Concrete Core Research Articles

Force Transfer Mechanism and Behavior Insights for a Large-Diameter CFST Column to Steel Beam Connection

Concrete-filled steel tube (CFST) columns with internal ring-plate-reinforced connections are increasingly used in high-rise buildings. However, the behavior and optimal design of such large-scale connections is not well established. This study presents a numerical investigation of the structural performance of a ring-plate-reinforced CFST column to steel beam connection. The paper begins by reviewing a previous experimental study. Subsequently, nonlinear finite element models were developed and validated using the test results. Parametric analyses were conducted to evaluate the effects of the ring plate dimensions, friction coefficient, and concrete defects on the load transfer mechanism. The results showed that the ring plate and friction force together effectively transferred the beam load to the concrete core. An optimal ring plate width of 75 mm was identified. Concrete defects significantly reduced the load carrying capacity of the ring plate. The stress distribution in the concrete cross section transitioned from nonuniform to uniform over a length approximately equal to the column diameter. The connection design was found adequate for the prototype structure analyzed. The study provides valuable guidance for improving ring-plate-reinforced connection design in future construction.

Theoretical model for spontaneous combustion gangue coarse aggregate concrete filled steel tube stub columns

Spontaneous combustion gangue coarse aggregate concrete filled steel tube (SCGCA-CFST) provides a possibility for the structural application of spontaneous combustion gangue coarse aggregate (SCGCA) concrete. To establish an accurate stress-strain model for SCGCA-CFST, 12 SCGCA-CFST specimens and 18 SCGCA concrete specimens were tested under monotonic axial compression with steel tube thickness and SCGCA replacement ratio (0%, 50%, 100%) as variables. The experimental results demonstrated that as the SCGCA replacement ratio increased, the elastic modulus of SCGCA concrete decreased by 6.65%–11.65%, the cylinder compressive strength decreased by 11%–21.95%, and the axial strain at peak axial stress increased by 7.1%–14.27%. Furthermore, the crack extension forms and dilation properties of the core concrete in SCGCA-CFST differed significantly from those of normal coarse aggregate concrete filled steel tube (NCA-CFST). The incorporation of SCGCA reduces the effectiveness of steel tube confinement, which causes the existing stress-strain models of NCA-CFST overestimate the enhancement effect of steel tube confinement on the strength and deformability of core SCGCA concrete. Based on this, the analysis-oriented stress-strain model for NCA-CFST was modified to be applicable for SCGCA-CFST by incorporating the influence of aggregate characteristics, and the accuracy of that was verified.

Development of an axial constitutive model for alkali-activated slag recycled concrete–filled circular steel tube columns

Alkali-activated slag recycled concrete (ASRC) effectively utilises slag and construction waste; nevertheless, its poor mechanical properties limit its popularization and application in construction engineering. Therefore, the ASRC–filled circular steel tube column structure (ASRC–FCSTC) is innovatively proposed, and its mechanical properties and constitutive model are studied. The influence of steel ratio and coarse aggregate type, the failure mode, bearing capacity, deformation capacity, and constitutive relationship of core concrete were investigated. The research results show that the failure of ASRC-FCSTC was caused by the shear failure of the core alkali-activated slag recycled concrete, resulting in the overall component failure. In addition, the steel ratio increasing can increase the bearing capacity of ASRC–FCSTC by 47.6-125.4%, and increase the ductility coefficient by 41.6-76.6%. Using recycled coarse aggregate can reduce the bearing capacity of ASRC–FCSTC by 3.3-22.2%. Moreover, the axial compression constitutive model of ASRC–FCSTC core concrete is established considering the effect of steel ratio. Last, the finite element model is established and verified, and the parameter extension analysis is carried out.

