Reduction accompanied by no CO2 emissions to global warming has become an urgent task. CO2 emissions in the cement industry has also become an important issue, is valid expanded use of mixed cement as the method. ground granulated blast furnace slag is free to set the substitution ratio in accordance with the concrete application and conditions are expected as admixture since it is possible widespread use than blast furnace cement. Concrete with ground granulated blast furnace slag is enhanced long-term strength can be expected, there is for initial strength development is slow problem. It is effective to use the specific surface area increases the ground granulated blast furnace slag as its improvement. Currently, ground granulated blast furnace slag is the study of a range of specific surface area as specified in JIS A 6206 has been reported, the development of powder technology, ground granulated blast furnace slag powder having a specific surface area greater than it be so available became. Therefore, targeting a wide range of ground granulated blast furnace slag from a specific surface area of 4000 to 30000 (cm2/g) , and long-term study of strength development the usefulness of concrete combination of specific surface area and the replacement ratio was variously set. Moreover, it was quantitatively clarify the relationship between the conditions and the concrete strength development effect of such specific surface area and degree of substitution ground granulated blast furnace slag. (1) As various factors ground granulated blast furnace slag, substitution rate and specific surface area of the ground granulated blast furnace slag has revealed the effect on the strength. (2) Quantitatively examined the relationship between strength development effects of blast furnace slag concrete, ordinary Portland cement and ground granulated blast furnace slag strength development effect of the strength development effect as blast furnace slag concrete ordinary portland cement revealed.
In order to address global environmental problems, the construction industry has introduced various strategies to save resources and energy, and to reduce the amount of waste produced. Earth materials have many environmental advantages, such as the abundance of resources and minimal contamination during disposal. Earth materials have traditionally been used in Japan, such as for clay walls on bamboo lathing and rammed-earth. These methods are problematic in modern day construction because they require a high degree of skill and many processing steps. This paper proposes the use of non-burnt earth block as the masonry unit for load bearing wall. Since non-burnt earth block does not require large facilities or high energy costs for their construction, they may be widely adopted in various countries around the world, including in developing countries. When non-burnt earth block is used in construction, simple dry solidification of the earth can result in problems with the strength and water resistance. Thus, it is necessary to stabilize the materials to improve their performance. Magnesium oxide is a low alkaline solidification material with minimal environmental burden that may be used to enhance the compressive strength and water resistance of earth block. This study puts its focus on making mechanism that can find the optimum mix proportions of earth block that satisfy the required quality and manufacturing conditions. The details of the experiment are as follows: Experiment 1. These experiments were performed to identify the factors that influence the strength development of MgO. Compressive strength tests and thermal analysis (TG-DTA) were performed on MgO mortar, exploring factors such as different water-MgO ratio and curing conditions. Test results indicate that the hardening mechanism of MgO is due to the formation of magnesium hydroxide, and this phenomenon was most notable at the beginning of the sealed curing. Furthermore, it was found that the compressive strength increases as the water-MgO ratio decreases. Experiment 2. These experiments were performed to confirm which factors influence the production conditions and quality conditions of the earth block stabilized with MgO. From the experimental results, the following things were confirmed: (1) The state of the mixing sample is related to the proportion of fine particles (clay and sand-blended clay passed through 75 μm + MgO) and water. (2) The length change rate can be estimated from the proportion of MgO and water. (3) The compressive strength can be inferred from the water-MgO ratio. Experiment 3. These measurements verified that the relationship confirmed in Experiment 2 can be applied even when using clays sampled from different areas.
