Ultra-high Performance Concrete Deck Research Articles

Flexural Behavior of the Composite Girder of a Prestressed Segmental UHPC Channel and a Reinforced Conventional Concrete Deck

The present study was conducted to clarify the flexural behaviors of the Composite Girders of a Prestressed Segmental Ultra-High-Performance Concrete (UHPC) Channel and a Reinforced Conventional Concrete Deck (PSUC-RCCD). The girders can be used as bridge superstructures with the advantages of structural efficiency, cost-effectiveness, and easy construction. A total of five specimens were tested. Three of them were PSUC-RCCD specimens, including two semi-segmental girders (the channel beams were composed of five segments with dry-joints) and one integral girder (the channel beams were integral ones without dry-joints). The two other specimens were P-UHPC girders composed of PSUC and UHPC deck slabs; one was semi-segmental and the other was integral. The flexural behaviors of the specimens were investigated, including the load-displacement curves, crack distribution, cracking moments, and ultimate flexural capacity. The study compared the influence of the segment number and deck material on the flexural behaviors of semi-segmental girders and introduced and validated methods for calculating the cracking moment and flexural capacity of both semi-segmental and integral sections in PSUC-RCCD and P-UHPC girders. The results show that the entire loading process of all the specimens can be classified into the elastic phase, the cracks development phase, and the failure phase. Compared to the integral girders, the number of segments has little effect on the flexural behavior of the semi-segmental girders, but it has a significant effect on the cracking moments. The cracking moments of the semi-segmental girders is only 0.58~0.60 of the integral girders. Reducing the strength of the deck slab by changing the material from UHPC to CC does not significantly affect their flexural behaviors. Based on the test results, this work proposes a method for predicting the cracking moment and flexural capacity of the semi-segmental girders, the results of which fit well with the test results, and it is applicable in the structural design of such members.

Flexural behavior and crack width prediction of UHPC slabs reinforced with FRP bars

This paper aims to investigate the effects of FRP-bar configurations on the flexural behavior of the FRP-reinforced ultra-high-performance concrete (UHPC) deck slab and to propose the calculation method of crack width. Firstly, flexural tests were performed on six FRP-reinforced UHPC slab specimens with varying bar diameters, reinforcement ratios, cover thickness, and slab thicknesses. The load-deflection responses, load-FRP strain relations, and cracking behavior are measured and discussed. The results show that under service loads, the maximum crack widths of all specimens are around 0.03 mm–0.04 mm, which is significantly less than the permitted 0.5 mm in international codes for FRP-reinforced structures. At similar reinforcement ratios, a small FRP-bar diameter with a corresponding reduced bar spacing increases the ultimate capacity and energy dissipation ability. The effects of FRP-bar configurations are minor under service loads, while beyond these loads decreasing the bar diameter is beneficial for reducing the bar strain and crack width. Subsequently, by developing a practical calculation method of the stress of FRP bar embedded in UHPC slab and calibrating the bond coefficient between FRP bar and UHPC against test data, an engineer-friendly calculation method of crack width is proposed. Comparisons between predicted and experimental results indicate the proposed method is capable of producing accurate and safe predictions. The results may give guidance to designers on the appropriate FRP-bar configurations and the control of crack width for the FRP-reinforced UHPC deck slab.

Flexural Behavior of Ultra-High Performance Concrete (UHPC) Deck with Joints subjected to an Improved Steel Wire Mesh (SWM) Treatment

Prefabricated Ultra-high performance concrete (UHPC) decks are often connected using UHPC wet joints to create the overall deck structure. The UHPC deck is, nevertheless, made weak by the fiber discontinuity at the contact interface. In this study, the fiber at the interface was made to serve as a bridge using an embedded steel wire mesh, and experiments were utilized to determine how the contact between the fiber and the steel bar affects the flexural behavior. The results show that the fiber significantly affects the ductility and flexural strength without reinforcement. The combined action of the fiber and reinforcement of the reinforced specimen somewhat increases the flexural capacity and ductility. The flexural capacity of decks with joints was finally calculated using three different ways, and it was found that the method that simplifies the tension and compression zones into rectangles is the most appropriate.

