This research examined reinforced concrete girders which had been exposed to a chloride damage environment on the east coast of the main island of Okinawa Prefecture for 40 years, and had undergone severe chloride induced deterioration. The state of deterioration was analyzed by visual examination and material investigation before samples cut from the girders were subjected to static and repeated loading tests, and mechanical characteristic was examined on the basis of the deflection stiffness and strain properties of the salt-degraded reinforced concrete girders. In addition, sample girders which simulated the progression of deterioration, based on the state of deterioration of the bridge, were repeatedly tested to destruction in static and repeated loading tests, to indicate the failure characteristics of reinforced concrete girders which had been corroded under extreme conditions.
Sea salt spray, which consists of small particles of seawater, harms long term durability of concrete structures at coastal areas due to its generation from the interaction of sea waves and, wind. In this study, a comprehensive numerical scheme in which waves, wind, and sea salt spray generation and transport mechanisms coupled together, is proposed with a wide range of applicability to real structures problems. Field measurements were also carried out to confirm the validity of the numerical results. Furthermore, through the numerical scheme a numerical model that can treat generation and transportation of sea salt spray considering coastal waves and atmospheric winds was proposed. It was confirmed that numerical results of sea salt spray concentration agree with the filed measurements data. Long-term sea salt spray distribution affected by waves and wind condition was estimated by the computational scheme of sea salt spray of this work.
Deployable reinforcement cage using PC strands as longitudinal reinforcement has been developed in order to improve construction of bored cast-in-place concrete piles in narrow space or small overhead clearance. Different from the similar construction method of bored cast-in-place pile using strands that has been invested previously, in this research, as pre-grouted PC strands were adopted, the construction of PC pile has been made possible. The cyclic loading tests of normal reinforced concrete (RC) pile, strand RC pile and strand prestressed concrete (PC) pile were performed to investigate flexure behaviors and examine applicability of the existing design method on skeleton curves. The results show that the strand RC and PC piles had higher yield displacement and smaller energy absorption than those of the normal RC pile. It is found that the strength and deformation properties of the strand RC and PC piles can be evaluated by the existing design standard which is based on Bernoulli-Euler theory. Besides, since the reinforcement ratio of the longitudinal strands becomes smaller when high tensile strands are use, the minimum required ratio of the longitudinal strands is also examined in this paper.
In this study, the estimating method for ground anchors’ tension were considered using X-ray stress measurement to measure the surface stress on the bearing plate which is one of the constituted member of the ground anchor. In investigate about the relationship between the tension and the surface stress on the bearing plate, at first, the way that three dimensional finite elements method was used, and, these relationships were revealed by using strain gages. The second, formulations that estimate ground anchors’ tension were made from using these strain gages’ results. At last, correcting functions were derived to match measuring data between using the X-ray and strain gages, and that formulations were completed to include these functions. As a result, ground anchors’ tension were estimated within about 15% accuracy from measuring the surface stress on the bearing plate if the thickness is 20mm.
In order to evaluate the resistance of chloride ion penetration into mortar mixed with granulated blast furnace slag fine aggregate (BFS), the diffusivity of the mortar specimens mixed with several types of BFS produced by seven manufacturers were examined. In addition to this, the effects of the grain size and amorphousness of BFS on the diffusivity of chloride ions was investigated. Furthermore, the improvement mechanism of the diffusivity of chloride ions in mortar using BFS was discussed on from the point of view of porosity, microstructure and fixation of chloride ions. As a result, it was concluded that the improvement of the diffusivity of chloride ions in mortar using BFS was attributed mainly to the densification of the interfacial transition zone of the BFS due to reactions.
We conducted a life span simulation for a LNG underground tank by reproducing actual construction process in a three dimensional multi-scale integrated analysis. Thermal stress at early age, control of cooling temperature after enclosing LNG, moisture transport and seismic action in long term operation etc. have been evaluated unitarily in order to predict continuous response behavior more precisely in time domain. Through this study, the validity of the conventional design method was verified. In addition, the multi-scale integrated analytical technique showed potential to be used practically not only for design verification but also for maintenance in the near future.
Requirements for concrete structures are changing to meet emerging needs such as higher earthquake resistance. Those requirements include higher densities of reinforcement, but they could lead to defective construction due to inadequate compaction. It is obvious that reinforcement patterns influence concrete compaction, but such influence is difficult to evaluate quantitatively. Constructors expect designers to develop designs that include reinforcement patterns allowing for concrete compaction and to specify concrete slump requirements that take concrete compaction into consideration. Even with the latest technology, however, it is difficult to determine reinforcing bar diameter and spacing requirements, taking concrete compaction into account. Constructors, therefore, have to make a concrete compaction plan for achieving an adequate degree of filling by an appropriate method of compaction while meeting the specified reinforcement pattern and slump requirements. Since, however, quantitative evaluation of compaction is difficult, appropriate concreting planning is no easy task. This paper introduces a newly developed measuring system designed for quantitative evaluation of compaction completion energy, which consists of the energy necessary for concrete to flow through the spaces between reinforcing bars and the energy needed to compact concrete, and proposes a method for evaluating the compactibility of concrete flowing between reinforcing bars by using the newly developed system.