Surface-layer air permeability depends strongly on the water content of concrete. Therefore, newly built structures, which contain a large amount of water, require water content evaluation during inspections. The relationships among the material age, surface-layer air permeability, relative humidity, and air permeability coefficient of newly cast concrete have been reported, but there have been few studies on the relationship between the water content and air permeability of young concrete. In this study, the effects of the water content of young concrete on surface-layer air permeability were investigated to propose a method for evaluating the durability of newly built concrete structures. To study the relationship between water behavior and air permeability in concrete in indoor and outdoor environments, specimens and actual-size walls containing embedded ceramic sensors were produced from ordinary Portland cement, Portland blast furnace cement type B, and fly ash cement. The relationships among the water content of concrete, Wenner method resistivity, and air permeability were determined. In addition, pore structure was analyzed by the mercury intrusion technique and discussed. The effects of the relationship between pore structure and water content on air permeability varied according to material age for different kinds of cement in an indoor environment. The results indicated that it is possible to evaluate the durability of concrete aged 28 days or older, for which the effects of structural changes can be removed.
The Young's modulus of concrete should be at least 0.8 times of the value calculated by the equation in JASS 5 (AIJ calculated value). Whereas one of the major factors affecting the Young's modulus of concrete is the Young's modulus of coarse aggregate, the information on the Young's modulus of coarse aggregate that satisfies the target value of JASS 5 is not shown clearly. Furthermore, whereas it is necessary to confirm the Young's modulus of concrete of the mixture proportion which is more dangerous than the actual mixture proportion prior to the construction, the definition of "more dangerous mixture proportion" is not shown clearly. In this study, based on the results of experiments for high strength concretes using crushed stones with the maximum size 20 mm, the influences of the Young's modulus and volume of coarse aggregate on the Young's modulus of concrete were investigated. An ordinary portland cement and a cement for high strength concrete containing silica fume were used as cements. Mainly, an andesite crushed sand was used as fine aggregate. Three kinds (andesite, hard sandstone, limestone) of crushed stones were used as coarse aggregates. Using specimens (φ50×100 mm) taken from ores, the compressive strength and the Young's modulus of coarse aggregates were measured. Range of water-cement ratio of concrete was 0.15-0.40. Range of absolute volume of coarse aggregate per unit volume of concrete was 0.09-0.36 m3/m3. Additionally, the mortars of mixture proportions which are removed coarse aggregates from concretes were produced. Preparing standard cured specimens (φ100×200 mm) of concretes and mortars, the compressive strength and the Young's modulus of them were measured at the ages of 7, 28 and 91 days. It was confirmed that the Young's modulus of high strength concrete is possible to be estimated based on the Young's modulus and the component ratio of each phase (mortar and coarse aggregate). However, in the case which the Young's modulus of concrete was small, the measured value tended to be slightly smaller than the estimated value by Hashin-Hansen equation3). Thus, by combining the equations for estimating the Young's modulus of mortar and concrete and for estimating the compressive strength of concrete6),9), the evaluation method of the relationship between the compressive strength and the Young's modulus of concrete based on the Young's modulus of coarse aggregate was proposed. The Young's modulus of coarse aggregate was evaluated to be between 5.5-7.0×104 MPa by this proposed method when the Young's modulus of concrete was about the same value as AIJ calculated value. On the other hand, the Young's modulus of coarse aggregate was evaluated to be about 4.0×104 MPa by this proposed method when the Young's modulus of concrete was about 0.8 times of AIJ calculated value. Based on this results, the reference value of the Young's modulus lower limit of coarse aggregate was shown as 4.0×104 MPa in order to meet the target value of the Young's modulus of concrete in JASS 5.
