Longitudinal Tensile Reinforcement Ratio Research Articles

Experimental investigation of the effect of longitudinal tensile reinforcement ratio on ductility behaviour in GPC beams

This research first determined the strength of the cylindrical geopolymer concrete materi- als under compressive stresses. Secondly, conventional and geopolymer-reinforced concrete beams were manufactured in different reinforcement ratios, and their mechanical properties were compared under bending. The main aim of this study is to experimentally compare the effect of reinforcement ratio on the ductility behavior of an alkali-activated geopolymer con- crete (GPC) beam with that of an ordinary Portland cement (OPC) beam. First, balanced reinforcement calculations were made considering the mechanical properties obtained from the material tests. The load-displacement, moment-curvature, and crack development results obtained from beam tests are interpreted with this information. OPC and GPC beams exhibit- ed similar strength and crack development behavior. However, the behavior of GPC and OPC concretes differs regarding the ductility index. Therefore, to achieve similar ductility in the conduct of GPC and OPC beams, the balanced reinforcement ratio and section dimensions of GPC beams should be chosen to be larger than OPC.

Behavior of hollow self-compacted concrete beams reinforced with aluminum sections

This paper presents a study on improving the flexural performance of self-compacting hollow concrete beams with embedded aluminum sections, both experimentally and numerically. The experimental program involved testing three specimens to illustrate the impact of the bare and aluminum-reinforced voids on the mechanical properties of the hollow beams relative to the solid reference beam. A three-dimensional (3D) non-linear finite element model (FEM) was initially developed using ABAQUS software and validated against experimental results. The validated model examined the effects of void area (16–49% of the beam cross-section), void configuration (square or circular), longitudinal tensile reinforcement ratio (0.41–1.19%), and shear reinforcement ratio (0–0.56%) on the failure patterns and load–displacement relationships of hollow reinforced concrete (RC) beams with or without reinforced internal aluminum sections. Results showed that the embedded aluminum reinforcement promoted a more uniform distribution of flexural cracks along the effective length of the hollow RC beams and delayed the formation of shear cracks compared to the bare specimens. Furthermore, the embedded aluminum reinforcement effectively restored the ultimate capacity of the hollow beams with a void area ranging from 16 to 36% of the beam cross-section. Despite having the same area, the ultimate load-carrying capacity of both bare and reinforced beams featuring circular voids was higher than those with square voids.

Effect of the outer UHDC layer on shear and flexural behavior of RC beams produced with low binder concrete

Composite beams with a cement distribution along the cross-section more efficient can be used to increase their durability and simultaneously decrease the ecological footprint related with cement production. The higher dosages are used only on the cover layer, to provide a higher protection of the steel reinforcement, and the core of the beams is produced with a low cement concrete, using in this case 125 kg of cement per m3. In addition, the core is not subjected to such higher normal stresses as on both bottom and top of the cross section, so the mechanical performance of this concrete is not so challenging and, consequently, the cement dosage can be thus reduced.This experimental study aims to analyze how the strength capacity and stiffness of beams are affected using the ‘superskin’ concept, particularly the influence of how the external layer made with an ultra-high durability concrete (UHDC) is applied, being the core produced with a low binder concrete (LBC).Nine different beams were tested, until bending or shear-controlled failure occur, varying the longitudinal tensile reinforcement ratio and the way how the UHDC layer is applied: i) one single layer with a ‘U’ shape around cross-section and, ii) three separated thin plates, cast against the core concrete. The followings parameters were analyzed: load–displacement relation, flexural strength, shear strength, ductility, crack pattern and failure mode. The results show that this type of beams present a better structural behavior relatively to the reference beams, beyond the two benefits already identified, the durability and eco-efficiency increase. In certain beams the flexural strength increased around 70% and the shear strength almost 90%. The results also reveal the advantages of using a monolithic UHDC layer, namely, in terms of cracking.

