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Chloride attack severely impacts the performance of reinforced concrete. The total and free chloride ion concentration (CIC) of self-compacting concrete (SCC) prepared with three supplementary cementitious materials (SCM) – fly ash (FA), blast furnace slag (BS) and silica fume (SF) – were measured by accelerated salt immersion tests. The apparent chloride diffusion coefficient (CDC) at any exposure time and erosion depth were calculated using the Boltzmann–Matano method. The influence of the type and content of SCM, the water–binder ratio (W/B) and the type of salt solution on CIC and CDC were investigated. Both the introduction of SCM and the reduction of W/B effectively reduced the CIC. The SCM that most effectively reduced CIC was SF, followed by BS and then FA. Free CIC was reduced to a greater degree than total CIC in FA and BS concrete, but the opposite was true for SF concrete. The presence of calcium chloride in salt solution increased total CIC while reducing free CIC. Apparent free CDC dropped over exposure time and initially increased with erosion depth but eventually stabilised. A model of apparent free CDC considering time–depth dependency was created, which shows that time reduction factors of CDC is greater in SCC containing SCM than in control SCC. [ABSTRACT FROM AUTHOR]

As worldwide infrastructure is ageing, significant efforts have been paid to the development of strengthening techniques that will restore or increase the initial capacity of existing structures. Considering that it is expected that shear failure happens in a less ductile mode than that observed under bending actions, special attention has been devoted to shear strengthening methods. These methods included externally bonded fiber reinforced polymers (EB‐FRP), near‐surface mounted (NSM‐FRP) method, and the embedded trough‐section (ETS) technique, among others. In this paper, ETS method is used for the strengthening in shear of a reinforced concrete railway bridge located in Finland. The ETS method consists in the embedment of FRP or steel bars through predrilled holes into the concrete core. The bars are bonded to the concrete using adhesives. The paper includes a brief review of recent advances in the use of ETS and comparison with other available techniques, the description of the case study, instrumentation of the bars using fiber optic sensors (FOS) for strain monitoring, the procedure used for the installation of the bars in the field, and a preliminary analysis of the data collected. [ABSTRACT FROM AUTHOR]

The objective of this paper was to study the contribution of shear deformation in reinforced concrete (RC) shear-critical beams. A 2D concrete material model based on smeared fixed crack was presented and incorporated into a commercial finite element (FE) software. A method of calculating shear and flexure deformation separately out of total deformation in the shear span was presented and implemented into the FE analysis. Several experiments of RC shear-critical beams were simulated and good agreement between the experimental and numerical results was obtained in terms of total deformation, flexure deformation, shear deformation and crack patterns. The results show that after shear cracking, the contribution of shear deformation to total deformation increases rapidly. The shear span-to-depth ratio, the longitudinal reinforcement, the shear reinforcement and the load level could be the critical factor to influence the contribution of shear deformation. It appears that for RC shear-critical beams without shear reinforcement, the deformational behaviour is governed by flexure deformation. However, for RC beams with shear reinforcement, the contribution of shear deformation is not negligible after shear cracks develop. Moreover, the measuring method could also affect the measured shear deformation. Finally, future work on experimental investigation into this topic is recommended. [ABSTRACT FROM AUTHOR]

This paper presents a parametric investigation, based on non-linear finite element modeling, to identify the most effective configuration of carbon fiber-reinforced polymers (CFRP) for strengthening reinforced concrete (RC) dapped-end beams. Following a field application and laboratory tests, it focuses on effects of 24 externally bonded (EBR) and near surface mounted reinforcement (NSMR) configurations on yield strain in steel and the capacity and failure mode of dapped-end beams. The investigated parameters were the mechanical properties of the CFRP, the strengthening procedure and the inclination of the fibers with respect to the longitudinal axis. Two failure scenarios were considered: rupture and debonding of the FRP. The results indicate that high-strength NSM FRPs can considerably increase the capacity of dapped-end beams and the yielding strains in reinforcement can be substantially reduced by using high modulus fibers. [ABSTRACT FROM AUTHOR]

A reinforced concrete railway trough bridge in Örnsköldsvik, Sweden, was strengthened in bending with rods of carbon-fibre-reinforced polymer and loaded to failure. The aim was to test and calibrate methods developed in the European Research Project ‘Sustainable Bridges’ regarding assessment and strengthening of existing bridges. A steel beam was placed in the middle of one of the two spans and was pulled downwards. Failure was reached at an applied load of 11.7 MN. It was initiated by a bond failure caused by a combined action of shear, torsion as well as bending after yielding in the longitudinal steel reinforcement and the stirrups. The bond failure led to a redistribution of the internal forces from the tensile reinforcement to the stirrups, causing the final failure. The computer models developed to simulate the loading process were improved step by step from linear shell models to more detailed models. The most developed model, a three-dimensional nonlinear finite element model with discrete reinforcement, gave accurate accounts of the response of the bridge. [ABSTRACT FROM PUBLISHER]

