Box-section Beams Research Articles

A novel approach for the optimum cross-section design of thin-walled box section beams subject to oblique bending based on both adequate-strength and local stability conditions

This study presents a new analytical procedure developed for the optimum cross-section design of the thin-walled box sections subject to oblique bending. The box sections designed in this study have been assumed to be achieved by hollowing out the rectangular solid sections at different subtraction ratios including arbitrary, optimum, and maximum. The optimum subtraction ratio has been determined based on the adequate-strength condition while the maximum subtraction ratio has been determined taking into account both adequate-strength and local buckling conditions. The optimal design of the box sections for the arbitrary subtraction ratio has been attained by minimizing the maximum normal stress, taking into account the adequate-strength condition. Conversely, the cross-sections of the box profiles for the optimum and maximum subtraction ratios have been optimized by minimizing their cross-section area, accounting for the defined combined strength condition involving adequate- strength and local stability requirements. An equivalent box section design model that allows checking the local stability of the box sections possessing dissimilar wall segment thicknesses has been developed to perform the local buckling control on the designed optimum box sections with unequal wall thicknesses. The new local stability conditions have been defined relying on this developed equivalent box section design model. The analytical results, validated through numerical predictions obtained from linear elastic local buckling and post-buckling analyses performed using Abaqus software, have shown that the optimally designed box section achieves substantial material savings per unit length compared to its corresponding equivalent box section.

Shape sensing of the thin-walled beam members by coupling an inverse finite element method with a refined quasi-3D zigzag beam theory

In structural safety field, the inverse finite element method (iFEM) is an effective methodology to reconstruct full-field displacement on beam, plate and shell structures, independently of the loading conditions and of the material properties. However, the current iFEM in principle requires uniform shear distribution over the thickness of beam, which is practically hardly possible due to these thin-walled beam with the general cross-section shape, such as I-section beam, hat-section beam and box-section beam, and there is no effective method to realize deformation online monitoring at home and abroad. To relieve this issue, a novel iFEM strategy is proposed to establish the shape sensing model of the thin-walled beam, where the thin-walled beam is replaced with an equivalent layered composite one based on a generalized layered global-local beam (GLGB) theory, and the improved quasi-3D zigzag shear deformation theory is presented to describe deformation field of the equivalent layered composite beam. The proposed iFEM method accounts for not only thickness stretching but also interlaminar continuity of shear stresses and displacements. Besides, the proposed iFEM formulation does not need any shear correction factors. Accuracy and effectiveness of the established shape sensing model are demonstrated through several case studies. The numerical results show that the proposed iFEM can accurately reconstruct the deformation of the thin-walled structure and the reconstruction accuracy can be improved by 5 %.

Shear behavior of box‐section concrete beams reinforced by FRP bars and FRP stirrups

AbstractA few research studies are available on the behavior of reinforced concrete (RC) box section beams with fiber‐reinforced polymer bars (FRP) and FRP stirrups. Consequently, the behavior of these beams needs to be investigated. This article studies experimentally, numerically, and analytically the effect of some variables on the behavior of RC box section beams. This article investigates many variables, such as the shear span‐to‐total depth ratio, the flexural FRP reinforcement ratio, and the FRP vertical and horizontal web reinforcement ratio. The experimental program consists of nine simply supported reinforced concrete box section beams. The numerical models using the nonlinear finite element program ANSYS V.15 are carried out. The results are compared to the experimental results using load‐deflection curves, crack patterns, failure loads, and failure modes. The shear capacities based on Egyptian ECP 208‐2019 and ACI 440‐2015 codes are compared to each other and to the experimental results. The findings show an adequate agreement between the experimental, numerical, and analytical results for the range of the studied parameters. The results reveal that increasing the shear span‐to‐depth ratio by 50% decreases the carrying capacity, toughness, and displacement ductility by 2%, 28%, and 12%, respectively. The increase in main FRP reinforcement rebars by 20% increases the carrying capacity and toughness by 59% and 62%, respectively. Increasing vertical FRP stirrups by 79% increases the failure load and toughness by 26% and 15%, respectively, and displacement ductility increases only by 0.8%. The increase in horizontal FRP stirrups by 79% increases the failure load, toughness, and displacement ductility by 33%, 8%, and 4%, respectively. Both Egyptian and American codes are conservative in some cases and unconservative in others, while the numerical results are unconservative.

