Journal of Bridge Engineering

Deterioration and aging of concrete structures are not the only reasons why critical members, such as beams, need to be strengthened. Other possible reasons include upgrading of design standards, compensation for faulty design or construction, changing usage of the structure, and exposure to unpredicted loads, such as impacts or excessive earthquakes. The current study proposes a new analytical method for predicting the torsional capacity and behavior of RC multicell box girders strengthened with carbon-fiber-reinforced polymer (CFRP) sheets. The conventional softened truss model is modified to consider the influence of CFRP strengthening on the torsional response as an external reinforcement of multicell box girders. The proposed method involves solving the concrete torsional problem by combining the equilibrium conditions, compatibility conditions, and constitutive laws of materials, taking into account the confinement of concrete with CFRP sheets. A specific algorithm was developed to predict the torsional behavior of RC multicell box girders with and without CFRP strengthening. Verification of this method was achieved using extensive comparisons between analytically predicted behavior curves and experimentally obtained ones. The experimental work comprised a series of four torsion tests for single- and triple-cell box girders. Good agreement between the results was obtained, confirming the feasibility of the newly proposed method. Based on the outcome of the comparisons, it was revealed that the only currently available, recommended torsion design method was generally conservative, suggesting that further refinement is essential to make it a suitable design method for torsional strengthening using CFRP sheets.

This paper presents, for analysis of prestressed concrete (PC) bridges, a spatial embedded slip model that is based on a three-dimensional isoparametric element, truss element, and nonthickness bond element, to simulate concrete, tendon, and the interface of the two, respectively. The bond element is embedded into the slip model via the virtual nodes introduced at the intersection points of tendon and concrete. Based on the displacement-based finite-element framework and the constitutive relations of each component, the elastic finite-element equilibrium equation for the slip model is deduced according to the virtual work principle. The quasilinear regression method is used to fit the creep coefficient in the Chinese bridge design code. Then, based on the elastic equilibrium equation and theoretical incremental formula of creep analysis, the equilibrium equation for analyzing time-relative coupling effects of creep and prestress is derived and the finite-element program is developed. The proposed model allows tendon to go through concrete in any pattern, without consideration for layout and direction of tendon and therefore with convenience in a finite-element mesh. The freedoms of the virtual nodes can be reduced in the formation of the equilibrium equation. Verified by a numerical example of a simply supported beam with a rectangular section, the embedded slip model is proved to support accurate linear and creep computation within an elastic range of materials.

In current engineering practice, safety checks on serviceability and determinations of ultimate limit states of segmental bridges built by cantilevering are generally performed, either considering separately the contributions of axial force $N$, bending moment $M$, and shear force $V$, or considering the interaction effects through approximate expressions supplied by building codes. During construction stages and service life, the interaction between internal forces can be of fundamental importance in establishing the actual degree of structural safety and, for this reason, a different philosophy for performing checks in segmental bridges is proposed in this paper, plotting $N\text{-}M$ and $M\text{-}V$ interaction domains for cracking, construction stages, and serviceability (elastic domains) as well as $M\text{-}V$ interaction domains for ultimate limit states (failure domains). Delayed deformations as a result of creep are considered, as are bonded and unbonded prestressing. A model is developed for plotting bending-shear domains at the ultimate limit state, underlining the strength reduction that occurs in concrete sections with external prestressing versus beams with full internal prestressing. A numerical application on an actual segmental bridge built by cantilevering was performed to show the proposed methodology, based entirely on strength domains, for safety checks. The load and stress paths in the construction stages are highlighted by considering the effects of creep in concrete, whereas bending-shear interaction is evaluated in the two cases of fully bonded prestressing and partially unbonded prestressing. The results show that safety checks which are performed based on approximate assumptions and expressions that do not explicitly consider the interaction effects can lead to unsafe evaluations, and it also shows that the proposed methodology allows engineers to take into account simultaneously any aspect related to cross-sectional strength on serviceability and ultimate limit states.

