Search Results (17)

The modern construction industry has witnessed a marked shift towards the utilization of high-strength steel reinforcement, exhibiting yield strengths exceeding 600 MPa in reinforced concrete structures. Tension stiffening is a critical factor for accurate prediction of deflection and crack width. The current study evaluates the accuracy of state-of-the-art models in predicting curvature in Reinforced Concrete (RC) beams reinforced with high-strength steel (HSS) bars. This study employed three design code methods (Eurocode 2, ACI 318-14, and ACI 318-19) and two other models: the Bischoff model and Kaklauskas and Sokolov’s model. An RC beam with HSS bars was tested, and experimental data on another 63 RC beams reinforced with HSS rebars were collected from various published studies. The test data ranged in various geometrical and material characteristics and were evaluated across a wide range of steel stress intervals. An inverse analysis was carried out to calculate the resultant internal force of tensile concrete (tension stiffening) from the experimental moment–curvature diagram. The inverse analysis demonstrated that the fully cracked RC section reached stiffness at a bending moment of about 3M_cr, where M_cr is the cracking bending moment predicted according to the EC2 design code. Statistical analysis showed that the predicted mean normalized curvature (κ_th/κ_exp) across several reinforcement stress levels ranged from 0.99 to 0.81 for different models. The design codes tend to underestimate curvature. The coefficients of variation ranged between 17.8% and 24.9% for different models. Full article

The long-term behavior of reinforced concrete (RC) structures under sustained loading is strongly affected by creep and cracking, particularly under service conditions where tension stiffening and curvature changes are significant. This study investigates the flexural response of cracked RC beams through combined numerical and experimental analyses. A new 1D finite element model is proposed, integrating nonlinear material behavior, damage mechanics, and time-dependent effects, including creep in both compression and tension. The model relies on a layered fiber section approach and uses a Newton–Raphson iterative procedure to solve equilibrium, allowing accurate prediction of strain, curvature, and internal force evolution over time. The model shows excellent agreement with experimental observations and ABAQUS simulations, accurately capturing deflection trends and crack development. Its performance is further validated using a database of 55 RC beams, including specimens with recycled aggregates and fiber reinforcement. Across this dataset, 84.5% of predicted deflections fall within ±1 mm of measured values, with an R² of 0.960, demonstrating strong reliability. A Sobol-based sensitivity analysis identifies load ratio as the most influential parameter on long-term deflection, followed by concrete strength and humidity. Overall, the model offers an efficient and robust tool for long-term deflection prediction, bridging simplified design rules and complex 3D simulations. Full article

In this paper, the forked-web joint configuration was introduced first, in order to transfer the shear and moment forces better and avoid the local buckling problem that usually happens in narrow steel beams and concrete-filled steel tubular (CFST) column joints. Experiments including three specimens of that joint were then conducted, considering different axial compression ratios of the column. The test results indicated that no failure phenomenon happened to the proposed joint when the equivalent rotational angle was no more than 1/50. However, the final failure mode of each specimen was still local buckling and tearing failure of beam flanges due to the excessively large stress. Finally, based on the tests and FEA results, a corresponding improvement, including a single-web configuration with U-shape and triangular stiffeners, was thus brought forward and numerically verified in terms of rotational stiffness, failure mode, and the hysteretic curve. The FEA results revealed that the rotational stiffness of the proposed single-web joint with triangular stiffeners for beams and U-shape stiffeners for CFST columns efficiently increased from 0.87 to 3.83, and it was almost twice that of the narrow beam-column joint with internal horizontal diaphragms. Moreover, the previous undesirable tearing failure mode was finally avoided by adopting high-strength steel Q550 for the joint beam part. Full article

This study introduces an innovative connection to improve the seismic performance of I-beam–to–concrete-filled circular column joints. The concept employs a steel box with optimized internal and external stiffeners, eliminating continuity and doubler plates to simplify construction. Calibrated finite-element analyses were first conducted to select three configurations for experimental testing under cyclic quasi-static loading, measuring energy dissipation, stiffness, ultimate moment, panel-zone rotation, and strain distribution. The best-performing specimen was then identified, followed by a numerical parametric study varying beam and column dimensions to determine the minimum steel-box thickness beyond which further increases offer negligible benefit and to assess its effect on connection rigidity. Experimentally, stiffeners aligned with beam flanges significantly improved moment capacity, stiffness, and energy dissipation. Based on parametric analyses, connections with appropriate box-to-flange thickness ratios achieved over 95% of the maximum flexural strength and stiffness, confirming the reliability of the proposed non-dimensional design approach. Numerical analyses showed that the proposed non-dimensional thickness ratios accurately predict connection behavior, where appropriate flange-to-box proportions ensure over 95% of maximum flexural strength and stiffness, leading to stable and rigid joint performance. Overall, the proposed detailing offers a constructible alternative to conventional plate-intensive solutions while achieving superior cyclic behavior. Full article

