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The use of hollow concrete columns (HCCs) as piers and piles for bridge applications is widespread due to their higher load-carrying capacity, stiffness, and strength-to-mass ratio compared to the solid section. This study aimed to examine the behavior of HCCs reinforced with glass fiber–reinforced polymer (GFRP) bars and spirals under different loading conditions, analyze the impact of various parameters on their load-carrying capacity, and expand the research database with numerous load–moment interaction diagrams. Ten large-scale GFRP-HCCs, which had a height of 1,500 mm and inner/outer diameters of 113/305 mm, were tested under different levels of eccentricity (concentric, 8%, 16%, 33%, and 66%). A parametric study was conducted to examine the effects of the hollow ratio, longitudinal reinforcement ratio, bar compressive strength, longitudinal reinforcement type, and concrete compressive strength on HCC behavior. The study highlighted the importance of considering the compressive strength of the longitudinal GFRP bars because neglecting it underestimated the axial load and bending moment capacities of the HCCs. The results revealed that initial eccentricity had a greater impact on bending moment than second-order effects. [ABSTRACT FROM AUTHOR]

Exceptional mechanical properties of ultra-high performance concretes (UHPC) offer strong strengthening capacities in bending and shear when used as overlay on normal strength concrete (NSC) structures. Nonetheless, lack of simple and intuitive design models for hybrid elements in design guidelines refrain designers from using UHPC overlays for structural applications. Thereby, a simplified sectional analysis model for NSC-UHPC hybrid elements was developed based on the philosophy of the Canadian Bridge Design Code CSA-S6. By using a new average stress distribution for NSC in hybrid elements that considers the strain at the extreme compressed fiber, equilibrium of forces can be solved by a second-degree equation with direct computation. The simplified model provides the complete moment–curvature behavior of hybrid elements for design purposes, thus allowing verifications in service and ultimate state conditions. An empiric equation is also proposed to evaluate the maximum bending capacity of hybrid elements for predesign. It only uses an approximation of a lever arm between forces in the hybrid cross section and thus offers a quick and easy way to evaluate the bending capacity. Both tools were validated on a detailed and iterative sectional analysis program and with results of four international experimental campaigns. The simplified sectional analysis model and empirical equation showed very good accuracy at reproducing the behavior of a wide range of NSC-UHPC hybrid elements configurations. [ABSTRACT FROM AUTHOR]

Abstract The challenging task of structural design under structural safety, economic efficiency and environmental sustainability constraints has led to the development of several efficient materials. In this context, steel fiber reinforced concrete (SFRC) stands out due to the post-cracking behavior related to its enhanced toughness. Recent structural design normative codes consider this composite, suggesting good structural performance and broadening its applicability. Nevertheless, literature still lacks a comprehensive constitutive model to precisely describe its tensile behavior. This paper analyzes and compares three of the main European constitutive models, investigating factors that possibly influence their behavior. This study was conducted based on the cross-sectional analysis method, so that load-CMOD graphs could be obtained. Statistical analysis was conducted to classify the models, regarding several relevant parameters, such as mean compressive strength of the matrix and fiber volume. Results show that the constitutive law proposed by the fib Model Code shows the best performance. Also, from the set of considered parameters, ultimate tensile fibers strength presents the greatest sensitivity concerning structural post-crack behavior.

To investigate the performance of concrete-filled corrugated steel tubular (CFCST) columns under combined axial compression and bending, numerical and theoretical analyses were conducted in this paper. Firstly, a refined finite element model was established and validated against the existing test results. The stress distribution of steel and concrete with different eccentricities was then analyzed. It was found that the sectional area of concrete region under compression and the stress of corrugated steel plates decreased gradually with the increase of eccentricities. The impacts of cross-sectional dimensions, corrugation dimensions, and material strengths were studied through a parametric analysis. The results indicated that the effect of cross-sectional dimensions on the performance of CFCST columns was more significant than that of corrugation dimensions, and increasing the steel bar strength was more beneficial to improving the ultimate resistance of the CFCST column than increasing the concrete strength. Finally, a theoretical model of compression-bending performance of the CFCST column was established based on the sectional analysis method, and the N - M interaction curve was presented. The proposed N - M interaction curve could conservatively predict the load-bearing capacity of the CFCST column, and the error of 90% of the numerical examples was less than 10%, which could be used for the design of CFCST columns. • A novel CFCST column was introduced for greater load-resistant efficiency. • A refined finite element model was established and validated. • A parametric analysis was conducted to investigate the impacts of key parameters. • The combined axial and flexural behavior of CFCST columns was explored theoretically. • The N - M interaction curves were proposed with good accuracy. [ABSTRACT FROM AUTHOR]

In this paper, a new interpolation method for developing full 3-dimensional (3D) interaction diagrams for arbitrarily shaped reinforced concrete columns subjected to an axial force and biaxial bending is proposed. The interpolation method uses six stationary points that can be determined by searching unconstrained nonlinear optimization solutions or through manual calculations. The weighted sum of a quadratic and linear equation along the meridian and parallel directions is used to preserve the convexity of the interaction diagrams. A coordinate transformation is applied to asymmetrical sections wherein the vertical axis of the meridian diagram is tilted. The proposed interpolation method is applied to various reinforced concrete sections to evaluate the full 3D interaction diagrams. The error ratios of the interpolated diagrams are less than 5% when optimum weighting factors are used. A weighting factor of 0.7 is recommended for the meridian and parallel interpolations of rectangular and asymmetrical sections. [ABSTRACT FROM AUTHOR]

