Bending Capacity Research Articles

Behaviour of square concrete-filled steel tubes reinforced with internal latticed steel angles under bending

The bending properties of square CFSTs (concrete-filled steel tubes) reinforced with internal latticed steel angles were experimentally investigated through four-point bending test, and test results of moment vs deflection curves, moment vs strain curves, bending capacity and concrete cracks were acquired, the test results showed that the latticed steel angles can restrain the cracking of concrete and delay the upwards movement of the neutral axis. After the experiment, firstly, the corresponding finite element (FE) models were established by ABAQUS and validated through comparison with test results; secondly, the bending mechanisms of the tested specimens were analysed and discussed; thirdly, the parametric analysis was conducted to investigate the influence of the main parameters, such as the yield strength and thickness of steel tube, the yield strength and area of latticed steel angles. The research results indicated that the steel tube contributed the most to the bending capacity, hence the yield strength and thickness of steel tube have the most significant influence on the bending capacity. Moreover, the design equations for the bending capacity were proposed based on the superposition method and plastic stress distribution method, and the calculation results showed that the design equations can conservatively and safely predict the bending capacity.

Mechanical properties of corrugated steel lap joint under combined compression and bending

The lap joint of a prefabricated corrugated steel structure is one of the most critical components to be considered during design. Full-scale mechanical tests under combined compression and bending (N–M) were conducted to investigate the effect of axial forces and bending moments on the mechanical behavior of lap joints. Numerical methods were used to examine the effects of different axial forces on the bending behavior of the joint. Analysis revealed that buckling of the corrugated steel plate lapped on the upper layer, located near the innermost row of bolt holes, was the failure mode of the lap joint. The yield of the bolt holes on the compression (crest) and tension (valley) sides was accelerated and postponed by the axial force, respectively. Additionally, three phases with linear, nonlinear, and linear characteristics were identified from the bending moment-rotational angle (M–θ) curves. The initial rotational stiffness of the joint was the highest and decreased gradually with increasing axial force. The residual rotational stiffness of the joint was minimal and was only minimally affected by the axial force. A greater axial force on the joint lowered the bending capacity. Compared with N = 0, when N = 1200 kN, the corresponding bending moment decreased by approximately 17.1% and 9.6% for θ = 0.02 and 0.1, respectively. An empirical formula for calculating the joint rotational stiffness (Kθ) was proposed based on the N–M–Kθ relationship. These findings provide a reference for the joint design of prefabricated corrugated steel structures.

Exploring the potential of the critical shear crack theory for reinforced and post-tensioned glass beams: Initial analysis and experiments

In the evolution of structural glass beam elements, the requirements for post-fracture load bearing capacity and safe failure behaviour have led to the development of reinforced and post-tensioned beams. Maximum bending capacity in the post-fracture state is normally associated with extensive yielding of the reinforcement, providing a safe failure mechanism through apparent ductility of the composite beam section. This can be achieved as long as the propagation of primary flexural cracks does not compromise the transfer of shear from the load points to the supports. Although shear failure is typically not critical for the ultimate limit state design of ’normal’ unreinforced glass beams, it may govern the load-bearing and deformation capacity in the post-fracture state for reinforced and post-tensioned glass beams. This paper presents exploratory experiments and initial analysis of the shear failure phenomenon in the post-fracture state of reinforced and post-tensioned glass beams. Potential shear transfer mechanisms are identified based on the critical shear crack theory developed for reinforced concrete members and applied in the analysis of shear failures observed in four-point bending tests of post-tensioned glass beams. The behaviour of fractured laminated glass under mixed-mode (tension+shear) loading is explored on a limited set of small-scale double-notched glass specimens, demonstrating the feasibility of the applied test methodology. Preliminary findings of the present study may serve as a basis for further investigations of shear resistance of glass beams. Typical shear failure kinematics and suitable constitutive laws of the applied materials need further investigation in order to provide design recommendations for the prediction of shear resistance of reinforced and post-tensioned glass beams.