Flexural performance of steel-reinforced geopolymer concrete one-way slabs: Experimental and numerical investigations

This paper investigated the out-of-plane flexural performances of ambient-cured steel-reinforced slag and fly ash-based geopolymer concrete one-way slabs, in which the activator was the blend of NaOH and sodium silicate solutions (SiO2/Na2O = 3.1–3.3). Twelve specimens were prepared and tested, which included six OPC concrete specimens. The test parameters were concrete type (i.e., geopolymer and ordinary Portland cement (OPC) concrete), concrete compressive strength (i.e., 30 MPa, 40 MPa, and 50 MPa) and longitudinal tensile reinforcement ratio (i.e., 0.82 % and 1.20 %). The failure modes, crack patterns, load–deflection relationships and load–strain relationships of all specimens were carefully studied and reported. Further, a two dimensional (2D) finite element (FE) analysis was conducted to validate the test results. The results of the study indicated that: (1) the geopolymer concrete specimens presented lesser crack width and crack spacing owing to the improved bond between rebar and geopolymer concrete; (2) the cracking load and initial stiffness of geopolymer concrete specimens were slightly lower than that of OPC concrete counterparts; (3) the current Codes of Practice GB50010-2010 and ACI 318-19 provided reasonable predictions of the cracking load and flexural load capacity of the steel-reinforced geopolymer concrete specimens; (4) the developed FE model provided a good prediction of the flexural performance of the tested slabs, and could be used for further parametric investigation.

Bond Behaviour of Near-Surface Mounted Strips in RC Beams-Experimental Investigation and Numerical Simulations.

This paper presents an investigation of the bond mechanism between carbon fibre reinforced polymer (CFRP) laminates, concrete and steel in the near-surface mounted (NSM) CFRP-strengthened reinforced concrete (RC) beam-bond tests. The experimental program consisting of thirty modified concrete beams flexurally strengthened with NSM CFRP strips was published in. The effects of five parameters and their interactions on the ultimate load carrying capacities and the associated bond mechanisms of the beams are investigated in this paper with consideration of the following investigated parameters: beam span, beam depth, longitudinal tensile steel reinforcement ratio, the bond length of the CFRP strips and compressive concrete strength. The longitudinal steel reinforcement was cut at the beam mid-span in four beams to investigate a better assessment of the influence of the steel reinforcement ratio on the bond behaviour of CFRP to concrete bond behaviour. The numerical analysis implemented in this paper is based on a nonlinear micromechanical finite element model (FEM) that was used for investigation of the flexural behaviour of NSM CFRP-strengthened members. The 3D model based on advanced CFRP to concrete bond responses was introduced to modelling of tested specimens. The FEM procedure presents the orthotropic behaviour of the CFRP strips and the bond response between the CFRP and concrete. Comparison of the experimental and numerical results revealed an excellent agreement that confirms the suitability of the proposed FE model.

Neutral Axis Depth versus Ductility and Plastic Rotation Capacity on Bending in Lightweight-Aggregate Concrete Beams.

This article presents an experimental study on the evolution of the neutral axis depth at failure in the critical section with the flexural ductility and plastic rotation capacity of reinforced concrete (RC) lightweight-aggregate concrete (LWAC) beams. For this, the results of a previous experimental program involving RC LWAC beams tested in flexure until failure are used. The variable studies were the concrete compressive strength (between 22.0 and 60.4 MPa and dry density between 1651 and 1953 kg/m3) and the longitudinal tensile reinforcement ratio (between 0.13% and 2.69%). The flexural ductility and the plastic rotation capacity of the RC LWAC beams are characterized by a ductility index and a plastic trend parameter, respectively. The influence of the variable studies, as well as the relation of the flexural ductility and plastic rotation capacity with the values for the neutral axis depth at failure are analyzed and discussed. Some conclusions are drawn which can be useful for the design of RC LWAC beams for flexure. In particular, it is shown that the practical rule of limiting the neutral axis depth at failure to ensure ductile behavior, as used in normal-weight aggregate concrete beams, is also valid for RC LWAC beams.

