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Curved beams are sometimes used in practical framed structures due to good mechanical properties and artistic design. In a framed structure, curved beams may undergo large displacement and experience nonlinear behavior as same as the other straight slender beam-column members. Thus, a geometrically nonlinear curved beam element plays an important role in the analysis of framed structures with curved beams. However, most existing curved beam elements are not accurate enough and still need several or even dozens of elements to accurately describe the behavior of a curved beam with a large subtended angle. To fill this gap, this paper presents a novel geometrically nonlinear curved beam element based on the element-independent co-rotational (EICR) method. The proposed element can simulate a curved beam using only one single element in the analysis and design of most practical framed structures. Moreover, this element is directly derived in a Cartesian coordinate system and can be directly and conveniently used with straight beam-column elements in nonlinear structural analysis. In this manuscript, the derivation of the proposed geometrically nonlinear curved beam element is detailed and several benchmark problems are proposed to verify its accuracy and efficiency.

Superstructure rotation method (SRM) can optimize bridge construction in terms of reducing impacts on traffic, safety and overall budget. This paper focus on the key scientific problems of the swivel arch bridge, and takes the world’s largest high-speed railway swivel arch bridge on soft soil foundation over Hu-Hang highway as the engineering background. Construction technologies of this project including the installation process, design of the traction system and the precision control method are introduced. Optimum design method of tension force of the tie bars which considering 7 different load conditions during the construction process is proposed. As the key element of the construction of swivel arch bridge, a complete design process of the spherical hinge is present in detail. Exact analytical solution to determine the relationship of radial stress and upper load, which based on the solution of concentrated force acting on the half-plane body in the elastic mechanics, has been firstly put forward and compared with the simplified method recommended by codes. Meanwhile, reasonable ranges of geometric and material parameters have been given and elaborate design flows of the spherical hinge have been presented. Besides, overturning resistance checking design of the spherical hinge during the construction process have been presented also, which are particularly instructive for engineers and designers.

Only few studies have been reported on the flexural behavior of steel-ultra high performance fiber reinforced concrete (UHPFRC) composite beams subjected to negative moment. Addressing this limitation, this paper presents the experimental and analytical studies on the steel-UHPFRC composite beam. Two large-scale beams, including one made of normal-strength concrete (NC) slab and another consisted of UHPFRC slab, experienced four-point bending test to investigate their flexural behavior. In this study, the steel girders and NC/UHPFRC slabs were made composite by embedding the stud shear connections in the pockets that were preformed on the precast slabs. The experimental results showed that the use of UHPFRC slab increased the stiffness and improved the crack control capacity of the composite beam. In addition, the full composite action was achieved in both tested beams, evidencing the sufficiency of the stud shear connectors for the tested conditions. The flexural strength and crack width were calculated through simplified analytical approaches. Good agreement was achieved between the measured and computed values.

External prestressing technology has been successfully adopted for enhancing the load-carrying capacity of beams in bridge engineering. Previous studies on the shear behaviour of externally prestressed concrete (EPC) beams mainly focused on the ultimate shear strength. The post-cracking shear behaviour of EPC beams remains unclear. This study aims to investigate the post-cracking shear behaviour of EPC beams. To this end, nine EPC beams with different design parameters were tested to failure. The investigated parameters included the prestressing condition, shear span to depth ratio, shear reinforcement ratio, and bend angle of external tendons. In contrast to reinforced concrete beams, the EPC beams demonstrated shear tension sliding with concrete spalling failure. The applied prestressing increased the concrete shear contribution by 68%. The percentage of the concrete shear contribution out of the total shear strength of the test beams ranged from 45% to 79%. The post-cracking shear strength reserve ability index, defined as the ratio of the shear strength and shear cracking strength, ranged from 1.72 to 2.96 in the EPC beams. A new ductility index, defined as the ratio of the ultimate deflection and the deflection corresponding to first shear cracking, was used to evaluate the post-cracking deformability of EPC beams. The ductility index of the EPC beams ranged from 3.0 to 7.6, indicating considerable post-cracking deformability. The beam’s stiffness at first shear cracking was 39–81% of the beam’s initial stiffness; the beam’s stiffness at the ultimate state was 18–41% of the beam’s initial stiffness. Finally, the current shear provisions were evaluated by the test results.

This paper presents an experimental study on the static behavior of large stud shear connectors embedded in ultra-high performance concrete (UHPC). Test parameters included stud diameter, stud aspect ratio, concrete strength, and concrete slab thickness. Headed studs of two sizes, 22 mm and 30 mm in diameter, were used in this study. Extensive splitting cracks on concrete slab were detected for the normal strength concrete specimen whereas no cracks were found for the UHPC specimen with 30 mm studs, indicating that UHPC matches well with large studs. The shear strength, shear stiffness and ductility of a stud with 30 mm diameter were approximately 15%, 45% and 60% higher than those of a stud with 22 mm diameter, respectively. Stud aspect ratio and concrete slab thickness showed no obvious influence on the static behavior of the test specimens and short stud shear connectors with an aspect ratio of 2.3 could develop full strength in UHPC slabs. An empirical equation taking into account stud diameter was proposed to predict the shear load-slip curve of headed studs. Lastly, the current stud shear strength design provisions were evaluated using the experimental data.