This study investigated the flexural behavior of composite beams with ultra-high performance concrete (UHPC) T-section and hot rolled steel (HRS) H-section. First, a four-point bending test on six specimens was conducted. The effects of stud spacing and tensile reinforcement ratio on flexural performance were investigated in terms of crack patterns, failure modes, ultimate load, load-strain response, relative interfacial slip, and ductility. The experimental results indicated that the stud spacing and the presence of tensile reinforcement had a visible effect on the crack patterns of UHPC web. The distribution of group cracks was observed at UHPC web of specimens with unreinforced UHPC bulb. During the failure stage, the whole HRS H-section in the constant moment region yielded. In particular, the partial cross section of HRS entered the strain hardening stage. In addition, an analytical approach verified by six tested specimens was developed to study the moment-curvature response of HRS-UHPC composite beams (HUCBs). The comparison results indicated the good accuracy of the analytical approach. Then, the proposed sectional analysis model was utilized to investigate the effects of the strength of HRS and UHPC, the total depth of cross section, and the depth of HRS H-section on yielding moment, including ultimate moment and ductility. The analytical results revealed that the strength of HRS and the total depth of cross section had a significant impact on the moment-curvature response of HUCBs. The sectional analysis also illustrated that the yielding point was mainly determined by the yielding of HRS H-beam. Compared with UC120, the ultimate moment and ductility coefficient of the composite beam using UC200 increased by 20.6 % and 87.7 %, respectively. However, the tensile strength of UHPC had a slight influence on the yielding and ultimate moment as well as ductility. • Composite beam with UHPC T-section and hot rolled steel (HRS) H-section. • Experimental investigations into flexural behavior of HRS-UHPC composite beams. • Influence of stud spacing and tensile reinforcement ratio on flexural behavior. • Sectional analysis for studying the moment-curvature response of composite beams. • Effects of strength of HRS and UHPC and depth of cross section. [ABSTRACT FROM AUTHOR]

The use of fibers in reinforced concrete offers an opportunity to optimize the structural design while increasing durability. A sectional analysis that considers the stress-crack-width relation obtained for steel fiber–reinforced concrete (SFRC) and polyolefin fiber–reinforced concrete (PFRC) was used for the structural design of two fly-over bridge typologies. Moment-curvature diagrams were produced using an iterative process that took into account not only the strain conditions but also the crack appearance and evolution. The contribution of fibers to the shear resistance was calculated following the formulation proposed by Model Code 2010. The results obtained showed that the contribution of the fibers enabled a reduction in flexural reinforcement of up to 40% and 30% in the cases of SFRC and PFRC respectively. In relation to shear stirrups, notable reductions could be achieved for both SFRC and PFRC but could be greater in the case of PFRC. Lastly, the economic impact of the use of fibers in the construction costs was quantified. [ABSTRACT FROM AUTHOR]

Steel fiber reinforced concrete (SFRC) is known for improving the tensile post‐cracking fatigue behavior of concrete. This paper presents a method to obtain the cyclic tensile behavior of SFRC through sectional analysis, using a limited amount of input parameters. The analytical model is divided into two parts: a monotonic and cyclic model. The monotonic model calculates the uniaxial stress‐crack width curves or constitutive laws of SFRC that fulfill the beam's equilibrium with the smallest error. Afterwards, when the constitutive law is known, the cyclic model predicts the behavior during progressive load cycles. Two methods are used to implement the damage caused by cyclic loading: based on the experimental stiffness during cyclic direct tensile tests (DTTs) and based on a relation between the plastic crack width and the crack width at unloading. The latter option is preferred as no additional DTTs are needed. The proposed methodology therefore eliminates the need for challenging DTTs and only requires more feasible monotonic three‐point bending tests (3PBTs) for model calibration. The model is validated by means of DTTs and cyclic 3PBTs and its potential for extension to fatigue loading is shown. [ABSTRACT FROM AUTHOR]

A novel method for obtaining complete interaction diagrams of arbitrarily shaped reinforced concrete and composite sections is presented. A mathematical optimization is used to apply the force criterion that maximizes the biaxial bending capacity of a section. A strain criterion for limiting the ultimate strain can be selectively applied through the bound constraint of the optimization problem. Three of the strain parameters for defining the deformation of the section are not fixed, to determine the true ultimate strength at the specified locations in the interaction diagram. A sequential quadratic programming algorithm is used to find the solution. A rotated atan2 function is introduced to overcome the discontinuity in the objective and constraint functions. A tilted axis is used for unsymmetrical sections. Interaction diagrams are obtained for various examples and demonstrate the robustness and versatility of the proposed method. The force criterion provides accurate interaction diagrams for the section, for both normal and high-strength materials. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a prediction method based on artificial neural network was developed to rapidly determine the residual shear resistance of reinforced concrete (RC) beams after fire. Firstly, the temperature distribution along the beam section was determined through finite element analysis using software ABAQUS. A residual shear strength calculation model was developed and validated using the test data. Using this model, 384 data entries were derived for training and testing. The input layer of neural network involved parameters of beam height, beam width, fire exposure time, cross-sectional area of stirrup, stirrup spacing, concrete strength, and concrete cover thickness. The output was the shear resistance of RC beams. It was found that use of BP neural network could precisely predict the post-fire shear resistance of RC beams. The predicted data were highly consistent with the target data. Thus, this is a novel method for computing post-fire shear resistance of RC beams. Using this new method, further investigation was also made on the effects of different parameters on the shear resistance of the beams.

