Journal of Structural and Construction Engineering (Transactions of AIJ)
Online ISSN : 1881-8153
Print ISSN : 1340-4202
ISSN-L : 1340-4202
Volume 86, Issue 781
Displaying 1-17 of 17 articles from this issue
  • Takumi NOGUCHI, Yukio HAMA
    2021 Volume 86 Issue 781 Pages 343-351
    Published: 2021
    Released on J-STAGE: March 30, 2021
    JOURNAL FREE ACCESS

     Frost damage is one of the serious deterioration cases of concrete structures in cold regions. The probability of its occurrence depends on temperature, solar radiation and water content of concrete. In addition, various researches have been conducted to evaluate the regional characteristics of frost damage using weather conditions and to estimate deterioration based on freezing process and material conditions. On the other hand, it has been clarified by Aono et al. that the pore volume of 40-2000 nm in diameter which affects the frost resistance increases due to drying conditions. However, existing methods of frost damage assessment and deterioration prediction still not take into account the decrease in frost resistance caused by drying. Therefore, in this study, we propose a calculation method for predicting deterioration after taking into account the decrease in frost resistance due to drying.

     A formula expression between the amount of pores and the durability factor has been established, but a relational expression between the pore volume and the amount of decrease in relative dynamic modulus per cycle has not been established. Therefore, after obtaining the pore volume range suitable for the objective variable of the relative dynamic modulus decrease per cycle, the relational expression was derived.

     A method using maturity of temperature and humidity has already been proposed as a method for predicting pore volume change of 40-2000 nm in diameter due to the drying conditions. This method cannot take into account the change of pore volume of 40-2000 nm in diameter due to the other factors except the water-cement ratio. Therefore, the ratio of the maturity of temperature and humidity and the initial pore volume of 40-2000 nm in diameter to the pore volume of 40-2000 nm in diameter after drying (the rate of change in the pore volume of 40-2000 nm in diameter) was obtained. As a result, the natural logarithm of the rate of change in the pore volume of 40-2000 nm in diameter and the square root of maturity of temperature and humidity have a linear relationship. The slope and the upper limit can be expressed by the water cement ratio.

     In order to predict the decrease in the relative dynamic modulus, the number of freezing and thawing cycles in winter and the amount of decrease in the relative dynamic modulus per cycle are required. Since the equivalent cycle to ASTM test is the one·year weather condition converted into number of freezing and the.wing cycles, so the number of freezing and thawing cycles in winter can be expressed using this index. Here, a method for calculating the amount of decrease in relative dynamic elastic modulus after drying was established from the relational formula between the amount of decrease in relative dynamic elastic modulus and the amount of pores per cycle and the relational formula between maturity of temperature and humidity and the rate of change in pore volume. By calculating these coefficients, the amount of decrease in the relative dynamic modulus per year can be determined. Therefore, it is possible to predict the decrease in the relative dynamic modulus considering of the decrease in the frost resistance due to drying by integrating the amount of decrease in the relative dynamic modulus which is calculated every year and subtracting it from the initial value.

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  • Masayuki TSUKAGOSHI, Masaki NAKAMORI, Takao UEDA, Kyoji TANAKA
    2021 Volume 86 Issue 781 Pages 353-360
    Published: 2021
    Released on J-STAGE: March 30, 2021
    JOURNAL FREE ACCESS

     A polymer-modified cement waterproofing membrane is a construction material (PCWM) with a high polymer to cement ratio (P/C) of 100 to 200% by weight, which improves waterproofing and elongation performance. When PCWM is applied to horizontal surfaces such as roofs and floor slabs, the cement component will settle in the material due to the difference in specific gravity of polymer and cement. As a result, a significant amount of cement hydration products are expected to be present on the underside of the waterproofing membrane. When the water content is increased in order to conveniently improve the workability, there is a high risk of material separation. There is a concern that the crack followability of the substrate concrete, and fatigue resistance due to repetition of expansion and contraction of cracking due to changes in the environmental temperature will be reduced. Furthermore, when used outdoors, the performance will be affected by weathering caused by such influences as solar radiation and heat.

     In this study, the cross-sectional microstructure of PCWM was observed by scanning electron microscopy, and the state of material separation between cement and polymer was clarified. In addition, the relationship between the microstructure and substrate crack followability and fatigue resistance were investigated. As a test specimen for observation of the microstructure, a sheet shape waterproof membrane was prepared. Then, a sample was cut out for observation. In order to observe the cross-sectional direction, depth of grinding into the sample from the surface was controlled to expose the observation surface. 10 locations were observed at 0.2 mm intervals at a depth of 0.1 mm from the surface. Fatigue resistant test specimens were prepared measuring 100 mm wide, 380 mm long and 2.0 thick. PCWM was applied on the substrate slate plate. Cracks were generated in the substrate slate, which were then expanded and contracted to produce movement of the area just above the crack in PCWM. Movement consisted of three levels of; 0.25- 0.5 mm, 0.5-1.0 mm and 1.0-2.0 mm, respectively. The number of fatigue cycles was 1500 for each level, with a period of 0.5 Hz. During applying movement, condition of the cracks in PCWM was observed.

     From results obtained in these investigations, the following was concluded:

     (1) Difference in specific gravity between polymer and cement for constituting PCWM, depending on mix proportions, cement hydration products may settle at the bottom and cause non-uniformity in the material.

     (2) Tensile strength and elongation of PCWM with uneven distribution of materials are reduced even if the P/C is the same in the mix proportion.

     (3) Tensile strength and elongation rate were reduced due to the weathering. The higher P/C and W/B were strongly affected by weathering and the rate of reduction was greater.

