Flexible Bearing Research Articles

Experimental and modelling investigation on chloride transport and flexural behaviour of RC beams subjected to simultaneous deteriorating factors of carbonation, FT cycles and multi-type sustained stress

Reinforced concrete (RC) structures are often exposed to coinstantaneous deterioration effects such as carbonation, chloride corrosion, freeze–thaw cycles and external loads which causing deterioration of concrete and reinforcement. This paper discussed the effects of carbonation, freeze–thaw cycles and sustained loads on chloride ion transport and proposed a chloride ion transport model taking porosity as the main coupling variate. The attenuation law of the corroded beams under coupling corrosion factors was studied. Through chloride immersion tests, it was found that applying freezing and thawing cycles and sustained tensile stress can enhance chloride transport capacity by coarsening the pores; Carbonation and low compressive stress can repress the chloride ion transport by densifying concrete, but the compressive stress beyond about 0.7 times the compressive strength and tensile stress would enhance the penetrating capacity due to the damage of the internal microstructure of concrete. Then, a comprehensive and unified theoretical model of chloride ion transport considering the coupling of carbonation, freeze–thaw cycle, sustained loading and other factors was proposed and verified by taking porosity as the main coupling variable quantity. This model could essentially explain the effects of various factors on chloride ion transport and has good consistency with the test results. Finally, the flexural bearing capacity of the corroded beams was tested, and the failure characteristics, crack characteristics, ultimate bearing capacity, load–displacement relationship and strain distribution of the corroded beams under different corrosion conditions were researched. The results show that the flexural capacity of the corroded beams suffered the coupling effects of multiple corrosion factors degrades, and the bearing capacity decreases with the increase of the corrosion degree of carbonation-freezing thawing cycles; The continuous tensile stress applied to the test beams in the corrosion process intensifying the degradation of bending bearing capacity and ductility, the continuous compressive stress increases the flexural capacity and improves the ductility slightly, but excessive compressive stress significantly degrades the flexural capacity; When chloride ions are used as the third kind of corrosive substance for coupling corrosion, the tensioned or without-load corroded beams have obvious degradation in bending bearing capacity, while the corrosion beams bearing continuous compressive stress have no obvious degradation in bending bearing capacity.

Flexural Behavior of Precast UHPC Segmental Beams with Unbonded Tendons and Epoxy Resin Joints

Precast concrete segmental bridges (PCSBs) with hybrid tendons may be the most competitive solution for achieving the advantages of rapid construction and favorable structural performance. Therefore, the flexural behavior of precast concrete segmental bridges (PCSBs) with unbonded tendons and epoxy joints was experimentally investigated in this study, and the effects of the joint types were recorded. Investigations were carried out on the ultimate loads, prestressed strand stresses, deflections, as well as failure modes, while an unbonded monolithic beam was tested for comparison. In addition, the strain measurement proved that the average strains agree with the assumption of plane section, regardless of whether the joints were set. The flexural strengths of prefabricated components were 9~15% lower than those of the monolithic beams with unbonded tendons. Meanwhile, the shape of the joints also influenced the flexural bearing capacity; the bearing capacity of the dual-tooth joint beam was 4.5% lower than that of the single-tooth one, and the bearing capacity of the flat butt joint member was 5.7% lower than that of the dual-tooth joint beam. Moreover, the experimental deflection curve and ultimate bearing capacity of the models with different shear keys showed a good correlation with the FE results. These research outcomes will aid in comprehending the roles of joints in the flexural behaviors of precast UHPC segmental bridges.

Mechanical properties of energy sustainable round bamboo - Phosphogypsum composite floor slabs

Round bamboo is a natural building material with excellent mechanical properties and has broad application prospects in green buildings. To realize the protection of round bamboo and promote the resource utilization of phosphogypsum, a kind of round bamboo-phosphogypsum composite (BPC) floor slab is proposed in this paper. To study the flexural performance of the round bamboo-phosphogypsum composite floor slabs, considering the factors of the thickness of the phosphogypsum, the number of dovetail nails, the number of round bamboo poles and the span, the flexural tests of 11 floor slabs were carried out, the influence of the factors on the flexural performance of the floor slabs was analyzed, and the calculation methods of the flexural stiffness and bearing capacity of the floor slabs were established. The results show that the bearing capacity, ductility coefficient and flexural stiffness of the control specimen are increased by 31.26%, 51.19% and 3.39 times compared with the bamboo skeleton. The ductility and flexural stiffness of the floor slab decrease with increasing span. The bearing capacity of floor slab increases with the increasing bamboo number and decreasing span. The calculation methods of flexural performance of the floor slabs established in this paper have certain accuracy. The round bamboo-phosphogypsum composite (BPC) floor slab realizes the efficient utilization of resources, which has reference significance for green buildings and sustainable development.

