Continuous Box Girder Research Articles

Seismic Design Assessment of Bridge Piers Location Effect on the Structural Capacity of Supports under Earthquake Action

The objective of this study was to assess the seismic performance of two types of bridges structures under effect of earthquake by using different locations and numbers of piers. The results of D/C ratio showed that simply supported I girder bridge appeared higher structural capacity than continuous box girder bridge which was resisted the seismic demand. Continuous box girder bridge had higher seismic demand and lower structural capacity comparing with simply supported I girder bridge. Commonly, the seismic design for two types of bridges models with increasing of piers numbers was suitable to resist the earthquake action for region type B. The results of non-linear static analysis (pushover method) showed that the increasing of piers numbers had significant effects on the seismic design of bridges structures to increase the displacement capacity, force capacity, and decreasing of seismic demand to reduce the effects of earthquake action on the bridges structural members. The bridge type simply supported I girder had higher capacity in longitudinal direction than continuous box girder bridge. Whereas, for continuous box girder bridge appeared higher capacity in transverse direction than simply supported I girder. The performance points which were based on displacement were decreased with increasing the piers numbers for bridges structures supports.

Risk-Based Multiobjective Optimal Seismic Design for RC Piers Using the Response Surface Method and NSGA-II

In this paper, a risk-based multiobjective optimal seismic design method for reinforced concrete (RC) piers is proposed. This method is used to determine the size and reinforcement ratios of piers to minimize the seismic risk of bridge systems and the construction cost of piers. The Pacific Earthquake Engineering Research- (PEER-) based probabilistic seismic risk assessment approach and the response surface method (RSM) are adopted to develop the seismic risk response surface model, which represents the relationship between the design parameters of piers and the seismic risk of bridge systems. The Pareto optimal solutions of piers are determined by applying an improved version of the nondominated sorting genetic algorithm (NSGA-II). As a case study, the proposed optimal seismic design method is applied to a continuous concrete box girder bridge. The optimal design schemes of piers according to two strategies are determined from the Pareto optimal solutions. The results show that the seismic risk response surface model can be used to accurately describe the relationship between the design parameters of piers and the seismic risk of bridge systems. The case study demonstrates the effectiveness of the proposed optimal seismic design method. The analysis of the Pareto optimal solutions allows designers to more rationally conduct the seismic design of piers.

SHM-Oriented Hybrid Modeling for Stress Analysis of Steel Girder Bridge

Stress monitoring is always a challenging task in bridge structural health monitoring (SHM) since the measured pointwise stress is not enough for fully reflecting structural conditions. Therefore, a novel hybrid modeling technique was proposed in this paper, which calculates stress distribution with the aid of finite-element (FE) submodels from limited measured data. However, unlike common FE analyses, the requirement of complete input information is avoided by an FE model-based partial least-squares regression (FEM-PLSR) method. First, the regression equations among the FE model, unknown structural input, and output were set up, into which measured displacements, rotations, and strains were fused simultaneously. By solving the regression equations, the boundary conditions of the FE submodel can be precisely estimated. Then, the stress distribution can be calculated through FE analyses under the assumption of known local vehicular loads. Numerical simulations of a continuous steel box girder bridge were carried out for verification. Corresponding results indicated that the accuracy of the calculated stress distributions was competitive to the widely used multiscale FE model, even if the structural input information outside the submodel was not directly measured. Furthermore, the proposed method was also proved insensitive to random measurement errors. Finally, a large-scale experiment was designed to validate the accuracy of the hybrid model under three loading conditions. The strain distribution over both space and time accorded well with the measurement. Thus, the present hybrid modeling offered a novel way to obtain unmeasured structural responses, revealing great potential in the field of bridge SHM.

