Flexural Members Research Articles

Shear strength of reinforced concrete flexural members without web reinforcement in compliance with mechanical analysis

Reinforced concrete (RC) beams are important components and critical bearing members in concrete structures. Owing to the complexity of shear behavior for RC beams, most current design approaches to predict shear capacity are highly empirical, which cannot physically explain the shear failure mechanism and, consequently, should only be used within the bounds of the testing regimes from which they were derived. To accommodate this issue, a mechanics-based shear model, which can explain the physical process of shear failure mechanism with a clear physical meaning, was established to quantify the shear capacity of RC beams without stirrups with any type of longitudinal reinforcement and concrete. In this study, the force on each part of the critical failure diagonal crack plane of the RC beams without web reinforcement was analyzed, and the variation of sliding strength with any given inclination angle of diagonal crack was derived. Furthermore, the inclination angle of the critical diagonal crack along which failure occurs with the shear-span ratio was determined by the correlation analysis. The model was validated using 9 test specimens with steel longitudinal reinforcement performed in this study, with a further 452 published shear tests of FRP-reinforced beams without web reinforcement. In addition, the selected design codes and available models were used to calculate the shear strength of test beams. The comparison result shows that a reduction to different degrees in both the mean and scatter of the ratio of the experimental-versus-predicted shear capacity result for the proposed mechanics-based model. Meanwhile, the proposed model can accurately reflect the influence of the main shear parameters, and the prediction accuracy shows no obvious correlation with the wide range variation of these shear parameters.

Flexural strength of innovative thin-walled composite cold-formed steel/PE-ECC beams

A detailed experimental investigation on the flexural behaviour of an innovative precast composite element combining cold-formed steel (CFS) and engineered cementitious composites (ECC) is presented in this paper. Bonding ECC to the lightweight thin-walled CFS sections enhanced the buckling, bearing, and torsional properties of the composite sections. The proposed composite system will be used as precast flexural members in framed structures with large spans or as a rehabilitation approach for corroded cold-formed and hot-rolled steel flexural members. Simply supported beams with comparatively long spans with span-to-depth ratios of 6.83 and 13.48 were installed back-to-back and tested under a 4-point loading configuration. The behaviour of composite CFS/ECC beams under bending was investigated and compared with the bare CFS sections. Composite CFS/MOR beams incorporating high-strength mortar (MOR) as an ECC replacement were also investigated. The test specimens were divided into three series with sixteen tests in total. Series A (SC300) included six tests utilising 300-mm height SupaCee sections, Series B (C300) included four tests using 300-mm height lipped-Cee sections, and Series C (SC150) included six tests utilising 150-mm height SupaCee sections. The composite CFS/ECC beams exhibited high load-bearing capacities after reaching their plastic section capacities, while the bare CFS beams failed to reach their yield section capacities due to distortional buckling. Composite CFS/MOR beams could not reach their plastic moment capacities due to debonding between MOR and CFS after MOR crushing. The moment capacities of the composite CFS/ECC beams increased up to 140.0% over their duplicate bare CFS sections, while composite CFS/MOR beams showed only a 72.0% increase over CFS sections. Lastly, design equations to predict the moment capacity of composite CFS/ECC beams are presented, based on the experimental results.

Web crippling design of channel beams: Carbon steel, stainless steel and aluminium

Recent trends in the construction industry have sought to use cold-formed (CF) carbon steel, CF aluminium and CF stainless-steel as flexural members and in some instances as primary load-carrying members. Flexural members when subjected to concentrated loads undergo various failure modes, a major failure mode being web crippling. The large width-to-thickness ratios of these thin-walled beams makes them vulnerable to local buckling failure. Although there are four loading conditions to consider, this paper focuses on Interior-One-Flange (IOF) loading condition. Currently, individual design equations are available for determining the web crippling capacity of CF carbon steel, CF aluminium and CF stainless-steel under IOF loading. However, to-date there has been no attempt to produce a unified web crippling design equation. An all-encompassing numerical study focussed on the key web crippling parameters, both cross-sectional dimensions and mechanical properties and a unified grade, fy = 220 MPa, was achieved across the three structural materials to allow for a unified design equation. A total of 378 Finite Element (FE) models were obtained. It was found that AS/NZS 4600, AISI S100 and Eurocode 3 provided good agreement, but with a higher coefficient of variation (COV) values than recommended. Additionally, AS/NZS 1664.1 was found to be unsafe. CF carbon steel parametric study results validated existing equations, which were accurate and able to predict the web crippling capacity under IOF loading. However, unified web crippling design equation was modified which can improve the accuracy when predicting the web crippling capacity of CF aluminium and CF stainless-steel lipped channel sections (LCBs) under IOF loading conditions. The unified equation was supplemented by web crippling coefficients specific to each of the structural materials.

