Residual Bearing Capacity Research Articles

Constitutive model of confined concrete with stirrups by acid rain erosion

In order to study the influence of stirrup corrosion level on the peak stress, peak strain, ultimate strain and shape of stress-strain curve of the confined concrete, 15 reinforced concrete prism specimens were subjected to acid rain erosion by artificial climate simulation technique followed by axial pressure tests. Based on Mander’s model and the existing research results, the calculation formulas of the peak stress f’ cco, peak strain £cco, ultimate strain ε cco, ultimate strain ε cu0 and shape factor r of the uncorroded specimens are determined. The factor calculation formulas for peak stress, peak strain, ultimate strain and shape factor of corroded specimens is developed by regression analysis of test data, respectively, and then the constitutive model of confined concrete by acid rain erosion is established. By comparing the simulation results with the experimental data, it can be found that all the peak stress, peak strain, ultimate strain and stress-strain curves shape of the specimens obtained by the proposed method are in good agreement with the experimental data. Thus the constitutive mode for confined concrete established in this paper can accurately reflect the mechanical performance of RC prism specimen by acid rain erosion, indicating its adaptiveness for estimating the residual bearing capacity and the seismic performance of RC structure under the acid rain environment.

Experimental Study on Residual Bearing Capacity of Existing Prestressed Concrete Hollow Slab Beam

Through the reconstruction and expansion of expressway, it has become the new normal of expressway construction in China to improve the traffic capacity and operation service level of the existing road. However, the reconstruction and expansion of expressways are faced with problems such as the degradation of the existing bridge performance and the original design bearing capacity that can’t meet the current load standards, which restrict the full utilization of the existing expressway bridges. Based on the reconstruction and expansion project of Beijing-Shanghai Expressway (Shandong section), this paper selects the prefabricated and prestressed concrete (PC) simply supported slab bridge with span of 10m and 13m. It evaluates the bearing capacity of HSB based on technical condition checking calculation and load test, and carries out the ultimate bearing capacity test at the same time. According to the checking calculation of bearing capacity and test results, it is concluded that the technical condition of the existing bridges in the expressway (Shandong section) is evaluated as class 1 prefabricated simply supported slab bridge. By adding 150mm integral cast-in-place pavement, the bending capacity of the HSB in the mid of span section meets the current load standard, while the shear capacity of supporting point section does not meet the current load standard, but the difference is within 5%. After the reconstruction and expansion of expressway, the existing bridges mainly bear the load of small vehicles, the load effect is far lower than the current load standard, the bearing capacity meets the current load standard, and can be fully utilized in its original state.

Traffic Capacity Assessment of the Urban Elevated Bridge after Near-Field Explosion Based on the Response Surface Method

The traffic capacity of the urban elevated bridge is assessed after it is attacked by a near-field explosion, using the residual bearing capacity of the damaged pier as the assessment index. First, the finite element model of a reinforced concrete slab under near-field explosion is established by ANSYS/LS-DYNA software and compared with the experimental results, which verifies the effectiveness of the ALE (arbitrary Lagrangian–Eulerian) algorithm and the accuracy of the mesh size and material properties. Then, an “explosive-air-pier” coupling analysis model is constructed using the finite element method, and the damage of the reinforced concrete pier under three types of car bombs is evaluated. Furthermore, a response surface model for the residual bearing capacity of the pier is utilized to calculate the failure probabilities of various damage levels of the pier under the three types of car bombs and to assess the traffic capacity of the bridge after near-field explosion. The established assessment method can be used to predict the probability of bridge structural damage at various levels under different types of car bombs and to provide a reference for exploring a probability-based safety assessment method of post-explosion bridges.

