The effect of elevated temperature history due to heat of hydration on physical properties and hydration system in the cement paste were investigated. The elevated temperature in early ages is known to cause stagnation of strength development. Therefore, the degree of hydration of each mineral component as well as hydrates is determined by X-ray/Rietveld analysis and cement paste properties, namely, the degree of hydration of each mineral, the amount of calcium hydroxide, chemically bound water, water content, density of hardened cement paste and mechanical properties were investigated. As a result, compressive strength, young's modulus, and shear modulus of hardened cement paste, regardless of W/C differences, can be evaluated with gel/space ratio of hardened cement paste with a single curve.
To build up a resource recycling society, the environmental issue of concrete is approached comprehensively with a new technique using aggregate coating with dielectric material and microwave heating. The increase of concrete strength is achieved by 1.2 times using improved coating agent mixed properly with silica-fume and by-product powder. The recovery of high-quality aggregate can also be achieved with low energy by using microwave heating selectively for coating layer. In addition, about 90% of original aggregate can be recycled. Thus, the trade-off relationship between “strength of concrete” and “recovery of aggregates” and another trade-off between “energy consumption” and “aggregate quality” have been solved simultaneously.
Young's modulus, Poisson's ratio, and bulk modulus of hardened cement under controlled different relative humidities were measured by ultrasonic method as well as direct tensile loading test. It was experimentally confirmed that Young's modulus, Poisson's ratio, and bulk modulus of hardened cement paste decreased as decrease in equilibrium relative humidity especially in the range above 40%RH. And in the range below 40%RH, experimental results of direct tensile loading test showed the decrease in Young's modulus and Poisson's ratio while the experimental results of ultrasonic test showed slight increase of Young's modulus and almost constant behavior of Poisson's ratio. For the decrease of Young's modulus and Poisson's ratio can be explained by the reduction of load-bearing water in the hardened cement paste due to drying, and slight increase under 40%RH by ultrasonic test can be explained by the increase of Si-O network of C-S-H due to drying.
Damages such as rising and cracking due to thickening growth of roots are quite often observed in the components such as path pavements, curbs, retaining walls and garden furniture. To avoid the failures, root resistance of those components used for roof gardens should be estimated by a suitable test before actual applications of them. In this study a test apparatus and a test method to evaluate root resistance caused by thickening growth of root were developed. First, the simulated root for similarly reproducing the thickening growth was developed on the basis of the actual behavior of the root of a cherry tree. It consists of two half cylinders of aluminum and a hydraulic jack inserted between them, and the whole simulated root covered with EVA sheet to give the similar mechanical property of the root. Then, the test was carried out using the simulated root for an asphaltic pavement and concrete blocks which were used for roof garden. It was found that the simulated root was useful for evaluating root resistance of those components.
In this paper, a simple method of predicting the critical deformation of composite materials with interfacial cracks was carried out under mode of II conditions using singularity strength Ki, and the fracture criteria of the interface between concrete and cementitious mortar bonded with ceramic tile finishing are evaluated. singularity strength Ki are considered by two types of stress intensity factors K1 and K2 on the basis of the interfacial fracture mechanics. The stress distribution and singularity at the interface between dissimilar materials are obtained by two-dimensional elastostatic boundary element analyses under a plane strain state. singularity strength Ki determine the mixed mode fracture criteria of the interfaces. Prediction of the first delamination and its development by these factors are compared with the empirical results of compressive tests on composite model specimens containing several types of tile finishing. It was confirmed that critical deformation could generally be predicted by the simple method.
The design live load for residence is often used for designing rooftops of residences, but the validity of using residence live load for rooftop gardens has not been confirmed. In the present study, new design value of live load for rooftop gardens are proposed based on the building survey results from 24 steel-framed houses in Tokyo area. The proposed design live load value will allow for the rational structural design of residences with rooftop gardens and also allow rational consideration of future changes to rooftop occupancy.
The earthquake response analyses of the Iwagasaki High School, the RC building of which was slightly damaged during the 2008 Iwate-Miyagi Nairiku Earthquake, are performed to examine the correspondence relation of the analysis result and the actual damage. In the analyses, the soil structure is estimated by performing the simulation analyses of the aftershock records obtained at this site, and the soil response during the main shock is analyzed using both the estimated soil model and the main shock record obtained at the JMA Kurikoma site near this building. The earthquake response analyses of the structure on the pile foundation considering the nonlinear interaction of the soil-pile-structure system are performed by continuously inputting the soil response during the main shock and the aftershocks to the 3-D model. For the model installed the lateral soil spring showing the resistance caused by the embedded footing beam, the maximum story drift angle of the structure in the part of main shock is in agreement with the value estimated on the basis of the actual damage. The predominant frequency of the model in the part of aftershocks is also in agreement with that estimated using the records. From these results, it is shown that the lateral soil spring influences the actual behavior of this building.
