Behavior Of Such Beams Research Articles

Moment capacity of cold-formed steel channel beams with edge-stiffened and unstiffened elongated web holes

Cold-formed steel channel beams (CFSCB) often incorporate web holes to accommodate building services, but this reduces their moment capacity due to decreased web area. Recent studies have shown that a new type of edge-stiffened web holes can enhance moment capacity, especially for circular ones, and can now be extended to elongated web holes. However, there hasn't been research on the moment capacity of such CFSCB with elongated web holes. This paper uses finite element analysis (FEA) to examine the moment capacity and flexural behaviour of such beams with both elongated edge-stiffened web holes (EEH) and elongated unstiffened web holes (EUH). After validating the FEA models against experimental results available in the literature, a comprehensive parametric study involving 2160 FEA models was conducted. Results showed that CFSCB with EEH exhibited, on average, a 9 % increase in moment capacity compared to those with EUH. Additionally, the parametric results were compared with the design capacities calculated from existing standards for CFSCB with unstiffened web holes. It was found that the current design equations for CFSCB with EUH were overly conservative by 9 % and 66 %, on average, for distortional or local buckling failure and lateral-torsional buckling failure, respectively. Consequently, modified Direct Strength Method (DSM) design equations were proposed to calculate the moment capacity of CFSCB with both EEH and EUH. Finally, a reliability analysis was conducted to assess the accuracy of the proposed design equations.

The Effect of Opening Size and Expansion Ratio on the Flexural Behavior of Hot Rolled Wide Flange Steel Beams with Expanded Web

In some design cases, such as in castellated beams, cellular beams, or steel beams with expanded web, it is advantageous to strengthen and enhance the performance of steel beams by increasing the web depth. However, expanding the web of a steel beam is a unique engineering strategy. This modification not only enhances its ability to bear heavy loads but also reduces any bending or flexing while enabling longer distances between supports. The expanded steel beams can be achieved by making a horizontal cutting in the steel beam web and then adding an increment plate (with the same web thickness), called spacer plate, between the two halves of the web sections, thus improving stiffness and strength. To evaluate the behavior of such beams, nine specimens of HEA steel beams with expanded web ratios of 150%, 200%, and 250%, and one specimen as a reference beam, were fabricated. The specimens were evaluated under two-point load over a clear span length of 280 cm. From the experimental work it was found that for steel beams with expanded web that have 18 openings with 80 mm, the beams with an expansion ratio of 150% had the best performance according to load-deflection behavior with a reduction in load capacity by only 11%. Additionally, the beams with expansion ratios of 200% and 250% had no economic viability according to the analysis of load-deflection behavior with a reduction in load capacity by 49% and 62%, compared with the solid expanded steel beam with the same expansion ratio. For the second type of steel beam with expanding web with 9 openings of 160 mm width, the beams with expansion ratios of 200% and 250% were observed to perform better than the first type with a reduction in load capacity by 28% and 50%. Using larger opening width and a smaller opening number is considered the best option for beams with expansion web ratios of 200% and 250%, while on the contrary, using smaller opening width and higher numbers seems to be a better option for beams with 150% expansion web ratio. Expanding the depth of a steel beam provides design flexibility, reduces deflections, and allows for longer spans. These benefits enhance material efficiency and open up new architectural possibilities.

Behaviour of New Curved in Plan Composite Reinforced Concrete Beams

New composite reinforced concrete beams, in which reinforced concrete component is connected to steel T-section, are proposed. The stirrups of the beam were utilized as shear connectors by passing them through drilled holes in the web of the steel T-section. Experimental test and numerical analysis were conducted to determine the behaviour of such beams when subjected to combined shear, torsion, and bending stresses. Full scale one conventional reinforced concrete curved in plan beam C1, and four composite reinforced concrete ones, C2 to C5, were tested. The degree of shear connection between the two components of beams C2 to C5 was changed by varying the number of stirrups which are used as shear connectors. The increase in load carrying capacity of the composite reinforced concrete beams reached 55 % for beam C4 as compared to that of ordinary reinforced concrete beam. The experimental results demonstrated that the stirrups are very effective in providing the interaction between the two components of the beams. The degree of shear connection emerged not to have effect on the behaviour of tested beams. Three-dimensional finite element analysis was conducted using commercial software ABAQUS. To model the shear connection in composite reinforced concrete beam, the stirrups were connected to the web of the steel T-section by springs at the location of the stirrups. Good agreement is obtained between the results of the experimental tests and the finite element analysis.