This paper presents a sectional analysis of cracked fiber reinforced concrete (FRC) under flexural loading. The approach considers three separate loading conditions: monotonic, cyclic, and creep bending loads. Different parts of the approach are experimentally calibrated and validated with tests on polypropylene FRC. In the monotonic regime, numerical optimization is used to find the optimal stress–strain relation of FRC to capture the experimental bending behavior as closely as possible, while satisfying the horizontal force and bending moment equilibrium. To model the cyclic behavior, the constitutive law is extended by introducing a tension‐only scalar damage function. The agreement between the predicted and measured response is again very good, and the measured upwards shift of the neutral axis during unloading is predicted as well. Finally, the flexural creep response of a cracked FRC beam is simulated by using uniaxial creep data. The approach predicts the time‐dependent crack widening under sustained flexural loading and can be used to check SLS criteria in the design of FRC elements. [ABSTRACT FROM AUTHOR]

Summary: The purpose of this study is to evaluate the structural behavior of concrete‐filled steel tube (CFT) column to H‐beam connections with vertical through‐plate through full‐scale experiments and examine retrofit methods using the finite element method to improve the connection performance. For this purpose, monotonic loading tests were performed on three full‐scale specimens with varying thickness of vertical through‐plate. The experiments showed that the specimens suffer from a brittle failure due to the stress concentrations and residual stresses at the welds before the beams reach their plastic moment capacity. A series of sectional analyses were conducted to evaluate the effects of the thermally induced residual stresses due to welding and then the strain concentrations in the welded connection were estimated by comparing the experimental maximum strain and the analytical mean strain values. Based on these results, a retrofit model for reinforcing a stiff plate on the upper flange of the beam was proposed and analyzed to reduce the stress concentrations in the welded connection. The results showed that using the proposed retrofit approach, the stress concentration at the connection between the vertical through‐plate and the top flange is reduced by 72%, and the strength of the connection is increased by 70%, which is 10% higher than the analytical plastic moment capacity of the beam. [ABSTRACT FROM AUTHOR]

This paper reports the axial–flexural test results for 12 high-strength concrete (HSC) columns reinforced with glass fiber-reinforced polymer (GFRP) rebars to evaluate the implication of using HSC. The parameters were the applied eccentricity, the longitudinal GFRP reinforcement ratio, and concrete compressive strength and investigate their influence on the load-carrying capacity, deflection, ductility, strains in the concrete and reinforcement, failure modes, and flexural stiffness. All the columns failed in a compression failure mode due to concrete crushing. The GFRP bars developed higher tensile strains in the HSC due to the axial–flexural load compared to columns made with normal-strength concrete (NSC). A minimum reinforcement ratio of 1% in the case of HSC proved practical. Increasing the reinforcement ratio to 2.5% improved the postpeak behavior and yielded a second peak for specimens tested at eccentricities corresponding to 30%, 40%, and 60% of the cross-sectional depth. This study integrated the results to develop an analytical model able to establish moment–curvature and effective-stiffness relationships. The results were also evaluated for the tested specimens and compared to the theoretical expressions used for NSC. [ABSTRACT FROM AUTHOR]

• A new sectional analysis tool for concrete member torque-twist response is presented. • Elastic shear strain distribution assumed for post-cracked torsional behaviour. • Framework is flexible, permitting any constitutive model for concrete or steel. • The approach is validated against a large set of experiments in the literature. • Detailed results obtained with lower computational costs then nonlinear finite element analysis. This paper presents a sectional analysis tool which can compute the complete torque-twist behaviour of reinforced concrete beams and shells. The cross section is modelled as a 2-D grid of triaxial elements representing the concrete and uniaxial elements representing the longitudinal reinforcement. Fixed strain patterns based on kinematic assumptions are used instead of using the finite element method to calculate strain distributions corresponding to sectional strains. Constitutive models for the concrete are based on the Modified Compression-Field Theory, though tension stiffening is neglected in the proposed model's current implementation. A key assumption used in this model is that the shear strain distribution caused by twists obtained from a linear elastic analysis can be used to describe the nonlinear behaviour of a member following cracking. The validity of this assumption when applied to rectangular sections is confirmed based on a study of 115 tests from the literature. Excellent agreement of peak strength and overall torque-twist behaviour are observed when comparing the model predictions and experimental data from these tests. Areas of future work are to improve the capabilities of the model are identified. [ABSTRACT FROM AUTHOR]

• Sectional analysis and moment curvature approach provide accurate results. • Type of material models strongly affect the predicted fire resistance and deformation of a column. • Temperature elongation of materials has significant effect on column deformation. In the paper, a numerical procedure for investigation of slender reinforced concrete columns and steel-concrete composite columns at normal and high temperatures is presented. The procedure is based on sectional analysis and moment-curvature approach. Its applicability is illustrated on validation examples in which the results obtained by the simulations are compared with the test data given in literature. It is shown that the procedure provides sufficiently accurate results. The procedure was implemented in an in-house MATLAB code. The code is employed for the calculation of the examples presented in the paper. The code was also included in freely available scientific computer programs. The procedure is applicable for normal and high temperature conditions and for columns of symmetrical cross-sections of any type and shape. It is applicable in connection with any type of temperature-time curve, heat transfer model, and material models. [ABSTRACT FROM AUTHOR]

• A story curvature based RC shear wall damage assessment method is presented. • Story drifts and shear wall design data are used to calculate story curvatures. • Story curvature damage limits are discussed based on sectional analysis. • The method can consider the influences of shear wall design data on the damage limits. • The method can assess the damages at the bottom and the upper stories of wall panels. Reinforced concrete (RC) frame–shear wall structures are extensively used in urban areas. As a major part of the lateral load resisting system, the shear wall is a key component for the seismic performance assessment of such structures. In this study, a method for the seismic damage assessment of shear wall components is proposed by using the story curvature as the engineering demand parameter (EDP). The method involves (1) a shear wall story curvature calculation method and (2) a shear wall damage limit determination method that uses the story curvatures as the EDP. The story curvature adopted in this study denotes the maximum shear wall curvature within each story level. Based on the piecewise linear assumption of the curvature distribution, the story curvature calculation method requires story drifts and shear wall key design parameters as inputs. Meanwhile, based on the plane cross-sectional assumption and sectional analysis, the damage limits can be determined by considering the influences of the shear wall key design parameters, such as the axial load ratio, shear wall component length, and material information, thereby yielding more accurate estimation. Finally, the proposed method is validated by comparing it with the numerical results of several wall panels and an RC frame–shear wall structure. It is further validated by comparing it with the experiment results obtained from six shear wall tests and a full-scale shaking table test of a seven-story shear wall structure. [ABSTRACT FROM AUTHOR]