In late years, poor grout filling and steel bar corrosion are the major issues of prestressed concrete structures. Hence, a practical use technology to detect these defects are demanded. Particularly, there are many unsolved problems about the nondestructive detection of the steel bar corrosion covered with sheath pipe. The goal of the research is a development of an electrochemical technique which enables to detect these defects from the surface of the prestressed concrete nondestructively. Analyses of multilayer substances utilizing electrochemical frequency response of materials caused by dielectric dispersion are carried out widely in various fields. For example, measurements of frequency response (AC impedance method) of reinforcing rod are mainly performed for corrosion diagnosis in the civil engineering and construction. Dielectric relaxation measurement applied to this research is one of the electrochemical techniques to estimate the internal microstructure of materials by analysis of electric charge behavior which causes polarization. Shape analysis of human body cell using dielectric relaxation technique are well known in the medical fields. The dielectric relaxation indices, such as electric capacitance and conductance relate to the quantity of reaction activated by electric charges. Furthermore, the change rate of indices according to frequency changing reflect increments of the reactions that are activated at each frequency. Large electric polarization will occur in low-frequency range because electric charges can reach the edge of materials and form capacitors. Accordingly, the measurement system behaves like a large capacitance double layer capacitor. In contrast, a direction of electric field changes extremely fast at the high-frequency range and electric sensitivity charges vibrate to positive and negative with small amplitude without being able to shift a long distance. The electric capacity becomes small when the system cannot be greatly polarized. The vibrations of electric sensitivity charges are observed as big conductance because electric charges are always trying to move toward positive or negative at high measurement frequency range. Authors conducted some dielectric relaxation experiments which relate to measurement repeatability, a variety of the electrodes, applied voltage magnitude, and materials configuration of specimens and results were obtained as below. 1. Conductance requires close attention about its repeatability. 2. A variety of the electrodes and applied voltage magnitude have influences on the characteristics of lower frequency behavior of capacitance and conductance. 3. Behaviors of polarization charges reflect the specimen configuration and shape.
In this study, a new method of permanent displacement estimation and simplification of seismic ground motion is developed. In the method, the displacement is extracted from the acceleration record or the velocity record using wavelets. The basic wavelet used in this study is expressed as a product of the Gaussian function and the complex exponential function. To extract the characteristic element of original wave including the pulse-like ground motion causing the permanent displacement, a wavelet set defined as the linear combination of basic wavelets is used. Each wavelet in the linear combination reflects a permanent or transient displacement component. Acceleration records by servo accelerometers usually have baseline fluctuation. Caused by this feature, the displacement by integration of the acceleration usually diverse like a quadratic function. Although the effect of the baseline change of the acceleration can be removed by fitting the velocity as a multilinear function in many cases, the displacement becomes unrealistic if the baseline change is small. Applying the method to the ground motion records at KiK-net Mashiki and K-NET Ozu during the 2016 Kumamoto Earthquake, the validity of the method is demonstrated. The former record includes relatively large baseline change of the acceleration. As a result, the displacement is extracted adequately using low order wavelet sets with the high-cut filter or high order wavelet sets without the filter if the baseline change of the acceleration is not corrected. If the baseline change of the acceleration is corrected, the displacement is extracted adequately using any wavelet set with the high-cut filter. On the other hand, the latter record includes small baseline change of the acceleration. As a result, the displacement is extracted adequately using low order wavelet sets and high-cut filter without the baseline change correction. Therefore, the method is particularly useful in the case of the ground motion record which has slight change of the acceleration baseline. In addition, it is shown that the method is available to simplification of the seismic ground motion by applying to the strong motion record at Takatori station during the 1995 Southern Hyogo Prefecture Earthquake. The acceleration record is rapidly decomposed to element waves by the method compared to the result using Ricker wavelet. Furthermore, the velocity response and the pseudo-velocity response spectrum are well simulated by the extracted wavelet sets. The efficiency of decomposition increases with the order of the wavelet set. Especially, a complicated wave element can be extracted by the method. This is caused by the feature that the wavelet set used in this study seems to be a Fourier series in the limited time interval. Using the wavelet sets proposed in this study, the length of the extracted element wave can be determined by the order of the wavelet set. The higher the order of the wavelet set is, the longer the extracted element wave becomes, vice versa.
During the 2011 off the Pacific coast of Tohoku earthquake, large response displacements were observed on upper floors in super high-rise buildings at sites far from the earthquake source. These phenomena were due to long-period and long-duration ground motions developed in the thick sedimentary basin. Since building responses to strong ground motions are significantly influenced by the value of the damping factor of the building, it is important to do a quantitative estimation of the effects of the damping factor on building response based on recent data including long-period and long-duration ground motions for aseismic design. In this paper, the damping function is defined as the ratio of the pseudo velocity response spectrum to the energy spectrum (Akiyama and Kitamura, 2006). The damping function is available for the prediction of the maximum response, and has ever been used as an index to evaluate the seismic performance conveniently. The damping function is also available to estimate the input energy of ground motions to buildings, because it means the relationship between the maximum response and the accumulative response. While the knowledge of the damping functions in the period less than a few seconds has been accumulated, there are few knowledge of the damping function for long-period and long-duration ground motions. First we have examined the applicability of the damping functions presented in previous studies to longer periods and longer duration using a lot of recent records including long-period and long-duration ground motions. Then we have developed new damping functions for long-period (from 0.5 to 6 seconds) and long-duration (up to about 400 sec) strong motions. Using the new damping functions, we have showed a method for estimating the energy spectrum from the pseudo velocity response spectrum. We have obtained the results that the estimated energy spectra correspond to the observed energy spectra regardless of the period ranges. The new damping function can be used as a criterion to judge the adequacy of the input energy of predicted ground motions and design ground motions except for pulsive ground motions such as strong ground motions observed in Kobe during the 1995 Hyogoken Nanbu, Japan, earthquake.
