Bolted joints in steel structures are generally subject to combined actions. The research on ultimate capacity of bolted joints under combined tension and shear actions, twin shear actions, and combined tension-twin shear actions is relatively limited. The aim of this paper is to calibrate the fracture locus of grade 10.9 bolts using the mesoscale critical equivalent plastic strain (MCEPS). We use ductile fracture simulation to numerically evaluate the ultimate resistance of bolts subject to multiaxial loading and compare the results with the current design standards. The results show that predictions for grade 10.9 bolts subject to multiaxial loading in Chinese code GB 50017 and American code AISC-360 are not on the safe side, while predictions in European code EN1993-1-8:2005 are slightly on the conservative side. We propose two modification factors to improve prediction of bolt strength subject to multiaxial loading; namely the multiaxial loading factor for shear resistance ξ_v and the multiaxial loading factor for tensile resistance ξ_t.

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In addition to general shear loading, perfobond shear connectors (PBLs) also undertake tensile uplift forces at the interfaces between steel parts and concrete components. The tensile behavior of PBLs is as significant as the shear behavior to the safety of composite bridge structures. For further evaluating the combined shear-tensile response of PBLs, it is necessary to first investigate the tensile mechanism of PBLs. Accordingly, uplift tests with three specimens under static and cyclic loading were performed to investigate the tensile behavior of PBLs. The test results showed that the breakouts of concrete blocks dominated the failure of PBLs in tension. The residual separation was negligible when the tension force was below 30 percent of the capacity. Subsequently, a detailed finite element (FE) model for the uplift test was established and validated based on the test results. The strain path inside concrete blocks was presented as a cup shape, whose dimension was relevant to the embedded depth of holes and the boundary conditions. Further, 360 FE models with varying hole diameters, perforated rebar diameters, embedded depths, and concrete strength were conducted to explain the tensile mechanism and provide databases for the theoretical analyses. The results showed that the diameter of perforated rebars was irrelevant to the tensile capacity and stiffness of PBLs, while both the tensile capacity and stiffness increased with the embedded depth and concrete strength. Besides, the tensile stiffness was also related to the hole diameter. Consequently, according to the forms of existing tensile capacity expressions for headed studs and Mindlin's solution, the equations for the tensile capacity and stiffness of PBLs were derived.

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The prestressed concrete girder with corrugated steel webs is one of the most promising steel-concrete hybrid structures applied to highway and railway bridges, owing to its excellent mechanical properties and efficient material utilisation. Composite bridges with corrugated steel webs (CBCSWs) have undergone rapid development in China since 2005, resulting in remarkable technical progress in many aspects. A state-of-the-art review of CBCSWs in China is presented. Based on data collected for over 90 CBCSWs built in China during the years 2005-2018, characteristics relating to bridge span, structural type and construction methods are comprehensively analysed. Some mechanical issues regarding the design and construction of typical CBCSWs are elaborated to understand fully their structural performance and promote their development. Furthermore, a few representative CBCSWs are expounded in relation to their innovative structural design and construction techniques; their respective characteristics are highlighted. Finally, several conclusions are drawn and future research directions are predicted: the CBCSW is a competitive bridge solution when 80-200 m main spans are required; advanced materials, innovative structure types and advanced construction methods making good use of corrugated steel web are the source of its development. The experiences in this study can serve as a useful base for constructing more excellent and impressive CBCSWs.