Research on fatigue performance of steel-plate-concrete composite slab

Fatigue has become one of the critical issues for bridge deck with the rapid development of bridge engineering. Steel-plate-concrete composite slab has been more and more applied as bridge deck for the advantages in high bearing capacity, good fire resistance and less demand on framework. In order to study the mechanical behavior and fatigue performance of steel-plate-concrete composite slab under low-cycle fatigue loads, static test and the constant amplitude fatigue test were performed. The effects of layout of studs, arrangement of steel plate with openings, shear ratio, as well as amplitude of fatigue load on the damage development and the failure mode of steel-plate-concrete composite slab were researched and discussed. During the test, indices such as the dynamic deflection, strain of concrete and steel plate, residual deflection and residual bearing capacity were measured. The results implied that the amplitude of fatigue stress of bottom steel plate had a direct influence on the fatigue life of composite slab, while the layout of studs and the number of steel plate with openings had little effect on the fatigue performance. No slippage on the interface between concrete and bottom steel plate was discovered and the distribution of strain generally agreed with the plane-section assumption. All the specimens experienced similar development of fatigue damage and finally failed in the mode of fatigue fracture of steel plate, followed by the concrete crush in compression region. Finally, the method for prediction of the stiffness development and fatigue life of steel-plate-concrete composite slab was preliminarily established.

Effect of elevated temperature on thelow-velocity impact performances of reinforced concrete slabs

Reinforced concrete structures may suffer some accidental loadings, such as fire, impact(or blast), etc.To study the effects of high temperature and impact on the performance of RC slabs,a three-dimensional simulation model was established in the present work. A two-step analysis methodwas utilized to consider the combined effect of fire and impact loadings. Namely, the thermal conduction behavior of the concrete slab was simulated firstly, and then, the “result output”ofthe temperature field was used as the “initial condition” to simulate the impact behavior of RC slabs. On the basis of verifying the rationality of the three-dimensional simulation model, the influence of fire exposure time on the impact performance of RC slabs was analyzed. The difference of impactperformances between RC slabs under high-temperature exposure and after cooling downwas discussed. Thus, the failure mode and failure mechanism of the RC slabswere revealed. The simulation results showed that the impact performance of RC slabs subjected to fire and cooling down, in terms of failure pattern, overall deformation, energy dissipation, responses of impact and reaction force as well as acceleration, is better than that under high-temperature exposure, but still worse than that at room temperature.This difference becomes larger with respect to fire duration. As the fire duration increases, the residual bearing capacity and natural frequency which reflects the overall stiffness of the RC slab decrease, but the displacement and energy dissipation increase.

Research of the Residual Bearing Capacity and the Work of Damaged Reinforced Concrete Beams’ Inclined Sections

The article is devoted to studies about the stress-strain state and the residual bearing capacity of inclined sections of reinforced concrete beams with concrete damages in the compressed zone near support areas. The developed method of calculating the bearing capacity of the inclined sections of damaged beams is described. The numerical test of prototypes was performed in the LIRA-CAD 2017 software complex. A comparison of the results of laboratory tests, a numerical experiment and calculation results by the proposed method is shown. It is stressed that with an increase in the area of damage, the bearing capacity decreases. The nature of the change in the stress-strain state under the presence of damage is described. It is pointed out that in the damaged samples, there is an inclination of the neutral axis in the cross section of the element – it tilts, the neutral axis becomes, almost, parallel to the front of the damage.

Multilaser spot tracking technology for bridge structure displacement measuring

During the structural health monitoring of bridge structures, simultaneous noncontact determination of relative displacements in different points is preferred. The existing measurement displacement methods and systems used for bridge structures deprived of this ability or have the low accuracy and thus automation level that makes their usage for long-term monitoring of bridge structure elements becomes impossible. To avoid the imperfections of existing methods and determining displacements simultaneously in different construction points, we proposed to use the laser spot tracking technology, in which the laser modules are mounted in certain points, and their rays are directed to the translucent screen of a recording device. After screen images recording and processing, one determines displacements of different spots formed by the laser modules on the translucent screen by specialized software. Potential opportunities for this technique are demonstrated during research of a concrete beam deflection in laboratory conditions. The errors of the proposed measurement algorithm were analyzed using computer simulation and laboratory study. The influence of laser modules and screen different spatial positions on the beam deflection measurement was also estimated. Practical application of the proposed system for underground crossing overlap vibration measurements has been showed. Based on the obtained data, several evaluations of its technical state and the residual bearing capacity of a reinforced concrete are made.