Highlights • Structural behavior of HSC columns reinforced with GFRP bars and ties. • Failure mechanisms of HSC columns reinforced with GFRP bars and ties. • Assessing the compressive contribution of GFRP bars in HSC columns. • Developing the P-M interaction diagram of GFRP reinforced HSC columns. Abstract In recent decades, high-strength concrete (HSC) has been widely used in bridge elements, tunnels, and precast-concrete members. Only a limited number of studies, however, have investigated the structural behavior of HSC columns reinforced with glass-fiber-reinforced-polymer (GFRP) bars. Moreover, most concrete codes do not explicitly cover concrete with strengths above 55 MPa. This paper investigates the structural behavior of HSC columns reinforced with GFRP bars and ties when subjected to eccentrically axial loads. Eight full-scale concrete columns with a 400 × 400 mm cross section and 2000 mm in height were tested under axial monotonic loading. The test variables were the eccentricity-to-width ratio, concrete strength, and reinforcement type using steel and GFRP bars and ties. The test results indicate that the failure of the test specimens under different levels of eccentricity was not triggered by rupture of the GFRP bars on the tension side, up to attaining the maximum section capacity governed by concrete-strain limitation. The load–axial displacement, load–lateral displacement, failure mode, and reinforcement strain responses of all the GFRP-reinforced HSC columns are presented and compared to that of the steel-reinforced HSC columns. The structural behavior of HSC columns reinforced with GFRP bars and ties subjected to eccentric axial loads were evaluated by drawing axial force–flexural moment interaction diagrams and comparing them to that for the steel-reinforced columns. An analytical method (layer-by-layer approach) was applied to predict the axial- and flexural-load capacity of the GFRP-reinforced HSC columns. A parametric study was used to examine the effect of increasing the reinforcement ratio and concrete strength and to investigate the strength contribution of GFRP compression bars. [ABSTRACT FROM AUTHOR]

This study investigates the effects of hooked-end fiber geometry and volume fraction on the flexural behavior of concrete pedestrian decks. To achieve this, three different fiber geometries, i.e., three-dimensional (3D), four-dimensional (4D), and five-dimensional (5D), and volume fractions of 0.37%, 0.6%, and 1.0% were considered. Test results indicate that a higher number of hook ends can more effectively enhance the flexural strength and flexural strength margin at all volume fractions than a lower number, so that the order of effectiveness of hooked-end fibers on the flexural strength parameters was as follows: 5D > 4D > 3D. To satisfy the ductility index of 0.39, the amounts of 3D, 4D, and 5D hooked steel fibers should be in the range of 0.98%‒1.10%. Moreover, at a fiber volume fraction of 1.0%, only multiple cracking behaviors were observed, and the numerical results indicated that the volume fraction should be equal to 1.0% to guarantee a deflection-hardening response of pedestrian decks, regardless of the hooked-end fiber geometry. Consequently, a 1.0% by volume of hooked-end steel fiber is recommended to replace the minimum longitudinal steel rebars and guarantee a ductile flexural behavior with multiple cracks for pedestrian decks made of high-strength concrete. [ABSTRACT FROM AUTHOR]

Highlights • Flexural behaviour of SMA RC beams during loading and unloading is investigated. • A simplified sectional analysis method is developed, validated and adopted. • Flexural behaviour of SMA RC beams is investigated through a parametric study. • Equations to estimate optimum amount and length of SMA bars are provided. Abstract Trend of using smart structures, which can adjust when exposed to severe unexpected loading, is increasing. One of the methods to achieve such structures relies on smart materials. For example, replacing conventional steel reinforcing bars in Reinforced Concrete (RC) structures with superelastic Shape Memory Alloy (SMA) bars significantly reduces the residual deformations caused by post-yielding behaviour. This paper provides in-depth understanding of the flexural behaviour of SMA RC beams. A sectional analysis method, which predicts the flexural behaviour of SMA RC beams during both loading and unloading stages, is adopted and validated using available experimental data. An extensive parametric study is then carried out to investigate the effect of different geometrical properties. Recommendations for the optimum amount and length of SMA bars are drawn based on results of this study. [ABSTRACT FROM AUTHOR]

• The GFRP tube cracks almost at the same time when the inner steel tube yields. • The ascending trend slows down significantly when concrete in the compression zone begins to crack. • The adoption of UHSC could delay the plastic hinge formation in inner steel tubes and improve the bond with PBLs. • A theoretical analysis yields very accurate predictions (6% error) of the design load of a hybrid DSTB. Hybrid double-skin tubular beams (DSTBs) with the external fiber-reinforced polymer (FRP) tube-annular concrete-inner steel tube configuration have excellent mechanical performance and corrosion resistance, but are prone to slip problems. In this study, perfobond shear connectors (PBLs) are proposed to reduce the slip between infilled concrete and inner steel tube. Moreover, using ultra-high strength concrete (UHSC) as the annular material could further improve the structural performance and magnify the lightweight merit of hybrid DSTBs, while hybrid DSTBs with PBLs and UHSC have not been investigated yet. To this end, three-point bending experiments were conducted to hybrid DSTBs with PBLs and UHSC to study the flexural behavior. The mid-span load–deflection curves revealed a three-branched behavior: (i) a first linear ascending branch up to the first yielding at the extreme tension fiber of inner steel tube; (ii) a transition branch to the peak load with a significant slope deterioration when infilled concrete in the compression side reached the unconfined failure strain; (iii) a post-peak residual branch characterized by progressive load reductions over a number of load plateaus. The adoption of UHSC could significantly delay the plastic hinge formation in inner steel tube, and meanwhile improve the bond with PBLs. Thus, the slips between infilled concrete and inner steel tube were minimal (less than 0.2 mm) for most of the specimens, except for those with foamy sheet insertions between PBLs (at around 1 mm). In the end, the design loads of the hybrid DSTBs were predicted by a sectional analysis with high level of accuracy (average error at 6%). [ABSTRACT FROM AUTHOR]

