This paper describes the influence of the core specimen's number on the sample mean and the standard deviation of concrete strength in structure. In this study, about 10～40 core specimens collected from the three reinforced concrete structures at each floor, built at about 1955～1965, are used. As a result, it is revealed that the mode of sample mean at three core specimens almost equals to the population mean, and that the mode of sample standard deviation at six core specimens almost equals to the population standard deviation.
In this research, the relation between the flatness of the end of the high strength concrete specimen and its compressive strength was examined. The results of the examination are shown as follows. (1) The flatness of the end of the specimen can be evaluated by measuring 17 points with a device shown in JIS A 5308. (2) Flatness of the end of the specimen will change with the time passing. Therefore, specimens should be ground just before the strength test. (3) Every flatness of the end of the grounded specimen was within the limits regulated in JIS A 1132. (4) In this experiment, compressive strength decreased as the roughness of the end of the specimen increased. (5) In this experiment, the influence of the flatness on the strength reduction rate increased with the rise of the compressive strength level.
The purpose of this study is to examine a relationship between loads of lower limbs during concrete finishing work and slab flatness. Experiments were taken with 5 different concretes and forms which were size of 2,700 mm × 3,600 mm. Electromyogram (EMG) signals during work were recorded from 4 muscles of lower limb of skilled laborer and sensory tests about workability were taken. Slab flatness was measured with straightedge method. Results showed that at lower workability concrete, the integrated EMG were greater and slab flatness was low grade. It was suggested that the loads influenced slab flatness.
This report concerns a research on cover concrete thickness implemented for a number of members at 18 completed reinforced concrete buildings through non-destructive inspection and an analysis of the distribution and fluctuation of cover thickness. On the basis of the disclosed actual state of deviation within a member and among members, it has become obvious that the smaller deviation within a member on one hand and the larger deviation among members on the other hand lead to the large cover thickness fluctuation within a building as a whole.
This paper theoretically examines and proposes simple computational methods of the carbonation progress of concrete when the quality of surface layer and internal concrete aren't the same but cementitious materials have been combined at the surface layer of concrete. It is based on the model that carbon dioxide moves at steady rate of diffusion according to Fick's law; reacts instantaneously with calcium hydroxide (Ca(OH)2) at the boundary of the carbonation area and the non-carbonation area; and the boundary moves inside sequentially. The carbonation progress is simulated using data from previous papers.
Various kinds of PVC sheets are used as a finishing material for buildings. These PVC sheets are considered as appropriate material for recycling, because PVC has thermoplastic. In this study, fundamental mechanical property tests were carried out on recycled PVC specimens. The following conclusions were obtained. 1) The influence of waste PVC compound mixing rate on the quality of recycled PVC sheets was confirmed. 2) The mechanical properties of the recycled PVC sheets were influenced from the composition ratio of polymer, plasticizer, and calcium carbonate. 3) The prediction equation of mechanical properties of recycled PVC sheets was proposed.
We have developed a semi-active base-isolation system using semi-active hydraulic dampers that can be switched between two primary damping coefficients. The time lag of the damping force (in other words, the time constant) was measured through triangular wave excitation by means of displacement control, and its dependence on the piston velocity was clarified. Sliding mode control considering the time constant of the damper was developed based on a bilinear optimal control theory and a control law for simultaneous bidirectional control was proposed. It was clarified through shaking table tests that the proposed control reduces the acceleration response of the building, while keeping the deformation of the seismic isolation story relatively small.
We develop empirical regression relations for estimating waveforms of horizontal and vertical ground motions in a period range of 0.1 to 10 seconds caused by subduction-zone and crustal earthquakes using many strong motion records all in Japan. The relations are provided for 5 % and 1 % damped acceleration response spectra, energy spectrum, average of group delay time, and standard deviation of group delay time. The waveforms with site-specific amplification and phase spectra are easily calculated by the empirical relations using the outer-fault parameters, rupture starting points, delay time among rupture starting points, and the location of the strong motion stations in interest. We show that waveforms calculated by the empirical relations for the hypothetical Nankai earthquake are consistent with waveforms calculated by the theoretical method using three dimensional structure model and inner-fault parameters as well as outer-fault parameters in previous studies.
In this paper, analytical examinations have been carried out in order to understand the torsional input motion induced by foundation's shape and the use of composite foundation. Analytical models are divided into five general categories; L-shape foundation or triangle-shape foundation supported by identical piles, square shape foundation supported by different diameter piles or supported by different length piles, and square foundation with partially embedment. It is clarified that the difference of pile section and partial embedment influences a lot on torsional input motion while the effect of foundation's shape and difference of pile length is not so much.
The purpose of this paper is to present a superposition technique for seismic waves from consecutive earthquakes. Seismic waves from each earthquake are synthesized by the waveform generation methods proposed in previous papers. The consecutive seismic waveforms are superposed so as to match the positions on the time history axis with respect to a wave arriving from the border between fault planes, considering the relationship between the distribution of phase differences and the time history of the accelerogram. By analyzing the dynamic behavior of high-rise buildings using the proposed superposition technique, it is indicated that a proper evaluation of ground motions is important in the case of consecutive earthquakes.