STRENGTHENING OF THIN FLEXURAL MEMBERS USING STRIPS EXTRACTED FROM USED TIRES

Present study investigates the ability of using the damaged tires in the field of structural engineering. The proposed reinforcement material in this study represents an innovative approach to reuse strips extracted from used tires to increase the ultimate flexural capacity of thin flexural members, include thin timber beams and steel plates, satisfying clean environment and economic considerations by consuming the waste materials in the structural field. Results showed that the proposed reinforcement increases the ultimate flexural load value of the thin timber beam specimens in the range of 24.113 % to 30.809 % respectively based on results obtained experimentally and numerically by ANSYS software compared to specimens without reinforcement. Similarly, the ultimate flexural load was increased in the range of 83.95% to 101.7% respectively based on the results obtained numerically and experimentally for the rib type steel plates specimens. Also, deflection has been reduced due to the proposed reinforcement method.

Optimum High-Strength Reinforcing Bar Grade for Reinforced Concrete Flexural Members

Optimum High-Strength Reinforcing Bar Grade for Reinforced Concrete Flexural Members

Simulation of Exterior Wrapping for Flexural Study on Beams

The need to retrofit existing reinforced concrete (RC) structures have increased over the decades due to corrosion of steel reinforcement inside the concrete, neglect and overuse, and increased loading. Experimental and numerical studies in this research field showed that using fibre-reinforced Polymer (FRP) materials to strengthen RC members in shear, flexure, and column confinement applications is an effective method to retrofit RC structures. This strengthening technology has numerous advantages over conventional steel plating, such as providing high strength-to-weight ratio, versatility, durability, and ease of use to strengthen RC members. The purpose of this paper is to study the effect of strengthening shear deficient RC beams with externally bonded (EB) carbon fibre-reinforced polymer (CFRP) sheets with and without U-wrap configuration.

Flexural Strength and Stiffness of Donut-Type Voided Slab

The voided slab system has been known as an effective technique to replace a heavy reinforced concrete slab system without the decrease in flexural strength. However, according to the previous studies, the flexural capacities such as flexural strength, stiffness and ductility of the voided slabs were practically lower than that of the solid slabs depending on the void shapes and details. Therefore, in this study, an analytical and experimental study were conducted to derive the optimal void shape and details focused on the flexural capacities of voided slabs. Based on a finite element (FE) analysis, a donut-type void shaper, which was a hexahedron with rounded edges and a hole penetrating the center, was suggested as the optimal shape in voided slabs, and an experimental study was conducted to verify flexural capacities of the donut-type voided slab. The flexural strength, stiffness and deflection of the donut-type voided slab were investigated by void shape and fixing method of void shaper as variables. The ductility of voided slab was also evaluated, because ductility is as important as strength for the safe design of slab member. The test results showed that the flexural strength of the donut-type voided slabs was equivalent to 98% and 105% that of the solid RC specimen, and the donut-type voided slab specimens had enough ductility for the flexural member. The stiffness of the donut-type voided slab was decreased about 8~9% compared with the solid slab, but it was improved up to 7% compared to the non-donut-type voided slab. Based on test results, the flexural design method of the donut-type voided slab associated with the void shape and fixing device of void shaper was suggested, and it was confirmed that the donut-type voided slab is one of the efficient alternatives to replace heavy flat plate slabs.

Estimating Flexural Strength of FRP Reinforced Beam Using Artificial Neural Network and Random Forest Prediction Models.