To investigate the initial rotational stiffness and ultimate moment of fully bolted connections in panelized steel modular structures, a finite element analysis was carried out on 20 joint models. High-fidelity models were developed using ABAQUS, and their accuracy was confirmed through comparison with experimental tests. A parametric study was performed to systematically evaluate the effects of the column wall thickness in the core zone, internal diaphragm configurations, angle steel thickness, and stiffener layouts on the joint stiffness and ultimate strength, leading to practical optimization suggestions. Additionally, a mechanical model and a corresponding formula for predicting the initial rotational stiffness of the joints were proposed based on the component method in Eurocode EC3. The model was validated against the finite element results, showing good reliability. Three failure modes were identified as follows: buckling deformation of the beam flange, buckling deformation of the column flange, and deformation of the joint panel zone. In joints with a weak core zone, both the use of internal diaphragms and increased column wall thickness effectively improved the initial rotational stiffness and ultimate bearing capacity. For joints with weak angle steel connections, adding stiffeners or increasing the limb thickness significantly enhanced both the stiffness and capacity. The diameter of bolts in the endplate-to-column flange connection was found to have a considerable effect on the initial rotational stiffness, but minimal impact on the ultimate strength. This study offers a theoretical foundation for the engineering application of panelized steel modular structural joints. Full article

In this work, a novel analytical equation is developed to accurately predict the mechanical behavior of thin-walled beams. The FEM was used for building the model and obtaining the results. The new equation developed is useful for the calculation of the displacement of a beam simply supported at its ends subjected to torsion loads, applied in opposite side areas of the Finite Element Method (FEM) model. The software Eureqa 1.24.0 was used to find hidden analytical models that were validated thereafter. The aim is to provide a formula that makes possible the comparison of analytic calculations with numerical calculations on bending and torsion combined load. A FEM model of a hollow-box beam with rectangular cross-section loaded with torsion was built and analytical calculations were performed. The analytic calculations were compared with the numeric results in order to know if the results are approximated. The results show good agreement. In the future, other models, such as internally reinforced beams, could also be tested with this methodology. Also, different conditions could be applied to the model studied in this work in order to evaluate the limitations and validity of the developed analytical model. Full article

In this study, we analyzed novel internally reinforced hollow-box beams to evaluate their strength using the finite element method (FEM) in ANSYS Mechanical APDL 18.1. Twelve different FEM models were subjected to static bending loads, and their performance was assessed based on Huber–Mises equivalent strength values. The results show that most optimized models exhibited improved strength compared to their initial versions, with some configurations achieving up to a 470% increase. These findings highlight the effectiveness of structural optimization in enhancing the strength behavior of hollow-box beams, providing valuable insights for engineering applications. Full article

To better understand the bending performance of rectangular high-strength steel fiber-reinforced concrete (HSFRC)-filled steel tubular (HSFRCFST) beams with internal stiffeners, ten beams were subjected to a four-point bending test. The primary considerations were the strength grade of the HSFRC, the steel fiber content, the internal stiffener type, and the circular hole spacing of the perfobond stiffener. The moment–curvature and flexural load–deflection curves were calculated. The mode of failure and the distribution of cracks of the infill HSFRC were observed. The presence of steel fibers greatly improved the bending stiffness and moment capacity of HSFRCFST beams, with the optimal effect happening at a steel fiber content of 1.2% by volume, according to the experimental findings. The type of stiffener influenced the failure modes of the exterior rectangular steel tube, which were unaffected by the compressive strength of the infill HSFRC. On the tension surface of HSFRCFST beams, the crack spacing of the infill HSFRC was virtually identical to the circular hole spacing of perfobond stiffeners. When the circular hole spacing was between two and three times the diameter, the perfobond stiffener worked best with the infill HSFRC. The test beams’ ductility index was greater than 1.16, indicating good ductility. The test beams’ rotational capacities ranged from 6.26 to 13.20, which were greater than 3.0 and met the requirements of the specification. The experimental results demonstrate that a reasonable design of the steel fiber content and the spacing between circular holes of perfobond stiffeners can significantly improve the bending resistance of rectangular HSFRCFST beams. This provides relevant parameter design suggestions for improving the ductility and bearing capacity of steel fiber-reinforced concrete beams in practical construction. Finally, a design formula for the moment capacity of rectangular HSFRCFST beams with stiffeners is presented, which corresponds well with the experimental findings. Full article