     (4) The higher the tensile strength and elongation rate of PCWM, tended to increase substrate crack followability and crack-fatigue resistance. In the case where the non-uniformity PCWM, the fatigue resistance was reduced. On the other hand, even in the case of large P/C and deterioration of mechanical properties due to weathering, if the material was homogeneous, it retained good fatigue resistance.

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  • Yutaro FUJII, Hiroki TAKAYAMA, Shintaro FUKUDA, Yutaka YOKOYAMA
    2021 Volume 86 Issue 781 Pages 361-370
    Published: 2021
    Released on J-STAGE: March 30, 2021
    JOURNAL FREE ACCESS

     Resin floor coating is used for the floors such as logistics facilities and production facilities. Those floors could be subjected to great complicated load by guided vehicles. Due to the load, the cases are reported that the problems with the floors occur. It is expected that durability against dynamic load of Resin floor coating is strongly affected by surface layer quality. Therefore, it is very important to secure surface layer quality. However, there are few cases that the relationship between durability against dynamic load of Resin floor coating and surface layer quality is considered. So, there is a lack of knowledge to avoid the problems in advance.

     Thus, in this study, the relationship between durability against dynamic load of Resin floor coating and surface layer quality is considered. The targeted dynamic load is the load applied when the casters of such as guided vehicles are carve. In addition, the effects of polisher and the process for finishing work and curing among the process for constructing slab are considered.

     Some various Concrete specimens are prepared. (Reference Fig. 1) The preparing conditions are showed in Table 1, 2. Especially, by varying finishing work conditions like Table 3, the specimens with various surface layer qualities are prepared. The concrete specimens are measured three kinds of surface layer quality. Those are surface intensity, moisture vapor emission, surface roughness. Table 4 shows the grades of surface intensity. Also, measurement of Tensile adhesive strength of slab and Resin floor coating was done.

     Twist load tester developed in this study was used for the durability against dynamic load test. This tester can reproduce the load applied when the casters of such as guided vehicles are carve. In order to reproduce real load, 5000N and 10000N load were chosen in the test. (Reference Fig. 2, Photo 1)

     The results are as follows: First, Fig. 3 shows the measurement results of surface intensity, moisture vapor emission. The result that the more finishing work conditions are improved, the more surface intensity increase, and the more moisture vapor emission decrease was obtained. It is also proved that surface intensity and moisture vapor emission have good correspondence with each other. (Reference Fig. 4)

     Secondly, the relationship of surface intensity between before and after polish is considered. The result shows surface intensity of polished specimens gets larger than before polish. (Reference Fig. 5)

     Finally, the relationship between surface layer quality and durability against dynamic is considered. As a result, it is proved that in addition to preparation of slab by the process shown in this study, securement of appropriate surface intensity could decrease the possibility of primary problems. (Reference Fig. 9, 10)

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  • Dai KOMIYAMA, Ashidmaa BATSUURI, Toru TAKAHASHI
    2021 Volume 86 Issue 781 Pages 371-380
    Published: 2021
    Released on J-STAGE: March 30, 2021
    JOURNAL FREE ACCESS

     We proposed a real-time estimation model based on the method of Takahashi model to understand the snow weight changes during every moment of snow season. This method uses Takahashi model, which is made up from three sub models, snowfall model, compaction model, and snow melting model. In addition, the hourly snow layer model and optimized parameter for each location have been newly introduced to real-time estimation.

     In hourly snow layer model, snow layer is formed by weather observation records obtained hourly from AMeDAS. The density at the hourly layer formation was calculated by the snowfall model. In addition, since it was assumed that the hourly layer was transitioning to the daily snow layer, only the infiltration of snowmelt water and rainfall was considered, while consolidation was not.

     The optimized parameters for each location are average values of several years of pre-calculation result of each location. However, in the analysis using these parameters, when the value is significantly different from the average year, the error might be large. In that case, if overestimation was occurred, consolidation was forcibly performed, and if underestimation occurs, the capture rate was corrected.

     The estimation accuracy was verified using this model. This paper covered Tokamachi, Shinjo, and Sapporo. The snow weight data used to compare calculation result were the observed record in Tokamachi and Shinjo, and for the Sapporo’s case, the value was calculated from the record of the cross-section observation, which was done twice a week. Also, the comparison of snow weight in the verification was based on daily data.

     In Tokamachi and Shinjo, the estimation results were sometimes low in the winter with little snow, they were almost accurate in the winter with a lot of snow. In Sapporo, although they were accurate in some winters, the error of the maximum snow weight was over 30% in winters with a lot of snow.

     In Sapporo in the winter of 2012/13, the obtained value by cross-section observation might be inaccurate and the snow weight might be less than the true value. On the other hand, the increase in snow weight due to rainfall from mid-February might be indication that the estimated layer is overly absorbing precipitation. Therefore, the actual snow conditions of the snow layer from mid-February to March is possibly changing to granular snow earlier than our estimation due to consolidation and precipitation infiltration, rainfall. In result snowmelt water and rainfall may not be retained and flowed out from the bottom of the snow. In addition, the temperature in Sapporo is extremely low in winter, so there are many days when the temperature drops below -2℃, which is set as the minimum snowmelt temperature. At this time, snow melting does not occur in the analysis, but there is a possibility that snow melting might occur due to solar radiation. If snow weight measurements are accurate, one of the factors might lead to overestimation since these mechanisms were not considered in our estimation

     Furthermore, there was a gap between the estimated values and measured values when the snow melted completely in the winter of 2012/13 in Sapporo. Since the gap was caused by the fact that amount of estimated snowmelt in early spring might be smaller than the actual one, it may be necessary to use different parameters depending on the season.