Investigation of Residual Bearing Capacity of Inclined Sections of Damaged Reinforced Concrete Beams

Abstract The article reports on the results of the numerical and the laboratory tests to determine the effect of concrete damages near support areas in compressed zone of the reinforced concrete beams on their residual bearing capacity of inclined sections. According to the experimental plan, 15 single-span freely supported experimental samples with dimensions of 100×200×1200 mm made with different artificial damages within the shear span aν (1d, 2d, and 3d) were tested. The numerical test of prototypes was performed in software complex LIRA-SAPR 2017. The results of laboratory and numerical experiments showed good convergence regarding the bearing capacity, however, the nature of the fracture in samples B11-B14 did not match. Empirical - conducting laboratory experiments on samples using modern methods of measurement; numerical modelling – using software complex LIRA-SAPR 2017; analysis and statistical processing of the obtained research results; comparison of the obtained results; abstraction; generalization; deduction; formulation of the main conclusions and recommendations. The analysis found that the bearing capacity decreases with increased area of damage and shear span. Conducting the calculations in software complex LIRA-SAPR allows to predict the work elements and determine the bearing capacity with good accuracy, but in comparison with the real data there still are some differences in the character of destruction.

Residual behavior of recycled aggregate concrete beam and column after elevated temperatures

This paper presents the results of an experimental study on the residual behavior of reinforced recycled aggregate concrete (RRAC) beam-columns after exposure to elevated temperatures. Two parameters were considered in this test: (a) recycled coarse aggregate (RCA) replacement percentages (i.e. 0, 30, 50, 70 and 100%); (b) high temperatures (i.e. 20, 200, 400, 600, and 800℃). A total of 25 RRAC short columns and 32 RRAC beams were conducted and subjected to different high temperatures for 1 h. After cooling down to ambient temperature, the following basic physical and mechanical properties were then tested and discussed: (a) surface change and mass loss ratio; (b) strength of recycled aggregate concrete (RAC) and steel subjected to elevated temperatures; (c) bearing capacity of beam-columns; (d) load-deformation curve. According to the test results, the law of performance degradation of RRAC beam-columns after exposure to high temperatures is analyzed. Finally, introducing the influence coefficient of RCA replacement percentage and high temperatures, respectively, to correct the calculation formulas of bearing capacity of beam-columns in Chinese Standard, and then the residual bearing capacity of RRAC beam-columns subjected elevated temperatures is calculated according to the modified formulas, the calculated results are in good agreement with the experimental results.

Strength evaluation of deteriorated girder ends. I: Experimental study on naturally corroded I-beams

Corrosion is a common cause for steel bridge deterioration, primarily attributed to malfunctioning deck expansion joints. Aged joints fail to prevent water or deicing mixtures from penetrating into the bearing area triggering a corrosive process which locally damages the steel beams. Topologically non-uniform and highly uncertain, the appearance of corrosion makes the residual bearing capacity quite challenging to be accurately assessed by inspectors and engineers. The present study, the first part of a companion set of two papers, aims to evaluate and improve the efficiency of current strength assessment policies for un-stiffened rolled I-beams, based on field corroded girders tested in the laboratory. A total of six full scale loading tests are reported on naturally corroded girders, which were extracted from structurally deficient bridges in the state of Massachusetts. The test results indicate that provisions underestimate the capacities of five out of the six specimens, while the sixth test highlights the harmful effect of a web's deviation from plumbness. An alternative load path is also revealed for specimens with holes extending along the bottom at the girder web.

