Journal of Structural and Construction Engineering (Transactions of AIJ)
Online ISSN : 1881-8153
Print ISSN : 1340-4202
ISSN-L : 1340-4202
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Showing 1-17 articles out of 17 articles from the selected issue
  • Tomomi SOETA, Shutaro ITO, Tomohiro FUJINUMA, Takamasa MIKAMI
    2020 Volume 85 Issue 767 Pages 1-9
    Published: 2020
    Released: January 30, 2020

     Exterior tile cladding can suffer debonding or adhesive failures as it ages. Failures that result in cladding tiles falling from the building are highly dangerous for people passing beneath, and consequently it is important to be able to identify debonding defects at an early stage to prevent tiles falling. This study aimed to develop a high-precision device for efficient detection of exterior tile debonding. This paper details the results of verification of a tile debonding diagnostic device and the detection parameter proposed in the previous paper by testing twelve exterior-tile wall specimens with artificially debonded areas. The device is characterized by having an impact force sensor and four microphones, and is calibrated using a glass-made standard specimen. The detecting parameter RAF is measured at each microphone. The outline and the results of this paper are as follows.

     1) Twelve exterior-tile wall specimens with artificially debonded areas were prepared. The types of tiles, bonding materials, debonded interface, debonded depth and debonded area were different for each specimen.

     2) Among all the impact points on each specimen of X0, X10, X20 and X30 having different debonded depth respectively, three characteristic points were selected, that is, point “a” as a representative point in the non-debonded area, point “b” as one at the center of debonded area and point “c” as one in the vicinity of the debonded boundary. The RAF value at each microphone was displayed as the size of diameter of circle at each microphone’s position on each figure of the specimens. In the case of impact at point “b”, the center of the debonded area, the RAF values of four microphones were much larger than those of point “a” in the non-debonded area, and the four RAF values were almost same as each other. In the case of point “c”, in the vicinity of the debonded boundary, the RAF value of the microphone positioned inside the debonded area was larger than the others. Therefore it is easier to detect debonding where at least one of the microphones is located inside the debonded area. In the case of point “a”, in the non-debonded area, all of the RAF values were very small, even if one microphone was in the debonded area.

     3) The maximum value of RAF of four microphones was defined as RAF-max, and the results of RAF-max were displayed as diameters of circles at the impact points on figures of the specimens. A threshold value of RAF-max was set based on the distribution tendency of RAF-max, and the results of detection of debonding were displayed on figures of the specimens. In the case of specimens with shallow debonded areas, it was possible to accurately detect debonding in the vicinity of the debonded boundaries. In the case of specimens with deep debonded areas, it became difficult to detect debonding clearly in the vicinity of the debonded boundaries, but the existence of debonding could be detected clearly further inside the debonded area. In the case of the specimens manufactured in this paper, it was possible to detect the existence of debonding to a depth of 39 mm.

     4) As stated above, in this paper, the effectiveness of the prototyped device and the proposed detection parameter was verified.

     Further research will be continued in order to develop reasonable methods for zoning the detected debonding points and determining debonding depth. In addition, on-site experiments will be carried out for further verification and improvement of the device and the system.

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  • Yutaro FUJII, Takeshi YOKOI, Shintaro FUKUDA, Yutaka YOKOYAMA
    2020 Volume 85 Issue 767 Pages 11-18
    Published: 2020
    Released: January 30, 2020

     Finishing material bonded to the wet slab peels off at high probability. We are researching in order to propose the moisture management index of slab surface. We focused on resilient floor covering and examined the quantitative relationship between adhesive and water content. In addition, we also examined that the relationship between joint tenting of floor covering and water content. As a result, it was shown that the boundary of the water content where the probability of the occurrence of the joint tenting raises at is different, too, when the curing conditions are different. From this result, it was inferred that it is necessary to measure moisture vapor emission, although the measuring methods until now were the method of measuring the moisture content.

     Based on these results, in this journal, we will understand the effects of different curing conditions on the moisture vapor emission and water contained. In addition, the relationship between joint tenting of floor covering and the moisture vapor emission of slab and moisture content of slab was also examined.

     The preliminary experiments were conducted. The contents of the preliminary experiment are to adopt the coefficient of thermal expansion as an index of failure to substitute the occurrence probability of joint tenting, and to examine the relationship between joint tenting and thermal expansion. As a result, the correspondence between the occurrence probability of joint tenting and the thermal expansion is good. It shows that the coefficient of thermal expansion can represent the occurrence probability of joint tenting (reference to Fig. 2).

     The relationship between the coefficient of thermal expansion of the floor covering and the moisture vapor emission from the concrete slab was also examined. The specimen was sized large enough to perform the test (reference to Fig. 4). Concrete was common on site (reference to Table 1). Two types of curing were applied to the specimens (reference to Table 2).

     The method of using the humidity test paper was adopted as the method of grasping the moisture vapor emission adopted. In this method, a test paper that changes color in response to moisture is attached to a concrete surface, and the moisture vapor emission is measured. In this study, a color reader was used as the method of color measurement to determine the color sample value as the moisture vapor emission (reference to Photo 2).

     The transition of the moisture vapor emission and the moisture content was recorded, and the relationship between the two was examined. As a result, we showed that even if the moisture content was the same, the moisture vapor emission was smaller in water sprinkling (reference to Fig. 6, 7, 8).