Nonlinear Analysis on Torsional Strengthening Of Rc Beams Using Cfrp Laminates

This research is devoted to investigate the behavior and performance of reinforced concrete beams strengthened with externally bonded Carbon Fiber Reinforced Polymer (CFRP) laminates under the effect of torsion. In this study a theoretical analysis has been conducted using finite element code ANSYS. Six previously tested beams are used to investigate reinforced concrete beams behaviorunder torsion, two of them are solid and the rest are box-section beams. Also, two beams are without CFRP reinforcement, which are used as control beams for the strengthened one, and the other four beams are strengthened with CFRP laminates with different number of layers and spacing. Numerical investigation is conducted on these beams, and comparisons between the available experimental results for these beams and numerical results from the current study are made. Conclusions from these comparisons are presented and discussed. An increase of about 15.6% in the ultimate torque for the solid beam and of about 9.8% in the ultimate torque for the box-section beam is observed after using the CFRP strips. A parametric study is carried out to study the torsional behavior of RC beams having different number of CFRP layers and concrete compressive strength; also U-wrap for the CFRP configuration is investigated.

Hysteretic performance of Q690 high-strength steel box-section columns with slender webs

High-strength steel (HSS) has a higher yield-tensile strength ratio and a lower fracture elongation than conventional mild steel, resulting in poor ductility in comparison to the latter. This paper aims to investigate the hysteretic performance of Grade Q690 steel welded box-section columns with slender webs. Four full-scale specimens were subjected to low-cycle horizontal reciprocating loading tests, and the failure mode, evolution of plasticity in the cross-section, energy dissipation capacity and ductility were studied. A finite element modeling procedure verified from the test results was used for a more extensive parametric analysis, and the influence of the width-to-thickness ratio, the axial compression ratio and the column slenderness ratio on the evolution of plasticity in the cross-section as well as the ductility were studied. The results show that plastic local buckling dominates the failure mechanism of welded box-section columns with slender webs. With an increase of the width-to-thickness ratio, axial compression ratio and column slenderness ratio, the evolution of plasticity in the cross-section and the ductility performance of the column gradually deteriorate, and the ductility coefficient within the selected parameter range is small, but it still has the capacity for energy dissipation. Limiting the axial compression ratio and width-to-thickness ratio to meet the requirements of elastic–plastic inter-story drift, HSS box-sections with slender webs can be incorporated in seismic design with low ductility requirements based on the concept of seismic performance design. In addition, a prediction formula for the ductility coefficient is proposed, which can provide a reference for the application of high-strength steel box-section beam–columns with slender webs in seismic design.

Local buckling and hysteretic behavior of Q690 high-strength steel box-section beam–columns

High-strength steel structures have favorable mechanical properties and perform economically, but their application in seismic design is limited owing to their poor deformation capacity. In order to evaluate the hysteretic performance of Q690 high-strength steel box-section beam–columns and to assess the rationality of applying Eurocode 3 (EC3) to classify cross-sections of high-strength steel, three non-thin-walled welded box-section beam–columns were designed, and horizontal cyclic loading tests under constant axial force were undertaken. The hysteretic response of the specimens was analyzed from the standpoint of the failure mode, the degree of plastic evolution in the cross-section, energy dissipation capacity and ductility. Following this, numerical models verified from the experimental results were used for a parametric analysis to obtain the hysteretic response over a wider range of variables. The test results show that the local buckling failure of the plate at the base of the beam–column determines the failure mode of all three specimens. For a low axial compression ratio, a section with small width to thickness ratio may experience fracture. The parameter analysis showed that there is a flange-web interaction, and the evolution of cross-section plasticity under axial force is also related to the plate width to thickness ratio. In addition, through an analysis of the degree of plasticity in the cross-section under different parameter combinations, it is found that the classification of high-strength steel box-sections by the current specification is not rational, and that EC3 may be unreliable for 690 MPa box-section columns with Class 1 and Class 2 cross-sections, especially with a large axial compression ratio. A new cross-section classification method suitable for high-strength steel columns considering the influence of web-flange interaction and axial compression should be explored.