This research is a preliminary study to evaluate the seismic force of nonstructural components (secondary system) beyond the elastic limit of steel buildings. The objective of this paper is to propose a convenient evaluation method of higher harmonics in a periodic response of an SDOF system with bilinear hysteresis subjected to sinusoidal ground motion. Firstly, numerical examples are demonstrated to show how the higher harmonics in a floor response affects the acceleration response of the secondary system. Two types of floor acceleration are considered. One is waveform obtained by nonlinear time history analysis and the other is a sinusoidal waveform having the same amplitude. The result shows that secondary response to these floor acceleration are significantly different if the frequency ratios of the secondary system to the input motion are close to or coincide with odd numbers. Secondary, this critical higher harmonics are formulated by specified dynamic characteristics of the building and its peak displacement. In order to simplify the formulation, floor acceleration waveform in the steady state condition is approximated using piecewise linear waveform defined by a post-yield stiffness ratio and a ductility factor. A closed form of Fourier coefficients of the higher harmonics is derived with respect to the approximated waveform. Furthermore, the solution is simplified by neglecting higher terms in the exact solution with respect to the post-yield stiffness ratio for practical application. Finally, the proposed solution is compared with the result obtained by discrete Fourier transform in time history analysis. The maximum ductility factor is assumed to be 100 in a numerical example. The post-yield stiffness ratio is in the range of 0.01 to 0.3, depending on the type of structures. The ninth higher harmonic is analyzed at most. The results show a good accuracy of the proposed solution in a wide variety of ductility factors.
Ground motions with increasingly large amplitudes have been recommended in a seismic design of super high-rise buildings for long-period ground motion in recent years. Increasing the number of dampers is an effective way to reduce story drift. An Excessively large amount of steel dampers in passively controlled buildings, however, potentially amplify floor acceleration in the small range of ductility factor. In order to overcome the trade-off relationship, this paper proposes the combination of a tuned mass damper and steel-type story damper to reduce both story drift and floor accretion in a wide range of seismic intensity. A moment resisting frame with nonlinear steel dampers is modeled as an SDOF system. A linear tuned mass damper (TMD) mounted on the rooftop are considered. A Bouc-Wen model is employed to represent hysteresis of the steel dampers. A Fokker-Planck equation is derived with respect to the 2-DOF model consisting of the building and the TMD. Stochastic time history analysis is conducted based on the statistical linearization in terms of two parameters. One is a stiffness ratio which is post-yield stiffness to the initial stiffness of the SDOF. The other is a ductility factor of the steel dampers. Firstly, optimal stiffness and damping ratio of the TMD is numerically estimated by solving nonlinear programming problem. The objective function is either inter-story drift or floor acceleration. It is confirmed that the optimal tuning ratio minimizing the story drift is approximately calculated in the followings concept without time history analysis. In the optimal tuning ratio, an initial natural frequency of the building is replaced by equivalent frequency computed by the scant stiffness corresponding to the peak story drift. An evaluation method of the optimal tuning ratio minimizing floor acceleration is also developed in a similar manner, provided that the corresponding story drift is slightly modified. This modification reflects the empirical fact that the optimal tuning ratio is almost unchanged from its initial value up to certain nonlinearity. Secondary, the seismic effectiveness of the TMD is summarized in terms of the stiffness ratio and the ductility factor. A practical evaluation method of the seismic effectiveness of the TMD is proposed based on the linear stochastic vibration theory. The predicted response show excellent agreement with the response obtained by the Fokker-Planck equation. Finally, peak deformation of the TMD is discussed. Peak displacement of the TMD to the floor displacement gradually decreases in association with the development of yielding in the steel damper. This is well explained by de-tuning phenomenon accompanied with elongation of an equivalent natural period of the SDOF system. As a result, large amplitude of the TMD is avoidable during strong ground motions. This is one of the advantages of the proposed passively controlled system.