The purpose of this paper is to propose simulated earthquake ground motions for the structural design of buildings subjected to a surface rupture with a large permanent displacement (fling step). The seismic waveform is synthesized as a pulse, with the Fourier amplitude based on the ω1 model and the Fourier phase consisting of uniform phase differences. It is shown that the time history of the displacement, obtained by integrating the synthesized wave, can be interpreted as the source time function associated with fling step, which is characterized by a large and permanent displacement of the ground in one direction. Moreover, it is demonstrated that the dynamic behavior of buildings is properly evaluated when the synthesized wave is used as input. The average slip velocity of fling step will provide an effective index for the dynamic analysis of structures.
Base-isolated high-rise buildings with large aspect ratios are apt to be acted by the tensile stress in the isolators. In this paper, models of such buildings are subjected to simulated strong ground motions representing hypothetical scenario earthquakes for the purpose of earthquake response analysis. The two main findings of the study are the following: (1) Fluctuations in axial force induced by horizontal motion increase for base-isolated high-rise buildings with greater aspect ratios when the input waveform is the site wave of a large earthquake or a coupled earthquake at the plate boundary. In this case, tension occurs in the isolator. (2) Vertical motion is greatly affected by the site wave of an intraplate earthquake along an existing active fault. This induces tension in the isolator of a base-isolated high-rise building, with tensile stress exceeding the conventional seismic performance design target of σt=1N/mm2 at these points.
In this paper, we propose a design method to control the displacement of base-isolation layer using an oil damper that can change its damping coefficient relative to the displacement. The present damper provides large damping to reduce the response displacement of the base-isolation layer in severe or extreme seismic events, whereas it provides small damping to reduce the response acceleration of the superstructure in moderate seismic events. A numerical optimization method, sequential quadratic programming, is employed to obtain an optimum set of parameters for the present damper. Design examples show that the base-isolation system with the optimally designed variable oil damper can satisfy the design criteria that cannot be satisfied with a system incorporating a conventional oil damper.
Simple theoretical equations in order to estimate the stress of pile and to evaluate the lateral load sharing ratio between piles and raft considering softening and plasticity of soil were derived for seismic design. The ground shear strain caused by raft friction closely near the bottom of raft is larger than it in the deep ground. The stress of plies is affected by the profile of ground displacement, so it is important to estimate accurately the ground displacement caused by raft friction considering the nonlinearity of soil deposit. This paper shows how to extend the theoretical equations which is derived in homogeneous soil deposit into nonlinear region. Employed stress-strain models of soil are Hardin-Drnevich model or Ramberg-Osgood model. These enhanced equations were compared with the lateral loading tests and numerical analysis on piled raft foundation subjected to lateral loading.
In the Kashiwazaki-Kariwa Nuclear Power Station, the seismic ground motion in the south side of the site, was significantly larger than that in the north side of the site, in the 2007 Niigataken Chuetsu-oki earthquake. In order to analyze the effects of geological structure below the site on the seismic ground motion characteristics in the site, we made 2-D soil model and simulated the seismic ground motion with the model using the finite difference method. The soil model was estimated by the result of the geological investigations and described the folding structure just below the Kashiwazaki-Kariwa Nuclear Power Station. For input motion, we defined point source or plane wave, and we considered many directions as the incidence angle. From the result of analysis, we concluded that seismic wave concentrated in the local area of the site with the influence of the complex ground structure, and the ground motion in the south side became larger than that in the north side.
Though the Kashiwazaki-Kariwa Nuclear Power Station was subjected to significantly strong ground motions of the Niigataken Chuetsu-oki Earthquake in 2007, the main facility buildings had almost no damage. Since a large amount of land subsidence was observed near the buildings, the soil around the buildings was expected to be in the strong nonlinear state during the earthquake. In this paper, the authors tried to clarify actual behavior of Unit No.7 reactor building during the earthquake through the simulation analyses using the finite element method. In our analyses, nonlinear effects were considered in contact conditions between the buildings and the surrounding soil by employing joint elements in addition to soil materials.
