In this study, Powder X-ray diffraction (XRD)/Rietveld analysis, which has been utilized in recent years as a technique for quantifying the crystal mineral phase of cement and cement paste, was applied to quantify the reaction rate of cement minerals and the proportions of hydration products. Its accuracy and availability was verified by comparing with the following properties, reaction rate of minerals by internal standard methods of XRD quantitative analysis, rate of heat liberation of cement by conduction calorimeter and amount of combined water of cement paste. Experimental factors were three types of cements, three levels of W/C, three levels of mixing/curing temperatures. The results showed that XRD/Rietveld analysis can quantify the hydration rates and products of cement paste with high accuracy.
The interior of a large-size concrete member is heated and cured under high-temperature condition in early ages by internal storage of the heat of cement hydration. This temperature rise of concrete is numerically predicted using the mathematical model for cement hydration and microstructure formation, which has been proposed in our previous study. The hydration rate is predicted using the model. The heat of cement hydration is calculated with its hydration rate. The heat transfer inside the concrete member is simulated by solving a heat conduction equation with heat of cement hydration as the heating element. The predicted concrete temperatures are compared with the concrete temperatures measured in various types of concrete members. The simulation system proposed in this study is useful for predicting the temperature rise of concrete member.
High-strength concrete using various types of cement, considering mix design and real environmental conditions, was studied on the cracking potential. As a result, behavior of autogenous shrinkage in portland cement concrete showed a change from shrinkage to expansion at the temperature peak under temperature-history cure, but it remained in shrinkage in the blast furnace slag cement concrete. The cracking potential in concrete subject to temperature-history cure was higher than that in concrete under other conventional cure, and stress strength ratio was independent of cure condition. An estimation method for the age of cracking was shown by evaluating strain of reinforcing bar on tensile loading.
The purpose of the experiments in this paper is to clarify the physical and dynamic properties of the concrete at seventy years age which was suffered from atomic bombing at 1945 in Hiroshima. The compressive strength and Young's modulus of the concrete by the side of an atomic bombed place showed the value lower than the other concrete specimens. The coefficient of water absorption of the concrete was very high and it became clear that there was almost no freeze dissolution resistance. And neutralization of concrete was progressing very unusually. Moreover, as concerns the concrete by the side of an atomic bombed place, neutralization from the outdoors side was higher than that of inner side. It is considered to have influenced the above-mentioned examination result greatly that especially concrete temperature rose in 500 degrees C-750 degrees C. The necessity for performing carefully the maintenance of the RC building which was suffered from atomic bombing was shown by this research.
In this study, the mortar (structural mortar) of which aggregate volume is increased by optimizing the grading of fine aggregate in order to control drying shrinkage was developed. It is expected that sure cast without segregation is possible by applying this mortar to structures instead of concrete because the segregation resistance of mortar is higher than that of concrete. To develop structural mortar, first, the grading of fine aggregate for structural mortar was optimized by aggregate test, and its advantage was confirmed by mortar test. Next, it was confirmed that the drying shrinkage strain of structural mortar is nearly equal to that of concrete. Furthermore, the prototype of structural mortar was manufactured at a ready-mixed concrete plant and was cast into a wall-like form, and it was confirmed that the compactability and the segregation resistance of structural mortar is high.
A test method for resistance of waterproofing membranes to the penetration of roots at lap joints was developed on the basis of the behavior of bamboo grass tips to penetrate the membrane. The resistance of the membranes at lap joints having non adhesives and different bonding strengths was determined as a measure of its vulnerability to root penetration. Results from field tests indicated that bamboo grass tips (rhizome) easily penetrated lap joints of non-adhesive membranes. Hence it was evident that waterproofing membrane systems having non-adhesive overlapped joints do not provide adequate resistance to root penetration of the membrane. The resistance to root penetration is dependent on the adhesive strength of the lap joint. The specimens with lap joints having lower bonding strengths were readily penetrated by the rhizome. From this knowledge, a test method was developed to assess the expected resistance of membrane lap joints to the penetration of a needle. The needle, in essence, emulated the shape of bamboo grass tips. Thereafter, the test result from field test on the resistance of membrane to the penetration of roots were compared to those obtained from tests using a penetrating needle. Results from the penetrating needle test indicated that the resistance measured at a 10-mm displacement of needle was effective means of evaluating the resistance of membrane lap joints to the penetration of roots.