The issue on an aged deterioration to a reinforced concrete (RC) building is revealing in recent years. Especially, a falling cover concrete is an urgent subject since it may cause harm to the surrounding people. Number of experimental studies on an aged deterioration have been performed to relate the corrosion cracking appearance on the concrete surface with the corrosion ratio of steel bars. It seems that corrosion cracking propagation also induces cover concrete to peel off. However, there is almost no study on the risk of exfoliation of a cover concrete. Accelerated corrosion tests were conducted to estimate the splitting tensile strength before and after corrosion cracking appearance on the concrete surface and to assess the risk of falling cover concrete. The specimens are concrete cylinders having 150 mm in diameter and 300 mm in length, and a single reinforcement of D16 was installed right in the center of the cylinder. All surfaces except for exposed opposite faces of 50 mm in width were coated by epoxy resin to avoid penetration of NaCl solution. The variable factor is accumulative current density (0, 30, 100, 200 and 400 mA·h/cm2). The specimens were cured for 28 days before accelerated corrosion test. During the accelerated corrosion test, the specimens were placed in the tank containing 3 % of NaCl solution. A direct-constant 10 voltage was given and the current was monitored and recorded using a data logger in 60 minutes increments. The cracks on the concrete surface were visually observed and the crack width at certain locations was frequently measured using a digital microscope having a resolution of 0.01 mm. After accelerated corrosion tests, the corroded steel bars were removed from the surrounding concrete by performing a split tensile test to evaluate a splitting tensile strength on the corrosion cracking surface. A removed bar was soaked into 10% diammonium hydrogen citrate solution. After chemically and mechanically cleaning, the weight loss of corroded rebars was measured. Since a corrosion rate before cracking was slower and increased after cracking, a corrosion ratios was estimated from the accumulative current density and using a bi-linear interpolation having a break point at cracking. The circular cross section was smaller than the rectangular cross section, and the pores to accumulate a corrosion product decreased, as a result, the corrosion crack width of a circular specimen became larger than that of a rectangular specimen. Split tensile test results indicated that the splitting tensile strength before cracking (up to corrosion ratio of 1.7%) nearly didn't deteriorate due to an occasional stain of corrosion product on the concrete surface, however, it gradually decreased after outflowing of corrosion product from a connected crack. It was reduced by 26% and 37% when the corrosion ratio increased to 4% and 10% respectively. A simple model was proposed to assess a retention factor of splitting tensile strength with increasing corrosion. Furthermore, a finite element analysis was conducted on the split tensile specimen to investigate a fracture energy of a cracked surface by corrosion because the corrosion crack did not progress uniformly but was unevenly distributed to the splitting surface. Analytical results showed that the mechanical behavior of the splitting tension test was overwhelmingly dominated by the tensile softening properties of the splitting surface and not only the splitting tensile strength but the crack width should be reduced similarly to obtain a result to be consistent with an experimental strength. Further study is required to improve a prediction of falling concrete from a width of corrosion cracking on the concrete surface due to the sensitivity to tensile softening properties and corrosion level.
To clarify the deterioration in coating materials exposed to outdoor conditions and the preventive effect of coating materials against carbonation and corrosion of reinforcing bars in reinforced concrete members, we conducted a 20-year outdoor exposure test using a model building constructed from concrete specimens with various finishing materials. We used W/C 55% and 70% concrete specimens and applied various coating materials and penetrants to the surfaces. According to the results of the evaluation of the deterioration of the coating materials, there was some peeling and cracking in thin coating materials; however, no remarkable deterioration of thick coating materials was observed. Some cracks were observed in the surface layer of some multi-layered coating materials, but the main coating layers were almost sound. We also confirmed that fluorine coating materials have a high weatherability. A correlation between the degree of chalking and the degree of peeling and cracking in the coating materials was found. According to previous studies, the limit state of an organic coating material is expressed by the extent of gloss retention. In these test results, we observed a high correlation between the gloss retention and the extent of deterioration of the coating material. It seemed that gloss retention was a useful indicator of deterioration of the coating material. We also investigated the preventive effect of the coating material against carbonation in concrete. We confirmed the effect of using coating materials based on the outdoor exposure results. The carbonation preventive effect as evaluated by an accelerated carbonation test was found to be different from the effect as evaluated by the outdoor exposure test because of the penetration of rain water into the applied concrete. Evaluation of the carbonation preventive effect of a coating material should take into account the influence of the moisture content in the applied concrete. Deterioration of the coating material was affected by the carbonation preventive effect except in the case of high-permeability coating materials. We satisfactorily estimated the depth of carbonation in concrete with a deteriorated coating material using the equation proposed by a previous study. Finally, we estimated the corrosion of reinforcing bars using the corrosion indicator method. We evaluated the observed corrosion depth of iron particles previously mixed in the concrete and took this as an indicator of the reinforcing bar corrosion. From the results, it was observed that some observed depths after 20 years were shallower than the depth after 11 years. It seemed that rain water had the effect of diffusing calcium hydroxide from the concrete core to the surface. All specimens were observed to have corroded iron particles in the carbonated area of the concrete. It seemed that the corrosion preventive effect of a coating material was mainly to delay the progress of corrosion of the reinforcing bar.
This paper describes estimation of the unbalanced wire tension acting on the electric distribution apparatuses in natural wind by means of the rainflow method in order to conduct the fatigue damage design. The unbalanced wire tension was measured by field test at several sites. From statistical analysis results of the unbalanced
wire tension calculated by means of the rainflow method, it is clarified that the amplitude and the frequency have a strong
correlation with the wind speed. Furthermore, we specify a distribution model of the amplitude of the unbalanced wire tension.