Role of macro fibers (steel and hybrid-synthetic) in the residual response of RC beams exposed to high temperatures

Inclusion of fibers can mostly enhance the mechanical properties of concrete; however, the role of those in reinforced concrete beams wherein the interaction between concrete, steel reinforcement, and fibers is crucial can be different. This paper provides an experimental study to evaluate the residual behavior of macro fiber-RC beams exposed to high temperatures. Thirty-six scaled reinforced concrete beams were designed and fabricated according to the ACI 318 criteria and requirements, subjected to high temperatures up to 800 °C. In this investigation, mechanical and deformation properties of heated RC beams, failure patterns, and confinement role of fibers were examined, discussed, and compared with non-heated specimens. This investigation indicated, adding steel fibers noticeably improved the residual bearing capacity and bond interaction between steel bars with concrete at high temperatures. Hence, this value for RC beams reinforced with steel and hybrid-synthetic fibers at 800 °C was 65% and 48% of their initial capacity, respectively; however, for plain concrete was about 40%. Moreover, the transformation of failure patterns depended on the type of used fibers and experienced temperatures.

Strength evaluation of deteriorated girder ends. II: Numerical study on corroded I-beams

Corrosion is one of the main aspects for structural deficiency of highway bridges. Steel girders are prone to deterioration development at the support area, where malfunctioning expansion joints allow leaking water to penetrate into the superstructure level. The present study is the second part of a companion set of papers, and aims to numerically address the evaluation of un-stiffened I-beams with corroded ends. A girder level finite element model based on experimental data presented in the first of the two papers and able to capture the end failure is developed and employed through a parametric analysis to explore the impact of the initial web imperfection, the geometry configuration and the corrosion characteristics to the residual bearing capacity. Finally, empirical equations are provided for bearing strength assessment of rolled girders with corroded webs above end supports. The efficiency of the proposed methodology is experimentally and numerically validated, providing overly improved predicted failure loads compared to the current provisions.

Analysis of defective prestressed pipe piles residual bearing capacity and treatment measures

Due to poor geologic conditions, unreasonable design principles, or construction method, many quality defects often occur during prestressed pipe piles’ field construction, which will greatly influence pipe piles’ normal service or result in engineering accident. To acquire some treatment measures of the defective pipe piles, we have carried out some theoretical researches on this type of pipe pile. First, the types of defective prestressed pipe piles were summarized. Then, we explored the force and deformation characteristics of the defective pipe piles and brought forward the relationship between pile-top displacement and residual bearing capacity. Finally, we offered some treatment measures for the defective pipe piles. The results show that the main performance of the defective prestressed pipe piles includes pile deviation, incline, and breakage. The residual bearing capacity of the incline pipe piles is less than half of the designed bearing capacity, and the top displacement of the incline pipe pile is positively correlated with the square of the sliding depth. Some treatment measures such as foundation adjustment, adding piles, splicing pile, and filling core can improve defective pipe piles. The research results can provide some references for similar engineering.

Study of CFRP retrofitted RC column under close-in explosion

To efficiently improve the anti-blast performance of current reinforced concrete (RC) structures, three different retrofitting methods using the carbon fiber reinforced polymer (CFRP) sheets were proposed. Field tests were carried out on the FRP retrofitted columns subjected to close-in and double-end-initiation explosions. The recorded dynamic damage characteristics of RC columns reveal that the proposed methods benefit the lateral resistance and local damage of columns to different extents. A residual bearing capacity experiment was conducted to evaluate different damage levels of the blast damaged column. Brittle failure was observed at both ends of the columns, which were demonstrated to be a vulnerable key to the axial bearing capacity, and where CFRP was inconvenient to wrap. The fine finite element (FE) model of the RC column was established on the LS-DYNA platform, which was validated by both the blast and axial bearing test data. The influences of axial load ratio (ALR), longitudinal reinforcement ratio (ρg), CFRP thickness (H), charge cylinder aspect ratio (D/L), and stirrup ratio (ρv) were studied using the developed model. A new formula to guide retrofitting RC columns based on the residual bearing capacity was proposed, which can quantitatively calculate the retrofitting contribution to the blast resistance of the RC column.