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Failure of bolts exposed to tension is generally avoided in the design of bolted connections due to the smaller deformation capacity of bolts than the connected plates. This is one of the reasons why few studies focus on the tensile failure behaviour of bolts. However, failure behaviour of bolts is essential for the advanced finite element analysis especially relevant to the deformation capacity and failure mode of bolted connections. This paper presents a numerical study on the fracture of partially threaded bolts under tension incorporating damage models, with which the failure mechanism of bolts can be better understood. The post-necking stress–strain relation is firstly calibrated to describe the behaviour of bolt threaded parts at large deformation. Then, direct tension tests on partially threaded bolts with different threaded lengths within the grip are modelled using ABAQUS with the explicit solver. Two criteria for fracture are investigated: the void growth model (VGM) and a model proposed by Bao and Wierzbicki (BW). The former is adopted to simulate the tensile fracture of bolts and the latter is used to predict the thread stripping failure. Results indicate that bolt failure modes of tensile fracture and thread stripping can be well predicted by combining the calibrated post-necking stress–strain relation and a suitable fracture criterion in the analysis. It is revealed that the large plastic strain in the threads introduced by thread rolling process is a major reason for the thread stripping failure.

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Many bolted connectors were proposed for use in steel-concrete composite structures over the past few decades. This is because using bolted connectors could make the assembly and disassembly of steel-concrete composite structures more convenient and reusing the dismantled structural components could also improve structural sustainability. Lots of static and fatigue experimental tests on steel-concrete bolted connectors were conducted but detailed finite element simulations including fracture of bolted connectors were rarely reported. This paper presents a series of simulations of a demountable steel-concrete bolted connector in push-out tests, which was proposed and reported by the authors of this paper before. Damage models of bolt and concrete materials are incorporated in the simulations to better understand the behaviour of the bolted connector and the failure mode of the push-out tests. Direct tension tests on bolts are simulated to calibrate the stress-strain relationship of bolt material and assumed pure shear tests on bolts are modelled to validate the fracture criterion used in the simulations. Results of modelling push-out tests indicate that the friction force at the steel-concrete interface accounts for a part of shear resistance of the bolted connector in push-out tests conducted. The load-slip curves and the fracture of bolts in push-out tests can be approximately predicted by incorporating damage models of bolt and concrete materials and considering an appropriate friction coefficient. The effects of concrete damage model, clearance in bolt hole, and pretension of short bolt on the shear performance of the bolted connector are discussed at last.@en

Numerical analyses incorporating appropriate damage models provide an opportunity to predict the strength and deformation capacity of steel structures. This paper presents a practical calibration for the ductile damage model of S355 and high-strength steel S690Q, S700MC, S960Q based on tensile coupon test results. A combined linear and power expression is adopted to calibrate the post-necking damaged stress–strain relations of the investigated steels, upon which the undamaged stress–strain relations are estimated further. Damage initiation criterion is based on the Rice-Tracey model and damage evolution law is related to the calibrated damaged stress and the estimated undamaged stress. Fracture of the tensile coupons is modelled using a critical damage variable. Tensile coupon tests on the investigated steels are modelled in ABAQUS with the explicit solver. Results show that combining the proposed post-necking stress–strain relations and ductile damage model generates very good predictions for strain localization and final fracture of the tensile coupons. Numerical engineering stress–strain curves agree well with the experimental results. It also indicates that high-strength steels are more susceptible to damage than S355. The damage variable of S960Q is about 2 times as large as that of S355 from the onset of necking to the final fracture.

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For long-span composite bridges with corrugated steel webs, the encased concrete near the intermediate support section increases the weight of the girder, reduces pre-stressing efficiency, and causes difficulties in the construction process. The authors in the companion paper [1] proposed a corrugated steel web with vertical or/and horizontal stiffeners to replace or shorten the length of concrete encasement. In parallel with experimental study described in the companion paper, this paper further investigates the shear performance of proposed stiffened corrugated steel webs by numerical and analytical methods. Firstly, finite element (FE) models considering material nonlinearity, welding residual stress, and geometric imperfection were established and validated against the experimental results. Then the effects of web thickness, corrugation depth, height and thickness of stiffeners on shear strength and failure modes were analyzed based on the validated FE models. Finally, both experimental and numerical shear strength were used to evaluate the applicability of existing calculation methods proposed by different scholars to predict the shear capacity of stiffened corrugated steel web. The comparisons reveal that calculation methods proposed by Hassanein & Kharoob [2] and Leblouba et al. [3] predict the shear capacity of pure corrugated steel web more accurately, and all existing calculation methods underestimate corrugated steel web with vertical stiffeners. Therefore, the analytical model for accurately predicting shear strength of stiffened corrugated steel web need to be developed, which will be investigated in subsequent studies.@en