Currently, energy dissipation system such as hysteretic dampers and viscous dampers have been used increasingly in new and retrofit constructions. Predictors of seismic structural demands of buildings with energy dissipation systems that are less time-consuming than nonlinear dynamic analysis can be useful for structural performance assessment and for design. In this study, based on Inelastic Modal Predictor (IMP) that Funahashi et al. (2002) have proposed to estimate the seismic demands of general buildings, a predictor of seismic structural demands of a building with hysteretic dampers is proposed. IMP consists of the square-root-of sum-of-squares rule of modal combination, and taken into account a first-mode inelastic spectral displacement and a post-elastic first-mode shape approximated by the distribution of the story drifts obtained through a nonlinear static pushover analysis (NSPA). However, IMP is not quite applicable as it is to estimate the seismic demands of a building with hysteretic dampers. The assumed tri-linear (or bi-liner) single skeleton curve for the inelastic single-degree-of freedom (SDOF) system equivalent to the multi-story frame may not be appropriate to consider the behavior of dampers, which generally yields sequentially and earlier than the frame. Kang and Mori (2014) have proposed an equivalent inelastic SDOF system with multi-springs (MS model) that can capture well the behavior of the sequential yielding of the dampers. The IMP with the MS model proposed by Kang and Mori (K&M predictor) can accurately estimate the seismic demand on low-rise buildings. However, it cannot estimate well the demand on mid- and high-rise multi-story frames because of the several problems. This paper discusses the possible improvements of the K&M predictor, and proposes the following three enhancements.
(i) The effective elastic stiffness of the inelastic spring equivalent to the bare frame is evaluated by Eq.(12) so that the natural period of the equivalent SDOF system is equal to the 1st elastic natural period of a multi-story frame with hysteretic dampers,
(ii) A new evaluation method for the higher modal responses is proposed to take into account the change of apparent natural period, mode vector and damping coefficient of a multi-story frame with hysteretic dampers caused by earlier yielding of dampers than the multi-story frame,
(iii) In the original IMP, NSPA is performed with the external load distribution based on the Ai-distribution, which is not quite appropriate to apply to a frame without smooth stiffness distribution. In the K&M predictor, NSPA is performed with the external load distribution proportional to the 1st modal shape to consider the stiffness distribution of multi-story frame with hysteretic dampers; however, there was a tendency to underestimate the response at upper stories. It is proposed in this paper that NSPA be performed with the external load distribution based on the average value of that based on the Ai-distribution and 1st mode distribution.
The accuracy and applicability of the proposed method, along with that of the K&M predictor, is investigated using the results of nonlinear time history analysis on a series of 6-story and 12-story steel moment resisting frames with hysteretic dampers considering a variety of locations and stiffness of the dampers. According to the results, the proposed method has well improved the K&M predictor and can provide sufficiently accurate estimates of the seismic demand for all models.
Optimization is receiving attention in the capacity of engineering. The technique is applied to a variety of engineering problems such as Pile foundation layout on a footing of the residential house; trees layout; materials decision and structural problems. In structural engineering, morphogenesis by using structural optimization techniques is also receiving attention. There are three kinds of optimization problems: size optimization; topology optimization and shape optimization. In the structural problem, obtaining minimum compliance or minimum weight of structure subjected to constraints such as stress, displacement or volume are the main objectives. The methods by using heuristics such as Genetic Algorithm (GA) or Simulated Annealing (SA) to solve structural optimization problems have been reported recently. Swarm Intelligence (SI), simulating behaviors of biology group in nature, is also being reported. Ant Colony Optimization (ACO), simulating behaviors of ants in nature, is one kind of the SI approach. ACO is a multi-agent approach and ants, the agent, test design points based on random search technique. Hence, it is possible to test a huge design domain by using ACO. However, due to the randomness of ACO, since only the local information is considered, it is not efficient to solve structural optimizations by using ACO. On the other hand, a method of using an evolutionary strategy such as Evolutionary Structural Optimization (ESO) method or Bi-directional Evolutionary Structural Optimization (BESO) method are proved to be suitable for solving a variety of structural optimization problems. The strategy of these methods is updating design variables based on the sensitivity number, defined by the stress or particular displacement which are calculated by the finite element analysis. Sensitivity number is defined by considering the evolutionary mechanisms of the structure. The strategy has been applied for shape optimization of truss problems. By integrating the ESO strategy into the ACO, it is possible to test a huge design domain by using the ACO strategy and modifying the design variables to consider the behavior of structure following the evolutionary mechanisms to solve structural optimization problems. In this study, the Evolutionary Ant Colony Optimization (EACO) is proposed by integrating the ESO strategy into the ACO to solve shape optimization problems of trusses. The EACO is then tested by solving some shape optimization problems of trusses. The results obtained in this study are as follow: 1) By integrating the ESO strategy into the ACO, it is possible to test a huge design domain by using the ACO strategy and modifying the design variables to consider the behavior of truss structure. 2) In the shape optimization of trusses, the optimal shapes can be obtained efficiently by using the EACO. 3) The EACO is a new approach which has been proved to be suitable for solving the shape optimization of truss problems.