Dynamic response and design evaluation of circular CFT columns with ring-shaped voids under transverse impact

Presently, the research on the impact performance of the concrete-filled steel tubular (CFT) members has never considered the problem of void defect. Hence, this paper fosters a refined finite element (FE) model of the circular CFT column with ring-shaped voids under transverse impact, which considers the initial contact status of concrete. After validating the accuracy of FE models, the effects of void ratio, steel ratio, impact speed and mass of the drop hammer on the dynamic behaviour of the circular CFT column with ring-shaped voids are explored. Detailed impacting mechanisms of the defect column are acknowledged by elaborating its dynamic time history curves, failure morphology, impact force diffusion path, contact process, and stress/strain distribution rule. Calculation methods for evaluating the impact resistance of the circular CFT column with ring-shaped voids are proposed. The results declare that the appearance of ring-shaped voids would significantly weaken the impact resistance of the CFT column. The impact force and energy dissipation are greatly decreased with the increase in void ratio. Under the transverse impact, the steel tube would be seriously depressed due to the absence of effective support acted by concrete with ring-shaped void, and the core concrete would be heavily damaged in return.

Axial compressive behavior of high-strength concrete-filled steel tube with multiple confinement effects

To study the axial compressive behavior and the confinement mechanism of high-strength concrete-filled circular steel tube with multiple confinement effects, five large size samples with horizontal stiffeners, longitudinal stiffeners, multilayer reinforcement cages, inner steel tube and separation steel plates were designed. The influences of these structures on the bearing capacity, ductility, stiffness, and residual deformation were then analyzed. Combining the strain analyses and finite element model analysis, the confinement mechanism of different structures and the coupling mechanism of different confinement effects were investigated. The results showed that the confinement effect of the horizontal stiffeners was similar to that of the stirrups. The longitudinal stiffeners did not provide a significant confinement effect on the concrete. The multilayer reinforcement cages had an effective confinement effect on the concrete, where the confinement effect increased from the outside to the inside, while the reinforcement cages had a slight influence on the concrete outside the reinforcement cages. The inner steel tube had an effective confinement effect on the core concrete and had a slight influence on the concrete outside the inner steel tube. The multicell steel tube showed the best confinement effect compared to the other structures and showed the best axial compressive behavior. In the confinement mechanism analyses, the calculation method of the stress–strain relationship of concrete with multiple confinement effects was proposed. The calculated F-Δ curves showed a good agreement with the test results.

Cyclic tests and finite element analysis on hybrid fiber–cement-based composite encased CFST columns

Six hybrid steel–polyvinyl alcohol (PVA) hybrid fiber–cement (HFC)-based composite encased concrete-filled steel tube (CFST) columns were tested for their seismic performance. The impacts of core concrete strength, steel tube thickness, and axial ratio on the seismic performance of the specimens were studied. According to the experimental findings, strengthening the core concrete can enhance the column's lateral bearing capacity and energy dissipation capabilities while also slowing the rate at which the steel tube's strain increases after yielding. Furthermore, HFC-encased CFST columns with a lower axial ratio and a thicker steel tube demonstrated superior seismic performance. An's equation of computation could better forecast the lateral bearing capacity of HFC-encased CFST columns when compared to other calculation methods. Finally, an experimentally validated finite element model of HFC-encased CFST columns was developed. Numerical studies showed that the seismic performance of composite columns can be significantly improved by increasing the strength of the HFC and the volume concentration of the steel fiber, and that PVA primarily acts in the plastic stage.

Sectional strength design of a double-skin truss-reinforced composite shear wall

The double-skin truss-reinforced composite shear wall is an innovative element which comprises two steel plates, core concrete, concrete-filled steel tubes (CFSTs), which act as boundary members, and steel truss connectors. Truss connectors decrease the out-of-plane deformation that affects the steel plates, and due to the resultant connection and constraint effects, the truss connectors enhance the bearing capacity of the wall. This paper briefly introduces the quasi-static test of five full-scale rectangular double-skin truss-reinforced composite shear wall specimens. The specimen exhibited shear compression failure with an aspect ratio of 2.0, and flexure shear failure occurred when the aspect ratio exceeded 2.0. Based on the analysis of actual stress state of the steel web and actual working performance of the infilled concrete, the shear strength and flexure strength design formulas of double-skin truss-reinforced composite shear wall were established. Comparison results with 26 specimens demonstrate that the design formulas exhibit remarkable accuracy, as most errors are within 20 % and 25 %, respectively. Which provide a preliminary sectional strength design proposal for the double-skin truss-reinforced composite shear wall.