An Analytical Model to Evaluate Short- and Long-Term Performances of Post-Tensioned Concrete Box-Girder Bridges Rehabilitated by an Ultrahigh-Performance Concrete Overlay

Potentially unfavorable stress redistributions could occur in post-tensioned concrete box-girder bridges upon deck rehabilitation by an ultrahigh-performance concrete (UHPC) overlay. The reason for such redistributions is that the deck forms an integral part of the load-resisting mechanism so that deck rehabilitation, namely, the process of removing the deteriorated deck and casting a fresh UHPC overlay, may cause large stress redistributions in the box girder. In addition, the significantly different shrinkage behavior between the freshly cast UHPC deck overlay and the old existing concrete deck below would result in restrained stress in the UHPC–old concrete interface. Therefore, how to evaluate the stress redistributions and the potentially unfavorable stresses in the box girder resulting from construction operations and the incompatible shrinkage is a crucial issue. Here, we propose an analytical model to assess the short- and long-term performances of the concrete box girder during and after deck rehabilitation. The analytical model was verified by using finite-element models incorporating the staged construction simulation and time-dependent behavior of materials. The model can be easily established and calculated with a great amount of time-saving compared with finite-element modeling, and it applies to different types of post-tensioned concrete box-girder bridges. The analytical model involves the balancing-load concept and the age-adjusted effective modulus method (AEMM). The balancing-load concept in the short-term analysis is to account for the prestressing force, and the AEMM in the time-dependent analysis is an effective tool to determine how stresses and strains vary with time due to the creep and shrinkage of a UHPC deck overlay. A parametric study was then conducted based on the analytical model, which involved the thickness of the deck layer to be rehabilitated and the addition of steel reinforcement in the new UHPC deck overlay. Analysis results indicated that pronounced tensile stresses developed in the UHPC deck overlay, which resulted from the restraint of the free shrinkage of the UHPC overlay by the subjacent concrete deck. An increase in the thickness of the newly cast UHPC deck overlay resulted in a decrease of the tensile stress in the UHPC deck overlay, and a rehabilitation thickness of 3.8–5.1 cm (1.5–2.0 in.) was deemed appropriate for the selected bridge according to the analysis.

Fatigue behavior of orthotropic composite bridge decks without cutout at rib-to-floorbeam intersection

The composite bridge panel consisting of an orthotropic steel deck with no extended cutout at the rib-to-floorbeam (RF) intersection and an ultra-high performance concrete (UHPC) rigid layer was proposed, which can simplify the manufacture process and enhance economic benefit. Refined finite element models were established to analyze the stress response of fatigue-prone details, and the approach of variable thickness rib was proposed to achieve an infinite fatigue life. The effect of critical geometric parameters on fatigue performance of RF joint was further investigated, and the parameter combinations with infinite fatigue life were determined. The results show that the rib-to-deck (RD) joint indicates infinite fatigue life, and the stiffness of panel meets the requirements of specification. There is a significant stress raiser at RF joint, and Dong's structural stress reveals that the surface stress at rib side is dominated by bending stress. The effects of the thicknesses of UHPC layer and deck plate on the stress are not significant. Increasing the thickness of the rib belly as well as decreasing the floorbeam thickness and spacing can reduce the stress range of rib side at RF joint, and the 10 mm thick floorbeam is preferable. The UHPC layer can be 50 mm if the rib with variable thickness is utilized, while the UHPC is required to be 60 mm and the floorbeam spacing is 2.5 m if the rib with uniform thickness is adopted.