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  • -Application of spatial filtering and rescaling method-
    Hidenori KAWAI, Tetsuro TAMURA
    2020 Volume 85 Issue 767 Pages 19-27
    Published: 2020
    Released: January 30, 2020

     Turbulent structure derived from meteorological disturbance with low-frequency fluctuation affects different characteristics for the distribution of wind pressure and the peak value of concentration in comparison with the inflow condition using turbulent boundary layer (TBL) over smooth or rough surface in usual cases. However, it is impossible to resolve turbulent field around buildings explicitly and difficult to reproduce high frequency component by only the mesoscale meteorological model. Thus, several researches show the connection method between mesoscale meteorological model with LES. However, when connecting mesoscale meteorological model with LES for turbulent field around buildings, tasks still remain in making inflow condition by adding the appropriate scale of fluctuation with high frequency to meteorological model results. Therefore, this study presents a method to add fluctuation components which are extracted by spatial filtering and rescaling technique to a velocity field of mesoscale meteorological model. In the presented method, the fluctuation with high frequency which is generated in the driver region is decomposed physically to the scale of original inflow and residual fluctuation. Then, the residual fluctuation is rescaled and imposed to inlet plane at an appropriate scale of fluctuation.

     Then, the proposed method is validated by a priori test applying the presented method to the filtered TBL. This study compares the calculation result and the original TBL before a filter operation. As a result of the comparison, it is confirmed that high-frequency components of fluctuation component are added to the filtered TBL at appropriate scale of fluctuation. Also, the turbulent intensity and power spectrum density which are lost in the filtering process are recovered by the presented method.

     Next, this study carries out WRF-LES for idealized atmospheric boundary layer and compares results between WRF-LES and TBL by Lund In the results of WRF-LES, mixing of vertical direction is strong and the fluctuation of velocity remains until the height of 800m. The comparison shows that the power spectrum density of WRF-LES in low-frequency component which decays in TBL by Lund corresponds to that of the Karman type spectrum without decaying. Also, the turbulent intensity near the ground is enough and it corresponds that of AIJ recommendation. This is because a periodic condition is employed in the WRF-LES in this study. However, the comparison of power spectrum density reveals that high-frequency component decays in the results of WRF-LES even in the case using spatial resolution of 25m.

     Finally, the presented method is applied to the WRF-LES results. In the results of the presented method, the turbulent intensity of v’ and w’ is slightly decayed because the vertical profile of u above the height of 100m is almost constant. However, the results show that the power spectrum density of low-frequency region is maintained. Also, the fluctuation of high-frequency which decays in WRF-LES is generated by the presented method. In the case where the presented method is applied, the range of frequency reproducing the fluctuation of high frequency is extended to the range almost same as that of TBL by Lund et. al.

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  • Misa MORIWAKI, Takashi HIRAI, Nobuo FUKUWA
    2020 Volume 85 Issue 767 Pages 29-37
    Published: 2020
    Released: January 30, 2020

     A seismic displacement brings us the useful information to analyze the seismic damage of infrastructure and buildings. In particular, a near-fault seismic ground motion including the huge residual displacement may cause the large response of tall buildings and base isolated buildings.

     The residual displacement due to the earthquake is obtained from geodetic observations such as GNSS, while the time series of the displacement including the residual component can be estimated using the strong ground motion record. Generally, residual displacements obtained by geodetic observations are more accurate. However, residual displacements estimated from strong ground motion records can be used to investigate the distribution of the displacement since the strong ground motion observation network is denser than GNSS network in Japan.

     The seismic acceleration record observed by a servo-seismometer is often contaminated by the baseline change due to the tilt motion of the apparatus, the effect of the electric hysteresis, and so on. For this reason, it is difficult to obtain the time series of the displacement including the residual component from the record. In such case, it is necessary to correct the baseline change of the accelerogram.

     In this study, a new calculation technique is proposed to estimate the seismic displacement from the strong motion acceleration record. In the method, the time series of the displacement including the residual component is obtained by eliminating the step function component from the acceleration record in the frequency domain. The parameters of the step function component are determined to reduce the fluctuation of the displacement of coda part.

     Applying the method to some acceleration records of the main shock of the 2016 Kumamoto Earthquake, the displacements are estimated more accurate than those estimated by existing method. In addition, the orbit of the particle motion can be drawn using the displacement estimated by the method. According to the result, it is revealed that the ground at Nishihara station went down about 150 cm and then consequently moved to east about 200 cm. Furthermore, the distribution of the residual displacement of the main shock of the 2016 Kumamoto Earthquake estimated by proposed method almost agrees with that obtained by GNSS observation.

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  • Applicability of extended correlation anomaly detection
    Taro YAOYAMA, Takenori HIDA, Tsuyoshi TAKADA
    2020 Volume 85 Issue 767 Pages 39-49
    Published: 2020
    Released: January 30, 2020

     In large-scale earthquake disasters, urban monitoring system would be effective in decision-making for emergency responses. For this purpose, we have proposed a data-driven technique for portfolio-monitoring of structures that adopts a machine-learning method called Correlation Anomaly Detection (CAD). This technique detects damaged structures in a portfolio by detecting a change in correlation property between dynamic characteristics of different structures. The key features of our proposed technique are summarized as follows.

     (i) The methodology can be categorized into data-driven techniques which require no priori information about the physical properties of systems, and therefore has versatility in terms of applied objectives.