Out-of-plane bending behavior of cross-laminated timber members enhanced with fiber-reinforced polymers

Carbon or basalt fiber-reinforced polymer (FRP) fabrics were bonded to the bottom of three-layer hemlock cross-laminated timber (CLT), aimed at improving its bending performance under out-of-plane loading. The FRP layer effectively enhanced bending strength by up to 23.8% and global bending stiffness with infinite shear stiffness by up to 18.4%. Carbon FRP was stronger and most effective, and combining it with an inner layer of cheaper basalt FRP also effectively reduced cost. Failure was not observed in the FRP layer, while failure at the transverse layer became more significant. Reinforcement of the transverse layer is therefore recommended to better realize the FRP enhancement effect. A predictive model for bearing capacity in bending for CLT with FRP fabric was developed and validated. Predicted bending stiffness results considering the offset of the neutral axis showed a good agreement with experimental results. The results support the application of FRP fabrics for improved bending performance for CLT panels under out-of-plane loading.

Experimental study on flexural capacity and fire resistance of high strength Q690 steel flush end-plate connections

High-strength steel is widely used in building structures, but fire-induced damage and collapse of high-strength steel structures cause huge economic losses. As a primary part of the structure, the reliability of beam–column joints is essential for the structure’s fire safety. This paper presents an experimental study on high-strength Q690 steel flush end-plate connections (Q690-FEC) at ambient and elevated temperatures. Ultimate bending capacity tests were conducted at ambient temperature to investigate its structural performance, where initial rotational stiffness, bending capacity, and ultimate rotation were obtained. Numerical models were developed to reproduce the tests, and parametric analyses were performed to investigate the influence of load ratio, end-plate thickness, and bolt diameter. Transient fire-resistance tests were performed on specimens with different end-plate thicknesses, where specimen temperature, furnace temperature, and joint rotation were measured. The test results indicate that increasing end-plate thickness has little influence on the critical temperature and fire resistance. Finally, a rotation-temperature relationship model was proposed to predict the fire behavior of Q690-FEC and validated against the experimental data.

Experiment and design methodology of an IODR flange connection under bending load

A new type of inner and outer double-ringed (IODR) flange was introduced in this paper, which can make full use of the inside and outside space of circular tube and reduce the dimensions of connecting bolt and flange plate. Five groups of down-scaled IODR flanges with different flange plate dimensions were designed and tested under bending moment to study the failure mode and force-transferring mechanism. The finite element model was built to further investigate the influence of connection dimensions on the bending performance from different aspects, such as bearing capacity, location of rotation axis and bolt tension ratio. It reveals that the failure of IODR flanges occurred due to the necking of bolt. The bolt tension ratio has an insignificant change when the applied load is smaller than about 80% of bending capacity, then it tends to increase until approaching 1.0. A theoretical method for rotation axis position and bolt force was proposed considering flange geometry parameters and bolt arrangement. It was found that the obtained rotation axis positions are about 0.7r, which is smaller than 0.8r recommended in DL/T 5629–2021, meaning that the existing design method is unsafe. Based on the theoretical analyses, the design methods of flange plate, stiffener and bolt were proposed and a corresponding design process was also established.

Flexural behavior of steel–concrete ultra-shallow floor beams (USFBs) with precast hollow-core slabs

This paper aims to predict the flexural behavior of steel–concrete composite ultra-shallow floor beams (USFBs) with precast hollow-core slab (PCHCS). A finite element model based on tests is developed. A parametric study is conducted, and the influence of the geometric parameters is discussed. The finite element results were compared with stress block analysis. It was concluded that the modeling with two symmetry planes offered better computational cost, and the flexural behavior of steel concrete USFBs was sensitive to dilation angles. From the parametric study, the models without steel tie bar through the web openings showed lower bending capacity. The variation of the reinforcement ratio of the concrete topping contributed to the cracking control. The plastic neutral axis position was measured, considering the mid-span vertical displacement at 10 mm, 50 mm and 100 mm. From the stress distribution it was observed that to define the resisting moment, the P.N.A. closest to the top tee can be considered. The theoretical model underestimated the resistance of USFBs with PCHCS.