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  • Kazuo YACHIUNE, Akira SUZUKI, Yuta SAITO, Masaki TOKUNO, Masahito KOBA ...
    2021 Volume 86 Issue 781 Pages 381-391
    Published: 2021
    Released on J-STAGE: March 30, 2021
    JOURNAL FREE ACCESS

     In recent years, there is concern about the occurrence of extreme ground motions that greatly exceed the amplitude levels and durations expected in conventional design level. Therefore, seismically isolated buildings are required to secure the seismic isolation performance for small earthquakes and to suppress the excessive displacement of the seismic isolation layer for extreme ground motions. As one of the effective means to meet the above requirements, in addition to an electromagnetic switching semi-active seismic isolation system, a cheaper and more reliable passive damper is being developed. Meanwhile, the authors have proposed a dead zone mechanism that is an accessory device connected to the existing oil damper.

     When the relative displacement of seismic isolation layer is smaller than the set amplitude (medium and small earthquakes level), the dead zone mechanism only slides and no damping force is generated in the oil damper, and when the amplitude is larger than the set amplitude (extreme ground motions), this mechanism generates damping force and suppresses excessive displacement. Furthermore, one of the features of this mechanism is that it has a mechanism that automatically returns the rod to the original position after the earthquake. In this paper, we analyze the seismic response of seismically isolated buildings using the dead zone mechanism to understand the response characteristics.

     1) When the publicly announced wave and pulse ground motions are used as input earthquakes, an oil damper with a dead zone mechanism is used in the seismic isolation building to ensure seismic isolation performance for small and medium earthquakes, while suppressing excessive displacement of the seismic isolation layer for extreme ground motions. It was confirmed that the desires effect of doing was obtained. In this analysis case, the most effective performance was shown when the dead zone width was set to 15cm.

     2) When the long period ground motions is used as the input ground motions, the acceleration response of the GAP model is larger than that of the OD model, but the acceleration is small at about 100~200cm/s2, which is considered to be within the allowable range for seismic isolation.

     3) It was confirmed that the automatic return spring in the dead zone mechanism automatically returns the rod in the mechanism to the neutral position at the end of the earthquake. Therefore, by automatically returning the dead zone mechanism to the automatic return spring in the dead zone mechanism, it is possible to maintain the structural performance assumed at the time of design even when multiple earthquakes occur in a short period of time.

     4) In all earthquakes, when the seismic isolation layer displacement reaches the dead zone width, the absolute acceleration increase in the lower layer. The cause is considered to be a reaction force due to the elements of the dead zone mechanism contacting each other. The 1/3 octave band analysis was applied to the time history waveform of the absolute response acceleration above the seismic isolation layer of each model. It was confirmed that the value was sufficiently smaller than the judgment value of the rank with the lowest anxiety level, compared with the evaluation curve in the anxiety level evaluation by Takahashi et al. Therefore, it was confirmed that the increase in acceleration response when the elements in the dead zone mechanism were in contact had little effect on the habitability.

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  • Rie OKAZAWA, Hiroshi KAMBARA
    2021 Volume 86 Issue 781 Pages 393-403
    Published: 2021
    Released on J-STAGE: March 30, 2021
    JOURNAL FREE ACCESS

     From the lessons of the recent great earthquakes, there is a need to design spaces in which people not only remain physically safe, but also free from anxiety. Therefore, the final goal of this study is to propose the method to reduce anxiety in response to the seismic motion. In a previous study, experiments with human subjects were performed to propose evaluation curves for human sensitivity to seismic motion. Ratios of people expressing anxiety and difficulty in taking action were adopted as indexes of sensitivity to each level of vibration, assuming a normal probability distribution function. The relationship between vibration characteristics and human sensitivity can then be determined using evaluation curves based on simple functions. However, since the scope of the subject attributes was limited and number of samples was not large enough in previous study, the relationship between vibration characteristics and human sensitivity may not show a general tendency. Therefore, in this paper, experiments were conducted by expanding the attributes of subjects to increase the number of samples. Following the experiments, the results were analyzed for each subject attribute and the evaluation curves were updated after comparing the experimental results for researcher subjects and non-researcher subjects. Also, additional experiments were conducted to confirm the effect of different duration, directions, and type of motion, and the effect of motion characteristics other than the size on the human sensitivity are analyzed based on the results of these experiments. Then, the applicability of the evaluation curves was confirmed based on with the past earthquake survey results. The findings are as follows.

     1) Comparing the human sensitivity to seismic motion between research engineers and others, who are more likely to feel anxiety and action difficulty especially for short period vibration.

     2) Anxiety and action difficulty are highly correlated with maximum acceleration A, and yet the correlation with maximum velocity V is low. The evaluation curve improved the correspondence with the experimental results by taking into account the wave period of the vibration.

     3) Among the characteristics of vibration other than the size, the sudden change in the direction of predominant shaking had the greatest effect on the human sensitivity. The effect of duration tends to increase with time of vibration with large amplitude, not with the total time of vibration.

     4) From the correspondence with the past earthquake survey results, it was confirmed that the effects of other than the size of vibration were small in the Kumamoto Earthquake, large in the 2011 Off the Pacific Coast of Tohoku Earthquake, and larger in anxiety than in action difficulty.

     5) Human sensitivity to the seismic motion could be evaluated in general for the epicentral earthquakes by using the evaluation curve. However, for the huge subduction earthquakes, it is necessary to consider the effects of other than the size of vibration. For the 2011 Off the Pacific Coast of Tohoku Earthquake, the effects of other than the size of vibration were converted to seismic motion level Δμ or the number of sections n, while the same value doesn’t always apply to other earthquakes. It is necessary to confirm with a new questionnaire survey whether these values can be applied to other earthquakes.