Flexural behavior of hybrid FRP-recycled aggregate concrete-steel hollow beams

Hybrid fiber reinforced polymer (FRP)-concrete-steel (FCS) hollow members are a new form of structural members possessing superior mechanical behavior and durability. Such members consist of an outer FRP tube, one or more inner steel tubes, and the concrete filled between the tubes. Existing studies on such members have been mainly focused on their use as columns; limited studies have been conducted on their use as flexural members. Besides, the effect of shear connectors between the steel tube and the concrete on the behavior of hybrid FCS hollow flexural members has not been investigated in detail. This paper, therefore, presents the results of an experimental program on the flexural behavior of hybrid FCS hollow beams with a rectangular hollow cross section. Recycled aggregate concrete (RAC) was used for the purposes of addressing the serious issue of construction waste nowadays and capitalizing the advantage of FRP confinement in enhancing the performance of RAC. The test results showed that such hybrid FCS hollow beams are very ductile, and the shear connectors play a significant role on the behavior of such beams. Finally, a theoretical beam model based on conventional section analysis was proposed to predict the results of the test hybrid FCS hollow beams.

Investigation on shear behavior of reinforced concrete deep beams without shear reinforcement strengthened with fiber reinforced polymers

Shear failure is an undesirable type of failure in terms of structural safety. Particularly, reinforced concrete (RC) deep beams without shear reinforcement are vulnurable to shear failure. In order to improve the shear behavior of such beams, externally bonded (EB) fiber reinforced polymer (FRP) as a strengthening technique is being applied to the outer part of the beams. However, investigations on the shear behavior of deep beams without shear reinforcement strengthened with FRP materials are insufficient in the literature. Therefore, a comprehensive experimental study was carried out on RC deep beams without shear reinforcements strengthened with fully wrapped FRP strips. The experimental parameters were chosen as the shear span-to-effective depth ratio (av/d), the number of carbon layers, the span length between carbon strips, and the type of FRP. A total of sixteen deep beams, four of which were reference beams, were fabricated and tested under three point bending load until failure. According to the experimental results, the gain percentage both in the shear and deflection capacities of strengthened deep beams increased with the av/d. Additionally, the failure modes and crack patterns of strengthened deep beams were different from those of the reference beams. Moreover, all test parameters affected the ductility behavior of deep beams having av/d of 1.5 and 2 positively. A comparative study was also conducted employing the methods commonly used in the literature and the methods based on the strut and tie model. It was observed that the methods based on strut and tie model provided superior estimates over the models commonly used in the literature.

An efficient assessment of the vibration behaviour of cracked steel–concrete composite beams using GBT

In this paper, a previously developed GBT-based finite element (Henriques et al., 2020) is extended to allow calculating, very efficiently, natural frequencies and vibration mode shapes of steel–concrete composite beams, accounting for cross-section deformation (including shear lag effects) and concrete cracking. This new finite element enables a straightforward characterisation of the vibration modes, due to the unique modal decomposition features of GBT. The element aims at helping structural designers assess, very easily, the vibration behaviour of such beams at the serviceability limit state. A physically non-linear analysis is first carried out, accounting for cracking and cross-section deformation. Then, the natural frequencies and vibration mode shapes are calculated from the associated eigenvalue problem, with a very small computational cost. To illustrate the accuracy and potential of the proposed approach, two numerical examples are presented and discussed. For validation and comparison purposes, shell finite element model results are provided, showing that the proposed element leads to very accurate results with much less DOFs.