A series of tsunami water tank experiments have been conducted to study global and local tsunami actions on low-to-mid-rise buildings with or without openings and piloti space. Each small-scaled experimental model produced by 3D printer is assumed as a three-story building of square plan with four corner columns and a center core. Wave pressures generated on several portions of external and internal walls are measured to discuss the local tsunami action, whereas wave forces acting on the whole building are measured to discuss the global tsunami action. Numerical analyses have been carried out to simulate the flow of tsunami inside and outside of the buildings and its effect on building structures through the comparison with experimental results. Based on experimental and analytical results, conclusions within this study are summarized as follows: 1) The existence of piloti space reduces the rise of water level and run-up on the front wall. 2) Breaking of glass windows causes the decrease in wave pressure on the external wall and the increase in wave pressure on the internal core wall. 3) Non-fragile windows cause the increase in water level and run-up at the front surface and consequently the rise of water pressure. 4) Maximum wave pressure tends to be generated on the internal core wall rather than on the external wall. 5) Tsunami flowing into the inside of building drains out of side and rear walls depending on flow velocity. 6) Horizontal wave force acting on the whole building decreases by 20 to 35% in the case with openings and piloti space compared to the case without openings and piloti space. 7) The core wall should be taken into consideration as a part of projected area in addition to exterior walls to evaluate horizontal wave force. 8) Vertical force acts downwardly in the case with openings and piloti space, although it acts upwardly in the case without openings and piloti space. 9) Tsunami simulation analysis based on VOF method is effective to evaluate both local wave pressure and global wave force. 10) The spatial distribution and time variation of wave pressure acting on the building and flow velocity inside and outside of the building can be accurately evaluated by tsunami simulation analysis. 11) Vertical force can be reasonably evaluated by slightly floating the building portion from the water bed in the analytical model.
The central disaster management council of the cabinet office and ministry of land, infrastructure and transport predicted strong motion which is considerably huger than conventional assumption. In base-isolated buildings, collision with retaining wall is concerned, recently experimental and analytical study done. Nonlinear characteristics of superstructure and characteristics response of laminated rubbers has been reported so far. In order to grasp ultimate states of base-isolated building, continued study is required. In this paper, under these circumstances, with the aim of response evaluation of laminated rubbers in case of collision with retaining wall, especially its vertical response, studied factors which have an influence on seismic response. Factors we studied in this paper are nonlinear characteristics of superstructure and laminated rubbers, and soil-structure-interaction. Change of overturning moment caused by nonlinear characteristics of superstructure affects vertical response. In case of considering the response of laminated rubbers in large deformation, it is desirable to consider horizontal-vertical interaction of laminated rubbers. Moreover, it is expected that the influence of Soil-Structure-Interaction (SSI) increased, because the excitation on vertical direction due to pulling out laminated rubbers. According to above background, this paper describes the investigation results by numerical simulations, which evaluate the vertical response of laminated rubbers in case of collision with retaining wall under considering these factors. Target building is seven story base-isolated building which we have been observing and studying, and input motion is a simple pulse wave. As a result, the following conclusion are obtained. (1) In order to study influence of horizontal vertical interaction of laminated rubbers, compare calculation result between Basic model and MS model. In horizontal response, there is not effects about differences in modeling, however in vertical response of laminated rubbers, vertical displacement of MS model is 1.7 times at the maximum in comparison with the Basic model because of decrease vertical stiffness of MS model. (2) In horizontal direction, maximum acceleration of superstructure reduce by SSI, the reduction effects correspond with height of soil spring constant. In vertical direction, the maximum vertical displacement of the laminated rubber reduce about 66% at the maximum compared with base-fixed. (3) In order to analyze the reduction factor of vertical response due to SSI, separate rocking vibration and vertical vibration from vertical response time history. In case of base-fixed, rocking vibration increased by collision with retaining wall, especially after 5Hz but these reduced by vertical of SSI. (4) Considering the non-linearity of superstructure, the vertical response of laminated rubbers is decreased. This effects is greatest among the three factors we studied, but if strength of superstructure is high, it is necessary to perform appropriate modeling for the effect of soil-structure interaction.