Flexural Behavior of Corroded Concrete Beams Strengthened with Carbon Fiber-Reinforced Polymer.

The present study investigates the flexural behavior of reinforced concrete (RC) beams; the longitudinal reinforcing rebars of the beams were corroded and then strengthened with carbon fiber-reinforced polymer (CFRP). The corrosion of the longitudinal tension reinforcing rebars in eleven beam specimens was accelerated in order to obtain different corrosion levels. Afterwards, the beam specimens were strengthened by bonding one layer of CFRP sheets to the tension side to restore the strength loss due to the corrosion. The failure modes, flexural capacity, and midspan deflection of the specimens with different corrosion levels of the longitudinal tension reinforcing rebars were obtained by the four-point bending test. It was found that the flexural capacity of the beam specimens decreased with the increase in the corrosion level of the longitudinal tension reinforcing rebars and that the relative flexural strength was only 52.5% when the corrosion level was 25.6%. The stiffness of the beam specimens decreased significantly when the corrosion level was higher than 20%. Through a regression analysis of the test results, a model for the flexural bearing capacity of the corroded RC beams strengthened with CFRP was proposed in the study.

Investigation on bond performance of concrete strengthened with CFRP plates

In this paper, concrete specimens with type I prefabricated cracks were prepared, and three-point bending tests were used to investigate the influence of parameters, such as carbon fiber reinforced polymer (CFRP) plate thickness, depth of the prefabricated crack, concrete strength, and loading speed, on the bonding performance of reinforced concrete structures with externally attached CFRP plates. The CCD cameras were used as the observation system, and the digital speckle technology is used to analyze the expansion characteristics of the prefabricated crack. The failure mode and crack development characteristics of the specimen are numerically simulated by finite element software. The results show that the reinforcement with externally attached CFRP plates can increase the flexural stiffness of concrete, significantly improve the flexural bearing capacity of concrete, and delay the development of cracks; under the same load, reinforcement with externally attached CFRP plates can reduce the propagation distance of prefabricated cracks and increase the bending deformation displacement of the specimen. The numerical simulation results show that, with the increase in the pasting length of the CFRP plate, the bearing capacity of the specimen gradually increases, the deformation capacity of the specimen gradually increases, and the failure crack moves from the middle to both sides.

Analysis of Strengthening RC Beams Using Stainless Steel Continuous Reinforcement Embedded at Ends Using ANSYS

Abstract: An innovative system for the flexural strengthening of RC structures designated continuous reinforcement embedded at ends (CREatE) is presented in this research work. The main charateristics and procedures for the application of this new strengthening techniques were described. To evaluate the performance and efficiency of this technique, a set of RC T-beams was subjected to a four pointed bending test setup. Different application arrangements and different amount of reinforcement were considered, and the CREatE technique was tested under monotonic and cyclic loading histories. The tests were modeled using the nonlinear finite element method (FEM) to predict the performance of the RC T beam, which allowed analysing, in detail and with good agreement with the experiments, the influence of the CREatE technique on the (1) strains developed in the concrete, (2) cracking patterns, and (3) strains developed in the stirrups. Apart from the expected increases in the flexural stiffness and load bearing capacity of the T beam, the result showed that the use of the CREatE technique led to higher ductility indexes in the displacement compared with traditional techniques. Moreover, with the CREatE technique, premature debonding of the reinforcement material from the concrete tensioned surface commonly observed in externally bonded reinforcement (EBR) strengthening system was eliminate.