High-cycle fatigue tests of pretensioned concrete beams

Pretensioned concrete beams are widely used as bridge girders for simply supported bridges. Understanding the fatigue behavior of such beams is very important for design and construction to prevent fatigue failure. The fatigue behavior of pretensioned concrete beams is mainly influenced by the fatigue of the prestressing strands. The evaluation of previous test results from the literature indicated a reduced fatigue life in the long-life region compared with current design methods and specifications. Therefore, nine additional high-cycle fatigue tests were conducted on pretensioned concrete beams with strand stress ranges of about 100 MPa (14.5 ksi). The test results confirmed that current design methods and specifications overestimate the fatigue life of embedded strands in pretensioned concrete beams.

Numerical study on bending resistance of cold‐formed steel back‐to‐back built‐up elements

AbstractCold‐formed steel back‐to‐back built‐up beams are efficient and very attractive structural elements which can also offer excellent efficiency in production, both in capacity and material savings. The connection between such built‐up steel components can be easily obtained by screws or bolts, but the developments in the welding processes also lead to other solutions like continuous (laser or MIG brazing) or discrete (spot welding). This paper presents a parametric numerical study on such elements where various shapes and cross‐section geometries will be analysed, using different types of connection between the built‐up steel elements. The results from the evaluation of local and global buckling behaviour of such beams will serve as a base for planning future experimental work. Based on the numerical model, the paper presents the influence of several parameters i.e., the type of the channel section (lipped or plain channels), length of the beam, continuous and discrete connections between channels, the number and the distance between discrete connections along the beam axis and along the beam height. From the parametric study, it is concluded that capacity of the cold‐formed steel back‐to‐back built‐up steel beams is highly affected by the type of connections.

Shear behaviour of concrete wide beams with spiral lateral reinforcement

ABSTRACT Wide beams are commonly used in reinforced concrete (RC) structures for architectural considerations such as facilitating the placement of services and providing adequate clear height. However, behaviour of these beams is not as efficient as normal width beams due to the small structural depth. Motivated by the lack of guidelines for wide RC beams with spiral reinforcement, this paper investigates their shear behaviour using innovative lateral reinforcement configurations. A comprehensive experimental program was conducted by testing nine beams under four-point loading. The effect of different parameters on the behaviour of such beams was investigated. These parameters included number, dimensions, and configurations of spirals. The experimental program also included testing of 18 standard cylinders spirally reinforced under compression to study the performance of confined concrete in the compression zone of wide beams. The results showed that the spiral lateral reinforcement is an efficient alternative for traditional closed stirrups for shear resistance in wide beams. Compared to regular closed stirrups, using spiral reinforcement or inclined links with regular closed stirrups can greatly improve the shear capacity and deformation. Also, reduction in the amount of lateral reinforcement can be achieved if the proposed lateral reinforcement is adopted instead of traditional stirrups. Based on the test results and the ACI 318–19 code, an equation is proposed and validated to estimate the shear strength of wide beams with regular/spiral lateral reinforcement.

Experimental Study on the Flexural Behavior of Reinforced Polystyrene Blocks in Concrete Beams

A new type of lightweight beam system was recently proposed by embedding polystyrene in beams to improve structural efficiency. This removes the non-performing concrete in the neutral axis and tension region to provide a comparable strength as a solid beam. There are, however, limited studies conducted to investigate the structural behavior of such beams. Therefore, this research presents an experimental investigation to assess the effect of polystyrene shapes in the beams. This involved testing a solid beam and five lightweight beams under flexural load using a four-point load test. The inclusion of polystyrene was estimated to have reduced the self-weight of beams by 8.6% to 11.8% when compared with the solid beam. The results also showed the ellipse polystyrene with a width of 70 mm and height of 50 mm produced the highest effective strength to weight ratio (sw) of 1.12 and performed 12% better than the solid beam. Moreover, the lightweight beams have more weight reduced than the strength, and those with ellipse polystyrene were found to have performed better than circular ones based on first crack load, ultimate load, and effective strength to weight ratio (sw). The beams with ellipse polystyrene allowed better stress distribution and this gave them a higher strength than sphere shape. For industry application, the polystyrene content is recommended to be greater than 10% while the effective strength to weight ratio (sw) of the beam is greater than 1. The successful reduction of the weight without affecting the structural performance has the ability to help in reducing construction costs.