A various type of seismic passive control system has been developed on many countries with frequent earthquakes. And also, these are categorized from the viewpoint of structural system, resistant mechanism, material, etc. as shown Tables 1, 2. Herein, a new passive control system called Scaling Frame (abbreviated SF) has been suggested as shown in Fig. 1. In our previous studies of SF structures, the fundamental resistant characteristics are investigated experimentally as shown in Fig. 2, and the analytical method of SF structures which is adopted on steel frames has been proposed. In this study, the ultimate seismic response behavior and response mitigation effects of SF on wooden structures are investigated by shaking table tests on one-story wooden framed test specimen. Herein, four test specimens of various structural types are prepared with SF and structural plywood installed as shown in Fig. 3 (a), (b). And the input wave are assumed as follows; 1) foreshocks to investigate the standard seismic performance, 2) main shocks to estimate the ultimate seismic response behavior, 3) aftershocks to analyze the fail-safe mechanism of SF structures, and 4) mega earthquake input to study the ultimate limit state of test frame specimens. From the test results (Figs. 9, 10, 11, 12), the following behaviors are observed; In case of test specimen which consists of plywood only, the slip behavior and deterioration of restoring force are generated (see Figs. 9, 10). And also, the response story drift becomes large after main shocks input because the plywood does not resist. On the other hands, in case of test specimen with SFD installed, the stable hysteresis loop is observed (see Figs. 9, 10). And the residual restoring force is obtained after main shocks input. Furthermore, it is observed that good plastic energy absorption of SFD is presented during ultimate seismic response (see Figs. 9, 10). From these observations, SFD has good seismic resistant performance from the point of seismic mitigation effects and plastic energy absorption. Furthermore, SFD becomes fail-safe element after the plywood is experienced under severe damage. The equivalent viscous damping factor is calculated from the test results, and it is clarified that the SF structure has high damping factor during ultimate state (see Fig. 13). Next, the analytical studies are performed to investigate the ultimate seismic response behavior and the accuracy of dynamic response analytical method. The skeleton curves of each member (frame, plywood and SFD) are extracted from the envelop curves of test results (see Fig. 14). And from the observation of test results, each restoring force characteristics model can be summed from the summation rule. The response analysis is performed, and the results are compared with test results, the accuracy of analysis method is concerned (see Figs. 9, 15). And also, the fail-safe mechanism during seismic response is presented analytically (see Fig. 16). Finally, the analytical results of equivalent viscous damping factor are calculated by use of above analytical method. From the comparison analytical results and test results (see Figs. 13, 17), it shows good agreement with each other. So then, the main conclusions of this paper are as follows: The specimen by use of only plywood shows the slip on hysteresis loop and the larger response displacement because of damage of plywood. However, the specimens with SF device installed don't show the above results after even plywood damage. Therefore, installing SF device shows equable hysteretic behavior, and mitigation effects of SF structure after plywood does not function as seismic resistant element during ultimate state. And also, the accuracy of response analysis method can be presented.
During the Tohoku earthquake in 2011, high-rise buildings were shaken for quite a long time resulting from the occurrence of long-period ground motions, even though they were located far from the hypocenter. Responses caused by such long-period ground motions can be reduced effectively by adding adequate dampers. This is, however, difficult in the case of high-rise RC buildings because of their high story stiffness and heavy weight. A new vibration control system using shear-walls with a pin at the bottom and oil-dampers is proposed here to achieve it effectively. The bottom of the shear-wall sustains a large axial load and repeated rotary deformation during an earthquake. Then, to establish a durable bottom, a laminated rubber is adopted at the bottom of the shear-wall as a rotary bearing, and is not connected to the base concrete to reduce the tensile deformation of the rubber. The objective of this study is to clarify the behavior of the unconnected laminated rubber in rotary deformation. First, rotary deformation tests are conducted for evaluating the stiffness, durability, and ultimate state. Since there is no connection, a large bending deformation is produced in the flange because of the uplift of the flange edge, and the tensile deformation of the rubber becomes small. After the tests, there are some changes in horizontal and vertical stiffnesses. The laminated rubber does not break off under the rotary deformation 0.03rad. It can deform in the rotary direction sufficiently regardless of the existence of axial load. Second, landing and uplift tests are conducted to simulate the actual behavior caused by a varying axial load under earthquake. An inclined plate (angle is 0.01rad) is set on the flange, and the axial load is varied from 0 to 30MPa. Under a low axial load, there is a slit between the sloping plate and the base concrete. But after increasing the axial load (over 5MPa), the slit vanishes completely. The bending moment in the landing and uplift test generally corresponds to that in the rotary deformation tests at 0.01rad. Finally, in order to conduct rotary deformation tests and to determine the optimal flange thickness, the finite element analysis (FEA) is conducted. Before the uplift of the flange edge, there is no difference regardless of the flange thickness. But after the uplift of the flange edge, the rubber tensile stress decreases with decreasing flange thickness. It is concluded that the laminated rubber bearing has high durability in the rotary direction, and is suitable as a rotary bearing.
