Reinforced Concrete T-beams Research Articles

Experimental study on shear behavior of fire-damaged reinforced concrete T-beams retrofitted with prestressed steel straps

Abstract This study examines the shear behavior of fire-damaged reinforced concrete (RC) T-beams confined by prestressed steel straps (PSS) able to provide active confinement. Twelve RC T-beams were fabricated and eleven of those were exposed to fire in accordance with the ISO834 standard fire. Then eight of the fire-damaged specimens were retrofitted with the PSS and the four-point bending tests were then conducted. The effects of various parameters on the shear failure mode and shear capacity of the specimens were studied including the heating time, the number of layers reinforced by straps and the spacing of straps. The test results showed that the shear capacity and ductility of post-fire retrofitted specimens were higher than those of the unstrengthened specimens. Therefore, the proposed PSS modification techniques were verified to be valid for confining RC elements after fire. Based on the test results, the corresponding calculation method for the shear capacity of fire-damaged specimens retrofitted with PSS was also presented in this paper. The aforementioned analysis can be used for the design of these retrofitted beams and provide an effective foundation for further research.

Experimental research on fire-damaged RC continuous T-beams subsequently strengthened with CFRP sheets

This paper presents experimental results of the structural performance of fire-damaged continuous reinforced concrete (RC) T-beams subsequently strengthened with externally bonded carbon fiber reinforced polymer (EB-CFRP) sheets. A series of seven specimens were tested with different fire exposure time and subsequent strengthening techniques. Experimental results showed that both the unexposed control beams and unstrengthened fire-damaged continuous RC T-beams exhibited flexure failure modes and significant redistribution of moment between hogging and sagging regions. The fire-exposed beams had notably degraded strength and stiffness attributable to the internal temperatures exceeding 500 °C for some portion of the exposure. The EB-CFRP strengthening of fire damaged beams was shown to mostly mitigate the effects of fire exposure. The EB-CFRP retrofit measures successfully restored the virgin capacity of the beam and were sufficient to also restore most of the lost initial stiffness. Simple prediction using plane sections analysis and the assumptions of the 500 °C isotherm method [1] were shown to accurately predict the behaviour of the fire-damaged specimens.

NUMERICAL INVESTIGATION OF THE PERFORMANCE OF INSULATED FRP-STRENGTHENED REINFORCED CONCRETE BEAMS IN FIRE


 
 
 Fiber reinforced polymers (FRP) have been widely used in retrofitting and strengthening of deteriorated or deficient reinforced concrete (RC) elements. A major concern about those systems is their performance under elevated temperature which limits the application of FRP for strengthening requirements. Fire protection of the strengthening FRP system can be made by applying an external coating layer of a thermal resisting material. In order to predict the fire performance of such insulated FRP-strengthened members and their efficiency, experimental investigations are required to be carried out for such elements under realistic fire conditions, which requires time and cost.
 This paper presents numerical modelling of RC beams strengthened with externally bonded FRP and insulated by a fire protection layer under elevated temperature specified by standard fire tests. The nonlinear time domain transient thermal-stress finite element analysis is performed using the general purpose software ANSYS 12.1 in order to study the heat transfer mechanism and deformation within the beam for fire conditions initiating at the bottom side of the beam. The finite element model accounts for the variation in thermal and mechanical parameters of the constituent materials such as concrete, steel reinforcement bars, FRP and insulation material with temperature. Application is made on an FRP-strengthened and insulated RC T-beam which has been experimentally tested in the published literature in order to verify the adopted modelling procedure. The obtained numerical results are in good agreement with the experimental results regarding the temperature distribution across the beam and mid-span deflection. The presented procedure thus provides an economical and effective tool to investigate the effectiveness of fire insulation layers when subjected to high temperatures and to design thermal protection layers for FRP strengthening systems that satisfy fire resistance requirements specified in building codes and standards.
 
