This paper discusses a measuring method of the premature stiffening zone formed at the top surface after placing of high-strength mortar with a water-binder ratio below 0.2. In this experiment, first a measuring method of the premature stiffening zone was devised by using penetration resistance measurements. The penetration resistance distribution, resistivity distribution and moisture content measurements of mortar specimens simulated high-strength concrete with a design strength of approximately 150N/mm² were then conducted to assess the appropriateness of the measuring method of the premature stiffening zone.
The results reveal that the measuring method was applicable to determining the occurrence and approximate depth of premature stiffening zone for high-strength mortar.

View full abstract

The strength development of concrete using various cement, i.e. ordinary portland cement, moderate heat portland cement, blast furnace slag cement type B etc. in structure are investigated based on the data of some experiments carried out in past time.
The purpose of this paper is to consider relationship strength development of core specimen from 28days to 91days and mean temperature, and to establish the strength correction value of concrete.
The following results were obtained;
The strength development from 28days to 91days of core specimen was about 5-10N/mm² ranges regardless of kinds of cement.
The compressive strength of core specimen at 91days was expressed by function of strength of core specimen at 28days and mean temperature.
The strength correction value of concrete was suggested.

View full abstract

Architectural concrete in Japan has been valuated from the viewpoint on design in the foreign countries, because the texture of the concrete using painting form is smooth liking a mirror and lucid, and the image is stern. However in the present circumstances, there were extremely few reports on quantitative analysis of the influence of the surface properties on the image of colored architectural concrete. In this study ,as a basic examination, the concrete test pieces was made by using color sand and pigments. The influence on the gloss and the color of concrete was experimentally examined using materials and forms. And using those test pieces, the image tests were carried out. The influence on the image of colored architectural concrete was experimentally examined using the surface properties of concrete. According to the result, the correlation between the surface properties of colored architectural concrete and the materials was clarified, the images of colored architectural concrete were extracted, and the relation between the surface properties and the image was quantified.

View full abstract

We show experimentally that retroreflective materials reduce the reflected heat. They can be used as the building materials to reduce urban heat island effect. We measure the retroreflective component of retroreflective materials for the first time. The procedures are as follows. First, the total reflectance is deduced from the thermal measurement. Then, the reflectance without retroreflection is measured by using a spectrophotometer with the integrating sphere. Finally, the retroreflective component is calculated by subtracting the latter from the former. The measured retroreflective components are about 10 percent for bead-embedded type, and 20 percent for capsule-lens type.

View full abstract

The uncertainty exists in loads acting on a structure. In general, this uncertainty contains both aleatory uncertainty and epistemic uncertainty. The former is virtually unavoidable, the latter is caused by the limited ability and/or the imperfect information and knowledge. Thus, the load factor derived from aleatory uncertainty is invariable, while that derived from epistemic uncertainty can be decreased when more reliable model or method is applied. This paper shows two examples of calculating the load factor when aleatory uncertainty and epistemic uncertainty are separated.

View full abstract

In order to avoid the difficulties involved in searching the design point by iteration using the derivatives of the performance function, a principle shortcoming of reliability methods based on the first-order reliability method (FORM), an explicit fourth-moment reliability index, which is derived from the fourth-moment standardization of performance function, is presented and investigated in the present paper. The proposed formula is simple, and does not require integration or solve nonlinear equations, which are necessary in current used formulas. Through the investigations of the present paper, it is found that the third-moment method can be significantly improved by the proposed simple fourth moment reliability index and the fourth-moment reliability index has sufficient accuracy as a reliability index based on the fourth-moment standardization of performance function.

View full abstract

A practical effective stress-strain model of sand is presented in which only the soil parameters directly obtained from a common site investigation and a laboratory test, i.e., G-γ, h-γ curve and liquefaction curve, are used as input parameters. A key mechanism simulating liquefaction and cyclic mobility behavior is modeled based on the accumulated damage concept for pore pressure generation with a generalized hardening model for shear behavior. The proposed model can simulate reasonably well the stress strain behavior of hollow cylindrical specimens subjected to earthquake loading.