Although high-performance computing devices and general-purpose optimization software continue to be upgraded, optimization techniques are rarely utilized in the practical design of building structures. One reason is that optimization algorithms tend to be complicated and difficult to understand. This study proposes a section determination system for steel structures using a simple algorithm. The results obtained by this study are as follows:
1. The optimization problem that minimizes steel weight was formulated by targeting the allowable stress design method of general steel structures, under the restricted condition of utility factor. Furthermore, in order to solve this problem easily, a simple algorithm consisting of decremental line search and automatic member grouping was proposed and the section determination system, combined with structure analysis, was built, analyzing the utility factor distribution and referring to the taboo list.
2. Termination criteria were proposed to easily reflect the design intent of the structural designer in the results of the proposed determination system. The system user can employ three parameters as termination criteria namely, the expected reduction ratio by member grouping, average utility factor of all section members, and number of groups.
3. Using a sample model of steel structures, the influence of each termination criteria on the design results was studied, and the range of each parameter to obtain practical design results was identified. Furthermore, in order to verify the validity of the proposed system, the obtained results were compared with those of structural designers, and the practicality of the proposed system was confirmed.
However, in the proposed system, only the utility factor for allowable stress method is considered as a constraint condition, hence other elements that are usually required for structural design such as eccentricity ratio and story drift angle are not considered. In order to develop further this practical system, it is necessary to take into account the previously omitted requirements. In addition, it is worth to include other requirements that seem difficult to deal with numerically such as workability.
In order to estimate dynamic wind load on the spatial structures, for which it can be critical load, by reproducing wind around them with high accuracy, three-dimensional large eddy simulation (3D LES) with high resolution model is required. For such a simulation, which leads to a large-scale problem, as it requires a large amount of computational time, development of calculation algorithm to speed up 3D LES is desired to promote practical use. In the case of using splitting method, where pressure and wind velocity are solved separately, computational time is mostly spent in solving pressure poison equation. In this paper, the multigrid preconditioned conjugate gradient (CG) method (MG method) using plural two-dimensional coarse meshes is proposed in order to reduce computational time for three-dimensional large eddy simulation around a structure with cylindrical roofs. So far, the authors proposed the MG method using singular two-dimensional coarse mesh for the model, which is constructed in the way that three-dimensional mesh is generated by extruding the two-dimensional mesh in the spanwise direction, namely the direction perpendicular to streamwise direction. In this model, however, three-dimensional flow field cannot be generated. Thus, in this paper, we propose the method using plural two-dimensional coarse meshes applicable to the model where analytical domain is added on either side of the structure in order to generate a three-dimensional flow field around it. Applicability of the proposed method is confirmed in comparison with diagonal preconditioned CG method (DIAG method) for two turbulence models, which are standard Smagorinsky model (SSM) and dynamic Smagorinsky model (DSM), and for two mesh resolution cases of Ny40 and Ny80 where the numbers of division in the spanwise direction of the analytical domain are 40 and 80, respectively. Major findings obtained from numerical results are described below: 1) Significant error of wind load between the MG method and DIAG method is not observed in terms of statistical amount, that is, mean and fluctuating pressure coefficient. 2) For each turbulence model and mesh resolution model, the MG method results in speedup ranging from 118.2% to 137.6% compared to the DIAG method. 3) For different turbulent models of SSM and DSM, equivalent speedup effect is confirmed although the number of convergence fluctuates only for DSM until about 2,500 step, when sine function by which inflow turbulence are multiplied to prevent from numerical instability at an initial stage reaches 1.0. 4) In the MG method, as the scale of mesh model increases, the number of iteration dose not increase and computational time on the coarsest mesh relatively decreases. Thus, it is expected that the MG method has more speedup effect for larger scale problems.
