It is easily imagined that there might exsist some effects of reflected wave from formwork on vibratory compaction of concrete. However detailed and reliable evidences of the effects have not been reported. In the present paper, analytical and described. In the analysis, we obtained resultant acceleration of direct and reflected waves based on the function for the wave spreading in the concrete from an internal vibrator. Illustrations of the calculated results showed that when the formwork consisted of flat plates, the effect would be less than that when it was cylindrical. The measurement of acceleration amplitude for the flat plate formwork implied the interference between direct and reflected waves near the plate. Concerning the materials of formwork, steel had naturally more effect on the reflection of the vibration than wood, and unexpectedly, lining of vibration proof hard rubber showed an intermediate effect between stell and wood, which might possibly be attributed to the hardness and smoothness of the surface.
There are several aspects related to ASR problem in concrete structures which have not been fully studied. One of these problems is the structural effects of ASR on reinforced concrete (RC) structures. For example, the characteristics of internal stress of ASR-ffected RC members under sustained load is not fully explained. The first object of this study described here is to investigate the characteristics of internal stress of ASR-affected RC beams and RC columns under sustained load. The second object is to evaluate the structural effects of concrete surface coating on ASR-affected RC beams and RC columns under sustained load. In this paper, laboratory test results and some structural analysis results are presented, and also some discussios are presented.
The purpose of this study is to establish a sectional analysis of a beam considering a tension softening curve and its size effect of steel fiber reinforced concrete (SFRC). In this paper a method to estimate a tension softening curve of SFRC was proposed, which is based on an agreement between both load-deflection curves measured and calculated by the sectional analysis. Validity of the present method was investigated from a comparison between both load-deflection curves measured and calculated by the cohesive force model analysis into which the estimated tension softening curve was introduced. Futhermore a size effect rule of the tension softening curve was induced based on a fracture mechanics concept, and its applicability was experimentally verified using SFRC beams of various sizes from a comnarison between both load-deflection curves measured and calculated.
In order to perform a highly reliable thermal stress analysis, it is important to consider analysis parameters as random variables which depend on materials in use, their mixture, environmental conditions, etc., and to evaluate their effects on thermal stress as well as on strength of concrete. Focusing on a slab-concrete, this paper investigates a sensitivity of thermal cracking index with respect to a variation of the parameters by using Monte Carlo simulation. Furthermore it is examined how a coefficient of variation of the parameters affects the relationship between a thermal cracking index and a probability of cracking.
The effective utilization of converter slag has not been found as yet. It is a serious environment problem for steel industry. The purpose of this study is to use dephosphorized converter slag as a construction cementation material, which is improved by a calcination and decreased in free CaO of dephosphorized slag, and it was clarified the properties of mortar of cement mixed with improved dephosphorized slag. Though strength of mortar replaced the cement by 10-30 wt% of improved dephosphorized slag was low at shorter ages, but it was expected to increases the strength at later ages. The adiabatic temperature rise was showed lower than OPC mortar. These properties was contributed by the existence β-C2S in dephosphorized slag, a product of C-S-H gel was confirmed in the hydrates. Change in length by dial gauge showed little expansion. The improved dephosphorized slag is a promising cementation material for concrete.
The triaxial testing equipment which is capable of non-axisymmetric loading was developed to investigate damage process under strain softening regime. In these tests, the discontinuous surfaces (damaged zone) can be inspected clearly in the one plane as two dimensional fracture. After triaxial tests, the epoxy resin with fluorescent paint was injected into specimens and the graphic image data of damaged zone were processed to determine the range of damaged zone. In this paper two items are discussed, (1) The Mohr-Coulomb's failure criterion is connected with the actual failure phenomena of concrete considering force transfer mechanism between aggregates. (2) The formation angle and range of damaged zone is quantitatively determined.
In recent years many reinforced concrete viaducts have been used for important traffic facilities, so it is vary important to evaluate their behavior during a big earthquake. In this analysis the interaction between the structure and the ground is taken into consideration. The purpose of this study is to evaluate the behavior of 2-story reinforced concrete viaduct during strong earthquakes and to consider the effect of ground characteristics on the dynamic behavior of such structures using the sway-rocking ground spring model. The following results are described from this study : (1) the increase of natural period of the structure which is accompanied by the damage is recognized, (2) the significant difference of the behavior of the structures is recognized even if they are built on the site of the same ground classification, and (3) the dynamic response of structure is influenced by the characteristics of the input earthquake waves.