Highlights • Flexural performance of RC beams with low reinforcement ratios is improved by adding steel fibers. • Lower ductility index is obtained with lower reinforcement ratio and higher steel fiber content. • Flexural strength margin and ductility of RC beams are deteriorated by adding steel fibers. • Flexural strength decrease of RC beams with decreasing steel bar amount is not recovered by adding steel fibers up to 1%. • Steel rebar cannot be replaced with discontinuous steel fibers at moderate amounts below 1%. Abstract This study aims to investigate the implications of hooked-end steel fibers on the flexural performance of reinforced concrete (RC) beams with very low reinforcement ratios. For this, four different fiber volume fractions, v f , of 0.25%, 0.50%, 0.75%, and 1.00%, were incorporated into the concrete mixture and plain concrete without fibers was considered as a control specimen. Four reinforcement ratios of 0.178%, 0.267%, 0.317%, and 0.406%, which are 44%, 66%, 78%, and 100% of the minimum reinforcement ratio, ρ min , were also adopted to evaluate the steel fiber effect on the flexural behavior of RC beams with various very low reinforcement ratios. The test results indicated that the overall flexural performance of RC beams, in terms of flexural strength, deflection capacity, post-cracking flexural stiffness, and cracking behavior, was improved by increasing the reinforcement ratio up to ρ min. Higher initial cracking and yield loads, post-cracking stiffness, and better cracking performance of RC beams were also obtained by including steel fibers. However, the enhancement of ultimate load carrying capacity by steel fibers was relatively minor, and the ductility index and flexural strength margin, used to guarantee a ductile failure mode, deteriorated with the inclusion of steel fibers. The lower reinforcement ratios and higher fiber volume fractions clearly led to lower ductility indices. Therefore, it was concluded that longitudinal steel rebar could not be replaced with discontinuous steel fibers at moderate volume fractions, v f ≤ 1.0%, in terms of ultimate load carrying capacity, ductility, and flexural strength margin. Lastly, analytical results considering material models for steel fiber-reinforced concrete (SFRC), given by the RILEM recommendation, generally overestimated the flexural capacities of reinforced SFRC beams, and the inaccuracy increased with increasing fiber contents. [ABSTRACT FROM AUTHOR]

For accurate assessment of performance levels in reinforced concrete (RC) members, it is important to well define deformation limits at particular damage states. For RC walled building, investigation of the deformation limits of RC structural walls is required to define limit states and corresponding limiting values. Numerical investigations were carried out on barbell shape and rectangular RC walls with confined boundaries to evaluate response curves and ultimate deformations. A nonlinear 2D and 3D finite elements (FE) models were built in order to simulate the load-deformation relations under monotonic loading as well as cracking and damage patterns of previously tested walls. The FE models were able to simulate the backbone curves with good accuracy as well as the ability of boundary columns in reducing damage level. The 3D FE model simulated very well the ultimate deformation compared to 2D models. A sectional fibre model combined with plastic hinge length and shear deformation component is proposed in order to simulate the backbone curves and the ultimate deformation with less computational cost compared to 3D FE analysis. The model was able to provide relatively accurate backbone curves with very good estimation of ultimate drift. [ABSTRACT FROM AUTHOR]

This study investigates the effects of hooked-end fiber geometry and volume fraction on the flexural behavior of concrete pedestrian decks. To achieve this, three different fiber geometries, i.e., three-dimensional (3D), four-dimensional (4D), and five-dimensional (5D), and volume fractions of 0.37%, 0.6%, and 1.0% were considered. Test results indicate that a higher number of hook ends can more effectively enhance the flexural strength and flexural strength margin at all volume fractions than a lower number, so that the order of effectiveness of hooked-end fibers on the flexural strength parameters was as follows: 5D > 4D > 3D. To satisfy the ductility index of 0.39, the amounts of 3D, 4D, and 5D hooked steel fibers should be in the range of 0.98%‒1.10%. Moreover, at a fiber volume fraction of 1.0%, only multiple cracking behaviors were observed, and the numerical results indicated that the volume fraction should be equal to 1.0% to guarantee a deflection-hardening response of pedestrian decks, regardless of the hooked-end fiber geometry. Consequently, a 1.0% by volume of hooked-end steel fiber is recommended to replace the minimum longitudinal steel rebars and guarantee a ductile flexural behavior with multiple cracks for pedestrian decks made of high-strength concrete.

The effect of polypropylene fibers (PF) on the flexural behavior of reinforced concrete one-way slabs with opening was investigated in this paper. The evaluated parameters included four different PF volume percentages (0, 0.3, 0.6, and 0.9%), with and without opening, two opening shapes (square and circular), and three opening sizes (100, 150, and 200 mm). Three groups of tested slabs were casted: without opening, with square opening, and circular opening, resulting in a total of 28 slabs. The behavior of each slab was evaluated in terms of the cracking load, ultimate capacity, initial and yielding stiffness, deflection ductility, and energy ductility. In addition, the steel and concrete strains, crack opening, and mode of failure were measured and monitored. The minimum design load capacities were calculated theoretically based on the sectional analysis and compared with the tested ones. The results showed that the use of PF at percentages greater than 0.6% significantly enhanced the performance parameters of the slabs with small opening size (2% opening ratio) and provided acceptable enhancement for slabs with large opening size (8% opening ratio). Therefore, the PF can be optimized to substitute the conventional steel reinforcement of slabs with small openings, especially circular openings. [ABSTRACT FROM AUTHOR]