Corrosion‐induced damages and failures of posttensioned bridges: A literature review

AbstractCorrosion of posttensioned bridges raises great concern, since the only way to safely assess the condition of the tendons is through destructive evaluation. In this scenario, this paper presents the results of an extensive literature review on reported cases of corrosion of posttensioned bridges and few prestressed structures. The aim is to increase knowledge about the structural consequences of possible corrosion‐induced failure mechanisms. The cases were rated according to the increasing severity of the observed damage and consequent interventions as follows: ordinary maintenance is effective, extraordinary maintenance is necessary, and maintenance is insufficient or absent. It was found that most corrosion‐sensitive structures were segmental and box section beam bridges. Most cases required extraordinary maintenance. Warning signs were often observed. The damage was mainly ascribed to design and execution mistakes that facilitated the ingress of external chlorides causing corrosion. The paper concludes with a discussion of the consequences for structural safety.

Assessment of the Bending Moment Capacity of Naturally Corroded Box-Section Beams.

The steel constructions of mine shaft steelwork are particularly exposed to aggressive environments, which cause large, nonuniform corrosion loss throughout the steel members. A correct assessment of corrosion loss and load-carrying capacity of shaft steelwork is crucial for its maintenance and safe operation. In this article, we present the results of laboratory, numerical, and analytical investigations conducted on naturally corroded steel guides disassembled from shaft steelwork. The steel guides considered had a closed profile formed by welding two hot-rolled channel sections. Laboratory bending tests were carried out on beams with various levels of corrosion loss, corresponding to compact, non-compact, and slender cross sections. Multiple detailed measurements of the thicknesses of naturally corroded walls were used in order to reproduce their nonuniform geometry in finite element (FE) models. The results of numerical simulations of five bending tests showed good agreement with laboratory measurements and replicated the observed failure modes, therefore confirming the applicability of this modeling approach for assessing the moment capacity of highly corroded steel beams when the deteriorated geometry is known. For the purpose of generalization, a series of derived models reflecting the natural corrosion pattern was then developed, and moment capacity statistics were collected through multiple simulations. They showed that the mean moment capacity is determined by the mean wall thickness. However, the minimum moment capacity is strongly affected by corrosion loss variation, particularly for the highly corroded beams. A simplified, analytical modeling approach was also examined, providing fairly good assessments of the mean; however, the minimum moment capacity could not be estimated. This study contributes to the body of knowledge on the mechanical behavior of highly corroded hot-rolled box-section beams.

Comparitive study on the flexural behaviour of glulam built-up beams based on ambient and standard fire tests

