When electric arc furnace oxidizing slag gravel (EFG) was used as coarse aggregate, cracks were easily formed after high temperature heating. It is assumed that the transformation of wustite to magnetite by heating caused the volumetric expansion of EFG and the concrete specimens developed cracks. It is assumed that concrete with EFG calcined for volume expansion heating at 500℃ decrease crack. The effect of calcined EFG on mechanical properties after high temperature heating was confirmed. Concrete with EFG calcined at 600°C showed a decrease in cracking of the specimens, and at 1000°C, no cracking was observed.
The quantitative evaluation of tensile ductility of steel fiber reinforced concrete (design strength 30-60 MPa) containing 0.5-1.0% steel fiber with hooks at the ends was investigated. The maximum value of tensile stress after cracking in the tensile softening curve could be roughly evaluated by the linear formula of compressive strength. The influence of aggregate type, coarse aggregate content and air content on the formula was relatively small. Similarly, the average value of tensile stress up to 1 mm crack width in the tensile softening curve could be roughly evaluated by the linear formula of compressive strength.
The effect of temperature change during curing of polyurethane sealants on the rate of strength development was investigated. Under a constant temperature environment, the curing rate of the sealant was accelerated at higher temperatures. However, after curing the sealant at a low temperature, the apparent curing rate became lower when the temperature was raised. It was found that at low temperatures, the amount of moisture required for the reaction was insufficient due to the reduced moisture diffusivity. Therefore, it is important to develop materials with a curing mechanism other than reaction with moisture to reduce defects in one-component sealants.
To establish of estimation for snow cornice on flat roofs, the authors conducted wind tunnel test using natural snow and field observation subjected to the two buildings, and then examined the methods to estimate the snow cornice using roof shape coefficient based on the wind speed.
As the results, the tendency that the snow cornice grows as the wind speed decreases in the wind tunnel test was similar to the field observation. It was clarified that the location of the snow cornice could be predicted using the snow depth estimated based on roof shape coefficient calculated on the wind speed.
Seismic risk analysis consists of seismic hazard analysis and fragility analysis using single index of ground motion intensity. Though the intensity of the index is identical, the responses of buildings may be different due to the difference in earthquake characteristics. Using the single index brings the large error in risk analysis, though it is more convenient than using plural indices or conducting multi-event analysis. This paper proposed the risk analysis method using the ground motion prediction parameter dependent seismic hazard analysis and fragility analysis. The efficiency of the method was proved by the trial application using model site and buildings.
Natural period and damping ratio are important values in seismic design because of their impact on the response of superstructures. However, observation records of buildings are affected by the soil-structure interaction (SSI). In this study, we propose a method to estimate the influence of SSI in horizontal and rocking direction and the vibration characteristics of the building itself. First, we verify the effectiveness of the proposed method for numerical analysis. Then, we apply the proposed method to a large shaking table test and evaluate the effect of each SSI according to the amplitude level.
In the seismic design of nonstructural components, inertial forces and relative displacements are usually considered separately. But the two factors should be appropriately combined in some cases of connecting conditions to the structural frames. In this paper, the correlation coefficients between the story drifts of structural frames and the displacements of secondary systems are investigated in linear seismic responses. An approximate evaluation formula for multistory buildings is presented and validated through response history analysis. It is shown that the correlations are relatively high in the range of periods shorter than the first natural periods of structural frames.
In this paper, a topology optimization method of compliant mechanisms considering geometrical nonlinearity is proposed. In the method, the HMPS method, which is one of particle methods, is used for the analysis considering geometrical nonlinearity. The CA-IESO (Cellular Automaton - Improved Evolutionary Structural Optimization) method is used for the topology optimization. In the formulations, we show the objective function and the sensitivity those are adapted to the topology optimization of compliant mechanism using the CA-IESO method. Several numerical examples are provided to demonstrate the effectiveness of the proposed method for the topology optimization of compliant mechanisms.
A form-finding method is proposed for free-form shells specifying the distribution of stresses projected to the horizontal plane. The surface shape is obtained as a solution to a linear system of the vertical equilibrium equations discretized by the finite difference method with respect to the heights at the grid points. Distribution of the shear stress is specified to generate various shapes with a region of negative Gaussian curvature and free boundary. Effect of elastic deformation is verified by finite element analysis, and the shape is iteratively corrected to achieve the specified projected stress distribution considering the material property.
