Finite element analysis of rectangular reinforced concrete columns wrapped with FRP composites

Fibre reinforced polymer (FRP) wrapping of reinforced concrete (RC) columns has increasingly become the most suitable method used to strengthen and rehabilitate RC columns. It is clear that limited studies have investigated the behaviour of eccentrically loaded RC columns wrapped with FRP composites. In the present study, a three-dimensional finite element (FE) model was developed to simulate the behaviour of rectangular RC columns wrapped with glass fibre-reinforced polymer (GFRP) sheets under concentric and eccentric loading. The FE model was developed in the finite element analysis software ANSYS. The variables within the FE model are the number of GFRP layers and the magnitude of load eccentricity. The FE analysis results showed that GFRP wrapping significantly improved the performance of the strengthened columns by delaying concrete rupture. The presence of load eccentricity reduced the load carrying capacity and performance of the strengthened RC columns. The FE model correlated well with the stress distribution trends observed in the literature

Sorptivity of self-compacting concrete containing fly ash and silica fume

This paper presents the surface water absorption of self-compacting concrete (SCC) containing fly ash and silica fume using sorptivity test. Ordinary Portland cement was partially replaced by various combinations of fly ash and silica fume. Test results show that the presence of fly ash and silica fume significantly reduce the surface water absorption of self-compacting concrete at a water-binder ratio of 0.38. When only fly ash is used to partially replace Ordinary Portland cement, a more noticeable reduction in sorptivity is found when the fly ash content is greater than 20%

Shear Behaviour of RC T-Beams with Externally Bonded Discrete CFF Strips – A Experimental and Finite Element Study

The application of fibre reinforced polymer (FRP) composites for retrofitting and strengthening of existing reinforced concrete (RC) structures has fascinated the attention of researchers and engineers in the recent decades.  This paper presents the results of experimental and finite element (FE) investigation of shear behaviour of reinforced concrete T-beams repaired with externally bonded bi-directional discrete carbon fibre fabric (CFF) strips.  The reinforced concrete T-beams were tested under four point bending system to investigate the performance of CFF shear strengthening scheme in terms of ultimate load carrying capacity.  These beams were modelled using LUSAS software.  To evaluate the behaviour of the simulated models, the predicted results were compared with the experimental results.  The experimental results show that the gain in shear capacity of the CFF repaired beams ranged between 20% and 40% over the control beam.  Thus, it can be concluded that the externally bonded CFF strips significantly increased the shear capacity of CFF repaired beams.  It was generally observed that the developed FE model shows better agreement with the experimental results.  The results of load-deflection profile, cracking pattern, modes of failure, and strain distribution in discrete CFF strips are presented

Experimental studies and theoretical models for concrete columns confined with FRP composites: a review

Advanced fibre reinforced polymer (FRP) composites have been increasingly used over the last two decades for strengthening, upgrading, and restoring degraded civil engineering infrastructure. Substantial experimental investigations have been conducted in recent years to understand the compressive behaviour of FRP-confined concrete columns. A considerable number of confinement models to predict the compressive behaviour of FRP strengthened concrete columns have been developed from the results of these experimental investigations. The purpose of this paper is to present a comprehensive review of experimental investigations and theoretical models of circular and non-circular concrete columns confined with FRP reinforcement. The paper reviews previous experimental test results on circular and non-circular concrete columns confined with FRP reinforcement under concentric and eccentric loading conditions and highlights the behaviour and mechanics of FRP confinement in these columns. The paper also reviews existing confinement models for concrete columns confined with FRP composites in both circular and non-circular sections. This paper demonstrates that the performance and effectiveness of FRP confinement in concrete columns have been extensively investigated and proven effective in enhancing the structural performance and ductility of strengthened columns. The strength and ductility enhancement depend on the number of FRP layers, concrete compressive strength, corner radius for non-circular columns, and intensity of load eccentricity for eccentrically loaded columns. The impact of existing theoretical models and directions for future research are also presented. Potential researchers will gain insight into existing experimental and theoretical studies and future research directions

Concrete-filled double skin steel tubular column with hybrid fibre reinforced polymer post fire repair

The concrete-filled double skin steel tubular (CFDST) column is becoming more popular nowadays due to its superior performance compared to conventional composite column and concrete-filled steel tubular (CFST) column. However, the use of this type of column is still limited to outdoor construction such as bridge piers and transmission towers where fire is not the main concern. Moreover, existing research studies on the CFDST column only focused on fire performance, and limited research studies can be found on the residual strength of theCFDSTcolumn. Residual strength can be used to determine the most suitable repair method needed in order to retrofit the column. Therefore, this study aims to study the effect of different parameters on the residual strength of the CFDST column. Among discussed parameters are the thickness of the outer steel tube (t0) and fire exposure time. In addition, this study also aims to determine the effectiveness of the repair method using Single and Hybrid fiber-reinforced polymer (FRP) of fire-damaged CFDST columns. CFDST columns were heated in accordance with ASTM E119-11: Standard Test Methods for Fire Tests of Building Construction and Materials until the temperature reached 600 °C. Afterwards, the temperature was kept constant for two different durations, i.e., 60 and 90 mins. The specimen was then left to cool down to room temperature inside the furnace before itwas taken out and repaired by Single and Hybrid FRP. The specimens were categorized into the following three groups: (1) unheated or control specimens, (2) heated and unrepaired specimens and (3) heated and repaired specimens. All specimens were subjected to axial compression loading until failure. The first and second category specimens failed by local outward buckling of outer steel tube, crushing of concrete and local buckling of inner steel tube, whereas specimens in the third category failed by rupture of FRP followed by similar local buckling and concrete crushing as those observed in first and second category specimens. Ultimate strength, secant stiffness and Ductility Index (DI) decreased as the temperature of the specimen increased. The loss in secant stiffness of thinner CFDST specimens exposed to 60 mins of fire exposure time is similar to thicker CFDST specimens exposed to 90 mins of fire exposure time regardless of their diameter. In addition, CFDST specimens exposed to 90 mins of fire exposure time were more ductile than control specimen. RSI and secant stiffness increased with the increase in fire exposure time. Interestingly, the highest RSI achieved is only 22% whichmeans the specimens were still able to carry more than 70% of their initial load after being exposed to 90 mins of fire exposure timewith only 3mmthickness of outer steel tube. Repairing the fire-damaged CFDST columns with Single and Hybrid FRP is proven to improve the ultimate compressive strength significantly. The increment in ultimate compressive strength is more pronounced in the specimen with Hybrid FRP and thinner outer steel tube. The secant stiffness and Ductility Index (DI) of repaired specimens were, however, not able to be restored to those of the control specimen