RESEARCH ON BENDING DAMAGE PROPRIETIES OF SANDWICH COMPOSITE L-JOINT WITH STIFFENER BY ABAQUS

For the damage proprieties of sandwich composite L-joint with stiffener under bending load, the Hashin failure criterion is used to predict the initial damage of L-joint, the principle of energy dissipation based on damage and material linear softening process is used to predict the stiffness degradation of L-joint, and the cohesive element based on traction and separation model is used to simulate damage of the interface layer. First, the finite element model (FEM) is established by Abaqus, whose rationality is verified by comparing the FEM results with the test results in other literature. Second, the influence of skin's thickness and chamfer radius at the intersection on the bending capacity is studied based on FEM. The results showed that increasing the chamfer radius is the best way to improve the joints' stiffness, and thickening the skin at the intersection is the best way to improve the bearing capacity of the joint.

Ballistic performance of ultralight multifunctional cellular sandwich plates with UHMWPE fiber metal laminate skins

While an ultralight sandwich construction with cellular core can be tailored to exhibit superior load-bearing capability and blast resistance, its ballistic performance is typically inferior to its equivalent monolithic counterpart. To improve the projectile penetration resistance while maintaining the capability of load bearing and blast mitigation, this work proposed a multifunctional sandwich plate with ultra-high molecular weight polyethylene (UHMWPE) fiber metal laminate (FML) skins and aluminum honeycomb core. A combined experimental and numerical approach was employed to quantify the ballistic performance, assess the penetration process, and reveal the underlying mechanisms of the novel sandwich construction. In addition to ballistic resistance, its performance under three-point bending as well as impulsive shock loading was also assessed for multifunctional applications. Relative to all-metallic honeycomb sandwich plate having identical areal density, incorporating UHMWPE composite layers into the skin improved significantly the penetration resistance: the failure mode of the laminate skin was changed from local shear-plugging to global dishing and cracking, enabling enhanced energy absorption of the thin metallic (titanium) layers. Moreover, the use of UHMWPE FML skin for sandwich construction led to not only significantly enhanced bending capacity but also reduced maximum deflection under impulsive shock loading. Hence, the proposed cellular sandwich plate with UHMWPE FML skins can be designed as ultralight multifunctional structure with simultaneous load-bearing and blast/ballistic resistant capabilities.

Experimental and numerical investigations into seismic behavior of corroded steel frame beams and columns in offshore atmospheric environment

With the strong promoting of “national carbon peak and carbon neutrality” strategy and the continuous deepening of “performance-based seismic design” concept, the seismic performance evaluation field of Chinese steel structures has developed rapidly. Nevertheless, previous studies are generally aimed at new building structures, ignoring the seismic performance degradation characteristics caused by the durability loss of existing structures under environmental erosion. Thus, in this paper, accelerated offshore atmospheric corrosion and quasi-static cyclic loading tests were carried out on five steel frame beams and four steel frame columns. The effects of corrosion level on the failure mechanism, hysteretic behavior, skeleton curve, bearing capacity, ductility, stiffness degradation and energy dissipation of steel frame members were revealed and analyzed in detail. The test results indicate that with an increase in corrosion level, the appearance of plate local buckling, steel cracking and final failure shows a forward tendency, and all seismic performance indexes significantly decrease. Moreover, the deterioration models of the maximum load, ultimate displacement and cumulative energy dissipation with weight loss rate for corroded steel frame beams and columns were proposed. In addition, a finite element analysis method for corroded steel frame members was established and validated, which considered the corrosion damage and introduced a nonlinear mixed hardening constitutive model and a stress triaxiality dependent ductile damage criterion. On this basis, the parametric analysis was further presented to systematically study the influence of corrosion level, plate width - thickness ratio and its assembly factors, and stress conditions on the mechanical performance of H-shaped steel members, then obtaining the regular expressions of bending capacity and plastic rotation capacity.