 

Experimental and numerical analyses of flexurally-strengthened concrete T-beams with stainless steel

This work presents the results and the main conclusions of a series of experimental tests carried out to evaluate the efficiency of post-installed stainless steel reinforcement on the flexural strengthening of Reinforced Concrete (RC) T-beams when the bonding techniques EBR (Externally Bonded Reinforcement), NSM (Near Surface Mounted) and MA-EBR (EBR with Mechanical Anchors) are used. The RC T-beams were also modelled using a commercial Finite Element (FE) software in order to predict their behaviour until the rupture. For this purpose, a set of single-lap shear tests were also carried out to evaluate the local bond-slip relationships developed within the Stainless Steel (SS)-to-concrete interface. Due to the experimental bond-slip relationships, the numerical simulations were able to predict, with good accuracy, the different behaviours of the RC T-beams until their rupture. Moreover, the different rupture modes observed on all the RC T-beams herein tested were very well estimated by the numerical analyses. The tests of the RC T-beams showed that all the strengthening techniques allowed their flexural stiffness to be increased. Nevertheless, the RC T–beams strengthened with the EBR and NSM techniques had premature ruptures, i.e. the rupture in the RC T-beams occurred even before the yielding of their steel reinforcements. The RC T-beam strengthened with the MA-EBR technique showed good ductility and the highest load bearing capacity, which means that the MA-EBR technique is the best bonding technique herein used.

Flexural strengthening of damaged RC T-beams using self-compacting concrete jacketing under different sustaining load

An experimental test is proposed in the present study to investigate the flexural behavior of damaged reinforced concrete (RC) beams strengthened by self-compacting concrete jacketing under different sustaining load. Eight RC T-beams with primary damages are designed and strengthened under different sustaining load. Then, the flexural testing test is employed to investigate the structural behavior of the strengthened beams. The influences of the sustaining load on beam response are clarified. The prediction method for the flexural capacity of the strengthened beams is also discussed. Results shows that the strengthening method proposed in the present study improves effectively the flexural behavior of beams, both in the stiffness after concrete cracking and the flexural capacity of the beams. Especially the flexural capacity, which becomes about twice as great. The interface treatment by surface roughening and rebar planting can provide effective bond strength between the substrate-new concrete. Sustaining load increase slightly the stiffness and the flexural capacity of beams until exceeding a critical value. The critical load was about 30% of the yield moment of beam before strengthening in the present test. The prediction of flexural capacity had high accuracy by the plastic limit analysis method and neglecting the strain-lag effects caused by the sustaining load during the strengthening process.

The use of Wire Mesh-Polyurethane Cement (WM-PUC) composite to strengthen RC T-beams under flexure

This paper presents the experimental behaviours of reinforced concrete (RC) T-beams strengthened using an innovative technique, namely, wire mesh-polyurethane cement (WM-PUC) composite. The flexural behaviour of WM-PUC-strengthened beams was investigated. This investigation considered three parameters: the amount of wire mesh used, the material into which the wire mesh was embedded, and the loading method. All beams were tested in a four-point bending setup. The test results indicated that relative to ferrocement-strengthened beams, the WM-PUC-strengthened beams exhibited significantly greater yield loads, ultimate loads and stiffnesses, and these enhancements increased with an increasing number of layers of wire mesh. Relative to ferrocement strengthening, WM-PUC strengthening was found to more effectively hinder crack expansion, mainly because no cracks appeared on the PUC surface after the concrete cracked until its failure. After strengthening with WM-PUC laminate, the decreased stiffness of a pre-cracked beam was not as easily detectable in the early stage relative to that of a non-preloaded beam. The good bonding performance of the PUC in the WM-PUC laminate indicated that no additional bonding aid is needed in WM-PUC-strengthened beams. These results demonstrate that WM-PUC strengthening shows potential as an external strengthening technique for concrete structures.

The effect of varying span on Design of Medium span Reinforced Concrete T-beam Bridge Deck

The effect of varying span on Design of Medium span Reinforced Concrete T-beam Bridge Deck

Evaluation of FRP-to-concrete anchored joints designed for FRP shear-strengthened RC T-beams

The objective of this paper is to evaluate the bond performance of different anchorage techniques that can in particular be used for fiber reinforced polymers (FRP) shear-strengthened reinforced concrete (RC) T-beams. The results of two different experimental programs are gathered and compared to highlight some common aspects. Overall, 25 bond tests on FRP-to-concrete joints with test setups that simulate the behavior of an anchored FRP shear-strengthened beam are examined. The anchorage techniques considered are mechanical anchors, FRP bars, longitudinal FRP plates, extensions to the underside of the flange, and carbon FRP (CFRP) ropes. The influence of concrete strength, plate width, bond length, and rope length on bond strength is investigated. Experimental results show that both bond strength and ductility are affected by the anchorage technique used. In light of the experimentally observed failure modes, some bond strength models provided in the literature and design standards are used to predict the maximum bond load of FRP-to-concrete joints and compared with experimental results.

