Finishing materials bonded to the wet slab peel off at high probability. We are researching in order to propose the moisture management index of slab surface. We are continuing to research the relationship between the joint tenting of the floor covering and moisture content of the slab. As a result of our series of research, It was revealed that the moisture vapor emission corresponds well with the coefficient of thermal expansion of adherend. In other words, it shown that it is not the moisture content in the slab but the moisture vapor emission from slab that directly affects for joint tenting. However, there are few studies focusing on the moisture vapor emission. In order to accumulate knowledge, we examined the influence of finishing conditions and curing conditions on the moisture vapor emission. Also we examined the relationship between the coefficient of thermal expansion of adherend and moisture vapor emission.

 We made some specimens that are different finishing conditions and curing conditions (reference Fig. 2). Specifically, one type of concrete used on site (reference Table 1), three finishing conditions (reference Table 2), and three curing conditions (reference Table 3).

 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. Then 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

 As a result, it was found that the curing conditions greatly affect the moisture vapor emission. Also It was found that even when the moisture meter readings were same, the moisture vapor emission was smaller in the specimens that had been cured. (reference Fig. 4, 5, 6, 7, 8)

 Finally, the relationship between the coefficient of thermal expansion of adherend of the floor covering, the moisture vapor emission and the moisture meter reading was examined. As a result, it was reconfirmed that it is appropriate to control the moisture content during construction floor covering with moisture vapor emission because the moisture vapor emission has a good correspondence with the coefficient of thermal expansion of adherend. (reference Fig. 9, 10)

 The 2018 Hokkaido eastern Iburi earthquake (M_J6.7, focal depth of 37km) caused large ground motions in the near fault region. Many studies on source, path and site effects on the strong motions have been done, but studies on broadband vertical motions have not been done except for the nonlinear site responses. Since not only horizontal motions but also vertical motions are needed as input motions to super high-rise buildings, studies on vertical motions are also important. In Satoh (2019), we estimated the broadband source model of the main shock by the empirical Green’s function method using horizontal records of the aftershock with Mw5.4 as an element event. In this paper we improve the broadband source model by adding an element event occurring after the study by Satoh (2019) for the northern strong motion generation area (SMGA3). Using the improved broadband source model, the horizontal and vertical strong motions are simulated by the empirical Green’s function method.

 Firstly, we examine the attenuation of peak ground velocities PGVs of horizontal and vertical components of the main shock and the element event with Mw5.4. The PGVs of both events in the near-fault region agree with the ground motion prediction equation for intraslab earthquakes in the Pacific plate. On the other hand, the PGVs of crustal earthquake with the same Mw5.4 occurring 50 km away from the element event are 1/2 to 1/3 of those of the element event. We show the difference of two Mw5.4 events are explained by the difference of the short period spectral level A by the spectral inversion.

 The improved broadband source model simulates records better than Satoh (2019), since the added element event is relevant as the Green’s function which can reproduce waveforms of the main shock including later parts caused by the 3D subsurface structure. By the improved broadband source model, we show that the strong motion generation area SMGA2 with the stress drop of 69 MPa located at depths 21-25 km in the southern region of the fault is the main cause of large ground motions of most stations in the near fault region. The SMGA2 is located at shallower parts of large slip area estimated by long-period waveform inversions by previous studies. The SMGA3 in the northern region with the stress drop of 27 MPa located at about 2 km shallower to SMGA2 generates the same level strong motions with SMGA2 at only northern stations but contributes to later parts of the other stations. Although the depths of SMGA2 and SMGA3 are about twice of the average of crustal earthquakes, the stress drop of SMGA2 is 3.8 times of the average of crustal earthquakes. The total A of SMGAs is the same level to the depth dependent M0-A relation for intraslab earthquakes and 2.8 times of the average of crustal earthquakes in the case of Mw6.8. This result verifies the conclusion by Satoh (2019) that the large A close to intraslab earthquakes is one of causes of large ground motions. Finally, we show that the empirical Green’s function method for far-field S-waves is applicable to predict vertical motions of S-waves as well as horizontal motions by the simulations of ground motions observed at 222 strong motion stations in the hypocentral distance less than 200 km.