Full-field geometric imperfection and effect on cross-section capacity of circular steel tubes

Measurements on the geometric imperfection of circular steel tubes used in building structures were limited to specific longitudinal lines of the outer surface in existing studies. This study is aimed at detecting full-field geometric imperfection of circular steel tubes and evaluating its influence on cross-section capacity. First, geometric imperfections of 71 specimens consisting of four common types (i.e., hot-rolled and cold-rolled carbon steel circular tubes, cold-drawn and cold-rolled stainless steel circular tubes) were measured using laser scanning techniques. Observations from 3D scanning models demonstrate that the dominant imperfections for seamless tubes (hot-rolled carbon and cold-drawn stainless steel circular tubes) are cross-section ellipticity and uneven thickness, while welded tubes (cold-rolled carbon and stainless steel circular tubes) are mostly influenced by cross-section ellipticity. Based on the measured geometric profile data, imperfection distribution modes of outer-surface and thickness were proposed separately, and then imported to finite element (FE) simulation. Parametric analysis was conducted to evaluate the influence of geometric imperfections on cross-section compression and bending capacity values. Totally, seven types of outer-surface and three types of thickness imperfection distribution modes were used. Simulation results indicate that considering geometric imperfections generates negligible influence on cross-section capacity for the circular steel tubes studied. Finally, the influence of mesh density on capacity prediction of circular steel tubes was discussed. This study illustrates the actual full-field geometric imperfection distribution of circular steel tubes and discusses its effect on cross-section capacity, which provides useful information for improving the efficiency and accuracy of FE analysis on circular steel tubes.

Behavior of high-strength stainless steel S600E welded I-section beams

S600E is a new type of high-strength stainless steel with sorbite microstructure. Its yield strength is as high as 600 MPa, and its cost is lower than the commonly used stainless steel due to its low content of precious metallic elements Ni and Cr. This paper studied the bending capacity of high-strength stainless steel S600E welded I-section beams with lateral-torsional buckling. Tests on seven I-section beams were performed using an innovative four-point bending test rig. Thereafter, comparisons between the bending capacities and the values predicted using the current Eurocode, American code, and Chinese specification were conducted. The results showed that the predictions of the three existing codes were all conservative. Finite element models for the beams were established and verified, meanwhile, parametric analyses based on the simplified models were carried out on the influence of key parameters. Subsequently, through the results of the test and finite element analysis, the design formula for the lateral-torsional buckling was modified and the design formula for the local buckling in the companion study was verified. The complete design procedure of high-strength stainless steel S600E I-section beams was developed by the combination of the two formulae. Finally, to prove the accuracy of the design method proposed in this paper, comparisons between the predictions of the proposed method with the test data and four hundred finite element models were conducted.

Analysis and prediction of masonry wallette strength under combined compression-bending via stochastic computational modeling

The out-of-plane flexural bending capacity of masonry is a fundamental property for understanding the behavior of masonry structures. This study investigates the behavior of unreinforced masonry wallettes subjected to combined compression-flexural loading using the discrete element method (DEM), and provides a novel framework to estimate the masonry strength. A simplified micro-modeling strategy is utilized to analyze a masonry wallette, including the variation of the mechanical properties in masonry units and joints. Stochastic DEM analyses are performed to simulate brickwork assemblages, assuming a strong unit-weak joint material model typical of most masonry buildings, including historical ones. Once the proposed computational approach is validated against the experimental findings, the effect of spatial and non-spatial variation of mechanical properties is explored. Two failure types are identified: joint failure and brick failure. For each failure mechanism, the variability of the response and the effects of the modeling parameters on the load-carrying capacity is quantified. Afterward, Lasso regression is employed to determine predictive equations in terms of the material properties and vertical pressure on the wallette. The results show that the most important parameters changing the response are the joint tensile strength and the amount of vertical stress for joint failure, whereas the unit tensile strength dominates the response for brick failure. Overall, this research proposes a novel framework adopting validated advanced computational models that feed on simple test results to generate data that is further utilized for training response prediction models for complex structures.

Nonlinear Behavior of Bonded and Unbonded Two-Way Post-Tensioned Slabs Pre-Strengthened with CFRP Laminates

