The objective of this study is to confirm the reduction effect of fly ash on autgenous shrinkage of high performance concrete. In this paper, we deal with the influence of admixtures on autogenous shrinkage of massive model specimens which were made from highly workable concrete. We measured strain of concrete and reinforcing rots, and compressive strength which were cured at standard condition. From these results we calculated tensile stress-strength ratio of highly workable concrete. The reduction effect of fly ash on autogenous shrinkage was observed, but fly ash also reduced strength development of concrete. As a result, the stress-strength ratio of fly ash concrete didn't become lower remarkably, but with expansion producing admixture, it became lower remarkably.

View full abstract

In this research, the changes of micropores and the mechanical properties of concrete with mix proportions at water cementitious material ratios between 17% to 33% after centrifugal compaction were compared with those during vibrating compaction to investigate the influence of centrifugal compaction on concrete in such a high strength region. The measurement of micropores was performed by two kinds of methods: air void measurement by linear traverse method and the pore size distribution method. In a mix proportion with water cementitious material ratio between 17% and 23%, the compressive strength and Young's modulus tended to increase in case of centrifugal compaction compared to vibrating compaction. The difference in the condition of micropores of these test specimens in centrifugal compaction and vibrating compaction did not exist in pore size distributions of 0.003 to 30 microns, but the air voids in case of centrifugal compaction tended to be lesser. It was concluded, therefore, that in high strength concrete with water cementitious material ratio between 17% and 23%, air voids between 30 and 1000 microns decreased due to the influence of centrifugal compaction and the strength increased.

View full abstract

Relations between cracks in self-leveling material and quality of floor groundwork surface are experimentally examined. As the first stage, an influence of surface strength was examined intended for high-strength concrete. Then, it was clarified that surface strength was not quite large even using high-strength concrete, and cracks occurred easily when surface strength was small. Finally, relations between degree (length and width) of cracks and surface strength (width of a scratch, pull out strength, and shear strength) of floor groundwork were shown as examples of evaluation indexes about surface layer quality of concrete floor groundwork corresponding to defect in self-leveling material.

View full abstract

Cracks are common causes for rain penetration through external walls. Little is known, however, on rainwater leakage liability of fine cracks in which water absorption of the wall materials play an important role on the penetration process. In this paper, the author introduces an equation for calculating the leakage occurrence time as an function of crack width, wall thickness, pressure difference, and water absorption rate coefficient of the wall material. Results of two series of experiments on water permeability of various cracks in mortar and concrete specimen are also described. From the experiments, values for the factors concerning crack shapes and the wall material needed for applying the above equation are obtained. The range of crack width for which leakage were not observed in the experiments corresponded the crack width range below which the calculated leakage occurrence time shows remarkable increase.

View full abstract

The response of a mechanically anchored waterproofing membrane system located atop a building when subjected to local wind conditions was measured and the results analyzed to predict the stain in the membrane as a function of the average velocity profile at the site. A waterproofing membrane section having dimensions of 1.8m by 1.8m size was constructed atop the roof at an elevation of 44m of a 10story building located in Yokohama, Japan. The observed response of the membrane system was measured in terms of the strain generated in the membrane and the forces induced in the fasteners when subjected to local wind conditions. The test period took place early in the spring when typically at this location, higher average wind speeds occur. Results showed a corresponding relation between large strains in the membrane at higher wind velocities. The peak energy of the membrane was evident at two frequencies - an intermittent frequency of 5 to 8Hz caused by the natural frequency of the sheet and 0.1Hz which is representative of the wavy movement of a flag in the wind. However, the force occurring in the fastener was almost unchanged over this time.

View full abstract

In this paper, to establish the occupational safety and health management system for construction industry, the accident occurrence rates and patterns were analyzed on the basis of the age of workers as the factor of skillfulness and physical strength. It was quantitatively shown that the risk of accident was high on the inexperienced workers or the aged workers. So the more improvement of facilities, work management, countermeasure to fatigue and health care were expected for the aged workers. On the other hand, for the young workers, safety and health education before/after employment was the most urgent need.