Since seismic isolation systems have high seismic performance, the number of the general commercial construction of base-isolated buildings has been increasing recently. For Nuclear Power Plants (NPPs), there have been also progressive researches to apply for seismic isolation systems. Recent seismic regulation shall require to evaluate seismic safety including ultimate behavior for NPPs generally, therefore, ultimate behavior of NPPs adopted the seismic isolation system must be also considered in the seismic residual risks. Breaking of rubber bearings or hard-stop of basement should be considered as ultimate behavior of a seismic isolation system. The seismic behavior of an isolation system beyond the design is evaluated from the peak responses or the response spectrum in seismic response analysis as the same manner in the design process. Additionally, in order to evaluate the residual performance of a seismic isolation system when some seismic isolators and structural members have been damaged, it is hopeful to use the mechanical energy balance as an evaluation index. In this paper, a novel seismic response analysis scheme is proposed for evaluating the mechanical energy balance as well as the peak responses or the response spectrum. By using the scheme one can evaluate ultimate behavior such as hardening or breaking of rubber bearings on a seismic isolation system. In addition, Mullins effect can be also confirmed, where restoring force curves of rubber materials have different strain-stress paths on the first loading and on the rest after the second loading one another. To consider these phenomena, the concept of the restoring force differences between conservative and non-conservative forces is employed newly in the seismic response analysis scheme. To show the effectiveness of the scheme for evaluating mechanical energy balance, numerical examples in the real-life are demonstrated for applying to a series of the E-defense shaking table tests on a large-scaled base-isolated specimen, where the restoring forces are modeled from static loading tests on a sole isolator. The main results in the paper are summarized as follows: 1) To evaluate the mechanical energy balance on ultimate behavior such as hardening or breaking of rubber bearings on a seismic isolation system, theoretical background of the seismic analysis scheme is presented with modeling the restoring force consisted of conservative and non-conservative forces. 2) The behavior of rubber bearings on breaking and after broken can be modeled by introducing two different coordinate systems, where the broken isolators are governed on the individual coordinate system after the horizontal load reaches over the friction limit load. 3) Duffing-typed functions and Exponential-typed functions are employed as restoring force model, which can be identified from static loading test records on an isolator. By using the modeling scheme, it can be confirmed that the differences between the static properties and the dynamic properties are investigated from the experiment records of unit loading tests and shaking table tests. 4) By considering the Mullins effect in the restoring force modeling, the proposed scheme gives accurate estimates for a successive earthquake motion with hardening of a lead rubber bearing (LRB). In addition, it is preferable to ignore the Mullins effect on horizontal hardening restoring force of rubber materials after thirty minutes or more interval time on the previous shaking. 5) It is shown as the energy transition mechanism that the elastic strain energy changed to the energy absorption consumed immediately when breaking of the LRB is occurred in the proposed scheme.
Let me start from defining the notation of the fundamental subspaces of matrix, which can simply denote by using the Moore-Penrose generalized inverse, for help to grasp more easily the meaning of expressions presented in this paper. The following topics have been presented, for examples, (1) Relation between actual solution and solution of new variable by a change of variables is shown. (2) It’s possible for displacement and stress to express to each other as functions of common variables from both of compatibility equation and equilibrium equation. Then, as applications of the functions, derivations of rigid-body stress and displacement under conditions of zero stress and zero loading have been shown.
A large settlement and tilting of detached house have been often observed due to ground liquefaction. In order to reduce the damage of the detached house, we have to predict the amount of deformation precisely. Finite element analyses with comprehensive constitutive models have been widely used for this purpose. However, quite a few material parameters in the constitutive model should be determined before the analysis. That process sometimes takes a long time and requires a high cost. In order to solve these problems, the authors have proposed a new numerical scheme based on the Lagrangian mesh free particle method with a very simple constitutive model. Model shaking table tests, validation analyses of liquefaction damage at Urayasu city during the 2011 off the Pacific coast of Tohoku Earthquake and prediction analyses of virtual ground model were also carried out. Based on a series of analysis, it was confirmed that the performance of the proposed method was very promising. The following shows the summary in present paper. 1) In chapter 2, conventional analytical and numerical methods are outlined, such as Building Standards Law, guideline and finite element analysis. Building Standards Law is found that we are able to get the bearing capacity of non-liquefied ground without consideration of ground liquefaction. The guideline is found to be able to obtain the possibility of ground liquefaction. However, it does not predict settlement or tilting of detached house. The finite element analysis with a comprehensive constitutive model can predict the settlement or tilting of detached house by ground liquefaction. However, limited number of engineers can handle those programs. Furthermore the standard penetration test is usually necessary to determine constitutive model parameters and its process is expensive for detached house owners. 2) In chapter 3, a new numerical scheme based on the Lagrangian mesh free particle method with a very simple constitutive model is summarized. In new numerical scheme, the Smoothed Particle Hydrodynamics (SPH) method capable of simulating large deformation is used to discretize the numerical area concerned in space. Furthermore, it is emphasized that the simple constitutive model needs a small number of mechanical parameters. 3) In chapter 4, model shaking tests are carried out to capture the localized deformation pattern of the ground next to the detached house during liquefaction. Then, we try to reproduce the localized deformation of the ground by using the proposed SPH scheme. The proposed numerical scheme is found to succeed in reproducing the localized settlement pattern of the model detached house quantitatively. 4) In chapter 5, a detached house severely damaged during the 2011 off the Pacific coast of Tohoku Earthquake is also targeted for the verification of the performance of the proposed SPH scheme. The proposed SPH scheme is found to reproduce a large settlement of a real detached house observed qualitatively. 5) Finally, in chapter 6, we try to predict the settlement of a detached house on the virtual ground by liquefaction using the proposed SPH scheme. Based on the virtual ground model simulation using proposed SPH scheme, it is found that we are able to predict the liquefaction damage level of the detached house. Furthermore it is confirmed that settlement of detached house is affected by Dcy and H1 from results of previous liquefaction judgment and proposed method.