In this study, hybrid nonlinear finite element models (FEM) were developed to examine the flexural performance and the ultimate load capacity of bonded and unbonded two-way reinforced concrete post-tensioned (PT) slabs that were pre-strengthened with external carbon-fiber reinforcement polymer (CFRP) laminates. Full 3D simulations, using ANSYS models, have been created for five different slab samples that were selected from a previously available experimental study. The model results were assessed to enable further numerical analysis. The result calibration included measurements of first crack loads, ultimate loads, deflections, strains in the extreme fiber of concrete, strains in CFRP laminates, and failure modes. The results proved a good correlation between FEM output and experimental ones. Based on this, the influencing parameters that affect plate stiffness, as well as the bending capacity of PT slabs, were examined by performing a detailed parametric study. The parameters included real-life load simulation, cable-to-CFRP strength contribution, and CFRP laminate location selection. The results demonstrated that strengthening using CFRP laminates have significantly increased the ductility index of both bonded and unbonded PT concrete slabs by 62.18% and 59.87%, respectively. In addition, strip strengthening locations near supports are much more effective than in the middle of slabs. Additionally, the CFRP strengthening contribution is very considerable in slabs with low PT ratios.

Research on the Development and Joint Improvement of Ceramsite Lightweight High-Titanium Heavy Slag Concrete Precast Composite Slab

Despite the continuous improvement in the research and development of concrete precast composite slab technology, problems like easy cracks and excessive weight at the joints remain. In this study, high-titanium heavy slag was mixed with different kinds of ceramsite to prepare ceramsite lightweight high-titanium heavy slag concrete. The joint of the composite slab was optimized to develop a novel ceramsite lightweight high-titanium heavy slag concrete precast composite slab, hereinafter referred to as “CLHCPCS”. Two CLHCPCS and one ordinary concrete composite slab were prepared. This study analyzed the effects of new materials and improved joints on the flexural capacity and crack resistance of CLHCPCS. It concluded that the density of high-titanium heavy slag concrete with shale ceramsite decreased by 12.0%, and the density of high-titanium heavy slag concrete with fly ash ceramsite decreased by 10.6%. At a 30% dosage of fly ash ceramsite, the compressive strength and splitting tensile strength of concrete reached the maximum. At a 20% dosage of shale ceramsite, the mechanical properties were optimal. Finally, fly ash ceramsite was selected as part coarse aggregate of CLHCPCS. CLHCPCS 1 and 2 demonstrated superior ultimate bearing capacity and crack resistance than ordinary concrete composite slab DBS1, with its ultimate bending capacity test value higher than the average value of ordinary concrete composite slab. ANSYS established the joint model of CLHCPCS for a bending simulation test. The stress and strain distribution of the model and the ultimate bending capacity under the plastic line method were obtained, consistent with theory and experimental analysis results.

Flexural behaviour and ultimate bending capacity of high-volume fly ash reinforced concrete beams

Large number of studies analyzed physical and mechanical properties of high-volume fly ash concrete, but only a few discussed its structural behavior. Material properties are an important input parameter for structural analysis, but they are insufficient for reliable conclusions to be made. This study analyses flexural behavior of reinforced concrete beams made with 63% of low-calcium class F fly ash in total cementitious materials mass, using experimental method and analyzing current code predictions (EN 1992-1-1). The analysis was done by comparing beams made with two longitudinal reinforcement ratios, made with traditional cement concrete (OPC) and high-volume fly ash concrete (HVFAC), both corresponding to concrete class C30/37. Beams were tested in a four-point bending test measuring vertical displacement, crack development, concrete strains and longitudinal reinforcement strains. According to this research, the flexural performance of HVFAC beams is similar to flexural performance of corresponding OPC beams in terms of ultimate bending capacity. The significant difference was noticed regarding cracking extent that was higher in HVFAC beams. Available ultimate bending moments code predictions can be applied on HVFAC beams with similar precision and variation of results, like for OPC beams. However, this cannot be concluded for parameters depending on the cracking behaviour, like cracking moments or deflections. Results and analysis presented in this study indicate that HVFAC can be used in structural elements subjected dominantly to bending, like beams and slabs. More research regarding structural behavior of HVFAC using full-scale long-term tests is needed to develop larger database for reliability analysis.

