Ultra-high Performance Concrete Steel Research Articles

Study of Fatigue Performance of Ultra-Short Stud Connectors in Ultra-High Performance Concrete

Steel–UHPC composite bridge decking made of ultra-high performance concrete (UHPC) has been progressively employed to reinforce historic steel bridges. The coordinated force and deformation between the steel deck and UHPC are therefore greatly influenced by the shear stud connectors at the shear interface. Four fatigue push-out specimens of ultra-short studs with an aspect ratio of 1.84 in UHPC were examined to investigate the fatigue properties of ultra-short studs with an aspect ratio below 2.0 utilized in UHPC reinforcing aged steel bridges. The test results indicated that three failure modes—fracture surface at stud shank, fracture surface at steel flange, and fracture surface at stud cap—were noted for ultra-short studs in UHPC under various load ranges. The fatigue life decreased from 1287.3 × 104 to 24.4 × 104 as the shear stress range of the stud increased from 88.2 MPa to 158.8 MPa. The UHPC can ensure that the failure mode of the specimens was stud shank failure. Based on the test and literature results, a fatigue strength design S–N curve for short studs in UHPC was proposed, and calculation models for stiffness degradation and plastic slip accumulation of short studs in UHPC were established. The employment of ultra-short studs in the field of UHPC reinforcing aging steel bridges can be supported by the research findings.

Experimental investigation on static mechanical performance of grouped-stud shear connectors in steel–UHPC composite beams

The static mechanical properties of grouped-stud shear connectors in steel–ultra-high-performance concrete (UHPC) composite beams are rarely investigated. In this study, the static mechanical properties of grouped-stud shear connectors in steel–UHPC composite beams are investigated via experiments and numerical simulations. Seven sets (14 specimens) of push-out tests are conducted by varying the parameters, including the concrete type, stud diameter, stud vertical spacing, and number of stud rows. The test results show that the shear bearing capacity of grouped-stud shear connectors increases by 27.5% as the stud diameter increases from 19 to 22 mm, by 13.2% compared with that of grouped-stud shear connectors in steel–UHPC and steel–normal concrete (NC), and by 5.8% when the stud vertical spacing increases from 125 mm (5.68d) to 200 mm (9.09d). However, the shear bearing capacity of the grouped-stud shear connectors remain almost unchanged when the number of stud rows is changed from two to four. The effects of stud diameter, stud tensile strength, stud vertical spacing, stud length, the cover thickness of the stud head, and stud transverse spacing on the shear bearing capacity of the grouped-stud shear connectors are investigated via numerical simulations. The results show that the stud diameter, stud tensile strength, and stud vertical spacing significantly affect the shear bearing capacity of the grouped-stud shear connectors, whereas the stud length, the cover thickness of the stud head, and stud transverse spacing exert almost no effect. Based on experimental and numerical analyses, an equation for predicting the shear bearing capacity of grouped-stud shear connectors in steel–UHPC is proposed and validated based on experimental and numerical results.

Flexural performance of a prefabricated steel–UHPC composite deck under transverse hogging moment

This paper aims to investigate the flexural performance of a prefabricated steel–ultra-high-performance concrete (UHPC) composite deck (PSUCD) consisting of an orthotropic steel deck (OSD) and a reinforced UHPC layer under transverse hogging moment. Ten full-scale steel–UHPC composite slab specimens were subjected to four-point flexural tests, which varied shear connectors, steel reinforcement, and wet joint interfaces. The results showed that all specimens exhibited typical flexural failure with excessive opening of critical cracks in the UHPC layer. The specimens utilizing notched perfobond strip connectors (NPBLs) with perforating rebars had higher nominal cracking strength (maximum crack width of 0.05 mm) and ultimate capacity by 15% and 27%, respectively, compared to those using studs. The perforating rebars in NPBLs improved post-cracking performance, increasing nominal cracking strength and ultimate capacity by 14% and 16%, respectively. The lateral interfaces of rectangular-tooth-shaped wet joints resulted in a local weak link in PSUCDs, leading to a 17% decrease in nominal cracking strength, and as much as 26% if interfacial roughening was omitted. Increasing the diameter of surficial reinforcement from 10 mm to 12 mm improved nominal cracking strength and ultimate capacity by 20% and 17%, respectively. Considering the influence of wet joint interfaces, prediction models for maximum crack width, nominal cracking strength, and ultimate capacity were developed and validated for the performance design of PSUCDs under transverse hogging moment.

