Damage Analysis of Hanshin Expressway Viaducts during 1995 Kobe Earthquake. I: Residual Inclination of Reinforced Concrete Piers

The damage suffered by elevated viaducts of the Hanshin Expressway Kobe Route during the 1995 Kobe earthquake is described with emphasis on reinforced concrete (RC) piers. Although many piers were severely damaged, it is also true that the damage to many piers appeared moderate or even mild. On the other hand, a number of piers suffered from large residual inclination in spite of the apparently light damage. By considering that the large residual inclination of piers included severe earthquake-induced damage, it is pointed out that almost all the RC single piers from P35 to P350 received consistently severe damage. The cause of large residual inclination, especially in apparently nondamaged piers, is studied. A dynamic analysis of a single RC pier is conducted to study the relationship between residual inclination and residual deformation of a pier. As a result, we find that the flexural residual deformation of a pier cannot explain the observed large residual inclination, but it is suggested that the pulling out of reinforcing bar from the footing can be a primary cause of the observed large residual inclination.     

Damage Analysis of Hanshin Expressway Viaducts during 1995 Kobe Earthquake. III: Three-Span Continuous Girder Bridges

Almost all the single reinforced concrete (RC) piers from P35 to P350 received consistently severe damage, considering the large residual inclination of piers included in earthquake-induced severe damage. However, some of the piers in the section from P35 to P350 remained lightly damaged, and this phenomenon is observed especially in many piers under fixed bearings in continuous girder bridges. In this study, using experimentally based models for metal bearings and installing them to an existing FEM code, a nonlinear dynamic response analysis of a continuous girder bridge system is conducted. It is shown that the results depend on the ground motion, but the fuse effect of the breaking of the bearings could have been a reason for the phenomenon.     

Evaluation of Prestressed Concrete Girders Strengthened with Carbon Fiber Reinforced Polymer Sheets

This paper details the use of carbon fiber reinforced polymer (CFRP) sheets to repair and strengthen prestressed concrete bridge girders in flexure and shear. Three specimens that were removed from an overloaded bridge (Bridge No. 56) in Graham County, Kansas were tested. Two of the specimens were repaired and strengthened, and all three were tested to failure to determine flexural capacity. Test results showed that two layers of longitudinal CFRP sheets increased the flexural capacity of the strengthened specimens by 20% compared to an unstrengthened control specimen. Shear capacity was also evaluated on both ends of each specimen. Two different cases were evaluated in shear. One case allowed shear cracks to propagate inside the transfer length of the prestressing strand, allowing a bond failure to occur. The second case forced the shear cracks to remain outside of the transfer length, thereby preventing a bond failure. The test results show that transverse CFRP sheets increased the shear capacity of the specimens tested by as much as 28%, but did not prevent bond failures.     

Shear Retrofit of Hollow Bridge Piers with Carbon Fiber-Reinforced Polymer Sheets

Hollow bridge piers are currently being used in high-speed rail and highway projects in Taiwan. The flexural ductility and shear capacity of such piers with the configuration of lateral reinforcement used in Taiwan has recently been studied.?This paper reports that circular and rectangular hollow bridge piers retrofitted by carbon fiber-reinforced polymer (CFRP) sheets were tested under a constant axial load and a cyclic reversed horizontal load to investigate their seismic behavior, including flexural ductility, dissipated energy, and shear capacity. An analytical model is also developed to predict the moment-curvature relationship of sections and the lateral load-displacement relationship of piers. Based on the test results, the seismic behavior of such piers is presented. The test results are also compared with the proposed analytical model. It was found that the ductility factors of the tested piers ranged from 3.3 to 5.5 and that the proposed analytical model could predict the lateral load-displacement relationship of such piers with reasonable accuracy. All in all, CFRP sheets can effectively improve both the ductility factor and the shear capacity of hollow bridge piers.     

