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As a new type of composite girders, composite girders with corrugated steel webs and concrete-filled steel tubular (CSW-CFST) truss chords are extensively utilized in bridge engineering. To examine the structural behavior of composite girders with CSW-CFST truss chords subjected to combined flexure and torsion, model tests and finite element analysis (FEA) are employed. Using these efficient tools, the strain distribution, deformation law, failure mode, and bearing capacity of these composite girders subjected to pure torsion and combined flexure and torsion are methodically obtained. The primary objectives are to probe the applicability of existing flexure-torsion relation curves and introduce the calculation method for the bearing capacity of composite girders with CSW-CFST truss chords subjected to combined flexure and torsion. The obtained results reveal that their failure mode is influenced by the initial torsional moment. Further, their bearing capacities due to the applied initial torsional and bending moments can be maximally enhanced by about 21.6% and 6.6%, respectively. The deviation between the predicted bearing capacity by the FEA and that obtained from the tests is less than 8.6%, demonstrating the high accuracy of the FEA model. The contribution of the torsional moment to the flexural bearing capacity is either ignored or underestimated by the existing flexure-torsion relation curves, with a minimum deviation of about 22.3%. By comparing the results acquired by the extended FEA and the calculation method proposed in this paper, it is proved that the proposed calculation method for the bearing capacity of composite girders with CSW-CFST truss chords subjected to combined flexure and torsion may reduce the deviation from 22.3% to 8.3%.

A novel composite structural member, UHPC-encased concrete-filled steel tubular (UC-CFST) column, is proposed in this study to address the shortcomings of the ordinary concrete-encased CFST (OC-CFST) columns. A total of 22 specimens subjected to axial compression loading were tested, including nine UC-CFST stub columns, nine OC-CFST stub columns, and four CFST stub columns. The experimental results showed that the encasing UHPC of UC-CFST columns was less damaged than the encasing ordinary concrete of OC-CFST columns and did not spall when the UHPC was crushed. The UC-CFST stub columns reached their ultimate load-bearing capacity when the encasing UHPC attained the peak compressive strain, which was much greater than that of the OC-CFST stub columns. Compared to the OC-CFST stub columns, the ultimate load-bearing capacity of UC-CFST stub columns improved markedly by 75%–289% and the compressive stiffness increased by 22%–49%, while the ductility decreased by about 50% on average. Furthermore, increasing the area ratio of the encased CFST in the UC-CFST stub columns was unfavorable for the compressive stiffness and load-ultimate bearing capacity. Finally, by comparing the different calculation methods for ultimate load-bearing capacity of OC-CFST columns recommended by Chinese standard CECS 188, American standard AISC 360, Japanese standard AIJ-SRC, and European standard Eurocode 4, it was found that the calculation methods applicable to OC-CFST columns would underestimate the ultimate load-bearing capacity of UC-CFST columns to varying degrees. Thus, a modified calculation formula based on the CECS 188 standard was proposed for accurate prediction of the ultimate load-bearing capacity of the UC-CFST stub columns.

A new type of composite structure, the composite box girder with corrugated steel webs (CSWs) and trusses, is proposed recently. In order to investigate the structural behavior under positive and negative bending moments, flexural tests of the continuous girder were carried out, and the failure modes, deformation patterns, strain distribution, and development of the concrete cracks were investigated. Finite element analysis was conducted to investigate the effect of the range of concrete in the steel tube and the thickness of CSWs on the flexural behavior. The experimental and numerical results show that the test beam has a good ductility and integrity under flexural load. The contribution of CSWs to the flexural bearing capacity is very small and can be neglected. Besides, the plane section assumption is still valid when only top concrete slab and bottom steel tubes are concerned. The concrete filled in bottom steel tubes increases the stiffness and the bearing capacity of the girder. Equations to calculate the flexural bearing capacity under positive and negative bending moments were put forward and then verified with experimental results.

CFST T-joints consisting of a concrete-filled circular chord and a circular hollow section brace have been used in CFST trussed arch bridges. The stress concentration factors (SCFs) of CFST T-joints have been found to be much lower than those of circular hollow section (CHS) T-joints in the existing researches. At present, no parametric formulae have been proposed for SCFs determination for fatigue design of CFST T-joints. In this study, three-dimensional finite element (FE) models of the existing experiments for CFST T-joints were developed to determine the SCFs distribution at the chord-brace intersection under axial force in the brace. After confirming the validity of the FE models by the comparison of calculated SCFs with existing experimental results, they were provided for the parametric analysis to reveal the influence of four non-dimensional parameters, i.e. diameter ratio (β), diameter to thickness ratio of chord (2γ), thickness ratio (τ) and relative chord length (α), on SCFs of CFST T-joints. In total, 212 FE models with different parameters were analyzed under tensile and compressive axial forces. Based on the results of parametric analysis, a series of parametric formulae to calculate the SCFs was proposed for CFST T-joints referring to those for CHS T-joints. The SCFs determined by the formulae showed good agreements with FE analysis results., Engineering Structures, 170, pp.103-117; 2018