A flexible bearing plate based on steel plate and rubber mat

The bearing plates used in plate load test for highway engineering are typically rigid. However, due to limitations in obtaining the accurate distribution of compressive stress at the bottom of the bearing plate, there is often a significant deviation between the measured subgrade resilient modulus and the actual condition. To address this issue, a flexible bearing plate can be used to test the subgrade and obtain a more accurate resilient modulus. In this study, we use variance and degree of mean deviation to quantitatively evaluate the distribution uniformity of compressive stress. To create a rigid-flexible bearing plate that is similar to a flexible bearing plate, we explore the combinatorial design of steel plates and rubber mats. We examine factors such as the thickness (10, 20, and 30 mm) of the steel plate, elastic modulus (5, 10, and 20 MPa) and thickness (10, 20, and 30 mm) of the rubber mat, friction coefficient (μ:0, 0,2, 0.4, 0.6, 0.8, ∞) between the bearing plate and subgrade, and the combined shape characteristics of the rubber mat and steel plate. To reduce friction between the rubber mat and subgrade, we use lubricant, and through our design process, we develop a flexible bearing plate with relatively uniform compressive stress. Our computations show that when μ = 0.05, the variance is 0.0001, and the degree of mean deviation is 0.0780. These results indicate that the distribution uniformity of the compressive stress is very close to the uniform distribution load, which meets the necessary accuracy requirements for engineering applications.

Flexural stiffness characterization of the corrugated steel–concrete composite structure for tunnel projects

Corrugated steel–concrete (CSC) composite structures are increasingly used in tunnel and culvert projects due to their good mechanical properties. The design of CSC composite structures is often governed by deflection limits in service, hence it becomes crucial to evaluate accurately their flexural stiffness. In this work, the deflection deformation mechanism of CSC composite structure is studied by experimental and numerical methods, and a simplified formula for calculating the flexural stiffness is established. In addition, the deflection results obtained by different methods are compared and analyzed. It is found that: (1) the flexural stiffness of the CSC composite structure is constant only when the load is small, and after the bending moment exceeds a certain value, the flexural stiffness will gradually become smaller as the bending moment increases. (2) The value of the bending moment corresponding to the end of the elastic stage of the bending moment-deflection curve increases with the increase of the axial force in the composite structure. (3) As the axial force of the composite structure increases, the flexural bearing capacity of the structure increases first and then decreases.

Nonlinear modeling of a misaligned rotor under non-stationary operating conditions

In this study, a novel model is developed to investigate the angular acceleration of the nonlinear misaligned rotor passing through the critical speeds under non-stationary operating conditions. The concerned rotor is modeled elastic with the effects of nonlinear inertia terms and flexible bearing. Nonlinear equations of motion are derived using the Lagrange method and solved with the finite element method. Effects of parameters such as shaft eccentricity, damping, and stiffness of the supports on the increase in the rotor angular speed passing through the critical speed are considered. The obtained results indicate that a small amount of eccentricity prevents exceeding the elastic critical speed of the rotor. According to the results, if the support parameters are not selected properly, the rotor will not even be able to pass its rigid critical speed.

Flexural behavior, failure analysis, and optimization design of a hybrid composite Kagome honeycomb sandwich structure

A carbon fiber-reinforced composite Kagome honeycomb is a new type of structure composed of hexagonal and triangular cells, exhibiting excellent mechanical performance and application potential in the aerospace, automobile, and marine industries. This paper proposes a new hybrid composite Kagome honeycomb sandwich (HCKHS) structure formed using the interlocking method with polymethacrylimide foam sandwich structure as the ribs. The bending characteristics and failure modes were analyzed by conducting three-point bending tests. The experimental results showed excellent flexural bearing and energy absorption capability. Second, analytical models of HCKHS specimens under bending were established. The 1D, 2D, and 3D failure mechanism maps were drawn, and the size effects were analyzed. Based on the principle of minimum specific strength, combined with 3D failure mechanism maps, the optimal design point of the HCKHS structure was obtained through specific strength functions. The proposed method is also applicable to the optimization and design of other 2D composite honeycomb sandwich structures.