Experimental investigation and design optimization on flexural behavior of new UHPC deck panel with longitudinal ribs reinforced by steel plates

Due to high strength and superior durability, ultra-high performance concrete (UHPC) is usually used in bridge deck panels to reduce self-weight and improve the anti-cracking capacity. In this study, two schemes of the UHPC deck panel with longitudinal ribs reinforced by steel plates were investigated basing on the Binzhou Yellow River Bridge, including the design considerations and advantages. The experiments were conducted to investigate the flexural behavior of this UHPC deck panel. The experimental results showed that the steel plate can improve the anti-cracking performance and stiffness of the deck more effectively compared to conventional measures of using steel bars. Cracks developed at the position where headed studs were placed due to the weakening of cross-section by high studs. Specimens failed with the appearance of the slightly compressive crack. In addition, the experimental test was simulated by finite element (FE) model in software ABAQUS. The cracking position, load-displacement relationship and strain response of testing specimens were verified by the FE model. For the design purpose, a numerical method was established to analyze flexural behavior including the stiffness, ultimate capacity and strain. The prediction results agreed well with the test results. Further, a parameter analysis was performed and it was clear that the narrow and high rib scheme provided superior flexural properties. Compared with UHPC tensile strength, the steel plate thickness had a more significant effect on the stiffness and ultimate capacity for the specimens. Finally, the segmental FE models were developed for the Binzhou Yellow River Bridge to obtain the actual stress state of the new UHPC deck. The calculation results indicated that the maximum longitudinal nominal stress in the UHPC deck was 7.6 MPa. In addition, when the diaphragm spacing was between 3.0 m and 5.0 m, the longitudinal stress would increase by about 12% with the diaphragm spacing increasing by 0.5 m. The comparisons between the actual stress and experimental results ensured the feasibility of the design.

Experimental Study on Flexural Performance of HSS-UHPC Composite Beams with Perfobond Strip Connectors

In order to explore the flexural performance of high-strength steel (HSS)/ultrahigh performance concrete (UHPC) composite beams, a total of six HSS-UHPC composite beams with varying levels of interfacial shear connectivity, arrangements of perfobond strip connectors (PBL), and variable thicknesses of concrete decks were fabricated and tested. The failure mode, flexural stiffness, load-deflection curve, strain history, and interfacial slippages obtained from the composite beams are presented and discussed. Experimental results indicated that despite the lightweight feature of such a hybrid system, the HSS-UHPC composite beams exhibited high flexural stiffness and favorable ductility. As the level of shear connectivity decreases, the bending resistance of HSS-UHPC composite beams decreases, while the beams’ ductility exhibits slight enhancement. The PBL arrangement has crucial effects on the behavior of HSS-UHPC composite beams, and the beams’ ductility was improved by approximately 48.9% by alternating uniformly distributed PBLs to a nonuniform distribution pattern. Experimental results also highlighted the influence of the UHPC deck thickness on the flexural performance of the composite beams. As compared to an 80.0 mm-thick UHPC deck, the 100.0 mm-thick UHPC deck witnessed increases in bending stiffness, yield moment, and ultimate resistance of the composite beam by 19.8%, 22.8%, and 14.6%, respectively. Comparisons between the results obtained from the tests and analytical procedures for predicting HSS-UHPC composite beams resistances were performed to assess the feasibility of existing design approaches. Results of the study confirmed that equations recommended by GB 50017-2017 have favorable accuracy in calculating the bending resistance of HSS-UHPC composite beams with uniformly distributed PBLs, while for HSS-UHPC composite beams with nonuniformly distributed PBLs, both the AASHTO LRFD and Ban et al. equations are recommended.

Evaluation of shear lag effect in HSS-UHPC composite beams with perfobond strip connectors: Experimental and numerical studies

