The drying shrinkage is the main cause of cracks in reinforced concrete. Therefore, it is important to the effect of drying shrinkage of material. In this study, it was shown the effect of drying shrinkage of cement and shrinkage reducing agent, considering mix proportion and drying ratio. In this experiment, several cements and shrinkage reducing agents were used. The results of experiments for drying shrinkage, a large effects of cements and shrinkage reducing agents, whereas a small effect of expansive additive. Moreover, the effects of drying shrinkage of materials were evaluated.

View full abstract

Fresh concrete, even high fluidity concrete is a special granular material rather than a purely viscous fluid. Obviously, its deformation resistance is greatly affected by its granular properties. When shear deformation takes place in fresh concrete, normal strain on shear plane will occur simultaneously, which is well known as dilatancy phenomenon of granular material. Dilatancy occurs essentially due to the existence of particle contact angle. The particle contact angle also greatly affects the flow resistance of fresh concrete, and changes with concrete's flow or vibration. In this study, in order to clarify the granular characteristics of fresh concrete, mechanical behaviors of a glass particle-silicon oil system in sheared state were firstly examined. Then, we performed the one-side shear test and vibration test to investigate the change of particle contact angles (PCAs) in sheared and vibrated states, using Laser-Aided Tomography (LAT). Also, the influencing factors of mean PCA were discussed, including shear stress, shear deformation, normal stress, particle shape, size distribution of particles, elapsed time of vibration, and vibration acceleration, etc.

View full abstract

First, an improved test apparatus for evaluating wind resistance of mechanically anchored waterproofing membrane system was furthermore developed on the basis of the previous apparatus. Then fatigue tests were carried out using it for the two kinds of mechanically anchored waterproofing systems for concrete substrate and for steel roof deck. The number of cycles to failure decreases according to increase of both vertical force and lateral force. Various defects were observed during the tests, such as rupture of membrane, large deformation of a fixing disk and enlargement of a hole in the disk for the former system, and pulling-up of a fixing screw from a disk for the latter system. It is concluded that improvement of each components elements in balance is needed to build a durable mechanically anchored systems against strong wind.

View full abstract

Rapid air permeability test using vacuum chamber was examined in testing conditions and the validity as the evaluation method of scaling resistance. The testing condition of rapid air permeability test was decided based on the outcome of an experiment. For the rapid air permeability test, the sealing width of 60mm was secured around the chamber and a distance of 150 mm was secured from the specimen edge to the center of the chamber. These test conditions reduced the coefficient of variation to 15% in the air permeability test. Rapid air permeability factor was found to be in good compatibility with Torrent air permeability factor. Also, this factor was found to be compatible with the amount of scaling by the ASTM C672 method. As a result, the usefulness of the rapid air permeability test method was proven.

View full abstract

The vertical wind velocity profiles dominate wind loadings acting on tall buildings. By AIJ (Architectural Institute of Japan) Recommendations for Loads on Buildings, velocity profiles are to be prescribed according to terrain conditions. The effects of terrain conditions can be treated by the surface roughness parameters such as the roughness length scale and the roughness density. These parameters, however, cannot fully explain the profile over urban areas since the urban buildings form a non-uniform roughness. In this study, numerical flow computations by LES (Large Eddy Simulation) are conducted to predict vertical wind velocity profiles over an existing urban area. The computed results are confirmed by the observation data obtained by a Doppler LIDAR (Light Detection And Ranging) system at neutral atmospheric conditions. Then the effects of roughness parameters to the velocity profiles are discussed by using present results. Finally evaluating equations are presented for predicting the power low index of vertical velocity profiles over urban buildings.

View full abstract

Tall buildings have been traditionally designed to be symmetric rectangular, triangular or circular in plan, but recent tall building design has been released from the spell of compulsory symmetric shape design, and free-style design is increasing. One important advantage for this trend is that rather complicated sectional/structural shapes are good with regard to aerodynamic properties for across-wind responses, which is a key issue in tall building wind-resistant design. A series of wind tunnel tests have been carried out to determine wind forces and wind pressures acting on the large number of tall buildings with various configurations. The results of these tests have led to comprehensive understanding of the aerodynamic characteristics of various tall building configurations.