View full abstract

The authors proposed a seismic retrofitting method by attaching CES frames consisting of only steel and fiber reinforced concrete to an existing RC building from the outside. This method has more advantage compared with previous proposed other seismic retrofitting methods that is not necessary to install the braces because CES frames in itself have excellent seismic performance. The purpose of this study is to investigate the seismic performance of RC frame retrofitted by CES frame, particularly to examine the behavior of unified sections by existing RC and strengthening CES. The dynamic loading test was carried out on four frame specimens, one RC frame and three retrofitted frames, with an experimental parameter of the amount of anchor used to connect the CES members to the RC members. This paper outlines the experimental program and shows that the proposed retrofitting method can improve the seismic performance of the existing RC frames and the ultimate strength of the retrofitted frames can be calculated by using the cumulative strength method.

View full abstract

Nonlinear soil properties as well as bedrock outcrop strong motions are back-calculated using 4-depth downhole strong motions recorded at the Kashiwazaki-Kariwa nuclear power plant during the 2007 Niigata-ken Chuetsu-oki earthquake. Adopted in the inverse analysis are genetic algorithms (GA) combined with a 1-D equivalent-linear response analysis in which strain-dependent damping ratios are assumed in the frequency domain. The inversion results show that the surface layer down to a depth of 70 m exhibited strong nonlinear behavior with a shear modulus ratio down to about 0.01 and a damping ratio up to about 35%.

View full abstract

Simplified theories are proposed for seismic peak response evaluation and preliminary design of buildings with bilinear oil dampers. 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 required, 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

It is important to predict the distribution of damage for the seismic design purpose. In this paper, in order to evaluate the damage distribution of weak-beam type multi-story frames influenced by the yield of column bases, an elasto-plastic response analysis on fishbone-shaped frames was carried out. The damage distribution is influenced by the distribution of the strength and the stiffness ratios of beam to column. From results of analysis, a basic rule which governs the damage distribution of realistic weak-beam type multi-story frames was proposed in a simple formula.

View full abstract

Collapse damages of suspended ceilings during recent severe earthquakes are focused as mentioned in references 3), 6). In order to establish aseismic design method of suspended ceiling, static lateral loading tests are conducted for both conventional and grid system ceilings that are partial models made of real components. Newly developed aseismic stiffeners are applied in the models and their availabilities are confirmed through the tests. Finally, evaluation formulas of buckling strength, which are based on Euler's formula, for combined bracing system are proposed.

View full abstract

The seismic breakdown probability of a building requires several parameters: the event probability of earthquakes, the variation of ground properties, and the seismic performance variation of a given building. In this paper, we discuss the influence of the ground property variation to the maximum displacement response of Japanese wooden houses. Monte Carlo simulation is employed to consider both the variation of ground properties and the seismic performance variation of a given building. As results, the variation coefficient of surface subsoil amplifying characteristic is 0.3 - 1.0 under 5.0Hz. The variation coefficient of surface layer has a large effect on the estimate values of maximum displacement responses by the result of Monte Carlo simulation.

View full abstract

Seismic performance of 72 two-story wooden houses build in Sapporo was grasped from seismic diagnosis that considered snow depth on roof. Photos and drawings of the wooden houses for seismic diagnosis were obtained from an outside walls renovation company. Seismic reinforcement for the wooden houses was estimated from evaluation of the seismic diagnosis. The results indicate as follows: for the seismic diagnosis as the snow depth 0m, the evaluations in lots of the wooden houses were more than 1.0. As the snow depth more than 1.0m, the evaluations were small so that the seismic reinforcement is needed. Reinforcement for capital and column base by steel plates was assumed as the seismic reinforcement. To have improvement effect for the wooden houses having poor seismic resistant in the seismic reinforcement was clarified.

View full abstract

A study of carbonate stress corrosion cracking in rebars has been carried out in the laboratory to investigate the cause of cracking/fracture that actually occurred in rebars in ASR-affected concrete. Cracking was reproduced in potassium carbonate-sodium bicarbonate solutions in concentrations realistic in ASR-affected concrete. The specimens were maintained at potentials that promote cracking. The occurrence of cracking in the simulated system shows a high possibility that the carbonate stress corrosion cracking is the cause of the failure in service.