In order to evaluate the shear lag effect of high strength steel (HSS)-Ultra high performance concrete (UHPC) composite beams with perfobond strip connectors (PBLs), this study involved the preparing and testing of six HSS-UHPC composite beams with different shear connections, deck width-to-thickness ratios, and deck width-to-span ratios. Failure mode, load-deflection curve, load-slip response, and stresses distribution of the HSS-UHPC composite beams were presented and discussed. Experimental results indicated that uniform elastic stresses in the UHPC deck cross-section were observed, and the stress distribution became uneven as the composite beam entered the plastic stage. Under a load of 0.3Mu, the bending stress at the cross-section top center of UHPC deck was 5.3% larger than that at the edges, and this stress discrepancy went up to 9.4% as load approached 0.9Mu. To gain insight into the plastic performance of the tested beams, the finite element (FE) model was further established for the composite beams. Numerical results indicated that the sectional stress hysteresis coefficient (λ) at L/4 near loading point was briefly similar to that of the mid-span in elastic stage, and the stress unevenness increased as the shear connection degree dropped. As the connection degree decreassed from 1.02 to 0.89 and 0.76, the λ of the investigated beams were magnified by 2.7% and 6.7%, respectively. Results also showed that the shear lag effects degraded as deck width-to-thickness ratio increased. The λ for the beams using width-to-thickness ratios of 4.50 and 4.09 were 13.3% and 18.6%, both smaller than that using the ratio of 5.63. Moreover, as the width-to-span ratio increased from 0.20 and 0.24, the stress hysteresis effect of HSS-UHPC composite beams barely varied.

Flexural behavior of UHPC joints for precast UHPC deck slabs

This study aims to experimentally investigate the flexural behavior of ultra-high-performance concrete (UHPC) joint connection for precast UHPC deck slabs. Twelve full-scale jointed UHPC deck slabs were tested and discussed with respect to their failure modes, load-displacement response, ductile behavior, and cracking characteristics. The experimental variables included shape of the joint connection, steel reinforcement diameter, restraining condition of the precast UHPC slab, and joint interface roughness. The experimental results showed that all specimens exhibited a flexural failure with yielding of steel reinforcement, local UHPC crushing at the top surface, and excessive opening of the flexural crack, but exhibited varying locations of the critical crack between the tests. In comparison to the integral casting detail, the rectangular joint had a lower cracking resistance, post-cracking stiffness, and flexural capacity as well as higher ductility, whereas the T-shaped joint led to a relatively higher cracking resistance, stiffness, and flexural capacity as well as lower ductility. Both joint shapes showed little influence on the specimens’ pre-cracking stiffness. In addition, increasing the steel reinforcement diameter not only improved the flexural capacity of the UHPC joint connection but also improved the cracking resistance (including the cracking load, the load at the crack width of 0.05 mm, and the crack width propagation rate). Moreover, the mechanical performance of the jointed UHPC slabs with different restraining conditions in the precast UHPC slab was similar. Furthermore, improving the interface roughness at the precast UHPC slab is in favor of increasing the cracking resistance, but played little effect on other mechanical characteristics. The present main outcomes might provide a reference for future flexural design on the precast UHPC deck slab with the UHPC joint connection.

Numerical analysis of bridge deck rehabilitation by ultra-high-performance concrete (UHPC) overlay

Rehabilitating the deteriorated deck of post-tensioned concrete box-girder bridges by ultra-high-performance concrete (UHPC) overlay is studied in this paper. Three post-tensioned concrete box-girder bridges in California were selected for the deck overlay analysis. Rehabilitation construction procedures for each bridge were described, including the practical lane closure and traffic re-routing. Detailed finite element models were established incorporating the staged construction modeling of the rehabilitation process, the time-dependent properties for existing concrete and prestressing tendon, and a “double-layer” modeling technique for the simulation of the deck. The time-dependent curves and equations of a specified UHPC were fitted based on experimental data, including creep, shrinkage, and elastic modulus, and this particular mix has been assumed in the FE analysis. How the thickness of the deck layer to be replaced affected the stress distributions in the UHPC overlay and the existing box girder was parametrically studied. Results indicated that stress variations in the existing box-girder were acceptable during the deck rehabilitation construction, but significant tensile stresses were developed in the newly placed UHPC deck overlay. Shrinkage-mitigation measures, such as adding the shrinkage-reducing admixture (SRA), should be considered during the placement of the UHPC overlay to control the shrinkage-induced tensile stress. Steel reinforcement may be adopted in the negative bending moment region to resist the flexural tensile stress by the live loads. The rehabilitation thickness of 3.8–5.1 cm (1.5–2.0 in.) is deemed appropriate for the bridges selected in this study.

