Support Beam Research Articles

Enhancing shear behaviour of the exterior beam-column joint using sufficient reinforcement details or ultra-high-performance fiber-reinforced concrete

This study aims to improve the low shear strength of an exterior beam-column joint (BCJ) by using a different reinforcement pattern or ultra-high performance fiber-reinforced concrete (UHPFRC) in the beam-column joint. The main studied parameters were the transverse reinforcement ratio, anchorage of the longitudinal beam reinforcement, beam-column depth ratio, and utilizing UHPFRC. Five specimens with a one-third scale were experimentally tested under one-direction cyclic loading. All the samples were compared to the control sample in terms of crack pattern, mode of failure, hysteresis and envelope behavior, ductility factor, energy dissipation, normalized shear strength, percentage of beam flexural capacity, and stiffness degradation. Compared to the control specimen, the joint shear strength increases by 13%, 25%, 9%, and 38% for specimens that were made better by increasing the transverse reinforcement ratio, increasing the beam anchorage bar length in the joint, lowering the beam-column depth ratio to 0.80, and using UHPFRC instead of normal concrete in the beam-column joint. The UHPFRC in BCJ can be used instead of increasing the anchorage of the beam bars or the transverse reinforcement within the joint to get the same or better shear strength performance.

Dowel action of the tensile reinforcement in RC beams without shear reinforcement: Novel experimental investigation and mechanical modelling

Dowel action is a well-known phenomenon in shear-related problems within structural concrete. The tests previously reported in the literature to evaluate this contribution in reinforced concrete beams without shear reinforcement were conducted without any initial activation of the tensile reinforcement.This paper presents the experimental results of dowel tests, performed in a novel experimental test setup. The test setup reflects more realistically the conditions of the tensile reinforcement in reinforced concrete beams without shear reinforcement. The test setup enables a realistic tensile activation of the longitudinal reinforcement before applying the dowel force.The tests show that even a low activation of the tensile reinforcement results in the development of horizontal- and inclined cracks, even before the dowel force is applied. This shows that the contribution from dowel action of the tensile reinforcement is not just simply governed by the splitting strength of the concrete cover.A method to determine the displacement of the dowel from photogrammetric measurements is presented. In addition, a linear elastic- and a rigid-plastic mechanical model are presented for estimating the shear force transferred by the tensile reinforcement in RC beams without shear reinforcement. The estimates are based on measurements of the dowel displacement. Comparison of the presented model and the experimental results shows fairly good agreement.

ВЛИЯНИЕ КОНСТРУКТИВНЫХ И ТЕХНОЛОГИЧЕСКИХ ФАКТОРОВ НА ПОКАЗАТЕЛИ ПОПЕРЕЧНОГО АРМИРОВАНИЯ ЖЕЛЕЗОБЕТОННЫХ БАЛОК

The paper considers the influence of various factors on the actual length of clamps in the design of sections of linear bending reinforced concrete elements. The aim of the work is to determine the degree of influence of clamps of various configurations and other factors on the length of the clamp at various cross-sectional dimensions of a linear bending element. The obtained data and dependences make it possible to obtain the most effective solutions for reinforcing inclined sections with minimal cost. The calculation-analytical research method was used, based on the analysis of the results of calculations for various types of transverse reinforcement, the ratio of the diameters of the longitudinal and transverse reinforcement, the values of the protective layer, the radius of the bend of the clamp and the dimensions of the section. An expression is proposed for calculating the actual length of the clamp, depending on the dimensions of the section, the coefficient of reinforcement and the thickness of the protective layer, taking into account the mandrels used. Graphs of the change in the length of the collar for various section sizes b×h from 20×40 cm to 55×80 cm and with a reinforcement coefficient of 0.1%≤μ≤3% have been obtained. The graphs show savings in the length of the clamp from 6.7-7.4%, when using working fittings Ø6, to 12.2-37.9%, when using working fittings Ø40. The dependencies of strength reduction under conditions of inaccurate binding of the working longitudinal reinforcement to the collars are analyzed. The data obtained indicate a decrease in the strength of normal sections of beams from 0.33% to 10.78%. The paper considers the influence of various factors in the design of the sections of linear bending elements on the actual length of the clamps in accordance with accepted standards. Thanks to the obtained data and dependences, it is possible to refine the consumption of transverse reinforcement in beams for its more economical use.