 In this study, we constructed a characterized fault model for the main shock of the 2016 Kumamoto earthquake based on the fault models used in previous studies, and the model was found to simulate the strong motion records around the seismic fault well. After estimating the contribution of the SMGA and LMGA at the observation points adjacent to the seismic faults, the effect of the difference in the top depth of the SMGA on the ground motion adjacent to the seismic faults was investigated. Finally, the effects of shallow and deep parts of fault ruptures on the near-fault ground motions were investigated using a simple seismic fault model. The conclusions of this study can be summarized as follows:

 1) By referring to Ozawa et al. (2016) and Yoshida et al. (2017), a characterized fault model that was consistent with surface ruptures was constructed. The characterized fault model consisted of three regions, the SMGA, LMGA, and background region, and its arrangement was estimated by forward modeling with reference to the fault models used in the earlier studies. As a result, one or two SMGAs were determined for each segment. LMGAs were set up to be continuous with SMGAs in the fault dip direction except for LMGA2 located between the Mashiki Town and Nishihara Village.

 2) The pulse-like ground motion with a period of around 1 s in KMMH16 made a large contribution owing to the upward rupture directivity effect. The accuracy of the simulation of KMM006 was improved by estimating multiple SMGAs lying directly under the Mashiki Town and dividing the contribution to the velocity pulses. The long-period velocity pulse at the Site 93048 was also affected by the Idenokuchi fault and the shallow part of the Futagawa fault, as has already been presented in Kido et al. (2019). However, the contribution of the SMGA to the synthetized results was found to greater than that of the LMGA not only for short-period components but also for long-period components.

 3) A sensitivity analysis was performed for the Site 93048 based on varying the width of the LMGA (W_LMGA). As W_LMGA became larger, the long-period EW component of theoretical ground motion at the Site 93048 became smaller and was underestimated compared with the observation record. Differences in the upper-edge depth of the SMGA affected evaluation of both the short-period and long-period components of the ground motion.

 4) The effects of the shallow and deep parts of the fault ruptures on the ground motion adjacent to the seismic fault were investigated using a vertical right strike-slip fault model with surface rupture. As W_LMGA became larger, the velocity response value adjacent to the seismic faults by SMGA became smaller in the broadband frequency range. The calculated ground motions in the vicinity of the fault also strongly depended on the rise time of the shallow slip velocity time function. When the rise time was short and the peak slip velocity was large, significant, large ground motions were generated in the LMGA alone.

 5) When the seismic fault approached near the ground surface, the ground motions evaluated using the full method, i.e., considering both the shallow and deep parts of soil the structure were sometimes different from those obtained using the substructure method, in which the site amplification of the shallow part of the soil structure was separately evaluated.

 In the 2011 Great East Japan Earthquake, cases had been reported in which gymnasiums did not satisfy this function as refuge bases owing to fallen ceilings and lightings. Therefore, measures to prevent ceilings from falling must be considered; in order to achieve that, it is necessary, first, to understand the collapse mechanisms of the ceilings. Therefore, at the E-Defense shaking table facility in 2014, vibration experiments were conducted on a full-scale gymnasium specimen with suspended ceilings. The experiments were conducted on non-resistant and earthquake-resistant ceilings, and the useful knowledge were obtained on the mechanism of ceiling collapse. In addition, Isobe et al. developed the numerical code that can simulate ceiling collapse phenomena under seismic excitation based on the adaptively shifted integration (ASI)-Gauss technique. However, the code has a problem that reproducibility of the collapsed ceiling area is not enough.