To predict the flexural strengths of steel girder-concrete abutment connections in fully integral abutment bridges with perfobond connectors, this paper analytically and numerically investigates the ultimate flexural behavior of these connections. A nonlinear finite element model was first established and validated against experimental results. Subsequently, another 89 nonlinear finite element models with different connector quantities, connector arrangements, abutment widths, and shear-span ratios were studied. An analytical calculation method considering the moment contribution of perfobond connectors and the shear force distribution on perfobond connectors at ultimate was then proposed, verified against experimental and numerical results, and was compared with current calculation methods. Results show that, compared with current methods, the proposed method predicts the flexural strengths of the connections with better accuracy, with the average predicted-actual ratio being 0.96 and the coefficient of variation being 0.09. The flexural strengths of girder-abutment connections are significantly affected by girder embedded length, abutment width, and the quantity and arrangement of perfobond connectors. The flexural strengths are higher when connectors are set close to the girder end. When increasing the quantity of perfobond connectors, the flexural strengths of the connections could increase by 86% at most. With the same connector quantity, the flexural strengths could vary 20% with different connector arrangements.

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To improve the shear behavior and design applicability of rubber ring perfobond connectors (RPBLs), a new rubber ring that aims to make the shear stiffness of RPBLs controllable was proposed. Firstly, the conceptual design and configuration of the new rubber rings were presented and discussed. Subsequently, finite element (FE) models for modified push-out tests of new RPBLs were established based on the validated modeling method. The initial shear stiffness is dominated by the horizontal projected contact area between hole walls and concrete dowels. γ is defined as the ratio of the horizontal projected length of hollows to the diameter of holes. The shear stiffness of new RPBLs is about 35%, 60%, and 82% of the shear stiffness of PBLs when γ equals 0.25, 0.5, and 0.75, respectively. Employing the new rubber rings with varying central angles on conventional PBLs is feasible to obtain the required stiffness for RPBLs. Further, the effects of the number of sectors, the size of side wings, the central angle of hollows, the offset angle, and the thickness of rubber rings were analysed. Based on the numerical results, the proper thickness of side wings is no larger than 2 mm. The thicker side wing could reduce the confinement effects provided by surrounding concrete on concrete dowels, resulting in a drop of the yield load of new RPBLs. The number of sectors is suggested to be no less than 6 so that the shear behavior of new RPBLs is irrelevant to the offset angle. Besides, the shear stiffness is not related to the thickness of rubber rings. To improve the yield load of RPBLs and obtain the moderate recovered stiffness, the thickness of rubber rings is recommended as 2 mm. Finally, the expression for the shear stiffness of new RPBLs was proposed.@en

Perfobond shear connectors (PBLs) are increasingly applied in steel-concrete composite structures. The out-of-plane (lateral) shear behavior of PBLs is still unknown to researchers and designers, although the connectors undertake considerable out-of-plane shear forces in some applications. Thus, push-out tests with three specimens were first conducted to investigate the lateral shear performance of PBLs and further used to validate the corresponding numerical models. The test results show that perforated rebars and concrete dowels are irrelevant to the lateral shear capacity, while they can reduce the separations and improve the ductility. Secondly, parametric FEA (finite element analysis) models for the push-out tests were built and validated based on the test results. The plastic strains in concrete mainly develop at the regions close to the fillet welds. Further, 144 extended FEA models with varying height, length, and thickness of perfobond plates and concrete compressive strength were conducted to reveal the lateral shear mechanism of PBLs. By enlarging the plate height, the lateral shear capacity slightly increases, while the shear stiffness remains as constant. The shear capacity and stiffness increase with the plate length and thickness, as well as the concrete compressive strength. Finally, based on the existing shear capacity equations for channel and angle connectors, and the theory of elastic foundation beams, the expressions for the lateral shear capacity and stiffness of PBLs were put forward. The proposed equations agree with the results of the parametric study.