     (ii) In the context of structural health monitoring (SHM), the methodology can be categorized into output-only techniques, which do not use input ground accelerations. This advantage allows its easy and cost-efficient implementation.

     (iii) Most of output-only SHM methodologies adopt assumptions on the characteristics of excitations or mode shapes of vibrations. Our proposed technique, however, does not make such assumptions and thus has applicability even to strong motion observations.

     The paper presents an improvement of CAD as Extended Correlation Anomaly Detection (ECAD), which utilizes the frequency content of time-series data, and examines its applicability to portfolio-monitoring of structures even in the case of different ground motions input to structures.

     We first show the summary of CAD and then formulates the ECAD algorithm, which could utilize the frequency content of time series. In ECAD, the covariance structure corresponding to each discretized frequency is modelled as a co-spectrum matrices among time-series data, in order to capture correlation anomalies in the frequency domain. The series of anomaly scores computed by CAD for different discretized freqeuncies is defined as correlation anomaly spectrum, whose integration gives anomaly score for each monitored objective.

     Second, we examine the applicability of CAD and ECAD to portfolio-monitoring of structures by numerical experiments. The portfolio is modelled by SDOF oscillators to which ground accelerations on different observation stations are input. The experiment shows (i) the good applicability of ECAD and its superiority to CAD even in the case of different excitations to structures, and (ii) the ability of ECAD to capture changes of natural frequencies.

     Finally, we demonstrate ECAD by using actual strong motion observations. The aim is to detect structural damages resulted from the main shock of The 2011 off the Pacific coast of Tohoku Earthquake. The demonstration reveals the following: (i) ECAD has the applicability even to actual structures; (ii) ECAD tends to underestimate structural damage of structures whose response is a wide-band or multi-modal process; (iii) ECAD tends to overestimate structural damage when a structure shows different vibration modes between in reference and test data.

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  • Takuya SUZUKI, Takaki TOJO
    2020 Volume 85 Issue 767 Pages 51-60
    Published: 2020
    Released: January 30, 2020

     In the seismic design of buildings, setting the damping ratio is of considerable importance, as this parameter greatly affects the prediction accuracy of building behavior during earthquakes. To this end, several studies have been carried out to identify the damping constants of buildings using earthquake records.

     Previous studies have indicated that it is important to consider the rotation input of building foundations when identify calculating the damping ratio using earthquake records. However, in most buildings, the rotational acceleration of the foundation has not been recorded. Therefore, it is difficult to identify the damping ratio considering the rotational acceleration.

     In this study, the feasibility of concurrently identifying the rotational input motion and damping ratio is examined. First, a method to identify the rotational input motion and damping ratio from horizontal acceleration records using modal iterative error correction is proposed. Then, the accuracy of the proposed method is examined using example problems.

     The main findings of this study are as follows:

     (1) A method to identify the rotational input motion and the damping ratio from horizontal acceleration records using a modal iterative error correction method is proposed. The modal iterative error correction method is based on inverse analysis, which addresses the inverse problem using many local stationary solutions.

     (2) Using shaking table test results as an example, the proposed method is used to determine the damping ratio of building models and rotational acceleration time histories inputted to building foundations. As a result, the damping ratio and rotation input time history could be calculated using the proposed method, which reproduced the horizontal acceleration records obtained from the shaking table tests with high accuracy. In addition, the calculated rotational input roughly agreed with the rotational input records of the test and the calculated damping ratio agreed well with the values determined in the case with known rotational input.

     (3) However, depending on the amount of perturbation set and the filtering method used, even if the horizontal acceleration can be reproduced, the calculated damping ratio may vary. Setting an appropriate amount of perturbation and selecting a suitable pre-filtering method to reduce this variation and identify a damping ratio with higher reliability is another problem of particular importance.

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  • Toshiaki KIMURA, Makoto OHSAKI, Kohei SATO
    2020 Volume 85 Issue 767 Pages 61-71
    Published: 2020
    Released: January 30, 2020

     Fracture around the connections between the roof and the columns in the supporting wall of a long-span structure was reported as a key issue in the recent earthquake disasters in Japan. A school gymnasium needs highest-level seismic resistance, because it is used as a shelter when in the event of earthquake disaster. Especially for a lightweight steel roof supported by stiff RC structure, deformation concentrates around the connections. Accordingly, slip occurs at the pin/roller supports, and the steel members near the support exhibit plastic buckling and fracture. This kind of damage may be due to vibration of cantilever columns in the gable wall as reported in previous studies. Therefore, it can be prevented by designing the roof and supporting structure simultaneously so that a global vibration mode dominates against seismic motions. However, most of studies focused on the characteristics of seismic response of school gymnasium or the method for seismic design, and few studies have focused on the design to reduce the seismic response of the connections of the steel roof. The second author proposed an optimization approach to design of the supporting columns of a long-span arch to reduce the responses of the arch. It has been shown that flexibility rather than stiffness of the columns reduces the response of upper arch especially in the normal direction of the arch.

     In this study, we propose an optimization method for stiffness design of RC columns of a school gymnasium to reduce the interaction forces between the steel roof and supporting structure under seismic motions. The objective function is the maximum force at the connections, which is evaluated using the SRSS method for the seismic motions corresponding to the specified acceleration response spectrum. Constraints are given for the total weight and the interstory drift angles of columns. The sizes of columns are optimized using simulated annealing (SA).