An accurate calculation of the flexural capacity of flexural members is vital for the safe and economical design of FRP reinforced structures. The existing empirical models are not accurately calculating the flexural capacity of beams and columns. This study investigated the estimation of the flexural capacity of beams using non-linear capabilities of two Artificial Intelligence (AI) models, namely Artificial neural network (ANN) and Random Forest (RF) Regression. The models were trained using optimized hyperparameters obtained from the trial-and-error method. The coefficient of correlation (R), Mean Absolute Error, and Root Mean Square Error (RMSE) were observed as 0.99, 5.67 kN-m, and 7.37 kN-m, for ANN, while 0.97, 7.63 kN-m, and 8.02 kN-m for RF regression model, respectively. Both models showed close agreement between experimental and predicted results; however, the ANN model showed superior accuracy and flexural strength performance. The parametric and sensitivity analysis of the ANN models showed that an increase in bottom reinforcement, width and depth of the beam, and increase in compressive strength increased the bending moment capacity of the beam, which shows the predictions by the model are corroborated with the literature. The sensitivity analysis showed that variation in bottom flexural reinforcement is the most influential parameter in yielding flexural capacity, followed by the overall depth and width of the beam. The change in elastic modulus and ultimate strength of FRP manifested the least importance in contributing flexural capacity.

Plastic Hinge Length Mechanism of Steel-Fiber-Reinforced Concrete Slab under Repeated Loading

The plastic hinge is the most critical damaging part of a structural element, where the highest inelastic rotation would occur. In particular, flexural members develop maximum bending abilities at that point. The current paper experimentally investigates the influence of steel fiber reinforcement at the plastic hinge length of the concrete slab under repeated loading, something which has not been reported by any researcher. Mechanical properties such as compressive strength and tensile strength of M20-grade concrete that are used for casting specimens are tested through the compressive strength test and the split tensile strength test. Six different parameters are considered in the slab while carrying out this study. First, the conventional concrete slab and then the steel-fiber-reinforced slab were cast. The plastic hinge length of the slab was calculated through different empirical expressions taken from methods by Baker, Sawyer, Corley, Mattock, Paulay, Priestley and Park. Finally, the steel fiber was added as per methods detailed by Paulay, Priestley and Park in the plastic hinge length mechanism in the concrete slab at 70 mm and 150 mm separately. The results arrived through experimental investigation by applying repeated loads to the slab, indicating that steel fibers used at critical sections of plastic hinge length provide similar strength, displacement, and performance as that of the conventional RCC slab and fully steel-fiber-reinforced concrete slabs. Steel fiber at a plastic hinge length of slab has a better advantage over a conventional slab.

New AISC and EC3 design for S690 plate girders at elevated temperatures

Recently, the determination of the strengths of bridge girders exposed to fire has become of great importance as a result of the failure of some famous bridges for the same reason (e.g. Birmingham and MacArthur Maze Bridges (USA)). On the other hand, S690 high strength steel is widely examined and used in bridges all over the world, such as Mttådalen Bridge in Sweden. With respect to the effect of elevated temperatures on the strength of flexural members, stocky I-section beams have been studied in the literature. On the opposite, the lateral-torsional buckling (LTB) strengths of laterally-unrestrained plate girders with slender webs, which are used extensively in bridges such as those of Birmingham and MacArthur Maze Bridges (USA), and particularly formed from S690 at elevated temperatures have not been addressed. Additionally, AISC (2016) and EC3–1-2 (2005) do not neither cover S690 steel elements nor IPGs with slender webs. Therefore, these girders are simulated in this paper using ABAQUS programme. Currently, the simplified finite element method used successfully by Chen and Young (2008) and Fang and Chan (2019), which utilises the reduced material properties of S690 above the room temperature, is used, which means assuming a balanced structure and a uniform temperature range. The parametric studies consider the variations of the cross-sectional radius of gyration and elastic section modulus. Since the main focus of this paper is strength predictions, strengths are first compared to design models initially proposed according to AISC and EC3–1-2, which are found to yield very conservative predictions. Then, modified AISC and EC3–1-2 design models are recommended, which can safely predict the strengths of S690 IPGs with slender webs at elevated temperatures.

