Flexural behavior of two-span continuous prestressed concrete girders with highly eccentric external tendors

[Abstract]: It is generally known that the flexural strength of beams prestressed with external tendons is comparatively lower than that of members with internal bonded tendons. One possible method of enhancing the flexural strength of such beams is to place the tendons at high eccentricity. To obtain an insight into the flexural behavior of beams with highly eccentric tendons, an experimental investigation is conducted on single-span and two-span continuous beams. The test variables include external tendon profile, loading pattern on each span, casting method, and confinement reinforcements. It is found that continuous girders with linearly transformed tendon profiles exhibit the same flexural behavior irrespective of tendon layout. The presence of confinement reinforcement enhances the ductility behavior but does not increase the ultimate flexural strength. The degree of moment redistribution is affected by the tendon layout and the loading pattern on each span. The results of the experimental investigation are discussed in this paper

Guidelines for Design and Construction of Grouting for Prestressed Concrete Structures

[Extract] The JPCEA has been involved in the development of various draft standards and manuals related to prestressed concrete technology since 1994, through investigations and research conducted by the Prestressed Concrete Technology Standards Committee on the request of organizations related to prestressed concrete. Recently, the importance of the grouting has become a priority item due to factors such as defective grouting (improper filling) that has resulted in breaking of prestressing steel which can potentially cause serious damage. Hence, it became evident to review the importance of grouting in prestressed concrete structures. As a result, the Japan Prestressed Concrete Contractors Association took the initiative to conduct training courses and revised the ''Grout Construction Manual" in order to improve the grouting. Moreover, major revisions of overseas standards, advancements in the grouting materials and development of new products, innovative construction technologies etc., demanded the need for standardization of grout for prestressed concrete structures. As a result, the, Standards Committee for Grouting" was established by JPCEA in July 2003. The Committee consisted of a coordinating group and four working groups with the aim of producing a performance based standard which is the current trend worldwide. This publication titled '·Guidelines for Design and Construction of Grouting for Prestressed Concrete Structures" was a result of the activities of this standards committee

Numerical simulation of shear behaviour of reinforced high-strength concrete members

The rapidly increasing use of high-strength concrete (HSC) is outpacing the development of appropriate recommendations for its application. A number of empirical formulae have been proposed for the prediction of the diagonal cracking shear capacity of HSC members. However, these incorporate no explicit consideration of fracture surface roughness or bond stiffness. This paper addresses this key qualitative knowledge on shear behaviour of reinforced high-strength concrete (RHSC) members. Currently, multi-directional fixed crack modeling is being used not only for design but also for maintenance. The diagonal cracking shear strength of RHSC beams, which are greatly affected by both fracture surface roughness and bond stiffness, was simulated using nonlinear finite element (FE) analysis. The test results were compared with predicted strengths using a two dimensional finite element method (2D-FEM). The average of the ratio of tested diagonal cracking shear strength to predicted was 1.04 with a standard deviation of 0.08. The multi-directional fixed crack approach was verified as a reliable structural concrete model in the case of HSC

Towards Moral Education Class Enrichment

指導法・実践報

Guidance to Nurture the Norm Consciousness

指導法・実践報

Renovate RC structures with newly developed mortar, considering chloride binding and inverse diffusion phenomenon

In Japan, many RC bridges and infrastructure along the coast line have been deteriorated due to ingression of chloride ions. The objective of this study is to develop high durable repair mortar with ion-exchange resin as an admixture to enhance life span by eliminating chloride ion from existing RC structures. And as a part of the objective, this paper discusses the effectiveness of typical commercially available anion exchange resin in preventing chloride induced corrosion within concrete by using its excellent ion-exchange and binding ability, though its real effectiveness with concrete is not still clearly identified. A number of immersion tests were conducted using small mortar specimens mixed with ion-exchange resin and high-early strength Portland and blast furnace slag cements. The volume contents of ion-exchange resin were 1.0, 2.0 and 3.0%. The specimens were immersed into 10% sodium chloride (NaCl) solution for one day and then exposed in drying condition for 6 days. These exposure procedures were repeated for 28, 56 and 84 days. Then total and free chloride contents at various depths in all tested specimens were measured in each time period. The inverse diffusion test was conducted with mortar specimens casted with high-early strength Portland cement maintaining 10% chloride ion only up to 8 cm while top 2 cm casting with 3% ion exchange resin mixed mortar. Total chloride was measured in four consecutive depths after 28 and 140 days. Test results showed the significant enhancement of chloride binding in newly developed mortar with ion-exchange resin compared to normal mortar. The linear relationship between free and bound chloride was also noticed in all specimens, irrespective to the cement types. The absorption of chloride by ion-exchange resin was further increased with increment of chloride concentration in order to achieve its optimum capacity. At last, the effective adsorption of chloride from matured concrete by newly developed repair mortar, using outward movement (inverse diffusion), was clearly observed

Skills teachers must possess

研究ノー

Advancements in retrofitting reinforced concrete structures in Japan using FRP sheets

In Japan, many reinforced concrete bridge structures collapsed in the recent severe earthquakes such as the 1995 Hyogoken Nanbu Earthquake and the 2004 Niigataken Tyuetsu Earthquake were designed and constructed before the introduction of the new seismic resistant design codes in 1980. Following the lessons learnt from these severe earthquakes and the continuous advancements of the state of the art and practice, further stringent performance based earthquake resistant design codes for both highway and railway bridge structures are recently enforced in Japan. For many existing structures, to meet the requirements of these new codes, proper strengthening schemes must be implemented. Among various strengthening techniques, the application of fiber reinforced polymer (FRP) has recently drawn a wide attention due to its advantages such as high strength to weight ratio, corrosion resistance, and ease of execution. This paper introduces the current issues related to the deficient reinforced concrete structural members in Japan and provides an overview of latest innovations and advancements in the technology and application of FRP sheets in structural retrofitting. The focus of this paper is mainly on the retrofitting of bridge superstructures and substructures including decks, girders, frames, and columns