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  • Nobuhide NARITA, Shuji TAMURA
    2021 Volume 86 Issue 781 Pages 405-414
    Published: 2021
    Released on J-STAGE: March 30, 2021
    JOURNAL FREE ACCESS

     The soil springs of a rigid foundation with isolated footings are often evaluated by a superposition of analytical solutions, such as Mindlin’s solution (Mindlin 1936) or Steinbrenner’s method (Steinbrenner 1934), or by finite element methods. However, these methods are unsuitable in practical design. They are computationally expensive, and it is difficult to understand the causal relationship between the design parameters of the foundation and the soil spring values. Therefore, with these methods, it is difficult to reflect the designer’s intention in the foundation design.

     In this study, we proposed a simple method for evaluating static soil springs of a rigid foundation with isolated footings on the surface of a layered elastic half space, and we verified the applicability of the proposed method. Specifically, we proposed a method of approximating the static soil spring by a combination of soil springs of a spread footing foundation. We compared the results of our proposed method with static solutions of the generalized reflection and transition (R/T) coefficient method obtained by Hisada’s procedure (Luco and Apsel, 1983; Hisada, 1994). The R/T coefficient method is well known as a highly accurate method of calculating Green’s function of a multi-layered elastic half space satisfying conditions of displacements and stresses at the layer boundaries.

     As a result of the comparison, the following conclusions were obtained.

     1) The results of the proposed method were in good agreement with the results of the R/T method.

     2) The results of the proposed method were consistent with theoretical values, both when footings were in contact with each other and when the spacing between footings was infinite. This fact ensure the accuracy of the results of the proposed method when the spacing between footings is sufficiently narrow or sufficiently wide.

     3) If the shear modulus of the second layer is higher than that of the first layer, then the interaction factor of an elastic half space gives the lower bound for the interaction factor of a layered half space. Otherwise, the interaction factor of an elastic half space gives the upper bound for the interaction factor of a layered elastic half space. It is considered that the interaction factor of an elastic half space can be applied to a layered elastic half space, if the lower or upper bound for the interaction factor is to be used for an evaluation on the safe side.

     In the future we will study the interaction between footings arranged irregularly, and the interactions between different types of foundations.

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  • Kazuo AOKI, Tangyi LI, Mina SUGINO, Yasuhiro HAYASHI
    2021 Volume 86 Issue 781 Pages 415-423
    Published: 2021
    Released on J-STAGE: March 30, 2021
    JOURNAL FREE ACCESS

     In the design and seismic diagnosis / reinforcement of traditional wooden buildings in Japan, it has become mainstream to use the limit strength calculation for the evaluation of seismic resistance. In the limit strength calculation of a traditional wooden building with multiple stories, a method is often used in which the restoring force characteristics of the seismic elements of each story are evaluated as independent for each story, and the deformation angle of each story by earthquake is calculated. In the past studies, authors showed that hysteresis characteristics and failure modes are different by rigidity and deformation distribution of each story of 2 storied frames, and suggested that it is necessary to set the restoring force characteristics that appropriately reflect the rigidity and displacement distribution of each story for each building in the limit strength calculation.

     In this paper, authors have developed a loading system capable of giving an arbitrary deformation distribution to the top and the middle story of a 2 story framed structure, and report the results of a loading experiment using the system. The experiment was conducted on a framed structure with 1 span and 2 stories with Toushi-bashiras (continuous columns through 2 stories), with multiple deformation distributions set. In addition, two different types of connections, Hanasen and Komisen, were set for the connections between the columns and Sashigamoi (middle beam), and experiments were performed.

     The findings obtained as a result of this experiments are shown below.

     1 ) The result was obtained that even if the deformation angle of the 1st story was the same, the shear force of each story changed by the difference of the deformation angle between the two stories. The smaller the ratio of deformation angle of the 2nd-story to that of the 1st story is, the greater the reverse shear force generated in the Toushi-bashiras.

     2 ) The magnitude of shear force that column bears changes depending on the position of the column against to the loading direction.

     3 ) At the beam-column connections, it was confirmed that the moment of the connections and the axial force of the Sashigaoi differed depending on the deformation distribution of each story.

     4 ) It was confirmed that the type of collapse of the frame was different depending on the difference of connection type of the Hanasen and the Komisen. In particular, in the case of the Komisen type test specimen, a fracture mode due to the splitting of the column was observed. The failure mode of the Komisen type test specimen can be explained by assuming that the column fiber was cut into a notched state by the force just before the fracture, and the splitting was caused by bending fracture starting from the notch.

     From the above, it was confirmed in addition to the previous research that the failure mode and the restoring force characteristics of each story differed due to differences in the rigidity, displacement distribution and connection specifications of each story of the two- storied framed structure. In particular, it was confirmed that it is necessary to consider the differences in rigidity / displacement distribution and connection specifications of each story when setting the restoring force characteristics of each story in the limit strength calculation of a two- storied building with Toushi-bashiras.

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  • Study on fatigue behavior of timber structures subjected to repeated earthquake motions: Part 2
    Yoshihiro YAMAZAKI, Satori NAKANISHI, Hiroyasu SAKATA
    2021 Volume 86 Issue 781 Pages 425-435
    Published: 2021
    Released on J-STAGE: March 30, 2021
    JOURNAL FREE ACCESS

     Mechanical performance of timber shear walls is clearly related to the loading protocol because the components indicate fatigue phenomenon. Several hysteresis models of timber structures for time history analysis have proposed, and some of them took the strength deterioration due to fatigue behavior into account. In this paper, a new hysteresis model considering fatigue behavior is developed. The key idea is to express the effect of fatigue behavior by downward modification of the envelope curve. In addition, equivalent linearization technique considering performance deterioration is discussed. The authors have reported that maximum earthquake response is not always controlled by response spectrum and the input energy is likely to be the additional parameter.