Dimensionamento à flexão de vigas em concreto armado com barras de FRP

Abstract The corrosion of steel rebars is the main cause of reinforced concrete degradation, which results in increasing costs with structural rehabilitation and repairs. As a solution, corrosion resistant rebars, such as those of FRP – Fiber-reinforced polymer –, have been used to replace conventional steel. This paper describes the development of a design program that calculates the flexural FRP reinforcement of T-shape beams. The possibilities as regards the neutral axis position, failure mode and concrete linear or non-linear behavior define the design scenarios for which their respective equations were deduced. The flexural strengths computed using the deduced equations showed agreement with experimental results for 125 beams, validating the proposed methodology. Since FRP rebars are vulnerable to creep rupture, the sustained stresses must be lower than the maximum allowed by ACI 440.1R-15, which may require increases in areas, modifying the flexural strength. Therefore, the equations to compute the new neutral axis depth and flexural strength based on the adjusted area were deduced and implemented in the computational program. Subsequently, this paper presents design examples considering all scenarios for which the equations were deduced. The design of one T-section considering different FRP rebars combined to normal and high-performance concretes is also reported. The results showed that beams reinforced with aramid and glass FRP required large areas to avoid creep rupture, whereas the areas of those reinforced by carbon FRP rebars were considerably small; however, they exhibited small curvatures and fragile failure when under-reinforced.

Numerical modeling of inverted-U-shaped connectors to enhance the performance of composite beams

Steel and concrete are the most essential and frequently encountered building materials. These materials are used in combined structural systems, such as concrete cores surrounded by steel pipes, as well as composite structures with steel and concrete components. In numerous countries, the combination of concrete cores, steel frames, and composite slab construction has become the typical construction approach for multistory commercial buildings. The shear stud connector is one of the elements used in the construction of composite sections. The use of inverted-U-shaped reinforcement experimentally and numerically significantly improves punching shear resistance for post-tensioned slabs compared with slabs that use stud connectors. Other experimental and numerical studies using inverted-U-shaped reinforcement in post-tensioned beams indicate an enhancement in their shear strength. Recently, an experimental investigation was performed on composite beams to inspect the effect of mild and rigid shear stud connectors. The experimental and numerical results for the composite beams showed good correlation. The goal of this study was to numerically model the capacity and deformation of composite beams with inverted-U-shaped connectors of varying configuration and mechanical properties and compare the beam performance with composite beams using shear stud connectors.

Numerical analysis on reinforcement ratio of RC beams using FRP and steel rebars

Reinforced Concrete Structures, traditionally using steel rebars, are vulnerable to corrosion under severe exposure conditions. This can result in several drawbacks such as concrete deterioration, reduced serviceability, increased maintenance costs, and reduced structural durability. To counter these issues, Fibre Reinforced Polymer bars have emerged as another possibility material for steel bars. FRP bars are anti-corrosive, have high tensile strength, weigh one-fourth of steel bars, and have a low thermal expansion coefficient similar to concrete. To enhance both load-carrying capacity and ductility, a combining steel bars and FRP bars has been effectively used because FRP bars are having brittle behaviour. This paper studies theoretical investigations of Reinforcement ratio when Fiber Reinforced Polymer bars and steel bars are used as reinforcement in Concrete beams with Af to As as 1 which balance both Flexural capacity and ductility.

Numerical Analysis of Torsional Reinforcement of Concrete Beams in Unconventional by ANSYS Software