Experimental and Analytical Investigations of a Locally Developed Ultrahigh-Performance Fiber-Reinforced Concrete

AbstractThis paper presents the experimental investigations and analytical modeling of the strength and flexural characteristics of a locally (Las Cruces, New Mexico) developed fiber-reinforced ultrahigh-performance concrete (UHPC). High-strength steel fibers were used to improve the strength and flexural properties of the UHPC. Mean compressive strength of the UHPC mixture was obtained as 138 MPa. The UHPC beams also exhibited favorable flexural responses with the deformational ductility indexes ranging between 6 and 10 and the performance factor between 4 and 6. The longitudinal tensile reinforcement ratio was 0.7%, and no transverse reinforcement was present. The moment versus curvature response was modeled analytically by considering the microscopic stress-strain relationship of the concrete and steel. This response was then integrated with a force-based distributed plasticity beam element. The analytical model thus created captured the experimental moment-curvature and force-deformation responses wit...

FLEXURAL DUCTILITY OF LIGHTWEIGHT-AGGREGATE CONCRETE BEAMS

This paper describes an experimental study on the flexural ductility of lightweight-aggregate concrete beams in­cluding concretes with compressive strengths between 22.0 and 60.4 MPa and dry densities between 1651 and 1953 kg/m3. Nineteen simply supported beams were tested until failure. Two symmetrical concentrated loads were applied at approxi­mately one third of the span. Ductility was studied by defining ductility indexes. The main variables are the concrete compressive strength and the longitudinal tensile reinforcement ratio. It is shown that the parameter with higher influ­ence on ductility is the longitudinal tensile reinforcement ratio. The test results are also compared with the requirements from some codes of practice. It is shown that ACI Code requirements give more guaranties as far as ductility is con­cerned, when compared with European codes.

PLASTIC ROTATION CAPACITY OF LIGHTWEIGHT-AGGREGATE CONCRETE BEAMS

This article describes a study on the plastic behaviour of lightweight-aggregate concrete beams. The experimental results of nineteen simply supported beams previously tested by the authors were used in this study. The experimental plastic rotation capacity of the tested beams was characterized by a parameter called Plastic Trend Parameter (PTP). The main variables studied were the concrete compressive strength and the longitudinal tensile reinforcement ratio. It was found that plastic rotation capacity slightly increases as the concrete compressive strength increases. An appropriate range for the longitudinal tensile reinforcement ratio to ensure plastic rotation capacity is proposed. The results of this study were also compared with the requirements from some codes of practice. From this analysis, it was shown that ACI Code requirements give more guaranties as far as plastic rotation capacity is concerned, when compared with European codes. First published online: 28 Jan 2016

Moment redistribution in RC beams – A study of the influence of longitudinal and transverse reinforcement ratios and concrete strength

In this paper, the results from an experimental programme, aimed at investigating moment redistribution in statically indeterminate reinforced concrete structures, are presented and compared with theoretical analysis of the structural behaviour. Due to the nonlinear structural behaviour of reinforced concrete structures, linear elastic analysis can lead to an inaccurate assessment of the behaviour and, therefore, it can become necessary to use more advanced methodologies to achieve sufficiently accurate analysis. Furthermore, more advanced methods can enable a higher degree of performance optimisation of structures than those resulting from the simplified approaches adopted by existing design codes based on linear elastic analysis with redistribution of internal forces. In order to assess the load-carrying capacity at the ultimate limit state (ULS), a model combining plastic and nonlinear analysis is presented. The evolution of moment redistribution to structural collapse was studied experimentally for continuous two-span beams. The focus of the experiments was on the influence of the longitudinal tensile reinforcement ratio at the intermediate support, the transverse reinforcement ratio and the concrete strength. The experimental response at the ULS was further compared with the predicted distribution of internal forces according to the theoretical model. Evaluation of the experimental study indicated a highly nonlinear structural behaviour of the tested beams with the distribution of moment differing from linear elastic analysis, even for low load levels. The evolution of moment redistribution and the moment redistribution at the ULS were appreciably dependent on the arrangement of longitudinal reinforcement, whilst the transverse reinforcement ratio had a marginal impact up to yielding of the longitudinal reinforcing steel, with the concrete strength slightly reducing the degree of moment redistribution. For those beams which failed in flexure, predictions from the theoretical model presented were in good agreement with the experimental results. However, several beams collapsed in shear-related failure modes.