     Chapter 2 introduces the algorithm of proposed hysteresis model. The rule to consider the fatigue behavior mainly follows the method the authors have proposed, but some improvements are made. Chapter 3 and chapter 4 introduce comparison between analytical results by the proposed model and experimental results of static random loading test and shaking table test, respectively. Chapter 5 introduces application of the fatigue evaluation to equivalent linearization technique. Chapter 6 concludes this paper. The followings are findings of this research.

     1) Hysteresis model considering strength deterioration due to the fatigue behavior was proposed. The key ideas are to express the strength deterioration by downward modification of envelope curve and to take the effect of interaction between positive/negative damages of plywood type walls into account.

     2) The proposed model could simulate experimental results of static random loading test and shaking table test.

     3) It was found that deterioration of equivalent stiffness Keq and equivalent damping ratio heq could be related to accumulated responses(f(Δ, n) and Δn/Δ) up to the maximum response. Evaluation method of Keq and heq considering the deterioration by energy spectrum were proposed.

     4) Based on the above method, equivalent linearization technique considering deterioration during earthquake response was proposed. Since lower limits of equivalent stiffness and equivalent damping ratio which were associated with deterioration were estimated, the proposed method could conservatively predict results of time history analysis.

     Although response spectrum method is originally to predict maximum earthquake response, input intensity which causes ultimate deformation is predicted. In order to extend the method to arbitrary deformation level, additional study is required, and it will be presented in the next paper.

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  • Xinyan CHEN, Noriko TAKIYAMA
    2021 Volume 86 Issue 781 Pages 437-447
    Published: 2021
    Released on J-STAGE: March 30, 2021
    JOURNAL FREE ACCESS

     In traditional wooden buildings, damage often occurs near the joints with cross-section defects during an earthquake. Also, in a wooden frame with large cross-section beam (called Sashigamoi), axial force generated in the beam when the columns inclined. Because the distance between columns geometrically shortened. Due to this axial force, the stress state generated in the column and the frame restoration force were changed, and there is a concern that damage might occur near the joint. Furthermore, in the calculation of critical strength, which is one of the calculation methods currently used to evaluate the seismic performance of traditional wooden houses, the restoring force characteristics are given to each seismic element without considering the different joint shapes or material property, and the restoring force characteristics of entire building is estimated by simply adding those shear forces. Seismic performance of the building may be overestimated or underestimated.

     Based on the above, the purpose of this paper is to quantify the variation of axial force and restoring force of the Sashigamoi, which were caused by the different joint shape of the column-Sashigamoi joint and the proportion of the frame. According to the data analysis of the full-scale frame experiment and the elemental experiment of joint, we conducted a series of studies such as the construction of the analysis model, and the proposal of the M-θ relation estimation formula considering the axial force of the Sashigamoi.

     The findings obtained are summarized below.

     (a) Based on the experiment and analysis results of the full-scale frame in the previous research, we compared the M-θ relationship occurred in joints with the same joint shape. It was confirmed that the proportion of the entire frame caused a big variation in the restoring force characteristics of the joint. It was shown that the existing method might not estimate the restoring force characteristics accurately. In addition, the relation between the inter-story deformation angle of the frame and the axial force fluctuation that occurs in the Sashigamoi is shown by an approximate expression.

     (b) Static bending experiment was carried out on eight elemental specimens with different proportions and grades as parameters, the axial force fluctuation of the Sashigamoi and variations in the M-θ relationship were confirmed. Even if the joint shape were same, the factors that affect the restoring force characteristics could change when the parameters of the specimen changed.

     (c) Based on past research, we proposed a formula for estimating the restoring force with consideration of the axial force of each Sashigamoi joint in this paper. We also constructed a simple model using the beam-column elements to simulate the experiment.

     (d) The relationship between the axial force of the Sashigamoi and the bending moment at both ends of the Sashigamoi was derived from each of the experimental results, estimation formulas, and analysis results. According to the comparation with the design value, it was shown that the experimental value was about 50% of the design value when the interlayer deformation angle was 1 / 30rad in some joint.

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  • Masahide MURAKAMI, Tomoki OYAKE, Ryuki ODANI
    2021 Volume 86 Issue 781 Pages 449-456
    Published: 2021
    Released on J-STAGE: March 30, 2021
    JOURNAL FREE ACCESS

     The formula for calculating the maximum bearing capacity of sheathed shear walls is derived assuming that the yield strength of the nails determines their maximum bearing capacity. When sheathed shear walls have high bearing capacity, the maximum bearing capacity may be often determined by shear buckling or shear failure of sheets. The formula to calculate the critical shear buckling stress of sheathed shear walls with nailing along all edges of sheets by using regression analysis based from the calculation chart has been already proposed by one of the authors.

     It is danger when sheathed walls with high bearing capacity which are not satisfied with the specification of nail arrangement of shear walls are structurally designed, because there is no formula to predict the critical shear buckling stress of sheets which are nailed along two parallel edges or three edges for e.g. hanging walls, spandrel walls, inner walls, and floors.

     The formula for the shear buckling of walls whose all edges are not nailed was made, and its validity was confirmed by experiments in this paper.

