Thin UHPFRC slabs without conventional reinforcement as light-weight structural elements
Ultra-High Performance Fibre-Reinforced Concrete (UHPFRC) is a material characterised by significantly improved mechanical and durability properties compared to other concretes. In recent years, an important research effort has been made to identify appropriate structural forms and to provide practical design rules allowing efficient UHPFRC structures to be conceived. This paper presents the results of an experimental and theoretical study on the structural behaviour of thin UHPFRC slabs without conventional reinforcement. It is shown that these elements can provide high bending resistance, and, applied in an appropriate structural arrangement, lead to strong and light-weight structures that cannot be built with ordinary reinforced concrete. The favourable behaviour of thin UHPFRC members results from material mechanical properties: high compressive strength and significant ductility in tension of thin UHPFRC members lead to a ductile bending response, even when conventional reinforcement is not provided. It is demonstrated that the theory of plasticity can be safely used to assess the bending failure load for thin UHPFRC slabs. A practical expression is proposed to define the resistant plastic moment, allowing an easy estimation of the bending load-bearing capacity of thin statically indeterminate UHPFRC elements. The results are compared with experimental data on slabs of various thicknesses, showing good agreement.
Innovative Design of Ultra High-Performance Fiber Reinforced Concrete Ribbed Slab: Experimental Validation and Preliminary Detailed Analyses
A new generation of cementitious composites, ultra high performance fiber reinforced concrete (UHPFRC), represents an important breakthrough for addressing civil engineering challenges. The most significant feature of UHPFRC is the nearly elasto-plastic ductile behavior in tension, which allows safe exploitation of the tensile and shear capacity in structural elements, while also potentially benefits the dynamic behavior of concrete structures. Where traditional steel elements have shown fatigue resistance problems at the connections in orthotropic slab bridge decks, an attractive application of UHPFRC has been developed within MIKTI coordinated R&D French national project. It consists in a thin 2D-ribbed slab, pre-stressed transversally, made of 2.5 m-long segments connected by post-tension, further connected to conventional longitudinal steel beams which take advantage of the slab lightness. A major critical aspect of the project consists in the safe accounting for local with respect to global bending, even under repeated local fatigue loading. Moreover, safety barriers have to be anchored at the edges of such a thin structure. The capacity of the deck to withstand the load representative of a truck shock, without being damaged before the fuse connecting system of the barrier yields, appears as highly critical also. The detailed design of this innovative structure has been carried out applying French interim recommendations for UHPFRC. However, detailed verifications of the local bending (corresponding to a wheel load directly applied and concentrated over the center of one “honeycomb” delimited by the transverse and longitudinal ribs) and of the behavior of the transverse joint under representative bending loads, require refined Finite Element analyses. Both general design and detailed analyses are being compared to scale one experiments.
Badush Dam, NW Iraq : A Geological Study
The river Tigris flows from Turkey towards Iraq in its northwestern part dissecting the whole Iraqi territory. During 1981– 1986 a very large earth fill dam was constructed, which is Mosul Dam impounding the flow of the Tigris River. It is the largest dam in Iraq and one of the largest in the Middle East. The geological conditions of the dam site and surroundings, however, are not suitable due to thick exposures of the Fatha Formation, which consists of marl, clay, limestone and gypsum. The gypsum and limestone beds are highly karstified causing severe problems to the dam foundation. Mosul dam suffers from serious problems due to the presence of karstified rocks; therefore, the Ministry of Irrigation in Baghdad, decided to construct a protection dam downstream of Mosul Dam; it is called Badush Dam. The geological conditions at Badush Dam site are the same as those at Mosul Dam site, which means the foundations of the dam are located on karstified rocks. Therefore, grouting works were planned and designed and it was partly performed from the beginning of the construction in 1988. The construction of the dam; however, stopped in 1991 due to the consequences of the First Gulf War. The constructed parts of the dam are (30 – 40) %. In this study, we have presented the main problems, which will cause real danger to Badush Dam, if its construction is re-started, and we have suggested many requirements to avoid any hazard that may cause the collapse of Badush Dam.