 In this study, accuracy of the numerical code was improved by introducing the eccentricity of hanger into the suspended ceiling model and improving detachment conditions of joint metal. In addition, the seismic excitation experiment of the gymnasium with suspended ceilings was reproduced using the code in order to validate the numerical model. Furthermore, the ceiling collapse mechanism of suspended ceilings was discussed in more detail from the numerical results.

 According to the numerical results, the acceleration and displacement response of the numerical model agreed well with the experimental results. Furthermore, the ceilings collapsed near the roof top as in the experiment. That is, the ceiling collapse phenomena were simulated with higher accuracy by improving the numerical model and detachment conditions. In addition, the ceiling collapse mechanism, which had not been obtained by the experiments, was revealed through the numerical examination. Additional forces exerted on the joint metals due to the buckling of suspended bolts and the vertical vibration of the ceilings caused by the eccentricity of hanger. As a result, the ceilings were damaged intensively near the roof top.

 Recently, the business continuity plan (BCP) is becoming a leading subject in the world and is being discussed with great concern in the construction and operating process of various built environments. In response to BCP, the structural health monitoring (SHM) has drawn much attention for evaluating the status of buildings and reducing post-earthquake impacts on our society. In developing SHM, the system identification (SI) methodologies, categorized as methods for inverse problems, play a critical role and the modal SI and physical SI are two major well-known branches. The physical SI has the advantage that the stiffness and/or damping coefficients of the structural model can be recovered directly and is well suited to the design of passive control systems. This is also quite useful for the damage detection. Although the physical SI is preferred in SHM, its development is quite limited and slow due to the strict requirement on multiple measurements or the necessity of complicated mathematical manipulation. In particular, investigation on physical SI of three-dimensional (3D) building structures with stiffness or mass eccentricities are more limited.

 This paper proposes a new method of frequency-domain physical-parameter system identification of three-dimensional building structures with stiffness eccentricity, which accompany torsional vibration. The two-directional story stiffnesses in the 3D building structure are identified from the horizontal accelerations recoded at the top and first floors. The proposed method has three processes. In the first process, equations of motion in the time domain are transformed into the frequency domain. The theoretical equations to identify the j-th two-directional story stiffnesses are derived from the dynamic equilibrium of the free body above the j-th story. In the second process, the responses on non-observation floors are evaluated from the horizontal accelerations recoded at the top and first floors with low-order modal shapes. In the last process, all responses are applied to the theoretical equations and the two-directional story stiffnesses are evaluated from the identification result near low-order natural frequency. Compared to the previous approaches, the proposed method has some features and advantages, which are as follows.

 ・ The proposed method is based on Fourier analysis method and avoids complicated mathematical manipulation.

 ・ The two-directional story stiffnesses in the 3D building structure can be identified from the horizontal accelerations recorded at the top and first floors of the building.

 ・ The data with high S/N ratio, which is selected based on low-order modal information, is used for the identification and this makes the proposed method robust for noise.

 ・ The two-directional story stiffnesses for each story can be identified independently. The identification result of one story doesn’t affect those of other stories.

 The proposed method is demonstrated through numerical simulations and scaled experiments. Numerical examples, including the comparison with the numerical simulation results, demonstrated that the proposed method is reliable and possesses an acceptable accuracy. It should be remarked that identification results of story stiffnesses are quite stable near the low-order natural frequency and are robust for noise. However, it should be noted that the accuracy of low-order modal shapes used for the identification highly affect that of identification results. In experiments using scaled models, although the dependences to amplitude and input direction of ground motion were slightly confirmed, the reliability and accuracy of the proposed identification method were made clear.

 In the current Japanese design code of pile foundations, the buckling behavior of pile member is not taken into account. This is because the surrounding ground restrains buckling of the pile member. However, when the ground liquefies, the stiffening force for horizontal deformation of the pile weakens. Therefore, when slender pile is subjected to high axial compression forces as a result of increased vertical loads by overturning moment of superstructure under the strong earthquake, flexural buckling may occur in pile member in soft ground. The buckling behavior of steel pile in liquefied ground has been studied previously. This study investigated the dynamic buckling behavior of reinforced concrete (RC) pile using a centrifuge model.