A modified curve-approximated hysteretic model for partially concrete-filled steel tube (PCFST) bridge piers is developed based on the previous research work. The proposed model, which consists of a series of quadratic and cubic curves and takes into account the P-Δ effect, pinching behavior in unloading-reloading hysteretic loops, and deterioration of strength and stiffness, can be used to precisely describe complicated hysteretic behavior of cantilever-type PCFST bridge piers. Parameters of this model are calibrated on the basis of quasi-static cyclic test results. To verify the validity of the proposed model, a total of 12 pseudo-dynamic tests were carried out. The detailed comparisons of different seismic performance indices between experimental and numerical results, such as the maximum response displacement, the residual displacement, and the amount of energy dissipation, indicated that the proposed model can be an acceptable complementary and assisting tool for the nonlinear seismic response assessment of PCFST piers.

The evolution of hinged joint structures in Chinese hinged hollow-slab bridges was summarized to study the mechanical performance of hinged joint structures in hinged hollow-slab bridges with gate-type steel bars. Parameter analysis was conducted with the nonlinear finite element method for a hollow slab bridge with a span of 8 m. The failure mode of the hinged joint structure with different parameters, including crack-occurring load and crack distribution, was studied. Countermeasures to improve the hinged joint structure were also discussed. Results showed that adopting a gate-type steel bar at the bottom of the junction surface did not improve the crack-occurring load of the hinged joint, but the load of the full-length crack was improved, and the occurrence of vertical full-length cracks on the junction surface and longitudinal cracks on the hinged joint was delayed. Increasing the diameter of the gate-type steel bar did not enhance the crack-occurring load, the load of full-length cracks on the junction surface, and the final distribution of cracks. Enhancement of the concrete strength did not improve the mechanical property of hollow slab and the junction surface remarkably. By contrast, enhancement of the bond strength of the junction surface improved the crack-occurring load of the hinged joint and reduced the distribution of cracks. Three layouts of reinforcement in the hinged joint and increasing the diameter of the gate-type steel bar, as proposed in existing references, did not fundamentally improve the mechanical property of the junction surface.

Experiment study on dumbbell-shaped CFST X-shaped arches subjected to spatial loads under non-directional loads is carried out. The mechanical behavior and failure mechanism of the arch model under spatial loads are revealed. Test results show that the failure mode of the arch model is the extreme point instability, and the arch model has a low initial geometric imperfection sensitivity. The arch model is mainly bearing compression and out-of-plane bending moment under spatial loads, and the out-of-plane bending moment is the main control factor of the ultimate stability bearing capacity of the arch model.

Previous studies have proven that CFST (concrete-filled steel tube) battened built-up columns (CFST-BBCs) exhibit good hysteresis energy dissipation capacity and deformation capacity under lateral cyclic repeated loading. To further understand the elastoplastic seismic response characteristics of such composite structures under strong earthquakes, two pseudo-dynamic tests of 1/8-scaled CFST-BBC pier specimens were first performed. The acceleration records obtained in the 1995 Kobe Earthquake and the 2008 Wenchuan Earthquake were used to investigate how ground motion intensity, ground motion characteristics, and aftershocks affect the seismic response of the CFST-BBC pier. Meanwhile, an extensive time-history analysis of 17 fiber-based finite element models (FFEMs) under 20 different ground motions was performed to reveal the influence of the ground motion intensity, the same-intensity aftershock, and the main structural parameters on the elastoplastic seismic response of the CFST-BBC pier. Finally, a two-stage checking method suitable for the seismic performance of the CFST-BBC pier under the E1-level frequent earthquake and the E2-level rare earthquake was proposed. Verified by experimental and FFEM analysis results, the proposed checking method can accurately and effectively evaluate the strength and deformation capacity of the CFST-BBC piers under strong earthquakes.