Structural behavior of steel-concrete-steel sandwich slender and deep beams considering different connectors

Steel-concrete-steel (SCS) sandwich deep beams, with a shear span ratio of less than 2.0, are commonly employed in high-rise buildings and bridges. However, their failure mechanism differs from that of SCS sandwich slender beams, which have a shear span ratio greater than 2.0. This study systematically investigates the failure mechanisms of SCS sandwich deep beams and compares them with those of SCS sandwich slender beams. To improve their structural performance, ultra-high performance concrete (UHPC) was utilized as the core material to form S-UHPC-S sandwich deep beams, with shear studs serving as the sole shear connectors. The influence of these shear connectors was explored in comparison to cross ties. Three S-UHPC-S sandwich deep beams were subjected to static loading, and their performance was compared with ten existing SCS sandwich deep and slender beams. The analysis focused on failure modes, mechanical behaviors, and contributions of each component, including the steel plate (SP), core concrete (CC), and shear connectors. The results revealed distinctions in force transferring models, load-displacement curves, and the contributions of cross ties in deep beams compared to slender beams. Additionally, finite element (FE) analyses were employed to examine the force transferring mechanism of shear connectors. Based on both experimental and FE simulation analyses, theoretical models for predicting the ultimate capacity of S-UHPC-S sandwich deep beams and slender beams were proposed, accounting for different shear connectors. These models offer valuable insights for practical structural design and application.

Experimental research on the flexural behavior of GFRP bar-reinforced composite beams with different shapes of prefabricated UHPC formwork

In this paper, the flexural behavior of eight composite beam with prefabricated permanent ultrahigh-performance concrete (UHPC) formwork and reinforced with glass fiber reinforced polymer (GFRP) bars were investigated based on four-point bending test and calculation. The types of prefabricated permanent UHPC formwork, bottom formwork thickness, and interface treatment methods were studied as experimental variables. It was found that the cracking load of beams with prefabricated permanent UHPC formwork increased by 77.4%–130.8 % compared with that of the reference beam. However, the ultimate bearing capacities of these composite beams, except for those of the beam with two-sided UHPC formwork and that with bottom UHPC formwork with a thickness of 50 mm (no debonding and an increase of 19.0 %), decreased by a maximum of 36.7 % due to the partial debonding between the prefabricated permanent UHPC formwork and core concrete. The overall performance of the composite beam improved as the bottom formwork thickness increased and the interface treatment existed. Based on the test results, a simplified calculation method was developed to predict the cracking moment of composite beams with UHPC formwork. The cracking moment obtained by the proposed calculation method matches the experimental results.

A Simplified Limit-State Design and Verification for Prestressed Concrete Cylinder Pipes under Internal Water Pressure

Ignoring the effect of a concrete core on bearing performance, the current design of prestressed concrete cylinder pipes (PCCPs) under internal water pressure only focuses on the fracture of prestressed steel wire, while the complexity of the AWWA C304 design method leads to a strong dependence on software that cannot be sufficiently mastered by the designers. In view of these issues, a simplified limit-state design process was induced to eliminate a large number of iterative operations and was verified by a three-dimensional finite element model (FEM) with a prototype test of PCCPs under internal water pressure. Meanwhile, the bearing performance of PCCPs was investigated using the parametric simulations of the FEM. The results showed that the cross-sectional area of the prestressed steel wire is higher by about 10% than that designed using the AWWA C304 method. The FEM provides a complete evolution process of the mechanical response of the structural constituents and simulates the strain mutation phenomenon of the prototype test well. The internal water pressure of the PCCPs designed using the simplified limit-state design process has enough safety to reach 4.7 times the working pressure at serviceability and 5.5 times the pressure at the ultimate limit state. A burst in the PCCPs took place under an internal pressure greater than 6.75 times the working pressure. The result of the FEM shows that an increase in the tensile strength of the concrete core is of great significance for improving the bearing performance of the PCCPs.