Deterioration of light-weight aggregate concrete due to frost damage is heretofore considered to be caused by deterioration of a part of cement pastes. But it is very difficult to explain the resistance to freezing and thawing of high-strength light-weight aggregate concrete consist of fine cement pastes and light-weight coarse aggregates with these water content of several percent mainly depends on only a part of cement pastes. This paper describes deterioration of high-strength light-weight aggregate concrete due to frost damage depends on not deterioration of cement pastes but that of light-weight aggregates.
In the previous paper, “Reversed cyclic loading failure” was proposed. Under reversed cyclic loading, shear resistance mechanism repeats temporary disappearance and rebuilding. This failure occurs when shear resistance mechanism is not rebuilt after the temporary disappearance. The temporary disappearance occurs because of the opening and closing of cracks under reversed loading. And this means the proposed failure mode is peculiar to reversed cyclic loading. The impossibility of rebuilding after the temporary disappearance is considered to be affected by the stiffness deterioration of cracked concrete due to reversed cyclic loading. Therefore, the occurrence of this failure mode is estimated not to be defined by the maximum value of shear load but to be defined by some index which is connected with the stiffness deterioration of cracked concrete. This failure mode has been considered to be a kind of shear failure because of the shear deformation increase when it occurs. The purpose of this paper is to clarify the difference of failure mechanism between “Reversed cyclic loading failure” and “Shear failure”. For this purpose, shear bending cyclic tests were carried out, in which the deformation behaviors of beams which were failed by shear failure or reversed cyclic loading failure were measured in detail. On the basis of the comparison of the deformation behaviors, the difference of failure mechanisms was confirmed.
The appearance of concrete walls or concrete structures change with the distance between the viewpoint and the place where the concrete stands. Seventeen architectural concrete specimens of nine hundred mm square with a variety of surface finishing were psychologically measured at the standpoint where the change of appearance occurs. Lightness and chromaticness were measured at every distance. The finding is that the concrete with smooth surface does not give people change of impression with distance, whereas the concrete with textured surface does people change of impression with distance. At the distance of fifty meter from the specimen, concrete with the face soft, smooth, light and abundant is felt comfortable. And rating scales with roughsmooth, lightheavy and abundantpoor feeling are corre-lated with lightness
In order to verify the mechanical characteristics for a composite bridge column consisting of steel pipes with outer ribs, precast concrete segments and filledin concrete, we conducted a cyclic horizontal loading test. The results of the test are : 1) This structure has equivalent ultimate strength and superior ductility as compared with a conventionally reinforced concrete structure. 2) The steel pipes with outer ribs are finely adherent to the concrete, and the observed strain distribution of cross sections are linear to the distance from neutral axis. 3) Displacement and strength capacities in yeild and ultimate states can be computed taking into account steel pipes as equivalent rebars.
In the assesment of a firedamaged building built in reinforced concrete, it is very important to estimate the residual bearing force of each member after fire. Accordingly, in order to estimate the residual bearing force, the heated temperatures in concrete must be grasped. The authors calculated the heated temperatures in onedimensional concrete members after fire by easy method and compared calculated values with experimental ones. And moreover, they analyzed the quadratic regressions with the former values and made the presumed equations of heated temperature distributions. In conclusion, they presumed the residual bearing forces of the members using the equations
Influence of mixing temperature on the fluidity of mortar was investigated with special emphasis on mineral composition of cement. Fluidity of mortar made from the cement containing 70 % belite was compared with that made from other cements containing various amounts of belite. Hydration of cements, adsorption of super plasticizer and zeta potential of cements were stuided for analysis. Influence of temperature on mortar flow and flow loss decreased with increasing belite content and decreasing interstitial phase in cements. This is explained by increase in zeta potential, decrease in BET specific surface area, and decrease in ettringite content after initial stage of hydration.