The mechanical behavior of a convex steel box section under axial compression is studied using loading test on reduced scale-model and nonlinear FE analysis, taking into consideration initial geometric deflection and residual stress. The actual bearing capacity of the convex steel section used for the arch ribs of the Yongjiang Bridge is obtained. The difference in critical stress among the stiffened plates is revealed. The influence of width ratio η between upper and lower boxes, stiffened plate width–thickness ratio R R and ratio of stiffener’s relative flexural rigidity to its optimum value γ / γ ∗ on the normalized stress–strain relation of the section are examined. It is found that the bottom plate has the lowest critical stress among all the stiffened plates in the convex section. A smaller width ratio increases the critical stress of the middle plate and hardens the post-buckling behavior. The effect of width ratio on the normalized stress–strain relation of convex section is so small as to be negligible. R R and γ / γ ∗ values influence the critical stress of the convex section and significantly affect the post-buckling behavior. Larger R R and smaller γ / γ ∗ values reduce the critical stress of the cross section. Equations representing the normalized stress–strain relation of the convex section under axial compressive loading are proposed as a function of these influential parameters and their validity is demonstrated through numerical analysis.

The seismic performance of an innovative lightweight bridge with CFST composite truss girder and lattice pier was studied in this paper. Took Ganhaizi Bridge as prototype, a 1:8 scale specimen with two spans and three lattice high piers was designed for multi-shaking tables test. Adopted design seismic wave of prototype, dynamic characteristics, seismic performance and failure characteristics were analyzed. Results indicate that the frequency ratio and the displacement ratio between specimen and prototype are corresponding to similitude relationship. Under transverse or longitudinal excitation, acceleration in lattice zones significantly amplifies, and decreases the acceleration of the deck. It is unnecessary to consider the influence of bi-directional excitations. Displacement on the top of pier is less than the value limitation under design ground motions. The corresponding finite element simulations, using OpenSees, were carried out and the accuracy was verified. The finite element analysis results agree with experimental data. In addition, the plastic hinges were predicted under transverse and longitudinal excitation respectively, revealed that lightweight bridge with CFST composite truss girder and lattice pier has a favorable seismic performance.

In previous research, the authors numerically investigated 212 finite-element (FE) models of concrete-filled steel tubular (CFST) T-joints under axial force in the brace to derive formulae for stress concentration factors (SCFs). The formulations involve four nondimensional parameters: diameter ratio β, diameter-to-thickness ratio of chord 2γ, thickness ratio τ, and relative chord length α. In the current study, the earlier formulation was extended to include four additional loading conditions: in-plane bending (IPB) in the brace, out-of-plane bending (OPB) in the brace, axial compression in the chord, and IPB in the chord. The validity of the new SCF formulae was demonstrated by comparing the SCFs obtained using the formulae with the results of numerical analysis., Journal of Bridge Engineering, 25(1), art.no.06019006; 2020

Fatigue tests on full-scale CHS K-joint models have been conducted, exploring the distribution of hot spot stress, fatigue crack development, and fatigue failure modes. A three-dimensional solid finite element model has been established to carry out a parametric analysis of the main influences on the stress concentration factors for CHS K-joints using the general software MSC.MARC. A novel stress concentration factor method based on the CHS K-joint stiffness has been proposed by combining a theoretical derivation and a regression analysis. The results reveal that the hot spot stress of a CHS K-joint can be obtained with a linear extrapolation. The location of the maximum hot spot stress appears on the crown toe point of the chord and tensile brace intersection welding seam near the chord intersecting line. A fatigue crack in a CHS K-joint belongs to the opening Class I crack category. When the fatigue crack penetrates the full thickness of the chord, the fatigue crack develops rapidly; the fatigue failure of the CHS K-joint belongs to the brittle failure category in the elastic range. A coupling action caused by the geometric parameters is demonstrated to exist in the stress concentration factor of CHS K-joints. Given the current stress concentration factor method for CHS K-joints is based on a regression analysis using a single geometric parameter, this limitation impacts its application in accurately in developing bridge structures. The novel stress concentration factor method encompassing the CHS K-joint stiffness proposed in this paper considers the coupling action on the stress concentration factor caused by the joint geometric parameters, in addition to improving the conservativeness and accuracy in evaluating and calculating the stress concentration factors of CHS K-joints used in bridge structures.

Nonlinear vibration of cables in cable-stayed bridges is usually studied by either a divide-and-conquer approach in which interaction between local motion of the cables and global motion of the bridge is not considered, or a coupled cable-beam system which can only represent a simple structure with few degrees of freedom. A cable finite element is presented in this paper which can account for in-plane and out-of-plane motions of the cable. A cable-beam system with frequency ratio of 1:1:2 is employed to verify feasibility of the cable element in analysing nonlinear vibration of the stay cable. Vibrations of the coupled cable-beam system under harmonic and random loadings are calculated and compared with the available analytical solutions that have been verified experimentally. The results demonstrate that the cable finite element can capture nonlinear vibration, in particular auto-parametric vibration of stay cables under both loading cases. Consequently it can be applied to practical structures with multiple cables.