Gantries and beams, as the main load-bearing structures of heavy equipment, usually belong to the box structure consisting of outer walls and inner stiffened plates. The structure of the stiffener layout is bulky due to empirical design, leading to higher material consumption and impacting mechanical performance. There are challenges in effectively identifying load-transferred paths within 3D box structures through direct topological optimization. A method for optimizing the layout of internal stiffened plates of large box structures based on load paths is proposed in this paper. Initially, based on the load conditions acting on the structure, the 3D box structure is decomposed into 2D functional sections. Subsequently, the load paths on the functional cross-section are visualized according to the load path method. Finally, the stiffener layout of the ultimate optimized structure is designed according to the effective load path distribution. Taking the gantry of a heavy-duty aluminum ingot composite processing unit as an example, the optimization results indicate that the maximum stress of the structure decreased by 14.9%, the maximum deformation reduced by 32.95%, and the overall weight decreased by 14.4%. This demonstrates that the approach proposed in this paper is practical and effective for optimizing stiffener layouts in large-box structures. Full article

The behaviour of seismically damaged steel joints with reduced beam section (RBS) at elevated temperatures has not been widely investigated yet. Therefore, the study summarized in this article aimed to (i) analyse the response of RBS joints at high temperatures and (ii) investigate the influence of plastic damage, due to cyclic loading, on the fire performance of the joints. A set of RBS joints with rib stiffeners on the both lower and upper beam flanges was designed according to European standards and the following parameters were considered: (i) location of the joint (i.e., internal or external joint) and (ii) reduction in the beam flexural resistance (i.e., 65% or 80% of the beam plastic moment). The mechanical response of these joints was simulated by means of finite element models (FEM). The accuracy and effectiveness of the adopted modelling assumptions to mimic the seismic response of the joints were validated against experimental results available from the existing literature. The numerical results highlight that under cyclic loading, all investigated joints exhibit ductile behaviour, allowing the concentration of the plastic deformation within the reduced segment of the beam. The designed reduction in the beam flexural resistance influences the joint fire performance, being impaired in the cases with lower flexural resistance. In contrast, the imposed cyclic pre-damage does not appreciably affect the fire resistance of the investigated joints. Full article

Based on the deflection theory and the characteristics of multi-tower self-anchored suspension bridges, considering the influence of longitudinal stiffness of main tower and bending effect of stiffening beam, the equilibrium differential equation and deformation coordination equation of multi-tower self-anchored suspension bridges are established. By “replacing beam” method, the practical calculation formula of internal force and deformation of multi-tower self-anchored suspension bridge was deduced, and the corresponding calculation program was implemented. The correctness of the analytical method and calculation program was verified by an example. The analytical method of static analysis of multi-tower self-anchored suspension bridges established in this paper can theoretically explain the mechanical characteristics of the structure, and the calculation method has a clear calculation flow. The internal force and deformation of the structure under live load can be approximately calculated only by inputting the main design parameters of the structure, which is suitable for structural design and parameter analysis of multi-tower self-anchored suspension bridge. Full article