Grouped rubber-sleeved studs–UHPC pocket connections in prefabricated steel–UHPC composite beams: Shear performance under monotonic and cyclic loadings

Prefabricated steel–ultra-high-performance concrete (UHPC) composite beams (PSUCBs) with grouped stud–UHPC pocket connections (GSUPCs) are a successful attempt of UHPC in bridge engineering, which offers significant advantages in accelerating on-site construction, enhancing structural performance, and improving environmental benefits. However, the uneven steel–concrete interfacial shear stresses distribution caused by the insufficient deformability of ordinary studs (OSs) in UHPC may result in the premature stud failure in large interfacial slippage regions. To address this issue, rubber-sleeved studs (RSSs) that wrapped rubber-sleeves around the stud roots were introduced to improve ductility and reduce the stiffness of connectors. However, the shear performance of grouped RSSs embedded in UHPC remains unclear, which hinders their application in practices. Against this background, systematic experimental and numerical studies were conducted to investigate the monotonic and cyclic shear performance of grouped RSSs–UHPC pocket connections. The results indicated that wrapping rubber-sleeve could increase the ultimate slip capacity and remained sufficient shear resistance, demonstrating great potentials of grouped RSSs–UHPC pocket connections in PSUCBs. Increasing the rubber-sleeve thicknesses and height effectively improved the ultimate slip capacity and deformation recovery, but led to the significant plastic deformation accumulation and cyclic stiffness degradation. Finally, design recommendation on rubber-sleeve configuration rationalization, ultimate shear resistance and load–slip relationship predictive models were provided.

Experimental and numerical analyses on the shear behavior of grouped single-embedded-nut high-strength bolts in steel–ultra-high-performance concrete composite slabs

Incorporating utilization of ultra-high-performance concrete (UHPC) slabs and single-embedded-nut high-strength bolts (SENHSBs) can optimize the structural performance and construction efficiency of steel–concrete composite slabs. Typically, SENHSBs are required to be densely arranged in groups to transfer sufficient interfacial shear forces in complex stress regions. However, the investigations focused on the performance of grouped SENHSBs embedded in UHPC slabs is limited. Against this background, 15 push-out tests were conducted, accompanied by comprehensive numerical analyses, to study the shear behaviors of grouped SENHSBs in steel–UHPC composite slabs. The test results demonstrated that the failure model was governed by SENHSB fracture. Specimens with the longitudinal spacing of twice the bolt diameter exhibited overlapping crushing areas in the UHPC slabs. The longitudinal spacing significantly influenced both the ultimate shear and ultimate slip capacities of the grouped SENHSBs, whereas the transverse spacing significantly affected both the shear stiffness and maximum slip of grouped SENHSBs. Additionally, the per bolt ultimate shear capacities of the specimens with multi-layer SENHSBs were significantly lower than those with single-layer SENHSBs. The SENHSBs located at various positions experienced different shear stresses, and the deviations became more significant as the longitudinal spacing decreased. Consequently, a formula was proposed to evaluate the strength reduction factor of the grouped SENHSBs. Furthermore, accurate models were developed for determining the ultimate shear capacity and load–slip relationship of grouped SENHSBs in steel–UHPC composite slabs.