In this study, a finite element analysis is conducted to study the behaviour of RC beams with different configurations of transverse reinforcement under torsion. These configurations of stirrups are traditional closed stirrups, circular spiral stirrups, and inclined rectangular spiral stirrups. The numerical torsional load values are compared with the experimental torsional load values from previous research. The numerical analysis determined by the ANSYS software shows a reasonable agreement with the experimental torsional load values. The numerical results demonstrate that the use of continuous rectangular spiral stirrups improved the torsional response compared to using another type of beam stirrup. Thus, numerical results show that continuous spiral stirrups are effective at increasing torsional capacity. It is also noted that the behaviour of these beams with continuous spiral stirrups is better than the behaviour of the beams with traditional stirrups. The beams with helical reinforcement, which are TB2, TB3, and TB4 spiral reinforcements, greatly enhanced the toughness. The equivalent stresses are 13.709, 13.728, 14.72, and 15.894 MPa, while the equivalent elastic strains are 0.00421, 0.00377, 0.00347, and 0.00539 mm/mm for the beams TB2, TB3, and TB4, respectively. The beam TB4 had the highest stress and strain value, so its strength improved its ductility properties. As a result, the stirrups' configurations enabled the detection of beam failure mechanisms by improving torsional behaviour when compared to the beam's traditional stirrups. As a result, this research adds more knowledge to the literature on the most effective spiral stirrups for transverse reinforcement to improve the torsional behaviour of beams. Doi: 10.28991/CEJ-2023-09-01-04 Full Text: PDF

Análise de efeito de escala nos mecanismos complementares de resistência ao cisalhamento e sua supressão por reforço transversal - contribuições para a NBR 6118

Abstract Size effects are known to be relevant in the shear transfer mechanisms of quasi-brittle materials like concrete. Bažant proposed an asymptotic approximation between plasticity theory and Linear Elastic Fracture Mechanics (LEFM), showing a proportionality of concrete nominal resistance with d - 1 / 2, where d is beam depth. Recently, the long-standing shear transfer mechanism expressions of ACI 318:2014 have been updated (ACI 318:2019), with introduction of a size effect factor. In Brazil, recent publications identified non-conservative trends in predictions of ABNT NBR 6118:2014 for larger beam depths; yet, the Brazilian code never considered size effects because they are suppressed by transverse reinforcement. Considering this background, in this manuscript we make a comprehensive analysis of NBR 6118:2014 shear strength predictions using as a reference the papers of ACI-ASCE DatStb 445-D database. The results exhibit strong tendencies in the model error regarding longitudinal reinforcement and effective depth for beams without transversal reinforcement. A two-step analysis is made herein to describe model errors: first, a nonlinear regression for longitudinal reinforcement is made; second, a linear regression is made for size effect. The reliability analysis corroborates that model error may be reduced by introducing size effect and longitudinal reinforcement factors. Next, for beams with transversal reinforcement, smoother tendencies regarding beam depth are noted, indicating a size effect suppression for the beams depths available in the database. However, as the analysis shows that the higher beam depths concentrate most of the results with unconservative model errors, further studies are necessary to accurately describe how transversal reinforcement suppress the size effect.

Structural performance of unreinforced full-scale façade concrete beam-column joint under cyclic load

Post-earthquake observations have shown that poorly reinforced concrete (RC) beam-column joints in existing structures determine premature brittle failures during seismic action. Failure of these critical parts, which transfer stresses and moments between beams and columns, resulted in the catastrophic collapse of structures in low to moderate seismic risk zones. Exterior (i.e. corner or façade) beam-column joints of buildings constructed without or with insufficient transverse reinforcements are commonly involved in the failure. The purpose of this study was to investigate the effective vulnerability of two full-scale exterior façade beam-column joints under transverse cyclic loading. Both the specimen design strategy and the test setup were conceived to emphasize the vulnerability of the joints and, therefore, to achieve shear failure in the joint panel prior to yielding both beam and column reinforcements under the simulated seismic action. In particular: (i) joint was characterized by the absence of any capacity design principle (i.e. total lack of stirrups in the joint panel) to highlight structural deficiencies typical of the 1960s-70s Italian construction practice; (ii) beams and columns were adequately designed to remain in the elastic field during the tests; (iii) the specimen was evaluated in the absence of axial load. In this work, the experimental seismic performance is compared to the one predicted by code/literature models. The test is then simulated using a numerical three-dimensional model for modelling crack propagation and fracture in concrete using the smeared crack technique. The model also allowed for a more comprehensive examination of the effects of certain assumptions on the mechanical performance of the RC joint during the experiment.