     It is shown in the numerical examples that the maximum interaction force is drastically reduced to about half of the reference model through optimization. The property of optimal solution to reduce the interaction force is investigated in detail from the mode shapes, natural periods, and effective mass ratios. It is shown that the depths of the RC columns of the frame in the longitudinal direction increases while the depth of the columns in the transverse direction decreases. As a result, the shear stiffness of the longitudinal frame is increased, the vibration mode of the top of the frame in the transverse direction is suppressed, and the maximum shear force of the bearing is reduced. Furthermore, the accuracy of SRSS estimation is confirmed by the time-history analysis against 10 artificial ground motions compatible to the design response spectrum. It is shown that the maximum interaction forces of optimal solutions using SRSS method is smaller than the average of the time-history analysis due to the difference of the damping factor between the dominant mode and the target value for generating the artificial ground motions. Besides, the results of the time-history analysis also show that the maximum shear force of the bearing is reduced due to the suppression of the dominant vibration mode.

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  • Yoshio SAKAMAKI, Keisuke KAGAWA, Nobuyoshi MICHIBA, Tsuyoshi MAKITA, S ...
    2020 Volume 85 Issue 767 Pages 73-83
    Published: 2020
    Released: January 30, 2020

     Herein, the stress of a wooden semi-rigid frame containing structural plywood that is used to secure rigidity has been elucidated via static racking tests and numerical simulations. The assumed semi-rigid frame composed of structural plywood is 4–6 m wide, and a lag-screw-bolt is used at the joint. When structural plywood is combined with a semi-rigid frame, the behavior of the plywood due to pull-out affects the behavior of the semi-rigid frame at the column. In our previous report, the stress in such a case was determined. The contents of the report are as follows.

     1) The temporary allowable shear force of a wooden semi-rigid frame composed of structural plywood was calculated by adding the reduction coefficient to each temporary allowable shear force of the wooden semi-frame and the structural plywood.

     2) When the structural plywood was nailed directly, nailing it on the inside of the wooden column instead of the outside is more advantageous.

     Herein, our previous research was extended. The target was a gate-type wooden semi-rigid frame and column details adopted in real houses. Tests were conducted on a sample in which the nail was directly attached to the inside of the wooden column and on a sample in which plywood was installed on a wooden semi-rigid frame. Moreover, several numerical analysis simulations were performed and statistically analyzed.

     The following conclusions were obtained.

     1) If a plywood wall is nailed directly on a wooden column, the column is restrained by nails. As a result, the applied shear force at the same deformation angle is larger than the shear force of the un-nailed column.

     2) The shear force of the wooden semi-rigid frame composed of structural plywood can be calculated by combining the single wooden semi-rigid frame and the single plywood by multiplying the coefficients.

     3) If the wooden semi-rigid frame is directly nailed, the axial force of the plywood directly affects the wooden semi-rigid frame column. The yield of the Lag-screw-bolt accelerates at the same deformation angle. Therefore, limiting the deformation angle at the Lag-screw-bolt yield point is necessary.

     4) By securing the elongation of the Lag-screw-bolt and increasing the plastic region after the yield point, the limitation of the deformation angle can be eliminated.

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  • SeungWoung HO, Masayuki KUROKI, Kenji KIKUCHI
    2020 Volume 85 Issue 767 Pages 85-95
    Published: 2020
    Released: January 30, 2020

     1. Introduction

     Yamakawa et al. proposed an emergency retrofit method using stressed external hoops with respect to the R/C column suffered shear damage and discussed its effects. The aim of this paper is to identify the bond splitting strength of main bars after the emergency retrofit, τbru, as a part of the development of this emergency retrofit method.

     2. Test Specimens

     The total number of test specimens is 29, where the cross-sectional dimension is 250 mm×250 mm. The main test variables are damage level, diameter of main bar, db, number of main bars, n, compressive strength of concrete, σB, external hoop reinforcement ratio, pwpc, and initial lateral pressure, σr (see Fig. 1 and Table 1).

     3. Test Method

     First, a cantilever type monotonic tensile test was conducted to introduce a damage to the test specimen, where load was applied until the maximum splitting crack width reaches target for respective test specimen. After the damage introduction loading, external hoops were installed as the emergency retrofit (see Fig. 1). And then, main bars were pulled until failure. Displacement transducers measure slip displacements at free end for each main bar (see Fig. 3).

     4. Test Results

     In the loading after emergency retrofit, all test specimens failed in side split failure mode (see Fig. 5). The larger the bond slip displacement at the end of damage introduction loading, scd, the smaller τbru (see Figs. 4 (a), (b), (c)). Also, the larger σr, the larger τbru (see Figs. 4 (d), (e), (f)).

     5. Discussions on Bond Splitting Strength after Emergency Retrofit

     The test results showed that scd is adequate as a damage index that indicates deterioration in bond capacity caused by the earthquake (see Fig. 8). Based on this, Equation (7) was derived as a formula for calclating τbru. However, since scd cannot be evaluated directly in an actual column member, it needs to be evaluated based on any measurable physical quantity. In this study, we evaluated scd indirectly based on crack area and crack width, respectively, and examined performance of those evaluations (see Figs. 14, 15, 16 and 17).

     6. Conclusions

     1) scd was found to have a close correlation with τbru. This suggests that scd can serve as a damage index.

