Search Results (124)

The effects of wide-ranging service temperatures on interfacial bond transfer and slip evolution in high-strength concrete-filled steel tube members have not yet been systematically characterized. A test program involving 15 circular specimens was carried out at temperatures between −60 °C and 60 °C with steel tube wall thicknesses of 2 mm, 3 mm, and 4 mm. Particular attention was given to interface failure patterns, slip development, and stress transfer during loading. Cooling markedly enhanced the interfacial resistance, whereas heating produced a moderate reduction. The increase observed at subzero temperatures was smaller than that commonly reported for conventional concrete-filled steel tubes. Bond capacity also declined as the diameter-to-thickness ratio increased because of reduced confinement from the steel tube. Regression of the experimental data produced expressions for ultimate bond strength and the associated slip. A piecewise constitutive relation was then formulated to represent the complete bond–slip process. The proposed relation was implemented in ABAQUS through distributed nonlinear connector elements and temperature-dependent material properties. Numerical predictions showed close agreement with the measured load–slip responses, characteristic loads, and stress distributions. These results provide a modeling basis for HSCFST members exposed to severe cold and large temperature fluctuations. Full article

The FRP–concrete–steel double-skin tubular column (DSTC) is a novel composite column designed to meet the structural demands for high strength, exceptional durability, and lightweight characteristics. To investigate the axial compression performance of DSTCs, this study conducted axial compression tests on 16 circular DSTCs and three circular fully filled columns (FCSCs). This research focused on analyzing the effects of steel tube wall thickness, void ratio, rubber content, steel fiber content, and GFRP tube wall thickness on stub columns’ failure modes, load–displacement curves, load–strain curves, and stress–strain relationships of concrete. The results demonstrated that GFRP tube wall thickness is the most critical parameter influencing the bearing capacity and deformation capacity of the column. The ultimate bearing capacity of all specimens ranged from 1606.9 to 3447.9 kN; the peak displacement of the specimens ranged from 7.49 to 17.77 mm. Increased void ratios decrease bearing capacity but enhance ductility, whereas steel tube wall thickness and steel fiber content have relatively minor effects. Based on the experimental results, models for the ultimate bearing capacity, ultimate strain, and stress–strain relationship of short columns were proposed, taking into account rubber content. The average predicted-to-experimental capacities ratio is 0.97 and the predicted load–displacement curves match well with the experimental curves, indicating the very high accuracy of the proposed models. Full article

Predicting the mechanical properties of bolted connection nodes in prefabricated Concrete-Filled Steel Tube (CFST) column–steel beam assemblies remains challenging due to complex nonlinear relationships, high degrees of parameter coupling, and limited generalization capabilities of traditional empirical formulas. This study proposes a data-driven prediction model integrating an Improved Particle Swarm Optimization (IPSO) algorithm with a Deep Neural Network (DNN). Drawing upon 196 sets of experimental data on CFST column–steel beam nodes with Extended Hollo-Bolt (EHB) connections from the published literature, the model employs bolt diameter, steel tube wall thickness, concrete compressive strength, beam–column cross-sectional parameters, and connection configuration parameters as input variables, while designating ultimate moment capacity, initial stiffness, and joint ductility coefficient as prediction targets. A multi-layer DNN is constructed to capture the highly nonlinear mapping between structural parameters and mechanical responses. The IPSO algorithm, enhanced with adaptive inertia weight and Lévy flight perturbation, performs global optimization of the network weights and hyperparameters to improve convergence speed and prediction stability. Five-fold cross-validation is embedded within the IPSO fitness evaluation loop to guide hyperparameter selection, while dropout regularization and early stopping are applied during final training to mitigate overfitting; prediction performance is ultimately verified on an independent hold-out test set. Experimental results demonstrate that the proposed IPSO-DNN model outperforms a tuned shallow neural network (SNN), Support Vector Regression (SVR), and Random Forest (RF) models across the coefficient of determination ($R^2$), root mean square error (RMSE), and mean absolute error (MAE), effectively capturing the nonlinear mechanical characteristics of CFST nodes under complex loading conditions. Full article