View full abstract

A construction method in which the foundation beams are low in stiffness or omitted is partly applied to base-isolated structures supported by piles. In the method, the laminated rubber bearings are subjected to large lateral displacement and end rotation during earthquakes, and this sort of deformation is thought to greatly affect the mechanical characteristics of the laminated rubber bearings. This paper describes widely applicable conclusions concerning the mechanical characteristics of the laminated rubber bearings applied to the above-mentioned construction method. Theoretical formulas for the horizontal stiffness, end rotation and buckling load of a laminated rubber bearing considering the flexibility of a pile foundation are derived using a model of a laminated rubber bearing-pile-soil-foundation beam system on a uniform soil ground. The model representing the laminated rubber bearing is based on the theory developed by Haringx, and expanded considering the end rotation of the laminated rubber bearing. The effects of the pile and soil characteristics on the mechanical characteristics of laminated rubber bearings have been analyzed numerically.

View full abstract

In this paper, earthquake response of an existing mid-rise steel reinforced concrete (SRC) building which is composed of both brittle and ductile members is evaluated based on the equivalent single-degree-of-freedom system model reduced from multi-degree-of-freedom system, and the applicability of equivalent linearization technique to existing buildings is discussed. The results show that the accuracy of the equivalent linearization technique is strongly depends on the nonlinear characteristics of seismic input in case of existing buildings. The influence of the change of collapse mechanism due to higher mode response to the peak of the first modal response also discussed.

View full abstract

The purpose of this paper is to propose a practical method for optimum design of oil dampers with relief mechanism installed in multi-story buildings. The optimum design problem is formulated so as to minimize the maximum interstory drift under design earthquakes in terms of a set of relief forces subject to an inequality constraint on maximum ratio of the damping force to the relief force and an equality constraint on sum of relief forces of oil dampers. The proposed method to solve the optimum design problem is a successive procedure which consists of two steps. The first step is a sensitivity analysis including nonlinear time-history analyses, and the second step is a modification of the set of relief forces based upon the sensitivity analysis. Numerical examples are conducted to present the effectiveness and validity of the proposed design method.

View full abstract

In this study, torsional behaviors of high-damping rubber bearings under various bi-axial seismic waves observed in the site are investigated by time-history analysis with single mass system. A simplified numerical model for the shear properties of the bearings composed of a hysteretic damping element and a viscous damping element is proposed for the analysis. The influences of the characteristic of the seismic wave to the torsional strain generated in the bearings by the effect of damping elements are evaluated. Furthermore, relations between the behavior of the bearings during seismic response and the oval-loading test which is specified for the test of bi-axial ultimate characteristics are examined.

View full abstract

We evaluated the fault parameters of asperity models for inland earthquakes caused by long strike-slip faults based on the procedure proposed by Dan et al. (2011)¹⁾, and simulated strong ground motions by these asperity models. The models had a constant dynamic stress drop averaged over the entire fault of 34 bars and that on the asperities of 122 bars. We presented five models with the fault length of 25 km, 50 km, 100 km, 200 km, and 400 km, and simulated strong ground motions from the three models with the fault length of 50 km, 100 km, and 400 km. The simulated motions were consistent with the records of the 2000 Tottori-Ken Seibu, Japan, earthquake, and the 2002 Denali, Alaska, earthquake as well as the attenuation model of peak accelerations and peak velocities proposed by Si and Midorikawa (1999)²⁾. These results verified the procedure proposed by Dan et al. (2011)¹⁾ for evaluating fault parameters of asperity models.

View full abstract

Impact hammer tests and direct transient response analyses of finite element method were conducted to demonstrate the vertical dynamic characteristics of light frame joist floors with several aspect of openings using 3.64m-long-span and 4.55m-wide joist floor consisted of eleven 2" by 8" dimension lumbers and 15 mm-thick plywood subfloor.
The results indicate, i) Existence of opening less than 1.8m by 1.8m hardly affects the natural frequencies, ii) The natural frequencies and mode shapes simulated by finite element method agree with those obtained by the impact hammer tests, iii) The static calculation using the impact coefficient derived from the direct transient response analyses predicts the dynamic maximum displacements of the joist accepted the impact force.

View full abstract

This paper proposes an accurate, member-by-member analytical model for two-story timber structures having energy dissipation walls and/or plywood shear walls. Various member joints are modeled by using nonlinear spring elements whose properties derived from numerous test results. The analyses were found to reproduce both local and global responses obtained from shaking table tests of a variety of two-story timber frames. Moreover, unsteady behavior of slip-hysteretic structure, energy absorption performance and deformation state of energy dissipation wall arranged in 2nd floor are discussed.