 This paper investigated the dynamic buckling behavior of reinforced concrete (RC) pile using a centrifuge model. Three specimens with soil densities and input waves as variables were tested by uni-axial shaking. Buckling failure occurred in the pile members of all centrifugal models after the ground were liquefied. All pile members formed three plastic hinges at the pile head, lower side, and middle position. The measured buckling strength of the centrifuge RC pile model was evaluated by extending the tangent modulus theory. In the shaking table test under a 40 G field, the specimen used RC pile models, saturated soil (Toyoura sand) with a relative density of 30%, footing and a superstructure model with a natural period of 0.027 sec (prototype scale: 1.10 sec). Shakings were two Sweep wave (maximum acceleration: 4.19 m/s², 4.44 m/s²) and one Rinkai wave (maximum acceleration: 7.36 m/s²). The lateral displacement of the pile foundation was fully restrained so that the only the vertical load (the sum of the sustained load of the superstructure and the temporary load by overturning moment) acted on the piles.

 Buckling failure occurred in the pile members of the centrifugal model after the ground was liquefied. After the pile buckled, the footing sank, and the seismic response of the superstructure decreased. The measured buckling strength of the centrifuge RC pile model was evaluated by extending the tangent modulus theory (Engesser and Schanley). Since concrete (mortar) is a non-linear material, the tangential stiffness changes according to the acting axial force. Also, even if the ground liquefies, the stiffening force for horizontal deformation of the pile members does not become zero. Therefore, in order to evaluate the buckling strength of RC pile members in liquefied ground, it is necessary to consider the influence of the non-linearity of concrete and the decrease in the stiffening force of the surrounding ground.

 This paper presents a new hysteresis model, consisting of the differential equations, that is capable of generating various hysteresis loops. Its hysteresis model is expanded using the author’s hysteresis model to capture the pinching phenomena and degrading stiffness due to the cyclic loading. The force and displacement relationships for structures against major earthquakes, which exceed the design basis ground motion, would be nonlinear characteristics with hysteresis loops. In order to accurately verify the seismic response of structures, a hysteresis model that can generate hysteresis loops close to actual phenomena is necessary because the seismic response of structures to be assessed depends on the hysteresis characteristics. The seismic fragility assessment has been performed as one approach to clarify the seismic performance and is assessed through the seismic response against the major earthquakes exceeded the design basis ground motion. However, the hysteresis laws and the programing code to implement the seismic response analysis result in complexity according as increasing the response deformation for the structures. They will lead to difficulty for the seismic response assessment considered of ultimate behavior for the structures.

 The author’s proposed the hysteresis model which can reflect any skeleton curve functions, as the differential equation type. Although this model can generate the various hysteresis loops, it cannot model a hysteresis loops with the pinching phenomena and degrading stiffness. To overcome these problems, this paper describes the coefficients to capture the hysteresis loops with the pinching phenomenon and the degrading stiffness using the author’s hysteresis model. The most significant feature of this model is that it can generate the hysteresis loops without the hysteresis rules even in the hysteresis loops with pinching phenomena. The extended author’s model was verified by comparing of tests and analytical results.

 This paper is divided into three main groups. The first is to describe the basic author’s hysteresis model, which is without the pinching phenomena. The second is to propose the coefficient to control the hysteresis loops. The third is to demonstrate the applicability of hysteresis model into the SC structure and the RC structures by comparing of test and analytical data. The primary results are summarized as follows:

 The extended hysteresis model can:

 1) Express the hysteresis loops with the pinching phenomenon and the degrading stiffness by multiplying the proposed coefficient, h, by the force, F, of the hysteresis loops having arbitrary skeleton curves, which includes the non-point symmetry of the skeleton curves.

 2) Capture the hysteresis loops due to the cyclic loading using the coefficient, h, of the cumulative energy type.