Continuing from the previous report, we discuss the buckling strength of wooden materials. The 50th %ile lower limit and the 5th %ile lower limit of the Young's modulus were obtained by two type of the non-destructive test and bending tests. Applying these values to Euler's buckling strength formula, we compared the calculation results and the experimental results. The calculated values with 5th %ile lower limit were to be close to the lower limit of buckling strength test results. The calculated values with 50th %ile lower limit weren’t useful for estimating the average of buckling strength in this study.
This research proposes a structural system for CLT shear wall that demonstrates high CLT shear performance, high deformation capability, and a method for determining its target performance. CLT shear wall with steel beams, using tensile members prevent the brittle failure occurring at the tensile joint, is proposed. To verify the validity of the proposed method, experiments for full scale CLT shear wall specimens are conducted. Test results are simulated by analysis models. By using material property values that are close to the actual conditions in the experiment, the analysis model is able to accurately reproduce the experiment results.
Displacement mode including torsion when subjected to major earthquake is clearly related to strength balance of each frame while elastic torsional vibration is characterized by stiffness balance. In the previous research, we presented a displacement mode prediction method especially focusing on single-story timber structure having large strength eccentricity. The method is improved by taking the effect of plasticity of transverse walls and bi-axial input motion into account. Finally, necessary additional strength for seismic design of torsionally coupled structure is calculated and is related to eccentricity index. The accuracy of the evaluation method is demonstrated via numerous time history analyses.
In-plane lateral loading tests were conducted to investigate the structural performance of SFRC shear walls. The test results revealed that steel fiber reinforcement mitigated damage to the walls and enhanced their shear capacity. The number of shear cracks on the SFRC walls at an interstory-drift angle of 1/200 was twice as significant as on the RC wall, and the maximum and residual crack widths were approximately half. Shear stiffness degradation after cracking reduced as the steel-fiber volume ratio increased. 0.5% and 1.0% steel-fiber volume ratios increased the maximum shear capacities by 11% and 17%, respectively.
In this study, static loading experiments were conducted to study the structural performance of pile cap for single pile with horizontal two-way eccentricity and to establish its strength evaluation method. The results indicated that the maximum residual crack width and stresses of the reinforcements were lower than the limit values when the capacities of the specimens reached the allowable strengths. In addition, it was shown that the calculated results of the ultimate strength for each members using the bending analysis by the fiber model were showed good agreement with the maximum capacities of all specimens in this paper.
The effect of an adjacent member on the flexural buckling of compression member is examined. Formulas for equivalent rotational stiffness of the adjacent column affecting the focused column is presented. The effect of the adjacent column is classified in three groups, that is the focused member is perfectly braced, buckle simultaneously and the adjacent member is perfectly braced, according to the critical flexural stiffness ratio. Relations between the equivalent rotational stiffness and above mentioned 3 groups are discussed, and the critical flexural stiffness ratio characterizing the groups are shown, taking the height ratio, axial load ratio etc. as the parameter.
The superior design solutions (SDSs) of seven-story steel office buildings complying with the US seismic design standards (USSDSs) are compared with the SDSs using the Japanese standards (JPSDSs). Both SDSs are obtained in the same optimization algorithm for a space frame system and perimeter frame systems in moment frame (MF) and those with buckling restrained braces (BRBF). The lateral stiffness in MF required in USSDSs is 45% of that in JPSDSs and the lateral strength in BRBF is similar between JPSDSs and USSDSs with relatively greater strength in the main frames in USSDSs.
The objective of this study is to propose the axial load ratio which assure that strengths of CFT beam-columns attain the full plastic moment. CFT beam-columns subjected to constant vertical load and monotonic increasing moment are analyzed and the maximum strengths are obtained, taking the moment gradient ratio, the value of stability index α, strengths of materials and width-thickness ratio of steel tube as analytical parameter. After examining the effects of parameters on the maximum strength, required conditions for attainment of full plastic moment are consequently summarized as Eqs. (12)-(15).