The experimental study presented in this paper proposes a type of glulam beam with a hollow cross-section that can further optimise solid glulam beams. The study investigated the structural behaviour of glulam built-up box-section beams under four-point flexural bending at both ambient and elevated temperatures. A total of eleven 3100-mm long simply supported beam assemblies were experimentally examined: seven beams were tested at ambient temperature; and four beams were subjected to CAN/ULC-S101 standard fire. Five of the seven beam assemblies tested at ambient temperature were fabricated using self-tapping screws, while the other two assemblies were built using industrial polyurethane adhesive. Each built-up beam assembly was made of four glulam panels, all of 44 mm thickness except the bottom flange panel which had 86 mm thickness. Through ambient testing, it was concluded that when the spacing of the screws connecting the top and bottom flange panels of the built-up section to its web panels was decreased from 800 to 200 mm, the flexural resistance of the beam assembly was increased by about 45%. Whereas further reduction of the spacing from 200 to 100 mm for the screws connecting the bottom flange panel to the web panels over a distance equals to one-third of the span length of the beam from both supports, where shear stresses are maximum, increased the flexural resistance of the beam additionally by 10%. However, the experimental results of the glued beam assemblies show significantly high flexural strength that was almost equal to the calculated strength of an equivalent hollow-section glulam beam. In a subsequent phase, only the strongest beam assemblies (two screwed and two glued) were tested under the effect of standard fire while subjected to monotonic loading that caused a bending moment that is equivalent to the beam full resistance moment calculated for ambient condition. Fire tests' results show that both screwed and glued glulam built-up box-section beams can sustain the applied design load under standard fire exposure for more than 30 min without any fire protection.

LVL–structures made as combined section with small-compliance connections, consistent with stress-strain state of structural elements

The use of composite structures of LVL elements of I-beam and box-shaped cross-section is the most expedient from an economic point of view. Applications for connecting the individual parts of the cross-section of ductile connections - self-tapping screws, allows you to assemble such structures at a construction site. The use of self-tapping screws installed in accordance with the direction of the tensile internal forces of the structure makes it possible to force self-tapping screws to work mainly in tension. At the same time, the most rational work of the joints is achieved — minimum work on bending and maximum work on stretching. According to the results of tests, manufactured and designed beams of composite section, it was concluded that box-shaped beams have greater load-bearing capacity and less deformability. The ratio of actual and calculated bearing capacities of composite box-section beams is higher, the required value of the safety factor, and the destruction of the test beams occurred wood, which indicates the safety margin of the connection of the elements of the composite section on the stretched self-tapping screws.

Simplified calculation method for flexural moment capacity of cold-formed steel built-up section beams

Cold-formed steel built-up section beams are commonly employed in cold-formed steel framing owing to their excellent mechanical performance. In order to develop a simplified approach for obtaining the flexural moment capacity of built-up section beams, both experimental study and numerical analysis on the flexural behavior of cold-formed steel built-up I-section and box section beams under flexural load were carried out in this study. The I-section beams are assembled from two back-to-back cold-formed steel lipped channels, and the box section beams consist of a cold-formed steel plain channel overlapping a lipped channel. First, four-point bending tests were performed on 30 simply supported specimens having 10 different configurations, and the moment capacities and failure modes of built-up section beams at ultimate loads were investigated. The failure characteristics observed were the interaction of local and distortional buckling of the web and top flange for I-section beams and local buckling of the web and top flange in pure bending for box section beams. Then, finite element models were developed to simulate the tested specimens and validated against the experimental results in terms of the moment capacities and failure characteristics. Moreover, extensive parametric studies, including section height-to-width ratio and flange width-to-thickness ratio, were conducted with the validated numerical models to identify the key factors influencing built-up section beams. Finally, a simplified calculation method considering the reduction factor of the gross section modulus of the built-up section to predict the flexural moment capacities of cold-formed steel built-up I-section and box section beams was proposed.

Analysis of composite hollow RC beam strengthened with mild steel sections

The Advancements in Construction in terms of aesthetics and appeal has led to a need of creating spaces with more compact and convenient designs. There is a hierarchy of load transfer for a building. The changes in weight of any preceding member will change the dimensions of succeeding members in the hierarchy. The reduction in the self-weight of beam due to introduction of a hollow section changes the flexural behaviour and the shear behaviour of the beam and also makes it economical section. There is also the advantage of reduction in the depth of beam giving more floor space to user. This paper focuses on Comparative study of Conventional beam and RC beam strengthened with Mild Steel Pipe Section/Mild Steel Box Section. The Composite Section is obtained by embedding Reinforced Concrete beam with MS Pipe/Box Section in Longitudinal Direction. Load – deflection behaviour of conventional beam and RC beam with MS hollow sections are modelled in ABAQUS Software and their performance studies are conducted with stiffness as parameter. The Hollow RC beam strengthened with MS pipe Section showed more stiffness than the MS box section and conventional beam for 1P, 2P and UD loadings making it the most economical section.

