Current codes of reinforced concrete design, mainly concerned with ductile steel reinforcements, do not yet address the use of brittle FRP (Fiber Reinforced Plastic) tendons. In order to use them more frequently in structural applications in industry, reliable design methods and code coefficients should be established, taking into account the material properties. This paper discusses the flexural design of concrete beams prestressed with FRP tendons with emphasis on the strength reduction factors in the USD (Ultimate Strength Design Method). According to the code requirements, the reduction factor should consider the degree of ductility. New reduction factors for the flexural design are recommended based on a reliability analysis, in which the target reliability indices have been set in due consideration of the ductility. The recommended factors range from 0.7 to 0.9 depending upon the degree of ductility. The factors are lower than that (=0.9) of beams with steel reinforcements, allowing for the possible lack of ductility in beams with FRP tendons.

The Hong Kong Mass Transit Railway Corporation, carrying a daily patronage of over 2 million, has a prime objective of providing a safe and reliable railway transportation system to the public in Hong Kong. The existing Urban Line System is situated mostly underground through soft, marine deposits and/or rock. The aggressive underground conditions in the coastal regions had resulted in various degrees of deterioration to the tunnel linings in a period less than 10 years from completion. The problem was most serious where precast concrete (PCC) lining was adopted because of the existence of segmental joints. A special method of repair was jointly developed by MTRC and Skanska International Civil Engineering AB. A robotic high pressure water jet system (hydrodemolition) is used to remove the surface delaminated concrete, and the surface repaired with a 75 mm layer of low permeability, fibre (polypropylene) reinforced shotcrete. Repair has to be implemented in the short time window during non traffic-hours each night with absolutely no disruption to the daily traffic.

In the aftermath of the Great Hanshin-Awaji Earthquake of 1995, the seismic retrofitting of existing structures has been implemented on a nation-wide basis throughout Japan, and it is in this context that new methods for seismic retrofitting utilizing aramid fiber reinforced plastic rod have been developed. Aramid fiber rod is not only lightweight and flexible, but has superior strength and corrosion resistance characteristics, which make it an ideal material for use in the seismic retrofitting of reinforced concrete structures. AWS method involves the use of aramid fiber rods to introduce prestress into wall-type piers, again improving the ductility and shear strength of the existing wall. Testing of scale models gave results showing this method to provide sufficient strength. The guidelines available for retrofitting of highway bridge piers in Japan are presented. The design equations for ultimate shear strength and ductility of retrofitted RC structures are introduced. AWS method is now used in the seismic retrofitting wall-type piers of highway bridges.

In this paper, shear strengthening of RC beams by confining shear critical region is experimentally and theoretically investigated. Confinement is implemented using vertical post-compression force in the shear critical region with steel plate, bolts and angles. The loading tests include (1) loading beams to first major shear crack, then shear strengthening, and reloading to complete failure, (2) strengthening beams from beginning and loading to complete failure, and (3) loading unrepaired beam to complete failure. Influences of concrete strength, shear span length, longitudinal tensile reinforcement, level of post-tensioning, presence of shear reinforcement, use of continuous plates, and presence of shear crack are studied by testing twenty-four RC beams. Test results show that in the presence of post-compression stress, as low as 0.04f'c for strengthening, shear strength increases significantly and the mode of failure of the beams changes from brittle shear to ductile bending. Also, for this level of post-compression, influence of all other parameters is limited, while a ductile failure is dominant. Calculations based on Mohr’s theory also indicate that this method of strengthening is very effective, and provides ductile flexural behavior in beams with inadequate shear strength.

Electro-migration and diffusion of ions in electrolyte solution are theoretically described by the Nemst-Plank equation. Also, electro-migration and diffusion of ion can be related by using the Einstein’s equation in dilute solution. In concrete, however, the relationship between electro-migration and diffusion is still unclear, for the influence of the concentrations in pore solution is unknown. Previous work of the authors has shown that it is possible to assess the diffusion coefficients of chloride ion in an ordinary Portland cement mortar through conduction tests by following the Nemst-Plank equation, Debye-Huckel theory and electro-neutrality. This paper evaluates the adaptability of this method to mortars made of several binders, such as ordinaly Portland cement, high-early strength Portland cement, sulfate-resistant Portland cement, low-heat Portland cement, Portland blast-furnace slag cement, ordinary Portland cement with fly ash, ordinary Portland cement with silica fume. In these cases, the concentrations of calcium, sodium, potassium, chloride, and hydroxide ions are different from that of the ordinary Portland cement case. Thus, the adaptability of this method is confirmed in mortar made of a wide range of binders.