     In the past studies, since there is only a calculation chart for the theoretical values of pined support along all edges, the formula for critical shear buckling stress of sheets with pined support along two parallel edges was derived by regression using the results of FEM eigenvalue analysis as the correct values. Regarding the shear buckling of pined support along all edges of sheets, the error between the FEM eigenvalue analysis results and the values obtained by the calculation chart are about 20%. Therefore, the FEM eigenvalue analysis results were used as the correct values when the formula of the critical shear buckling stress with pined support along all edges was derived by regression.

     When only one edge of sheets is not nailed, the theoretical value of the critical shear buckling stress can be estimated by the model for two parallel edges. Because the critical shear buckling stress for walls with only one free edge is much closer to that with pined support along two parallel edges than that with pined support along all edges.

     In the experiments, split failure along nailing on frames and shear failure of sheets were often observed at the shear stress much lower than the critical shear buckling stress calculated with the size of sheets divided by stiffing members. The current study empirically confirmed that the critical shear buckling stress of sheets with stiffing members which is influenced by split failure is twice higher than that without stiffing members.

     At present, it is not possible to estimate the strength of split failure of wood, so the specification of minimum nail spacing must be satisfied.

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  • Effect of joints performance on in-plane strength and stiffness
    Kento SUZUKI, Yasunobu NODA, Hirofumi IDO, Seiichiro UKYO, Ken-ichi SU ...
    2021 Volume 86 Issue 781 Pages 457-467
    Published: 2021
    Released on J-STAGE: March 30, 2021
    JOURNAL FREE ACCESS

     Diaphragm need to have high in-plane strength and stiffness of shear walls to perform in structure. However, it is difficult to regard timber diaphragm as rigid due to characteristics of timber structures. Considering this background, there are a lot of studies about in-plane performance for timber diaphragm. However, few studies have focused on the in-plane performance of CLT diaphragm, which has become popular in recent years. There are generally two types of CLT diaphragm. One is the diaphragm sheathed with CLT panels on floor frame. The other is the diaphragm constructed by only CLT panels jointed without floor frame. There are some data about the former diaphragm; some studies showed the in-plane performance obtained by experiments and analysis. On the other hand, the study about the latter is not found. Thus, it is necessary to clear in-plane performance of the CLT diaphragm without floor frame. In the present study, we discussed about in-plane performance of the CLT diaphragm without floor frame, modeling method to predict in-plane performance and the effect of joints performance on the in-plane performance.

     Chapter 2 showed the experimental outline and the results about the lateral loading test of the full scale CLT diaphragm to clear in-plane performance. It is shown that in-plane performance of CLT diaphragm is higher than timber diaphragm nailed thick plywood considered to have high performance. The effect of the shear behavior on the rotational behavior was observed at the boundary position of each CLT panel.

     Chapter 3 showed the experimental outlines and the results about the joint tests to get their seismic performance of joints were used on CLT floor. In this chapter, it was focused on the shear performance of spline joint, the tensile performance of metal plate, in particular metal joint STF (χ mark), and the compression performance of CLT-to-CLT.

     In Chapter 4, mechanical model based on mechanism to resist lateral load of CLT diaphragm was proposed. The model was validated as a predictor of in-plane performance and local behavior.

     Finally, in Chapter 5, the effect of the structural performance of joints on the in-plane performance of CLT diaphragm was discussed by parametric study. The shear performance of joint (Asp), the tensile performance of metal joint (Amp) and the pitch of shear joint (Ap) were dealt as parameter in the study. On the whole, the higher Asp and the lower Ap were, the higher in-plane performance was. Focus on the effect Amp. The influence was small even though Amp was higher, in case of shear yield occurring. On the other hand, in case of bending yield occurring, the influence was big. In particular, the influence of Amp on yield force was big. If tensile performance of metal plate was short, yield force of diaphragm decreased and the effect of Asp became less. Therefore, the importance of tensile performance of metal plate was shown. In addition, focus on the stiffness, specification of joint to regard CLT diaphragm as almost rigid was shown. The specification can be obtained by comparing the torsional stiffness with KθUL derived from specification of joint of CLT diaphragm.

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  • Hisamitsu KAJIKAWA, Shota HIRAGA
    2021 Volume 86 Issue 781 Pages 469-479
    Published: 2021
    Released on J-STAGE: March 30, 2021
    JOURNAL FREE ACCESS

     In recent years, the construction of medium- to large-scale buildings with timber structures is being promoted enthusiastically around the world from the perspective of global environment issues. However, in terms of the structure, as the scale of the building increases, the stress on the joints also increases, presenting the need for joints with high strength and rigidity. This issue has long been a concern in the field of timber structures. Based on these circumstances, the authors decided to focus on glued-in rod joint. Currently, since a formula to calculate the pull-out strength of glued-in rod has not been established, experiments are required to determine the pull-out strength and pull-out rigidity before actual use.

     This paper contains the following research objectives. A formula to calculate the pull-out strength is proposed by improving the formula of Johansson, Gustafsson, et al. to model a glued-in rod with an adhesive layer that has a round thickness using the Volkersen model. Furthermore, the pull-out strength is clarified through pull-out test of the glued-in rod joint with embedment length (25mm~800mm), base material cross section, adhesive type, and rod diameter as the parameters, in order to verify the results against the proposed formula to shed light on its applicability. In addition, the properties of the impact that each parameter in the proposed formula has on pull-out strength are clarified.

