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The seismic performance of a reinforced concrete pier structure depends greatly on the plastic hinge region at the base of the pier. To improve the plastic hinge region of the structure, we propose using ultra-high-strength fibre-reinforced concrete (UFC) IntroductionIn the event of bridge damage following a major earthquake in which the concrete of reinforced concrete piers supporting the superstructure is crushed, the capacity to retain flexural strength and axial force is diminished, thus reducing the serviceability of the piers. In order to establish a system for early post-quake relief and recovery, earthquake damage must be minimized even in the event of a major earthquake. There is also a considerable need for damage-free bridge pier structures that can be used in locations where post-quake inspection would be difficult, such as bridge piers in river channels and piers located on median strips. It is generally known [1,2] that if a reinforced concrete pier with a rectangular cross-section is subjected to seismic forces in two horizontal directions and in the vertical direction, the ductility of the pier is lower than in the case where only one direction is considered. In order to ensure the post-quake serviceability of reinforced concrete piers, it is important to prevent crushing failure of the concrete even under earthquake loading in two horizontal directions, where damage processes are complex.To address these needs, the authors propose a reinforced concrete pier structure made from ultra-highstrength fibre-reinforced concrete (UFC), a concrete-based material with high compressive and flexural strength, in the form of precast formwork constituting the base structure of the pier (hereinafter referred to as "UFC piers") [3,4]. The authors have also demonstrated that the proposed structure has high ductility with respect to external forces acting in two directions [5]. The basic idea behind this pier design is to increase the strength of the concrete cover in the plastic hinge zone by using UFC precast formwork. The concrete cover made of UFC can resist seismically induced flexural compressive stresses, enabling the seismic performance and ductility of the pier to be provided by the undamaged core concrete. Moreover, in order to resist flexural loading in two directions, the thickness of UFC precast formwork at corners can be increased to avoid damage in the corner regions.The UFC precast formwork has a number of horizontal joints in order to distribute earthquake-induced flexural cracks and thus minimize the concentration of damage, particularly at cross-sections. The initial idea was to form horizontal joints by laying wire netting in layers to separate steel fibres in UFC [5]. However, the number of induced cracks turned out to be smaller than expected and to be only about two or three in each zone after a cyclic loading test. The UFC piers may not have been able to achieve the anticipated performance because of premature rebar damage. For the horizontal joints capable of inducing a stable number o...

Fracture tests with a wedge-loading device are carried out on mortar and concrete specimens so as to have stable crack growth. Using laser speckle technique the length of macrocrack and the distribution of crack opening displacement are measured. Results are compared with those obtained by the boundary element method (BEM) analysis for a Dugdale-Barenblatt-type model of a fracture process zone. The governing mechanism in fracture of concrete and the mechanism which is represented by the model are discussed with special attention to the microcracking zone. It is deduced that a Dugdale-Barenblatt-type model does not represent the microcracking zone, thus implying that the microcracking zone and the bridging zone correspond to the pre-peak nonlinear part of the stress-strain curve in a uniaxial tension test and the post-peak tension-softening curve, respectively. It is concluded that the effect of microcracking on the maximum load is less significant than that of bridging. Possible models which include the effect of microcracking in addition to that of bridging are proposed.

<p>In urban expressways, lightweight orthotropic steel decks are widely used. However, fatigue cracks occur in the orthotropic steel deck. To address this problem, we developed a light weight highway- bridge deck with high durability using ultra-high performance fiber-reinforced concrete (UHPFRC). The slab of the UHPFRC deck is 40 mm thick and the rib height is 83 mm. A UHPFRC deck has very thin components as compared with the conventional concrete deck, thus we validated the safety of this thin deck structure using finite element analysis. We also verified its fatigue durability using the wheel running fatigue test. In load conditions twice as high as those accounted for in the original design, several cracks of 0.04 mm or less developed on the side surface of a rib. However, the stiffness of the deck was not compromised. Therefore, we verified the high fatigue durability of the UHPFRC deck and feasibility for its application.</p>

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