Study on Flexural Behaviour of Box Section Bamboo‐Steel Composite Beams

To take full advantages of the bamboo and cold‐formed thin‐walled steel, a new type of box section beam combined with bamboo and steel channel was proposed in this paper. Five composite beams with different parameters were tested to evaluate the effects of bamboo plywood thickness of composite beams and thickness and sectional dimension of steel channel. The results of experiment showed that the proposed composite beams exhibited excellent flexural bearing capacities and stiffness. The increase of bamboo plywood thickness and sectional dimension of steel channel could improve bearing capacity and flexural stiffness of composite beams, while the increase of steel thickness could enhance the bearing capacity and safety margin of composite beams. Furthermore, a new method to predict the deformation and bearing capacities of composite beams was proposed and matched well with the experimental results.

Research on Shear Lag Effect of Three-span Continuous Curved Steel Box Girder Bridge

The normal stress of box-section beam under symmetrical load is the non-uniform characteristic called shear lag effect. Based on actual engineering project, the plate-beam finite element method is used to study the shear lag effect of the three-span continuous-curve steel box-girder bridge under the variety conditions of the curve radius, and the width span ratio, and the distribution of the shear lag effect in the longitudinal and horizontal direction under the symmetrical load are summarized in this paper, providing references for design of steel box-girder bridge. The results show that the shear lags of steel box girders are all positive shear lags under symmetrical loads. Under the conditions of three parameters, the curve radius and the width-span ratio have a great influence on the shear lag effect of steel box girders, and the high-span ratio change has no obvious effect on the shear lag effect, and the shear lag effect of bottom plate is far less severe than the top plate.

Sidewall Thickening as Strengthening for Box-Section Laminated Bamboo Beam under Transverse Load in Shear Failure Mode

This study aimed to compare the mechanical properties of the box-section beams made from laminated bamboo by strengthening the sidewall thickening. The base of this research was that the box-section beam had a higher bending strength than the solid cross-section with the same material volume but lack of shear strength due to the reduced sidewall thickening. A way to increase the shear strength of the box-section beam was to thicken the sidewall on the areas that receive the maximum shear force that was one-third of the span from both supports. In this research, the sidewall thickness variations in the maximum shear force areas were 2 cm (unreinforced group), 3 cm, 4 cm and 4.8 cm. The results of this research were; first, there was a significant increase in the shear strength of the box-section beam reinforced by the sidewall thickening compared to the unreinforced ones. Second, there was no significant difference in the modulus of elasticity of the box-section beams in all samples. Third, the average serviceability load of the box-section beams was 39.11% of the maximum load. And fourth, the sidewall thickening on one-third of the support span saved the material used compared to the thickening on the entire support span.

An improved method for analyzing shear lag in thin-walled box-section beam with arbitrary width of cantilever flange