Calculation Method for Flexural Bearing Capacity of Composite Girders with CFST Truss Chords

To study the flexural behavior of composite girders with concrete-filled steel tubular (CFST) truss chords under positive and negative bending moments, model tests, and theoretical analysis were carried out to investigate the evolution of their flexural behavior and the flexural bearing capacity. The results showed that the web members and joints of composite girders with CFST truss chords subjected to positive and negative bending moments had high strength and rigidity, which ensured that joint failures did not occur before the failure of the entire cross section. The longitudinal strains along the member axis changed linearly along the cross-sectional height, which confirmed the correctness of the plane-section assumption. The failure mode was due to the yield of the steel tube used in the chord and the rebars in the concrete slab under positive and negative bending moments, respectively. The contributions of the web members to the flexural bearing capacity under positive and negative bending moments were 12.5% and 8.6%, respectively. Calculation methods considering the contributions of the web members to the flexural bearing capacity under positive and negative bending moments were proposed. The deviation between the results of the proposed calculation methods and the test and the results of the finite-element parametric studies was less than 8.1%.

Research on flexural performance of glulam spliced joints connected by self-tapping screws in different arrangements

Tests were conducted to determine the flexural bearing capacities of glulam spliced joints connected by self-tapping screws (STSs) in five different configurations. The flexural performances and failure modes of these joints were analyzed and an extended finite element method was utilized to establish numerical models of the STS-connected glulam spliced joints while considering crack propagation. The simulation results were in excellent agreement with the test. Moreover, theoretical formulas for the flexural bearing capacity and a flexural stiffness model of STS-connected glulam spliced joints were developed. The research findings indicated that the vertical STSs were more effective in enhancing the bending capacity of the joints than the angled STSs in the vertical plane. Specifically, when using full 90° STSs, the bending capacity increased by 35.57% compared to when using full 60° STSs. The elastic rotational stiffness values of the joints were also improved by using a mixed-angle arrangement of STSs. Specifically, when utilizing a mixed arrangement of 90° and 60°, the elastic stiffness values increased by 33.44% and 63.20% compared to when using full 90° and full 60°, respectively. However, while using STSs in the horizontal plane at the vertical gap significantly enhanced the flexural bearing capacities of the spliced joints, it also led to a significant reduction in the ductility of the joints.

Flexural Behavior of Damaged Hollow RC Box Girders Repaired with Prestressed CFRP.

In recent years, numerous studies have explored the benefits of utilizing prestressed carbon fiber-reinforced polymer (CFRP) for strengthening concrete structures. However, research on the reinforcement of prestressed CFRP on full-scale hollow RC box girders, particularly damaged bridges, remains limited. In this study, both experiments and finite element analysis (FEA) were performed to investigate the flexural behavior of full-scale hollow RC box girders with varying degrees of damage, which were strengthened using CFRP with different levels of prestress. The adhesive behavior of the CFRP-concrete interface was considered in the FEA. Numerical simulations were conducted to assess the flexural behaviors of the girders, including failure modes, yield and ultimate loads, and deflections. The results revealed that the application of prestressed CFRP efficiently increased the yield and ultimate loads of the box girders. Specifically, when the degree of damage of the hollow box girder was less than 23%, the flexural bearing capacity of the repaired girder could be recovered after being strengthened with two prestressed CFRP strips measuring 50 mm in width and 3 mm in thickness. However, the risk of premature debonding at the CFRP-concrete interface increased when the prestressing level of CFRP and degree of damage of hollow RC box girders exceeded 35% and 40%, respectively. These findings suggest that the use of prestressed CFRP may be a promising method for repairing damaged hollow RC box girders, but careful consideration of the degree of damage and prestressing level would be necessary to ensure the effectiveness and safety of the repair.

Seismic performance of concrete-filled steel tubular column connections using blind bolts

In this study, a demountable connection that connects the upper and lower concrete-filled steel tubular columns with an inner sleeve section and blind bolts (referred to as Hollo-Bolts in this study) is proposed. The utilization of Hollo-Bolts allows them to be installed outside the steel tubes prior to the concrete casting and renders such connection to be readily dismantled after typical service loading. In order to study the seismic performance of the concrete-filled steel tubular column-column connection, six specimens were designed in the present study. The studied parameters included the axial load ratio, length of the inner sleeve, and location of the connection. The results demonstrated that the proposed connection exhibited good ductility performance, and the disassembly and reassembly of the connection after a service loading had no significant effect on their seismic performance. Additionally, the load-transfer mechanism of the concrete-filled steel tubular column-column connection was explored. Simplified formulae of anti-slip flexural bearing capacity of the connection were proposed, and the predicted values agreed well with the test results on the safe side.