Precast concrete (PC) structures are increasingly adopted in building construction for their sustainable construction advantages. However, theoretical models for seismic design of precast concrete walls with concrete-filled steel tubular (CFST) elements remain limited. The lack of such models hinders the performance-based seismic design and resilience assessment of these hybrid structures. This study investigates the seismic mechanism and develops a restoring force model for precast concrete superposed shear walls with CFST end columns (PCSSWEC). A refined three-dimensional finite element model was established using ABAQUS and validated against quasi-static cyclic test results of three full-scale specimens. The four-stage loading mechanism—elastic, wall cracking, elastoplastic yielding, and ultimate failure—was revealed, with the precast–postcast concrete interface identified as the primary weak link governing post-peak strength degradation. Comprehensive parametric studies examined the influence of shear span ratio (λ = 0.75–3.25), axial compression ratio (n_a = 0.1–0.6), steel tube width-to-thickness ratio (B/t = 20–80), and concrete strength (C30–C60) on seismic performance. Results indicate that intermediate walls (λ = 1.75–2.25) exhibit optimal ductility, and a steel tube with B/t = 40–60 provides a balanced combination of strength and deformation capacity. A tri-linear backbone curve model with explicit formulae for equivalent stiffness and load capacity was developed, along with modified Clough-based hysteretic rules incorporating stiffness degradation through a common yield-point approach. Validation against experimental and numerical results demonstrates reliable model performance for primary structural parameters: lateral load bearing capacity and ultimate drift ratio are predicted within ±10%, while yield load and ductility predictions show larger scatter due to inherent challenges in cyclic behavior characterization. The proposed restoring force model provides a practical tool for performance-based seismic design and resilience assessment of precast concrete buildings. Full article

The seismic design of spatial joints in long-span concrete-filled steel tube (CFST) arch bridges under complex stresses remains a critical challenge in high-intensity seismic zones. This study investigates the seismic performance and failure mechanisms of CFST spatial KT-type joints, using the Pingnan No. 3 Bridge as a case study. Based on similarity theory, four scaled test specimens were designed. The core variable was the axial compression ratio of the main pipe, while the load on the K-branch served as the parametric variable. Quasi-static tests were conducted under constant static loading on the main pipe and K-branches, coupled with low-cycle cyclic loading on the T-branch. Furthermore, nonlinear finite element analysis (FEA) was performed using Abaqus for cross-validation. The results indicate that the primary failure mode of this joint configuration is the shear-punching failure of the main pipe wall at the T-branch intersection. The load–displacement hysteresis curves exhibit a robust “bow-shaped” profile, indicating substantial plastic energy dissipation capacity. Comparative analysis confirms that hollow steel pipe T-branches offer superior ductility in long-span arch bridges compared to concrete-filled alternatives. By extracting shear stress distribution characteristics from the FEA model to precisely locate the neutral axis, this study proposes a theoretical correction to the ultimate load-carrying capacity calculation model. The derived theoretical values demonstrate good agreement with the experimental results. The relative errors between the calculated and experimental bearing capacities of KT783a, KT783, KT700, and KT607 were 1.99%, 0.23%, 2.26%, and 2.45%, respectively, referring to the T-branch out-of-plane bearing capacity predicted by the proposed formula. The proposed theoretical model provides a reliable quantitative basis for the seismic design and local strengthening of similar spatial joints in long-span CFST arch bridges. Full article

The depletion of natural river sand resources in the construction industry and the pollution caused by iron tailings storage in the steel industry are the two major challenges currently faced. The use of iron tailings in construction materials is widely regarded as one of the most sustainable and cost-effective approaches. Based on C30 concrete, 12 steel tube iron tailings sand (IOT) concrete columns with different IOT substitution rates were designed and fabricated in this paper, and axial compression test research was conducted on them; finite element simulations were conducted for comparison with the experimental results, focusing on the influences of IOT substitution rate (0–100%), steel pipe wall thickness (1–4 mm), and steel strength (Q235, Q355, Q390, Q420, Q460) on the bearing capacity of concreted steel tube columns were parametrically analyzed. By comparing the calculation methods of the bearing capacity of concrete-filled steel tube columns in five relevant standards, the calculation formula for the bearing capacity of IOT columns was corrected and obtained. The results show that the failure mode of the IOT column is similar to that of the ordinary column, and the steel tube wall has all undergone circumferential band shear buckling. As the replacement ratio of IOT increases, the load-bearing capacity of columns initially improves and then declines. The finite element analysis results show that the bearing capacity of the IOT column is directly proportional to the wall thickness of the steel pipe, and increasing the wall thickness of the steel pipe can effectively improve the bearing capacity of IOT columns. The discrepancy between the predicted and experimental bearing capacities of IOT columns obtained based on the revision of the “Technical Code for Concrete-filled Steel Tube Structures” (GB 50936-2014) is within 10%, which can effectively predict the load-bearing capacity of IOT columns within a certain range. Full article