View full abstract

The aim for this study is to clarify the shear stress transfer mechanism on the concrete crack surface. In the previous paper, it was confirmed that the stress softening was occurred on local crack surface by the authors experiments. However, the shear stress transfer models considering this phenomenon haven't been constructed. Therefore, it is needed to be proposed such a shear transfer model, and authors tried to do it. The proposal model is based on the contact theory in two-dimension. Moreover this model and other previous models are compared with the experimental curves in order to be verification of the models adaptation. In this paper, the formulations of the proposal model and results of comparing are presented. As the result, it is concluded that the proposal model can fit authors experimental results much better than any other previous models.

View full abstract

In this research, fiber model, which is able to take account of volume change of concrete, is proposed. And using the proposed fiber model, bending behavior of reinforced concrete (RC) column with ultra high-strength concrete is simulated with parameters of axial force ratio, reinforcement ratio, yielding stress of rebar, and the amount of autogenous shrinkage. As a result, autogenous shrinkage make the very small difference in maximum bending moment of RC column, and the autogenous shrinkage affect much on the curvature at the yielding of compressive rebars, slightly on the curvature at the yielding of tensile rebars, and on the point which compressive core concrete attains the ultimate bending strain. Therefore, in the case of allowable stress design, reinforced ultra-high strength column is allowed only for very small external moment. But according to the results of numerical analysis, compressive yielding of reinforcement will not affect much on the performance of RC column when the combined stress of reinforcements of sustained loading with the stress produced by autogenous shrinkage is under allowable stress for sustained loading.

View full abstract

This study investigates the influences of shear-mode mullion-type walls on the performance of RC rigid-frames. To express shear-axial coupled motion occurred with shear failure of walls, shear-axial softening behavior was modeled using the theory of plasticity and the concept of failure surface contraction. Pushover analysis was then conducted to RC frames that have various combinations of column over-design factors and wall breadths to simulate response to the seismic load and collapse mechanism. Some frames with low column over-design factor showed partial collapse after shear failure of walls, while others showed more ductile mechanism. The results revealed how shear-mode mullion-type walls can affect the performance of RC frames with different configurations.

View full abstract

A series of cyclic loading tests were conducted on steel frames incorporating RC walls with large openings. The RC walls of these specimens were designed reflecting the design of the walls in an existing 14 story-condominium building, which mostly consist of spandrel and mid-span walls. Despite the large openings, the RC walls showed brittle behavior, but gave large initial stiffness and maximum strength to the system. The spandrel walls maintained substantial resisting capacity to large drift level. This force acting on the column lead to shear failure in one specimen designed in the Weak-column manner, but in the Weak-beam frame system, the spandrel wall increased the overall shear capacity, without causing any undesirable effect.

View full abstract

In this paper, the energy absorption capacity of a hysteresis damper installed in a damage control structure was investigated. The performance of a hysteresis damper is limited by its fracture. The method predicting the metal fatigue life is extended to apply to the evaluation of the life of dampers. However, the method based on the energy absorption is necessary for the earthquake-resistant design. The conclusions obtained from this paper can be summarized as follows. (1) The energy-based method to evaluate the ultimate performance of a hysteresis damper was proposed based on the results of the cyclic loading tests. (2) The characteristic of the distribution of the energy response of the damage control structure is clarified based on the results of the earthquake response analyses. (3) By using these results, the simple method to predict the energy absorption capacity of the damper was proposed.

View full abstract

The framed-tube structure consists of rigid moment frames in the perimeters and floors which provide lateral-support to prevent perimeter column buckling. When perimeter columns deform toward the outside of the structure, simple connections between floors and perimeter columns may rupture in tension. This behavior is simulated by static tests for laterally-supported columns, where lateral drifts are imposed at each story under the constant axial load. Drift mode shape, axial loading level, and the number of lateral-supports are varied. It is found that: (1) the test results are similar to the predicted response, (2) as the lateral-support strength decreases and as the constant axial load increases, the rupture of lateral-supports occurs at smaller drift demand level, accelerating the progressive collapse, and (3) when higher drift mode shape is imposed on the column with small lateral-support strength, the progressive collapse may occur at very small drift demand level.