Numerical and experimental study of a segmentally prefabricated orthotropic steel–ultra-high-performance concrete composite deck for long-span cable-stayed bridges

Utilizing the high strengths, toughness, and durability of ultra-high-performance concrete (UHPC), a segmentally prefabricated orthotropic steel–UHPC composite deck (POSUCD) system has been developed for long-span cable-stayed bridges. The deck system combines an orthotropic steel deck (OSD) with a reinforced UHPC layer using notched perfobond strips (NPBLs). The UHPC layer is prefabricated onto the OSD of the girder segment in the factory to form the POSUCD. After the precast UHPC layer is cured, the girder segments are transported to the bridge site and assembled. The precast UHPC layers are then connected via transverse wet joints before tensioning stay cables. Against the background of the Danjiangkou Reservoir Bridge with a main span of 760 m, finite element (FE) analysis was conducted to examine the stress state and flexural tests were carried out on local full-scale models to verify the feasibility of POSUCD. The results show that the prefabricated UHPC layer reduces the maximum static compressive stress of the steel deck in the girder system by 21%, and the stress ranges at fatigue-prone details of the steel deck are decreased by 28%–90% compared to traditional OSDs with asphalt overlay. Since the prefabricated UHPC layer helps withstand dead axial load in the main girder, the high compressive strengths of UHPC can be utilized more effectively than in deck systems with UHPC only used as a cast-in-situ overlay to resist vehicular wheel loads. The transverse wet joint interfaces were identified as the weakest aspect of the POSUCD, whether under tension or compression; however, their nominal flexural strengths along the longitudinal direction meet the required design standards. The shear resistance of NPBLs was also well confirmed by the minimal interfacial slip on the specimen when it reached the ultimate capacity under positive bending moment.

Experimental and numerical study on shear performance of grouped bolt–UHPC pocket connections under static loading

Prefabricated steel–ultra-high-performance concrete (UHPC) composite beams using grouped single embedded nut bolts (SENBs) in full-depth precast slabs are a competitive alternative for accelerated bridge construction (ABC), with advantages such as shortening on-site construction time, improving structural quality, and conveniently dismantling deteriorated components. In this study, a systematic experimental and numerical study was conducted to investigate the shear performance of grouped bolt–UHPC pocket connections. The experimental results indicated that a dense arrangement of SENBs led to a slight reduction in shear capacity (less than 5%) and ductility. Increasing the number of bolts in the pockets can effectively improve the shear performance of the connections. Significant reductions in the per-bolt ultimate shear capacity and initial shear stiffness were observed for specimens with multi-row bolts compared to their single-row counterparts. In addition, specimens with grouped bolt–UHPC pocket connections achieved a considerable shear capacity, low shear stiffness, and better slip capacity than those with monolithic casting slabs. Based on the validated finite element models, extensive parametric studies were carried out. Accordingly, a conservative recommendation of 4d (d is the bolt diameter) was suggested as the minimum bolt spacing in both the longitudinal and transverse directions. Furthermore, more accurate formulae were developed to predict the ultimate shear resistance and load–slip relationship of the grouped bolt–UHPC pocket connections in prefabricated steel–UHPC composite beams.

A simplified analysis method for long-span suspension bridges within the deck overlay retrofitting process from asphalt to UHPC

The steel-ultrahigh performance concrete (UHPC) lightweight composite deck (LWCD) is increasingly adopted by in-service steel bridges to address the fatigue cracking issue for orthotropic steel decks (OSDs) and the premature damage issue for asphalt overlays. While for in-service long-span suspension bridges that need to be retrofitted by LWCDs, the response of the UHPC layer in casting is complex. Within the UHPC casting process, the moment of the stiffening girder changes continuously as the self-weight of the stiffening girder changes in casting, and the change of moment will produce strains in the UHPC portion set earlier; in other words, the UHPC portion cast latter will produce strains in the UHPC portion cast earlier. If the resultant tensile strains are too high, the UHPC layer may crack within the casting process, which should be avoided. In this paper, a simplified analysis method, based on the linearized deflection theory, was proposed to rapidly obtain the response of long-span suspension bridges in retrofitting without significantly compromising the accuracy of the analysis results. A new solving method based on exponential functions was proposed, which is simpler than the commonly used hyperbolic function-based method. The proposed method was implemented as computer codes in Matlab and verified through two examples: a single-span suspension bridge and a three-span suspension bridge. The simplified analysis method was used to perform a detailed analysis for the Yichang Yangtze River Expressway Bridge (YYREB), a 960-m-long single-span suspension bridge in China, for which the existing asphalt overlay was replaced by an LWCD in 2021. In the analysis, three cast sequences were considered for the UHPC layer, i.e., from end to end, from mid-span to ends, and from ends to mid-span. It is revealed that the mid span-to-ends cast sequence produces the minimum tensile strain in UHPC, so the cracking risk of UHPC could be well controlled by using this casting method. Thus, the mid span-to-ends cast sequence was adopted by the YYREB within the deck overlay retrofitting process from asphalt to UHPC.