Experimental investigation on the shear performance of prestressed self-compacting concrete beams without stirrups

In this work, eight prestressed reinforced self-compacting concrete (SCC) beams were tested in order to investigate the shear stresses transfer mechanism, the shear failure mode and the shear performance of prestressed SCC beams without stirrups. The principal parameters included concrete compressive strength, longitudinal tensile reinforcement ratio ρl and prestressing force. The results indicated that the shear resistance corresponding to the first flexure-shear crack increases with the amount of longitudinal tensile reinforcement and the prestressing force. The ultimate shear resistance Vu increases with the increase of the concrete compressive strength. Vu increases also with ρl and the prestressing force. The failure mode of the tested beams is similar to a reinforced normal concrete beams without stirrups, namely diagonal compression failure. The diagonal crack location was analyzed in this work and the values obtained are acceptable in comparison with the test data. The shear transfer mechanism can be explained by an arch system. The predictions provided by ACI and Eurocode were compared with those obtained by the experimental test.

Experimental Study of Flexural Behavior of RC Beams Strengthening with BFRP Sheets

This paper presented the results of testing reinforced concrete beams strengthening with the BFRP sheets. Five specimens were cast and tested. All specimens were 2600 mm total span with a cross section of 150mm width and 250mm depth. Out of the specimens, two specimens were designed as reference specimens. The rest specimens were repaired with the BFRP sheets. The variables examine in the experiment were the longitudinal tensile reinforcement ratio, the different layers of the BFRP sheets and the anchoring measures of BFRP sheets. All specimens were tested under simply supported condition. 3D nonlinear finite element (FE) numerical models by ANSYS10.0 software were conducted to accurately predict the ultimate bearing capacity and response of reinforced concrete specimens strengthening with BFRP sheets subjected to four-point bending loading. The nonlinear constitutive material properties of concrete and steel reinforcement were considered in the finite element model. The results of the FEM simulation were compared with that of the experimental specimens. The results showed that it was significantly effective for the flexural capacity of the BFRP sheet-bonded reinforcement in tensile zone for reinforced concrete beams. Moreover, it implied excellent results on the stiffness of the reinforced concrete beams. The flexural strength enhancement of the reinforced concrete beams strengthening with the BFRP sheets varied between 19% ~ 44% over the control beam. This study further identified that the BFRP sheet technique significantly enhanced the stiffness and flexural capacity of reinforced concrete beams.

Punching Shear Resistance of Interior GFRP Reinforced Slab-Column Connections

This paper deals with the punching shear resistance of flat slabs reinforced with glass fiber-reinforced polymer (GFRP) reinforcing bars. A total of six large-scale interior GFRP and steel reinforced slab-column connections with the varying longitudinal tensile reinforcement ratio were tested. A new fracture-mechanics-based empirical formula for estimation of the punching shear resistance of interior GFRP reinforced slab-column connections is also presented in the paper. The formula takes into account effects, span to the effective slab-depth ratio, depth of the compression zone, dowel action, and the size effect on the punching shear resistance of flat slabs reinforced with GFRP bars. The accuracy of the proposed formula was verified against test results obtained by the authors and also by other researchers. In comparison with already known formulas, the proposed formula is in good agreement with the test results and provides predictions of the punching shear resistance with the smallest scatter. A physically reasonable relation between experimental punching resistances and reinforcement ratios of both the GFRP slabs and the steel reinforced concrete (SRC) slabs was obtained when equivalent GFRP reinforcement areas were used for SRC slabs. Predicted punching resistances of SRC slabs, calculated based on the equivalent GFRP reinforcement area, were found to be approximately equal to the resistances of GFRP slabs when the behavior (load-displacement diagram) of SRC slabs resembled the one of GFRP reinforced slabs.