Finite element analysis of rectangular reinforced concrete columns wrapped with FRP composites

Fibre reinforced polymer (FRP) wrapping of reinforced concrete (RC) columns has increasingly become the most suitable method used to strengthen and rehabilitate RC columns. It is clear that limited studies have investigated the behaviour of eccentrically loaded RC columns wrapped with FRP composites. In the present study, a three-dimensional finite element (FE) model was developed to simulate the behaviour of rectangular RC columns wrapped with glass fibre-reinforced polymer (GFRP) sheets under concentric and eccentric loading. The FE model was developed in the finite element analysis software ANSYS. The variables within the FE model are the number of GFRP layers and the magnitude of load eccentricity. The FE analysis results showed that GFRP wrapping significantly improved the performance of the strengthened columns by delaying concrete rupture. The presence of load eccentricity reduced the load carrying capacity and performance of the strengthened RC columns. The FE model correlated well with the stress distribution trends observed in the literature

Graphene oxide's regenerative acidity and its effects on the hydration of type II Portland cement.

Incorporation of graphene oxide (GO) has been found to considerably improve the hydration process, strength and durability of Portland cement. However, the exact nature of its chemical interactions with the cement are unclear. In this study, GO of varying amounts of hydroxyl groups were synthesized to investigate the effects of these interactions on the hydration of an environment-friendly Type II Portland Cement. XPS, Raman, and FTIR analysis verified the functional group differences between the GO types, and SEM and AFM observations illustrated the existence of a hydronium layer coating the high-hydroxyl GO (HGO). The hydronium layer neutralizes small base additions as measured through titration, and regenerates via protonation of resulting water by HGO's hydroxyl groups, confirmed via zeta potential analysis. In cement, HGO shows accelerated and greater early-age hydration, measured via heat of hydration and XRD. Finer microstructural density of HGO-cement was also observed from BET and microCT analysis. On the other hand, low-hydroxyl GO (XGO) cement ‘locks’ C-S-H on the GO sheet, preventing its propagation in the cement microstructure, as observed by Si-O bond changes during hydration. Lastly, HGO-concrete showed significantly improved workability (>40%), 28-day compressive strength (29%), and 28-day flexural strength (24%) with respect to control. Conversely, XGO-concrete showed reduced workability (−40%), and smaller 28-day strength improvements (compressive by 5%, and flexural by 8%). This research leads to new understandings of how GO may improve the strength, workability, and durability of concrete, with potentially less overall cement consumption and superplasticizer use

Nano-Silica modifier asphalt concrete under rutting resistance and shape memory component

Permanent deformation is pavement distress that has been the root cause of failure of roads globally. With the formation of a rut, follows cracking which inevitably damages the asphalt and sub-base layers. To curb the rutting distress, this study investigates the use of nanosilica, miniaturized silica particles to the power of 10-9 to modify the binder of the asphalt concrete. The nano-silica was added at 4%, 6% and 15% by weight of bitumen into the asphalt mixture. Marshall Mix design method was used to prepare the forty-eight samples used in the study. Repeated Load Permanent Deformation (RLPD) test and Shape Memory (SM) were performed at two temperatures (25°C and 40°C). It was found that the rutting resistance and shape memory had the best performance with the addition of 15% nano-silica at 40°C. Addition of nano-silica at 15% by weight of bitumen had the best amelioration of not only permanent deformation resistance but also shape retention thus enhancing pavement performance

Tumor histoculture captures the dynamic interactions between tumor and immune components in response to anti-PD1 in head and neck cancer

Abstract Dynamic interactions within the tumor micro-environment drive patient response to immune checkpoint inhibitors. Existing preclinical models lack true representation of this complexity. Using a Head and Neck cancer patient derived TruTumor histoculture platform, the response spectrum of 70 patients to anti-PD1 treatment is investigated in this study. With a subset of 55 patient samples, multiple assays to characterize T-cell reinvigoration and tumor cytotoxicity are performed. Based on levels of these two response parameters, patients are stratified into five sub-cohorts, with the best responder and non-responder sub-cohorts falling at extreme ends of the spectrum. The responder sub-cohort exhibits high T-cell reinvigoration, high tumor cytotoxicity with T-cells homing into the tumor upon treatment whereas immune suppression and tumor progression pathways are pre-dominant in the non-responders. Some moderate responders benefit from combination of anti-CTLA4 with anti-PD1, which is evident from better cytotoxic T-cell: T-regulatory cell ratio and enhancement of tumor cytotoxicity. Baseline and on-treatment gene expression signatures from this study stratify responders and non-responders in unrelated clinical datasets