Structural Response of Post-Fire Exposed Reinforced Concrete Column with Pre-Load

This paper presents the results of experimental and numerical studies of the fundamental response of normal concrete (NSC) columns under fire exposure with pre concentric load. The present study aims to investigate experimentally the behavior of reinforced concrete columns exposed to fire flame with concentric axial load, post-fire behavior under the effect of axial eccentric load. Also, it aims to give a comprehensive account of the fire effects on the ductility and stiffness of these columns. The test results indicated that columns lost about (47.60-51.4) % of bearing capacity after exposure to fire at 500 °C with one hour. Moreover, increased decrease in residual bearing capacity significantly with increasing load level applied during fire exposure. Also, Non-linear finite element (FE) analyses of postfire exposed RC columns with axially load using the ABAQUS computer program is discussed in this paper.

Dynamic response and damage assessment of spherical robot GFRP spherical shell under low velocity impact

Abstract In the normal operation of a spherical robot, its spherical shell structure is often accompanied by low velocity impact. At the same time, the spherical shell structure should take into account its protective ability against high strength impact of small probability. Glass fiber reinforced polymer (GFRP), which has high specific strength, specific stiffness, corrosion resistance and an impact energy dissipation coefficient, can be used as the ideal spherical shell material for spherical robots. In this study, the low velocity impact damage of GFRP spherical shell is studied based on the background that a thin-walled shell structure of spherical robot may suffer from large deformation and dynamic load. This study is divided into three aspects: experiment, simulation and calculation. The dynamic response and residual bearing capacity of the GFRP spherical shell is obtained through experiments; the progressive damage model of the composite structure, which demonstrates expounded stress distribution, a structural deformation mode and an energy dissipation mechanism under impact, is established based on the Hashin criterion. Low velocity impact-penetrating failure of the elastic brittle thin-walled GFRP spherical shell is calculated according to the geometrical principle and energy method. In this paper, the material dynamic behavior and impact damage of a GFRP spherical shell are systematically studied. This is of great significance for the development of high-performance spherical robots and the realization of accurate control.

Axial compression behavior of ultra-high performance concrete columns confined by high-strength stirrups

Based on the axial compression test of 5 ultra-high performance concrete (UHPC) columns confined by high-strength stirrups and 4 UHPC columns confined by normal-strength stirrups, the bearing capacity, failure mode, steel strain and stress-strain curve for the confined UHPC columns were studied, and the influences of volume stirrup ratio, strength, spacing and configuration of stirrup on the axial compression behavior of confined UHPC were analyzed by combining ductility and toughness index. The results show that all the specimens have ductility damages, and the damage degree of UHPC columns confined by high-strength stirrups is lighter. The confined UHPC columns with high volume stirrup ratio, closely spaced, high-strength and complex ties configuration have good confinement efficiency, bearing capacity and deformation performance, which also leads to an ideal axial compression behavior. The effect of volume stirrup ratio on the axial compression behavior of specimens is greater than that of stirrup strength. Among the three factors affecting the volume stirrup ratio, such as spacing, configuration and diameter of stirrup, the stirrup spacing contributes most to the improvement of confinement performance, followed by the configuration and diameter of stirrup. The UHPC confined by high-strength stirrups presents better axial compression performance and residual bearing capacity than the normal-stirrups. The micro-bending of the longitudinal bars accelerates the cover spalling, while the high-strength stirrups with close space effectively delays the buckling of longitudinal bars, and significantly improves the overall performance of the confined UHPC. The micro-bending of longitudinal bars weakens the confine effect of the high-strength stirrups on the core UHPC, and the combination of high-strength longitudinal bars and stirrups is suggested. Based on the test data, the formulas to determine the bearing capacity of UHPC columns confined by stirrups are drawn.