     2) If the bond splitting strength in case when stressed external hoops are installed without initial damage, τbu, is taken as a standard, there was no significant difference in the decrease rate of τbru/τbu due to an increase of scd despite of difference in db, σB, and pwpc. On the other hand, the decrease rate is different with σr. Based on this fact, Equation (7) was derived as a formula for calculating τbru. Equation (7) provided the bond strength of 1/0.834 to 1/1.28 times the experimental value.

     3) If scd was evaluated indirectly with the area of bond splitting crack, Equation (7) provided the bond strength of 1/0.727 to 1/1.61 times the experimental value. Also, if scd was evaluated with the maximum width of bond splitting cracks which can be obtained more easily, Equation (7) provided the strength of 1/0.700 to 1/1.68 times the experimental value.

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  • Kozo NAKADA, Tetsuo YAMAKAWA, Pasha JAVADI, Mohammad Zahid NOORI, Kazu ...
    2020 Volume 85 Issue 767 Pages 97-104
    Published: 2020
    Released: January 30, 2020

     A strength–ductility–type seismic retrofit technique for soft first-story reinforced concrete (RC) buildings via addition of wing walls or panel walls was proposed by Yamakawa4). This method is called the thick hybrid wall (THW) technique and is performed by jacketing an RC column and an additional wing wall using channel-shaped steel plates connected together by high-strength steel bars (PC bars). The steel plates and PC bars make steel formworks inside the RC frames during the additional concrete casting. Furthermore, they can serve for shear strengthening and confinement of RC columns after hardening of additional concrete. No longitudinal and transverse reinforcements or anchorage systems are provided in the additional wing wall; therefore, the construction is easy and cost-effective. The previous investigation6) of the one-bay one-story RC frame retrofitted by the THW technique verified that both lateral strength and ductility are considerably improved compared to those of the non-retrofitted RC frame. This study aims to propose equations that can be used to estimate the ultimate moment resistance and the minimum wing-wall length of RC columns retrofitted by the THW technique.

     The ultimate moment resistance of the RC column with a wing wall (THW technique) is calculated by considering the whole section as a united section. In the proposed method, the strain distribution of the THW column section is divided into three fields, such as field A, B, and C, based on the location of the neutral axis changes according to the axial force levels. The unified THW column section is asymmetric about the centerline of the square column section; hence, the wall side is considered in compression only. The moment capacity equation is derived by considering the equilibrium of internal tension and compression forces with the external vertical axial load. Assuming the location of the neutral axis depth, a generalized equation is obtained based on the equivalent rectangular stress block parameters for concrete in compression that is adopted by the American Concrete Institution (ACI). Practically, the THW technique is applied in the field A, where all the rebars in the tension and compression sides of the existing RC column yield in tension, and the limit axial force ratio of the field A is represented as η1.

     The ultimate moment resistance of the THW column section is more accurately calculated by the fiber model method. The stress-strain model of concrete in the fiber model analysis is considered as Monder’s model11). In Section 4, the calculated results of the proposed equation, fiber model analysis, and simplified equations8) are in good agreement with the previous test results of both-sided (R03WC-P200S)4) and one-sided wing-wall (R03WO-S)5) specimens retrofitted by the THW technique.

     The equation used to calculate the minimum wing-wall length of the THW technique is proposed in Section 5 based on the limit axial force ratio (η1) in the field A. The calculated results based on the minimum wing-wall length equation show that the additional wing-wall length ratio β increases with increasing the axial force ratio η. Furthermore, β decreases with increasing the ratio of the compressive strength of concrete κ and depends on the tensile rebar ratio q.

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  • Yoshikazu SAWAMOTO, Jun KUBOTA, Makoto OHSAKI
    2020 Volume 85 Issue 767 Pages 105-115
    Published: 2020
    Released: January 30, 2020

     In Tohoku earthquake (March 11, 2011), highrise steel buildings of the Tokyo downtown area shook for a long moment under the influence of long-period ground motion. To prevent damage under such ground motion, evaluation on deformation capacity of steel member (welded beam end, etc.) has been required under multi-cycle loading.

     In this paper, deformation capacity of the steel beam with local buckling and ductile fracture is assessed by the FE analysis based on the fracture rule (cyclic damage rule and monotonic damage rule) and recontact of removed element. The cyclic damage rule is a fatigue damage law based on Continuum Damage Mechanics (CDM), and the monotonic damage rule is a damage rule for a large ductility factor equivalent to monotonic loading. The validity of this fracture rule and re-contact of removed element is verified by the simulation of past experiments under cyclic loading. Two past experiments are selected. One is an element experiment using specimens modeling beam flange and web, in which tensile and compressive repeated force is applied in the axial direction. The other is a partial frame experiment using field welding type specimen having a ¼ circular weld access hole of compound circle with R25 and R10 at the beam-end, in which constant cyclic displacement is applied. For an element experiment, simulation of monotonic loading and repeated loading with constant amplitude is performed using FEM with solid elements and shell elements. We can simulate the reduction of peak load using FE analysis, and it is found that the deformation capacity under multiple cyclic loading conditions can be evaluated. For a partial frame experiment, simulation using shell elements is carried out. As a result of the FE analysis, it is found that a crack occurs at the toe of the weld access hole on the beam flange, and propagates in the flange width direction. Using FEM it is possible to simulate the situation where the welded beam-end fractures, and it has been verified that the load and deformation relationship of FE analysis has good agreement with test results.