With the increasing functional and geometric complexity of modern steel buildings, irregular beam-to-column joints are becoming increasingly common in engineering practice, while their seismic performance and force transfer mechanisms remain insufficiently understood. Based on previous full-scale cyclic loading tests on unequal-depth steel beam (UDSB) and staggered steel beam (SSB) joints incorporating inclined internal diaphragms, this study presents numerical simulations and parametric analyses of irregular steel beam to concrete-filled steel tube (CFST) column joints. Three-dimensional nonlinear finite element models were developed using ABAQUS and validated against experimental results. The strengthening effects of internal diaphragms and concrete infill were then comparatively investigated. The results indicate that internal diaphragms increase the initial stiffness and load-carrying capacity of the joints to approximately 2.0–2.3 times and 1.16–1.8 times, respectively, compared with joints without diaphragms, whereas concrete infill provides smaller enhancements of about 1.3 times in stiffness and 1.2–1.3 times in strength. In addition, the hysteretic response of joints without diaphragms shows good agreement with the post-fracture behavior observed in the experiments, validating the diaphragm fracture mechanism. A parametric study further demonstrates that, under cyclic loading, the beam depth ratio, staggered floor ratio, column wall thickness, column width, diaphragm thickness, and diaphragm opening diameter have significant influences on joint strength and stress distribution, while the effect of axial load ratio is relatively minor. Finally, a strength prediction method applicable to inclined-diaphragm UDSB and SSB joints is proposed, and corresponding fitted expressions are derived based on the parametric results. The findings provide useful guidance for the seismic design of irregular steel beam–CFST column joints incorporating internal diaphragms. Full article

This study proposes a design method for a novel bolted endplate rigid connection between circular concrete-filled steel tube (CCFT) columns and wide-flange (WF) steel beams, with particular emphasis on the parametric behavior governing joint performance. Based on the preliminary quasi-static tests, finite element simulations are conducted to evaluate the flexural behavior and failure mechanisms under beam-end maximum moment, followed by an extensive parametric study examining the effects of square tube dimensions, high-strength grout, and column axial load. The numerical results show that the wall thickness of the square steel tube significantly affects grout indentation. A 60% reduction in wall thickness led to a 503% increase in indentation. In contrast, variations in tube dimensions, grout strength, and column axial load within the studied range caused less than a 16% change and did not influence the flexural performance. These results indicate that the constraints on tube dimensions and axial load may be relaxed. The proposed connection effectively overcomes the limitations of conventional CCFT-to-beam joints, including unfavorable stress transfer, complex detailing, and construction inefficiency, by modifying the load-transfer mechanism and reducing the demand on tensile-critical welds, thereby enhancing ductility. Based on the parametric findings, a design method is established, and theoretical analysis confirms that the proposed connection satisfies the stiffness requirements for fully rigid connections. Future quasi-static tests with different member sizes are recommended to validate these findings. Full article

This study presents a comprehensive numerical investigation into the combined bending–shear behaviour of hollow-flanged cold-formed steel (HFCFS) beams filled with lightweight concrete (LWC). Although previous research has independently examined the pure bending and pure shear responses of these composite members, their structural performance under simultaneous bending and shear remains unexplored. In this work, advanced three-dimensional finite element (FE) models were developed in ABAQUS to simulate the nonlinear behaviour of LWC-filled HFCFS beams subjected to various shear-span ratios. The modelling approach was validated using published experimental data and extended through a systematic parametric study that considered three beam geometries, two steel yield strengths (350 MPa and 450 MPa), two lightweight-concrete strengths (30 MPa and 50 MPa), and aspect ratios ranging from 1.5 to 3.5. The results demonstrated a clear progression of governing failure modes, from web shear buckling at low aspect ratios to combined shear–flexure interaction at intermediate spans and flexural-dominated failure at larger spans. Normalised shear and bending demand–capacity ratios (V/Vu and M/Mu) were used to identify the dominant limit state, revealing a predictable transition from shear-controlled to flexure-controlled behaviour. The findings enhance the understanding of composite thin-walled steel–concrete systems under combined actions and highlight the need for dedicated design rules for CF-HFCFS beams operating within the bending–shear interaction domain. Full article