Electric activation curing behaviour of reinforced concrete beam under severely-cold environment: Breakthrough of rapid concrete manufacturing at cold region

Rapid on-site fabrication of concrete structure in severely-cold environment is a tough problem. Electric activation (EA) curing exhibited significant advantage on preparing laboratory-scale cement mortar at negative temperature, however, the feasibility of this curing method on manufacturing full-size concrete structure needs to be investigated. In this work, EA curing was proposed to rapidly manufacture on-site reinforced concrete (RC) beam in practical cold environment. The specific development regularity of the electrical resistance for EA cured RC beam was theoretically predicted and experimentally verified, and the electrical resistance of EA cured beam kept in a stable increasing trend during the whole curing process, regardless the harsh environment. Moreover, the temperature field distribution inside the structure was also clarified, it was found that EA curing could maintain a uniform temperature field distribution of RC beam at around 45 ℃ during the whole EA curing process. Further, mechanical property results revealed that EA curing could rapidly promote the strength formation of RC beam under severely-cold environment with the 2-day compressive strength of 28.4 MPa, reaching C30 concrete strength grade. In addition, this work firstly revealed the structural performance of EA manufactured RC beam, which exhibited higher ultimate flexural bearing capacity (233 kN) comparing with standard curing manufactured beam of 215 kN. This work gives a thorough investigation over the performance development of RC beam subjected to EA curing under extremely-harsh environment, making a breakthrough towards rapid fabrication of high-quality concrete structure at winter in cold regions.

A novel vertical waterproofing joint with trapezoidal steel plate connections for steel–concrete underground silos: Bending test and numerical simulation

Steel-concrete silo is a popular option in green grain storage project due to its pretty stiffness and better waterproof. However, the structural form and mechanical properties of vertical joints in the prefabricated steel–concrete silo are two key problems, which restrict its wide application. Consequently, a novel vertical waterproofing joint with trapezoidal steel plate (TSP) connections is proposed for steel–concrete underground silos. The TSP is welded laterally between the adjacent prefabricated silo walls, and it also needs to undertake part of the axial force transmission of underground silos. Firstly, the steel–concrete specimen of two-TSPs’ deformation, interior force, failure mode and mechanism are analyzed comprehensively. Secondly, two numerical model of the steel–concrete silo wall with non-TSP and two-TSP are established on ABAQUS. Finally, the effect of different parameters on mechanical properties are analyzed. Experimental results show that, compared with the specimens with non-TSP, the deflection of the proposed two-TSP connection is decreased by 270% and the yield load of internal waterproof steel plate is increased by 29%. When the internal waterproof steel plate is yield, the compressive strain of external waterproof steel plate and TSP in the upper part are similar, while its internal tensile strain in the lower part have a little gap. TSP can cooperative work with both internal and external waterproof steel plates. Numerical results are difference from test results by only 5.34% and 4.48% respectively, which verifies that the numerical model is effective and feasible. Meanwhile, it is also found that the proposed novel connection has the greatest strength enhancement effect on flexural bearing capacity of vertical joint, and the greatest effect on improving the flexural bearing capacity of vertical joint.

Flexural behavior of concrete beams reinforced with high-strength steel bars after exposure to elevated temperatures