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Design optimization of fiber-reinforced polymeric (FRP) composite products is essential to facilitate their applications in engineering structures. For bridge structures, the main design optimization goals are the reduction of FRP material consumption and the structure weight, which aim to reduce the initial construction cost and achieve a longer bridge span. Compared with conventional steel–concrete composite bridges, FRP-steel composite bridges possess more design variables and more complex design process, which necessitate the simplified optimization models. This paper aims to propose a two-scale design optimation method for FRP bridge deck on the steel girder. The macro behavior of the pultruded FRP composite bridge deck is analyzed. Regarding the micro level, the equivalent properties of pultruded GFRP lamination are calculated by combining micromechanics and classical lamination theory (CLT). The above-mentioned macro pultruded GFRP bridge level and the micro fiber/resin level were bridged based on the assumption that the micro-component effective homogenized strain equals to the corresponding macro strain. The two-scale lamination optimization of pultruded GFRP bridge deck is finally achieved by finding optimized two-scale design variables that can achieve the minimum bridge weight or the lowest initial construction cost with all listed constraint requirements satisfied. A pultruded FRP deck supported on equally-spaced steel girders was selected as a case study to show how to obtain the optimized two-scale parameters by using this proposed optimization method. The optimized results of the top flange thickness, t_u, the bottom flange thickness, t_l, the web height, h_w, and the web thickness per meter, t_w, are 46.02 mm, 45.86 mm, 300.0 mm and 37.42 mm, respectively. Results also showed that the optimized ratio of the 0°-lamina, 45°-lamina, and the 90°-lamina are77.9%, 17.1%, 5.0%. The optimized fiber volume fraction is 65.2%.

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Steel-concrete composite structures have been extensively used in building, bridges, and other civil engineering infrastructure. Shear stud connectors between steel and concrete are essential in composite members to guarantee the effectiveness of their behavior in terms of strength and deformability. This study focuses on investigating the shear stiffness of headed studs embedded in several types of concrete with wide range of compressive strength, and their effects on the elastic behavior of steel-concrete composite girders were evaluated. Firstly, totally 206 monotonic push-out tests from the literature were reviewed to investigate the shear stiffness of headed studs embedded in various types of concrete (NC, HPC, UHPC etc.). Shear stiffness of studs is defined as the secant stiffness of the load-slip curve at 0.5Vu, and a formulation for predicting defined shear stiffness in elastic state was proposed, indicating that the stud diameter and the elastic modulus of steel and concrete are the main factors. And the shear stiffness predicted by the new formula agree well with test results for studs with a diameter ranging from 10 to 30 mm in the concrete with compressive strength ranging from 22.0 to 200.0MPa. Then, the effects of shear stiffness on the elastic behaviors of composite girders with different sizes and under different loading conditions were analyzed, the equations for calculating the stress and deformation of simply supported composite girders considering the influence of connection's shear stiffness were derived under different loading conditions using classical linear partial-interaction theory. As the increasing of shear stiffness, the stress and deflection at the most unfavorable section under partial connected condition tend to be those under full connected condition, but the approaching speed decreases gradually. Finally, the connector's shear stiffness was recommended for fully connection in composite girders with different dimensions under different loading conditions. The findings from present study may provide a reference for the prediction of shear stiffness for headed studs and the elastic design of steel-concrete composite girder.