In long-period ground motions, high-rise buildings are subjected to large cumulative deformations as well as large story drifts. Retrofitting with dampers may be one of the most effective solutions reduce such seismic responses. This study examines the influences of steel dampers partially installed into the lower part of high-rise buildings. A series of dynamic response analyses are conducted for typical steel high-rise buildings. A long-period ground motion is adopted whose energy spectrum has a peak amplitude at three seconds, and twenty-one story buildings and thirty-five story buildings are substituted by frame models. The results show that the total energy absorption of the dampers installed into forty-percent stories can be equivalent to that of the dampers installed into the whole stories. On the other hand, the maximum drift of the story located right on the lower part having dampers would become 1.4 times larger than those of the lower part.
This study proposes a structural system which aims at improving the seismic performance of new and existing wooden houses making use of oil dampers. Problems to install any special damping devices into wooden structures are known, for one thing to be the wood being brittle in bending and the other the strength of the joint between the device and wood being relatively low. Therefore, to get rid of these problems, we developed an oil damper which works only when subject to compression and is provided with relief valves to limit the maximum resistance. First part of the study deals with a series of harmonic loading tests to see if the damper exhibits the same properties as designed beforehand. Then, the dampers are mounted as knee braces at the corners of wood panels which is subject to dynamic loading tests in two ways. First one is a test to apply sinusoidal inertial force to an isolated panel. Second one is a shaking table test on full scale single-story wood frames. From these tests, we confirmed that the damper can absorb as much as nearly 60% of seismic input energy. It is also confirmed that the installment of the damper makes it possible for wooden frames that collapses at the first strike of strong ground motion to withstand the same ground motion several times with no significant damage accumulation to main structures. Lastly, these test results are compared to analytical results and it is concluded that the proposed structural system do work to improve seismic safety of wooden houses.
The response of buildings subjected to near-source pulse-like ground motions may be severe damaging than that subjected to ordinary ground motions. Particularly, for tall,long-period buildings, large drift response will occur because of it's higher mode excitation caused by distinct velocity pulse input under large earthquake. This paper evaluate the elastic story drift angle response of MDOF systems under sine wave pulse input motion based on modal analysis to understanding fundamental drift response characteristics of long-period buildings subjected to near-source pulse-like ground motions.
This paper aims at estimating the maximum dynamic response of the structure with time-invariant random natural circular frequency and damping factor subjected to random excitations. In the stochastic response analyses, the λ-PDF probability density function and the Gegengauer polynominal approximation is used to deal with the bounded parameter uncertainties. In order to estimate maximum responses, the 4th moment and the beta distribution model are used. Two types of probability density function for parameter uncertainties are studied, and evaluation method of high-order moment is introduced in each case. A series of numerical analyses show that the proposed method estimates the maximum response quite accurately. The method is applied to calculating response spectra considering parameter uncertainties to investigate the required accuracy of the damping factor in the seismic design.
H/V spectral ratio of microtremor is used to estimate dynamic properties of the soil by applying a theory based on a horizontal layer assumption. It is often the case, however, that there exists an irregularity such as a slope in reality. Characteristics of H/V ratio of such an irregular ground are not well understood. In this study, H/V ratio of an irregular ground with a slope has been examined through microtremor measurements and 2-D finite element analysis. Comparison between those results shows that the characteristics of H/V ratio change drastically due to the influence of landform and soil structure irregularity.
In this paper, the parameters describing the material property of wall clay blended with fibers for plastering are modeled by cohesion and angle of shear resistance based on soil mechanics. The unconfined compression experiments are carried out in order to obtain the cohesion and angle of shear resistance from Mohr - Coulomb's failure criteria, young's modulus and consumption energy from the stress-strain relationship. According to above experiments, the values of cohesion, angle of shear resistance and consumption energy indicate the constant between 0.2 kg to 0.4kg per 100L of fiber ratio for plastering against wall clay. The later, those parameters decrease lineally with the increasing of fiber ratio. However, the young's modulus increase with the fiber ratio by being affected the bond between fiber and wall clay. Then, the optimal fiber ratio against wall clay is obtained as 0.4kg/100L from above experiments.
In this study, estimation of maximum shear stress of mud-plastered wall based on material testing of Nakanuri mud was conducted. Firstly, the range of material strength of Nakanuri mud was investigated from the material testing of 29 kinds of Nakanuri mud all over Japan. Secondly, mud-plastered wall specimens using three Nakanuri muds chosen among the 29 kinds of Nakanuri mud were constructed. From the test results of the shear loading tests of the wall specimens, the relationship between the compressive strength of Nakanuri mud and the maximum shear stress of Nakanuri-layer of the wall specimen was evaluated. Finally, comparison between maximum shear stresses calculated from other test results of various mud-plastered walls and the shear stresses from this test results was conducted.
