Effect of Time-Dependent Chloride Profile and Temperature Variation on Chloride Diffusion in Concrete

Reinforcement corrosion due to chlorides diffusion is one of the main problems in reinforced concrete structures exposed to certain environments. The diffusion rate is function of chloride surface concentration, concrete temperature, humidity, composition and microstructure. The intruded chlorides are partially chemically bound by the concrete and it is the unbound or free chloride which upon exceeding a defined threshold initiates corrosion. The time to corrosion initiation depends on the above variables; therefore, it is important to model their spatial and temporal variations in a manner that will yield a realistic estimate of the actual initiation period. In this study, the chloride surface concentration and temperature temporal variations are approximated in several ways to gauge the sensitivity of the chloride diffusion kinetics to them. Temperature profiles with constant 6-hours, daily, monthly, seasonally and yearly variations are used to approximate the actual temperature variation recorded for Toronto, Canada in a typical year. The surface chloride concentration is assumed either constant or allowed to vary monthly according to the reported values for Toronto. It is discovered that due to the limited temperature range encountered even in cold regions like Toronto, the diffusion kinetics is not very sensitive to the temperature approximation method, but it is more sensitive to the way the surface chloride variation is approximated. For structures subjected to deicing salt applications, assuming constant seasonal temperature and monthly chloride variation in the analysis may yield a realistic estimate of the time to corrosion initiation and thus the prediction of the life-time of the structure

Nonlinear finite element analysis of strength and durability of reinforced concrete and composite structures

The finite element method has emerged as the most powerful and versatile numerical method for solving a wide range of physical problems in science and engineering. Today a large number of commercial programs exist that can be used to solve diverse problems in structural and fluid mechanics, heat transfer and many other phenomena. However, certain critical problems related to durability of concrete structures, especially corrosion of reinforcement, cannot be readily solved using the available software. This paper presents two finite element formulations, developed by the writers, one dealing with the nonlinear analysis of composite concrete-steel bridges, and the other with the durability of concrete structures, with emphasis on the corrosion of reinforcement. The validity and accuracy of the proposed models are demonstrated by comparing their results with appropriate experimental data

FRP-RC/PC members subjected to combined actions

The capacity provisions of conventional Reinforced Concrete (RC) and Prestressed Concrete (PC) beams subjected to combined action of torsion, shear and flexure are well known and stated by international/national codes. Similar provisions lack for concrete members containing Fibre Reinforced Polymer (FRP) reinforcements. In general, there is paucity of research on the treatment of torsion combined with other stress resultants for FRP-RC/PC members. In this paper the theoretical method proposed by the Canadian standard CSA S806 for FRP-RC/PC structures is presented. The critical issues, related to this topic, such as the appropriate strength and inclination of the diagonal struts and failure criteria are critically analyzed and addressed. In order to assess the reliability of this study a comparison between available experimental data regarding FRP-RC/PC beams subjected to combined actions and their corresponding theoretical provisions derived by the CSA S806 standard is shown. Furthermore, another approach, available in literature, which is based on the space truss model, is examined and used for comparison in order to evaluate the theoretical provisions offered by this model against the tests value of the set of the beams analyzed in this study. Based on the critical analysis of the results, it can be highlighted that the CSA method is able to conservatively predict the capacity of these beams

Pseudo-ductile Failure of Adhesively Joined GFRP Beam-Column Connections:An Experimental and Numerical Investigation

Glass Fiber Reinforced Polymer (GFRP) I-beam-column adhesively bonded connections are tested under combined bending and shear. The special feature of the novel connection is the wrapping of the seat angles at the connection by a carbonfiber reinforced polymer (CFRP) fabric wrap. The wrap is primarily intended to alter the connection failure mode from brittle to pseudo-ductile, thus providing adequate warning of impending failure. Four moment resisting connection configurations are tested, including the reference configuration without the wrap. It is observed that the connection failure is initiated by the fracture of the adhesive, but the provision of the wrap, together with a steelseat angle, alters the failure mode from brittle to pseudoductile. The post-peak load deformation is achieved without a large drop in the resistance of the connection. On other hand, the connection with the wrapping and a GFRP seat angle can also change the failure mode to pseudo-ductile, but it could not be done without a large reduction in theconnectionresistanceafterthepeakload

Discussion on “Malešev, M.; Radonjanin, V.; Marinković, S. Recycled Concrete as Aggregate for Structural Concrete Production. Sustainability, 2010, 2, 1204-1225”

The authors are to be congratulated for their comprehensive research work on the use of RCA as aggregate in structural grade concrete [1], but some of their conclusions with regard to the effect of aggregate type and RCA content on the fresh and hardened properties of concrete made with coarse RCA, termed RAC for brevity, need discussion

Discussion on “Malešev, M.; Radonjanin, V.; Marinković, S. Recycled Concrete as Aggregate for Structural Concrete Production. Sustainability , 2010, 2 , 1204-1225”

The authors are to be congratulated for their comprehensive research work on the use of RCA as aggregate in structural grade concrete [1], but some of their conclusions with regard to the effect of aggregate type and RCA content on the fresh and hardened properties of concrete made with coarse RCA, termed RAC for brevity, need discussion.n/a

Inelastic load distribution in multi-girder composite bridges

To accurately assess the ultimate load capacity of concrete slab-steel girder bridges, the effects of concrete nonlinearity and steel yielding on the truck load distribution in simply supported composite bridges are investigated using the nonlinear finite element (FE) method. In this study, fifty cases are analyzed to investigate the effect of the aforementioned parameters as well as the effects of other parameters including longitudinal and transversal truck position, number of loaded lanes (2\u20134), bridge length (12\u201320 m) and width (8\u201316 m), number of girders (3\u20136), girder spacing (2\u20133.75 m), and slab thickness (175\u2013275 mm). The moment in each girder, based on the nonlinear FE analysis, is used to obtain its Load Distribution Factor (LDF) at different load levels up to failure and is compared with the corresponding elastic LDF according to AASHTO LRFD specifications. The results show from zero to 54% increase in the internal girder LDF (average 32%), and from zero to 29% decrease in the external girder LDF (average 17%) as the bridge traverses from the elastic to the ultimate state. This redistribution can be advantageously used when evaluating the load carrying capacity of existing bridges.Peer reviewed: YesNRC publication: Ye

Strain rate effect on development length of steel reinforcement

Accidental or premeditated explosions have detrimental effects on the infrastructure near the center of explosion and pose major threats to human life. Thus, research is currently underway to study the effects of explosions on infrastructure systems with the ultimate goal of minimizing infrastructure damage and saving lives. Because reinforced concrete is the most common building material used in blast-resistant infrastructure design and construction, understanding the effect of blast loads on reinforced concrete components is essential to reaching this goal. The prevailing design philosophy for blast-resistant structures is energy dissipation through reinforcement yielding (ductility) and large bending deformations without the incidence of nonductile failure modes such as shear and bond. However, information regarding the bond behavior and strength of steel reinforcement-concrete bonds under blast loads is rather scant; therefore, this paper reports on an experimental program designed to investigate the strain rate effect on steel reinforcement-concrete bond. Reinforced concrete beams longitudinally reinforced with 15M, 20M, or 25M were tested in a shock tube under simulated blast loading. The test results show that high strain rate increases the steel reinforcement-concrete bond strength and thus, that the static load development lengths of these bars are adequate for developing their dynamic yield strengths at high strain rate. The dynamic increase factor for bond stress is determined to be 1.11 for 15M, 2.24 for 20M, and 3.68 for 25M bar