Conventional buckling-restrained braces (BRBs) with rectangular steel tube confinement suffer from stress concentration and inefficient material utilization, limiting their seismic performance. To address these limitations, this study proposes a novel non-rectangular concrete-filled steel tube BRB system incorporating elliptical and corrugated cross-sections. Comprehensive finite element simulations using ABAQUS are conducted to systematically investigate the influence of key geometric parameters—wall thickness (1–14 mm), corner radius (40–55 mm), and corrugation angle (30–75°)—on hysteretic behavior, load-bearing capacity, and failure modes. The results demonstrate that optimized non-rectangular sections achieve load-bearing capacity comparable to conventional rectangular designs (e.g., elliptical section with 12 mm wall thickness reaches 10.02 MN, a 75% increase over 1 mm thickness) while significantly improving material efficiency. Corrugated sections exhibit enhanced weak-axis performance, with equivalent viscous damping ratios exceeding the NIST-recommended threshold of 0.25. Parametric analyses reveal that wall thickness above 12 mm yields diminishing returns; corner radius reduction to 40 mm triggers local buckling yet increases peak capacity; and corrugation angles exceeding 50° induce instability. All non-buckling models satisfy AISC compression strength adjustment factor requirements (β ≤ 1.3). This study systematically evaluates non-rectangular BRB geometries, filling a critical gap in the literature and providing design guidelines that leverage shape optimization to enhance both seismic resilience and material economy. Full article

To further improve the seismic behavior of high-strength foam concrete filled cold-formed checkered steel composite wall structures, it is crucial to investigate the bond–slip behavior between the cold-formed checkered steel (CFCS) and foam concrete (FC) within the wall. Hence, six CFCSFC specimens were designed and subjected to monotonic and cyclic loading tests to study the influence of anchorage lengths on failure modes, bond strength-slip displacement curves, and characteristic bond strength. Results indicated that with the anchorage length increases, the ultimate bond strength of the specimens continuously decreases, and the specimens exhibit more severe failure under cyclic loading than monotonic loading. Compared to the specimens with a 400 mm anchorage length, the ultimate bond strength decreased by 4.8–9.6% for those with a 500 mm length, and by 10.7–16.0% for those with a 600 mm length. Strain along the inner flange of the steel section generally decreased with increasing anchorage length, with loading end strain significantly exceeding free-end strain. Finite element simulations revealed that specimen failure primarily manifested as steel section yielding when anchorage lengths ranged from 1400 mm to 1800 mm. Furthermore, a calculation formula for characteristic bond strength as a function of anchorage length was proposed. Full article

Special-shaped concrete-filled steel tube (CFST) columns are increasingly adopted as efficient vertical load-carrying members in integrated residential structural systems. However, their intrinsically nonuniform confinement promotes early local buckling and bulging of tube plates and limits deformation stability under axial compression. This study presents an experimental assessment of an L-shaped CFST column enhanced by a fully bolted threaded-rod transverse tie (RT) system, which is intended to strengthen confinement delivery and delay tube instability. Two 1500 mm-high specimens with identical cross-sectional dimensions (400 mm × 200 mm legs; 6 mm wall thickness) were fabricated using Q235 steel and C30 concrete: one conventional baseline (L1) and one RT-improved column (L2) with pre-drilled bolt holes at 150 mm spacing and installed threaded rods (10 mm nominal diameter) to provide a distributed transverse restraint. Monotonic axial compression tests were conducted under staged load control while recording the axial shortening, mid-height lateral deflection, and longitudinal and transverse steel strains. The RT detailing postponed the onset of visible local buckling, tightened the lateral deflection envelope, and increased the measured peak axial resistance from 4354 kN (L1) to 5354 kN (L2), corresponding to an increase of approximately 23%. The combined deformation and strain evidence indicates that the RT system improves the confinement effectiveness by stabilizing the tube dilation and promoting a more controlled instability evolution. Overall, the fully bolted RT approach offers a practical and fabrication-compatible pathway for enhancing the axial strength and deformation performance of L-shaped CFST columns. Full article