Key Design Parameters Analysis and Calculation Theory Research on Bending Performance of Steel–UHPC Lightweight Composite Deck Structure

This paper aims to study the influence of key design parameters (e.g., reinforcement ratio, cover thickness, stud spacing, and thickness of the ultra-high-performance concrete (UHPC) layer) on the longitudinal and transverse bending performance, as well as the cracking load and ultimate bearing capacity calculation theory of steel–UHPC lightweight composite deck (LWCD) structure. Four transverse bending tests and four longitudinal bending tests on steel–UHPC composite plates and steel–UHPC composite beams were conducted, respectively. The refined finite element models of components with different key design parameters based on ABAQUS were established. The influences of different key design parameters on the transverse and longitudinal flexural behaviors (e.g., load-mid-span displacement curve, cracking stress, stiffness, elastic limit load, critical slip load, ultimate bearing capacity and ductility) were compared and analyzed in detail. The ultimate bearing capacity can be improved by increasing the thickness of UHPC layer and the reinforcement ratio of longitudinal reinforcement, and reducing the cover thickness and the spacing of studs. According to the longitudinal bending characteristics of the steel–UHPC lightweight composite deck structure, the calculation formulas for the cracking load and the ultimate bearing capacity of the steel–UHPC composite beam are proposed, and the calculated values are in good agreement with test results (the errors are basically within 10%), which is convenient for practical engineering applications.

Aerodynamic performance evaluation of steel-UHPC composite deck cable-stayed bridges with VIV countermeasures

The steel-ultrahigh performance concrete (UHPC) composite girder makes the bridge deck thinner and more streamlined, but their effects on the aerodynamic performance of cable-stayed bridges are unclear. With the developed equivalent girder analysis method, the overall aerodynamic performance (e.g. vortex-induced vibration (VIV), flutter, aerostatic and buffeting performance) of a steel-UHPC composite girder cable-stayed bridge with various VIV countermeasures are systematically evaluated by conducting a series of wind tunnel tests and numerical calculation. The results show that the developed equivalent girder analysis method could simplify the sectional model design of the composite girder for wind tunnel tests. Only the guide vane removal cannot suppress the torsional VIV responses among various combinations of guide vanes removal, while the two VIV countermeasures (e.g. the removal of outside railing cornerstones, the removal of four guide vanes and outside railing cornerstones) could reach about 76% and 72% of the torsional VIV amplitudes, respectively. Although two VIV countermeasures could slightly reduce the critical flutter wind speed, their torsional divergence critical wind speeds are much larger than the limited design requirement. Moreover, the removal of four guide vanes and outside railing cornerstones has the capacity of improving the aeroelastic and buffeting performance of the bridge, as the best overall aerodynamic performance.