It is important to grasp the residual seismic performance of damaged buildings as soon as possible after an earthquake for the early recovery of life. The objective of this paper is to construct the system to judge the safety of damaged wooden buildings after an earthquake by residents themselves. The static lateral loading tests of wooden frame structures are performed to clarify the relationship between the connection deformation and the story drift angle. We also construct the formula for the estimation of the story drift angle from the connection deformation. In addition, we have proposed the low cost sensor, which is supposed to be installed by residents themselves, recording the maximum deformation of column-to-beam connections. With the constructed formula and the proposed low cost sensor, the maximum story drift angle of wooden frame structures can be estimated.
The slip behavior which damage concrete and deteriorate the performance of strength and ductility can be yielded on multi-story shear wall (MSSW) after flexural yielding under cyclic loading. This paper studied the mechanism of slip behavior on MSSW under cyclic loading after the flexural yielding by conducting experimental tests using column-shaped wall. Five specimens which were scaled models of 7-story MSSW were designed preceding flexural yielding. The parameters of specimens are axial load and arrangement of bond character of the main bars at the bottom of wall. The test results show that (1) in case that the axial force is zero, the slip behavior after the flexural yielding was occurred easily, (2) the result that the slip behavior after the flexural yielding can be controlled by increasing the axial load was verified, (3) the effectiveness of steel cylinders for stopping (controlling) slip behavior is also verified, (4) a method to estimate the stiffness and displacement on the slip behavior were presented; however, crushing of concrete at the bottom of wall should be considered by reinforcing.
Recently, the seismic performance of buildings with types of connection condition at pile heads has been studied widely. However, it has been difficult to evaluate the influence of the connection conditions at the pile head on the response of superstructures, because the seismic input is influenced by the connection condition at pile heads. The purpose of this study is to reveal how types of the connection condition at pile heads affect responses of superstructures under the investigation from the viewpoint of seismic energy. The result of the analyses shows that the response of elastic superstructures depended on types of the connection condition at pile heads. But if the superstructures standing on well foundation soils have been yield, they have little effect on the seismic performance of superstructures.
The PC-Mild-Press joint method is one of the methods which can control damage of structures with concrete. Authors have already carried out study and have clarified its mechanical behavior and damage. However, the effects of the floor slab on the structural behavior of the frame have not been clarified. In this study, experiments were conducted on a cruciform frame with a floor slab constructed by the PC-Mild-Press Joint method to determine its mechanical behavior and damage. The study focused on the effects of damage control when an prestress force was introduced into the floor slab using unbonded prestressing bars for the main floor slab reinforcement. The evaluation of damage in the floor slab derived from the crack width and the section analysis of interface's M-θ are proposed.
In this numerical study, the behavior of one-story steel rigid frame subjected to horizontal force is presented, involving the post-lateral buckling of beams in the frame. It is well known that the strength of a beam remarkably deteriorates after the lateral buckling occurred. However, the numerical analysis results show that the strength of frame does not deteriorate very much, even if the lateral buckling occurs to beams constituting multi-span frame. The behavior of frame is considerably stable after the lateral buckling of beams.
In this paper, the static characteristics of new exposed column-bases were investigated by element test and cyclic loading test. The new exposed column-base used the anchor-bolt that consists of two parts, one is energy restoring part by plasticity and the other is anchorage part in the foundation concrete. The new exposed column-base exhibits spindle type restoring force characteristics by plasticity of anchor bolt, although existing exposed column-base exhibits generally slip-type restoring force characteristics by plasticity of anchor bolt.
Pull-out tests on anchor bolts for fastening lead damper to concrete foundation were conducted to evaluate factors affecting pull-out behavior of anchor bolts. The main parameters were type of anchor bolt commonly used for anchorage of lead damper and layout of reinforcements around anchor bolt. The following results were obtained : (1) Vertical reinforcements arranged around anchor bolt contribute to increase in concrete breakout strength. (2) For long nut type anchor bolt, long nut length covered anchor bolt must be treated with enough care to avoid slipping anchor bolt. Because slipping failure lead to decrease in tensile strength and increase in pull-out displacement at failure. (3) The slope of the concrete cone was much flatter than 45 degree assuming in design procedure, regardless of the embedment depth, anchor type and reinforcement pattern. (4) Based on test results, simple concrete failure model was proposed. Using this model, effective radius of projected area were assessed 0.81le - 0.96le. These values were close to effective radius 1.0 le in existing design formula according to AIJ.
The discusser believes that the presented system by the author must be compared with a simple additional damper system instead of TMD system. Because the presented system needs a fixed point for reaction force that TMD system does not need. The comparison of these performances was conducted by the discusser. The results show that the performance of the additional damper system is superior to the presented system. However, the presented system has an advantage that it increases the stroke displacement of dampers.
The authors thank Dr. Masashi Yamamoto for the useful discussion, and the answers are as follows: (1) The presented system by the authors, which consists of a rotating inertia mass, spring and viscous damper, is dynamically the same as TMD (Tuned Mass Damper) though it needs a fix point. And it has the feature of enlarging the mass ratio easily more than usual TMD. There, it is appropriate to compare the author's system with usual TMD. (2) The authors are assuming the case where the beam-end is a fulcrum. In that case, it is difficult to use a simple additional damper. There, it is not appropriate to compare authors' system with a simple additional damper.