The study provided a systematic evaluation of the pullout behavior of straight and hooked-end steel fibers embedded in ultra-high performance concrete (UHPC) with various angles using a single fiber pullout test. Three steel fibers, including one straight fiber and two hooked-end fibers, were aligned at 0°, 30°, and 45° with respect to the loading direction. The fibers were pulled out from non-fiberous UHPC matrix with a compressive strength of 151.5 MPa. Experimental results showed that when the fiber embedded angle increased from 0° to 30° and 45°, the average bond strengths of straight fibers were increased by 19.2% and 52.9%, while the average bond strengths of hooked-end fibers were increased by 10.3–13.6% and 16.2–26.1%, respectively. The percentage of end hook contribution to total pullout energy ranged from 50% to 56.8%, indicating significant mechanical anchorage contribution. Two types of fiber failure modes, including fiber pullout failure and fracture failure, were found, depending on fiber angles. From Scanning Electronic Microscopy (SEM) observation, interfacial transition zone failure, fiber surface scratching, and matrix failure were identified. Two new indices, namely energy dissipation index and bond strength index, were proposed to evaluate the fiber-matrix bond behavior. It was found that hooked-end fibers with a smaller diameter could be a better choice for structural application according to the proposed evaluation indices. The proposed indices offered an alternative and practical method to assess the fiber-matrix bond behavior.

This paper presents an experimental study on the punching shear behavior of concrete flat slabs partially reinforced with ultra-high-performance concrete (UHPC). The effects of the area and depth of UHPC on the failure mode and punching shear capacity are investigated. Test results indicate that the application of full-depth UHPC at the punching shear area changed the failure mode from a brittle punching shear failure to a ductile punching shear-flexural failure, while the application of partial-depth UHPC at the punching shear area caused brittle punching shear failure. By using full-depth UHPC, the first crack strength and punching shear strength of the slabs were increased by up to 65% and 117%, respectively. Partial-depth UHPC did not increase the first crack strength and punching shear strength. According to the testing results, the optimal application of UHPC in the flat slabs is to use full-depth UHPC within the area enclosed by a perimeter located at a distance equal to the slab thickness away from the column face. A new energy dissipation ductility index is proposed to characterize the post-peak load energy dissipation ability. Finally, an analytical model based on yield line theory is proposed to estimate the punching shear strength of the flat slabs. The proposed model reached a good agreement with the testing results while the current ACI model, Chinese model and fib MC2010 model under-estimated the punching shear strength of the test specimens.

The study provided an experimental and theoretical investigation on the bond behavior of reinforcing bars in ultra-high performance concrete (UHPC) via a series of pullout tests. Test parameters included depth of concrete cover, bar embedment length and bar diameter. Failure mode, crack pattern and load-slip response were recorded and discussed under different test parameters. Test results indicated that inadequate concrete cover depth led to splitting failure while short embedment length resulted in concrete cone failure, corresponding to lower bond strengths. The bond strength increased up to 229.8% and the pullout energy increased 401.4% as the concrete cover depth increased from 0.5d to 2d. The development lengths were recommended to be 6d and 8d corresponding to the concrete cover depth of 2d, 1.5d, respectively. A theoretical bond strength model using fiber–matrix discrete concept was proposed and validated by comparing the calculated values with the test results and 343 test data collected from literature. The average ratios of the calculated results to the test results and collected data were 0.996 and 1.039, with a standard deviation of 0.255 and 0.252. The proposed model established the connection between the meso-scale bond property of fibers and matrix and the macro-scale bond strength of steel bars and UHPC, offering an alternative perspective in understanding the bond performance of steel bars in UHPC.

Lignite chars were prepared in a fixed bed reactor under various oxygen concentrations (0–15 vol%) and pyrolysis temperatures (873 K–1173 K). Characterization techniques such as Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and BET were applied to reveal the impacts of temperature and oxygen concentration on char structure evolution during pyrolysis. Combustion performances of the prepared chars were examined on a thermal gravimetric analyzer, using ignition and burnout temperatures as indexes of char reactivity. On a whole, oxy-pyrolysis char is more reactive than the char derived under inert (N2) atmosphere. Raman analysis indicates that the presence of oxygen during pyrolysis can reduce the extent of char graphitization at high temperatures and favors the removal of oxygen containing groups and aliphatic structures. Pore volume and specific surface area can be improved due to the presence of oxygen in pyrolysis. There is a critical oxygen concentration at high pyrolysis temperatures. Releasing behaviors of sulfur and nitrogen, and their speciation and distributions on the prepared chars were also discussed.

The 5th Nanjing Yangtze River Bridge is a three-tower cable-stayed bridge with a main span of 600 m and a composite cross section consisting of a steel box girder- and precast ultra-high performance concrete (UHPC) deck slab. The precast UHPC slabs are connected using cast-in-place UHPC, and joints between the UHPC slabs are prone to cracking under negative bending moment. This paper investigates the flexural behavior of an innovative dovetail UHPC joint in seven UHPC slabs under negative bending moment. An innovative method using steel wire mesh is presented to enhance the interface between precast and cast-in-place UHPC at the joints. Test parameters of the UHPC slabs included interface treatment method, joint material, reinforcing bar overlapping form, and prestressing level. The steel wire mesh generated fibers that bridge the interface between the precast and cast-in-place UHPC, thus significantly enhancing the mechanical performance of the jointed UHPC slabs: (1) the nominal cracking strength was increased by 2.4 MPa; (2) the post-cracking stiffness was retained at about 80% of the initial stiffness; (3) the ultimate stiffness was retained at about 35% of the initial stiffness; and (4) closely-spaced multiple cracks occurred at the joints. A new ductility index defined as the ratio of the ultimate deflection and the flexural cracking deflection is proposed to characterize the post-cracking ductility. The research findings are useful in understanding and improving the flexural behaviors of UHPC bridge decks subjected to negative bending moment.