The objective of this paper is to investigate the characteristics of critical loads for parabolic fixed steel tubular arches. An advanced nonlinearity finite-element program, taking into account the geometric and material dual nonlinearity, is employed. The influence of nonlinearity and initial crookedness on arch critical load is discussed. It is found that the effect of rise-to-span ratio on the critical load of arch is significant. Therefore, a new equivalent beam-column method is proposed for estimating the corresponding in-plane critical loads of arch, in which a buckling factor K1 is employed to consider influence of rise-to-span ratio and a reduction factor K2 to consider the effect of initial crookedness. Pragmatic formulas and tabulated data are provided based on the present different Chinese design codes. It is proved that the presented method is sufficiently accurate to predict the in-plane critical load of parabolic fixed steel arch subjected to compression or to both bending and compression.

This paper examines local vibrations in the stay cables of a cable-stayed bridge subjected to wind gusts. The wind loads, including the self-excited load and the buffeting load, are converted into time-domain values using the rational function approximation and the multidimensional autoregressive process, respectively. The global motion of the girder, which is generated by the wind gusts, is analyzed using the modal analysis method. The local vibration of stay cables is calculated using a model in which an inclined cable is subjected to time-varying displacement at one support under global vibration. This model can consider both forced vibration and parametric vibration. The response characteristics of the local vibrations in the stay cables under wind gusts are described using an existing cable-stayed bridge. The results of the numerical analysis show a significant difference between the combined parametric and forced vibrations and the forced vibration.

This paper focuses on the nonlinear vibrations of stay cables and evaluates the dynamic characteristics of stay cables by using the nonlinear enhanced MECS approach and the approximate approach. The nonlinear enhanced MECS approach is that both the girder-tower vibrations and the cable vibrations including parametric cable vibrations are simultaneously considered in the numerical analysis of cable-stayed bridges. Cable finite element method is used to simulate the responses including the parametric vibrations of stay cables. The approximate approach is based on the assumption that cable vibrations have a small effect on girder-tower vibrations, and analyzes the local cable vibrations after obtaining the girder-tower responses. Under the periodic excitations or the moderate ground motion, the differences of the responses of stay cables between these two approaches are evaluated in detail. The effect of cable vibrations on the girder and towers are also discussed. As a result, the dynamic characteristics of the parametric vibrations in stay cables can be evaluated by using the approximate approach or the nonlinear enhanced MECS approach. Since the different axial force fluctuant of stay cables in both ends of one girder causes the difference response values between two approach, it had better use the nonlinear enhanced MECS approach to perform the dynamic analyses of cable-stayed bridges.

Concrete-filled steel tubular (CFT) arch bridges have been rapidly developing in China since 1990. Research has focused on the static behavior, thermal stress and erection technique, however, and there has been very little research of natural vibrations and dynamic responses of these bridges. Japan's first CFT arch bridge in highway bridges, the Second Saikai Bridge, is now under construction in Nagasaki Prefecture. Furthermore, this bridge has a pedestrian bridge that is suspended under the girder, which is rare. Therefore, the natural vibration properties are examined, and the influence of pedestrian bridge structure on the natural vibration of main bridge is discussed first. Response analysis under a moving vehicle and pedestrian is carried out, and the response characteristics and response level are clarified. The natural vibrations and responses are compared to those of CFT arch bridges that have been constructed in China. Results show the fine performance of both main bridge and pedestrian bridge of the Second Saikai Bridge.

The technology of concrete filled tube (CFT) arch bridges has developed rapidly in China since 1990. More than one hundred CFT arch bridges have been built or are now under construction. However, since the weight of a CFT arch rib is greater than that of a steel rib and the arch action is not effective in the out-of-plane direction, the seismic safety of CFT bridges should be evaluated. This paper examines nonlinear seismic responses of the Second Saikai Bridge, which is the first highway bridge in Japan to be a CFT arch bridge. This bridge has a main span length of 240 m. The natural vibration characteristics of this bridge are discussed using a three-dimensional FE model. A nonlinear seismic analysis is performed using the strong ground motions observed in the Hyogo-ken Nanbu Earthquake of Japan. The nonlinear seismic characteristics and seismic safety of this bridge are examined in detail by subjecting the bridge to earthquakes in the out-of-plane direction, longitudinal direction and combined out-of-plane and longitudinal directions. It is found that the analysis should consider the combined out-of-plane and longitudinal excitations.