View full abstract

In this paper, it is proposed an evaluation method for crack width of reinforced concrete members caused by drying shrinkage. The proposed method can be divided into two analyses. One is evaluation for crack interval by solving a differential equation for bond-slip characteristics of one-dimensional RC member, and the other is 2-dimensional non-linear finite element analysis using smeared crack model. This evaluation method is applied to two cracking tests, and it is confirmed whether it is able to evaluate cracking age and crack width with enough accuracy using this evaluation method.

View full abstract

The weight of construction material waste discharged from demolition work is essentially equal to the total weight of construction material contained in existing buildings. However, it is extremely difficult to calculate accurately the total weight of construction material contained in these buildings, and it is not necessarily required a such high level accuracy in usual demolition work. In this report, the total weight of construction material(such as structure, total floor, by use, structural material and finishing material) based on reliable database are shown. Judging from verification, these results might be applied to the estimating method of the amount of construction material waste discharged from demolition work.

View full abstract

We place this research as a basic study to simulate aging with orthotic devices and to estimate the effect of the aging for various residential environments' arrangement. At the first, we decided the best component of the orthotic devices to simulate aging from the viewpoint of biomechanics. Then, the decided orthotic device was applied for the comparative study on the effect of aging on evaluation of three factors - shape and position of handrail, height of toilet seat, C.S.R of floor - that were taken to support standing up and sitting down movements in the bathrooms. As the result, it is easier for the aged to suffer the influence of the factors' change than young people.

View full abstract

A spectrum method was proposed for predicting peak responses of a single-degree-of-freedom system that pounds against rigid adjacent structure(s) during an earthquake. Pounding was considered to occur on either one side or two sides of the system. The Kelvin body that combines a spring and a dashpot in parallel was used to simulate the collision. Based on free vibration and harmonic vibration both involving pounding, the equivalent period and damping of the system were obtained and used to predict peak displacement as well as collision force. Extensive numerical experiment, which covered a variety of combinations of system properties, contact element properties, separation distances, and earthquakes, demonstrated good accuracy of the proposed method.

View full abstract

Simplified theories on seismic peak response evaluation and preliminary design of the visco-elastically damped building are proposed. They are based on the single-degree-of-freedom (SDOF) idealization of multistory building, and produce the so-called "control performance curve" expressing the peak responses as a function of stiffnesses of all components, based on spectral characteristics of the earthquake. Against the target peak response stipulated, the curve clearly shows necessary stiffness balance between damper and other elements. A rule to convert the SDOF design to multistory design, with a consideration to distribute damper stiffness over the building height, is also presented. Accuracy of the design approach is demonstrated via numerous time history simulations of a wide range of multiple-degrees-of-freedom (MDOF) models.

View full abstract

The structural analyses based on the condition for the existence of a solution are usefully applied to any type of structures. In the situation where the condition is satisfied, the solution is always found from the idea of small deformation. As a topic in this case, the explicit solution forms derived from the stress method are investigated to show the difference with the usual treatment. When the condition is not satisfied, on the other hand, the analysis of the finite deformation is asked to obtain the solution. One method, which is available in the finite deformation, is proposed and applied to the shape-finding and structural analyses of some cable-net type structures to prove the validity. These analyses are supported by using the properties of the Moore-Penrose generalized inverse.

View full abstract

We performed the plate loading test and investigated the influence that the plate compacter and the tamping rammer gave to the compaction on the ground. As a result, we found that the use of plate compacter was appropriate on extremely soft ground with a bearing capacity of less than 30kN/m^2. And the use of tamping rammer was appropriate on normal ground with a bearing capacity of more than 30kN/m^2. And we found the impact acceleration test was efficient for evaluating the effect of compaction procedures on the foundation of detached house.

View full abstract

The box foundation composed of the uniting outer continuous underground wall, internal piles or lattice continuous underground wall has excellent earthquake resistance from the viewpoint of stability. Because the behavior during earthquake of the box foundation is complicated, the characteristic has not been clarified enough. Moreover, the evaluation method has not been necessarily established. In this study, the characteristics of this foundation during an earthquake were clarified by verification experiments. Moreover, this paper proposes a practical and reasonable dynamic aseismic design method. It is based on the lumped mass model. It models friction springs and passive resistance springs between the soil and foundation reasonably. Results of simulation analyses, it was confirmed that the proposal method provides a more efficient aseismic design.