Massive earthquakes (e.g. the Southern Hyogo prefecture earthquake in 1995 and the 2011 off the Pacific coast of Tohoku earthquake) cause damage in many of the piles supporting a structure. However, very few experiments have been undertaken on the failure behavior of piles during an earthquake. Especially, experiments targeting soil-pile (reinforced concrete member with a large cross section) -super structure interaction have not been conducted. This paper investigated the relationship between the damage of large cross section cementitious piles and the dynamic response of the super structure using a centrifuge test apparatus. The authors proposed a simple cross section pile model consisting of aluminum rod and mortar. The diameter of the pile model is 1.25 m which is based on real scale. A simple pile model subjected to compression and bending had sufficient plastic deformation capacity. A dynamic specimen used the above simple pile models, Toyoura dry sand of relative density 60% and a super structure model of a natural period of 0.63sec. In the shaking table test under a 50G field, excitation was a total of 10 Rinkai waves at different amplitudes. The maximum acceleration of each of the excitations ranged between 33gal to 632gal. In the dynamic specimen, shear failure of the pile model finally occurred and the inclined deformation of the structure rapidly increased.
Based on these studies, the following results were obtained. 1) The simply pile model used in the centrifuge test was mostly able to reproduce the elasto-plastic deformation behavior of the reinforced concrete pile member with a large cross section except local buckling of longitudinal bar and rupture of shear reinforcement. 2) The centrifuge test demonstrated the behavior of the dynamic specimen displaying the ultimate response when the second hinge forms at the middle length part of the pile underground. 3) In the excitations after the specimen exhibited the ultimate response, the maximum input acceleration increased while the inertia force of the super structure decreased. 4) The damage of the pile member can be evaluated by the maximum horizontal displacement of the foundation during an earthquake. However, the residual horizontal displacement did not interrelate with the bending failure behavior of the pile member. 5) The residual tilt angle of the super structure correlated with the damage level of the piles. However, until shear failure at the pile heads occurred, the residual angle was small.
A Sodium-cooled-Fast-Reactor, which is characterized by operation at high temperature and low pressure, employs liquid sodium as a coolant. Since components of the SFR have thin-walled structures to reduce thermal stress, components such as the reactor vessel have disadvantageous characteristics against seismic loading. Thus, to ensure structural integrity against seismic events, application of seismic isolation technology is essential. Conceptual design and validations of isolated seismic response performance for the SFR have been performed through parametric response analysis concerning specification of the isolation system such as horizontal and vertical natural period. The results of previous study show that structural integrity of main components against seismic events was ensured by employing thick rubber bearings with a horizontal natural period of 3.0 s or more, and a vertical natural period of 0.125 s or more. The thick rubber bearings, which have a rubber layer roughly two times thicker in comparison with conventional rubber bearings, have been developed by the authors to ensure seismic safety margins for components by reducing the seismic response for the reactor building in the horizontal and vertical direction. The thick rubber bearings, 1600 mm in diameter at full-scale have been designed to provide a rated load of about 10000 kN with a horizontal natural period of 3.4 s and a vertical natural period of 0.133 s. Moreover, a linear shear strain limit of the thick rubber bearings was designed to accept a horizontal displacement of 700 mm or more, corresponding to shear strain of 226%, to ensure a two-fold safety margin for the response displacements due to the design basis ground motion which has a maximum input acceleration of 8.0 m/s2. The first shape factor of thick rubber bearings which satisfies the above design requirement is out of JIS K 6410. Additionally, variations of shear and compression on stiffness, under designed response region have been not clarified yet since previous studies concerning the thick rubber bearings are few. Moreover, ultimate characteristics are required, and must be utilized for PRA which is performed in order to reduce residual risk. Therefore, the purposes of this paper can be divided into three main groups. The first is to clarify variations of shear and compression on stiffness, for the thick rubber bearing using 31 half scale models. The second is to investigate, through the breaking tests, the linear strain limit, tensile yield stress and breaking stress or strain as ultimate characteristics, and these results are defined as breaking surface. The third is to evaluate the ultimate characteristics, which are horizontal hardening characteristics and vertical softening characteristics, using two types of analytical model, 3D-FEM model and modified macroscopic mechanical model which is modified to capture the tensile breaking under offset shear strain. The primary results are summarized as follows: 1) Variation of horizontal and vertical stiffness for provided design values and provided design formulas is small. Even if variation in stiffness is considered to be 95% confidence interval, the confidence interval in horizontal and vertical direction is -4.3% to +5.8% and -3.9% to +4.2%, respectively. Thus, the design formulas have sufficient accuracy. 2) The average breaking shear strain under compressive region was 415.4%, which is a sufficient margin against basis design ground motion. In addition, thick rubber bearings have comparable breaking capacity, compared to conventional rubber bearings. 3) The skeleton curves obtained by two types of analytical models for ultimate characteristics are consistent with measured values under each test condition. These analytical models are useful in order to evaluate the ultimate restoring force characteristics for thick rubber bearings.