Static behavior of a steel-ultra high performance concrete continuous composite box girder

To improve the crack-resisting behavior of normal-strength concrete (NC) bridge deck and to reduce the deadweight of conventional steel-concrete composite girders, a new steel-ultrahigh performance concrete (UHPC) continuous composite box girder was proposed. Aiming to reveal the static behavior of the proposed structure, including the load-deflection response, the strain distribution, the crack development, the moment redistribution and the failure mode, a comparative experimental study was conducted on two types of the composite girder, namely a steel-UHPC continuous composite girder (SUCG) and a prestressed steel-concrete continuous composite girder (SCCG). The test results indicated that the ultimate loading capacity of the SUCG was 20.4% higher than that of SCCG; the nominal cracking strength of the SUCG was 22.9 MPa, and its corresponding cracking moment was 2.1 times higher than the conventional one; the crack development mode of UHPC slab were significantly different from the SCCG, the cracks appeared in UHPC slab dominated by microcracks with smaller length were numerous and intensive. It is also shown that the SUCG has smaller degree of moment redistribution. Thus, the current study verified the SUCG could be one of effective solutions for long-span continuous composite girder bridges.

Defect investigation and replacement implementation of bearings for long-span continuous box girder bridges under operating high-speed railway networks: a case study

Bridge bearings easily suffer damage when exposed to various loading and environmental changes during their lifetime. This effect can have a considerable impact on the bridge service performance, and bearing replacement should be performed if damage occurs. Compared with highway bridges, bearing replacement for long-span bridges under operating high-speed railways (HSRs) is more challenging due to the higher safety requirements for the operation of trains, the larger jacking reaction forces for single piers and the complex bearing structures. In this paper, the defects of bearings in five larger-scale HSR bridges are investigated through field detection, followed by a bridge jacking scheme that includes a temporary support with a continuous height adjustment, a large bearing capacity and good stability. Finally, a replacement method using the invented temporary support and a developed reverse disassembly or assembly technology as well as safety monitoring is proposed and implemented on the bridge. The results show that most defects are caused by the problems remaining from bearings installation, which are aggravated during a long service period, and that the proposed jacking scheme is feasible, which sheds light on the maintenance and replacement of bearings for long-span bridges under operating HSR networks.

Temperature Field and Gradient Effect of a Steel‐Concrete Composite Box Girder Bridge

To study the effect of the temperature field and gradient of a steel‐concrete composite box girder bridge, a 5 × 35 continuous composite box girder bridge is used as the research object. The temperature measuring point is set by selecting a typical cross section, and the temperature change data are measured. The temperature field of the different positions in the composite box girder bridge is studied, the global and local temperature differences are compared, and the law of temperature distribution and the main factors affecting the temperature field are formulated. The most unfavourable expression function of the vertical temperature gradient of the section is simulated using the measured data, the existing standard temperature gradient mode is compared, the finite element model of the bridge is established, and the influence of the actual temperature gradient mode on the stress and deformation of the composite girder is further analysed. The conclusions show that the temperature differences of different azimuth sections and the local temperature differences between the steel and concrete joint parts of the steel‐concrete composite box girder bridge are not significant. The temperature gradient heating and cooling model fitted by the measured temperature field can be used as a reference for the structural design of similar local bridges.

Force analysis of variable cross-section continuous box girder bridge

Force analysis of variable cross-section continuous box girder bridge

Study on Diagnosis and Treatment Technology of Cracks in Consolidated Continuous Box Girders of Middle Piers during Construction

In this paper, taking the cast-in-place reinforced concrete continuous box girders of a bridge as the research object, we studied the cracking type of the box girders and their construction. Combined with the calculation and analysis of the construction, the causes and effects of the cracks of box girders during the construction were further studied. Then the maintenance and strengthening scheme that UT10 super-highperformance concrete should be used on the bridge floor was proposed, which will provide reference for the diagnosis and treatment of similar bridge structures.

