In our previous report (PartⅠ), the correlation between the characteristics of recycled aggregate and the unit water content, compressive strength and Young's modulus of recycled aggregate concrete was investigated. And this paper described how the characteristics of recycled aggregate were correlated with durability such as drying shrinkage, carbonation and freeze-thaw resistance. Through a series of our reports, the effects of mortar particles on the behavior of recycled aggregate concrete were able to be systematized. This has led to the conception of a method for producing modified recycled aggregate free of mortar particles.
For the purpose to study about the characteristics of the process of the corrosion-induced deterioration detected on surface of RC wall with mortar finish, RC wall specimens were electrified and measured the amount of the deteriorations as crack, delamination and spalling by hammer and visual examination periodically. From the results, in the case the cover thickness was small, the delamination increased with the progress of the rebar corrosion, which behavior were not liner but agogics. And in the case the cover thickness was large, the cracks along the rebar increased on mortar surface with the progress of the rebar corrosion.
Part 2 of this study examined the relationship between height and surface area of ready-mixed concrete loaded in rotating drum by geometric analysis. As a result, the following was shown within the scope of this study.
1) Rotating drum of truck agitator could be represented by geometric model based on the combination of cones and cylinder.
2) Partial surface areas of cone and cylinder cut diagonally with respect to rotating drum are expressed by integral equations. The relationship between height and surface area of ready-mixed concrete loaded in rotating drum could be quantified.
The author has estimated a broadband source model of the 2021 Fukushima-ken oki earthquake (MJ 7.3) using S-net and KiK-net strong motion records by the empirical Green’s function method. Three strong motion generation areas (SMGAs) with very high stress drop are estimated around the edge of the fault. One SMGA is located at shallow area in oceanic crust. The other two SMGAs are located at deep area where slip estimated by previous source models without using S-net is small. The two SMGAs at deep area make a larger contribution to strong motions at S-net than those at most of KiK-net.
Improved deformation history integral type hysteresis model (DHI model) is proposed. Original DHI model was elasto-plastic model and developed mainly for high-damping rubber bearings. While the model can represent the complex behavior of high-damping rubber bearings, there is an issue that the model cannot consider the performance change. Thus, the model was improved by defining the material parameters as a function of performance change ratio. In order to confirm the accuracy of the proposed model, time history analysis was carried out and compared the result of analysis with that of substructure real-time online testing system.
In this paper, we propose a method for designing the optimal specifications of inertial mass dampers and oil dampers between two buildings by using the input energy analysis. The proposed method is characterized by the use of both the simulated ground motions (double impulse) and the area of the input energy to reduce the input energy over the wide band of ground motion frequency. We clarify the effectiveness of the proposed method for a wide range of earthquake characteristics by comparing with the ordinary methods using the time history analysis and transfer function.
This study discusses the column overdesign factor required to prevent story collapse in 6- and 9-story RC structures with multi-story shear walls. Time history response analysis was conducted by changing the column overdesign factor from 0.8 to 2.0 by 0.2. As a result, for a 6-story frame, column overdesign factor of 1.2 was required, whereas for a model including shear walls a value of 1.4 was required in order of the strength of shear walls. These values may be reduced by 0.2 to 0.6, depending on the allowable rate of change of the maximum story drift angle.
This paper is intended for a case where folded-roof plates are attached to H-shaped steel purlins that have large lateral buckling slenderness ratio. After obtaining elastic lateral buckling strength by theoretical formula and clarifying its relationship with the lateral buckling slenderness ratio, we conducted element experiments on folded-roof plates and lateral buckling experiments on H-shaped steel purlins to which folded-roof plates are attached in order to examine their lateral buckling behavior, in conjunction with the results of finite element analysis that modeled stiffening effect of folded-roof plates using horizontal stiffening rigidity and rotational stiffening rigidity.
Simple seismic damage evaluation of the steel tower for power transmission considering global buckling of braces was proposed, which can be used as an index for seismic performance screening of the existing steel towers focusing on the large seismic ground motions. The evaluation index value can be calculated simply by defining seismic performance curves and frame limit displacements of typical steel towers and based on the energy balance concept, and it can be easily used in Japanese transmission structural engineer’s practice in which stress calculation method based on Cremona diagram is common.
The collapse behavior of steel floor structures under elevated temperatures in fires was investigated by detailed FEM analyses. The floor structure in the fire compartment is composed of uninsulated secondary-beams and steel-deck composite slabs, supported by insulated primary-beams, adjacent to unheated floor structures. Under the elevated temperatures, the secondary-beams and bolted simple connections lose strength and alternatively slabs carry the vertical load associated with large sagging deformation. The floor structure collapses when the reinforcement around the secondary-beam ends fails. The behavior and failure mechanism observed in the FEM analyses were confirmed by a simultaneous heating and two-directional loading experiment.