revision of technical standards for port and harbour facilities

    NAGAO Takashi

    15 Mar. 2013, 土木學會誌, 98 (3), 24 - 25, Japanese

  • Strong Motion Pulse Generation Areas for Huge Subduction Earthquakes : Their Scaling with Overall Earthquake Size

    野津 厚, 長尾 毅

    港湾空港技術研究所, Sep. 2012, 港湾空港技術研究所資料, (1257), 2 - 22, Japanese

  • スペクトルインバージョンに基づく全国の港湾等の強震観測地点におけるサイト増幅特性

    野津 厚, 長尾 毅

    港湾空港技術研究所, Dec. 2005, 港湾空港技術研究所資料, (1112), 1 - 56, Japanese

  • A Study on Simple Estimation Method of Target Safety Level of Breakwaters

    長尾 毅, 辻尾 大樹, 熊谷 健蔵

    土木学会, 2012, 土木学会論文集. B2, 海岸工学, 68 (2), 876 - 880, Japanese

  • A fundamental study on the simple seismic performance checking method for caisson type quay walls against level-one earthquake ground motion

    桑原 直範, 長尾 毅

    中央復建コンサルタンツ, Jan. 2011, Chuo Fukken Consultants technical report, (41), 22 - 34, Japanese

  • A study on the improvement of the accuracy of failure probability of breakwaters in view of sliding displacement by Monte Carlo Simulation

    長尾 毅, 吉岡 健, 尾崎 竜三

    土木学会, Oct. 2008, Journal of coastal engineering, JSCE, 55, 941 - 945, Japanese

  • ANALYTICAL STUDY ON EARTHQUAKE RESISTANT EVALUATION METHOD FOR PILE-SUPPORTED WHARVES

    NAGAO Takashi, TASHIRO Souichi

    土木学会, 21 Jul. 2002, 土木学会論文集 = Proceedings of JSCE, 710, 385 - 398, Japanese

  • PROBABILISTIC SEISIMIC HAZARD ANALYSIS WITH FOCUS ON FOURIER AMPLITUDE AND GROUP DELAY TIME

    NAGAO Takashi, YAMADA Masayuki, NOZU Atsushi

    土木学会, 21 Oct. 2005, 土木学会論文集 = Proceedings of JSCE, (801), 141 - 158, Japanese

  • Performance Based Design of Port and Harbor Structures

    NAGAO Takashi

    This paper describes the outline of Performance-based Design of port and harbor structures. The technical standards for port and harbor structures in Japan were revised in 2007 and the performance-based design framework was newly introduced. The new technical standards are in consistent with the international standards such as ISO codes, and domestic standards such as code PLATFORM. In the new technical standards, new concept for the evaluation of design earthquake ground motion was applied and earthquake resistant design method was revised. In addition, reliability-based design method was introduced.

    地盤工学会, 01 May 2008, 地盤工学会誌 = / the Japanese Geotechnical Society, 56 (5), 14 - 17, Japanese

  • ケーソン式防波堤の耐震性能設計に関する研究

    長尾 毅, 尾崎 竜三

    中央復建コンサルタンツ, Jan. 2005, 中央復建C.技報, (35), 39 - 49, Japanese

  • A fundamental study on the simple seismic performance checking method for caisson type quay walls against level-one earthquake ground motion

    桑原 直範, 長尾 毅

    土木学会, 2009, 応用力学論文集, 12, 589 - 599, Japanese

  • The effect of the incident angle on the site amplification factors for deep basin structures by use of two-dimensional finite element analyses: for Osaka and Kushiro sedimentary basin

    長尾 毅, 山田 雅行, 野津 厚

    土木学会, 2009, 応用力学論文集, 12, 579 - 588, Japanese

  • A statistical analysis on correlation between deformation of quay-wall during earthquake and its damage

    長尾 毅, 尾崎 竜三

    中央復建コンサルタンツ, Jan. 2009, Chuo Fukken Consultants technical report, (39), 12 - 18, Japanese

Presentations

  • 特別講演「土木構造物の性能設計法の動向について」

    長尾 毅

    第458 回構造懇話会平成25 年度総会, 2013, Japanese, Domestic conference

    [Invited]

    Invited oral presentation

  • 地震動の増幅特性とその評価法について

    長尾 毅

    第175回オープンゼミナール, 2013, Japanese, Domestic conference

    Public discourse

  • 鬼首地域における地震動増幅の要因分析

    山田 雅行, 長尾 毅, 野津 厚

    第33回地震工学研究発表会, 2013, Japanese, Domestic conference

    Oral presentation

Research Projects

Industrial Property Rights

  • ケーソン、ニューマチックケーソン工法及び構造物

    長尾 毅, 小宅 知行, 大石 雅彦

    特願2019-121870, 28 Jun. 2019, 国立大学法人神戸大学, オリエンタル白石株式会社, 特開2021-008720, 28 Jan. 2021

    Patent right

  • 根入れ式岸壁

    長尾 毅, 小宅 知行, 二宮 庸平

    特願2020-202185, 04 Dec. 2020, 国立大学法人神戸大学, オリエンタル白石株式会社, 特開2022-089637, 16 Jun. 2022

    Patent right