Structural Behaviors of a Low-Profile Steel Plate–Reinforced UHPC Deck Panel with Longitudinal Ribs

Abstract This paper proposes a lightweight low-profile steel plate-reinforced ultrahigh-performance concrete (UHPC) deck panel with only longitudinal ribs as an alternative to traditional bridge de...

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.

Experimental Investigation of Bending Behavior of Reinforced Ultra-High-Performance Concrete Decks

Ultra-high-performance Concrete (UHPC) has a wide range of potential civil engineering applications, owing to its excellent mechanical properties and durability. To investigate the bending behavior of reinforced UHPC components, nine reinforced UHPC deck specimens were tested by conducting four-point bending experiments. The crack development, load-carrying capacity, and strain distribution were observed, and the tests results revealed that the introduction of steel fibers into UHPC obviously improved the structure’s toughness and crack resistance. Based on the tests results, a theoretical formula was derived for calculating the bending stiffness of the UHPC decks during the entire loading process, which was divided into three representative stages based on the initial cracking and yielding. The results for the load-deflection response obtained by the formulas are in good agreement with the experimental results.

Experimental Study on Basic Performances of Reinforced UHPC Bridge Deck with Coarse Aggregates

In order to reduce the self-weight of conventional steel-concrete composite girders and to improve the crack-resisting behavior of normal strength concrete (NC) bridge decks for long-span cable-stayed bridges, an innovative steel–ultrahigh performance concrete (UHPC) composite girder was proposed. Coarse aggregates (CA) were added to UHPC to control shrinkage and cost. On the basis of the Fifth Nanjing Yangtze River Bridge (FNYRB), a 2 × 600 m cable-stayed bridge in China, a series of experimental tests was conducted. The studies aimed to reveal the material properties of UHPC with and without CA and the static and fatigue flexural performances of the reinforced UHPC deck with CA. The test results implied that the UHPC with CA had compressive strength and flexural strength comparable to UHPC without CA, but the former exhibited much lower shrinkage strains under the natural curing condition. The static bending test results showed that the steel fibers and steel reinforcement bars could effectively control the propagation of cracks in UHPC. The average nominal cracking strength of the UHPC bridge deck specimens was 13.8 MPa, about 1.97 times the maximum tensile stress in the design requirement of the FNYRB under serviceable design loads. Further, the fatigue bending test results demonstrated that the cracks in UHPC propagated very slowly under cyclic tensile stresses, and the residual flexural loads were only 7.2% and 10.9% lower than the ultimate loads obtained for specimens free from the fatigue loading processes. Thus, the current study verified the safety of applying UHPC with CA to long-span cable-stayed bridges.

Static behavior of grouped large headed stud-UHPC shear connectors in composite structures

Accelerated bridge construction (ABC) utilizing precast systems offers many benefits such as faster onsite construction and lower traffic impacts. Ultra-high performance concrete (UHPC) becomes an innovative solution that facilitates some types of ABC. This paper proposes a novel steel-UHPC composite system and large studs with diameter of 30 mm. Push-out tests are conducted to investigate the shear behavior of large studs embedded in UHPC and compared with normal strength concrete (NSC). A total of 6 single stud and 18 grouped studs specimens are used to investigate the effects of casting method, precast deck strength, infilling material strength and transverse reinforcement in the shear pocket. Test results showed that grouped stud effect in the UHPC specimen was insignificant. Ultimate strength of grouped stud in precast UHPC deck was 10% higher than that of NSC precast slab while interfacial slip of UHPC specimen was 17% lower. Noting that grouped large studs better match with UHPC since no visible crack was observed at failure in UHPC slab while NSC slab displayed a number of cracks. Finally, load-slip relationship for large grouped studs embedded in UHPC was proposed based on experimental results and comparisons between the test results of strength and codes predictions were made.