View full abstract

Within three days immediately after earthquake fire often breaks out. When fire fighters cannot approach such a structure because of traffic congestion caused by earthquake, it is necessary to prevent somehow the structure from collapsing. Assuming that a steel building frame undergoes permanent relative horizontal story displacement due to an earthquake and it is subsequently subjected to fire, this paper has studied the ultimate temperature of the damaged structure. To this end, refined finite element analyses as well as a simplified theoretical analysis have been conducted. It is found that, although the damaged frames are apparently weakened in fire resistance due to earthquakes and their ultimate temperatures are more or less decreased compared with those of frames without damage, the reduction in ultimate temperature remains slight for the frames consisting of short columns (columns with slenderness ratio of 0.2 to 0.4) which are commonly used in seismic design in Japan.

View full abstract

The cylinder edge failure of the steel cone-to-cylinder socket connection subjected to uniform compression was investigated by means of experiment and FEM. The FEM analysis revealed the friction coefficient between cone and cylinder as well as the shape imperfections of the socket which well follow the experimental load-displacement curves. The previously proposed model for the yield load was found satisfactory, while the models for the full-plastic and ultimate loads were modified to Eason-Shield model which provides better predictions.

View full abstract

This paper describes the bearing strength of concrete filling in a steel column. Single or double tubular column specimens filled with concrete that have mechanical shear keys, were tested under compressive and tensile load. The test results verified that the width to thickness ratio of column influenced on the bearing strength of concrete filling in a steel column, and the influence of number of the mechanical shear keys, embedded depth of the inside column and eccentricity of the inside column were small. Local stress states near the mechanical shear keys were modeled and the yield condition by Mohr-Coulomb applied to the stress state. Based on the model, the equations of evaluating the bearing strength were derived and its validity was confirmed.

View full abstract

Steel columns embedded in reinforced concrete pile support live load under construction in the top-down construction method. Axial force supported by steel columns is transferred to reinforced concrete pile by shear resistance of stud connectors and bond resistance between steel and concrete. This paper describes transfer mechanism of axial force from steel columns to reinforced concrete pile. Based on the experimental results, parametric studies by FEM are conducted. Evaluation methods of axial strength and shear force distribution of stud connectors are proposed. The proposed methods are applicable to the evaluation of shear force distribution and axial strength.

View full abstract

In this study, three dimensional non-linear FEM analysis of beam-column joints for composite CES structural systems is conducted to verify applicability of the analysis method and modeling, together with examining the stress transferring mechanism for the CES joints. The analytical results show good agreement with the experimental ones on the story shear versus story drift response for the CES joints, namely it is found that the behavior of CES beam-column joints can be approximately simulated by the analytical method. It is confirmed that analyzed shear force in the outer concrete without steel are contributed as almost the same level as those in the inner concrete surrounded by the steel flange of the beam and column at the maximum capacity of the beam-column joint. It is also shown that the ultimate shear strength of the CES beam-column joints can be evaluated by a method based on the AIJ design standard for SRC structures.

View full abstract

Bending tests of friction type high strength bolted joints at elevated temperature are conducted in order to obtain the relationship between bending moment and rotational angle of joints. Steel beam joints fastened by high strength bolts have rotational capacity under elevated temperature, because high strength bolts do not fracture at temperature above 500°C while shear deformation of bolts are less than the diameter of bolts. Bending deflection behavior of steel beam joints is approximated by the relationship between shear force and shear deformation about high strength bolts.

View full abstract

The paper is intended to summarize findings from high-temperature tests on headed stud shear connectors conducted as part of a study on the fire resistance of composite beams. Two headed stud shear connectors on a H-shaped steel beam are embedded in two types of slab models, representing a reinforced concrete slab and a composite slab with profiled steel decks, respectively. The test parameters other than model configurations include strength of concrete, level of shear loading, and heating conditions. A total of sixteen models were tested. It is found that the most crucial design parameter is the temperature at the bottom of a headed stud shear connector. Based on the test results, a new formulation is proposed to calculate with a good accuracy the shear capacity per stud only taking account of the heat-induced degradation of steel / concrete materials.

View full abstract