A unified formulation for axial compression of steel tube-confined concrete and concrete-filled steel tube stub columns

Steel-confined concrete (STCC) columns and concrete-filled steel tube (CFST) columns have different load boundary conditions. In STCC columns, the steel tube transmits minimal axial load. Existing design practices employ different formulas to predict the axial load-bearing capacity of STCCs and CFSTs based on these varying load boundary conditions. However, there has always been a practical and challenging demand for researchers and engineers to develop a unified design formula that accommodates composite columns with different sections and load boundary conditions. This demand aligns with the contemporary design concept of continuous structural design optimization. This paper proposes an analytical solution for the elastic deformation of circular STCCs under axial compression, considering the specific load boundary conditions in circular STCC columns. This solution is then extended to encompass polygonal sections, resulting in a unified formula for determining the strength of STCC columns. Additionally, the influence of load boundary conditions on the confined effect of the core concrete is quantified by reformulating and simplifying the proposed formula. These adjustments are informed by the formulation for the axial load capacity of CFST columns proposed by Yu Min et al. Finally, a simple and convenient unified formulation for calculating the axial compressive strength of both STCC columns and CFST columns is proposed for practical engineering applications.

Finite Element Analysis and Calculation Method of Concrete-Filled Stainless Steel Tubes under Eccentric Tension

Concrete-filled stainless steel tubes (CFSST) could be used as structural members in corrosion-prone environments. A detailed numerical investigation of the mechanical performance and calculation method of CFSST members under eccentric tension is carried out in this paper. A finite element analysis (FEA) model that adopts three-dimensional elements is established, and related experimental results of CFSST and conventional concrete-filled carbon steel tubes (CFST) subjected to tension are used to validate the FEA model. Then, the calibrated FEA model is used to investigate the performance of CFSST eccentrically tensile members, especially the composite actions and stress distribution laws between the stainless steel tube and the concrete core, which play a key role in the load-carrying capacity of the composite member. To quantitatively determine the influence of different parameters on the load-carrying capacity of CFSST tensile members, a wide-range parametric analysis is performed. Finally, a calculation model is proposed to be used to predict the ultimate tensile strength of CFSST members subjected to eccentric tension, and the model-predicted values show good agreement with the FEA-computed results.

Axial compression behavior of square CFST short column with triangular-corner gap

In order to investigate the impact of the triangular-corner gap between the outer steel tube and the core concrete on the axial compression behavior of square concrete-filled steel tubular (SCFST) columns, this study conducted axial compression tests on 117 SCFST columns and three reference hollow steel tubes. The main test parameters included steel tube thickness, concrete strength, side length of the triangular gap, and axial gap depth. The test results revealed four typical damage modes in the SCFST columns with triangular-corner gaps. The presence of the gap defect had a significant effect on the ultimate bearing capacity of the SCFST columns, causing a decrease in the range of 1.66 %–17.72 % when the gap ratio ranged from 0.45 % to 12.50 %. Moreover, the influence of the gap ratio on the ductility and initial stiffness of the SCFST with triangular-corner gaps was dependent on the concrete strength and the steel tube thickness. Finally, a simplified formula for calculating the ultimate bearing capacity of SCFST columns with triangular-corner gaps was proposed based on the test data and force analysis. The maximum error between the theoretically calculated value and the test value is within 15 %.

Field and Laboratory Investigation of a 60-Year-Old Precast Prestressed Concrete Building in Japan

In Japan, the application of the prestressed concrete (PC) system has become quite popular, especially in bridge and building constructions. Since it was first introduced in the early 1950s, the number of buildings using the PC system has substantially increased. However, following a certain period in the service life of the PC system, the serviceability of such structures especially following an earthquake has become a primary concern, especially when exposed to severe corrosion-prone environments. In this research, the City Hall building of Nandan Town, Awaji Island in Japan, was chosen to investigate the influence of corrosion on the durability of the building structure, which was initially constructed in1957 as the first building that used PC members for beams. This paper describes the building and results of the field crack inspection and corrosion test results on concrete core samples from the building. Accordingly,the study found that the building had material deteriorations due to its corrosive surrounding environment and severe damage on the concrete cover of the PC anchorage.