This paper explains the mathematical foundations of a method for modelling semi-rigid unions. The unions are modelled using rotational rather than linear springs. A nonlinear second-order analysis is required, which includes both the effects of the flexibility of the connections as well as the geometrical nonlinearity of the elements. The first task in the implementation of a 2D Beam element with semi-rigid unions in a nonlinear finite element method (FEM) is to define the vector of internal forces and the tangent stiffness matrix. After defining the formula for this vector and matrix in the context of a semi-rigid steel frame, an iterative adjustment of the springs is proposed. This setting allows a moment–rotation relationship for some given load parameters, dimensions, and unions. Modelling semi-rigid connections is performed using Frye and Morris’ polynomial model. The polynomial model has been used for type-4 semi-rigid joints (end plates without column stiffeners), which are typically semi-rigid with moderate structural complexity and intermediate stiffness characteristics. For each step in a non-linear analysis required to adjust the matrix of tangent stiffness, an additional adjustment of the springs with their own iterative process subsumed in the overall process is required. Loops are used in the proposed computational technique. Other types of connections, dimensions, and other parameters can be used with this method. Several examples are shown in a correlated analysis to demonstrate the efficacy of the design process for semi-rigid joints, and this is the work’s application content. It is demonstrated that using the mathematical method presented in this paper, semi-rigid connections may be implemented in the designs while the stiffness of the connection is verified. Full article

The flexural strength of Slender steel tube sections is known to achieve significant improvements upon being filled with concrete material; however, this section is more likely to fail due to buckling under compression stresses. This study investigates the flexural behavior of a Slender steel tube beam that was produced by connecting two pieces of C-sections and was filled with recycled-aggregate concrete materials (CFST beam). The C-section’s lips behaved as internal stiffeners for the CFST beam’s cross-section. A static flexural test was conducted on five large scale specimens, including one specimen that was tested without concrete material (hollow specimen). The ABAQUS software was also employed for the simulation and non-linear analysis of an additional 20 CFST models in order to further investigate the effects of varied parameters that were not tested experimentally. The numerical model was able to adequately verify the flexural behavior and failure mode of the corresponding tested specimen, with an overestimation of the flexural strength capacity of about 3.1%. Generally, the study confirmed the validity of using the tubular C-sections in the CFST beam concept, and their lips (internal stiffeners) led to significant improvements in the flexural strength, stiffness, and energy absorption index. Moreover, a new analytical method was developed to specifically predict the bending (flexural) strength capacity of the internally stiffened CFST beams with steel stiffeners, which was well-aligned with the results derived from the current investigation and with those obtained by others. Full article

In stepped-sine testing of strongly nonlinear structures with the classical force-control strategy, corrective force perturbations of a standard controller used to capture the reference signal in the proximity of turning points of frequency response curves may often lead to a premature jump before reaching the actual resonance peak. Accordingly, a classical force-control approach is not suitable to identify backbone curves of strongly nonlinear structures. This paper shows that currently available commercial modal test equipment can accurately identify backbone curves of strongly nonlinear structures by using Response-Controlled stepped-sine Testing (RCT) and the Harmonic Force Surface (HFS) concept, both recently proposed by the authors. These methods can be applied to systems where there are many nonlinearities at several different (and even unknown) locations. However, these techniques are not applicable to systems where internal resonances occur. In RCT, the displacement amplitude of the driving point, rather than the amplitude of the applied force, is kept constant during the stepped-sine testing. Spectra of the harmonic excitation force measured at several different displacement amplitude levels are used to build up a smooth HFS. Isocurves of constant amplitude forcing on the HFS lead to constant-force frequency response curves with accurately measured turning points and unstable branches (if there are any), which makes it possible to identify backbone curves of strongly nonlinear structures experimentally. The validation of the proposed approach is demonstrated with numerical and experimental case studies. A five degree-of-freedom (DOF) lumped system with five cubic stiffness elements, which create strong conservative nonlinearity, is used in the numerical example. Experimental case studies consist of a cantilever beam and a control fin actuation mechanism of a real missile structure. The cantilever beam is supported at its free-end by two metal strips constrained at both ends to create strong stiffening nonlinearity. The control fin actuation mechanism exhibits very complex and strong nonlinearity due to backlash and friction. Full article

Advanced materials have been created for structural application during the past decades. Engineers, however, faced severe problems due to the absence of a reliable technique for ensuring the required structural properties minimising the amount of material used. A lack of constitutive models for the analysis of the structural systems also exists. Residual stiffness of flexural concrete elements subjected to short-term load is the focus of this research. Tension-stiffening models were developed to represent the deformation response of the members reinforced with internal bars. This study examines the suitability of the tension-stiffening modelling approach for simulating the deformation behaviour of the composite specimens comprising glass fibre-reinforced polymer (GFRP) pultruded profile adhesively bonded to the tensile surface of the concrete beam. The study employs a nonlinear finite element approach and analytical model to simulate the deformation behaviour of the flexural elements. Full article