Shear performance of high-strength friction-grip bolted shear connector in prefabricated steel–UHPC composite beams: Finite element modelling and parametric study

As a competitive alternative for accelerated bridge construction (ABC), prefabricated steel–ultra-high-performance concrete (UHPC) composite beams containing high-strength friction-grip bolt (HSFGB) shear connectors offer numerous advantages, including reduced on-site construction time and ease of replacing/removing deteriorated components. However, the failure mechanism of HSFGBs in UHPC remains unclear due to the lack of internal stress analysis, which hinders the design of these innovative composite beams. To clarify the shear performance of HSFGBs in prefabricated steel–UHPC composite beams, an effective finite element model (FEM) considering the non-linearities of materials and geometry was developed through ABAQUS. Based on the experimentally verified model, the internal stress transfer mechanisms of HSFGBs and the failure mechanism of precast UHPC were revealed. According to the extension parametric analysis results, a stronger HSFGB presented better shear performances in terms of ultimate shear strength, initial shear stiffness and slip capacity. Adopting oversized holes with appropriate bolt-to-hole clearance can improve the constructional efficiency without considerable strength and stiffness reduction. HSFGBs with low bolt pretension exhibited unfavorable initial shear stiffness, while smaller slip capacity in high bolt pretension conditions. A smaller ductility was observed as the steel beam tensile strength and slab concrete strength increased. Additionally, the ACI 318–19, Eurocode 3, and AASHTO LRFD specifications underestimated the shear strength of HSFGBs, whereas the Eurocode 4 presented acceptable predictions in determining the ultimate shear capacity of HSFGBs in prefabricated steel–UHPC composite beams.

Fatigue Performance of Steel–UHPC Composite Bridge Deck System with Large Longitudinal Rib

A critical problem in the development and application of orthotropic steel bridge decks (OSDs) is fatigue cracking, which is determined by the deck’s structural system, mechanical characteristics, load, and external environmental factors. The development of bridge deck systems with high fatigue resistance is increasingly gaining interest in the field of bridge deck design. An effective method for improving the fatigue life of OSDs is the introduction of an ultra high performance concrete (UHPC) layer to enhance OSD’s stiffness. In this study, two types of experiments were performed to investigate the transverse and longitudinal fatigue behaviors of a steel–UHPC composite bridge deck with large longitudinal ribs. The experiments show that the application of a 70-mm-thick UHPC layer effectively reduces the stress intensity at key fatigue details in OSDs. The influence of the UHPC layer on the OSD fatigue performance was evaluated by experiments and finite element analysis. After the formation of microcracks on the UHPC surface layer, the composite bridge deck system continued to exhibit adequate fatigue performance. Moreover, the effects of damage accumulation on the UHPC layer and studs in transverse specimens were evaluated.

Study on Shear-Lag Effect of Steel–UHPC Ribbed Slab Composite Structures Using Bar Simulation Method

Recently, Ultra-High Performance Concrete (UHPC) has attracted increasing attention in civil engineering. Numerous steel–UHPC composite structures have been constructed around the world. The proper consideration of the shear-lag effect has a significant influence on the safety of structures. In view of the shear-lag effect of steel–UHPC ribbed slab composite structure (SU-RSCS) in the elastic stage, a theoretical calculation model based on the bar simulation method is first developed. Then, the feasibility and accuracy of that are verified using both experimental data and numerical simulation. Moreover, many factors (including width-to-span ratio, the ratio of rib height to UHPC layer thickness, the ratio of rib width to rib spacing, and the number of transverse ribs) are parametrically investigated to further investigate the structural shear-lag effect using the proposed method. In addition, the orthogonal analysis is applied to determine the sensitivity of each parameter to the shear-lag effect. The parametric interactions are also considered. At last, the comparison between calculation results of the proposed method and specifications are discussed. The results show that the proposed approach can accurately predict the shear-lag effect on SU-RSCSs in the elastic stage. It is also found that the width-to-span ratio has a great influence on the structural shear-lag effect, while the number of transverse ribs has no significant influence on that.