Experimental and nonlinear analytical investigation of the flexural performance of single-box double-chamber steel–bamboo composite beams

Steel–bamboo composite structures present excellent and stable engineering performance. This study presents a novel single-box double-chamber steel–bamboo composite beam consisting of cold-formed thin-walled steel and bamboo scrimber. Nine single-box double-chamber steel–bamboo composite beams were prepared with various section parameters. A four-point bending test was conducted to evaluate the flexural behaviour of the beams. The failure mode, deflection deformation, and load-carrying capacity were analysed based on the test phenomena and data; the influences of the various parameters on the flexural behaviour were explored. Finally, nonlinear analytical models were developed considering the nonlinear constitutive law of beams and the influence of the steel–bamboo interface slip. The results indicated that lateral instability and local buckling behaviours were effectively avoided, and two failure modes were identified. The bending resistance was improved by reducing the flange bamboo width–thickness ratio, steel height-thickness ratio, and increasing the height of the web. The bending capacity depended more on the bamboo than that on steel. The nonlinear analytical models provided accurate predictions for the beams with tensile failure. Discrepancies between the experimental and analytical results were less than 8.6%.

Seismic Behavior of Assembly Joint with CFST Column and H-shaped Steel Beam

Existing concrete-filled steel tubular (CFST) structures are mostly based on cast-in-situ concrete construction technology. The beam-column joint emphasizes the horizontal connection, while the vertical connection of columns is mostly based on a steel tube connection instead of a precast CFST column connection; this is detrimental to the control of the concrete pouring quality and the full assembly of the structure. Thus, the investigation of an assembly joint that enables the full connection between the beam and CFST column is the key to the improvement of the construction quality and the promotion of the development of the assembled structure. This work proposes an assembly joint between an H-shaped steel beam and a CFST column, and the seismic behavior of the joint was investigated by low-cycle loading experiment. The finite element model of the joint was then established by the numerical analysis method. After verifying the rationality of the finite element model, the influences of both the endplate thickness and the bolt diameter on the energy dissipation performance of the joint were investigated via parametric analysis. The results reveal that with the increase of the endplate thickness and the bolt diameter within a certain range, both the bearing capacity and energy dissipation capacity of the joint will be improved. Moreover, the cooperative bearing mechanism of the column connector and concrete can be fully exerted. Thus, these conclusions indicate the feasibility of the use of the proposed assembly joint in practical engineering applications. Finally, the mechanical mechanism of the assembly joint was studied, and the calculation formula of the joint bending capacity was proposed.

Effect of surface roughness on strain distribution during bending

The limited formability of ultra-high strength steels (UHSS) poses some challenges for the bending process in the form of strain localisation, surface defects and pseudo-polygonal “nut-like” shape of the bend. Bendability is well known to be affected by surface quality, and especially shot blasting. Therefore, in this study, the effect of surface roughness on bendability of UHSS grade is investigated with 3-point bending tests, utilising Digital Image Correlation (DIC) for measuring the strain distributions on the outer curvature. Investigated bending samples of 4 mm thick commercial martensitic were tested in different surface conditions: As-rolled (with scale), “lightly” shot blasted (SB I), “roughly” shot blasted (SB II), dry electropolished (As-rolled P) and a combination of “rough” shot blasting and dry electropolishing (SB II P). Shot blasting increased the surface roughness and subsurface hardness. Utilizing a commercial dry electropolishing process reduced the surface roughness, although this also had major effect on the hardness. Bending results showed that coarser surface roughness decreased the bending capacity, i.e. reduced maximum bending angle and critical strain. A strong correlation between surface roughness (with Rv: the maximum valley depth below the mean surface) and critical bending angle was found, likewise with the subsurface hardness and critical bending angle.

A Parametric Investigation of the Influence of Knots on the Flexural Behavior of Timber Beams

The presence of knots significantly influences the mechanical behavior of timber. This research presents a parametric finite element analysis of the effect of knot characteristics on the flexural capacity of timber beams. Parameters include knot radius, longitudinal and vertical positions, length, and diving angle. The generation of the FE model is based on a technique developed in a previous research stage. The validation of the model is done via bending tests on a set of beams as well as a number of independent research studies. The numerical model accurately recreates the three-dimensional geometry of the knot and related fiber deviations. The capacity of the beams under bending is evaluated via the Tsai–Wu failure criterion. Findings reveal that the presence of knots in the tension zone leads to an early tensile failure and insufficient utilization of compression capacity, the decrease of bending capacity may rise significantly (up to 39% in this investigation), the knot inclination may positively or negatively influence the behavior depending on the diving angle, and moderate knot length can be detrimental to flexural capacity.