View full abstract

This paper is intended as an investigation of the static and dynamic buckling behavior of double-layer latticed domes with various mesh patterns. The treated mesh patterns are a square pattern (S-pattern) and a diagonal pattern (D-pattern). The combining mesh patterns for the domes as "mesh pattern for upper layer+mesh pattern for lower layer" are "S-pattern+S-pattern", "S-pattern+D-pattern" and "D-pattern+S-pattern". The static or dynamic loads are applied to the nodes in proportion to the distribution of dead load. The methods of numerical analyses are an elastoplastic buckling analysis (static analysis) and a time history response analysis (dynamic analysis) taking into account the geometrical and material nonlinearities. In the dynamic analysis, the input waveform is a vertical step wave. Based on the results, first, the effects of the mesh pattern and the half subtended angle of dome on the static and dynamic buckling behavior are made clear. Then, the static ultimate loads and the dynamic buckling loads are estimated by using Modified Dunkerley Formulation as a function of generalized slenderness ratio A with knock-down factor γ. Finally the strain and input energy obtained by the static and dynamic analyses are compared and discussed.

View full abstract

In the seismic area the direct correlation between the strain energy and the axial stress resultants for latticed cylindrical shell structures, has previously been discussed, and an alternative static load modeling associated with the dynamic vibration analytical results has then been proposed. The distribution functions of the previously proposed static seismic load modeling are corresponding to the displacement functions for simple supported shallow shell. In this paper, an alternative static load modeling procedure using the continuum shell analogy has been proposed. The adopted analytical parameters are of the section size of roof members, the horizontal resistance of sub-structure and the total weight of sub-structure. It has been suggested that the present seismic load modeling procedure contributes to the simplicity of seismic design for shell-like space frames.

View full abstract

This study focuses on the seismic performance of soft-first-story buildings, which are demanded especially in urban areas. Six-story reinforced concrete buildings are studied, and the seismic responses of the soft-first-story structures and typical frame structures are statistically assessed based on the results of dynamic response analyses. The mean annual frequencies of the maximum interstory drift ratio exceeding the specified values are computed and shown as drift hazard curves. Finally the probabilities of the structures exceeding the safety limit states in 50 years are computed and compared.

View full abstract

During the past earthquakes, the insufficient seismic performance of low-rise to mid-rise reinforced concrete buildings due to the undesirable brittle shear failure of RC columns designed with pre-1971 Japanese design code has resulted in considerable loss of human lives and properties. Moreover, in order to satisfy the demand of high energy absorption by large seismic excitation, it is necessary to increase both the strength and ductility or only strength of the column. Considering this fact, a retrofit concept of thick hybrid wall utilizing additional concrete sandwiched by steel plates and high strength steel bar prestressing for bare frame either as opening type wing-wall or non-opening type panel wall is experimentally investigated and also analytically evaluated in this paper. The main goal of this research is to verify whether the proposed retrofit technique for bare frame is effective or not in respect of enhancing the story shear capacity and ductility.

View full abstract

Even the main aim of the earthquake resistant design is to protect life in very severe earthquakes, the recent demands of building owners have been changed to be able to use the buildings again with small repair cost. Good repairability is required to enable the reuse of buildings after severe earthquakes, even for RC members. A beam with diagonal reinforcements is very ductile with large number of concrete cracks. De-bonded diagonal reinforcements and a small design of narrow U-shaped notches near the end of the beam are one solution to reduce damage and increase the ability to absorb energy. The experimental results of the members with proposed design showed an effective means to reduce damage with greater energy dissipation ability.