Feasibility of Reusing Damaged Steel Beams in Temporary Structures

This study addresses the feasibility of reusing pre-damaged steel beams in temporary structures. The extensive structural investigation of notch-damaged, unrepaired, and laterally unsupported steel beams was performed experimentally and numerically. The simply supported specimens were tested in two-point loading with the study parameters being the location and size of the notch. Some beams had one notch on one edge of the tension flange at different locations, and some beams had two notches on both edges of the tension flange. Three-dimensional numerical models were generated to simulate the behavior of the test beams. After verifying the model, the numerical analysis was extended to cover additional different notch depths and widths. The study showed that the capacity of beams with single notch was more influenced by the notch depth increase than it was by the increase in the notch width. Beams with double notches exhibited an even more pronounced and distinct decrease in the capacity as the notch depth and width increased. This investigation supports the feasibility of reusing pre-damaged steel beams in temporary structures under service loads and certain levels of damage, where the behavior of such beams is within the elastic range and the beam maximum defection is less than the allowable one.

Coupled axial-bending dynamic stiffness matrix and its applications for a Timoshenko beam with mass and elastic axes eccentricity

The dynamic stiffness matrix of a coupled axial-bending Timoshenko beam is developed to investigate the free vibration behaviour of such beams and their assemblies. Applying Hamilton's principle, the governing differential equations of motion of a Timoshenko beam in free vibration is derived by considering the axial-bending coupling effect arising from the mass axis eccentricity with the elastic axis of the beam cross-section. The differential equations are then solved in an exact sense, giving expressions for the axial and bending displacements as well as the bending rotation. The expressions for axial force, shear force and bending moment are formed using the natural boundary conditions which resulted from the Hamiltonian formulation. Next, the frequency-dependent dynamic stiffness matrix of the coupled axial-bending Timoshenko beam is derived by relating the amplitudes of the axial force, shear force and bending moment to the corresponding amplitudes of axial displacement, bending displacement and bending rotation. The resulting dynamic stiffness matrix is effectively applied to investigate the free vibration behaviour of axial-bending coupled Timoshenko beams by making use of the Wittrick-Williams algorithm as solution technique. The results with emphasis on the axial-bending coupling effects and the importance of the shear deformation and rotatory inertia in free vibration behaviour of coupled axial-bending Timoshenko beams and frameworks are discussed with significant conclusions drawn.

Experimental investigation into the bending energy absorption of hybrid aluminum/high strength and mild steel thin-walled sections joined by clinching

The employment of hybrid material thin-walled sections in the vehicle body structure is an emerging approach adopted towards manufacturing of lightweight energy-absorbing components in the automotive industry. Utilizing multi-materials such as aluminum-steel in the automotive industry poses some manufacturing challenges in terms of joining technologies of dissimilar materials. Clinching is a cold forming process that includes severe local plastic deformation of the sheets leading to permanent mechanical interlock. This study undertakes the experimental investigation of bending energy absorption of the clinched top-hat thin-walled beams by means of a series of quasi-static three-point bending tests. Different types of clinched beams including homogeneous as well as hybrid material beams, with aluminum alloy Al5052/SPCC mild steel and Al5052/SPFC 390 high strength steel combinations, are studied. The bending behavior of such beams under two different loading conditions is investigated and compared in terms of crashworthiness indices such as specific energy absorption ( SEA), initial peak force ( Fip) and crash force efficiency (CFE). It is found that although the hybrid clinched beams show higher SEA as well as lower Fip than their steel counterparts, their CFE values are lower than the steel beams. Furthermore, the sheets arrangement change with respect to the punch and the die is shown to influence the energy absorbing capability of the hybrid clinched beams. Moreover, it is revealed that while the clinched beams show reduced Fip under the load applied to their hat-shaped part, they exhibit lower CFE values compared to when the load is applied to their plate part. Finally, considering SEA, Fip, and CFE as three criteria, TOPSIS as a multi-criteria decision-making method is employed to select the best compromise design solution.