     The insights that became clear through pull-out test of glued-in rod joint and verification of the proposed formula for calculating pull-out strength are as follows. A calculation formula for pull-out strength was derived by devising a model for glued-in rod inserted with an adhesive layer that has a round thickness using the Volkersen model. The relationship between pull-out strength, the average shear stress at the wood boundary per unit of adhesion area when under maximum proof stress, and embedment length was clarified through pull-out test of the glued-in rod joint. By comparing the values from the experiment with the pull-out strength from the proposal formula, it was confirmed that the proposal formula can be recreated with good precision. Its applicability was proven. The parameters for the formula were studied to clarify how each variable in the formula affect pull-out strength and the average shear stress at the wood boundary per unit of adhesion area when under maximum proof stress. To be specific, the smaller the modulus of rigidity of the adhesive layer, the greater the pull-out strength, and the deeper the embedment length, the more significant the impact.

     Future tasks include the proposal of a formula to calculate pull-out rigidity in addition to pull-out strength and verification of the input values when using the calculation for design.

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  • Yizhe WANG, Noriyuki TAKAHASHI
    2021 Volume 86 Issue 781 Pages 481-489
    Published: 2021
    Released on J-STAGE: March 30, 2021
    JOURNAL FREE ACCESS

     In evaluating the reparability of reinforced concrete building structures, it is very important to properly evaluate the crack amount (crack width, crack length). However, in actual seismic design, it is general to evaluate that the proof stress of the building structure exceeds the specified external force. Even if the seismic response is evaluated during the seismic design, seismic crack width control is not in an explicit form. In recent years, research has been continued toward acquisition of a database of damage amount of RC structural members that contributes to reparability evaluation. However, the measurement crack width has been classified according to the traditional damage level classification criteria because of the labor required to measure the total amount of cracks in experimental filed and the enormous amount of data to be collected. Therefore, in this study, we constructed a high-precision damage amount measurement system using an image processing and morphological operations, and we verified whether or not the number of cracks could be measured in detail for RC wall.

     Firstly, image process was performed to extract crack area from RC wall damage image, then it was utilized that the morphological operations proposed in this paper to calculate crack width distribution characteristics which was defined as the ratio of crack length with each crack width class to the total crack length. The morphological operations for damage measurement was divided into two parts; normal measurement and special measurement. Normal measurement was designed for calculating crack width which was at smooth crack contour as edge pixels. And the special measurement was designed for calculating crack width which was at corner of crack contour. Based on the crack width obtained from normal measurement and special measurement, linear interpolation to acquire crack width distribution was performed. Through the above-mentioned process, crack width distribution characteristics were available.

     Secondly, the crack width distribution characteristics was compared between RC wall and RC beam. The variance of the lognormal distribution simulating the crack width distribution characteristics of RC walls was smaller than that of RC beam members. It was implied that it was limited to one or two cracks that widen in RC beams, whereas more cracks were similarly widen in RC wall.

     Finally, verifying the image processing measurement method, the reason why the maximum crack width by image processing measurement method did not match to the visual measurement by human power was discussed. One reason was the difficulty of binarization threshold setting due to ambiguity of crack area boundary. Second reason was the counting the corner of crack. If the corner was accurately considered, the crack width becomes locally thick, but the locally thick portion is not recorded as the crack width by visual measurement. However, if the precise crack distribution characteristics are acquired, it is only necessary to delete the local crack width that is practically unnecessary. It is considered that the validity can be secured much more than fabrication of unmeasured data.

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  • Koji HIROISHI, Takanori ISHIDA, Ryota MASEKI, Hiroyuki NARIHARA, Satos ...
    2021 Volume 86 Issue 781 Pages 491-500
    Published: 2021
    Released on J-STAGE: March 30, 2021
    JOURNAL FREE ACCESS

     Many Low and Middle-rise steel moment frames are verified for seismic safety by horizontal load capacity calculation with push-over analysis assuming one-directional force. In this case, it is a general rule to design the column's strength to be sufficiently larger than that of the beam or panel so that an overall sway mechanism in which the beams or panels yield prior to the columns is formed. However, under bi-directional input, the column strength decreases compared to the one-directional input because of bi-axial bending moment and additional axial force by over turning moment, and it becomes easy to form the weak column mechanism. When the weak column mechanism is formed, there is concern about the strength deterioration of column due to local buckling and the accompanying excessive story drift.

     When evaluating the effects of horizontal bi-directional input, it is useful to conduct seismic response analysis using a three-dimensional frame model that considers the effects of biaxial bending and varying axial forces of columns. In this case, two-component simultaneous input with different phases or 45° uni-directional input is assumed as the input wave, but it is not sufficiently clear how different the responses are under each assumption.

     In this paper, in order to grasp the effects of input direction for Low and Middle-rise steel moment frames, seismic response analyses with three-dimensional frame model that can evaluate the effect of varying axial forces and the strength deterioration of column under uni-directional input on the structural plane, 45° uni-directional input and two-component simultaneous input are conducted. The difference of the collapse mechanism and the story drift depending on the input direction is studied under various conditions with the strength ratio of columns to beams and panels and width-thickness ratio of columns as parameters.

     From the analytical results, the following knowledge was obtained.

     1) The column damage and the maximum story drift angle are likely to be the largest in the case of 45° uni-directional input as compared with the uni-directional input on the structural plane and two-component simultaneous input. This tendency is particularly remarkable under conditions where the plastic deformation of the column is likely to proceed, such as when the external force level is large, the column strength ratio γ is small, or the column width-thickness ratio is large. In addition, at a response level where the plastic deformation is so small that the column does not deteriorate, there is no significant difference in column damage and story drift between 45° uni-direction input and two-component simultaneous input.