The present paper discusses on a seismic performance of braces of sport halls reinforced by hysteretic dampers installed in the longitudinal direction. Based on the elasto-plastic dynamic analysis depending on varying input levels, the ductility index, d F, and the seismic performance index, d Is , are re-studied. As numerical parameters, a capacity limit deformation and a yield base shear coefficient of original braces are considered together with the natural period of original substructure and the yield base shear coefficient of added hysteretic dampers, and their effects on the ductility index are investigated. The ductility index of the reinforced structure can be estimated by the strength ratio of hysteretic dampers to those of original braces, and the seismic performance index of the reinforced structure, d IsR, can be estimated based on that of the original structure, d Is0.
The studies on saddle-shaped HP lattice shells are still few compared with those on other lattice shells such as EP lattice shells or HP lattice shells that have straight edges. It appears that saddle-shaped HP lattice shell has a peculiar buckling behavior, so that it has compression and tension members together under vertical distributed load. The present paper discusses the basic buckling behavior of saddle-shaped HP lattice shells with a square plan under vertical distributed load. First, mathematical formulae for linear buckling are derived based on continuum analogy. Then, the buckling behavior of saddle-shaped HP lattice shells is examined by a series of analyses in consideration of several parameters. Finally the initial yield load and the ultimate load are estimated by using modified Dunkerley formulation as a function of generalized slenderness ratio Λ with knock-down factor γ. In addition, Experiments of buckling are carried out in order to confirm buckling behavior of HP lattice shells using the small scale model which is designed by using modified Dunkerley formulation.
In this paper, the loading tests of wooden frames with mad plaster wall and their numerical analysis are reported. Three mud plaster are made of 3 different blend of clay, sand, and straw. Results are as follows: 1) if there is no separation phenomenon of mud plaster from a lath, the horizontal resistant force characteristics of wooden frames with mud plaster wall are close to calculated by proposed method. 2) The hypothesis of mud plaster separation phenomenon represents that the tensile strength of mud plaster gives the separation horizontal load of the wooden frames with mud plaster.
The timber frame work construction has the majority of the house in Japan. These buildings have the very large slipping properties in the hysteresis characteristics. In this paper, the seismic peak response forecast was verified about a single-degree-of-freedom (SDOF) elasto-plastic system of slip hysteresis characteristics. The seismic peak response forecast was done by the elasto-plastic response analysis, the property of energy conservation, and the equivalent linearization. And the accuracy of each forecast method was verified. Result, the property of energy conservation doesn't consist when the slip ratio of slip hysteresis characteristics is large, and the equivalent linearization can forecast the seismic peak responses for slip hysteresis characteristics.
This study proposes an accurate mechanical model of a wooden frame with knee-brace type oil dampers. The oil damper used in this study has two remarkable mechanical properties; the one is that the damper works only when subject to compression, and the other is that it is provided with the relief valves to prevent members of framework from being subjected to excessive internal force. In this paper, firstly a dynamic sinusoidal loading test on the damper is conducted to show its dynamic mechanical properties, and it is confirmed that a nonlinear Maxwell model exactly simulates the experimental results. Then, a mechanical model of the wooden frame with knee-brace dampers is constructed taking into consideration a relation between deformation of the damper attached as a knee-brace and story deflection angle. Lastly, a dynamic loading test of the wooden frame installed with dampers is conducted. It indicates that the hysteretic loops and energy calculated by proposed model accurately agree with those obtained by the experiment.
We tested specimens to see behaviors of shear walls without column on compressive side, especially after flexural yielding. The most important parameter was the ratio of wall thickness to neutral axis depth. Flexural deformation capacity of shear wall was almost proportional to the ratio. Other important parameter was amount of tie bars in compressive area. They increased deformation capacity of shear wall. We proposed a simple equation to estimate deformation capacities of these walls.
This paper presents a plastic design method of steel frames with a vibration control system with U-shaped steel dampers based on a quasi-linear motion mechanism. Firstly, a plastic collapse load of the damper system is evaluated using the upper bound theorem where the U-shaped dampers are assumed to have three plastic hinges. The accuracy of the evaluation is examined by comparing the cyclic loading test results. Secondly, the plastic design is discussed for steel frames considering some collapse mechanisms. The shear stress in the beam web is also discussed for the beam attached with the U-shaped dampers. Finally, for the sake of introducing the proposed device into the practice, nonlinear finite element analyses are conducted for the three-story three-span steel moment frames with and without the damper system. Relationships between the story shear and story drift obtained from the static pushover analysis are examined. The Von-Mises stress distributions are also examined to reveal the influence of the proposed device on the steel moment frame.