 3) Accurately represent the measured hysteresis loops and the cumulative energy by defining the skeleton curve functions which are combined with the different functions according as the measured hysteresis loops even when the measured hysteresis loops have the discontinuous skeleton curves.

 The range of use of timber has expanded rapidly in recent years, and it is expected that the timber structures will become larger and taller in the future. As the scale increases, it is possible to apply a composite or hybrid structures which combines other material such as steel. It is difficult to accurately predict the burden stress of changing wood from moment to moment, and the evaluation of viscoelasticity of wood is indispensable. Based on these backgrounds, we have studied the purpose of clearly positioning viscoelasticity of wood in the rheology field.

 In this paper, we examined a method for obtaining the relaxation spectrum from static test conditions, which are a common problem in the rheology field. The method studied is not based on the current approximate solution, but based on the Fourier transform. To adopt this method, it is necessary to solve the ill-posed problem in numerical computation. We showed that it can be solved by adding three ideas; noise rejection, ensuring continuity and adding calculation assistance. These ideas are due to numerical problems associated with the discrete Fourier transform, and the optimal method for calculating the relaxation spectrum is shown in this paper. The study began with a numerical experiment using a simple Gaussian function, and then verified the applicability to a complex relaxation spectrum combining multiple Gaussian functions.

 In addition, we assumed that there is significant data only in a limited calculation range of about 3 months as experimental data that can be actually obtained, and we also examined the calculation method. It was confirmed that the required calculation accuracy was ensured by numerical tests that assumed experimental data contained measurement noise. In the case of limited data containing such noise, the conventional approximate solution method significantly decreases the calculation accuracy. On the other hand, it was confirmed that the calculation method based on the Fourier transform shown in this paper can obtain appropriate calculation results regardless of the presence or absence of noise.

 In recent years, utilization of timber-based materials for low-rise non-residential buildings has been actively promoted for environmental considerations, advances in timber design, and the development and support of new laws. However, compared with other structural materials, it is difficult to secure the rigidity and strength of joints in timber-based structures, so additional seismic elements such as shear walls and braces are typically required. Therefore, in this study, a moment frame without the need for such seismic elements was developed. The proposed frame is a hybrid structure that uses steel for the columns and wood materials for the beams, whilst ensuring good overall toughness. A timber-steel hybrid joint (where the timber and H-shaped steel are connected by lag screws and a steel dog bone) is used. The dog bone at the ends of the beam bends at an early stage to avoid damage to the timber. This is expected to improve seismic energy absorption performance comparable to that of a steel rigid joint at the beam ends.

 The fracture behavior and mechanical properties were verified through cyclic bending tests of 1:2 scale partial specimens of the proposed joint. Subsequently, equations for evaluating the rotational stiffness and strength of the joint were proposed. The results of the experiment were reproduced using the obtained values from the equations. Finally, detailed example of a timber-steel frame model and a steel frame model were designed by using the joint rotational stiffness obtained from the experiments. Nonlinear response history analysis was undertaken based on the Ai distribution and artificially generated seismic waves (BCJ-L1 and L2). The seismic performance comparison of the two models was performed using time-history analysis, and the feasibility of the timber-steel hybrid structure building was verified.

 The following shows the findings and results obtained in this study:

 1) In the testing of the proposed timber-steel hybrid beam-to-column joint specimens, the dog bones yielded before the laminated timber joint in all tests, and a stable elasto-plastic bending moment-rotation angle relationship was obtained. While, it was confirmed that slip failure may occur depending on the lap length and the presence or absence of wedges.

 2) The proposed equations for evaluating the rotational stiffness of bonded timber joints and dog bones gives an error of 20% compared to the experimental values. The behavior of the non-linear rotating spring-loaded wire rod model with the estimated value of rotational stiffness showed reasonable agreement with the experimental results.