Static strength design of local thickened plate joints between multi-cell concrete-filled steel tubular column and steel beam

A new-type local thickened plate joint (LTPJ) between multi-cell concrete-filled steel tubular columns (CSTC) and steel beams is adopted in residential building structures. However, no available strength design method for such beam-column joints is reported. This paper presents the mechanical behavior and static strength design of such joints. The local thickened plates are adopted to replace the normal thickness plates of the CSTCs within the LTPJ region. The rectangular section and L-shaped section of the multi-cell CSTC are involved in the joint study, respectively. Firstly, a finite element model (FEM) of the LTPJ between CSTCs and steel beams is established, which is then adopted to investigate the mechanical behaviour and static load-bearing capacity of the LTPJ. Codirectional and inverse bending moments are applied on the beams on two opposite sides of the LTPJ to simulate lateral loads (arise from wind or earthquake) and dead gravity loads, respectively. It is revealed that the LTPJ experiences shear failure when subjected to lateral loads, whereas it succumbs to bending failure when under dead gravity loads. The shear-bearing capacity of the LTPJ results from the three-part contribution of the steel tube web, the steel tube flange, and the core concrete. The bending-bearing capacity of the LTPJ is determined by the plate normal tension-bearing capacity of the steel tubes, which is predicted by adopting the theory of yielding line and numerical fitting. Finally, the load-bearing capacities of LTPJ under bidirectional bending moment are investigated numerically, and accordingly, some strength design recommendations are proposed in practical application. To conclude, these results provide a method for accurately predicting the load-bearing capacity of the LTPJ subjected to lateral loads and gravity loads, which holds the potential to expand and enhance the application of LTPJs and CSTCs in the design of high-rise residential buildings.

Calculation of ultimate bearing capacity of concrete-filled double steel tubular under compression based on the unified strength theory

Concrete-Filled Steel Tube (CFST) components are widely used in the engineering field due to their superior performance. However, the actual stress state of CFST components under axial compression is complex. As a result, calculations for CFST components are often simplified using material equivalent assumption formulas and empirical equations to determine their load-bearing capacity. These simplifications require the introduction of many coefficients and mechanical performance indicators, and the actual material principal stresses are not adequately considered. This approach weakens the completeness of the theory and adds to the burden of experimental research.The aim of this work is to develop a load-bearing capacity calculation formula for Concrete-Filled Double Steel Tubular (CFDST) components that considers the different stress states of the inner and outer steel tubes, the core concrete, and their interface interactions. This formula is designed to be convenient for engineers to understand and use. By comparing the results of this formula with experimental data collected from domestic and international scholars, it is evident that the results of this formula closely align with the collected experimental data. This validation confirms the accuracy and effectiveness of the formula developed in this paper. Furthermore, when compared with existing axial compression load formulas for CFDST, the formula presented in this paper demonstrates good accuracy. The research results provide a convenient and accurate calculation formula for the axial compression load-bearing capacity of CFDST components, bridging the gap between theoretical derivation and practical application.

The effect of near-fault earthquakes and wavelet-generated artificial near-fault earthquakes on the seismic behavior of rockfill dams

Strong earth vibrations may destroy high asphalt concrete core rockfill dams (ACCRDs) and cause unanticipated economic and social losses. Due to favorable geographical, geological, and environmental characteristics, ACCRDs are always near ruptured fault zones. Compared to far-field and non-pulse earthquakes, near-fault (NF) earthquakes with pulse effect may put high dams under stress. However, seismic design and dynamic assessments of high ACCRDs under pulse-type earthquake stimulation are less popular than NF earthquake recordings. The fundamental explanation is that most earthquake data pertain to non-pulse-type seismic occurrences, whereas pulse-type earthquakes have more sophisticated seismology. This work uses the finite element approach to illustrate the seismic behavior of the ACCRD under pulse-type NF, non-pulse-type NF, and far-fault (FF) earthquake excitations. The pulse-type artificial NF earthquakes are generated using wavelet multi-scale decomposition incorporation (WMSDI), a simplified wavelet theory-based approach. Next, the WMSDI approach of artificial NF earthquake synthesis is tested and compared to earthquake data and structure responses. Forward-directivity pulse-type and fling-step pulse-type earthquakes may induce higher horizontal accelerations and stresses of the high ACCRD than FF earthquakes. FS and FD earthquake excitations with high PGV/PGA ratios cause severe residual deformation and relative settlement ratio to the high ACCRD. The dynamic response of the high ACCRD under pulse-type artificial NF earthquakes also depends on the pulse parameters of the artificial equivalent pulse mathematical models. Thus, pulse-type NF earthquake seismology should be included in rockfill dam seismic design assessments.