Seismic isolation systems are effective in ensuring seismic safety of nuclear power plants. In cases where a nuclear reactor building is seismically isolated, it is necessary to identify seismic characteristics of not only the seismic isolator but also the reinforced concrete foundation that supports the seismic isolator. Few experimental studies have been made, however, to evaluate the coupled characteristics of a seismic isolator and its reinforced concrete foundation, and no study has dealt with the large deformation range leading up to breaking of laminated rubber bearings at a nuclear power plant. This study focuses on the combination of a seismic isolator and its reinforced concrete foundation (pedestal) designed for use at a nuclear reactor building. A series of static loading tests was carried out by using specimens designed to simulate a realistic combination of a seismic isolator and a pedestal. The test specimens were 1/2-scale models of a design example shown in JEAG4614-2013, and four specimens were used. The seismic isolator used was a lead rubber bearing 800mm in diameter, and a pedestal measuring 1200mm by 1200mm was used. The test parameters were the level of compressive axial stress made to act on the seismic isolator, compressive strength of concrete, and the existence or non-existence of reinforcing bars at the top of the pedestal. Basically, compressive axial stress was assumed to be a constant stress of 10MPa to simulate the stress at the center of a building. In the specimen designed to simulate the region near the edge of the building, compressive axial stress was increased proportionately to simulate large deformation. The compressive strength of concrete of 42MPa was assumed to be a standard value, and an experiment using a 60MPa specimen was also conducted to evaluate the effect of high-strength concrete. The test results revealed the behavior of pedestal under strains up to the rubber breaking level (shear strain= 450%) exceeding the limit assumed at the design. The test results also clarified the cracking patterns, load－deformation relationship, the strain behavior of concrete and reinforcement at and near the pedestal surface in contact with the seismic isolator. And a design method for preventing bearing failure of concrete under high compressive axial stress was proposed. From the results of this study, the following conclusions can be drawn: (1) The reinforced concrete foundation showed structural integrity within the range assumed in the design. Even during large deformation at the rubber breaking level, damage was not observed in the case where the compressive axial stress at the center of the building was kept at 10MPa. (2) In the case where the compressive axial stress acting on the rubber bearing was considerably large in the area near the outer edge of the building, concrete cracks were observed when the compressive axial stress was 20MPa, but brittle failure did not occur and axial force was maintained. (3) In the case where a compressive axial stress of 30MPa or more acted on the seismic isolator, bearing failure occurred at the surface of the reinforced concrete foundation. High-strength concrete is effective in preventing bearing failure and reducing damage in the ultimate state.
In this paper, a scheme of shape optimization is proposed for obtaining the maximum strength of free-form steel reticulated shells. In order to discuss the effectiveness of objective functions with respect to the strength, several different optimizations using GA are applied to two roof structures. Both examples are shallow steel single layer reticulated shell structures consisting of rigidly jointed tubular members. One of the examples has a square plan with a side length of 50m. All nodes on the outer periphery are pin-supported. Another example has a free edge at the peripheries and two surfaces which are concave down. The objective functions to be searched and compared are, respectively, strain energy minimization, linear buckling load maximization, initial yield load maximization, and buckling strength maximization. The buckling strength as a target for the fourth optimization is evaluated based on Modified Dunkerley Formula. With respect to the obtained free-forms based on the four optimization schemes, elasto-plastic buckling behaviour is investigated and compared. The conclusions are as follows in the present study. 1) The ratio of bending strain energy Ub to total strain energy U of the shape which is obtained from strain energy minimization is the smallest of all. On the other hand, there is a tendency that the value of Ub/U of the shape which is obtained from linear buckling load maximization, buckling strength maximization and, initial yield load maximization is larger than initial shape. 2) The elasto-plastic buckling strength of Opt1 indicates relatively good results in all configurations. However, the ratio λelplcr(imp)/estλelplcr showing the accuracy of estimation of the elasto-plastic buckling strength fluctuates a little around 1.0 but almost independent generalized slenderness Λe(m) (Fig. 12(b)). For this reason, the elasto-plastic strength of Opt1 isn't necessarily the largest of all model. 3) Because of the displacement-to-load factor shows the load factor still increasing even after initial yielding of the structure, maximizing the initial yielding load factor is effective to obtain the configuration which has higher buckling strength. However, if generalized slenderness Λe(m) becomes larger, the discrepancy between λy(FEM) which denotes the initial yield load which is obtained by elasto-plastic buckling analysis, and λy estimated from linear acting force gets bigger. Therefore, it is preferable to impose a limitation of Λe(m), when the initial load maximization is conducted. 4) The knockdown factor α0 takes the value within a range of 0.4 to 0.7 in this paper. This tendency is same with the classical reticulated shell structures which are dealt in the previous research. 5) The buckling strength of free-form shells which are investigated in this study can be evaluated by generalized slenderness ratio Λe(m). However, the magnitude of Λe(m) will change by optimization schemes. Therefore, multiple objective functions have to be considered for maximizing the buckling strength. And then, it is necessary to evaluate the generalized slenderness ratio of obtained shape to judge the validity for buckling strength.