The conditions for plane sections remaining plane

The Euler–Bernoulli hypothesis that plane sections before bending remain plane after bending is a cornerstone of the sciences, especially in mechanics and engineering, and an enabler of the Second Industrial Revolution. Although it is widely applied in science and engineering, especially in structural engineering, its general validity has never been established theoretically, except in some special cases such as linear elastic and small deformation conditions. Its applicability to a particular problem requires extensive experimental evaluation or practical observation. Through a thought experiment commonly used in the derivation of physics theory, this paper rigorously deduces the theorem that gives the conditions for the Euler–Bernoulli hypothesis. The new theorem is general and applies to flexural members composed of any number of different materials, regardless of the properties of the materials, magnitude of deformation, and elastic or plastic strain conditions. This new theorem paves the way for future secure applications of this hypothesis without the need for experimental verification before use.

Measuring support reactions and damage detection in steel beams using distributed strain sensing

While visual inspections are an important tool in the assessment of steel bridges, they cannot provide quantitative information about the bridge’s behavior. Distributed fiber optic sensors (DFOS) have the potential to provide added insight into the performance of bridges through the measurement of full strain profiles along a member as well as other key performance indicators that can be derived from these measurements. This study investigates the use of DFOS measurements to derive support reactions and detect local damage along the flexural members in a bridge. A series of load tests were undertaken to develop the method for support reaction estimation, starting with a simply supported beam, then continuous beams, and then finally a full model bridge. The beam test support reactions were evaluated against load cell measurements and variations in geometry were shown to have an impact on the measurements that could be accounted for through calibration. The model bridge reactions matched the total applied load and showed the expected distribution for the loading configuration applied. A second model bridge test was undertaken where the shear stress in the connection between the beams and the slab exceeded the capacity of the connection and localized damage occurred. Using the DFOS measurements, the neutral axis was calculated and used to detect this localized damage.

Experimental investigation on flexural and ductile behaviors of rebar‐reinforced ultra‐high‐performance concrete beams

AbstractThis paper experimentally investigated the flexural and ductile behaviors of ultra‐high‐performance concrete (UHPC) beams. The failure modes, deflection, ductility, concrete strain, and reinforcement strain were tested using eight UHPC rectangular beams. The experimental parameters were the reinforcement ratio, the reinforcement diameter, and the UHPC cover thickness. The experimental results showed that all specimens exhibited flexural failure characterized by the yielding of steel rebars, multiple micro‐cracks, one localized macro‐crack, and slight crushing of UHPC. It was concluded that increasing the reinforcement ratio significantly enhanced the stiffness, flexural capacity, and ductility of the rebar‐reinforced UHPC beams, whereas showed little effect on their cracking load. Meanwhile, both the reinforcement diameter and UHPC cover thickness in the range investigated here had little influence on the flexural performance of UHPC beams in the elastic stage and crack development stage, whereas exhibited different influences in the yield stage. Besides, increasing the reinforcement ratio was in favor of presenting the deflection‐hardening behavior, while the reinforcement diameter and UHPC cover thickness had little influence on the deflection‐hardening behavior. The analytical models were established to predict the yielding load, peak load, and ultimate load of rebar‐reinforced UHPC beams, and the predictions showed good agreement with the experimental results in this study. Also, the steel reinforcement could show a dominant role in the bearing capacity by increasing the reinforcement ratio. A post‐yielding capacity factor λ was proposed, which could reasonably evaluate the deflection‐hardening and deflection‐softening behavior of UHPC flexural members in the present study. Based on other experimental results collected in literature, three different ranges for the post‐yielding capacity factor, namely, λ ≤ 0.7, 0.7 < λ < 0.9, and λ ≥ 0.9, were identified, corresponding to the deflection‐softening behavior, transition stage, and deflection‐hardening behavior, respectively.

Flexural behaviour of seawater–sea sand concrete beams reinforced with GFRP bars: Effects of the reinforcement ratio, stirrup ratio, shear span ratio and prestress level