 3) In the test specimen with a wedge and a wrap length, the theoretical maximum strength of the steel lap was higher than the experimental maximum strength of the dog bone. The experimental results showed that the laminated timber was almost intact, and the validity of the yield strength evaluation formula was confirmed.

 4) It was confirmed that the timber-steel frame model can be designed with a smaller floor weight and stiffness in earthquake design than the steel frame model, and the timber-steel frame model could suppress the maximum response inter-story drift angle in the time history response analysis than the steel frame model.

 The purpose of this study is to establish a design method for installing stiffeners on the web. Installing stiffeners on the web as a reinforcement is one of the effective methods to prevent the local buckling of the beam members and to increase the buckling strength. Current design methods for the stiffeners, however, do not reflect its torsional rigidity. Also, the current design methods are established based on the simple assumption (e.g., pure compression, pure bending, or pure shear). In reality, the stress distribution is more complicated because the combined stress acts on the web installed the stiffeners. Therefore, it is necessary to take these effects into account to maximize the stiffening effects.

 In this study, based on the energy method, the effect of installing stiffeners is investigated employing the rigidity ratios of the stiffeners to the web. The subject of this study is the web which is two stiffeners are placed equally on one side for comparison with analytical results with one stiffener. From calculation results, the stiffener size effect on the increase rate of local buckling strength has been confirmed. Also, an evaluation formula for the optimum rigidity ratio γ^*, the width-to-thickness ratio for the web to ensure the full plastic moment M_p, and the elastic local buckling strength of the web installed the stiffeners have been established. Finally, a required width-to-thickness ratio that satisfies these conditions has been derived.

 The following findings have been obtained.

 1) The main factor that determines the elastic buckling strength of the web installed stiffeners subjected to bending moment and shear force is the flexural rigidity ratio γ. The stiffening effect lessens when the area ratio δ and the flexural rigidity ratio γ exceed the proper range. The stiffening effect saturates when the bending moment gradient β and the ratio of the shear force to the bending moment η become large. The stiffening effect decreases with the increment of the torsional rigidity ratio γT/γ. The tendency of the stiffening effect is almost the same as the results installed one stiffener.

 2) An evaluate formula of the optimum flexural ratio for installing two stiffeners on the web has been proposed. The evaluate formula is expressed as a function ηβ which is multiplied the ratio of the shear force to the bending moment η and the bending moment gradient β. The optimum flexural ratio γ^* becomes large when the value ηβ is large.

 3) In each case, the bending yielding and shear yielding, the application range of the web width-to-thickness ratio for satisfying the full plastic moment M_p by installing stiffeners with the optimum flexural rigidity ratio γ^* has been examined. The boundary of the required number of stiffeners for satisfying the full plastic moment is expressed as a function α, the ratio of the shear stress to the bending moment stress.

 4) A design formula for the elastic local buckling strength of the web with the optimum longitudinal stiffeners has been proposed. And in case of the stiffeners have not enough, another solution deriving elastic buckling strength by drawing a graph has been proposed.

 5) A design method for satisfying the optimum flexural rigidity ratio has been proposed. And the satisfying the optimum rigidity can be obtained from the relationship between the width-to-thickness ratio of the stiffeners and the web.

 Although the structural system was slightly damaged, damage to the nonstructural components could lead to the complete or partial closure of buildings. Lessons learned from recent earthquakes indicate that protecting the nonstructural components is very important for structural engineers to realize functional continuity of buildings after earthquakes. Especially from the damage of the 2011 Tohoku earthquake, a number of research has been conducted to investigate the structural behavior and damage mechanisms of ceilings as non-structural components. And based on the research, seismic design procedures were established to avoid the fall of ceilings in order to save human life and to keep functional continuity. On the other hand, a reconnaissance of recent earthquakes reported that light-gauge steel (LGS) stud partition walls were also damaged, and its damage led to the complete or partial closure of buildings. Following the previous research project for ceilings, a number of research on LGS partition wall has to be conducted to reduce the seismic damage to the walls.