Fatigue performance of prefabricated coarse aggregate ultrahigh-performance concrete deck subjected to negative bending moment

The concrete deck of a steel–concrete composite bridge is vulnerable to cracking under negative bending moments of fatigue loads. Thus, this work performed fatigue tests on the prefabricated decks to study the influences of the curing method and stress level on the fatigue behavior of the prefabricated ultrahigh-performance concrete (UHPC) deck in an assembled steel–UHPC composite beam under negative bending moments. A numerical simulation was further conducted to investigate the behavior of the decks with joints. The results indicate that the effect of the curing method on the fatigue performance of reinforced UHPC decks is not as pronounced as that on their static performance. The prefabricated UHPC decks exhibit excellent fatigue performance, and fatigue cracks do not form until 13 million loading cycles when the upper fatigue limit is near the breaking load. On the other hand, the deck with a joint has a substantially lower fatigue cracking resistance than the prefabricated ones. The maximum fatigue crack width of the deck with a joint is 0.08 mm at low stress amplitudes. As a result, even though the UHPC has high fatigue performance, further joint reinforcing is recommended.

Tensile behavior of a prefabricated Steel–UHPC composite deck system with notched perfobond strips

This paper proposes a prefabricated steel–ultra-high-performance concrete (UHPC) composite deck (PSUCD) system equipped with notched perfobond strips (NPBLs) for long-span cable-stayed bridges. Compared with the use of an ultra-thin UHPC overlay, the proposed deck system better leverages the high compressive strength of the UHPC. Seven full-scale composite panel specimens with varying details of joint interfaces and shear connectors are subjected to tensile tests. The experimental results reveal that compared with a monolithic UHPC layer, the tensile strengths of the UHPC layer at the initial and nominal cracking (corresponding to a maximum crack width of 0.05 mm) are reduced by 47 % and 64 %, respectively, when flat joint interfaces are introduced and by 16 % and 40 %, respectively, when the interfaces are rectangular-tooth-shaped. The higher steel reinforcing ratio derived from the use of NPBLs placed across the joint interfaces leads to a distinct improvement in the post-cracking performance of the wet joints. Considering the weakened tensile strength and sectional area ratio of the joint interfaces, a prediction method for the crack widths at the wet joints in PSUCD systems is developed, and its prediction accuracy is verified.

Experimental and Numerical Study on the Shear Performance of Short Stud Shear Connectors in Steel–UHPC Composite Beams

Steel–ultra-high-performance concrete (UHPC) composite beams offer numerous advantages, such as structural self-weight reduction, bending stiffness improvement, and tensile cracking limitation in slabs. However, few studies have focused on the shear performance of short stud shear connectors in steel–UHPC composite structures. To this end, push-out tests were carried out to evaluate the effect of slab thickness, stud diameter, and casting method on the failure mode, load–slip relationship, ultimate shear strength, shear stiffness, and ductility. The test results indicate that by increasing the slab thickness from 50 to 75 mm, the stud shear capacity and initial shear stiffness were improved by 11.38% and 23.28%, respectively. The stud shear capacity and initial shear stiffness for specimens with stud diameters of 25 mm were 1.29 and 1.23 times that of their 22-mm-diameter counterparts. In addition, adopting precast UHPC slabs could achieve comparative shear resistance (94.91%) but a better slip capacity (108.94%) than those containing conventional monolithic cast slabs. Based on the experimental results, a finite element (FE) model was established to reflect the plastic behavior of the tests and the damage process in the short stud shear connectors. Based on the validated FE model, a parameter study was then performed to further explore the influence of the stud diameter, stud tensile strength, steel beam tensile strength, monolithic slab concrete strength, precast slab concrete strength, and shear pocket concrete strength on the shear performance of short studs in steel–UHPC composite structures.