Mechanical performance of glulam products made with Portuguese poplar

Due to its average mechanical properties, poplar, a fast-growing species, has been disfavored compared to stronger species for several decades. Wood-based products may help changing that perspective and thus, poplar has been gaining its market share for structural uses. A state-of-the-art review concerning the use of poplar to produce glued laminated products, with special focus on the use of Portuguese poplar, is presented. The Portuguese forest produces a great variety of species. The most common poplar species found in this country are Populus x canadensis, P. nigra L., and P. alba L. Despite its limited availability, and the market hesitation on its structural application, recent studies on poplar grown in the Portuguese forest showed its suitability for structural purposes. Glued laminated timber (GLT) beams made with this species revealed a very promising mechanical behavior. Bending strength tests evidenced a ductile behavior on more than 70% of the beams, which motivated deepening the study on the raw material used to produce those beams. To predict the mechanical behavior of such beams, a 3D numerical model was developed. The numerically predicted results were compared with the experimental ones, showing very good agreement between both approaches.

Moment Redistribution in Continuous RC Beams Top Strengthened with Steel and CFRP Plates

It is common practice to retrofit continuous reinforced concrete (RC) beams by fiber reinforced polymer (FRP) or steel plates. This can cause a significant amount of moment redistribution (MR) which results in an efficient and economic design when taken into consideration. There is lack in research regarding MR in continuous RC beams when strengthening plates are applied only at the top side at the hogging regions. The main purpose of this paper is to assess MR in continuous RC beams top strengthened with steel and/or carbon fiber reinforced polymer (CFRP) plates. In this respect, a nonlinear finite element model was developed using ABAQUS 6.14 and validated using experimental research program. The model was found capable of stimulating the behavior of such beams and hence assessing the percentage of MR which can be achieved using steel and CFRP strengthening. A parametric study is conducted to investigate the effect of various parameters, different from those investigated in the experimental program, on the MR in continuous RC beams. Parameters related to the concrete compressive strength, reinforcement ratio, beam thickness and thickness of strengthening plates were considered in this study. The results showed that significant amounts of MR can be achieved using either steel or CFRP plates and that MR is enhanced with the change in concrete compressive strength. Moreover, it was found out that the change in steel bars reinforcement ratio or in thickness of the strengthening plates has different effect on the beams strengthened with steel plates than those strengthened with CFRP plates.

Finite element modeling of RC gable roof beams with openings of different sizes and configurations

This paper presents numerical simulation performed by using a commercial finite element program package of ABAQUS/CAE version 2018 to investigate the flexural behavior of 13 existing simply supported reinforced concrete (RC) gable roof beams including openings of different size and configurations subjected to monotonic loads. Since insertion of openings in a RC beams result in complicated behavior due to geometric discontinuity and discontinuities or disturbances in the normal flow of stresses therefore, this study aims to propose a numerical model, including a reliable finite element model technique and constitutive material models, to simulate nonlinear behavior of such beams. Comparisons between numerical and experimental models in terms of load-deflection and crack patterns are presented and good agreement is shown. The average ratio of ultimate loads and deflection of numerical models to that of the experimental tested beams, was 1.04 and 0.98, respectively. Therefore, finite element analysis can be considered a preferable and reliable technique to simulate non-linear behavior of RC gable roof beams with openings, from the view point of complicated, difficulty, time saving, human effort and budget.