Mortar finishing external wall is one of a typical external wall for wooden houses in Japan. It is constructed using sophisticated plasterer's technics, which is able to be given various textures on the surface. The mortar finishing external wall shows good fire resistant performance, however, not a few mortar of the external walls fell off under earthquake in the past. The reasons of the falling off of the mortar were use of inadequate materials and execution method, decay of timber, corrosion of metal materials, etc. To improve its durability and prevent falling off of the mortar, ventilation method for the mortar finishing external wall has been introduced. With the ventilation space, since moisture is vented out of a wall, it is able to be kept dry.
To investigate the failure mode and the seismic performance of mortar finishing external wall with the opening which was built by ventilation method, static shear loading tests of specimens with 4550mm of wall length which had various openings were conducted. There are two kinds of opening, namely, door type opening and window type opening. Each type has three opening widths, 910mm, 1820mm and 2730mm. In addition to these six specimens with the one opening, three specimens with no opening were also prepared. The repeated static shear load was applied to the beam of the specimen until 3.3% of story drift and after that one directional loading followed.
Average maximum shear strength of the specimens with no opening was 42.8kN at around 2% of story drift. The maximum shear strength of the specimens with door type opening decreased with the opening width. The shear force ratio (Fr) with 910mm, 1820mm and 2730mm opening were 85%, 63% and 40%, respectively. Where, the shear force ratio (Fr) is defined as a ratio of the maximum shear strength of the specimen with opening to the one with no opening. Each maximum shear strength was at about 2% of story drift. Maximum shear strength of the specimens with window type opening were remarkably higher than the ones with door type opening. The maximum shear strength decreased with the opening width except for the specimen whose opening width was 910mm. The shear force ratio (Fr) with 910mm, 1820mm and 2730mm opening were 104%, 87% and 67%, respectively. During the loadings, the mortar layer did not fall off. From the relationship between shear force ratio (Fr) and the ratio of the mortar area to the area of whole wall area(β), the regression line Fr =1.8β-0.7 was derived. Especially at 0.5% and 2% of story drift, the good agreement between the two values was shown.
Moreover, to understand the shear stress and displacement distribution of connectors, FEM analysis of mortar finishing external walls with and without the one opening was conducted. Finally, considering the shear displacement distribution of connectors, the simple equations to evaluate shear strength of mortar finishing external wall were proposed. While the calculated shear strength by the proposed equation at 0.5% of story drift is conservative compared to the experimental value, it is close to the value by FEM. The calculated value at 2% of story drift, on the other hand, is slightly higher than the experimental value. However, it is considered that the proposed equations are usable to evaluate shear strength of mortar finishing external wall.
From these experimental and analytical studies, the failure mode and the shear strength of this type of mortar finishing external wall came to be clear. It is expected that the number of mortar finishing external wall increases and the sophisticated plasterers' technique is transmitted to the younger generation.