The shear lag effect can significantly affect the performance of wide-box structures, and even becomes one of the most important influencing factors endangering structural safety. This paper develops a theoretical analysis method, which is designated as PM analysis for analyzing shear lag phenomenon in thin-walled box-section beam with arbitrary width of cantilever flange. In this method, the introduction of initial shear rotation (or initial shear strain) γ0i, due to the effect of web restraint on flanges, is innovatively proposed and further employed in describing the additional warping displacement in top lateral cantilever flanges, and a practical and straightforward procedure of coefficient α3 is designed (DP) based on the proposed assumptions. In addition, a modified method to PM-DP analysis is developed for improving the defects of the hypothesis of shear-lag warping displacements in top lateral cantilever flanges, that is, PM-DP(M) analysis. The differential equations for generalized displacement w(x) and the standard magnitude of shear-lag warping displacement U(x) of the beam are deduced by means of the principle of minimum potential energy (MPE) and solved with the given boundary conditions. Numerous models of thin-walled box-section with arbitrary width of top lateral cantilever flanges under distributed load are chosen and built through a software program (ABAQUS). The results obtained from PM analysis (PM-LB, PM-DP and PM-DP(M)) are summarized into a series of curves indicating the distribution of normal stress and the displacements for various examples, and compared to those obtained from the finite element method (FEM). The study widely demonstrates the strong applicability and high precision of PM-DP(M) analysis, which can be considered as an ideal solution in predicting shear lag effect for thin-walled box-section beam with arbitrary width of cantilever flange and, possibly, be adopted as valuable reference for the design of related thin-walled structures.

Local buckling of highly corroded hot-rolled box-section beams

The steel structures of conveyance guiding systems, particularly steel guides used in mine shafts, are commonly made of box-section beams welded from hot-rolled channel sections. Hot-rolled profiles are generally resistant to local buckling; however, long-term exposure to the aggressive environment of a mine shaft leads to high corrosive loss of the material and reduction of the wall thickness. Some industrial regulations on shaft steelwork design and maintenance allow more than 50% corrosion loss for guides; however, they do not require local buckling calculations. This study investigated the buckling resistance of box-section beams welded from hot-rolled channel sections under bending, in terms of uniform corrosion loss. Laboratory bending tests were conducted on five beams for three levels of web thickness reduction achieved by etching and the results were compared with those obtained from finite element (FE) simulations. Linear modal analyses and nonlinear Riks simulations with imperfections were performed. The hot-rolled box-sections, which are generally resistant to local buckling, were found to be susceptible to local buckling at 46 and 60% corrosion losses in the plastic state and at 71% corrosion loss in the elastic state. This study highlights the need to consider local buckling when using hot-rolled closed profile beams at high corrosion loss.

Theory and application of new automated concrete curing system

The traditional curing method of concrete members in China is through manual water curing based on the experience of engineers and at an arbitrary time. This method, however, may induce early-age cracks and reduce durability of materials. In this paper, an automated curing system is proposed, which can decrease and even eliminate the early-age cracks by controlling the relative humidity and temperature of the concrete. More specifically, (1) the interval time of curing spray, calculated based on the cement hydration and real-time monitored data, is automatically identified by a programmable logic controller; and (2) the fog spray curing is operated under a constant water pressure by a variable frequency technology. A field test was conducted on 20 box-section beams to evaluate the performance of the proposed system based on the temperature evolution, humidity variation, and compressive strength of the concrete. Compared with the traditional manual water curing, the concrete beams cured by the automated system show higher early-age compressive strength, better appearance without water stains, and no early-age cracks.

Nonlinear bending of box section beams of finite length under uniformly distributed loading

In this paper, the bending response of box-section beams of finite length is investigated by using energy methods. The basic assumptions used in the present study are that the total strain energy of a box-section beam subjected to uniformly distributed loading can be simplified into a two-stage analysis process. One is the local bending response of the webs and flanges behaving as plates; the other is the overall bending response of the beam with a deformed cross-section. Analytical solutions for both static and dynamic instabilities of box section beams of finite length subjected to transverse uniformly distributed loading are derived by applying the minimum potential energy principle. To validate the analytical solutions developed, geometric nonlinear finite element analyses are also conducted. Good agreement between the present solutions and the FEA results is demonstrated. Finally, the effects of beam length on the limit critical uniformly distributed load are also discussed.

Identification of Cracks in Box-Section Beams with a Cracked-Beam Element Model

AbstractBox-section steel members are widely used in different types of engineering structures. Identification of cracks in box-section members poses a particular challenge because of the section g...