Half-joint beam design based on the CFP theory

The present work complements recent attempts to investigate the causes of vulnerabilities inherent in half-joint structures. Herein, such vulnerabilities are attributed to shortcomings of the mechanism of force transfer underlying the adopted methods of design, rather than the detailing of the specified reinforcement as widely believed. The work is intended to demonstrate that the forces in half-joint beams are transferred by beam action, and not by the strut-and-tie mechanisms assumed to develop in the presence of the specified reinforcement. Through the use of the compressive force-path method, which has been developed on the basis of a beam mechanism of load transfer, it is shown that the predictions of half-joint beam behaviour correlates closely with the findings of a finite-element analysis package which was at first shown to be capable of successfully reproducing the experimentally-established structural behaviour of such beams.

Ability of steel fibers to enhance the shear and flexural behavior of high-strength concrete beams subjected to blast loads

The provision of steel fibers improves many of the properties of high-strength concrete (HSC), including its tensile capacity, ductility, toughness and fragmentation resistance. These enhanced features also make high-strength fiber reinforced concrete (HSFRC) an ideal material for the blast resistant design of structures. One of the established applications of fiber-reinforced concrete is in beams, where fibers can be used to increase shear capacity and replace transverse reinforcement. While extensive research exists on the behavior of FRC and HSFRC beams under static loads, studies examining the blast behavior of such beams is scarce. Accordingly, this paper presents the results of an experimental program which studies the effect of steel fibers on the blast performance of high-strength concrete beams. As part of the study, ten HSFRC beams are tested under either static loads or simulated blast loads using a shock-tube. Test variables include the effects of fibers, fiber content, fiber type, longitudinal steel ratio and combined use of fibers and transverse reinforcement. The results show that the use of fibers in HSC beams increases blast resistance, improves control of displacements and results in superior damage tolerance. In addition, the results show that steel fibers can substitute for transverse reinforcement and prevent blast-induced shear failures. The analytical investigation shows that the use of SDOF analysis, with development of non-linear resistant functions, can be used to predict the blast response of HSFRC beams with good accuracy.

Numerical and Analytical Behavior of Beams Prestressed with Unbonded Internal or External Steel Tendons: A State-of-the-Art Review

This paper presents a detailed state-of-the-art chronological account of past studies dating back to the late 1980s consisting of an overview of the vast majority of prediction equations for the stress at ultimate in prestressed unbonded internal or external steel tendons of simply supported concrete beams. The paper also details past studies carried out to investigate the complete nonlinear behavior of such beams throughout loading. Past and relevant studies were carefully reviewed in detail and then synthesized in the most reduced, yet accurately depicted, format in an effort to capture the pertinent highlights. For each review, the most relevant factors considered by the authors were highlighted, including span-to-depth ratio, second-order effects, length of the plastic hinge, friction and/or slippage at deviators, and experimental verification. An evaluation was carried out to compare and contrast the various nonlinear analysis studies using a simple tabulated format. Gaps were identified, and recommendations for future research were further proposed by the authors.

Shear strength of steel-fibre-reinforced concrete beams with web reinforcement

The use of steel-fibre-reinforced concrete, mainly due to its improved mechanical characteristics beyond cracking, has been increasing recently. A particular purpose of using steel fibres is to enhance the shear characteristics of reinforced concrete beams against a brittle shear failure. While a considerable amount of research on the shear behaviour of steel-fibre-reinforced concrete beams without web reinforcement has been conducted, the studies on the shear behaviour of such beams with web reinforcement are still limited. In this study, an experimental programme aiming to examine the effects of steel fibres on the shear behaviour of reinforced concrete beams with web reinforcement was carried out. A total of nine beams having various amounts of steel fibre and web reinforcement were tested under three-point loading. In addition to the experimental study, a number of equations for predicting the shear strength of steel-fibre-reinforced concrete beams with web reinforcement were assessed by using a limited number of beams available in the literature.