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To investigate the influence factors of the ultimate bearing capacities of Q420 steel U-rib stiffened plates subjected to axial compression, four model tests with different dimensions were conducted, and ultimate bearing capacities, instability modes and failure mechanism were discussed. The results showed that the instability modes of Q420 U-rib stiffened plates can be classified into three sorts, which are local buckling failure, global buckling failure and hybrid buckling failure. When the ratio of bending stiffness between U-rib and plate decreases, the instability mode changes from local buckling to global buckling or hybrid buckling. JRA underestimates the ultimate bearing capacity of U-rib stiffened plate, while AASHTO predicts more accurately.

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The headed stud connectors are widely used in a variety of innovative engineering applications of the infrastructure sector. The fatigue life of headed studs is significantly affected by the residual stress introduced from welding procedures. It is very important to develop a reliable numerical method to predict the fatigue performance of headed stud connectors. In this paper, the efficiency of fatigue life prediction, using the nominal stress (NS) and the hot spot stress (HSS) methods based on finite element simulation, is compared. The limitation using the NS method to predict the fatigue life of studs is discussed in this paper. The efficiency of the HSS analysis technique is validated by the fatigue test results in the literature.

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This paper proposes an innovative use of corrugated steel plates as the webs of the crossbeam in the tower of a suspension bridge to get better seismic performance. Three 1/4-scaled models of composite beam with corrugated steel webs considering different shear-span ratio were fabricated to conduct quasi-static test. The structural behaviors including failure modes, hysteretic curves, ductility, strength and stiffness degradation, energy dissipation capacity, deformation recovery ability, shear force distribution and strain responses were investigated. Test results indicate that the specimen with large shear-span ratio presents ductile flexural failure, and the hysteretic curve is stable and plump with slight pinching, which indicates good energy dissipation performance. However, the specimen with small shear-span ratio fails due to brittle shear buckling of corrugated steel web, showing remarkable pinching phenomenon and poor hysteretic behavior. With the increase of shear-span ratio, the load-carrying capacity and lateral initial stiffness are reduced, but the ductility and energy dissipation ability are improved significantly. The energy dissipation capacity of such composite beam is better than that of the RC structures, the strength degradation is slight for the specimen with a proper shear-span ratio, and the deformation recovery ability is good for all test specimens. The corrugated steel web carries about 80% of the shear force and shear stress uniformly distributed along the web height. The test results demonstrate that the composite beam with corrugated steel web of a reasonable shear-span ratio can be applied in anti-seismic structure with superior energy dissipation performance. In addition, simplified formulas were proposed to evaluate the flexural strength and shear buckling strength of a composite beam with corrugated steel webs, the calculated results agree well with the test results, verifying the accuracy of these proposed formulas.

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This paper presents experimental and analytical studies on the shear behavior of GFRP perforated connectors (GPC)embedded in concrete. A series of 26 pultruded GPC specimens were fabricated and tested under pull-out load. The experimental variables included the effects of plate thickness, plate hole's radius and penetrating rebars. Concrete dowel failure and GFRP shear-out failure were the two main failure patterns of GPC specimens. GFRP failure occurred in specimens with a thin plate, and ultimate strength is mainly affected by the hole's radius. The specimens with concrete dowel failure presented more ductile than the specimens with GFRP shear-out failure. The shear stiffness of GPC was determined based on load-slip curves. Finally, the ultimate strength equations of GPC incorporating the stress concentration in the GFRP plate and the restraint effect of penetrating rebar were proposed based on the test results. Good agreement between experimental and theoretical results was achieved. A critical thickness of GPC plate was proposed to guarantee sufficient strength and ductility.