View full abstract

Main purpose of this paper is to investigate residual seismic capacity for RC frames. An evaluation method for contribution of each member to the performance of the whole structure was proposed based on strength and energy dissipation. It was shown that the proposed method was of more accuracy and wider application compared to previous methods through pushover analyses of prototype frames. Moreover, an approximation method was developed and obtained a sufficient prediction of the contribution factor of each member. Finally, the proposed method was applied to a static loading test result of a single-story frame and its applicability was discussed.

View full abstract

Recently, core wall structures are increasing because of the needs for omitting columns and beams inside living space. It is realized with a new kind structure with ECC coupling beam that consume seismic energy. ECC have larger tensile capacities and crack width restriction effect resulting from small cracks dispersion under tensile stress. However, bond splitting failure of ECC coupling beams has not been grasped well. Therefore, investigations in terms of stress conditions and resisting mechanisms for bond splitting failure have been conducted to suggest new evaluation method. This study is summarized as follows; 1) reinforcing effect due to the tensile capacity of ECC is similar to that of reinforcement. 2) The bond splitting strength of ECC beams without lateral bar is about 1.5 times higher than that of NC beams. 3) New evaluation method was suggested in this study.

View full abstract

This paper discusses experimental results on the seismic performance of RC frames retrofitted by additional steel braced frame using a hybrid connection and conventional connection. The ultimate strength and ductility of the hybrid connection are compared with the conventional connection, and test results of ten specimens retrofitted by two type connection were examined under cyclic loading tests. The main finding is that the proposed hybrid connection can satisfy the demand of high energy absorption for retrofitted RC frames under large seismic excitations. The hybrid connection obtains superior structural performance in viewpoint of strength and ductility in comparison with conventional connection.

View full abstract

Flexural-torsional buckling strengths are approximately calculated by using compressive strut model and sandwich model. In the compressive strut model, flexural buckling strengths of the flange of H-shaped beam-columns are calculated so as to obtain the flexural-torsional buckling strengths. The sandwich model is used to calculate the flexural-torsional buckling strength of beam-columns subjected to axial compressive force and equal bending moment at both ends. The moment-axial force interaction curves obtained in this study and those from the design formulas proposed by authors are compared, taking the moment ratio and slenderness ratio as analytical parameters.

View full abstract

In this research, in order to clarify the coupled instability behavior of H-shaped steel beams under the bending shear stress, the cyclic loading tests was carried out, with a comparatively large web plate slenderness. As a result, the useful factor for coupled buckling design method of H-shaped steel beams was proposed.
This method can treat systematically lateral buckling, local plate buckling and those coupled instability behavior. Its attention is paid to elastic lateral buckling strength and elastic plate local buckling strength. Characteristic of buckling behavior, coupled effect and range of coupled instability were clarified using both buckling strength ratio.

View full abstract

In order to adapt to anchor bolts of exposed bases in steel moment frames, we propose a hysteretic damper of tubular shaped steel for use in a bolt joint. The damper is expected to deform stably over a large plastic deformation range after local buckling occurs in the tubular part. The present paper describes axial loading tests of the elemental dampers and cyclic loading tests of exposed bases with the dampers for purpose of development of the new device. The test results reveal the technical viability and optimal design condition.

View full abstract

The writer proposes a nonlinear shear force-deformation model for the panel zone within concrete-encased and concrete-encased-and-filled steel tubular column beam-to-column moment connections with a steel beam for predicting the elastoplastic behavior of the panel zones. The proposed model is based on a trilinear shear-deformation relationship for the steel tube superposed on one for the reinforced concrete element, where the total shear strength is equal to the sum of their strengths at identical deformation. The results predicted using the model are found to agree approximately with experimental results up to large shear deformation.

View full abstract

For rapid construction of concrete barriers against sudden terrorist bomb attacks, blast-resistant slabs composed of precast small elements such as thin plates and blocks, which were made of polyethylene fiber-reinforced concrete (PEFRC), were manufactured and used for contact detonation tests. The main results obtained are as follows: 1) the blast resistance of the 100-mm-thick solid-type slabs, which are constructed with thin plates or solid blocks, is almost equal to that of the 100-mm-thick PEFRC single slab; and 2) the hollow-type slabs composed of thin plates or hollow blocks possess better blast resistance than the single slab, because an element on the detonation side behaves as a sacrificial element in these slabs.

View full abstract