Prediction of Capacity for Moment Redistribution in FRP-Strengthened Continuous RC T-Beams

AbstractBecause of the premature debonding of fiber-reinforced polymer (FRP) materials that results in a reduction in ductility, the problem of how to exploit moment redistribution (MR) in FRP-strengthened continuous reinforced concrete (RC) structures is unresolved. To date, limited research has been conducted into MR in such structures; a reliable and rigorous solution for quantifying MR throughout the loading cycle remains elusive. This paper aims to quantify MR and predict the capacity at reasonable accuracy, to encourage the use of FRP for the strengthening of existing continuous RC structures. Experiments conducted on 12 continuous T-beams are reported, and the findings are discussed. Strengthening configuration and anchorage scheme are the main variables. A new analytical strategy is described for quantifying MR, and the analytical results are then validated against the experimental results. Both experimental and analytical results confirm that there is no reason to restrict MR into strengthened zo...

Shear strengthening of full-scale RC T-beams using textile-reinforced mortar and textile-based anchors

This paper presents a study on the effectiveness of TRM jacketing in shear strengthening of full-scale reinforced concrete (RC) T-beams focussing on the behaviour of a novel end-anchorage system comprising textile-based anchors. The parameters examined in this study include: (a) the use of textile-based anchors as end-anchorage system of TRM U-jackets; (b) the number of TRM layers; (c) the textile properties (material, geometry); and (d) the strengthening system, namely textile-reinforced mortar (TRM) jacketing and fibre-reinforced polymer (FRP) jacketing for the case without anchors. In total, 11 full-scale RC T-beams were constructed and tested as simply supported in three-point bending. The results showed that: (a) The use of textile-based anchors increases dramatically the effectiveness of TRM U-jackets; (b) increasing the number of layers in non-anchored jackets results in an almost proportional increase of the shear capacity, whereas the failure mode is altered; (c) the use of different textile geometries with the same reinforcement ratio in non-anchored jackets result in practically equal capacity increase; (d) TRM jackets can be as effective as FRP jackets in increasing the shear capacity of full-scale RC T-beams. Finally, a simple design model is proposed to calculate the contribution of anchored TRM jackets to the shear capacity of RC T-beams.

Shear Strengthening of Reinforced Concrete T-Beams with Hybrid Composite Plate

AbstractThis paper aims to evaluate the effectiveness of hybrid composite plates (HCPs) technique for the shear strengthening of the reinforced concrete (RC) T cross-section beams. HCP consists of a thin plate of strain hardening cementitious composite (SHCC) reinforced with carbon fiber reinforced polymer (CFRP) laminates. Two HCPs with different CFRP laminates percentage (ρfw=0.08% and ρfw=0.14%) were adopted for the shear strengthening of the beams. The HCPs were bonded to substrate in two different ways. In the first case, the HCPs were bonded using epoxy adhesive, whereas in the second case they were bonded using epoxy adhesive and fixed by mechanical anchors. The effectiveness of this technique was limited by the tensile strength of the concrete cover of the strengthened beams. Therefore, in the second case, mechanical anchors prevented a premature debonding of the HCPs and a certain concrete confinement was applied in the zone of the beam to be strengthened, resulting in favorable effects in terms ...

Experimental Investigation of Shear Behavior of Deep RC T-beams Under Indirect Loading

The main goal of present study is to experimentally and analytically investigate the behavior of indirect loading, deep flanged reinforced concrete (RC) beams. The load is applied via shear on the side arms of the beam with bearing plates. Eighteen reinforced concrete deep T- beams designed to fail in shear. The beams without web reinforcement were tested under indirectly loading conditions. The beams were divided into three groups according to the ratio of shear span to effective depth. The specimens had different flange depth and flange width in order to investigate the effects of flange dimensions. The behavior of beams was observed; cracking load, ultimate loads, concrete strain, deflections and crack widths. Experimental results indicate that the indirectly loaded deep beams can carry additional loads after diagonal cracking. The study includes numerically predicted the Ultimate Loads carrying capacity with strut-and-tie method (STM) which is based on the ACI Building Code (318-08). The prediction results of ultimate shear capacity for (STM) models are agreed with the experimental finding. As well as the

