To improve the transportation and lifting efficiency of precast staircases, a novel UHPC shaped thin-plate ribbed staircase was proposed and investigated under flexure by the accumulation load test. ...The flexural behavior of the proposed UHPC staircase was compared to the precast staircase made of Normal Strength Concrete (NSC), and the effects of fiber contents (0.75%, 1.0% and 1.5%) and the presence of steel bars in the UHPC staircase were experimentally investigated. The development of cracks and the comparison of load–deflection curves showed that the flexural behavior of the UHPC staircases was less susceptible to the disturbance of cracking than the NSC staircase. Besides, increasing the fiber content was beneficial to improve the crack resistance of the UHPC staircases, weaken the stress concentration effect of step roots on rib slabs, thereby improving the load-bearing capacity. The absence of rebar had no significant effect on the flexural behavior of UHPC staircases before cracking, but negatively affected the bending behavior after cracking. Furthermore, by means of the effective moment of inertia method and the introduction of a modified steel fiber conversion area parameter, a short-term stiffness model for UHPC stairs was proposed with a deviation within 6%. Finally, a parametric study was conducted based on a validated FE model, and suggestions are provided on the selection of section size to improve the flexural performance of the proposed UHPC staircases.
By taking advantage of the superelastic effect of shape memory alloy (SMA) and the cohering characteristic of repairing adhesive, a smart self-repairing concrete beam with damage self-repairing ...performance has been developed. In order to verify the potential self-repairing capacity of smart concrete beams reinforced with SMA wires and brittle fibers containing adhesives, static loading tests were conducted. Experimental results show that the superelastic SMA wires added self-restoration capacity to concrete beams, the deflection of the beams reversed and the crack closed almost completely after unloading. After the release of adhesive from the broken-open fibers into the cracks from the first loading, stress was redistributed to the uncracked section where a new crack was formed, while the sealed crack remained closed during reloading for the smart concrete beams reinforced with SMA wires and brittle fibers containing adhesives. While the original cracks experienced reopening, the load was carried directly by the wires during reloading for concrete beams reinforced with SMA wires.
In order to determine the design strengths of P. edulis bamboo material, this research carried out a series of material tests on the full-culm P. edulis bamboo specimens, including compression tests ...parallel to the grain, bending tests, tension tests parallel to the grain, shear tests parallel to the grain and compression tests perpendicular to the grain. The standard values of different strengths for bamboo material were obtained by the Bootstrap method. The influence of the load combination and load effect ratio on the relationship between reliability index β and resistance factor γR was analyzed. A method for calculating the target reliability index of bending strength was proposed. The design strengths of the P. edulis bamboo material were determined and the adjustment method considering different design situations was also put forward. The research results show that the target reliability of the bending strength of bamboo material is suggested to be 3.57. With the same β value, γR is the maximum under the combination of constant load + snow load, and γR is the minimum under the combination of constant load + live load on the office building floor. Under the same load combination and load ratio, the shear strength along the grain has the maximum γR and the compression strength along the grain has the minimum γR. The design strengths of the P. edulis bamboo material were determined by the larger γR of two cases (one is that the load ratio of constant load over live load on the residential building floor is 1.0 and another is that the constant load over live load on the office building floor is 1.0). The design strengths can provide reference for the design and application of bamboo structure.
The "U-shaped ferrule joint bars connections" have a stable mechanical property, requiring a low level of construction accuracy and a relatively simple connection process, which significantly ...increase the construction speed. Based on the "U-shaped ferrule joint bars connections" technology, a new type of prefabricated concrete underground utility tunnel was proposed. This prefabricated technology realizes a formwork-free construction and vertical support-free assembly of the top plate on site. Through the full-scale model static test and numerical analyses, the mechanical properties, i.e., the crack development law and bearing capacity, were systematically investigated to validate the effectiveness of the "U-shaped ferrule joint bars connections". The test results indicated that the performance of the "U-shaped ferrule joint bars connections" is reliable. During the loading process, the prefabricated utility tunnel experienced three stages, i.e., cracking, stiffness degradation, and ultimate failure. The numerical analysis results correlated with the test results well. The simulation results showed that the bearing capacities of the prefabricated underground utility tunnel and the cast-in-place utility tunnel were similar. The longitudinal joint connections of the prefabricated utility tunnel allow the structure as an integration to maintain favourable mechanical properties.
