1,721,151 research outputs found
Structural effects of FRC creep
No full textResearch studies in the last 20 years allowed to obtain reliable rules for designing structures made of fiber reinforced concrete (FRC). However, design aspects like the long-term behavior of FRC, especially when synthetic fibers are adopted, require further research. Long-term behavior includes aging and creep. Aging represent the change of fiber properties into the concrete environment, which may reduce the structural bearing capacity; when present, it is an important issue for the structural safety, especially when fibers are the only reinforcement. Aging of fibers must be proven by experimental tests. Creep is a complex phenomenon, roughly considered by building codes even for traditional reinforced concrete (RC) structures. The introduction of fibers do not change anything in concrete matrix and, before cracking, in the material concrete creep behavior is not expected any change. After cracking, the structural effect of FRC creep depends on the degree of structural redundancy and on the presence of rebars since creep produces a stress redistribution in the structure or from FRC to the rebars. When FRC post-cracking resistance is necessary for equilibrium requirements, in structures with cracked sections in service conditions the structural deferred response has to be analyzed by considering the FRC creep behavior. When FRC is used for resisting secondary actions and rebars are present for equilibrium requirements, the response of a FRC element (with rebars and fibers) will be identical to a conventional RC; FRC contributes by controlling the crack development under both short and long term loading
On Durability of Fiber Reinforced Concrete
No full textCosts for maintenance and repair of conventional reinforced concrete (RC) buildings and structures have become a serious economical, ecological and social problem. A large percentage of worldwide infrastructure needs repair measures. This situation motivates great care when developing new construction materials, such as Fiber-Reinforced Concrete (FRC), whose enhanced toughness contributes to more durable structures. In fact, fibers could be introduced in RC structures to reduce the cracking phenomena thus helping the structural durability.
In the present paper, fracture behaviour and water permeability of fiber reinforced concrete are studied. The effect of different crack openings is analysed in order to study its influence on the
mechanism of ingress of water
New Trends in Fracture Mechanics of Concrete
No full textFracture Mechanics of Concrete and Concrete Structures, Volume 1 of the Proceedings of the 6th International Conference on Fracture Mechanics of Concrete and Concrete Structures, Catania, Italy, 17-22 June 2007, 3-Volumes
[101029.EG da
Experimental study of a reinforced concrete bridge pier strengthened with HPFRC jacketing
No full textAs a consequence of material degradation, increasing traffic loads and seismic actions, a large number of existing reinforced concrete bridges are no longer safe and may represent a risk for human lives and for the robustness of the road network. Replacement of these bridges is often not practical given the cost of demolition and rebuilding in addition to the social costs of traffic interruption. As an alternative to the replacement of the entire structure, the service life of a bridge can be extended by adopting reliable strengthening techniques. Among these strengthening techniques is High Performance Fibre Reinforced Concrete (HPFRC) jacketing, which was experimentally investigated in this research project. The mix design of HPFRC was studied with the goal of producing a material with enhanced mechanical performance as well as excellent rheology. In this study, the bridge pier studied was subjected to cyclic horizontal loads both before and after strengthening, up to failure. Experimental results show that the HPFRC jacketing remarkably increased the bearing capacity of the pier as well as its ductility. The jacketing also enhanced the structural response in terms of crack control, which significantly governs the structural durability
Fiber-reinforced concrete
No full textPlain concrete is a brittle material with low tensile strain and strength capacities; the use of short, discontinuous fibers allows us to strengthen and toughen such material. Fibers are not generally added to concrete to increase its strength; the main role of the fibers is to bridge across the matrix cracks that develop as concrete is loaded, and thus to provide some postcracking ductility (or toughness). The latter may allow for a reduction of conventional reinforcement and, in structures with a high degree of redundancy, a complete replacement of rebars. The enhanced crack control makes fiber-reinforced concrete (FRC) particularly suitable for a longer durability of the structure; here, the additional cost of fiber reinforcement may be justified by savings in the maintenance costs. The consequent reduction in labor time has become a key issue for the industrialization process in the precast industry, where the rebar substitution becomes particularly convenient in thin or irregularly shaped sections. FRC is now treated as a performance-based material in several recent building codes
A parametric numerical study on the behavior of large precast tunnel segments during TBM thrust phase
No full textDuring the last two decades, Fiber Reinforced Concrete (FRC) was adopted in several segmental tunnel linings. The benefits related to the inclusion of fiber reinforcement in cementitious composites are mainly related to the increase of post-cracking tensile residual properties. FRC allows to reduce or avoid conventional reinforcement leading to a more efficient segment production process. The application of Tunnel Boring Machine (TBM) thrust jack forces during the lining construction stage is one of the most demanding loading conditions, since high-concentrated forces are introduced in last installed segments, especially for large diameter lining. Hence, special attention should be devoted to this phase by considering parameters which may affect segment structural response. To this aim, the behavior of a lining having large diameter during TBM operations was investigated by means of a broad parametric numerical study concerning segment configuration, irregularities and lining slenderness. The following reinforcement solutions were also considered: traditional steel rebars only, steel fibers reinforcement only and a combination of them (hybrid solution). The study clearly proved that segment configurations as well as irregularities strongly affect the structural behavior of segments. The hybrid reinforcement or FRC only solution having high post-cracking performance may guarantee the same response of RC solution
Reinforced concrete elements in crack stage subjected to chloride-rich environment
No full textThe durability of reinforced concrete (RC) structures is the main challenge to overcome for global sustainability. Crack width plays an important role through which aggressive agents can penetrate and initiation of corrosion begins. Several researchers have looked into the relationship between crack width and corrosion level, but there has yet to be agreement among the authors. With this aim in mind, 31 tension ties (90 mm x 90 mm x 830 mm) with Ø12 rebar were cast, pre-cracked to different crack widths, subjected to permanent tensile load and exposed to wet and dry cycles of water containing 3.5% NaCl solution for 280 days. The experimental results show that the corrosion initiation began after the first cycle (except for a small delay in the sample with a 0.1 mm crack width). Currently, our focus is on evaluating corrosion propagation. Tension ties are going to be cut to extract rebar, measure pitting corrosion, and analyse the relation between crack width and corrosion
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