View full abstract

It was attempted to evaluate the seismic performance of an old medium-rise R/C residential building. The building constructed in 1963 consists of varieties of brittle columns. Collapse tests were conducted for half-scale models of the columns. And based on the test results, the seismic behavior of the building including post-peak regions was studied. The study has revealed that 1) as far as ground motions with maximum velocity of 50cm/s are considered, the amplitude of inter-story drift angle remains as small as 0.7% due to short period and high strength of the building, but 2) if ground motions with maximum velocity of 75cm/s are considered, it increases to 6% due to the severe strength deterioration that the columns undergo.

View full abstract

Objectives of this study were to examine axial load carrying capacities of R/C columns after shear failure. For this purpose static loading tests of R/C columns were conducted. Confinement of hoop reinforcement to core concrete was one of the most important effects to be discussed so different hoop reinforcement details were studied, i.e. welded hoop for good confinement type, hoop with 135 deg hook for normal confinement type and hoop with 90 deg hook for poor confinement. Using these specimens centrical axial loading test to examine the basic confining effects and lateral loading test under constant axial load to examine the axial load carrying capacity were conducted.

View full abstract

This paper presents seismic test results of hinge isolated reinforced concrete beams with/without openings at beam-ends. At the hinge region of the beams, main bars were un-bonded in order to reduce damage of concrete and supplementary main bars were arranged to resist bending moment and shear force. The major subjects studied in this paper were as follows, which were required to establish the design guideline of this structural type of beams: structural details for enhancement of structural and constructive performance; limitation of concrete strength and shear stress level; openings located at the boundary of un-bonded hinge isolated portion; and discussion of modeling of restoring force characteristics of beams with openings.

View full abstract

If there were cracks in steel material, they could be the rupture starting points and the important factors for the fracture of steel structures. In the beam-to-column of steel structure, it is difficult to weld members completely, so there also be defects. When the earthquake would occur, the existence of cracks would involve a high degree of risk for the fatal fracture of the steel structure frame. Therefore we need to understand the quantitatively of the defects and the mechanical property in column-to-beam joints, or estimate the member's strength for the case that there were cracks. In this article, we proposed the method for evaluating defects in welded joints with J-integral and compared with the method described in WES 2805 at first. Next, We estimate the fracture of welded joints with cleavage fracture stress. Then we presumed the mechanical property of heat-affected zone with the hardness and stress-strain relationship of steel material. To get material's cleavage fracture stress, we conducted tensile and elastic-plastic finite element method. 1) We can evaluate the fracture in beam-to-column joints with the cleavage fracture stress. Then the rupture starting points might be un-welded points and the points with ductile cracks. 2) When we evaluate the fracture at heat-affected zone in beam-to-column joints, we can used the cleavage fracture stress of steel for columns or beams

View full abstract

Incorporating additional braces is representative method for seismic retrofit for steel structure. In the case of installing the braces, the welding of steel and chipping of floor concrete cause noise and vibration. In order to solve this problem, the previous paper proposed a new method using a shear-key plate adheared to concrete slab with epoxy resin. The failure of this method is brittle, but on the assumption that a buckling restrained brace with low yield steel of its core is applied, this joint is useful for a practical structure. This paper reports the strength of the adheared portion.

View full abstract

The authors used thin steel plates partially supported as seismic shear wall of small steel buildings. This paper describes buckling strength and post buckling strength of thin steel plate partially supported with steel frames. The stress distribution is studied and the approximation formula of the buckling strength used by the tensile-compressive bracing model is proposed. It is compared with the buckling mode analysis and the geometric nonlinear analysis by FEM. Also, C the approximation formula of the post buckling strength about thin steel plate combined with steel stiff frame is proposed in consideration of stress distribution and yield condition.

View full abstract

This paper describes characteristics of strong ground motions attributable to near-fault rupture directivity during some crustal strike-skip earthquakes in California and Japan. The directivity effects generate moderate long period pulse waves in fault-normal component. Compared with the fault-parallel component, these effects are more distinctly recognized in the fault-normal component. Theses effects make the amplitude larger and the predominant period longer. PGVs of records in case of non-directivity effects conform to the predicted values using the past attenuation relation, while in case of directivity effects occurrence PGVs in fault-normal component become 1.5 times larger than the predicted values.

View full abstract