We carried out monotonous tension tests for full scale specimens of the end of beam having widened flange welding steel pieces to both sides, and examined using method of fracture mechanics. The specimen's variable factors are widening angle and method of the installation welding of widening plates. As a result, the followings became clear. 1. It is desirable to make widening angle equal to or less than 30°, and to make the penetration of welding of widening plate and beam flange sufficiently. 2. It is desirable to change smoothly the section at the starting point of widening on which the strain concentrates.
Anchor-bolt-yield-exposed-column-bases show various restoring force characteristics, that maximum bending moments fluctuate due to axial forces, especially variable axial forces including tension causing many resisting mechanisms. The column-bases with multi-rows of anchor-bolts generally used show multi-linear cyclic curves. The column-bases with anchor-bolts on the centroid axis show discontinuous slip-type cyclic-curves. In this paper, an experimental study on multi-rows of anchor-bolts column bases subjected to variable axial forces including tension and cyclic bending moment were carried out and the experimental results were examined to clarify the resisting behavior of the column bases.
Researchers, including the authors of this paper, are striving to develop main members of built-up structures using 780N/mm2 high-strength steel for a new built-up structural system that prevents buildings from collapsing or being damaged by a severe earthquake (JMA seismic intensity 6.5) and enables rapid functional recovery. The authors propose a weld-free built-up structural member that has a cross section of two channel steel members made of high-strength steel stitched together with bolts. This member has high strength, so that its cross section can be small and it becomes slender, thus creating the possibility of buckling problems. In this study, lateral-torsional buckling tests were conducted on beams with various stitching bolt pitch under uniform bending moment and bending moment gradient along the member axis. Then, a calculation formula for the flexural strength was presented. The values of the flexural strength obtained from calculation were compared with those obtained from the lateral-torsional buckling tests. As the long distance between the supporting points was required for the elastic lateral-torsional buckling tests, a new loading apparatus was fabricated. Precision, supporting conditions, and loading conditions of the apparatus were verified before the experiments. These results show that: 1) Although a twist angle appeared from an early stage, the initial stiffness remained substantially unchanged in the relationship between the bending moment M and the support point twist angle. 2) When the bolt pitch was increased, the lateral buckling strength was reduced. The effect produced by the stitching bolt pitch on the lateral buckling strength was relatively large. 3) If the bolt pitch remained within the range from 200mm to 800mm, the calculated values of lateral buckling were almost same as the experimental values for both cases of uniform bending moment and linearly changing bending moment.
High strength bolted friction type joints may have gap in the contact plane because of permissible deviation of steel plate thickness. In the “Part 1” of last paper, we proposed analytical method to evaluate the slip load of such joints tightened by turn-of-nut method. The validity of the proposed analytical method was verified, because the calculated slip load by the analytical value of the contact force was in good agreement with the experimental results. We consider popular three methods which may prevent from the reduction in slip load of gapped joint. One is the way increase the preliminary tightening torque value, the other is increase the nut rotation of tightening, further, the effect of the bolt location are discussed based on the analytical method which is described in the last paper.
To reduce the weight of buildings, the lightening of slabs would be very effective way because the slabs are generally the heaviest members in the building skeleton. In this paper, the sandwich panel system has been investigated on account of the reduction of self-weight as well as the increase of bending rigidity. The present sandwich panels are of an ALC (autoclaved lightweight aerated concrete) core adhesively bonded with steel skins. In order to grasp the fundamental structural behaviors, the four-point bending tests were carried out. The test results have been discussed referring to the analytical results by the simple theory for laminated beams or the previous test results for ALC panels.
It is important to evaluate the local buckling and post buckling strength at high temperature accurately. A part of authors have proposed a simple method to evaluate buckling strength of flange plate model at room temperature. In this paper, from the experimental and numerical results of cruciform section steel stub column at high temperatures, we will analyze a plate buckling behavior at high temperatures. Here, we examine the stub column test with the parameter width-thickness ration (b/t=8,10,12) and temperatures (room temperature, 400°C,500°C,600°C). Furthermore, we will verify the applicability our evaluate method of plate buckling behavior at high temperature.