     In addition, as a result of conducting the analysis with the beam web thickness changed, it demonstrates that the initial crack initiation timing is delayed and the fracture timing is delayed accordingly because the stress concentration at the weld access hole bottom with thinner beam web is relaxed.

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  • Yoshihiro KIMURA, Motoko ANDO, Sachi FURUKAWA
    2020 Volume 85 Issue 767 Pages 117-127
    Published: 2020
    Released: January 30, 2020

     With an embedded type column base, or a fixed column base, column bases of the first story columns for frames designed following current design codes may yield simultaneously when the second story beams yield, because it cannot be avoided that the bending moment become substantially large at the base. Kimura et. al [4] has proposed the concept to realize beam yielding mechanism of a steel moment-resisting frame by applying a pin-support column base system to midpoints of the first story columns. With a proposed column support system, or mid-story pin column base system, it can be reliably designed that the first story columns remain in elastic until the maximum story drift of a frame exceeds 0.03 rad. While seismic performance of the frame is significantly improved with this new column base system, yielding of columns must be prevented or collapse mechanism may be formed.

     In practice, structural design requires multiple trials to optimize selection of structural components whether their combinations meet seismic demands on a frame. The D-value method [3] is a design method based on fundamental structural mechanics to predict story drift distribution of a moment-resisting frame under designated lateral force distribution. The D-value method has advantage to predict structural performance directly with respect to structural properties.

     This paper evaluates seismic performance, especially flexural demand on columns for a moment-resisting steel frame adopting a mid-story pin column base to maintain them elastic until a frame reaches the ultimate limit state. Because the original D-value method is only applicable to a frame with linear structural behavior and with a conventional column base, it is extended to predict elasto-plastic behavior of frames. In the proposed modified D-value method, replacement of column base to a mid-story pin column base is simply considered as shift of the location of an inflection point in the first story column. In addition, rotational restriction of the column by plastic beams is neglected to calculate moment and displacement distribution of the plastic stories in the incremental steps, assuming a beam has the perfect-plastic behavior.

     The major findings of this paper can be summarized as follows:

     1) The proposed modified D-value method successfully predicts mechanical behavior calculated by static analysis.

     2) Series of static analysis shows that beam yielding mechanism is formed by reaching a story drift ratio of larger than 0.03 rad, and that required flexural demand on the column reaches twice as large as the full-plastic moment of the beams for a 3-story frame and exceeds for 6- and 9-story frames.

     3) Seismic analysis shows that column moments calculated by the modified D-value method sufficiently agree with those calculated by simulation while response of frames remains in elastic range. Once the response of frames goes into the plastic range, calculational errors are increased up to 21%, 31% and 18% for 2-, 6- and 9-story frames. Seismic analysis tends to yield larger column moment, but still the global trend such as in the relation between the maximum moment of the column and the maximum story drift is sufficiently reproduced by the modified D-value method.

     4) The larger maximum moment of the column calculated by simulation is thought to be caused by two reasons: one is that story shear distribution at recording the maximum moment of the column becomes closer to triangle story shear distribution rather than Ai distribution, which is adopted in calculation by the modified D-value method, and the other is that sequence of beam plasticity of the frames are substantially changed from those assumed in the D-value method.

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  • Ryosuke OBA, Hiromitsu MORIOKA, Tomohiro KINOSHITA, Yuji KOETAKA, Keii ...
    2020 Volume 85 Issue 767 Pages 129-139
    Published: 2020
    Released: January 30, 2020

     In recent years, high strength steels, whose tensile strength is more than 780 MPa, have been developed in Japan and are used mainly for columns of high rise buildings. However, in case of high strength steels, not only securing strength and toughness of welding parts but also preventing cold crack need severer welding conditions, i.e. low heat input and preheat, than in case of ordinary steels. In Japan, square hollow sections are most well used for columns, however stiffeners at the joints with beam flanges, i.e. diaphragms, are necessary to restrain local deformation of the joints. In this study, exterior-diaphragm type beam-to-column connections are focused on, because this type of diaphragm has advantage to overcome the difficulties being faced during welding of high strength steels.

     To improve convenience of construction and transportation efficiency of columns preassembled with exterior diaphragms at fabrication factories, this study introduces square exterior diaphragms with the thick steel plates, whose depth is smaller than conventional exterior diaphragms. In case of exterior diaphragms, local deformation of the joint, more specifically out-of-plane deformation of column plates and in-plane deformation of exterior diaphragm, occurs against the force transferred from the beam flange. Therefore, the methods to evaluate elastic stiffness and yield strength of beam-to-column connections in consideration of local deformation of the joints are essential for structural design. Evaluation methods of elastic stiffness and yield strength of beam flange joints have been established theoretically using partial tensile model, and the validity of evaluation methods has been confirmed based on experiment or FEM analysis (reference [2]). However, in the reference [2], concrete filled steel tube column (CFT column) to beam flange joint has not been studied, and evaluation methods of elastic stiffness and yield strength of beam end connections including beam web joints have not been proposed. Consequently, it is needed to clarify elasto-plastic behaviors of beam-to-column connections, on which each of hollow column and CFT column is adopted.

     First, outline of evaluation methods of elastic stiffness and yield strength are described based on the reference [2]. FEM analysis of box-section CFT column-to-beam flange connections with the exterior diaphragm is conducted to compare calculated values based on the reference [2] to numerical results. As a result, it is clarified that most calculated values of elastic stiffness correspond numerical results with discrepancy of about 10 — 20 %. Furthermore, it is verified that the evaluation method of yield strength proposed in the reference [2] is appropriate for predicting the strength at the elastic limit even in case of CFT column.