In a portfolio seismic loss analysis for buildings located in a wide area, it is important to estimate the effect of damage correlation, because a probability mass function of physical loss such as the restoration cost of buildings undergoes effect of correlation except mean value. This paper proposed a practical prediction method for the loss probability mass function of buildings located in a wide area due to earthquakes. The method takes damage correlation into account, which depends on the relative distance between buildings, and a numerical technique based on the theorem of total probability was employed. Numerical results by the proposed method were verified by Monte Carlo simulation, and a good agreement was obtained. A loss probability mass function of 10 buildings located in the Tokyo area due to a scenario earthquake was evaluated for applicability.
For predicting the strong ground motions from scenario earthquakes, two theoretical equations and one empirical equation are applied to evaluation of the three parameters out of the following six parameters: the area of the entire fault, the seismic moment, the averaged stress drop, the area of the asperity, the stress drop on the asperity, and the amplitude of the acceleration source spectrum in the short-period range. We carried out the dynamic simulation of fault rupturing of rectangular crack models and asperity models to verify the empirical equation relating the stress drop on the asperity and the size of the asperity to the amplitude of the acceleration source spectrum in the short-period range. The background of the fault was found to generate the short-period seismic waves less than the asperity of the fault as granted in the current researches. But, some of our results showed that the background generated the short-period seismic waves as much as the asperity did.
A rocking pillar base isolation system applicable to masonry houses in developing countries was proposed. Masonry walls solidified by supplemental RC members are supported by rocking pillars having spherical caps at both ends. This paper describes structural scheme of the base isolation system and presents results of vibration tests of a 1/4 scale specimen of the structural system. Seismic performance of the new system is discussed.
The authors have studied phenomenon of indoor seismic casualty from a probabilistic standpoint. The purpose of this paper is to unveil a relationship of estimation formulas for seismic casualty between an actual model using hypergeometric distribution and an approximate model using binomial distribution. The problem is solved comparing the differences of probability values between the two models to human density calculated the number of human per the floor space. As a result, it was found that the differences are extremely small under most indoor spaces including residences. In conclusion, the approximate model using binomial distribution has high usability compared with the actual model using hypergeometric distribution.
We learned from the 1995 Hanshin Awaji earthquake that most of the death toll arised from many vulnerable wooden houses collapsed by seismic ground motions and seismic strengthening wooden houses is the highest priorty strategy for preventing death. This paper discusses effective strategy of seismic strengthening houses for reduction of death toll. In the first part, we construct the equations by which the death toll in districts can be estimated with considering the rate of seismic strengthening that is increased by rebuilding or seismic repairing, and the negative effect as aged deterioration of house. In the second part, we apply the equations to the area of 4 prefectures in Tokai district and estimate the time variation of death reduction in order to figure out the effect of some kinds of seismic strengthening strategies. As a result we simulated that when the seismic repairing of houses is planed in target districts the strategy giving priority to vulnerable houses is more effective to decrease the death toll than any other strategies having no priority on structural strength of house.
This paper describes the plasticity model which can take account for gradual plastification and hardening for steel beam-columns subjected to axial force and biaxial bending moment. The beam model composed of fibers, in which plastic regions expand in one direction, is developed. It is clarified how the basic equations (the yield function, the plastic flow rule and the hardening rule) should be formulated in bilinear stress-strain relation using an additive decomposition technique of the total displacement for the beam model. Finally, numerical examples are shown to examine the performance of the model with the return mapping algorithm and a convenient evaluation method of the plastic regions.