Residual Bearing Capacity of Damaged Large-Diameter Drum-Welded Spherical Joints Post Disaster

Building structures may encounter strong wind, earthquake, snowstorm, and other disaster loads during their service period. Therefore, the members and joints may incur different degrees of damages. However, some damaged members and joints can continue functioning after reasonable assessment and repair. In this study, drum-welded hollow spherical joints (DWHSJs) that are used in Beijing’s New International Airport were considered as research objects. Experimental and numerical analyses were conducted to investigate the compressive bearing capacity of the DWHSJs and their degradation when they suffered damage. Then, using parametric analysis, the effect of various factors on the degradation of the bearing capacity of damaged joints was revealed. Finally, according to the experimental and numerical analysis results, a practical formula for calculating the bearing capacity of damaged joints under axial compression was proposed. A reduction factor of the bearing capacity based on the residual deformation of joints was introduced in the formula. A comparison showed that the calculation results were relatively consistent with the experimental results.

Impact resistance of RC beams under different combinations of mass and velocity: mesoscale numerical analysis

The concrete structures under impact loading duress may be destroyed within an extremely short period of time. The importance and complexity of exploration on the impact resistance of concrete members make this area still open for discussion. In the present study, a 3-D mesoscale numerical model was established to investigate the effect of the combination of impact mass and velocity on the mechanical behavior of reinforced concrete (RC) beams subjected to impact loadings. Heterogeneity of concrete and strain rate effects of concrete and steel bars were taken into account. Furthermore, nonlinear interaction between the concrete and steel bars was considered herein. Results from macroscale and mesoscale simulation were compared with the available physical tests, indicating that the mesoscale numerical model can better represent the influence of heterogeneity of concrete on the mechanical behavior of RC beams. Five different impact energy levels were involved to study the effect of the combination of impact mass and velocity on the impact resistance of RC beams. At last, the residual bearing capacity and natural frequency of impacted RC beams were numerically calculated and their relationship was discussed. It is indicated that the deformation of RC beams is influenced strongly by the impulse, which increases with the increasing impact mass at identical impact energy. Besides, the failure mode of RC beams turns from shear-dominant failure mode to bending shear failure mode with the increase of impact mass, accompanied by the increase of energy dissipation of steel bars and the whole member. Despite this, in the present work, the combination of the impact mass and velocity had little influence on the damage extent (based on the performance) of the RC beams. Moreover, an empirical relationship between the residual bearing capacity and the natural frequency of the impacted RC beams was established as a rough reference for damage evaluation in engineering practice.

Flexural behavior of concrete-filled double-skin steel tubular beams after subject to high temperature

Concrete-filled double-skin steel tubular (CFDST) specimens that exhibit lightweight, good ductility, and better bending resistance, can be used for beams. However, fire often causes great damage, and the flexural behavior of CFDST beams after subject to high-temperature has not been studied. To investigate the flexural behavior of CFDST beams after subject to high temperature, seven CFDST specimens after subject to high temperature were carried out four-point bending tests. The main parameters explored in the test include hollow ratio (0.31, 0.52, 0.72) and temperature (300 °C, 500 °C, 800 °C). The corresponding finite-element analysis (FEA) models were established, and the results showed good agreement with the test. The in-depth mechanism and systematic analysis including the influence of different hollow ratio, material property, and temperature on the whole process curve of CFDST after subject to high temperature are carried out using FEA models. It is found that the ultimate bending moment of CFDST after subject to high-temperature increases with hollow ratio and material property, but decreases with the temperature. The outer steel tube contributes the most to the ultimate bending moment, and the inner steel tube improves the ductility at a later stage. Specimens with a large hollow ratio (χ ≥ 0.52) have better bending capacity, and the ultimate bending moment of specimens with a small hollow ratio (χ < 0.52) decrease the least with the change of temperature due to the protection of concrete. Based on the findings from the test and numerical studies, a temperature effect coefficient kr is proposed to represent the residual bearing capacity after subject to high temperature, and combined with three different codes to evaluate the ultimate bending moment. A comparison of test results showed the calculated results following the T/CCES 7–2020 (2020) had a good agreement.