     2) For the frame targeted in this paper, by setting the column strength ratio γ to 1.5 or more, or γ to 1.25 and the column width-thickness ratio to 22 or less, week column mechanism and deterioration of column can be avoided under Lv. 2 earthquake motions (the maximum earthquake motions to be considered by Building Standards Law of Japan). On the other hand, in a frame with a column strength ratio γ = 1.0 and a column width-thickness ratio of 29 or more, there is a high possibility that the columns deteriorate at Lv. 2 input and a story drift angle of 1/20 rad or more occurs under Lv. 3 earthquake motions (1.5 times Lv. 2).

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  • Sachi FURUKAWA, Naoki TAMURA, Yoshihiro KIMURA
    2021 Volume 86 Issue 781 Pages 501-511
    Published: 2021
    Released on J-STAGE: March 30, 2021
    JOURNAL FREE ACCESS

     According to current design practices of steel moment-resisting frames, formation of plastic hinges is unavoidable when the frames are supported by conventional column base systems, i.e., exposed-type and embedded-type column base systems, due to unequalized flexural moment demand on the top and base of the first story columns [1]. Kimura et.al [3] has proposed mid-story pin column base system to avoid columns from yielding and to realize formation of beam-yielding mechanism by applying pin connection between the upper steel column and the bottom RC column at the midpoints of the first story. Previous analytical study [3~7] indicated that the frames with the proposed column base system exhibits superior seismic behavior than those with conventional base column systems, mitigating probability of column yielding. However, it is also revealed the difficulty to realize beam yielding mechanism for frames with commonly adopted column-beam strength ratio of 1.4-1.8. Dual structural system is the system that the main structural frame resisting lateral force is backed up by secondary structural system. Previous studies [8~15] shows secondary structural systems, such as a force-demand spreading column [12] and rocking wall [14], sufficiently contribute to redistribution of the inelastic demand over the height of the frames.

     In this paper, mechanical characteristics is examined about a steel moment-resisting frame with mid-story pin column base system upgraded by implementation of continuous column over the height of the frame. The continuous column is named as multi-layered leaning column (M. L. column), hereinafter. A theoretical formulation based on equilibrium equations between dual structural system (the main frame and M. L. column) is presented, in which those of the main frame is formulated by the previously presented modified D-value method [16]. Nonlinear static and time-history analysis is implemented to validate the theoretical observations on the effect of M. L. column on the mechanical characteristics of the main frame (story drift concentration and flexural demand on structural components) and quantify the required flexural stiffness and strength of the M. L. column. Additional theoretical method is also presented to characterize the significant effect of high-order mode responses on flexural demand on the M.L. column based on modal decomposition method.

     Static analysis of three-, six-, nine-story frame validates the theoretical formulation to sufficiently predict mechanical behavior of the frame with M. L. column. The flexural stiffness ratio of M. L. column η is presented, where it is indicated that almost no advantage can be obtained with the M. L. column of η < 0.03, while little further improvement can be expected with the M. L. column of η > 3.3. With the M.L. column of η = 0.33, about the half of the mitigation effect provided by a fully rigid M.L. column (η = 3.3) can be expected. Seismic time-history analysis shows that the maximum story drift concentration rate and flexural demands on the column of the main frame during earthquake excitation are well-predicted by the theoretical formulation with an external force regarding to Ai distribution, while the maximum flexural moment of the M.L. column exceeds the predicted value by 2.0 times. Theoretical formulation with proposed external force considering secondary mode response enhanced by seismic excitation successfully predicts the maximum flexural demand of the columns simulated by dynamic analysis of three to nine-stories frame with the M. L. column of η = 0.03 to 3.3.

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  • Takayuki KIKUCHI, Takeo HIRASHIMA
    2021 Volume 86 Issue 781 Pages 513-523
    Published: 2021
    Released on J-STAGE: March 30, 2021
    JOURNAL FREE ACCESS

     Regarding the load-bearing capacity of timber elements subjected to fire heating, knowledge of not only the charring behavior but also the mechanical properties at elevated temperature are required because the temperature of the non-charring area gradually increases during the cooling decay phases in fire. Therefore, in order to predict the fire resistance of timber elements, it is necessary to grasp the changes in strength and elastic modulus of the timber materials with temperature rise.

     In this study, elevated temperature compression tests of structural glulam timbers made of Japanese cedar and larch were carried out for the purpose of understanding the influence of moisture in the timber on the compressive behavior at elevated temperature. The tests parameters were tree species, furnace temperature condition below 200 °C, and heating time. Influences of moisture in the specimens on the compressive behavior were discussed from the test results on the relationships of heating time and weight changing. Another purpose was to obtain a numerical model of stress- strain curves at elevated temperature to analysis the fire resistance of timber elements.

     Main findings of this study were summarized as follows:

     (1) Compressive strength at elevated temperature decreased significantly from the start of heating to 1 hour, and became the minimum during 1 to 2 hours. After that, the strength recovered with drying, and finally, it returned to the strength at ambient temperature.

     (2) The reason why the compressive strength decreased significantly from the start of heating up to 1 hour was that the steam softening and the change of water content due to migration of the moisture had a great influence12).

     (3) Compressive strength of both Japanese cedar and larch decreased significantly when the internal temperature of the timber increased from ambient temperature to 70°C, and the lower values of the results up to around 100°C were close to the strength ratio of Eurocode5.

     (4) The modulus of elasticity at elevated temperature decreased significantly from the start of heating to 1 hour, and became the minimum during 1 to 2 hours, similar to change of the compressive strength.

     (5) Results of the load-displacement relationships indicated that the decrease of the rigidity and the maximum load in the initial stage of heating depended on the temperature rising rate.

     (6) The stress-strain curve for compression within 1% strain was approximated by Richard’s equation.

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