The Response of reinforced concrete wall-frame structures subjected to earthquake motion was investigated by testing a full-scale six-story specimen on the world's largest tri-axial shaking table “E-Defense”. The test specimen consisted of three parallel three-bay frames in the longitudinal direction. The central frame had a multi-story structural wall in the center bay continuous from the 1st to the 6th story. To be able to monitor shear force carried by the structural wall at the 1st story, 3-component force transducers were instrumented between foundation beams and the shaking table. The test specimen was subjected to a series of strong earthquake motions and finally nearly collapsed caused by shear failure of short columns and shear slipping failure of the structural wall at the 1st story. This paper outlines measurement plan of 3-component force transducers and also examines the shaking table test results for rigidity at the bottom of the wall, restoring force characteristics of the structure, and measured shear force carried by the 1st-story structural wall.
Ten 1/3-scale precast prestressed concrete columns under anti-symmetrical loading were tested. Experimental parameters were axial load level, prestressing force level, shear reinforcement ratio and grouting. The flexural capacities were evaluated by the ACI equivalent rectangular stress block and the plane section assumption. The evaluated results agreed well to the test results. An evaluation method of column shear strength based on the shear-friction model was proposed. One specimen lost its axial load capacity by shear failure, which could be predicted by the method. However, an appropriate value for the shear-friction factor μ should be discussed further. Load-deformation curves were analytically derived by specifying the decompression moment and the maximum load carrying capacity.
A standard base plate connection is commonly adopted for column bases of low-rise steel structures. In most practical design, the column bases are likely covered by shallow concrete slab to hide the bolted base plate and level the slab. Cyclic loading tests are conducted, and the effects of thickness and shape of slab are investigated with reference to the standard base plate connection. That experiment showed that shallow embedded-type column base's strength and stiffness was better than exposed-type's. But its strength decreased at large deformation area. So we reinforce the column base with steel bars because we intend to prevent its strength from decreasing. The test show that the covering slab and steel bars contributes to both the initial stiffness, ultimate strength and strength decreasing.
This paper presents results of fullscale tests conducted to evaluate deformation capacity and failure mode of welded beam-to-column connections adopted in moment frames for early highrise buildings around 1970s. Test specimens are designed and fabricated to reproduce the moment connections at that time according to the welding details and steel work procedures. Loading tests are conducted by cyclic loading protocol to simulate the response of frames subjected to long-period ground motions. The obtained capacity of specimens evaluated by cumulative plastic rotation satisfied deformation demand predicted by numerical response analysis.
This paper considers effects of vertical load on seismic damage prediction of component members in strong-column type steel moment frame. Initially, the relationship between type of collapse mechanism and vertical load on beam is shown. Secondly, earthquake response analysis is carried out in order to identify damage of member. The result shows that the mechanism that has a plastic hinge at the center of beam causes more serious damage than the other mechanisms. Finally, a damage estimate method considered effects due to vertical load is proposed. The applicability of the proposed method is confirmed through comparison with the analytical result.
Buckling behaviors of open section steel members are generally divided into two styles which called local buckling and overall buckling depending on the assumption of boundary condition. However, local buckling and overall buckling may happen at the same time when thin plates are widely used in steel structures, and somewhat overestimation will cause without considering the interaction of each other. As the results shown in the previous studies, buckling behavior may be dominated by coupled buckling. Therefore, it is important to solve this problem by theoretical method especially for seismic design. This paper uses an energy method of analysis to study coupled buckling of H-shaped beams under bending shear. Moreover, on the basis of the theoretical analysis results, the evaluation of coupled buckling strength is proposed by using parameter of geometrical shape of H-shaped member.
This paper describes an experimental study on the compressive strength of the confined concrete at high temperature. The tests were conducted on cylindrical confined concrete specimens subjected to temperatures of 20, 200, 400, 600 and 800 °C. The coarse aggregate were crushed andesite. Test results indicated that there are straight-line relationships between the first invariant of the stress and the second invariant of the deviatoric stress in the confined concrete strength at high temperature. The Drucker-Prager failure criterion is suitable for concrete at high temperature under multiaxial stress states.