Meso-scale modelling of size effect on shear behavior of Basalt fiber reinforced concrete deep beams

The work aims to examine the size effect on shear failure of deep concrete beams with Basalt Fiber Reinforced Polymer (BFRP) bars. A mesoscale numerical model for the deep concrete beam with BFRP bars was built to explicitly model the shear failure, considering concrete heterogeneity and concrete/bars interaction. The mesoscale simulation approach was firstly verified against the available test observations. It was then utilized to study the shear failure of geometrical-similar concrete deep beams having different structural sizes with BFRP bars and steel bars. The influence of beam depth, stirrup ratio and reinforcement type (i.e., steel bars and BFRP bars) on the shear failure and the corresponding size effect of concrete deep beams was explored. The simulation results indicate that: 1) the failure modes of concrete deep beams with BFRP bars and steel bars are basically similar, and they all exhibit noticeable size effect; 2) stirrups (i.e., steel bars and BFRP bars) can hinder the development of diagonal cracks within concrete, and thus weaken the size effect in shear strength; 3) the shear failure in beams with BFRP bars presents more substantial size effect than that of beams with steel bars; 4) the calculation models of shear capacity in the international codes do not apply to concrete deep beams with BFRP bars. Moreover, it is found that the size effect law developed previously can also be suitable for the shear failure of concrete deep beams with BFRP bars.

A criticism on strengthening glued laminated timber beams with fibre reinforcement polymers, numerical comparisons between different modelling techniques and strengthening configurations

The application of CFRP for strengthening timber structures has proven its efficiency in enhancing load-bearing capacity and, in some cases, the stiffness of structural elements, thus providing cost-effective and competitive alternatives both in new design and retrofitting existing historical buildings. In this study, glued laminated timber beams strengthened with CFRP were examined. A number of test beams with different reinforcement configurations and beam sizes were selected from the literature. These beams were analysed with three different methods as numerical, theoretical and code perspective. For the numerical method, a 3D nonlinear finite element model which includes damage and fracture mechanics was constructed. All test beams were studied with different methods and results were compared with respect to initial flexural stiffness, midspan vertical displacement and failure load. The effectiveness of methods and strengthening configurations were stated and suggestions for practical application of FRP-strengthened timber beams were presented.

Análise das tendências nos mecanismos complementares de resistência ao cisalhamento de vigas de concreto armado

abstract: The study of shear failure in concrete beams is one of the subjects growing in importance due to both the recent reformulations, and increasingly higher cross-section depths used. For instance, the recent updates in the ACI 318 (2019) shows the need to incorporate the size effect in the design of reinforced concrete elements. In this study, the same database adopted by the ACI-ASCE Committee DAfStb 445-D has been used to calculate shear strength, with and without the consideration of size effect, i.e., the design prescribed by ACI 318 (2014), ACI 318 (2019), Frosch et al. (2017), and the ABNT NBR 6118 (2014). Later these predictions are compared with test results. A dispersion analysis has outlined the trends regarding compressive strength, span to depth ratio, longitudinal reinforcement ratio and beam depth. Every variable was discussed per interval, delineating the causes related to the observable trends. Regarding the most prominent influences (effective depth and longitudinal reinforcement ratio), the approaches considering them directly through factors had provided results with no appreciable trends, with lower coefficients of variation (COV) and substantially more conservative for higher cross-section depths. As the Brazilian code does not consider both, a correction factors, determined by a two-step regression analysis on these parameters to adjust this design, are briefly introduced.

Behavior of Self Compacted Concrete Deep Beams Reinforced With Polypropylene Fibers

Behavior of Self Compacted Concrete Deep Beams Reinforced With Polypropylene Fibers

Flexural Reinforcement of Over-Reinforced Beam by Ultrahigh Performance Concrete Layer

In order to improve the failure state of over-reinforced beams and enhance their ductility, an innovative reinforcement method was proposed by adding an ultrahigh performance concrete (UHPC) layer on the top surface of the over-reinforced beam to take advantage of the high compressive strength of UHPC. The numerical simulation method was used to carry out the research. The validity of the finite element model was verified by comparing it with the experimental results, and the effectiveness of the new reinforcement method was verified by comparing it with the calculation results after adding the UHPC layer. Then, a detailed parameter study was carried out, including the thickness of the UHPC layer, the cross-section area of longitudinal tension rebar, and concrete strength. The load-deflection curve, flexural bearing capacity, and deflection ductility coefficient were studied. The results show that the bearing capacity of the UHPC-reinforced over-reinforced beams is significantly increased by 88.1%. And the stiffness and ductility of the beams are also significantly increased, with the ductility coefficient reaching 23.85. In addition, flexural bearing capacity increases with the thickness of the UHPC layer and sectional area of longitudinal tension rebar. Finally, a prediction model for the flexural bearing capacity of UHPC layer-reinforced over-reinforced beams is proposed, which further verifies the effectiveness of this method.

