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This study investigates the effectiveness of modified graphene (MGE) for developing novel structural adhesives and their application in concrete beam reinforcement. The research aims to reveal the mechanism of MGE and evaluate the effect of different reinforcement methods on the flexural performance of concrete beams. Two adhesive formulations – original structural adhesive (OSA) and functionalized graphene-based structural adhesive (FGSA) – were examined alongside two reinforcement methods: the grouting reinforcement method and the adhesive fiber-reinforced polymer (FRP) method. The results show that the increased spacing of the functionalized MGE flakes improved their dispersion in epoxy resin, enhancing cohesive forces through bonding interactions and leading to the enhancement of the basic mechanical properties of FGSA by 6% to 12%. Compared to OSA, the application of FGSA improved the flexural properties of concrete beams, with the degree of improvement depending on the reinforcement method, while the failure mode of the beams remained unchanged. In addition, the FGSA/FRP combination showed the most significant improvement in the fracture parameters (220% to 480%) compared to the unreinforced control, highlighting its efficiency and cost-effectiveness as a reinforcement method. These findings offer valuable insights into reinforcement strategies for concrete beams, addressing the limitations of structural adhesive bond strength and optimizing reinforcement techniques. [ABSTRACT FROM AUTHOR]

Concrete-filled steel tube (CFST) widely applied in engineering structures due to its superior behavior requires monitoring and assessment for damage level. Here, the acoustic emission (AE) technique was used to monitor the fracture process of concrete core in CFST stub columns subjected to axial compression. Test and analyzed results show that the damage process of CFST specimens can be divided into four stages: compaction, elastic-plastic stage, strengthening and secondary strengthening. In the elastic-plastic stage, the evolutionary features of the AE event rate, cumulative energy, Ib-value and crack classification are capable of providing an early warning for cracked concrete core. Full crack propagation can be identified by the rapid increase in the proportion of shear cracks near the inflection point of load, which is impermissible in engineering structures. According to the analyses of the AE event rate and signal intensity in the elastic-plastic stage, the confinement of steel tube with thicker wall thickness or higher strength is delayed, which implies that this confinement is suggested to be triggered early. It is indicated that the AE technique has the potential to monitor and evaluate the damage process of CFST stub columns under axial compression, which can provide additional insight into the failure mechanism and assist in the scheme of repairs. [ABSTRACT FROM AUTHOR]

A new adjustable and combined reinforcement method consisting of arch rib and steel beam is proposed in this paper. The principle is to redistribute the internal forces of the structure through the support of the arch rib and to form a combined structure by using steel and concrete. Symmetrically loaded bending tests were carried out with five different combined strengthening schemes. The analysis of the test process was conducted adopting a FEM model, and the equations for calculating the RC beam's load capacity under combined strengthening were derived while considering the slip effect. The experimental results indicated that the combined reinforcement method had a synergistic effect when the ultimate load capacity had increased by more than 95% after reinforcement. As the size of the arch ribs and profile beams increased, a better reinforcement effect was seen. However, beyond a certain range, the RC beams had already broken down and had failed before the reinforcement material could yield. The combined reinforcement method changes the force system of the original RC beam, resulting in a smaller angular inclination trend of the cracks in the original purely curved section and a smaller crack extension. The non-linear finite element results are generally consistent with experimental loads, displacements, and ductility, while the average ratio of experimental to calculated ultimate Load capacity is 0.95, demonstrating that non-linear finite elements and theoretical formulas are accurate. [ABSTRACT FROM AUTHOR]

This study aimed to investigate variations and relationships between molecular components and rheological properties during the long-term aging of SBS-modified asphalt by the action of moisture. The chemical components and changes in molecular weight during aqueous PAV aging were observed using a four-component test and GPC test, and these morphological changes were quantified. Viscosity tests, time-scan tests and damage-healing tests were carried out to investigate the rheological properties during the aging process. Finally, the mechanism of asphalt aging under the influence of moisture was discussed. The results showed that moisture facilitated the long-term aging of asphalt and complicated the aging behavior under pressure-aging conditions. The dissolution of certain hydrophilic groups may be responsible for the decrease in resin content. The fatigue and self-healing properties of asphalt were weakened by moisture during the aging process. This was mainly attributed to a decrease in the composition of the asphalt colloidal dispersion medium, which resulted in earlier and faster development of microcracks under repeated loading as well as retardation in the rate of asphalt surface approach, wetting and spreading. Under long-term aging in the presence of moisture, the molecular components of the asphalt showed significant correlations with the rheological properties. The results of this study can contribute to further explaining the influence of moisture on the thermal-oxidative aging of asphalt. [ABSTRACT FROM AUTHOR]

In order to simplify the completion process of cable force optimization and adjustment in long-span concrete-filled steel tube arch bridges, a new method was proposed in the present study. To this end, a reasonable completion cable force calculation method was proposed based on the influence matrix principle of cable force optimization. Then combined with the mechanical characteristics of concrete-filled steel tube arch bridge, the weighted matrix was introduced to simplify the influence matrix of cable force and optimize the suspender cable force. The performed comparative study showed that the maximum difference of single cable force between the measured and calculated values is less than 5%, and the calculation error satisfies the requirements of the specification. It is concluded that the proposed method can accurately control the suspender tension construction in the arch bridge, optimize the cable force of long-span concrete filled-steel tube arch bridge, and realize the comparison and selection of various optimization schemes. The research results have been successfully applied to the suspender force adjustment of Third Pingnan Bridge, which greatly simplifies the adjustment steps and the total cable force difference in the whole bridge is 1.37%, the difference between the measured and designed suspender tensions of Heshan Hongshui River Bridge at completion state is less than 2%. The successful application of this method effectively saves the labor and material cost of suspender adjustment and further enhances the superiority of steel tube concrete arch bridge. The proposed method is expected to be an excellent choice to monitor constructions, adjust the bridge completion stage, and provide a reference for the suspender tension construction control of similar bridges. [ABSTRACT FROM AUTHOR]