The fundamental design theory of reinforced concrete deep beams is not consistent with that of shallow beams due to non-compliance with the plane section assumption. This paper proposes a grid model that is valid for the flexural capacity prediction and reinforcement design of both shallow and deep beams, which unifies the design process and extends the sectional analysis to deep beams. The grid model is actually based on structural analysis such that stress distribution can be calculated automatically without the plane section assumption. In order to apply sectional design principles, it assumes that design of the critical section is independent of the status of other sections, which means that other sections will remain elastic when the critical section fails. As a result, by inserting the concerned section into the grid model with non-linear material constitutive relationship and failure criteria, the capacity prediction and reinforcement design on that section can be achieved. The axial grid in the grid model guides the design of the flexural reinforcement in two kinds of layouts. Two series of experiments are listed to validate the model. The results of the proposed method are also compared with other wellestablished methods, for example traditional sectional method, layered section approach and strut-and-tie model (STM) method. [ABSTRACT FROM AUTHOR]

This paper presents a theory related to a two-dimensional linear cross-sectional analysis, recovery relationship, and a one-dimensional nonlinear beam analysis for composite wing slender structure with initial twist. Using VABS including a related theory, the design process of the composite rotor blade has been described. Cross-sectional analysis was performed at cutting point including all the details of geometry and material. Stiffness matrix and mass matrix were linked to each section to make 1D beam model. The 3D strain distributions within the structure were recovered based on the global behavior and load of the 1D beam analysis and visualize numerical results. Comparison between the analytical and experimental results shows that the proposed analytical procedure can provide an accurate and efficient prediction of the both deflection, flexural stiffness, strain of multilayer composite slender structure. Verified comparison results can be used to efficiently design accurate complex slender structure properties for detail design and manufacture. These sentences will appear after the conclusion when an article is finally published. [ABSTRACT FROM PUBLISHER]

Global behavior of RC structures during fire events can be predicted using complex nonlinear thermal-structural numerical simulations. However, such simulations are computationally expensive, which limit their use by design engineers. A practical approach to track the performance of RC frames during fire exposure is proposed and validated in this paper. A previously developed simple heat transfer technique is used to calculate an average 1D temperature distribution for heated RC sections. Consequently, the flexural and axial stiffnesses as well as the unrestrained thermal deformations are evaluated using sectional analysis. Based on rational assumptions, simplified expressions are also driven to evaluate those values. The proposed method can be easily applied using available commercial linear structural analysis software to predict the fire performance of RC framed structures. Additional experimental and analytical work is required to validate the proposed method in non-standard fire scenarios. [ABSTRACT FROM AUTHOR]

This paper studies the deformation evolution of concrete under high-cycle fatigue loads. First, uniaxial and eccentric compressive fatigue loads were exerted on prism concrete specimens to observe the mechanical properties of concrete under fatigue loading. Fatigue tests showed that elastic modulus does not always decrease, but strains always increase as loading cycles accumulate. Moreover, strains on the cross-section of each eccentrically fatigued specimen always maintain linear distributions. Based on these experimental findings, a simplified constitutive model for concrete under high-cycle fatigue loads was adopted; hence, a fatigue deformation prediction model was developed to analyze the strain and stress distributions on a cross-section under both cyclic axial forces and bending moments. The proposed model demonstrated its validity by predicting fatigue deformations in good agreement with experimental results. Finally, based on the new prediction model, a case study was conducted, which found that fatigue could pose a big influence on the long-term deformation of concrete bridges. [ABSTRACT FROM AUTHOR]

So far, limited research has been conducted on high-strength concrete (HSC) columns reinforced with fiber-reinforced polymer (FRP) bars under axial and eccentric compressive loads. The behavior and failure modes of steel-reinforced HSC (steel-RHSC) columns are well known: they fail in compression by concrete crushing and/or in tension (steel yielding). The strength and failure mechanisms of HSC columns reinforced with carbon-FRP (CFRP) bars and spirals has not, however, been investigated yet. This paper presents test results from an experimental program conducted to study the failure mechanism and axial–moment capacity of 10 circular HSC columns reinforced with either CFRP or steel bars and tested under different levels of eccentricity. All the specimens measured 305 mm in diameter and 1500 mm in height. The test variables included different eccentricity-to-diameter ratios and two types of reinforcement (CFRP and steel). Laboratory recorded load–axial displacement, load displacement, failure mode, and reinforcement strain responses of the CFRP-RHSC columns were compared to the steel-RHSC columns. A further analytical study was then conducted based on the test results and plane section theory. Based on this study, the axial and flexural capacity of CFRP-RHSC columns can be accurately predicted using plane sectional analysis. Furthermore, a comprehensive parametric investigation was conducted to generate numerous axial force–flexural moment ( P-M ) interaction diagrams. [ABSTRACT FROM AUTHOR]

Discrete hoop reinforcement is preferable over continuous spiral reinforcement due to ease of construction in bridge applications. This research presents the experimental results of full-scale circular concrete columns reinforced with glass-fiber-reinforced-polymer (GFRP) bars and confined with GFRP discrete hoops subjected to combined axial compression loads and bending moments. The findings of the experimental work were integrated with a theoretical analysis based on the strain computability and force equilibrium to extend the parametric study. The lowest and highest bounds of the mechanical properties of GFRP reinforcement along with concrete strength and reinforcement ratio were employed. Sets of axial force–bending moment ( P-M ) interaction diagrams and indicative guide charts are introduced, and recommendations drawn. The compressive-strength contribution of GFRP reinforcement is reviewed and discussed. The results reveal that the GFRP bars developed compression and tension strains up to −0.003 and 0.008 at peak loads and up to −0.015 and 0.0135 at failure on the compression and tension sides, respectively. The confinement provided by GFRP discrete hoops (9.5 mm) spaced at 80 mm prevented the buckling of longitudinal GFRP bars up to and even past the peak load until failure occurred. Based on the experimental and theoretical results, the minimum GFRP longitudinal reinforcement ratio was found to be 1% in order to prevent tension failure (GFRP-bar rupture), provided that the mechanical properties comply with the limits of the available codes and standard. [ABSTRACT FROM AUTHOR]