 In this research, a systematic experimental program for investigating the structural behavior and damage mechanism of LGS partition walls will be conducted to establish the seismic design procedure. As the first step, element tests of stud-to-track connections were conducted to evaluate the ultimate strength. The main test parameters are the length of track, the clearance between track and stud, the pitch of bolts which connect the track to the reaction jig, and the number and spacing of studs. Here, a clearance of 10mm is employed at the top side of stud for workability on construction site. Power actuated fasteners are widely used for tracks to concrete slab connections, and a distance around 900mm is recommended for a pitch of the fasteners in standard specification of construction work.

 The test results can be summarized as follows:(1) the structural behavior of stud-to-track connection is dominated by the out-of-plane bending of one-side flange plate of track. Therefore, effects of cyclic loadings on ultimate strength are few; (2) the strength is affected by the length of track and inversely proportional to the clearance between track and stud: (3) the total strength of multiple studs is not in proportional to the number of studs because the multiple studs share the effective width for strength evaluation; (4) a strength evaluation model has been established from the test results.

 1. Introduction

 Nowadays, there is a move to legislate the examination the performance of the buildings against long-period ground motion earthquake. Systematic experimental study of CFT columns has been desired for constructing the evaluation method for the strength deterioration behavior because there are many parameters affect the structural performance and strength deterioration of CFT columns. The objective of this study is to discuss the limit cycle of square CFT beam-columns subjected to cyclic lateral load under constant axial load with constant displacement.

 2. Outline of test

 Test parameters are effective length-section depth ratio l_k/D (20, 14, 10, 8), axial force ratio n (0.15, 0.3 0.45, 0.5, 0.6), lateral rotational angle amplitude R₀ (1, 1.25, 1.5, 1.5, 2, 3), width-thickness ratio B/t_f (25, 17), steel tube (BCR295, SA440Mod) and CFT beam-columns or hollow steel tube beam-columns. The loading program is monotonic loading and cyclic loading. The number of test specimens is seven for monotonic loading and twenty three for cyclic loading. The compressive strength of concrete are about 65~81N/mm² for BCR 295 specimens and 81N/mm² ~90N/mm² for SA440Mod specimens.

 3. Test results and discussion

 Lateral load and rotation angle relationships and the tendency of load deterioration were shown. Transition of the ratio of the lateral load at each cycle Q_i to maximum lateral load Q_max were shown as the load deterioration. When the buckling length-depth ratio is 8 and 10, strength of specimens with hollow section declines more than CFT specimens. When the buckling length-depth ratio is 20, strength of hollow section specimens decline more than CFT specimens when the number of cycles is small. Relation between limit cycles and rotation angles are shown and the effects of the test parameters are discussed. Limit cycles N_95%, N_90%, N_85%, N_80% are defined as the number of cycles when the lateral load decline to 95%, 90%, 85%, 80% of the maximum lateral load.

 4. Relation between limit cycles and plasticity ratio

 Relation between limit cycles and plasticity ratio are shown. Regression analysis is carried out and the regression equations are obtained. The accuracy of the equations are discussed by multiple correlation coefficients.

 5. Conclusions

 The conclusions derived from this study are as follows:

 1) As for the cyclic loading, limit cycles of 57 test specimens are shown (Table 7).

 2) The effect of axial force ratio, buckling length-depth ratio, width-thickness ratio of steel tube, yield strength of steel tubes on the relationship between the rotation angle and limit cycles are discussed. The limit cycles become smaller as the axial force ratio increases, and the effect of the axial force ratio becomes larger in case of N_80% compared with the case of N_95%. The limit cycles become larger as the buckling length-depth ratio and the yield strength of steel tube increases or the width-thickness ratio decreases.

 3) Relation between limit cycles and plasticity ratio are shown and the regression equations are obtained by the regression analysis. The value of multiple correlation coefficient in case of N95% is about 0.73, however, in other cases variation are relatively large.