To study the flexural behavior of concrete beams reinforced with high-strength steel bars after exposure to elevated temperatures, flexural tests were conducted on twelve concrete beams reinforced with high-strength steel bars. The influences of exposure temperatures (room temperature, 200, 400, 600, 800, and 1000 °C), holding times (0, 1, and 2 h), yield strength grades of steel bars (600 and 500 MPa), and the number of heating sides (2 and 3 sides) on the flexural behavior of beams, including failure mode, load–deflection response, flexural bearing capacity, ductility, and concrete strain, were investigated. The results showed that all beam specimens presented flexural failure mode. When the exposure temperatures were below 600 °C, the flexural capacities changed negligibly, decreasing significantly when the exposure temperatures exceeded 800 °C. The peak loads of specimens with HRB600 bars after exposure to 800 and 1000 °C decreased by 12.9% and 38.7% relative to that under room temperature. The flexural capacities decreased more significantly when the holding time was 2 h relative to that was 0 h and 1 h, of which peak load decreased by 2.4% and 9.4%, respectively. The number of heating sides had no obvious effects on the load - deflection response of the specimens. The load - deflection curves were similar in the elastic stage and yield stage between the specimens were heated on two and three heating sides. At last, combining the temperature distribution on the cross-section obtained by the elevated temperature tests, the calculation methods on the flexural capacities of concrete beams reinforced with high-strength steel bars after exposure to elevated temperatures were proposed based on the equivalent section reduction method and the material reduction method, respectively. Comparing the calculated results with test results, a good agreement could be noted.

Experimental Investigation and Theoretical Prediction Model of Flexural Bearing Capacity of Pre-Cracked RC Beams

Cracking is one of the main diseases of small- and medium-span reinforced concrete (RC) bridges. It is a key problem to determine the change in mechanical properties of RC beams after cracking in bridge-performance evaluation. The present study performs static loading tests on seven simply supported T-beams with different crack damage conditions. The influences of crack location, crack depth and steel-bar diameter at a prefabricated crack on the stress, deflection and crack distribution pattern of pre-cracked test beams are investigated. The failure mode and mechanism of pre-cracked beams are revealed. Based on the experimental results, a finite element model of a pre-cracked beam is developed and validated. Following this, a theoretical prediction method is proposed to calculate the ultimate load of pre-cracked RC beams. The results indicate that the direct damage to mid-span section size can significantly affect the stiffness of the RC beam. The local damage of the tensile steel section has insignificant influence on the overall stiffness of the beam. The stiffness degradation of the pre-cracked beam at the quarter span is smaller than that of the pre-cracked beam at mid-span. The strain of the T-beam section in the pre-cracked test conformed to the assumption of the flat section. The experimental observations are in good agreement with the theoretical predictions, which can provide a theoretical basis for the performance evaluation of existing RC beams.

Seismic performance of cruciform bolted joints with various reinforcing details in modular steel construction

Extensive research has been done on exterior T-shaped joints of modular structures. The modular structure consists of stacked modules that are not only connected vertically but also need to be connected horizontally. The horizontal connection between modules is another key for the modules to form an integral structure and resist lateral forces. This paper proposes a novel bolted joint that can be applied to multi-column module internal and external connections. By designing special loading supports, three internal cruciform joints and three external cruciform joints of the modular structure were tested under column end loading. The effects of different strengthening measures and the ratio of beam to column flexural bearing capacity on the seismic performance of the joints were compared. The results showed that all the joints had good seismic performance and satisfied the requirements of SMF systems in terms of inter-story drift ratio. The stiffness and bearing capacity of the internal joints after the beam-beam combination increased by 33.2% and 17%, respectively. However, the stiffness and bearing capacity of the cruciform joints strengthened by the cover plate are not significantly improved. For joints that meet the conditions of strong columns and weak beams, modular beams can reach full-section plasticity and can meet the requirements of full-strength joints.

An experimental investigation on the dovetail notched connection for cross-laminated-timber-concrete composite slabs

This paper presents an experimental study on the behaviour of notched connectors with a dovetail shape. A series of three symmetrical push-out tests on connection specimens and a series of two full-scale flexural tests on slab specimens were carried out. The test results of the push-out tests showed high shear resistance and stiffness of the connectors. However, the ductility of the connectors was low, as the failure mode was governed by the shear failure of the cross layer of the CLT. In addition, it was shown in the flexural test results that the design of the composite slab is not limited by the flexural bearing capacity as a high value of the maximum bending moment was obtained in the tests. It is instead governed by the deflection of the composite slab. Besides, a modified gamma method was used to estimate the mid-span deflections and compared with the ones obtained from the flexural tests. A good agreement was obtained, validating the use of the method to estimate the stiffness of the CLT-concrete slab with Dovetail notched connection. In addition, a beam grid model was also employed in order to take into account the stiffness of the slab in the transversal direction.