Measurement of Prestressing Force in Pretensioned UHPC Deck Using a Fiber Optic FBG Sensor Embedded in a 7-Wire Strand

This paper presents the results of the performance test and long-term monitoring of the prestressing force inside concrete performed on a pretensioned Ultra-High Performance Concrete (UHPC) deck. The force is measured by applying a 7-wire strand embedded with an FBG (Fiber Bragg Grating) sensor. The performance test was conducted on a 3.7 m × 1.8 m pretensioned deck specimen through wheel loading tests to verify the applicability of the measurement method. In addition, a 12.3 m long and 4.8 m wide bridge with a pretensioned UHPC deck was erected and long-term monitoring was conducted over three years to verify the applicability of the method to real bridges. The effectiveness of the measurement method of the prestressing force inside concrete is verified, and the long-term monitoring data are used to investigate various temperature compensation methods. The results show that the proposed method enables effective measurement of small changes in the prestressing force inside the concrete. These changes are caused by the external forces acting on the bridge in service and provide sufficient durability for long-term sensing. The analysis of the prestressing force obtained through long-term monitoring reveals the necessity of conducting temperature compensation for the consistency of the data acquired using the FBG sensor. Moreover, the selection of the thermal expansion coefficient appears also to be of critical importance for temperature compensation.

Headed stud shear connector for thin ultrahigh-performance concrete bridge deck

Ultrahigh-performance concrete (UHPC) provides much higher compressive and tensile strength than conventional concrete. UHPC is advantageous for use as a bridge slab deck owing to its higher strength, stiffness, and durability. One drawback, however, is the fact that the joint region connecting the deck and girder generally has a thicker cross-section to ensure proper shear connection, which hinders making the overall UHPC deck thinner and lighter. In addition, the shear strength of stud shear connectors embedded in UHPC slab has not been verified to be the same as that in a conventional concrete deck. This study investigates a stud shear connector embedded in a UHPC deck through 15 push-out tests. The ultimate strength of the stud and relative slips are measured. The test parameters were chosen to prove the feasibility of a thinner slab. The stud aspect ratio, overall height-to-diameter, and cover thickness on top of the stud head requirement are also examined to verify the existing geometrical constraints specified in the AASHTO LRFD and Eurocode-4 design codes for UHPC decks. It was shown that the aspect ratio can be reduced from 4 to 3.1 without loss of shear strength of the stud, and the cover could be reduced from 50mm to 25mm without causing a splitting crack at the UHPC slab. However, the required ductility demand, 6mm, was not realized in all cases. Therefore, the stud shear connectors in a UHPC deck should be designed according to the elastic criterion.

초고성능 콘크리트 바닥판을 위한 스터드 전단연결재의 정적 거동

ABSTRACT Typical composite girder has been composed with conventional concrete deck and steel girder. Recently, ultra- high-performance-concrete (UHPC) deck is proposed in order to e nhance durability and reduce weight of deck as well as to increa se stiffness and strength of the composite girder. This study investig ates that a headed stud is still compatible as a shear conne ctor for the UHPC deck and steel girder composite beam. Twelve push-out specimens are prepared to evaluate the static strength of stud shear connectors embedded in the UHPC deck. The test program proves that the static strength of the stud shear connectors embedded in UHPC well meets with design codes described in AASHTO LRFD. Chosen experimental variables are aspect ratio of height to diameter of stud, thickness of deck and thickness of concrete cover over the head of stud. From the test program, aspect ratio and cover thickness are investigated to mitigate the regulations of the existing design codes. The minimum aspect ratio and the min imum cover thickness given in AASHTO LRFD are four and 50mm, respectively. This limitation hinders to lower the thickness of the UHPC deck. The results of the experiment program give that the aspect ratio and the cover thickness can be lower down to three and 25mm, respectively. Eurocode-4 regulates characteristic relative slip at least 6mm. However, test results show that stud shear connectors embedded in UHPC provide the characteristic relative slip only about 4mm. Therefore, another measures to increase ductility of stud should be prepared.