Mechanical behavior of PCCPs with broken wires under complex service conditions

Buried prestressed concrete cylinder pipes (PCCPs) are subjected to the combined effects of soil cover loads, internal water pressure, and additional loads. However, there is scarce research on their mechanical performance under complex service conditions after being buried. In this study, 3D nonlinear finite element (FE) models of PCCPs and soils, along with fluid models, were developed using ABAQUS and FLUENT, respectively. Fluid–solid coupling numerical simulations of PCCPs with broken wires under complex service conditions were conducted using the MpCCI platform. The study focused on investigating the mechanical behaviors of PCCP pipes with broken wires, aiming to determine the effects of different numbers and locations of broken wires, as well as the magnitude of operating water pressure. The results shows that the number of broken wires is a crucial factor affecting the mechanical behaviors of the PCCPs; the dynamic variation of internal pressure within the pipe can cause further damage to PCCPs with pre-existing defects; when wire breakage occurs alone the springline of the PCCPs, the outer concrete core exhibited a tendency to crack before the inner concrete core. Conversely, when wire breaks occurred at the crown and invert, the inner concrete core cracked before the outer concrete core. These results provide valuable insights into the behavior of PCCPs under complex conditions and contribute to the understanding of their structural integrity. The findings can aid in the development of improved design and maintenance strategies for PCCPs, ensuring their reliable performance in underground applications.

Axial Compression Performance Test and Bearing Capacity Calculation of RC Square Column Strengthened by FRP Textile Grid-reinforced ECC

In order to investigate the strengthening effect of FRP textile grid reinforced ECC composite (abbreviated: TRE) restrained RC columns, this study conducted experimental and theoretical studies on the axial compression performance of TRE strengthened RC square columns with RC square columns as the research object. The effects of the chamfer radius of the original column, the type of FRP grid and the number of layers of the grid on the axial compression performance of the TRE-strengthened RC square column were considered. The axial compression tests showed that the strengthened layer exhibited excellent crack control, the reinforced column cracked as a whole without breaking when it was damaged, and the strengthened layer adhered well to the core concrete. Compared with unstrengthened specimens, the compressive strength, ductility and deformation capacity of the RC square column under TRE restraint were significantly higher. The increase of chamfer radius of square column makes the TRE restraint effect better. Increasing the number of grid layers can significantly improve the ultimate bearing capacity and ductility of the strengthened specimens. The effects of TRE strengthening methods with different FRP grids differed, with the same number of grid layers, the ultimate bearing capacity of the specimens strengthened with CFRP grid reinforced ECC was higher, and the cracking load of the specimens strengthened with BFRP grid reinforced ECC was higher. A model for calculating the ultimate bearing capacity of the TRE-constrained RC square column was established, and the validity of the model was verified by comparing the results of this test.

Research on application of annular concrete-filled steel tube support in deep roadway

In this paper, through on-site investigation and monitoring, the characteristics of roadway deformation and the causes of deformation and damage are analyzed. Among them, the unreasonable support system is an external factor, and the nature of rock mass, deterioration degree of surrounding rock, and high ground stress are internal factors. A simulation method of CFST considering initial defects in core concrete is proposed and utilized to analyze the mechanical properties of CFST supports. Building upon numerical simulation results, we introduce an optimized support scheme comprising annular CFST support, segmental fissure surrounding rock grouting, and bolts. Field comparison tests demonstrate that the application of the new repair technology yields remarkable enhancements in the bearing capacity of surrounding rock and supporting structures while ensuring a more uniform stress distribution within the rock mass.