Steel-concrete composite girder bridges are subjected to reciprocal cyclic loading from vehicles, and the stud shear connectors are the key components for transmitting shear forces. Thus, it is ...necessary to study the fatigue performance of the stud shear connectors. At present, there are few studies on the fatigue crack propagation process of studs, and the variation curve of the crack depth of studs with the number of fatigue loading cycles is not clear. In this study, the degradation law of fatigue properties and the fatigue crack propagation law of stud shear connectors in steel-concrete composite structures are examined under fatigue loading. The fatigue properties, i.e., failure mode, the dynamic slip-fatigue number curve, cross-sectional characteristics, and the residual bearing capacity of the stud specimens, are first systematically studied through ten standard push-out specimen tests. The test results show that the relative value of the fatigue crack extension area increases, while the relative value of the residual bearing capacity of the studs decreases approximately linearly. Then, the expression of the relationship between the fatigue crack depth and the residual load-bearing capacity of the stud is proposed, based on the fatigue crack theory of fracture mechanics. Finally, combined with the ABAQUS and FRANC3D software, a fatigue crack propagation finite element analysis (FEA) model of the stud is established. The FEA results showed that the trends in the number of cyclic loads and the fatigue crack depth of studs are basically the same for the simulation curve, test curve and theoretical calculation curve.
Nano-TiO2 combined with cement slurry can be utilized to degrade nitrogen oxides (NOx) in vehicle exhaust, making it an excellent photocatalytic material for air purification. In practice, ...environmental factors can significantly affect the photocatalytic performance. In this study, a vehicle exhaust test system was developed, and the test methods and evaluation criteria for the degradation test are provided. This study investigated the photocatalytic degradation of NO2 using nano-TiO2 cement slurry through laboratory tests. The effects of temperature, relative humidity, ultraviolet (UV) radiation flux, cement slurry thickness, surface dust adherence, and the number of water rinsing cycles were examined. Additionally, nano-TiO2 cement slurries were applied to an expressway toll station. The results showed that the efficiency of photocatalytic degradation was significantly influenced by temperature and UV radiation flux, while the thickness of the cement slurry had minimal impact. The photocatalytic degradation efficiency was negatively correlated to the relative humidity, when the relative humidity of the cement slurry specimens was high. This is because the excess water (H2O) competes with NO2 for adsorption. The photocatalytic performance of the samples was significantly reduced by surface dust and rain erosion, as both led to a decrease in the amount of nano-TiO2 participating in the reaction. Furthermore, the photocatalytic material has wide-ranging potential applications. The findings of this study would support the promotion of environmentally friendly roads as a strategy to combat air pollution.
The secondary development of ABAQUS was carried out to calculate the shrinkage and creep of concrete, and a finite element model of the China Railway Track System (CRTS) II slab ballastless track was ...established. Then, the interlaminar stress of CRTS II slab ballastless track at different ages of the track slab during laying (AOTSL) caused by concrete shrinkage and creep was studied. The obtained results showed that the stress redistribution occurred in the sliding layer, which resulted in the generation of a gap. Although the gap length was slightly reduced due to the shear cogging, the sliding layer at the slab edge is more prone to produce gaps. Under the effect of shrinkage and creep of the ballastless track, large additional shear stress, up to 0.676 MPa, was induced at the interface between CA mortar and the track slab. Meanwhile, the appearance of additional vertical and lateral forces of the shear cogging was caused by the shrinkage and creep of the ballastless track. Additionally, by further analysis, the recommended AOTSL ranges from 120 days to 180 days.