     Additionally, for each of hollow columns and CFT columns, stress state and deformation state of beam end connections are assumed, and evaluation methods of elastic stiffness and yield strength of column to beam end connections are proposed in this paper. In order to compare calculated values to experimental values and numerical values, cyclic loading test and FEM analysis of cruciform frames are conducted. As a results, it is verified that calculated values of elastic stiffness and yield strength of connections are able to evaluate most numerical results with discrepancy about 10 – 30 %. Further, in case of specimen designed with yield strength of connections exceeding bending moment acted at the beam end under plastic strength of beam, it is confirmed that beam end connections keep elastic until the ultimate state of specimen, while plastic deformation of beams occur dominantly, in experiment and FEM analysis.

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  • Kikuo IKARASHI, Hayato SHIMOMURA, Jumpei YASUNAGA, Takuya UEKI, Junich ...
    2020 Volume 85 Issue 767 Pages 141-150
    Published: 2020
    Released: January 30, 2020

     The steel shear wall is the one of the seismic resistance devices which are installed in the frame of building to improve the horizontal stiffness and strength. Shear force is loaded on the steel plate shear wall when the horizontal force acts the building. In order to prevent the overall buckling, some stiffeners are welded on the shear wall in front and back cross arrangement. It is assumed that the buckling behavior of those steel shear walls are greatly affected by the surrounding frame member. However, the effect of the surrounding frame member on the buckling behavior of the steel shear wall stiffened by cross bracing is not quantitatively clarified.

     In this study, we clarified the influence of the surrounding frame members on the elastic buckling strength of steel shear wall by conducting eigenvalue analysis. In addition, we proposed the calculation method of the elastic buckling strength considering the effect of surrounding frame members. Also, we investigated the influence of surrounding frame members on the elastic-plastic behavior of steel shear wall by doing experiment and conducting large deformation analysis.

     Results are summarized as follows;

     1) We proposed the calculation formula of the elastic buckling strength of steel shear wall stiffened by cross bracing by applying the correction by the torsional rigidity ratio to the calculation formula of the elastic buckling strength of the orthotropic flat plate.

     2) The reduction rate of the elastic buckling strength of the stiffened plate due to the influence of the out-of-plane rigidity of the surrounding frame members can be evaluated by the bending rigidity ratio of the surrounding frame member and the stiffened plate and the ratio of buckling stress ratio determined from the out-of-plane rigidity of surrounding frame member.

     3) The rate of decrease in the elastic buckling strength of a stiffened plate under the influence of the out-of-plane rigidity of the vertical frame member and the intermediate vertical frame member with different bending rigidity in right and left can be evaluated by buckling stress ratio determined from out-of-plane rigidity of longitudinal frame members.

     4) It is possible to obtain a stable load-displacement relationship even when the out-of-plane rigidity of the surrounding frame member is relatively small, if the elastic buckling strength can be ensured to the extent that the shear yielding of the stiffened plate precedes.

     5) From the viewpoint of workability, the possibility that the end of stiffener is not rigidly connected to the surrounding frame member was also examined, and it was confirmed that the effect of the end constraint condition on the elasto-plastic behavior of stiffened plate was small.

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  • Masae KIDO, Keigo TSUDA
    2020 Volume 85 Issue 767 Pages 151-157
    Published: 2020
    Released: January 30, 2020

    1. Introduction

     The objective of this study is to examine the amplification factor of moment and rotation angle due to the PΔ effect. A sub-assemblage frame is analyzed by using the buckling slope deflection method, and amplification factors are obtained. Numerical analysis is performed taking the G factors, slenderness ratio λ and axial load ratio ny as the analytical parameters. An approximate formula for estimating the amplification factors is presented on the basis of the buckling load proposed by the second author.

    2. Analytical work

     The sub-assemblage frame shown in Fig. 2 is analysed, taking the geometric nonlinear effect into consideration. Equation (3) is obtained by the fundamental formula of buckling slope deflection method. Moment equation at point A and B becomes Eqs. (7) and (10), respectively, where GA and GB are G factors defined as Eqs. (9) and (11). From the story equation (Eq. (12)) together with moment equation, the rotation angle R of the member AB and the moment MAB and MBA of node A and B are obtained as Eqs. (13) ~ (15). In absence of axial force P, the rotation angle R and the moment MAB and MBA become Eqs. (18) ~ (20), and then the amplification factors are obtained by Eqs. (21) ~ (23).

    3. Results and discussions

     As the analytical parameters, G factors GA(=GB), slenderness ratios λ and axial load ratios ny are selected, and they vary as follows: G factors GA(=GB) : 0 (rigid beams), 0.5, 1, 2.5 and 5, slenderness ratio λ: 20, 40 and 80, axial load ratio ny: 0.1, 0.3, 0.5, 0.7. Figure 4 shows R/0RZ relations and M/0M-Z relations. A similar tendency is observed between R/0R and M/0M. Figures 6 and 7 show the effect of axial load ratio ny and G factors. From Fig. 6, it is shown that the ratios R/0R and M/0M become large as the axial load ratio increases. Approximate effective length factor Kdsn has been proposed by Eq. (29), and using this, the amplification factors am can be obtained by Eq. (33). The values of am agree well with the R/0R and M/0M, and the relative error is shown in Fig. 8. While the error increases as the value Z becomes large, the am fits with an error of 2% or less when Z is smaller than 1. Figure 9 shows the limit Zα where the amplification factor is guaranteed below the value of α. Moreover, an example for calculating the amplification factors of six-story and five-span steel frame shown in Fig. 10 is performed.