Glass fibre-reinforced polymer (GFRP) bar-reinforced seawater–sea sand concrete (SWSSC) has been widely regarded as a new structural material with great potential due to its environmental friendliness. To safely and economically utilize seawater and sea sand to cast GFRP bar-reinforced flexural members in coastal areas, an experimental study was conducted to investigate the flexural behaviour of 12 GFRP bar-reinforced SWSSC beams. The various considered parameters included the (1) reinforcement ratio, (2) stirrup ratio, (3) prestress level, and (4) shear span ratio. The experimental results for the GFRP bar-reinforced SWSSC beams were verified via a comparison to the calculation models of GB 50608-20 and ACI 440.1R-15 for FRP bar-reinforced normal concrete (NC) beams. The results indicated that the prestress level is the main factor controlling the cracking load of the GFRP bar-reinforced SWSSC beams, and the cracking load of prestressed beams was 81% higher than that of nonprestressed beams. The ultimate load of the GFRP bar-reinforced SWSSC beams was strongly correlated with the reinforcement and shear span ratios (the higher the reinforcement ratio or the lower the shear span ratio was, the higher the ultimate load). Under the influence of the reinforcement and stirrup ratios, the failure mode of the GFRP bar-reinforced SWSSC beams could be transformed from GFRP bar rupturing into concrete crushing. Moreover, the calculation model of ACI 440.1R-15 overestimated the ultimate flexural capacity of the nonprestressed beams, while the calculation model of GB 50608-20 yielded conservative estimation values for the nonprestressed specimens and overestimated values for the prestressed beams. To ensure safety, the calculation model of GB 50608-20 for FRP bar-reinforced NC beams can be adopted when designing nonprestressed GFRP bar-reinforced SWSSC beams. In contrast, a prediction model for prestressed GFRP bar-reinforced SWSSC beams should be further investigated.

Model Construction and Simulation Study on Bending Performance of Strengthened RC Beam in Externally Prestressing Industrial Reclaimed Steel Wire

Strengthening with external prestressing is a kind of reinforcement method which imposes prestress on concrete by setting prestressed steel bar outside concrete, a new strengthening with external prestressing technology can be put forward by using industrial reclaimed steel wire instead of prestressing steel bar. High-quality steel wire is extracted from waste tire after stripping and derusting, and this kind of industrial reclaimed steel wire with high tensile strength and good toughness is applied to building reinforcement by externally prestressing method; it can provide a new research direction for the country’s green, low-carbon, and high-quality development. In this paper, the new strengthening with external prestressing technology is used to study the bending static load test of test beams under different working conditions. The influence of reinforcement material and rotational degree on the bending performance of RC beam is discussed. The results show that the ultimate bearing capacity of the flexural members with industrial recycled steel wire is more effective under the new external prestressed reinforcement method. Under the same reinforcement method, when the reinforcement materials are the same, the increase of prestress can effectively improve the bearing capacity of flexural members in the reinforced beams with prestress of 30%, 40%, and 50%, respectively. In order to verify the reinforcement effect of industrial recycled steel wire on the bending performance of RC beam from multiple perspectives, the numerical simulation was carried out on the concrete specimens reinforced with different degrees of woven reinforced wire, and the simulation results were in good agreement with the experimental results. This study provides a new research direction for the recycling of industrial reclaimed steel wire and the reinforcement of concrete components and has a good promotion, role, and theoretical support for subsequent research.

Nonlinear Analysis of Reinforced Geopolymer Concrete Beams

To decarbonise the current construction sector and meet the global net-zero target, there is a pressing need to develop an environmentally friendly alternative to Portland cement concrete. Alkali activated and geopolymer concrete have much to offer in this regard. At present, however, there is limited study on the behaviours of alkali activated structural members, particularly on flexural members, which encompass most practical design situations. This paper presents a database of 37 tests on slender alkali activated and geopolymer concrete beams available in the literature, with the aim to investigate the flexural strengths of this alternative concrete when used as a structural member. In addition, the results of nonlinear finite element analyses on fourteen reinforced geopolymer concrete beams are presented to highlight key influencing factors governing the behaviour and failure of flexural members. Of particular interest is to study the influence of reinforcement ratio, compressive strength, and material brittleness on the overall strength and ductility. Overall, it is shown that the flexural response of geopolymer concrete beams under short-term loading is comparable to that of ordinary reinforced concrete beams.