In conventional non-linear seismic analyses of cable-stayed bridges, the non-linear characteristics of the girders, stay cables and towers are considered. The non-linearity caused by cable loosening should also be considered because a large axial force fluctuation is generated in the cables of a prestressed concrete (PC) cable-stayed bridge that is subjected to strong seismic motion. In this paper, the possibility of the cable loosening in a PC cable-stayed bridge is discussed by using a cable model that can express the cable loosening. Furthermore, the effect of the cable loosening on the responses of the cables, girder and towers is evaluated using the mean value for three seismic waves. Numerical analytic results imply that the cable loosening appears in the bottom cables of the multi-cable system and the dynamic response of the bridge is slightly increased.

Analysis and results for in-plane non-linear antisymmetric responses of a cable, supported at the same level, through bifurcation under in-plane symmetric sinusoidally time-varying load are presented. The non-linear equation of the in-plane motion of the cable is solved by a Galerkin method and the harmonic balance method. From the computed results the frequency range, where the antisymmetric response occurs, varies with the sag-to-span ratio of the cable and is broad in the particular sag-to-span ratios. The second unstable region is important compared with the principal unstable region. Strong coupling between symmetric and antisymmetric modes is observed in the unstable regions for the particular sag-to-span ratios.

A cable cannot resist the axial compressive force that may be induced during large amplitude vibrations. In this paper, the effect of cable loosening on non-linear vibrations of flat-sag cables is discussed by using the finite difference method that can express cable loosening. In the present method, flexural rigidity and damping of the cable are considered in the equations of motion of a cable in order to handle the numerical instability. The effect of cable loosening is evaluated explicitly in the present paper. Furthermore, non-linear vibration properties are evaluated for various parameters under periodic and step vertical loading. The effect of cable loosening on response under vertical periodic time-varying load is small and it is possible for the sag-to-span ratio to roughly equal the ratio for modal transition. The loosening under the vertical step loading in the direction opposite to the gravity appears at almost the same sag-to-span ratio.

This paper examines local parametric vibrations in the stay cables of a cable-stayed bridge. The natural frequencies of the global modes are obtained by using a three-dimensional FE model. The global motions generated by (1) sinusoidal excitations using exciter, (2) a traffic loading, and (3) an earthquake are analyzed by using the modal analysis method or the direct integration method. The local vibration of stay cable is calculated by using a model in which inclined cable is subjected to time-varying displacement at one support during global motions. This paper describes the properties of the local vibrations in stay cables under these dynamic loadings by using an existing cable-stayed bridge.

During the recent construction activity in China, concrete filled steel tubes (CFST) typology is innovatively applied in beam bridges with CFST composite truss girders and CFST lattice piers. The subject is Ganhaizi Bridge, one of the most unusual viaducts, has a total length of 1811m and is an experimental truss bridge that uses steel tubes for nearly the entire structure. This paper presents the study on nonlinear seismic performance of Ganhaizi Bridge. Seismic response characteristics, piers yielding order and internal force redistribution effect in plastic scope are investigated through a simplified fiber finite element model based on the second unit of this bridge. Take extreme edge strain of CFST columns as criterion, the horizontal most adverse seismic input direction for this curved bridge is perpendicular to the bearing connection on both ends, the influence of vertical ground motion should be simultaneously considered. After turn into plastic stage with increasing peak ground acceleration (PGA), the main stress direction of lattice piers and composite piers are both in plane, axial forces increase less than seismic, while displacements increase greater. Bending moments of high piers increase greater than short piers, which is expected to facilitate seismic performance of the whole bridge.

Reliability of a bridge is possible to be assessed by loading tests and finite element analysis. In this study, static loading tests were conducted to assess reliability of an existing concrete filled steel tubular (CFST) arch bridge according to Chinese code. Its static strains, deflections and crack widths were measured in static loading tests by arranging some vehicles at determined locations. Moreover, FE analysis was also conducted by employing the software of ANSYS. The results of measured and FE analysis were compared. The loading tests showed that integral stiffness of arch ribs is smaller than design values, and measured strains are larger than design values. The cross girders satisfy stiffness requirements, whereas out of the stress requirements. Cracks in deck enlarged by test loading and rarely recovered after unloading. The hangers have no loose appearance, they are basically stable.

The stability properties and dynamic performances of the Hechang Bridge, which is a concrete filled steel tubes (CFST) arch bridge in Fujian, China are examined in this paper. The differences of stability and dynamic performance between basket type arch rib and parallel type arch rib are also discussed using three-dimensional finite element models. Furthermore, the influence of inclined angle for basket-type arch rib on stability and dynamic performance is also studied in this paper. It can be used for reference of similar bridges in selecting the bridge type, the bridges main structures, and the static and dynamic analyses that need to be performed.