The application of prestress is a very effective way to prevent the cracking of the concrete slab in the negative-moment region of continuous composite girders, and using a prefabricated prestressed-concrete slab in this region is an easier option than posttensioning. To elucidate the structural response of a continuous composite box girder with a prefabricated prestressed-concrete slab, two large, 18-m-long specimens were fabricated and tested under short-term loading, and the results are reported in this paper. One, a control specimen, was a conventional composite girder with its concrete slab cast in situ, whereas the other was a composite box girder with a prefabricated prestressed-concrete slab in the negative-moment region. The relative slip between the steel girder and the concrete slab; the load-deflection response; the distribution of strain in the steel girder, reinforcement, and concrete slab; as well as the crack widths in the concrete slab were measured during the tests. The paper shows that, although the ultimate strengths of the two specimens are almost the same, the initial cracking load and serviceability limit state load of the specimen with a prefabricated prestressed-concrete slab are 3.16 and 2.61 times, respectively, those of the specimen with a conventional concrete slab. It is also shown that simple linear-elastic analysis leads to a close prediction of the load for initial cracking. By comparison, a continuous composite bridge beam with a prefabricated prestressed slab over its internal support is stiffer and less likely to experience the ingress of corrosive materials than one with a conventional RC slab is.

This paper presents a finite-element (FE) analysis of hybrid fiber-reinforced polymer (FRP)-concrete-steel double-skin tube (FSDT) in the form of columns. The FSDT columns that were examined consisted of a concrete wall sandwiched between an outer FRP tube and an inner steel tube. A FE software was used to develop a pushover analysis of three-dimensional FSDT models to simulate seismic loading. The FE models were validated against the experimental results gathered from seven FSDT columns tested under cyclic loading. The FE analysis results were in good agreement with the experimental backbone curves. The maximum error was 9% in predicting the bending strengths of the columns. A parametric study evaluated the effect of axial load level, concrete wall thickness, concrete strength, diameter-to-thickness ratio ($D/t$) of the steel tube, and number of FRP layers on the FSDT columns’ behavior. This study revealed that the behavior of FSDT columns is quite complex. It also revealed that this behavior is controlled by the interactions that occur among the steel tube’s stiffness, the concrete wall’s stiffness, and the FRP hoop’s stiffness. Local buckling occurred in all of the specimens examined. This buckling caused the FSDT system to rupture. Two modes of failure were defined as follows: (1) steel/concrete compression failure, and (2) FRP rupture. Compression failure was relatively gradual whereas failure due to FRP rupture was quite abrupt. Finally, the bending strength increased as the applied axial load, concrete compressive strength, and number of FRP layers increased. The bending strength also increased as both the concrete wall’s thickness and the $D/t$ decreased.

The Hathaway Bridge, an eastbound and westbound bridge pair, is located in Panama City, Florida. Each of the pair consists of a single-box precast concrete segmental girder with a deck width of 24.4 m (80 ft). The lengths of the eastbound and westbound bridges are 1,031.43 and 1,162.93 m (3,384 and 3,815 ft), respectively. To date, these are the largest single-cell precast segments without internal struts fabricated in the United States. During construction, many web cracks developed in the external anchorage areas. The purpose of this investigation is to identify the main causes of the cracks and provide some design recommendations for large precast concrete segmental box girders. First, a brief description of the bridge is given. Then, analytical models for the bridge, posttensioning forces, and construction forces are presented. The analytical results show that the external longitudinal posttensioning forces can cause significant high-tensile stresses in the interior face of the web around the anchorages. The information presented in this paper can assist bridge engineers in the design of concrete segmental box girder bridges.

As of the end of 2013, there were 79 long-span bridges built in the city of Chongqing. Among them, 14 are concrete cable-stayed bridges and 42 are concrete girder bridges. They were all built segmentally. This paper presents the design concept of three segmental bridges: one box girder bridge, one cable-stayed bridge, and one partially cable-supported girder bridge.