Behavioral nonlinear modeling of prestressed concrete flexural members with internally unbonded steel strands

In this article, a nonlinear analysis was carried out to develop two different models able to estimate the performance of partially prestressed concrete flexural members with unbonded post-tensioned strands, mainly; a methodology proposed by the first author and programmed using FORTRAN language, and the commercial finite element software program ABAQUS. These models intend to investigate the entire load-strain behavior and the corresponding load-deformation status of the structural concrete members with unbonded steel up to failure. The results of these two models were verified with the outcomes of the experimental work conducted by the authors. The experimental part consisted of testing 22 different simply supported flexural members (beams and one-way concrete slabs) post-tensioned by internally unbonded steel strands that varied by the cylinder compressive strength of concrete (fc′); jacking stress (fpj); prestressing index (ω); and span to depth ratio (ℓ/dp). The main objective of this article is to develop a numerical model applicable to investigate the performance of concrete flexural members reinforced by a combination of unbonded and bonded steel at various load levels. Compared to experimental data, the two developed models have the ability, with a large degree of agreement, to predict the overall behavior of these types of members in terms of cracking load, ultimate flexural resistance, load-deflection response, strain evolution, and total stress in unbounded strands.

Web crippling behaviour of cold-formed high-strength steel unlipped channel beams under End-One-Flange load case

High-strength Cold-Formed Steel (CFS) members are widely adopted as structural members in building structures due to its higher ultimate capacity. The flexural members are often subjected to concentrated transverse loads which may leads to buckling instabilities including web crippling. However, there is no appropriate design rules and studies are available to estimate the web crippling strength of high-strength CFS members. Hence, this paper presents a detailed numerical investigation on high-strength CFS unlipped channel sections subjected to End-One-Flange (EOF) loading condition with nominal yield strengths of 700 MPa, 900 MPa and 1000 MPa. For numerical simulation study, non-linear Finite Element (FE) models were developed and validated with the experimental results followed by an extensive parametric study using ABAQUS. In total, 243 FE models were developed with different geometric and material parameters including section thickness, material strength, web slenderness ratio, inside bent radius to thickness ratio and bearing length to thickness ratio. The ultimate web crippling strength results were compared with the available design guidelines to check their suitability and accuracy in terms of strength prediction. Then, new design rules to predict the web crippling capacity of high-strength CFS unlipped channel section under EOF condition based on unified and Direct Strength Method (DSM) approaches were proposed.

Nonlinear healing approach for reinforced concrete beams

ABSTRACT This paper has proposed a new formula relating the damage state and effective state of the flexural member, this formula enables studying different concrete healing variables. A new relation between the effective reinforced concrete healing/damage variable and the effective healing/ damage variables of concrete and steel has been introduced to relate concrete and steel healing/ damage and the reinforced concrete healing/ damage. The proposed formula has been verified with experimental results of full-healed flexural members, it has achieved good agreement. The flexural member stiffness has been studied considering different parameters like concrete healing variables, concrete cover and percentage of steel reinforcement. The flexural member stiffness has increased as the concrete healing variable has increased, it has increased as the concrete cover has increased and the steel reinforcement percentage of 1% has given the higher flexural member stiffness.

Application of Distributed Fibre Optical Sensing in Reinforced Concrete Elements Subjected to Monotonic and Cyclic Loading

Distributed fibre optical sensing (DFOS) is increasingly used in civil engineering research. For reinforced concrete structures, almost continuous information concerning the deformations of embedded reinforcing bars can be obtained. This information enables the validation of basic and conventional assumptions in the design and modelling of reinforced concrete, particularly regarding the interaction of concrete and reinforcing bars. However, this relatively new technology conceals some difficulties, which may lead to erroneous interpretations. This paper (i) discusses the selection of sensing fibres for reinforced concrete instrumentation, accounting for strain gradients and local anomalies caused by stress concentrations due to the reinforcing bar ribs; (ii) describes suitable methods for sensor installation, strain acquisition and post-processing of the data, as well as determining and validating structurally relevant entities; and (iii) presents the results obtained by applying DFOS with these methods in a variety of experiments. The analysed experiments comprise a reinforced concrete tie, a pull-out test under cyclic load, and a flexural member in which the following mechanical relevant quantities are assessed: the initial strain state in reinforcing bars, normal and bond shear stresses, deflections as well as forces. These applications confirm the benefit of DFOS to better understand the bond behaviour, but also demonstrate that its application is intricate and the results may lead to erroneous conclusions unless evaluated meticulously.