1. Introduction Application of energy dissipation devices for the passive vibration control of truss towers has been recently researched, because these towers were generally designed to resist wind load. However, as the earthquake load requirements increases, these towers are possibly to be damaged by large earthquakes. On the other hand, researchers have developed semi-active control device that produces any adjustable control force using variable dampers. This paper describes an investigation of applying semi-active control system to truss towers using variable dampers. First, hysteresis of variable dampers is examined using DDOF system. Second, the semi-active control system is applied to the truss towers to confirm the seismic response reduction compared with the passive vibration control. 2. Overviews of control method and analysis method In this study the Maxwell model is used to exhibit variable dampers. Modal control and optimal control theory are introduced to calculate command forces. For variable dampers, the damping coefficient can be adjusted between upper and lower limits to achieve the command forces. Optimal damping coefficients for passive dampers are applied for the upper limit of variable dampers. 3. Semi-active control of DDOF system The hysteresis curves of variable and passive dampers are compared using DDOF system. The shape of a theoretical hysteresis of semi-active controlled SDOF is a rhombus by adjusting damping coefficients of variable dampers. In DDOF system, when the variable dampers are placed at a location close to free end, or mass at fixed end is larger than that at free end, the shape of hysteresis similar to a butterfly. However, variable dampers can dissipate larger amounts of energy than passive dampers. 4. Semi-active control of truss tower structure A truss tower numerical model is created based on an actual telecommunication truss tower consisting of 15 layers. The damper arrangement of variable dampers is basically defined by the optimal locations of passive dampers. The effects of choosing control mode, damper arrangement, the number of dampers and value of maximum damping coefficient on response reduction effect are discussed using the numerical model. 5. Conclusions As a conclusion, the following results are obtained. 1) In DDOF system, when the variable dampers are placed at a location close to free end, or mass at free end is smaller than that at fixed end, the shape of hysteresis similar to a butterfly. However, variable dampers can dissipate larger amounts of energy than passive dampers. 2) In the case of truss tower, peak displacement of semi-active control is less than passive control by using only 1st mode as the control mode. However, then peak acceleration of semi-active control is higher than that of passive control at lower layers, because of adjusting damping coefficients of variable dampers. 3) When the variable dampers are installed at the optimal locations of passive dampers, the displacement response of the semi-active control is smaller than that of passive control. The effect of semi-active control on the displacement reduction increases, as that of passive control decreases. 4) The effect of semi-active control on response reduction is more significant compared to passive control as the number of dampers decreases. 5) The optimal damping coefficient of passive dampers provides the least displacement response in passive control. On the other hand, for semi-active control, the displacement response becomes smaller as the upper limit of damping coefficient of variable dampers increases.
This paper reports damage to an RC school building, particularly severe shear failure to secondary flat walls, by the 2016 Kumamoto
earthquake. The vibration characteristics of building were evaluated by micro-tremor observation. Additionally, the damage to the
building was investigated through numerical simulations. A series of parametric analyses revealed that the amount of the secondary
flat walls would affect the collapse mechanism. Ultimate deformability of the building decreased when a partial collapse mechanism
was formed, which was well evaluated by an evaluation method proposed herein.