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Steel-concrete composite high bridge pier has been applied increasingly in China and around the world. Most applied steel type in the composite piers are H-shaped steel and steel pipe, while seldom research or practice is associated with angle steel. This paper conducted parametric study on the composite column with equal-leg angle steel and aimed to investigate the ultimate load and displacement ductility of the composite columns with different parameters. The parameters include the type of shear connector (stud and perfobond connectors), the type of structural steel (H-shaped steel and angle steel), steel-plate hooping ratio, shear-span ratio, and axial compression ratio. Finite element analysis was conducted for each specimen, which incorporated the concrete confinement effect, as well as the inelastic behavior of concrete, structural steel, and longitudinal and transverse steel bars. The equal-leg angle steel composite column was found to have slightly higher strength and displacement ductility than H-shaped steel composite column. The increase of steel-plate hooping result in larger strength and displacement ductility for the composite column, and the increase of shear-span ratio and axial compression ratio decrease the displacement ductility. Research results suggest stud and perfobond shear connectors should be applied as axial compression ratio being larger than 0.2 and 0.3, respectively. This paper provides reference for research and engineering practice of the concrete encased angle steel composite columns and bridge piers.@en

We present an innovative prefabricated composite box girder with corrugated webs and concrete-filled steel tube slab to prevent cracking in the web and reduce the self-weight, which is suitable for long-span structures. We carried out systematic experimental and analytical studies to investigate the structural performance, including the loading capacity and dynamic properties of a prefabricated composite box girder bridge before and after erection. Firstly, we tested a prefabricated composite girder with a single box section before erection under monotonic loading, measuring vertical deformation, flexural strain on the slabs, and shear strain on the corrugated steel webs, and evaluating the load-carrying capacity and stiffness reduction. Secondly, we conducted field live-load tests, including a calibration test and a dynamic test, on a composite bridge with twin prefabricated box girders. We hired four-axle heavy trucks for a calibration test to explore the static responses in terms of displacement, bending strain on the slabs, and shear strain on the corrugated steel webs. In the dynamic tests, we carried out a modal test using ambient vibration method and a moving load test in order to determine the dynamic behavior, which involves natural frequencies, the mode shapes, and the dynamic load factor (DLF). Based on the test results, the structural performance was evaluated by the AASHTO bridge rating process. All the findings from the load-carrying capacity test at ultimate state, calibration and dynamic load tests at service state in this study may provide a reference for the design and construction of such type of bridges.@en

In order to evaluate the shear performance of sand-coated glass fiber-reinforced polymer (GFRP) perforated connectors (SCGPC) embedded in concrete, 8 pull-out tests were conducted. Finite element (FE) analysis considering GFRP failure and cohesion between GFRP and concrete of SCGPC were conducted for parametric analysis. Effects of surface treatment, hole's radius, embedment length, and multi holes were examined. The test and theoretical analysis revealed that the strength of SCGPC is considerably larger than GFRP Perforated Connector (GPC). The stiffness of SCGPC is determined by the adhesion between concrete and GFRP. When GFRP plate's thickness is less than the critical thickness, the embedment length plays a major role in the strength of SCGPC. When embedment length is less than the effective bond length, the shear strength of SCGPC is governed by both the adhesion and GPC's shear capacity; otherwise, the strength of SCGPC is governed by the adhesion strength. Furthermore, an empirical equation was suggested to predict the shear strength of SCGPC. The equation involves the failure mechanism of both bond and GPC and deals the strength of SCGPC into two ranges according to the embedment length. Good agreement was achieved between the strength prediction by the suggested equation and the parametric analysis result.@en

In this paper, analytical and numerical homogenization methods are proposed to effectively simulate the macroscopic characteristics of a pultruded composite lamina. A continuum damage model was implemented via user material subroutine to model fiber failure, while the Mohr-Coulomb plastic criterion is employed to model matrix damage. In order to simulate the damage of the fiber-matrix interface, the relationship between traction and displacement is established. The proposed theoretical and numerical models were verified by tensile, compressive, and shear test results. The outcomes of this study indicated that both theoretical, numerical prediction values agree well with experimental verification results confirming the validity of the proposed methodology in providing a reliable reference for structural design of pultruded fiber reinforced polymeric (FRP) composite structures.

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