Collapse Mechanism and Full‐Range Analysis of Overturning Failure of Continuous Girder Bridges

In recent years, failings of girders due to overturning in continuous girder bridges have repeatedly occurred in China. To investigate the overturning collapse mechanism and also to evaluate the rationality of anti‐overturning design method using beam element models that are commonly adopted in practical design, detailed 3D finite solid element models of a typical single‐column pier three‐span continuous box girder bridge were built and a full‐range numerical analysis of the models was conducted. The solid models included the prestressing effect and diaphragms. Both boundary and geometric nonlinearities were taken into consideration. Bearings were modeled considering the actual construction and dimensions of pot rubber bearings, the material characteristics and boundary conditions of rubber pads, and the contact properties between each part of the bearings. The analysis results revealed that the behavior of the bridge approached the nonlinear state at the onset of first bearing disengagement; the rotation (overturning) mechanism of the girder was gradually transitioned from deformable‐body rotation to rigid‐body rotation; all the end and middle bearings had been disengaged totally or locally at ultimate overturning failure. The analysis results also showed that bearing disengagements would lead to the ineffectiveness of the constraint in the transverse direction, which significantly reduced the overturning ultimate load and structural ductility before the final collapse. Prior to the first bearing disengagement, the vertical reactions calculated from the beam model were in good agreement with those from the solid model, while the transverse reactions were not. The behaviors were inaccurate after bearing disengagement in the beam models in which the movement of the rotation axis and transition of rotation mechanism failed to be realized. Reliable transverse stoppers and tensile anchors at bearing sections were recommended to efficiently improve anti‐overturning stability and ductility in practical design.

Theoretical prediction of the punching shear strength of concrete flat slabs under in-plane tensile forces

RC slabs can be subjected simultaneously to transverse loads and in-plane tensile forces, as it happens in top slabs of continuous box girder bridges decks, in the regions of negative moments, or in flat slabs subjected to horizontal loads, produced by wind or earth pressure. Tensile forces can reduce the shear punching capacity of slabs. However, few studies have been carried out to quantify this effect. With this purpose, a mechanical model has been developed to capture the influence of in-plane tensile forces on the punching shear strength and verified with punching tests under different in-plane tensile load levels. The model, presented in this paper, consists of an extension of the Punching shear Compression Chord Capacity Model to account for the effects of tensile forces on the resisting actions. A linear reduction of the punching shear strength as a function of the external load applied has been obtained for moderate tensile forces, whereas high level of tensile forces may produce premature yielding of the reinforcement and further reduction of the punching shear strength. The proposed model accurately captures the available test results, including the effects of the premature yielding of reinforcement when the tensile force produces concrete cracking. In addition, predictions of punching-shear-tensile tests available in the literature were made with different theoretical models included in design codes, which yielded in general conservative results and showed high scatter.

Force Analysis Of Variable Cross-Section Continuous Box Girder Bridge

In order to study the distribution of stress and deformation of variable cross-section continuous box girder bridge, in this paper, the finite element method is used to establish the model of variable cross-section continuous box girder bridge. Considering the layout of lane load, the combination of working conditions is calculated, and the stress and deformation of variable cross-section continuous box girder bridge are analysed. The results show that the maximum stress of the bridge generally occurs at the continuous beam span middle section or support, and sometimes the stress value at the vehicle load point is also large. These positions with large stress values should be considered in the design of box girder. The vertical displacement of bridge is small, removing settlement of end support. The maximum vertical displacement of bridge span middle section is 15 mm, and the bridge design scheme is safe, reliable and economical.

Analysis of continuous PC box girder bridges with CSWs by using equivalent computational model

The widespread usage of prestressed concrete (PC) box girder with corrugated steel webs (CSWs) can be attributed to its many remarkable merits over traditional concrete box girders, such as significantly reducing the deadweight of the girder, speeding up the construction process, avoiding the problem of web cracking and increasing the prestress introduction efficiency. Numerous previous studies were conducted to investigated the mechanical properties of CSWs as well as simply supported box girder bridges with CSWs, whereas very few studies focused on the FE modeling methods of continuous PC box girders with CSWs. In addition, experimental work on scale bridge models or full-scale bridges adopting the box girder with CSWs is very limited. In this paper, an equivalent orthotropic web (EOW) model was developed for CSWs and used to analyze the performance of the continuous PC box girder bridges with CSWs. To verify this model, a one-tenth-scale bridge model was developed for an existing continuous PC box girder bridge with CSWs. Both static and dynamic tests were carried out on this scale bridge model. The results obtained from the bridge finite element (FE) model with EOWs were compared to the results obtained from the bridge FE model with CSWs and also the experimental results from the scale bridge model. Good agreement was achieved between these results, indicating that the EOW model can provide a trustworthy and convenient tool in the FE analysis of PC continuous box girder bridges with CSWs.