Experimental Study on RC Beams Strengthened with CFRP Sheets

This paper presents the flexural performance of reinforced concrete (RC) beams with rectangular section. Seven RC beams strengthened using carbon fiber reinforced polymer (CFRP) sheets were subjected to four-point bending to investigate the effect of fiber reinforcement on the beams strengthened. The main experimental parameters included in the study are the pre-cracked width, CFRP sheet layers, the longitudinal tensile reinforcement ratio, the shear span ratio, and the concrete cover thickness. In total, seven beams were cast, one beam without any reinforcement as a control beam, two beams strengthened by CFRP sheets without making pre-cracks on the beam and four pre-cracked beams repaired with one layer or two layers CFRP sheets. Test results show the effectiveness and flexural capacity of the CFRP strengthened beams. The flexure enhancement of the CFRP strengthened beams varied between 41.7% and 124.1% over the control beam. This study confirms that the CFRP reinforcing technique significantly enhances the flexural capacity of reinforced concrete beams.

Experimental Study on Precracked RC Beams Strengthened with Externally Bonded CFRP Sheets

This paper presents the results of an experimental research work designed to study the flexural strengthening capacity and the modes of failure of Reinforced Concrete (RC) rectangular beams which are strengthened with external bonding of carbon fiber reinforced polymer (CFRP) composite materials to the tensile face of the RC beams. In total, seven beams were cast, one beam was preserved as control beam, two beams were strengthened without the application of preloading and the four beams were precracked and repaired with CFRP sheets. The main experimental parameters include the original damaged degree of RC beams, the amount of CFRP sheets, the longitudinal tensile reinforcement ratio, shear span to effective depth ratio, and the concrete cover thickness. All beams were tested in four-point bending over a span of 1500mm. Test results in the current study indicate that the effectiveness and flexural capacity of the CFRP strengthened beams. The flexure enhancement of the CFRP strengthened beams varied between 41% and 125% over the control beam. This study confirms that the CFRP sheets technique significantly enhances the flexural capacity of reinforced concrete beams. Finally, the contribution of CFRP sheets on the flexural capacity and rigidity of precracked and non-precracked RC beams is significant for the more longitudinal tensile reinforcement ratio.

Ductility Evaluation of Reinforced UHTCC Structural Members

Ultra-high toughness cementitious composite (UHTCC) is a PVA fiber reinforced cementitious composite. Tensile strain hardening behavior with ultimate tensile strain of more 3% under direct tensile loading is one of its important characteristics. In the current article, nine simply-supported reinforced UHTCC beams were subjected to four-point bending loading to experimentally investigate the influence of ductile deformation behavior of UHTCC on ductility capacity of reinforced structural members. Ductility index is determined by adopting three different parameters, i.e., deformation capacity, energy dissipation capacity as well as curvature capacity. The effect of longitudinal tensile reinforcement ratios on the variation of ductility in UHTCC reinforced beams was examined. It was found from the experimental results that the combination of ductile matrix (UHTCC) and steel bar prevents from occurrence of localized cracks in pure bending zone, showing high damage tolerance and ductile failure behavior. The results also show that as longitudinal tensile reinforcement ratio increases, deformation ductility and curvature ductility both exponentially decrease while a small reduction is demonstrated for energy ductility at ultimate failure.

