Results 1 - 10 of 19992
Results 1 - 10 of 19992. Search took: 0.052 seconds
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[en] Fiber reinforced polymer (FRP) reinforcements for concrete structures are gaining wide acceptance as a suitable alternative to steel reinforcements. The primary advantage is that they do not suffer corrosion and hence they promise to be more durable in environments where steel reinforced concrete has a limited life span. Concrete wharves and jetties are examples of structures subjected to such harsh environments and represent the general class of marine infrastructure in which glass FRP (GFRP) reinforcement should be used for improved durability and service life. General design considerations which make glass FRP suitable for use in marine concrete rehabilitation projects are discussed. A case study of recent wharf rehabilitation project in Canada is used to reinforce these considerations. The structure consisted of a GFRP reinforced concrete deck panel and steel - GFRP hybrid reinforced concrete pile cap. A design methodology is developed for the hybrid reinforcement design and verified through testing. The results of a field monitoring program are used to establish the satisfactory field performance of the GFRP reinforcement. The design concepts presented in the paper are applicable to many concrete marine components and other structures where steel reinforcement corrosion is a problem. (author)
[en] A polymer concrete was prepared adding luffa fiber with the aim of improving compressive and flexural strength as well as elasticity. Polymer concrete specimens were prepared with unsaturated polyester resin with 30 % in volume being the remaining 70% siliceous sand and luffa fibers at several concentrations (0.3, 0.6 and 0.9 vol%). Specimens without fibers were evaluated and gamma irradiating. The evaluation of the mechanical resistance to compression and flexion of the specimens were done in a universal testing machine while elasticity modulus was determined with ultrasound equipment. After the mechanical tests the luffa fiber areas were analyzed using a scanning electronic microscopy. The results show that compressive strength, flexural strength and elasticity decrease their values for the specimens with fibers. The properties improved for the irradiated specimens
[en] Fibre-reinforced concrete (FRC) allows reduction in, or substitution of, steel-bars to reinforce concrete and led to the commonly named structural FRC, with steel fibres being the most widespread. Macro-polymer fibres are an alternative to steel fibres, being the main benefits: chemical stability and lower weight for analogous residual strengths of polyolefin-fibre-reinforced concrete (PFRC). Furthermore, polyolefin fibres offer additional advantages such as safe-handling, low pump-wear, light weight in transport and storage, and an absence of corrosion. Other studies have also revealed environmental benefits. After 30 years of research and practice, there remains a need to review the opportunities that such a type of fibre may provide for structural FRC. This study seeks to show the advances and future challenges of use of these polyolefin fibres and summarise the main properties obtained in both fresh and hardened states of PFRC, focussing on the residual strengths obtained from flexural tensile tests.
[es]El hormigón reforzado con fibras (HRF) permite la reducción parcial o total de barras de acero en el hormigón armado, acuñándose término HRF estructural, siendo las fibras de acero las más usadas. Las macro-fibras poliméricas son una alternativa a las de acero, aportando estabilidad química y menor peso para resistencias residuales iguales. Además, las fibras de poliolefina ofrecen beneficios adicionales tales como mayor seguridad de trabajo, menor desgaste de equipos de bombeo, menor peso en el transporte y almacenamiento, y ausencia de corrosión. Otros estudios también han revelado beneficios medio-ambientales. Después de 30 años de investigación y práctica, sigue siendo necesario analizar las oportunidades que estas fibras de poliolefina pueden proporcionar al HRF estructural. Este estudio muestra los avances y posibilidades del uso de estas fibras y resume las principales propiedades obtenidas tanto en estado fresco como endurecido, centrándose en la resistencia residual obtenida en los ensayos de tracción por flexión.
[en] Concrete is a construction material that boasts great versatility in the shapes that it can adopt. Its early stages of development might be dated back to Romans . Regarding its mechanical properties, concrete is known by its remarkable compression strength although it has a reduced ductility and tensile strength . Traditionally, such lower properties have been improved using steel bars forming reinforced concrete (RC). More recently, randomly distributed short fibres have been added to concrete while mixing creating fibre reinforced concrete (FRC). By any of the previously mentioned options, the merger of the concrete properties together with the ones provided by the localized reinforcement of RC or by the continuous reinforcement of fibres of FRC have created a material suitable for a wide range of structures. The fibres added to concrete can be manufactured with several materials such as steel, natural substances or even polymeric compounds . Depending on the fibre type and dosage, fibres might not only improve the concrete behaviour when subjected to fire or prevent shrinkage cracking  but also might be considered in the structural design. This last option can be carried out only if certain requirements set on standards and recommendations are met [5-6]. The requirements established in the standards refer to the material behaviour obtained by means of laboratory tests of concrete subjected to flexural tensile stress states. Nevertheless, the relation between the flexural and tensile behaviour of a FRC is a matter that is still not fully understood. Furthermore, the influence of the distribution and orientation of the fibres within the concrete matrix is a matter that deserves being studied . It is important to relate the design parameters and the production conditions with the mechanical behaviour of concrete...