Behavior of short-headed stud connectors in orthotropic steel-UHPC composite bridge deck under fatigue loading

The short-headed stud connectors play a critical role on the interaction of the orthotropic steel deck (OSD) and the ultra-high performance concrete (UHPC) layer in orthotropic steel-UHPC composite bridge deck. In this paper, the fatigue behavior of these short-headed stud connectors was experimentally investigated in a beam test. The failure modes of the short-headed stud connectors were identified and classified into 5 types. The fatigue test results were analyzed by linear regression analysis neglecting run-outs and treating run-outs as failure respectively. On the other hand, the maximum likelihood estimation (MLE) approach was used to shape the S-N curve by considering the influence of run-outs. Additionally, the push-out and beam fatigue test data were compared, and the push-out test presented a relatively conservative result. Last, the applicability of existing specifications on design guidelines regarding the short-headed stud connectors design in orthotropic steel–UHPC composite bridge deck is discussed, and a design S-N curve with 95% survival probability is proposed.

Design and Mechanical Properties of Steel-UHPC Lightweight Composite Decks

Orthotropic steel decks (OSDs) have been widely used in long-span bridges due to their advantages of being lightweight, having high capacity, and allowing rapid construction. However, due to the insufficiency of local stiffness of OSD, fatigue cracking and pavement damage have been common problems of OSDs worldwide. It seriously affects the safety and durability of long-span bridges. Therefore, to solve this problem, this paper introduces an innovative steel ultrahigh-performance concrete (steel-UHPC) lightweight composite deck (LWCD). LWCD can reduce the fatigue stress of the conventional OSD by up to 80% and extend the fatigue life to twice the design requirements. Furthermore, engineering practices in China have proven that LWCD can effectively reduce manufacturing costs and maintenance costs throughout the whole life cycle of the structures. Thus, to provide references for design and maintenance of long-span bridges, this paper introduces the structural design, construction techniques, joint construction design, repair methods, and economic benefits of LWCD in detail. Furthermore, numerical simulations and laboratory tests are introduced in this paper to validate the superiority of LWCD.

Push-Out Behavior of Short Headed Stud Connectors in Steel-Ultra High Performance Concrete Composite Deck

A steel-ultra high performance concrete (UHPC) composite deck has good fatigue performance while the thin UHPC slab leaves a very limited space for the connector configuration. This is actually crucial to achieve the composite action. Current literatures concerning the short stud behavior are still limited for a general mechanism understanding. Therefore, a series of push-tests containing 15 specimens were conducted for investigating the mechanical behavior of short studs with various diameters and lengths in UHPC composite deck. And a parametric FEM analysis with nonlinear material constitutions was conducted as well for the bearing performance understanding. The push-out tests showed the shear fracture near stud roots is the leading dominant failure mode, and a longer stud length might introduce a higher percentage of stud shank bending deformation. It explained longer stud length could be helpful to improve the shear strength of stud in UHPC. Meanwhile, the shear stiffness of the push-out specimens were all increased with a larger stud diameter or length. On the other side, the analysis results showed that a pull-out failure could happen when the stud length was less than 25 mm in UHPC and the failure mode of stud could also be affected by the concrete strength. In addition to the tests and analysis, the safety redundancies of strength evaluations of short stud in UHPC based on several civil codes were discussed in terms of the comparison works.

Precast steel—UHPC lightweight composite bridge for accelerated bridge construction

In this study, a fully precast steel—ultrahigh performance concrete (UHPC) lightweight composite bridge (LWCB) was proposed based on Mapu Bridge, aiming at accelerating construction in bridge engineering. Cast-in-place joints are generally the controlling factor of segmental structures. Therefore, an innovative girder-to-girder joint that is suitable for LWCB was developed. A specimen consisting of two prefabricated steel—UHPC composite girder parts and one post-cast joint part was fabricated to determine if the joint can effectively transfer load between girders. The flexural behavior of the specimen under a negative bending moment was explored. Finite element analyses of Mapu Bridge showed that the nominal stress of critical sections could meet the required stress, indicating that the design is reasonable. The fatigue performance of the UHPC deck was assessed based on past research, and results revealed that the fatigue performance could meet the design requirements. Based on the test results, a crack width prediction method for the joint interface, a simplified calculation method for the design moment, and a deflection calculation method for the steel—UHPC composite girder in consideration of the UHPC tensile stiffness effect were presented. Good agreements were achieved between the predicted values and test results.