The objective of this study was to investigate the composite behavior of rectangular concrete-filled cold-formed steel (CFS) tubular stub columns under axial compression. A fine finite 3D solid ...element model of rectangular concrete-filled cold-formed steel tubular stub column was established by ABAQUS, which utilized a constitutive model of cold-formed steel considering the cold-forming effect and a triaxial plastic-damage constitutive model of the infilled concrete. Good agreement was achieved and the average discrepancy between the experimental and FE results was less than 5%. Based on the verified models, a further parametric analysis was carried out to reveal the influence of various factors on the strength and behavior of the concrete-filled rectangular cold-formed steel tubular stub columns. The factors included constitutive models adopted for cold-formed steel, length over width ratio of the rectangular section, wall-thickness and width, and concrete strength and yield strength of the cold-formed steel. A total of 144 FE models were analyzed. The stress nephogram was reasonably simplified in accordance with the limit state and a theoretical formula considering confinement coefficient was proposed to estimate the ultimate bearing capacity of concrete-filled rectangular cold-formed steel tubular stub columns using the superposition method. The calculated results showed satisfactory agreement with both the experimental and FE results, which proved the validity and accuracy of the formula proposed in this paper. In the proposed formula, the confinement coefficient of square concrete-filled cold-formed steel tubular stub columns is larger than that of hot-rolled steel counterparts but smaller than that of the stainless steel counterparts.
Simply supported prestressed concrete (PC) box girders have been widely adopted in high-speed railway bridges. In complex climatic environments, the corrosion of the prestressing strands always ...occurs and deteriorates the flexural behavior of PC box girders. In the present study, six T-shaped scaled beams were designed and fabricated according to the specifications for a high-speed railway PC box girder. The corrosion process of the prestressing strand in scaled beams was experimentally simulated by using the constant current accelerated corrosion method. The flexural behavior of corroded high-speed railway simply supported PC box girders was then investigated through four-point bending tests and theoretical investigation. The experimental results showed that strand corrosion significantly decreased the flexural behavior of the test beams. When the mass loss was 12.30%, the cracking load, ultimate load, and ductility decreased by 27.8%, 29.9%, and 11.5%, respectively. The effect of strand corrosion on flexural stiffness displayed a difference before and after concrete cracking. The failure mode changed when strand mass loss was above a critical value (7%). The flexural bearing capacity degradation law of corroded PC beams could be divided into two distinct stages. A strand mass loss of less than 7% could lead to a linear degradation law with a relatively slight reduction. As mass loss increased, it exhibited an exponential and sharp declining trend. An analytical model including the effects of strand cross-section reduction, strand property deterioration, and concrete cracking was also proposed to predict the flexural behavior of corroded PC beams. By comparison with the experimental data, it was found that the model could predict the cracking moment, flexural bearing capacity, and failure mode well.
This study investigated the bonding strength between various cement-based grouting materials (CBGM) and high-strength bolts, the flexural and compressive strength variation of different CBGM with ...curing age, and the failure characteristics of flexural, compressive and bonding strengths. Moreover, the morphological characteristics of bond-slip curves and their similarities and differences were discussed as well. Based on the mechanical property and safety analysis, a calculation model of the critical anchorage length of high-strength bolt in CBGM was proposed. The results indicate that the flexural and compressive strengths increase with the increase of curing age. The strength growth rate is faster at the initial stage of 3 days, which implies that the CBGM has a significant high-early strength characteristic. Depending on the diameter and type of high-strength bolts employed, the bonding strength of specimens can be divided into two failure forms, i.e., splitting and slipping pull-out. The specimens with threaded bolts easily take place a splitting failure form, but the specimens with plain round bolts tend to be destroyed with a slipping pull-out failure form. The ascending section of bond-slip curve is well fitted with the same stage of CEB-FIP 2010. However, a linear relationship can be employed to characterize the bonding strength between CBGM and high-strength bolt. The bond failure capacity is also linear correlation with the strength of CBGM.
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