This paper presents the results of experimental investigations on reinforced concrete slabs strengthened using fibre-reinforced polymers (FRP). Eight tests were carried out on four two-way slabs, with and without cut-out openings. Investigations on slabs with cut-outs revealed that the FRP can be placed only around the edges of the cut-out when retrofitting the slabs whereas, in the situation of inserting cut-outs combined with increased demands of capacity, it is necessary to apply FRP components on most of the soffit of the slab. The proposed strengthening system enabled the load and deflection capacities of the FRP-strengthened slabs, in relation to their un-strengthened reference slabs, to be enhanced by up to 121% and 57% for slabs with and without cut-outs respectively. [ABSTRACT FROM AUTHOR]

In this paper the trustworthiness of the existing theory for predicting the fiber-reinforced plastic contribution to the shear resistance of reinforced concrete beams is discussed. The most well-known shear models for external bonded reinforcement are presented, commented on, and compared with an extensive experimental database. The database contains the results from more than 200 tests performed in different research institutions across the world. The results of the comparison are not very promising and the use of the additional principle in the actual shear design equations should be questioned. The large scatter between the predicted values of different models and experimental results is of real concern bearing in mind that some of the models are used in present design codes. [ABSTRACT FROM AUTHOR]

Highlights • Robustness of multi-story load-bearing wall structure via non-linear FEA. • Response of axially loaded walls with cutout openings. • Influence of cutout openings on structural robustness. Abstract This paper presents the finite element analysis (FEA) results of a multi-story reinforced concrete (RC) building having precast and cast-in-place load bearing walls. Door-type cut-out openings (height: 2.1 m, width: 0.9–4.4 m) were created at the first and second story of the building. Results from experimental tests on axially loaded RC panels were used to verify the modeling approach. The influence of cut-out openings on the response of individual RC panels, failure modes, and load redistribution to adjacent members under increasing gravitational loads was analyzed. Moreover, the wall bearing capacities obtained from FEA were compared with the values calculated from design equations. The results revealed that the robustness of multi-story buildings having RC load bearing wall systems decrease considerably with the creation of cut-out openings. However, owing to the initial robustness of the buildings, large cut-out openings could be created under normal service conditions without strengthening of the building structure. Furthermore, design equations provided very conservative predictions of the ultimate axial capacity characterizing the solid walls and walls with small openings, whereas similar FEA and analytically predicted capacities were obtained for walls with large openings. [ABSTRACT FROM AUTHOR]

• The fatigue debonding rate was determined by the amplitude and level of the load. • The proposed model explicitly took into account the noted factors. • The d a /d N and the S ¯ · Δ S show a linear relationship in double logarithmic coordinates. • The debonded FRP has a significant effect on the subsequent debonding development. Externally bonded Fiber Reinforced Polymer (FRP) strengthening has been proven to be an efficient and reliable method for structural strengthening of reinforced concrete (RC) members. However, the beneficial effects of this method can be diminished due to the debonding of the FRP laminates. The mechanism of FRP debonding still requires further research, especially for strengthened members under fatigue loading. To understand and predict the FRP fatigue debonding process better, eleven FRP-concrete joint specimens were tested under static or fatigue loading. Both the theoretical derivation and the experimental study indicated that the debonding growth rate of the FRP laminate depended not only on the mean level (S ¯), but also the amplitude (Δ S) of the applied fatigue load. In addition, the debonded portion of the FRP laminate had a significant impact on the following debonding process due to the friction and mechanical interaction between the debonded FRP and the concrete surface. Therefore, a new nonlinear prediction model is proposed in this paper. The proposed model explicitly took into account the amplitude and the mean level of the fatigue loading, which enabled the effect of both to be modelled. Meanwhile, a correction term was also introduced into the model to account for the influence of the previously debonded FRP laminate. The predicted results of the debonding growth rate and the debonding length agreed well with the experimental results. [ABSTRACT FROM AUTHOR]

• CFRP plate debonding was observed in both static and fatigue tests but with different modes of propagation. • Fatigue damage accumulated in steel reinforcement during cyclical loading initiated CFRP plate debonding even when the CFRP plate strain was initially below the fatigue debonding strain threshold. • Accumulated fatigue damage in the steel reinforcement is coupled to fatigue debonding growth of the CFRP plate via stress redistribution and thus affects the fatigue life of strengthened beams. Externally bonded Fiber Reinforced Polymer (FRP) laminates are increasingly used to strengthen Reinforced Concrete (RC) members. However, FRP debonding remains a major drawback of this strengthening method. To better understand the mechanisms of FRP debonding, six RC beams strengthened with prestressed or non-prestressed Carbon Fiber Reinforced Polymer (CFRP) plates were subjected to static and fatigue loading. CFRP plate debonding was observed in both cases. However, the mechanism of debonding differed: under cyclical fatigue loading, debonding was initiated under both loading points simultaneously and propagated synchronously towards the nearest support whereas in static tests debonding began under a single loading point and progressed suddenly towards its adjacent support. The results also showed that stress redistribution induced coupling between accumulated fatigue damage in the steel reinforcement and fatigue debonding of the CFRP plate, accelerating the fatigue failure of the specimens. [ABSTRACT FROM AUTHOR]