Seismic fragility analysis of reinforced concrete piers of steel box girder bridges: A parametric study

The purpose of this paper is to investigate the influence of typical parameters on seismic fragility curves of reinforced concrete (RC) piers of continuous steel box girder bridges. Typical parameters considered include the pier heights, pier section types, and total length of bridges. Twenty recorded ground motions from historic seismic events are randomly selected for fragility analyses. The finite element analysis program, OpenSees, is employed to perform nonlinear dynamic analyses of the bridges. A set of damage states of bridge piers is proposed based on the damage index, which is based on the drift ratio of the pier. Fragility curves of piers are eventually generated using maximum likelihood estimation. The numerical analysis results show that the bridges with shorter piers are less vulnerable to earthquakes than those with higher piers. Moreover, the wall pier types have significantly improved seismic performance compared with the other types. The fragility analysis results also reveal that the total bridge length has notably affected to seismic response of bridges.

Long-term performance of prestressed concrete continuous box girders in the natural environment

A long-term load test performed for 470 days on two two-span prestressed concrete (PC) continuous box girders is reported in this paper. Load types were selected as the test variates, and structural responses such as support reactions, deflections, and concrete strains were monitored. Simultaneously, affiliated experiments such as material strength, creep, and shrinkage tests were conducted to investigate the time-dependent performances of the materials. Data obtained from these tests showed that deflections, strains, and support reactions develop rapidly in the beginning and stabilize afterward; the reactions of mid- and end-supports decline and rise over time, respectively. Time-dependent patterns of deflections and support reactions were analyzed on the basis of an effective modulus method, and a practical calculation method for long-term deflections considering reaction redistributions was proposed. The effects of the service environment on the performance of PC girders were evaluated through an incremental analysis method.

Study on Mechanical Properties of Main Girder of Continuous Box Girder Bridge Strengthened By A Cable-Stayed System

The local stress concentration of the main girder during the tensioning construction of the continuous box girder bridge strengthened by the cable-stayed system is more prominent, which may lead to the sudden damage of the structure. Therefore, this paper studies the key section stress and deformation of the main girder in combination with the real bridge test. The results show that the maximum tensile and compressive stress increase of the main girder appears at the root floor and midspan floor; The tensile action strengthens the compressive stress between the anchorage point of the long cable and the anchorage point of the short cable to the top of the pier, which releases some of the compressive stress across the mid-slab, improves the stress state of the main girder, and improves the shear load of the main girder ability; With the increase of the cable force, the main tensile stress of the web in the anchoring area first increases and then decreases. The lifting amount of the midspan section of the main girder accounts for 20.06% of the total deflection, and the effect of the cable-stayed system on improving the deflection of the main girder is obvious.

Study on mechanical behavior of new steel members of cable-stayed strengthening system

In the tensioning construction of continuous box girder bridge strengthened by a stay cable system, local stress concentration of steel joist and bracket is easy to be caused. This paper studies the stress and deformation of key section of steel joist and bracket by combining with real bridge test. The results show that the maximum stress of steel joist and bracket is less than the allowable stress. When the tensioning force value is 2.66 times of the completion cable force, the bottom plate first reaches the yield strength, and the stress change law of the bracket is not strong. The mid-span deformation of the steel joist in the early period of tensioning is gentle, and the change in the later period is large. When the tensioning force reaches the completion cable force, the value is about 1/400 of the span. In the early tensioning period, the relative displacement between the steel bracket and the girder is large, but the change in the later tensioning period is not large.