North America's current design codes and guidelines allow the use of fiber-reinforced polymer (FRP) bars as the primary reinforcement in concrete structures and provide design recommendations for using these bars. Because of a lack of experimental data, however, FRP bars have not been recommended for resisting compression stresses as longitudinal reinforcement in columns or compression reinforcement in flexural elements. This paper presents test results of an experimental program to investigate the structural performance of 10 full-scale circular concrete columns reinforced with carbon fiber-reinforced polymer (CFRP) bars and spirals subjected to combined axial compression loads and bending moments. The test variables include different eccentricity-to-diameter ratios and two types of reinforcement (CFRP and steel). The test results show that the CFRP- and steel-reinforced concrete columns behaved similarly up to their peak loads. The failure of the test specimens under different levels of eccentricity was not triggered by rupture of the CFRP bars in the tension side, but rather it was attributed to gradual concrete crushing, followed by bar crushing on the compression side. Based on the test results, a detailed sectional analysis and plane section analysis were then conducted. Furthermore, a comprehensive parametric investigation was performed to generate numerous nominal axial force-bending moment (P-M) interaction diagrams. The experimental and analytical results are discussed and compared. [ABSTRACT FROM AUTHOR]

Flexural behaviors of reinforced ultra-high-performance fiber-reinforced concrete (UHPFRC) beams were experimentally and numerically investigated in terms of reinforcement ratio. To do this, four UHPFRC beams with different reinforcement ratios (0%-1.71%) were fabricated and tested. Since we focused on the placement technique of the steel reinforcing bars, only a small number of reinforced UHPFRC beams were deliberately considered. Test results indicated that with an increase in the reinforcement ratio, post-cracking stiffness and load carrying capacity were increased, whereas first cracking load was decreased. The cracking behavior was characterized by numerous vertical micro-cracks up to near the peak, followed by crack localization with a gradual decrease in load carrying capacity. The number of cracks and average crack spacing were marginally influenced by the reinforcement ratio. Sectional analysis incorporating a linear compressive model and tension-softening curves obtained from inverse analyses and direct tensile test were performed and verified through comparison with the experimental moment-curvature responses. [ABSTRACT FROM AUTHOR]

Full range analysis of reinforced concrete (RC) members covering the post-crack and post-peak regimes is important for obtaining the deformation response and failure mode of structural members. When a RC member is subject to an increasing external load, the critical sections would exhibit cracking and/or softening. Due to stress relief effect in the proximity of crack opening and plastic hinging, unloading may occur at the adjacent regions. The variable stress states of discrete sections would lead to sectional variation of stiffness, which could not be accounted for by conventional structural analysis methods. In this paper, a nonlinear multilevel analysis method for RC frames whereby the frame members are divided into sub-elements and sectional analysis is utilised to evaluate stiffness degradation and strength deterioration is developed. At sectional level, the secant stiffness is determined from moment-curvature relation, where the curvature is evaluated based on both transverse displacements and section rotations of the frame member. Unloading and reloading behaviour of concrete and reinforcing steel is simulated. In implementing the multilevel analysis, secant iteration is performed in each step of displacement increment to obtain the convergent solution satisfying equilibrium. Numerical example of RC frame is presented to demonstrate the applicability and accuracy of the proposed nonlinear multilevel analysis method.

To predict the flexural behavior of ultra-high-performance fiber-reinforced concrete (UHPFRC) beams including straight steel fibers with various lengths, micromechanics-based sectional analysis was performed. A linear compressive modeling was adopted on the basis of experiments. The tensile behavior was modeled by considering both pre- and post-cracking tensile behaviors. Pre-cracking behavior was modeled by the rule of mixture. Post-cracking behavior was modeled by a bilinear matrix softening curve and fiber bridging curves, considering three different probability density functions (PDFs) for fiber orientation, i.e., the actual PDF from image analysis and PDFs assuming either random two-dimensional (2-D) or three-dimensional (3-D) fiber orientation. Analytical predictions using the fiber bridging curves with the actual PDF or the PDF assuming 2-D random fiber orientation showed fairly good agreement with the experimental results, whereas analysis using the PDF assuming 3-D random fiber orientation greatly underestimated the experimental results. [ABSTRACT FROM AUTHOR]

This study describes the flexural behavior of ultra-high-performance fiber-reinforced concrete (UHPFRC) beams reinforced with glass fiber-reinforced polymer (GFRP) rebars and hybrid reinforcements (steel + GFRP rebars). Three GFRP bar-reinforced beams and four hybrid reinforced beams with different reinforcement ratios were fabricated and tested. Owing to the strain-hardening characteristics of UHPFRC, all test beams exhibited very stiff load–deflection behavior after the formation of cracks and satisfied the service crack width criteria of CAN/CSA S806. In addition, deformability factors higher than the lower limit of CAN/CSA-S6 were obtained for all test beams. The increase in the reinforcement ratio of GFRP rebars resulted in the improvement of their flexural performances, including post-cracking stiffness, load carrying capacity, and ductility (or deformability). The use of hybrid reinforcements by replacing a part of a GFRP rebar with a steel rebar contributed to a higher post-cracking stiffness before steel yielding, but led to lower deformability. Based on a sectional analysis, both AFGC/SETRA and JSCE recommendations were appropriate for predicting the moment–curvature response of UHPFRC beams with GFRP rebars and hybrid reinforcements: the average ratios of the maximum moments obtained from experiments and numerical analyses were found to be 1.12 and 0.94, respectively. [ABSTRACT FROM AUTHOR]

The material characterisation of steel fibre reinforced concrete (SFRC) continues to be an ongoing topic of debate in the scientific community. When designing a structural element made of SFRC, its defining characteristic is its post-cracking residual tensile strength. Theoretically, a uniaxial tension test is the ideal test in gathering these parameters; however these tests are expensive in time and testing. Consequently, much effort has been placed on inferring the post-cracking properties of SFRC from simpler tests, such as a notched prism in bending. In this paper, the sectional analysis procedure of Zhang and Stang (1998) is adapted with the inclusion of the variable engagement model to describe SFRC in tension. The model is shown to accurately capture the load–deformation characteristics of the tested specimens and allows for the explicit identification of the components resisting load. [ABSTRACT FROM AUTHOR]