Innovative Repair of Severely Corroded T-Beams Using Fabric-Reinforced Cementitious Matrix

AbstractThis paper offers an innovative technique for rehabilitation of severely corroded reinforced concrete (RC) T-beams using fabric-reinforced cementitious matrix (FRCM). Eight RC T-beam specimens were constructed and tested to failure under four-point load configuration. One beam was neither corroded nor repaired to act as a benchmark. Seven beams were presubjected to accelerated corrosion for 5 months that corresponded to an average tensile steel mass loss of 22%. Corrosion was restricted to the tensile steel located in the middle third of the beam span. Six corroded beams were repaired with either carbon or basalt FRCM system whereas one corroded beam was left unrepaired. The fabrics were internally embedded within the clear cover of the corroded-repaired region and/or externally bonded along the beam span. Corrosion damage significantly reduced the flexural capacity and ductility of the unrepaired beam. The basalt FRCM system could not restore the original flexural capacity of the beam whereas the...

Investigation of Near Surface–Mounted Method for Shear Rehabilitation of Reinforced Concrete Beams Using Fiber Reinforced–Polymer Composites

This paper presents the results of an investigation of reinforced concrete (RC) T-beams retrofitted in shear with near-surface mounted (NSM) fiber-reinforced polymer (FRP) rods. Six full-scale 4,520-mm-long RC T-beams were tested to study the effects of important parameters such as the presence of NSM FRP rods, the presence of steel stirrups, and the steel stirrup ratio. This paper provides an insightful and comprehensive description of the behavior of strengthened T-beams under increasing load, from the formation of the first crack to ultimate failure. The results of this study and those gathered in the presented database show that existing steel stirrups and strengthening NSM FRP did not diminish each other’s effect when failure modes unrelated to shear resistance of RC beams were prevented. The experimental results of this study and those in the database were used to verify a newly proposed model to predict the shear contribution of NSM FRP rods and laminates in RC beams strengthened in shear. The proposed model showed an improved accuracy compared with the existing models in the literature.

Modes of Failure in Shear Deficient RC T-Beams Strengthened with FRP

The effect of laminate thickness on crack pattern, mode of failure, and strength of shear deficient reinforced concrete (RC) T-beams wrapped with glass fiber reinforced polymer (GFRP) laminates was studied experimentally and numerically. Eight specimens of 2.5 m span, designed to fail in shear, were tested for two point static loading. Displacements, strains, and crack pattern were monitored. The strength and mode of failure were found to depend on the crack pattern. For U wraps, increasing the fiber reinforced polymer (FRP) laminate thickness resulted in reduced web cracking and increased cracking near the free edge of the laminate.

Cyclic performance of reinforced concrete T-beams strengthened in shear with fiber-reinforced polymer composites: Sheets versus laminates

Much existing reinforced concrete (RC) civil infrastructure worldwide is in need of shear strengthening and rehabilitation. The use of externally bonded (EB) carbon fiber-reinforced polymer (CFRP) sheets and laminates to strengthen deficient RC beams in shear is now an acceptable and cost-effective practice, particularly under static loads. However, due to its complexity, the cyclic (fatigue) behavior and performance of shear-strengthened beams is not fully documented. Recently, use of CFRP continuous sheets wrapped over the shear length for fatigue upgrade has been studied. This technique may present drawbacks related to surface preparation and FRP debonding. Therefore, when possible, prefabricated CFRP L-shaped laminates can be a cost-effective alternative because they require less surface preparation and do not peel off easily. The objective of this paper was to present the results of an experimental investigation that compared cyclic (fatigue) and static (post-fatigue) behavior of two EB CFRP techniques (sheets vs. laminates) for shear retrofit of RC T-beams. In total, six laboratory tests on full-size 4520-mm-long beams were conducted. The specimens were subjected to fatigue loading of up to 6 million load cycles at a rate of 3 Hz. Specimens that sustained 6 million cycles were then tested monotonically up to failure. The variables examined in the paper were: (1) the EB CFRP strengthening scheme, and (2) the presence and ratio (spacing) of internal shear reinforcement. The test results confirmed the effectiveness of using EB CFRP shear-strengthening methods under cyclic loading. They also revealed that the fatigue performance of RC T-beams strengthened with L-shaped laminates is significantly superior in extending fatigue life compared to corresponding T-beams strengthened with U-wrapped sheets. This was quantified in terms of deflection response (47% increase due to fatigue loading for specimens with L-shaped laminates compared to 90% for specimens with U-wrapped sheets), and the level of increase in steel-stirrups strain range (9–42% vs. 62–114%) and in EB CFRP (36–97% vs. 58–163%).