Static Strength of Friction-Type High-Strength Bolted T-Stub Connections under Shear and Compression

The friction-type high-strength bolted (FHSB) T-stub connection has been widely used in steel structures, due to their good fatigue resistance and ease of installation. While the current studies on FHSB T-stub connections mainly focus on the structural behaviors under both shear and tensile force, no research has been reported on the mechanical responses of the connections under the combined effects of shear and compression. To make up for this gap, this paper presents a novel FHSB T-stub connection, which is simple in structure, definite in load condition, and easy to construct. Static load tests were carried out on 21 specimens under different shear–compression ratios, and the finite-element (FE) models were created for each specimen. The failure modes, initial friction loads and ultimate strengths of the specimens were compared in details. Then, 144 FE models were adopted to analyze the effects of the friction coefficient, shear–compression ratio, bolt diameter and clamping force on the initial friction load and ultimate strength. The results showed that the FHSB T-stub connection under shear and compression mainly suffers from bolt shearing failure. The load–displacement curve generally covers the elastic, yield, hardening and failure stage. If the shear–compression ratio is small and the friction coefficient is large, its curve only contains the elastic and failure stage. The friction coefficient and shear–compression ratio have great impacts on the initial friction load and ultimate strength. For every 1 mm increase in bolt diameter, the initial friction load increased by about 10%, while the ultimate strength increased by about 8.5%. For each 10% increase/decrease of the design clamping force, the initial friction load decreases/increases by 7.8%, while the ultimate load remains basically the same. The proposed formula of shear capacity and self-lock angles of FHSB T-stub connection can be applied to the design of CSS-enhanced prestressed concrete continuous box girder bridges (PSC-CBGBs) and diagonal bracing.

鋼材の腐食劣化が進行した PC 連続箱桁橋の構造性能評価 -妙高大橋の事例-

鋼材の腐食劣化が進行した PC 連続箱桁橋の構造性能評価 -妙高大橋の事例-

Control measures for thermal effects during placement of span-scale girder segments on continuous steel box girder bridges

In this study, we examined the thermal effects throughout the process of the placement of span-scale girder segments on a 6×110-m continuous steel box girder in the Hong Kong-Zhuhai-Macao Bridge. Firstly, when a span-scale girder segment is temporarily stored in the open air, temperature gradients will significantly increase the maximum reaction force on temporary supports and cause local buckling at the bottom of the girder segment. Secondly, due to the temperature difference of the girder segments before and after girth-welding, some residual thermal deflections will appear on the girder segments because the boundary conditions of the structure are changed by the girth-welding. Thirdly, the thermal expansion and thermal bending of girder segments will cause movement and rotation of bearings, which must be considered in setting bearings. We propose control measures for these problems based on finite element method simulation with field-measured temperatures. The local buckling during open-air storage can be avoided by reasonably determining the appropriate positions of temporary supports using analysis of overall and local stresses. The residual thermal deflections can be overcome by performing girth-welding during a period when the vertical temperature difference of the girder is within 1 °C, such as after 22:00. Some formulas are proposed to determine the pre-set distances for bearings, in which the movement and rotation of the bearings due to dead loads and thermal loads are considered. Finally, the feasibility of these control measures in the placement of span-scale girder segments on a real continuous girder was verified: no local buckling was observed during open-air storage; the residual thermal deflections after girth-welding were controlled within 5 mm and the residual pre-set distances of bearings when the whole continuous girder reached its design state were controlled within 20 mm.

Refined analysis and construction parameter calculation for full-span erection of the continuous steel box girder bridge with long cantilevers

To accurately control the full-span erection of continuous steel box girder bridges with complex cross-sections and long cantilevers, both the augmented finite element method (A-FEM) and the degenerated plate elements are adopted in this paper. The entire construction process is simulated by the A-FEM with the mesh-separation-based approximation technique, while the degenerated plate elements are constructed based on 3D isoparametric elements, making it suitable for analysis of a thin-walled structure. This method significantly improves computational efficiency by avoiding numerous degrees of freedom (DoFs) when analyzing complex structures. With characteristics of the full-span erection technology, the end-face angle of adjacent girder segments, the preset distance of girder segments from the design position, and the temperature difference are selected as control parameters, and they are calculated through the structural response of each construction stage. Engineering practice shows that the calculation accuracy of A-FEM is verified by field-measured results. It can be applied rapidly and effectively to evaluate the matching state of girder segments and the stress state of bearings as well as the thermal effect during full-span erection.