Full range analysis of reinforced concrete (RC) members covering the post-crack and post-peak regimes is important for obtaining the deformation response and failure mode of structural members. When a RC member is subject to an increasing external load, the critical sections would exhibit cracking and/or softening. Due to stress relief effect in the proximity of crack opening and plastic hinging, unloading may occur at the adjacent regions. The variable stress states of discrete sections would lead to sectional variation of stiffness, which could not be accounted for by conventional structural analysis methods. In this paper, a nonlinear multilevel analysis method for RC frames whereby the frame members are divided into sub-elements and sectional analysis is utilised to evaluate stiffness degradation and strength deterioration is developed. At sectional level, the secant stiffness is determined from moment-curvature relation, where the curvature is evaluated based on both transverse displacements and section rotations of the frame member. Unloading and reloading behaviour of concrete and reinforcing steel is simulated. In implementing the multilevel analysis, secant iteration is performed in each step of displacement increment to obtain the convergent solution satisfying equilibrium. Numerical example of RC frame is presented to demonstrate the applicability and accuracy of the proposed nonlinear multilevel analysis method. [ABSTRACT FROM AUTHOR]

In this study, ten large ultra-high-performance concrete (UHPC) beams reinforced with steel rebars were fabricated and tested. The experimental parameters included reinforcement ratio and steel fiber type. Two different reinforcement ratios ( ρ = 0.94% and 1.50%) and steel fiber types (smooth and twisted steel fibers) were adopted. In addition, three different fiber lengths ( L f = 13, 19.5, and 30 mm) for the smooth steel fibers and one fiber length ( L f = 30 mm) for the twisted steel fiber were considered. For a control specimen, a UHPC matrix without fiber was also considered. Test results indicated that the addition of steel fibers significantly improved the load carrying capacity, post-cracking stiffness, and cracking response, but it decreased the ductility. Specifically, with the inclusion of 2% by volume of steel fibers, approximately 27–54% higher load carrying capacity and 13–73% lower ductility were obtained. In addition, an increase in the length of smooth steel fibers and the use of twisted steel fibers led to the improvements of post-peak response and ductility, whereas no noticeable difference in the load carrying capacity, post-cracking stiffness, and cracking response were obtained according to the fiber length and type. Sectional analysis incorporating the suggested material models was also performed based on AFGC/SETRA recommendations, and the ratios of flexural capacities obtained from experiments and numerical analyses ranged from 0.91 to 1.19. [ABSTRACT FROM AUTHOR]

In this paper, the results of analytical and experimental analyses for the flexural response of steel-fiber-reinforced concrete (SFRC) beams are presented. In the analytical part, to predict the flexural response of SFRC beams according to the strength of concrete and steel fiber content, a model for compression was adopted from a previous research and a trilinear tension-softening curve (TSC) was suggested based on inverse analysis. To obtain the TSC, a number of notched SFRC beams with two parameters such as (1) strength of concrete (normal- and high-strengths) and (2) steel fiber content (0.0%, 0.5%, 1.0%, 2.0%) were fabricated and tested in accordance with the Japan Concrete Institute (JCI) standard. The suggested models were verified through a comparison of the previous four-point flexural test results and the sectional analyses. For the experimental part, the compressive strength and elastic modulus showed negligible changes with the inclusion of steel fibers, while the strain capacity and post-peak behavior were improved by including steel fibers. The addition of more than V f of 1.0% steel fibers resulted in the significant improvement of flexural strength, deflection capacity, and post-peak ductility, while the increase of compressive strength led to an increase in the flexural strength and a decrease in the post-peak ductility. Lastly, the fracture energy increased with the increase in the fiber content and the decrease in the strength. [ABSTRACT FROM AUTHOR]

To investigate the effect of the reinforcement ratio on the flexural behavior of ultra-high-performance fiber-reinforced concrete (UHPFRC) beams under impact loading, a total of four large-sized (200 × 270 × 2900 mm) beams were fabricated and tested using a drop-weight impact test machine. The incident kinetic energy and impact velocity were 4.2 kJ and 5.6 m/s, respectively. A higher reinforcement ratio exhibited lower maximum and residual deflections and better deflection recovery. The test results also indicate that the maximum crack width at a certain drop stage decreased with the reinforcement ratio. A nonlinear analytical model for predicting the impact behavior of a UHPFRC beam was developed using multi-layer sectional analysis and single-degree-of-freedom analysis, and the model was verified through comparison with the experimental results. [ABSTRACT FROM AUTHOR]

Highlights: [•] Numerical simulations require high computation demand and heat transfer knowledge. [•] Interaction diagrams for heated RC columns are constructed using practical approach. [•] Average 1D temp. distribution is predicted using an efficient heat transfer method. [•] Internal compression forces in concrete are calculated using closed form solutions. [•] The proposed formulas are validated using experimental and analytical results. [ABSTRACT FROM AUTHOR]

ABSTRACT A geometrically exact beam model for simulating the structural dynamic response of the CX-100 wind turbine blade is presented. The underlying geometrically nonlinear theory is detailed, and its implementation into a finite-element code, NLBeam, developed as part of this research is outlined. The parameters used to represent the varying cross-sectional distributions of stiffness and mass are calculated consistent with the geometrically exact beam theory by using the variational asymptotic method, as developed by Hodges and Yu et al. through the commercially available code, (VABS) variational asymptotic beam sectional analysis. Code and calculation verification are documented through a systematic grid convergence study applied independently to both the cross-sectional, and static and dynamic beam simulations. An initial assessment of the model is made by comparing simulation results with experimental test data for three cases: quasistatic loading, linearized modal dynamic behavior and steady-state oscillating dynamic loads. Simulation results are shown to be in reasonable agreement with experimental data. Future improvements to the model, as well as additional experimental characterization that can benefit such modeling efforts, are outlined. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]