Effect of End Anchorage in External CFRP Confinement on Shear Damaged RC Beams

In recent days many structures are strengthened or restored to make use of the existing structure to the current needs. Upgrading a structure by restoration and strengthening eliminates the need of devastating and reconstruction also saves energy. In repair and retrofitting of a structural elements or a structure, appropriate techniques has to be choose according to the damage level or the requirement. Epoxy or any polymer injection is a kind of method to repair the cracked region. Fiber reinforced polymer (FRP) wrapping is a kind of external strengthening techniques being in practice to retrofit a reinforced concrete (RC) structure without increasing the dead load. In this study the effectiveness of externally bonded carbon-fiber-reinforced polymer (EB-CFRP) system with end anchorage on retrofitting of damaged RC beams has been examined. To represent a severe damage condition, control beams are tested to failure, retrofitted, and then retested to failure for a second time. The test results demonstrated that retrofitting of severely damaged RC T-beams with EB-CFRP composite with proper end anchorage can fully restore the original shear capacity of the beams without increasing the dimension of the structural member. Also this end anchorage system significantly restricts the delamination of FRP during severe loading than EB-CFRP method.

Fire behavior of concrete T-beams strengthened with near-surface mounted FRP reinforcement

This paper presents results from experimental and numerical studies on fire behavior of reinforced concrete (RC) T-beams strengthened with near-surface mounted (NSM) fiber-reinforced polymer (FRP) reinforcement. Four RC T-beams, strengthened with NSM FRP reinforcement, were tested by subjecting them to ASTM E119 standard fire exposure and service load conditions. The test variables included load level, restraint conditions, and fire protection applied on the beams. Data from fire resistance experiments is utilized to validate predictions from numerical model to trace the fire response of NSM FRP strengthened concrete T-beams. Results from fire tests and numerical studies indicate that NSM FRP strengthened beams can sustain service loads for three hours under standard fire conditions, even without any external fire protection. In addition, fire induced axial restraint enhances the fire response of NSM FRP strengthened RC beams, while higher load levels lead to much larger deflections and lower fire resistance in these beams.

Shear Strengthening of Reinforced Concrete T-Beams Using Anchored CFRP Materials

Shear Strengthening of Reinforced Concrete T-Beams Using Anchored CFRP Materials

Fatigue behavior of RC T-beams strengthened in shear with EB CFRP L-shaped laminates

The use of externally bonded carbon fiber-reinforced polymer (EB-CFRP) to strengthen deficient reinforced concrete (RC) beams has gained in popularity and has become a viable and cost-effective method. Fatigue behavior of RC beams strengthened with FRP is a complex issue due to the multiple variables that affect it (applied load range, frequency, number of cycles). Very few research studies have been conducted in shear under cyclic loading. The use of prefabricated CFRP L-shaped laminates (plates) for strengthening RC beams under static loading has proven to be technically feasible and very efficient. This study aimed to examine the fatigue performance of RC T-beams strengthened in shear for increased service load using prefabricated CFRP L-shaped laminates. The investigation involved six laboratory tests performed on full-size 4520mm-long T-beams. The specimens were subjected to fatigue loading up to six million load cycles at a rate of 3Hz. Two categories of specimens (unstrengthened and strengthened) and three different transverse-steel reinforcement ratios (Series S0, S1, and S3) were considered. Test results were compared with the upper fatigue limits specified by codes and standards. The specimens that did not fail in fatigue were then subjected to static loading up to failure. The test results confirmed the feasibility of using CFRP L-shaped laminates to extend the service life of RC T-beams subjected to fatigue loading. The overall response was characterized by an accelerated rate of damage accumulation during the early cycles, followed by a stable phase in which the rate slowed significantly. In addition, the strains in the stirrups decreased after the specimens were strengthened with CFRP, despite the higher applied fatigue loading. Moreover, the addition of L-shaped laminates enhanced the shear capacity of the specimens and changed the failure mode from brittle to ductile under static loading. Finally, the presence of transverse steel in strengthened beams resulted in a substantially reduced gain in shear resistance due to CFRP, confirming the existence of an interaction between the transverse steel and the CFRP.