This paper proposes a novel mortise-and-tenon grouted masonry (MTGM) structure to enhance the mechanical performance and engineering applicability of masonry. The axial and eccentric compressive behavior of the system was systematically investigated through experimental testing and numerical simulation. A refined three-dimensional finite element model, developed in DIANA, effectively accounted for material nonlinearity and interfacial contact, with its high accuracy confirmed by experimental results. The parametric analysis of 52 numerical models elucidated the influence of block strength, core material type, wall thickness, steel fiber content, and geometric ratios on the compressive strength, deformation capacity, and failure modes. The results demonstrate that using steel fiber-reinforced concrete (SFRC) as the core filling material significantly enhances ductility and toughness; an SFRC content of 1.6% increased the ultimate strain by approximately 37%. Furthermore, increasing the eccentricity from 0.1 to 0.3 led to an average 40% reduction in load-bearing capacity. Theoretical analysis led to the derivation of calculation formulae relating to key axial compression parameters. Furthermore, a stress–strain constitutive relationship suitable for MTGM was established, featuring a parabolic ascending branch and a linear descending branch (R² = 0.992). For eccentric compression, a practical design method was developed based on the plane section assumption, which demonstrated superior predictive accuracy compared to existing code provisions. This study provides a reliable theoretical foundation and practical computational tools for the structural design and application of MTGM. Full article

To improve the seismic performance of buildings and reduce earthquake-related disaster risks, this study employs the MIDAS finite element analysis platform to establish a numerical model of a 15-story concrete-filled steel tube frame-shear wall structure. Recorded natural ground motion data are used as the primary input, and a main shock-aftershock sequence is constructed using an attenuation-based method. On this basis, a seismic fragility analysis framework is adopted to derive structural fragility curves, which are subsequently assembled into a comprehensive seismic fragility matrix. The results indicate that, under identical main shock-aftershock sequences, aftershock effects increase the collapse probability of the unretrofitted structure by approximately 17–37%. Furthermore, when buckling-restrained braces are introduced, the structural strength at the same damage state increases by about 8% under the action of the main shock alone and by nearly 24% when both the main shock and aftershocks are considered. Full article

Research on the configuration and mechanical performance of arch-column-tie beam joints, which combine features of arch-tie beam joints and tubular joints, remains limited, particularly for long-span structures subjected to heavy loads at high building stories. This study focuses on a joint in an engineering structure comprising a circular arch beam, a square-section inclined column, and a tie beam, where both the arch and the inclined column are concrete-filled steel tube (CFST) members. A novel joint configuration was proposed, then a refined finite element model was established. The joint’s mechanical mechanism and failure mode under axial compression in the arch beam were investigated, considering two conditions: the presence of prestressed high-strength rods and the failure of the rods. Subsequently, a parametric study was conducted to investigate the influence of variations in the web thickness of the tie beam, the steel tube wall thickness of the arched beam, the steel tube wall thickness of the supporting inclined column, and the strength grades of steel and concrete on the bearing capacity behavior and failure modes. Numerical simulation results indicate that the joint remains elastic under the design load for both conditions, meeting the design requirements. The joint reaches its ultimate capacity when extensive yielding occurs in the tie beam along the junction region with the circular arch beam, as well as in the steel tube of the arch beam. At this stage, the steel plates and concrete within the joint zone remain elastic, ensuring reliable load transfer. The maximum computed load of the model with prestressed rods was 2.28 times the design load. The absence of prestressed rods could lead to a significant increase in the high-stress area within the web of the tie beam, decreasing the joint’s stiffness by 12.4% at yielding, but have a limited effect on its maximum bearing capacity. Gradually increasing the wall thickness of the arch beam’s steel tube shifts the failure mode from arch-beam-dominated yielding to tie-beam-dominated yielding along the junction region. Increasing the steel strength grade is more efficient in enhancing the bearing capacity than increasing the concrete strength grade. Finally, a design methodology for the joint zone was established based on three aspects: local stress transfer at the bottom of the arch beam, force equilibrium between the arch beam and the tie beam, and the biaxial compression state of the concrete in the joint zone. Furthermore, the construction process and mechanical analysis methods for various construction stages were proposed. Full article