[en] The FRP reinforcing bar, which is a structural reinforcing bar made form filaments or fibers held in a polymeric resin matrix binder. The FRP bar can be made from various types of fibers such as glass (GFRP) or carbon (CFRP). FRP bars have a surface treatment that facilitates a bond between the finished bar and the structural element into which they are placed. FRP Bars are intended for use as concrete reinforcing in areas where steel reinforcing has a limited life span due to the effects of corrosion. They are also used in situations where electrical or magnetic transparency is needed. In addition to reinforcing for new concrete construction, FRP bars are used to structurally strengthen existing masonry, concrete or wood members . FRP bars are a new type of structural material for the civil engineering community. The basic constituent materials for reinforced concrete design have changed very little in the past 100 years. Traditionally, composite materials have been used extensively in aerospace and consumer sporting goods where their high strength to weight characteristics were first exploited. Corrosion of steel reinforcement in concrete structures causes deterioration of concrete resulting in costly maintenance, repairs and shortening of the service life of structures. Government agencies throughout the world have recognized the potential benefits to society if our infrastructure can last longer and are thus funding significant amounts of research in the field of FRP's  . In this paper, the bending resistance of FRP reinforced concrete beams is measured by the bending moment effect using tools such as Cathode-ray oscilloscope (CRO) and using a parallel plate capacitor to detect small displacements of the beam under pressure. CRO cathode ray oscilloscopes are used to measure small deformations of beams at different pressures. And parallel plate capacitors can detect changes in capacitance by different metal electrode spacing. The frequency is measured by the oscilloscope's Lissajous curve and compared to its theoretical frequency. In addition, according to the stress test results of the beam, the finite element analysis was performed using the constitutive material model of ordinary concrete to simulate the bending behavior of these beams. The simulation results are then used to determine the accuracy of the constitutive model used to predict the performance of FRP reinforced concrete beams.
[en] Discussed are the design and construction of nuclear reactor containments, their siting, loads and effects exerted on them. The considerations include five most significant and most frequently used design variants of concrete and steel sheet containments. (B.S.)
[en] The production and quality control of concrete and concrete materials for the construction of the twin-reactor Rajasthan Atomic Power Station with its 400 MW net capacity posed many challenges since many of the requirements for the properties of concrete were new and were being laid down for the first time in India. Some of the conditions for the concrete included leak-tightness against gas pressure, total absence of shrinkage in the containment even when the ambient temperature during concreting was as high as 45degC, placing concrete at a temperature as low as 8degC, the use of non-shrink and high strength grout, absolute impermeability against water, high density for radiation shielding, controlled modulus of elasticity for large machine foundations, high strength with high slump for the prestressed concrete dome, etc. Though the total quantity of concrete was not very much compared with a large river valley or steel plant project, (e.g., about 1.2 X 106 m3 for a 2-million tonne steel plant) it was quite significant, being about 70,000 m3 of normal density and 2,100 m3 of high density concrete. The production of these quantities entailed intensive material study and investigation, development of new mixes with additives not tried out before in the country, and design and quality control techniques which were unique in many respects. The paper deals with the production and quality control of concrete, including grouts used in the projects, but the actual concreting and construction operations are not discussed. (author)
[en] The study considers a concrete column undergoing emergency loading (compression and bending). Its surface is reinforced by means of a highly strong composite material. Loads yield micro-damage in the compression area of the element, without the attainment of bending and compression limit stresses of concrete and the reinforcing material. The present work is a continuation of previous studies where the authors proposed an approximate calculation method (ACM) of finding stresses and strains in elastically deformed structural elements. The analysis aims at the expansion of the ACM and assessment of the residual bearing capacity of the material. This is done by the introduction of appropriate assessment coefficients. The authors illustrate the approach presenting a test example. Key words: surface-reinforced concrete columns, micro damage, bearing capacity, residual resource