Investigation on Effects of Variables on Shear Capacity of Precracked RC T-Beams with Externally Bonded Bi-directional CFRP Discrete Strips

This study aims to investigate the shear performance of partially precracked Reinforced Concrete (RC) T-beams bonded externally with bi-directional Carbon Fiber Reinforced Polymer (CFRP) discrete strips. A series of twelve RC T-beams are fabricated with internal transverse steel reinforcement and subjected to four-point and three-point bending systems. The external CFRP reinforcement strips are applied on the web and soffit of the beam with two-component epoxy system. The parameters investigated in the experimental program included (i) longitudinal tensile reinforcement ratio, (ii) shear span to effective depth ratio, (iii) spacing, and (iv) orientation of discrete CFRP strips. The experimental results show that the bi-directional CFRP discrete strip reinforcement significantly increases the shear capacity between 18 and 54% over the control beams. It is found that the test variables have significantly influenced the shear capacity of the CFRP strengthened beams. This study also validates the obtained experimental results with different existing theoretical models.

Plastic analysis of HSC beams in flexure

This article presents an experimental study on the plastic behaviour of HSC beams in bending. Nineteen isostatic beams were tested up to failure. The loading consisted of two symmetrical concentrated forces applied approximately at thirds of the span of the beams. The main purpose of the analysis is to characterize the plastic rotation capacity in the beams’ failure section with an experimental parameter. Bearing this in mind, a global plastic analysis of the tested beams is presented. The main variables of this study are the longitudinal tensile reinforcement ratio and the compressive strength of the concrete. The results obtained here are completed with others presented before and the whole set of results is analysed and discussed. The plastic rotation capacity of the tested beams are analysed with the rules of some codes of practice. Finally, a summary of the main conclusions is presented.

Effect of Longitudinal Tensile Reinforcement Ratio and Shear Span-Depth Ratio on Minimum Shear Reinforcement in Beams

The equations in design codes for minimum shear reinforcement ratio currently give little consideration to the effects of the longitudinal reinforcement ratio and shear span-depth ratio (a /d) in avoiding abrupt shear failure. This paper presents the effects of longitudinal tensile reinforcement ratio and a/d on the minimum shear reinforcement in reinforced concrete beams. A total of 26 reinforced concrete (RC) beams having the minimum shear reinforcements required by ACI 318-05 were cast, instrumented, and tested. The test results indicate that the reserve shear (shear strength of the beam with minimum amount of shear reinforcement/shear strength of the beam without shear reinforcement) of the tested beams increased as the longitudinal tensile reinforcement ratio increased, but decreased as the a/d increased. These findings suggest that design codes should be amended to include longitudinal reinforcement ratio and a/d for determining minimum shear reinforcement.

Shear capacity of precracked and non-precracked reinforced concrete shear beams with externally bonded bi-directional CFRP strips

This paper exemplifies both the shear strengthening capacity and modes of failure of Reinforced Concrete (RC) rectangular shear beams bonded externally with Bi-Directional Carbon Fibre Reinforced Polymer (CFRP) Composites. In total, 16 beams were cast without any internal shear reinforcement. Out of this, four beams were preserved as control specimens, six specimens were precracked and repaired with CFRP strips (i.e. precracked/repaired beam) and the following six specimens were strengthened without the application of preloading or precracks (i.e. initially strengthened specimen). The variables examined in the experimental investigation were the longitudinal tensile reinforcement ratio, shear span to effective depth ratio, spacing of CFRP strips, and amount and orientation of CFRP strips. All beams were tested under simply supported condition. Tests result shows that the effectiveness and shear capacity of the CFRP strengthened specimens. The shear enhancement of the CFRP strengthened beams varied between 11% and 139% over the control beam. This study confirms that the CFRP strip technique significantly enhances the shear capacity of reinforced concrete shear beams. The experimental results of the shear-CFRP strengthened beam were compared with the theoretical results.