The Veterans’ Glass City Skyway (VGCS) is a posttensioned concrete segmental cable-stayed bridge in Toledo, Ohio. The baseline analytical model of the bridge was reviewed using the measured response to construction loads during two intermediate stages of construction. The boundary conditions and geometry of the model were updated during the various stages of construction and the properties of the structural elements were updated across all the stages so that the model accurately captured the response of the bridge at each stage. The behavior of the model during construction was verified using construction loads. Static and low-speed truck load tests were performed when the bridge was completed to verify the performance of the final model. These tests were conducted just before the bridge opened and again after two years of service. The measured response to these load tests correlated very closely with model response, thus confirming the efficacy of using construction loads to develop the bridge model. In a segmental bridge like VGCS, with well-defined stages of construction, the use of construction loads resulted in a tested baseline model that captures the as-built behavior.

The prestressed concrete (PC) box girder bridge with open webs, whose mechanical behavior is halfway between that of the traditional plain web and the lattice box girder bridges is a relatively new bridge form. The concept depends on new structural developments considering complex geometry that combines cast in situ and prefabricated elements. In this paper, the Abra Bridge (or Tavaro Viaduct) in France was measured and analyzed by using the so-called space frame lattice model. The paper discusses the advantages of this bridge type. The paper also presents the use of a space frame lattice computational method for structural analysis. Given the calculated results, to reduce the principal stresses in the webs, the shear stresses are reduced by the vertical preshear force provided by the external prestressed tendons along the whole bridge, which is proposed by the authors. At the same time, the vertical internal prestressed tendons in the webs can be designed to increase the vertical compressive stresses. The threaded bar can be designed along the hypotenuse side in each web. The space frame lattice model is an effective tool of calculation and analysis for PC box girder bridges with open webs. The reinforcements in webs can be designed according to the principal tensile stresses calculated by the model.

This paper presents the current state of practice in the development of ultrahigh-performance concrete (UHPC) bridge construction in Malaysia. Since 2006, Dura Technology (DT) has pioneered research in the optimal uses of UHPC in bridge construction through its Sustainable Bridge Construction Initiative. After several years of research and development work, DT has collaborated with the Malaysia Works Ministry to design and build bridges in some of their bridge projects, especially those bridges under the rural development program where sourcing of material, site access, and construction method are major challenges when using conventional methods. The most current information and details on the completed and ongoing UHPC bridge projects in Malaysia are presented. To date, a total of 26 segmental UHPC bridge projects have been constructed and opened for service. In this paper, a selected UHPC bridge case study is examined in terms of the design aspects, quality control, constructability, and of how UHPC has helped to make the bridge more affordable, sustainable, easier to build, and economical.

The time-dependent concrete creep and shrinkage effects on segmental bridges are more critical than on other types of concrete bridges. Creep strains develop more when concrete is loaded in a younger age than in an older age, and it affects more on loss of prestressing and displacements because of prestressing. Creep and shrinkage analyses are considered an essential part for segmental bridge design and analysis, especially for the cast in situ segmental bridges or concrete bridges with an application of large quantities of prestressing. The introduction of a creep/shrinkage mathematic model into the formation of a stiffness matrix limits the evolution of a finite-element analysis (FEA) package and the adoption of a new model. Based on the fact that the creep development is nonlinear only in the time domain and linear to loadings, this paper introduces a novel time incremental method for creep and shrinkage analysis and its implementation to a FEA package. The equilibrium after a tiny time step will be reached to balance whatever creep and shrinkage strains have developed during that time. The incremental redistribution loads will cause further creep effects at an older loading age. In addition to external loads caused by construction phase changes at specific time ordinates, each incremental redistribution load will act as an external load at a corresponding time. With today’s advanced computer technologies, the integration of these effects can be solved. The advantage of this simplified method is the separation of the creep/shrinkage model and FEA kernel. It is favorable to a modern modular bridge design and analysis system. A T-shape frame bridge constructed segmentally is included as a case study to illustrate the application of this method.