Shear Behavior of Hollow Ferrocement Beam Reinforced by Steel and Fiberglass Meshes

The purpose of this study is to investigate the shear behavior of hollow ferrocement beams of self-compacting mortar reinforced with various types of metallic (steel wire mesh) and non-metallic (fiber glass mesh) reinforcement. The experimental program consists of casting eight ferrocement beams with dimensions of 150×225×2000 mm, with 50 mm of ferrocement thickness and a polystyrene cork core of 50×125 mm. The study parameters were the type of shear reinforcement and the number of layers of wire mesh. The results showed that the ultimate load of the beams reinforced with several layers of the fiber glass mesh (1, 2, and 3) was decreased by (3.27%, 16.52%, and 9.38%) respectively, compared to the beams reinforced with layers of steel wire mesh (1, 2 and 3). The ultimate load of these beams increased by (33.71%, 73.28%, and 122.11%) respectively, compared to the beams without shear reinforcement. Also, the ultimate load of the beams reinforced with layers of welded wire mesh was increased by (38.23%, 107.56%, and 145.09%) respectively, compared to the beams without shear reinforcement. The ductility and toughness of the beams reinforced with several layers of the fiber glass mesh (1, 2, and three) were decreased by (1.68%, 2.11%, 2.68%) and (29.39%, 25.91%, 16.06%) respectively, compared to beams reinforced with several layers of steel wire mesh (1, 2 and 3). The crack propagation was reduced and its number and crack width decreased by using steel wire mesh and fiber glass wire mesh instead of stirrups, especially in beams with two and three layers of wire mesh. The results also showed that the use of glass fiber or welded wire mesh in the reinforcement of hollow beams instead of steel stirrups has a significant effect on the failure load, deflections, crack patterns, and shear stresses, despite the clear preference for beams reinforced with steel wire mesh.

Experimental study on re-centering behavior and energy dissipation capacity of prefabricated concrete frame joints with shape memory alloy bars and engineered cementitious composites

To enhance the seismic performance of prefabricated concrete frame joints, an innovative prefabricated beam-column joint with shape memory alloy (SMA) and engineered cementitious composite (ECC) materials was proposed in this paper. Four 1/2-scale test specimens, including one SMA–ECC prefabricated beam-column joint and three comparison joints (namely particularly reinforced concrete cast in situ joint, ordinary concrete prefabricated joint, and ECC-reinforced prefabricated joint) were designed and fabricated. A new type of semi-mechanical sleeve connector was designed to link the SMA bar with the longitudinal reinforcement of the precast beam. Through the low-cycle reciprocating loading tests on the specimens, the failure mechanism, bearing capacity, and self-centering performance of each frame joint were studied. The results show that post-pouring ECC in the plastic hinge zone of beam-column joints can significantly improve the cracking failure form and the ductility of the joints. Though the initial stiffness and energy dissipation capacity of the structure are slightly reduced when SMA and ECC are applied to the prefabricated beam-column joints. Nevertheless, the new composite materials can significantly enhance the ductility and self-centering capacity, reduce the residual deformation and the stiffness degradation rate of the structure. The SMA–ECC reinforced prefabricated beam-column joint can achieve better functional self-resilience ability after earthquake.