    4. Conclusions

     The conclusions derived from this study are as follows:

     1) The amplification factors of the moments and rotation angle are presented by Eqs. (21) ~ (23). The governing parameters are G factors and Z defined in Eqs. (9), (11) and (6).

     2) The amplification factors can be approximately calculated by using Eq. (33).

     3) The limit value of Z to assure the restriction of the amplification factors is proposed by Eq. (38).

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  • Kazuki ITO, Takenori HIDA, Tatsuya ITOI, Tsuyoshi TAKADA
    2020 Volume 85 Issue 767 Pages 159-168
    Published: 2020
    Released: January 30, 2020

     The current seismic design mainly focuses on the performance of structure. The human safety to earthquake shaking is considered implicitly by securing the structural performance. There exists some cases, however, of human injury due to earthquake shaking due to falling or bumping into the wall during past earthquakes. In order to ensure human safety during earthquakes, this study proposed an evaluation methodology of human behavior.

     First, the relationship between human injury and floor response during earthquake is developed using a seismic analysis model of human body proposed by our previous study. The maximum displacement of center of pressure (CoP) of human body is evaluated using the human body model to estimate the possibility of falling and hitting to the wall. Furthermore, head injury criterion (HIC) score during strong shaking is evaluated as a function of the maximum velocity of head. Then, the evaluation methodology of degree of head injury and displacement of CoP based on peak floor acceleration (PFA) and representative frequency are proposed.

     Then, in order to investigate the difficulty of action during earthquake shaking, the results of interview survey are shown that were conducted to the operators of the Kashiwazaki-Kariwa Nuclear Power Station to collect their experiences during the 2007 Niigataken Chuetsu-oki Earthquake. The CoPs evaluated by the above-mentioned methodology based on the strong motion records observed at the plant during the earthquake are shown to be comparable to the experiences of the operators, i.e., as the displacement of CoP increases, the human action is more difficult. This fact shows that the evaluation methodology of CoP can be used to evaluate the action difficulty of human during strong shaking.

     Then, the methodology to evaluate possibility of human injury is demonstrated combining the proposed method and estimation of the overturning ratio of furniture. A result from an example case indicates that, tall furniture overturns in smaller PFA than that of human injury, if the frequency is higher than 1.0 [Hz]. Whereas if the frequency is lower than 1.0 [Hz], PFA for overturning of tall furniture is almost equivalent to that of human injury.

     Finally, seismic design framework for building that focuses on human injuries during earthquakes was proposed. It is demonstrated that integrated evaluation of possibility of injury due to falling down on the floor, bumping into the wall, and overturning of the furniture as well as action difficulty due to shaking can be conducted using the proposed method to discuss the design criteria of the building for securing human safety.

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  • Takayuki KIKUCHI, Yusuke SHINTANI, Takeo HIRASHIMA, Mamoru KOHNO
    2020 Volume 85 Issue 767 Pages 169-176
    Published: 2020
    Released: January 30, 2020

     This paper presents results of high temperature compression tests of steel fiber reinforced concrete. The influence of steel fiber on the mechanical properties at high temperature was investigated from the difference of the test results between steel fiber reinforced concrete and plain concrete. Although research on prevention of concrete spalling by means of mixing steel fibers has been conducted, there is no report on mechanical properties of steel fiber reinforced concrete at high temperature in Japan, and there are few such reports in foreign countries.

     In this study, high temperature compression tests were performed using two types of concrete, i. e. steel fiber reinforced concrete (SF) and plain concrete (P). The tests consisted two kind of tests. One was load increasing tests under steady state at constant high temperatures (steady state tests, ST tests). Other was temperature increasing tests under constant stress (transient tests, TR tests) . In case of ST tests, the parameter was specimen temperatures ranging from ambient temperature to 800 °C. While concrete was heated to the target temperature, heating rate was controlled at 1.5 °C/minute. While stress or strain of concrete increased, the concrete temperature was kept the target temperature. From ST test results, stress-strain relationship, compressive strength, Young's modulus and absorbed energy were compared between SF and P. In case of TR tests, the parameter was level of the constant compressive stress ranging from 0 to 0.7.After applying the target stress, specimen was heated and the relative displacement was measured. From TR test, the thermal strain and total strain were obtained.

     Main findings of this paper were summarized as follows:

     (1) Compressive strength ranging from 200 °C to 400 °C was higher for SF than for P, meanwhile both the compressive strengths were approximately same above 500 °C. There was no significant difference in Young's modulus at high temperatures due to the presence or absence of steel fibers.

     (2) The absorbed energy of SF was larger than that of P between 100 °C and 500 °C, and the difference was the largest at 500 °C. On the other hand, the difference above 600 °C was relatively low.

     (3) The thermal strain ranging from 600 °C to 800 °C was lower for SF than for P.

     (4) Under stress level of 0.7 in TR tests, SF supported the load up to 477 °C, meanwhile P fractured at 78 °C. Under high load condition, the effect of steel fiber may be considerable.

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