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

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

Experimental investigation of innovative hybrid composite girders with GFRP and CFRP

This paper focuses on flexural behavior of innovative hybrid I-shaped girders consisting of Glass Fiber Reinforced Plastics and Carbon Fiber Reinforced Plastics. The experimental investigation revealed that the delamination at the interface of glass and carbon fibers in the compressive flange caused a sudden failure and lead to smaller loading capacity than the expected in the case of girders with smaller flange width. In the case of wider flange width, the local buckling of flange in compressive side was observed. It was experimentally found that the appropriate installation of web stiffeners is an effective way to prevent the local buckling of wide flange sections but that FRP materials cannot also exhibit their intrinsic material strength due to the delamination. In order to utilize the materials properties of FRP effectively, it is recommended that further study is conducted with a section having neutral axis towards the upper side of the section

AFRP retrofitting of RC structures in Japan

In Japan, many reinforced concrete (RC) bridge structures that were designed and constructed before the introduction of the modern seismic design codes collapsed in the 1995 Hyogoken-Nanbu Earthquake and the 2004 Niigataken-Tyuetsu Earthquake. Following the lessons learnt from these severe earthquakes, proper strengthening schemes were implemented for many existing structures to meet the requirements of the new performance-based earthquake resistant design codes. The application of fiber reinforced polymer (FRP) for strengthening techniques has drawn wide attention due to its advantages such as high strength to weight ratio, corrosion resistance, and ease of execution. This paper introduces current issues related to the deficient RC structural members in Japan and provides an overview of latest innovations in the technology and application of FRP sheets in structural retrofitting. Recent developments on the usage of mechanical anchorage system in strengthening beams of RC bridge frames with externally bonded AFRP sheets is also presented

Composite behaviour of a hybrid FRP bridge girder and concrete deck

This paper involves experimental investigation onto the composite behaviour of a hybrid FRP bridge girder with an overlying concrete deck. Two types of shear connections were investigated: epoxy resin adhesives alone and epoxy resin combined with steel u-bolts. The results showed that the steel u-bolts combined with epoxy resin provided a more effective connection; hence a full-size specimen was prepared based on this result. Four-point bending test was carried out to determine the behaviour of a full-scale composite hybrid FRP girder and concrete deck. The composite action resulted to a higher stiffness and strength with the hybrid FRP girder exhibiting higher tensile strain before final failure. There was a significant decrease in the compressive strain in the top flange of the FRP girder thereby preventing the sudden failure of the beam. The composite beam failed due to crushing of the concrete followed by shear failure in the top flange and web of the FRP girder

Mechanical behavior of hybrid FRP composites with bolted joints

The behavior of an innovative hybrid Fibre Reinforced Polymer (FRP) composite with bolted joints was investigated. Coupons and full-size specimens were tested to determine the effect of applied bolt torque and the contribution of adhesive bonding on the load capacity and failure mode of the hybrid FRP with bolted joints. The results showed that at different levels of applied bolt torque (10, 15, 20 and 25 N-m), little friction resistance developed. A slight increase on the load capacity was however observed with increasing tightening torque. On the other hand, the bolting accompanied by adhesive bonding provided resistance against slipping. The full-size hybrid FRP girder with joints using bolts and epoxy exhibited the same strength and stiffness as the girder without joints while bolting alone resulted to a beam with only 65% of the stiffness of those without joints. Theoretical analyses were conducted and result showed a good agreement with the experimental results

SHEAR CAPACITY OF REINFORCED HIGH-STRENGTH CONCRETE BEAMS WITHOUT WEB REINFORCEMENT

The Thirteenth East Asia-Pacific Conference on Structural Engineering and Construction (EASEC-13), September 11-13, 2013, Sapporo, Japan

RESTRAINING OF CHLORIDE INDUCED CORROSION IN RC STRUCTURES USING ION EXCHANGE RESIN

The Thirteenth East Asia-Pacific Conference on Structural Engineering and Construction (EASEC-13), September 11-13, 2013, Sapporo, Japan

RC pile foundation-soil interaction analysis using 3D finite element method

Seismic behavior of a structure is highly influenced by the response of the foundation and the ground. Hence, the modern seismic design codes stipulate the analysis of an overall structural system considering soil-structure interaction. In this paper, 3D FEM analysis was carried out to study the behavior of the pile and soil during earthquakes. Numerical simulations were carried out based on the two different experimental studies: a) Cyclic loading test of RC model piles embedded into sandy soil and b) lateral loading test on real-scale piles embedded into cohesive soil. The 3D FEM analysis used in the study could adequately simulate the behavior of the experimental specimens

Numerical modelling and full-scale testing of concrete piles under lateral loading

Full-scale lateral loading tests were carried out on hollow-pre-cast-pre-stressed concrete piles embedded into the ground. The results from the tests were used as the basis for the analysis where soil was modelled as 20-node solid elements; and for the modelling of piles comparison was done between 3-node beam elements and 20-node solid elements. It showed that the 3-node beam element modelling for pile largely underestimates its lateral capacity. The 20-node solid element modelling can, however, accurately simulate the experimental results when interface element between pile and soil, and the degradation of shear stiffness of soil in cyclic loading is considered