Experimental Study on the Structural Response of Reinforced Fly Ash-Based Geopolymer Concrete Members

Geopolymer concrete is concrete made from industrial materials, such as fly ash, GGBS, silica fume, and metakaolin, used as a cement alternative. In this study, geopolymer concrete will be based on fly ash as a binder material, alkaline activators of sodium hydroxide and sodium silicate, GPC beams of dimensions 800 mm × 250 mm × 100 mm, circular columns with diameter 350 mm and depth of 700 mm and GPC slabs of dimensions 500 mm × 500 mm × 100 mm are all cast with fly ash content of 350 kg/m3. The ratio of alkaline solution to fly ash was equal to 0.5 and was kept constant, and the Na2SiO3-to-NaOH ratio was 2.5 and the NaOH molarity was kept constant at 12 M. The beams reinforcement was changed to study the shear and flexural behaviour, and the slabs and columns reinforcement ratio was kept constant. The load capacity, stress–strain behaviour of the GPC and load-deflection behaviours of the members were also examined. The results showed that reinforced geopolymer members can be used as an alternative to reinforced concrete structural members, but they are more expensive than reinforced concrete. Further study is recommended to provide more practical design recommendations for incorporating geopolymer concrete into structural elements in order to accelerate the adoption of this concrete for large-scale field applications in the future.

Investigation of the use of textile carbon yarns as sustainable shear reinforcement in concrete beams

In recent years, textile reinforcement has been widely researched and used in reinforced concrete beams, slabs, and thin plates. However, the design for bending is completely different from that of the shear case. The use of textile carbon yarns in place of or in addition to traditional steel stirrups to reinforce the shear has been investigated. Eight beams with dimensions of 200 mm × 300 mm × 1500 mm were used in this investigation. These beams were tested in shear under four load points. Two specimens were used with and without steel stirrups as reference specimens, while the other six beams used textile carbon yarns instead of steel stirrups. The variables of this study were the length of overlap, which was 30%, 60%, and 100%, the spacing was 90 mm and 130 mm, while inclination was 45° and 90°, and bonding with or without steel fibers. The results showed that using 100% overlap length, 90 mm spacing, a 45° angle, and adding steel fibers increased the shear capacity, increased the deflection, and made the cracking behavior better.

Experimental and numerical analysis of RC beams strengthened with ECC and stainless steel strips

Strengthening of reinforced concrete (RC) structures may be required for several reasons and flexural strengthening of normal concrete (NC) beams is widely carried out using laminated fibres. However, the incompatibility of the concrete cover can lead to fibre debonding or concrete cover dislocation. These are some of the critical setbacks in common practice and the cost of fibre can be high. A novel flexural strengthening technique for NC beams is thus proposed: durable strips of stainless steel plate (SSP) bonded over a engineered cementitious composite (ECC), which is in complete contact with the flexural reinforcement of a slave beam through shear connectors. The flexural behaviour of NC beams strengthened with ECC and SSP strips was investigated experimentally and numerically. Three variables were investigated: the thickness of the SSP, the ECC layer with or without deformed steel bars and three different strengthening techniques. The experimental results showed that hybrid ECC–SSP strengthening improved the ultimate capacity of the NC beams by as much as 156%. A three-dimensional finite-element model (FEM) was developed and validated using the experimental results. The FEM accurately predicted the experimentally observed flexural behaviour of the NC beams with hybrid ECC–SSP strengthening. An analytical model to predict the ultimate load of NC beams with hybrid ECC–SSP strengthening was also developed.

Progressive collapse resistance of reinforced concrete beam-column connection under fire conditions

To reveal the reinforced concrete (RC) structural response under fire-induced progressive collapse scenarios, 3D finite element (FE) models were developed to investigate the effect of high temperatures on the collapse resisting mechanisms of RC beam-column connections. To describe the behavior of RC connections at elevated temperatures, temperature-dependent thermal and mechanical properties of concrete and reinforcing steel were adopted in the 3D FE model. The sequentially coupled thermal–mechanical analysis was performed with the explicit solver in a quasi-static manner. The concrete damaged plasticity (CDP) and ductile damage for metals (DDM) were adopted to better describe the failure of concrete and steel rebar, respectively. The proposed numerical model was validated by experimental data at different temperatures from literature. To understand better the collapse resistance of RC beam-column connections, a new loading scheme was adopted in the developed model. The load capacity of RC connection under fire conditions was investigated analytically and numerically. The effects of top and bottom reinforcement ratios, concrete strength, beam depth and fire severity on the collapse resisting mechanisms were investigated. The regulated chord rotation failure criteria recommended by the U.S. Department of Defense (DoD) were utilized and showed to be conservative on the collapse identification of RC structures under fire conditions.