For the structures with a flexible floor such as the wooden frame structures, the effects of the in-plane stiffness of the floor on the static and dynamic behavior of structures have been investigated so far. Among these works, several investigations are conducted on the effect of stiffness of orthogonal wall, restoring force characteristics of orthogonal wall, etc. However, there is no investigation focused on the orthogonal wall arrangement. In this paper, A new beam model which enables us to evaluate the effect of the orthogonal wall arrangement is proposed and the effect of the orthogonal wall arrangement on the sharing ratio of lateral force is discussed by using the proposed model. In Chapter 2, from the viewpoint of the formulation, the beam model is employed as the proposed model and the proposed model is derived from Timoshenko beam theory: the proposed model is built by interpreting the floor as the Timoshenko beam subjected to the action of the unidirectional force and the moment. In Chapter 3, the numerical calculation is carried out by using the proposed model, in order both to verify the effect of the orthogonal wall arrangement on the sharing ratio of lateral force and to confirm the difference of the sharing ratio of lateral force between by using allowable stress design and by using the proposed model. As a result, major findings are summarized as follows; 1) The change of the sharing ratio of lateral force, with the difference of the orthogonal wall arrangement, is essentially due to the change of the couple moment transmitted from the orthogonal wall. 2) The couple moment transmitted from the orthogonal wall consists of the effects of eccentricity and the in-plane deformation of the floor. The effect of the orthogonal wall arrangement appears as the constraint effect of the in-plane deformation of the floor. 3) According to the orthogonal wall arrangement, the sharing ratio of lateral force by using allowable stress design can be evaluated to the dangerous side.
In a sandwich structure having a thin plate, it is of critical importance to understand the buckling behavior of the surface material. The purpose of this study
is to seek to clarify the elastic buckling strength of steel sandwich panels under out-of-plane bending and evaluate it by simple formula. For this purpose, by
extending the previous theory for in-plane compression, the authors propose a theory for the elastic buckling strength of steel sandwich panels under
out-of-plane bending. Furthermore, the authors analyze effect of material properties of core and skin, shape of steel sandwich panel on elastic buckling
strength under out-of-plate bending, and propose simple formula for evaluating it.
Fiber reinforced polymers (FRP) are widely used in vehicle and aerospace applications because of their lightweight and
high-strength characteristics. Additionally, FRPs are increasingly applied to building structures. However, the elastic modulus of
glass fiber reinforced polymers (GFRPs) is lower than that of steel. Hence, the evaluating the buckling strength of GFRP members for
design purpose is necessary. The buckling strength is determined by Euler buckling mode as well as local buckling. In this study, the
compressive strength of a GFRP member was investigated under axial compression. The adopted GFRP member was a channel-
shaped GFRP, which was molded via pultrusion, at various lengths. Furthermore, we confirmed that the axial strength of a GFRP
member could be calculated by a theoretical evaluation method utilizing longitudinal elastic modulus and fiber volume fraction.
In case of fire, in addition to the stress due to permanent load, the thermal stress caused by the thermal expansion occurs in a steel frame. Therefore, if the deformation caused by the thermal stress at fire condition is concentrated at a connection, there is a possibility that the connection will be failed before the steel frame reaches its ultimate state. Considering such a phenomenon, in order to investigate the failure behavior of the steel structure connections exposed to fire in detail, it is necessary to analyze the stress and deformation of a heated steel frame in fire condition using thermal stress analysis. In the meantime, the analytical model that could represent the deformation behavior of the connection in fire is also necessary. Due to the severe high-temperature strength reduction of high-strength bolts, there is a possibility that the friction type high strength bolted splice connection (bolted connection) might be the weakest point of the whole frame in fire condition. In Europe, for a model of the bolted connection using in the frame analysis, the component-based model have been proposed. This model is a model in which each connection component (beam, splice plate and bolt) was defined independently and its characteristics (stiffness and strength) were determined by means of nonlinear load deformation curves. The component-based model is possible to consider both the shear deformation behavior of high-strength bolt and bearing deformation behavior of the bolt hole. This paper discusses a model of bolted connection on the basis of a component-based model. Connection type of a steel structure being used in Japan is different to that in Europe. And the component-based model of friction type bolted splice connection is less researched. Therefore, in order to investigate the deformation behavior of a bolted connection at elevated temperature, high temperature tensile experiments of two-sided friction bolted connections were performed. In this paper, firstly, component-based model outline is introduced. Afterwards, the analysis model based on the high temperature tensile test results of the bolted connection is derived, and is included to thermal stress analysis program. Finally, the suitability of this analytical model is shown by comparing the analysis results using this model with the previous experimental results. The results of this study are shown below. 1) By conducting an analytical study of bearing deformation behavior of steel plate used in a bolted connection at elevated temperature, the curve fit coefficients Ω (reference to the previous studies) were modified as corresponding to the load-deformation relationship of friction type high strength bolted splice connection according to the results of steady temperature tests. 2) The numerical analysis results approximately agreed with deformation behaviors and critical temperatures of elevated temperature tests of the bolted connection under constant load. Also, this analysis method could predict the deformation of each component in bolted splice connection and the failure type of bolted splice connections approximately. 3) The numerical analysis results approximately agreed with the deflection behavior of both ends fixed steel beams with the bolted connection under constant load in fire condition. Moreover, this analytical method could approximate the damage level of each component (beam, splice plate and bolt) at the bolted connection.