초고성능 콘크리트 바닥판과 역T형 강거더의 합성보를 위한 스터드 및 퍼즐스트립 전단연결재에 관한 연구

초고성능 콘크리트(UHPC)의 높은 강도 및 내구성으로 인하여 교량 바닥판에 UHPC를 적용하는 연구가 활발히 진행되고 있다. UHPC 바닥판은 강도 및 강성이 기존 콘크리트보다 월등히 높아 합성된 강재 거더 상부 플랜지의 구조적 역할을 대신할 수 있을 것이므로, 이 연구에서는 상부 플랜지를 생략한 역T형 거더를 UHPC 바닥판과 합성한 형식을 제안하고자 한다. 역T형 거더를 적용함에 있어 상부플랜지에 전단연결재를 용접하는 방식으로 전단연결재를 설치할 수 없으므로, 새로운 형식의 전단연결재의 개발이 필요하다. 이 연구에서는 3가지 형식의 전단연결재를 제안하고 이들의 정적 극한강도를 실험적으로 평가하였다. 첫 번째 형식은 웨브에 스터드를 횡방향으로 직접 용접한 전단연결재이고, 두 번째는 유럽에서 개발된 퍼즐스트립 형식의 전단연결재이며, 마지막은 횡방향 스터드와 퍼즐스트립을 조합한 전단연결재이다. 실험 결과 횡방향 스터드는 AASHTO LRFD에 제시된 기존 스터드 전단연결재의 강도 설계식 보다 평균 24% 크게 나타났으나, 바닥판에 쪼갬 균열이 현저히 발생하여 이를 방지하기 위한 새로운 대책이 필요한 것으로 나타났다. 퍼즐스트립은 기존 유럽의 연구에서 제안한 극한강도 평가식 보다 40% 큰 강도를 보여, 기존의 평가식이 지나치게 보수적인 것으로 나타났다. 마지막으로 2가지를 조합한 형식의 전단연결재의 극한강도는 각각의 전단연결재의 극한강도를 산술적으로 합한 것보다 작은 극한 강도를 보였고 바닥판에 균열 또한 현저하였으므로, 조합에 따른 상승효과를 기대할 수 없었다.

Dynamic Characteristics Evaluation of Innovative UHPC Pedestrian Cable Stayed Bridge

KICT (Korea Institute of Construction Technology) is conducting a project called “SUPER BRIDGE 200—Development of Low Cost and Long Life Hybrid Cable Stayed Bridge”. This project aims to reduce the construction and main- tenance costs of long-span bridges by 20% and double their lifetime through the exploitation of ultra-high performance concrete (UHPC). This paper presents the design and construction of the first pedestrian cable stayed bridge using UHPC developed by KICT. UHPC, compared to conventional concrete, has not only high compressive and tensile strengths but also high ductility. The UHPC developed at KICT is a steel fiber-reinforced cement compound presenting design compressive strength larger than 180 MPa and design tensile strength exceeding 10 MPa with water-to-binder ratio below 0.24 and admixing of 2 volume percentage of steel fiber. To show the applicability of UHPC to structures, a pedestrian cable stayed bridge (Super Bridge I) exploiting the characteristics of the developed UHPC has been planned, designed and erected at KICT. The dimension of UHPC deck is 2.7 m × 7 m as a precast segment with a typical thickness of deck of only 7 cm. However, harmful crack was observed in the deck at the time of the fabrication of the deck segments. Accordingly, new fabrication method was conceived and applied to prevent cracking of the UHPC slender deck. Four UHPC deck segments were fabricated successfully without any crack. After construction, the dynamic characteristics (natural frequencies and mode shapes) were evaluated through vibration tests since several users felt excess vibration. A vertical tuned mass damper (TMD) was proposed and installed on the parapet of the bridge. The TMD reduces the acceleration by about 30% from 0.0316 g to 0.0244 g when two pedestrians are crossing the bridge.