To study the safety and stability of the main truss arch structure during the concrete pouring process in a long-span CFST arch bridge, a combination of theoretical analysis and numerical simulation was adopted. The world's longest span CFST arch bridge, the Pingnan Third Bridge (main span 575 m) in Guangxi Province, was taken as an example. Firstly, the basic theory of stability and the concrete pouring technology of the main truss arch structure were summarized. Secondly, a three-dimensional finite element model of the main truss arch structure was established for the concrete pouring stage. Finally, the linearity, stress, and stability of the main truss arch structure during concrete pouring were studied. The results show that both vertical and transverse deflections occurred in the main truss arch structure during concrete pouring from the arch foot to the arch vault; the upper and transverse deflections of the main truss arch structure showed parabolic changes, and the upper and transverse deflections of the midspan section were larger than those of other sections. When concrete was poured near the 1/6 section of the main truss arch structure, the upper and transverse deflections of the middle section of the main truss arch structure peaked; the maximum upper deflection reached 113 mm, and the maximum transverse deflection reached 60 mm. In the process of concrete pouring from the arch foot to the arch vault, the stress in the steel tubes and concrete was constantly changing. Although upper and transverse deflections of the main truss arch structure occurred during concrete pouring, the stress in the steel tube and concrete in the main truss arch structure did not exceed the tensile strength, and the linearity of the main truss arch could be adjusted by retaining the anchor cables, which were set in the erection stage of the main truss arch structure at the 1/6 section of the main truss arch structure. During the concrete pouring process of the various steel tubes of the main truss arch structure, the stability coefficients of the main truss arch structures decreased gradually. During concrete pouring in a single steel tube, the maximum reduction in the stability factor was 21.32%, which occurred in the 1# steel tube, and the minimum decrease in the stability factor was 8.89%, which occurred in the 8# steel tube. The stability coefficients were greater than 4 after this reduction and met the requirements of the design specifications. This study can provide a reference for the optimization design and construction monitoring of long-span CFST arch bridges. [ABSTRACT FROM AUTHOR]

In order to study the influence of corrosion rate and shear span ratio on reinforced concrete beam, a numerical analysis method of corroded reinforced concrete beam was put forward. Bond-slip relationship formula between reinforcement and concrete was suggested. A three-dimensional finite element model of corroded reinforced concrete beam was established. Calculation method of ultimate bearing capacity for reinforced concrete beam was suggested. Ultimate bearing capacity experiment on 14 corroded reinforced concrete beams with different corrosion rates and shear span ratios was carried out. Numerical analysis results and experimental results were compared and analyzed. The results show that, for reinforced concrete beams with different corrosion rates and shear span ratios, load-deflection curve can be divided into elasticity stage and plasticity stage. With the increase of corrosion rate and shear span ratio, ultimate bearing capacity of corroded reinforced concrete beam decreased. When shear span ratio was 3.0, if corrosion rate increased by 1%, experimental value of ultimate bearing capacity decreased by 1.002 kN. When shear span ratio was 2.4, if corrosion rate increased by 1%, experimental value of ultimate bearing capacity decreased by 1.849 kN. The numerical analysis method put forward in this paper was feasible, and the suggested ultimate bearing capacity calculation method for reinforced concrete beam has a high accuracy. [ABSTRACT FROM AUTHOR]

In order to study a new reinforcement method for multilayer (4 layers) industrial building's vibration, firstly, a new reinforcement method using a short-pier shear wall was put forward. Secondly, an engineering example of a multilayer industrial building with abnormal vibration was introduced. A three-dimensional finite element model of multilayer industrial building was established, and field vibration test was carried out. Test results showed that abnormal vibration of industrial building was caused by resonance between machines and multilayer industrial building. Finally, multilayer industrial building was reinforced by a new reinforcement method, and vibration experiment was carried out after reinforcement. The results show that the new reinforcement method has a good reinforcement effect. Strength and stiffness of multilayer industrial building were obviously improved, and natural frequency of industrial building in the length direction increased from 2.45 Hz to 5.87 Hz, natural frequency of industrial building in the width direction increased from 2.94 Hz to 7.83 Hz, frequencies of machines and frequencies of multilayer industrial building were not in resonance range, acceleration and velocity vibration characteristics of multilayer industrial building were improved, which can provide reference for the reinforcement of multilayer industrial building with a similar structural configuration. [ABSTRACT FROM AUTHOR]

• Different epoxy resins to repair the post-fire concrete were studied. • The interface properties of epoxy resin adhesives and post-fire concrete was investigated. • The adhesive-failure constitutive model for epoxy resin adhesive and post-fire concrete was established. In order to investigate the influences of temperature that concrete has undergone on the resin/concrete interface bonding performance for different epoxy resin adhesives, 40 tensile specimens and 24 three-point bending specimens were heated to 200, 300, and 600 ℃, respectively. After natural cooling, resin was injected to form tensile specimens and sandwich specimens, which were subjected to pull-out tests and three-point bending tests, respectively. The interface bond-separation constitutive relationship was obtained to study the influence of fire temperature and different epoxy resin adhesives on the properties of the resin/concrete interface bonding. The results showed that the reinforcement of high-temperature concrete with different permeable epoxy resin adhesives caused the crack initiation load, interface strength, and fracture energy of the concrete/resin interface to increase slightly and then decrease sharply as the temperature of the concrete in the fire increased. When the fire temperature was 200 ℃, the peak value of the bonding performance of high-temperature concrete/resin interface was higher than that at room temperature. [ABSTRACT FROM AUTHOR]