The flush end plates connections have been researched in several countries. For example, in Japan, Kato, Sakuma and Mukai have presented the prediction method of ultimate moment strength of the connection, and in Europe, ECCS(2016) has presented the moment resistant and stiffness evaluation, and classification criteria for the rotational ductility. In addition there are numerous studies of the lateral buckling of H-shaped beams. For example, Ikarashi, Tomo and Wang(2011) have presented the effects of boundary condition and moment ratio on elastic lateral buckling strength of H-shaped beams. This paper presents a method to predict the ultimate strength of the H-shaped beams connected by flush end plates which fall into the lateral buckling or the connection failures. The method is based on the determination of the two boundary conditions due to yielding of flush end plates. The study is conducted by the following procedure: First, the behavior of the connection is researched by the no buckling experiment under the cyclic loading. As a result, it is found that the moment strength which cause the plastic deformations of the endplates and which contacts the deformed endplates on the surface of column can be predicted. In addition the non-linear FEM analysis is conducted to compare the moment-rotation relationship of the beams connected by flush endplates with those of the beams connected rigidly. As a result, they are similar. It means that lateral buckling strength can be predicted by the method based on the study of rigid connections. Next, the behaviors of the lateral buckling of the beams are researched by the buckling experiments under the cyclic loading, and then the boundary conditions of the beams are estimated by strain gauges put on the flanges. In addition the FEM analysis is conducted to estimate the boundary conditions of the beams from the lateral moment in flanges. As a result, it is found that the lateral moment is small in tension flange near the connection, so that the connection is not restraining warping of the end of the beam. We recommend that the boundary conditions of the beams connected by flush end plates are simple support or lateral bending support. The lateral buckling strengths under the two boundary conditions determine that which strength must be applied. Final, the several effects of factors are researched. Findings of this study can be summarized as follows: (1)The ultimate moment strength of the flush end plate connection is predicted by Eq. 2.4. In addition the moment-rotation relationship removed the effect of end plate deformation is similar to those of beams connected rigidly. (2) The lateral buckling strength of H-shaped beam connected by flush endplate can be predicted by determination of boundary conditions determined from Fig. 24. (3)The axial force is effective for the buckling strength, which was already studied by Kimura, Matsuo and Yoshino(2014). This study finds that boundary conditions are not influenced by the axial force. Moment strengths calculated by Eq. 3.4, and Recommendation for Limit State Design of Steel Structures and Eq. 3.5 suggested by Recommendations for the Plastic Design of Steel Structures are smaller than those of the experimental results.
Verification on both load-bearing and plastic deformation capacity for a steel beam-column welded connection at elevated temperature is of importance to secure fire safety of steel building structures. At the fire resistant design, it is required that the beam-column welded connection does not fracture before the adjacent heated steel beam exhibits stable plastic collapse mechanism. The AIJ design recommendation (Architectural Institute of Japan, 2017) cannot, however, offer a fire resistant verification method for the beam-column welded connection, because the fire resistance has not been verified experimentally. Main purpose of this study is to clarify both load-bearing and deformation capacity for steel beams including the beam-column welded connections at high temperature, by conducting their experiments under a condition on constant temperature and gradually increasing load. The beam-column welded connection with through diagrams is arranged in the center of beam specimen. The boundary condition is simple support and a shear force is applied through the medium of the column above the beam-column welded connection. In the welded connection, scallop working for a web plate in the wide flange section is not used. This kind non-scallop working is widely used for the actual beam-column welded connections to avoid brittle fracture at the structural design in Japan. The base metal and weld material are JIS SN490B and JIS YGW11, respectively. Stiffener plates to avoid local buckling of the flange plate in the beam are arranged near the beam-column welded connection, because the large tensile force is acted to the welded connection. The number of specimens is five and an experimental parameter is specimen temperature, which is given by ambient temperature, 600, 700, 800 and 900 °C. The specimen temperature was gradually risen by an electric furnace, and the shear force was applied after the temperature reached to the test temperature and kept constant it. Bending moment and rotation angle of the specimen are estimated respectively, and the shear force loading continued until the rotation angle exceeded 0.2. From minute investigations on the experimental results, the following knowledge was obtained. All specimens exhibited the beam bending collapse mode and the welded connections did not fracture. They possessed the larger bending strength than the full plastic moment at each temperature. The shear force applied at the high temperature experiments approximately kept constant with the specimen plastic deflection increase. From specimen observation after those experiments, the weld metal itself in the beam-column connection besides the beam largely deformed, however, ductile cracks in the weld metal and heat affected zone were not observed. It is expected that the beam-column welded connection with the high seismic performance by the non-scallop working also possesses the high load-bearing and deformation capacity at the fire. Furthermore, in-plane numerical analyses using a beam element were conducted, and it was clarified that both numerical and experimental specimen behaviors approximately agreed.