Reduction of Local Scour in the Vicinity of Bridge Pier Groups Using Collars and Riprap

The present study examines the use of independent and continuous pier collars in combination with riprap for reducing local scour around bridge pier groups. The efficiency of collars was studied through experiments. The data from the experiments were compared with data from earlier studies on single piers with collars and bridge pier groups without collars. The data showed that in the case of two piers in line, combination of continuous collars and riprap results in the most significant scour reduction of about 50 and 60% for the front and rear piers, respectively. In other cases for two piers in line, independent collars showed better efficiency than a continuous collar around both piers. It was also shown that efficiency of collars is more on a rectangular pier aligned with the flow than two piers in line. Experiments however, indicated that collars are not so effective in reduction of scouring around two transverse piers.     

Tests of RC Deck Girders with 1950s Vintage Details

Large numbers of conventionally reinforced concrete (CRC) bridges in the national bridge inventory built during the 1950s are lightly reinforced for shear. Inspections revealed many of these bridges exhibit diagonal cracks resulting in load postings, monitoring, emergency shoring, repairs, and unscheduled bridge replacements. A research program was conducted to investigate the behavior and capacity of CRC bridge girders with vintage details. Laboratory tests of large-size girders representative of 1950s design and construction practice were carried out. Various steel reinforcement configurations were tested. Loading conditions were varied to reproduce girder behavior at different positions in a bridge and various loading protocols were considered. Test results provide a comprehensive data set for comparison of analysis methods and repair strategies; and indicated that anchorage of flexural steel was key to developing higher ultimate capacity, initial crack damage may not necessarily contribute to the final failure mode, and crack width alone may not indicate the level of damage to the beam.     

Evaluation of As-Built, Retrofitted, and Repaired Shear-Critical Hollow Bridge Columns under Earthquake-Type Loading

The objective of this research is to investigate the seismic performance of as-built, retrofitted, and repaired hollow bridge columns with insufficient shear strength. Two as-built full-scale columns were first tested and repaired using carbon-fiber-reinforced polymer composites (CFRP) jackets and dog-bone-shaped bars and then retested. Another two columns having the same reinforcement as the as-built columns were retrofitted with CFRP jackets. In addition to the tests, the repairability of the failed hollow columns was investigated by analytical evaluation. The test results and analysis of the retrofitted columns showed that CFRP composites can effectively strengthen shear-critical hollow bridge columns and can successfully transform the failure mode from shear to flexure. The test results of the repaired circular columns show that dog-bone-shaped bars successfully repaired the flexural damage caused by the fractured longitudinal bars.     

Seismic Retrofit of Hollow Rectangular Bridge Columns

The seismic performance of rectangular hollow bridge columns is a significant issue of the high-speed rail project in Taiwan. The flexural ductility and shear capacity of such columns with the configuration of lateral reinforcement used in Taiwan have been studied recently. This paper reports that hollow rectangular bridge columns retrofitted with fiber-reinforced polymer (FRP) sheets were tested under a constant axial load and a cyclically reversed horizontal load to investigate their seismic behavior, including flexural ductility, dissipated energy, and shear capacity. An analytical model was also developed to predict the moment-curvature curve of sections and the load-displacement relationship of columns. Based on the test results, the seismic behavior of such columns will be presented. The test results were also compared to the proposed analytical model. It was found that the ductility factors of the tested piers are in the range from 3.4 to 6.3, and the proposed analytical model can predict the load-displacement relationship of such columns with acceptable accuracy. All in all, FRP sheets can effectively improve both the ductility factor and shear capacity of hollow rectangular bridge columns.     

High-Cycle Fatigue of Diagonally Cracked RC Bridge Girders: Laboratory Tests

Large numbers of conventionally RC deck–girder bridges are in the national highway system. Diagonal cracks have been identified in many of these bridges, which are exposed to millions of load cycles during service life. The anticipated life of these bridges in the cracked condition under repeated service loads is uncertain. Laboratory experiments were performed on full-size girder specimens to evaluate possible deterioration in shear capacity under repeated loading. Specimen variables included: T and inverted-T configurations, stirrup spacing, and flexural reinforcing details. Test results indicated bond deterioration increased diagonal crack displacements, and analysis methods to predict the shear capacity of diagonally cracked reinforced concrete girders subjected to high-cycle fatigue damage are provided. The AASHTO-LRFD shear provisions conservatively predicted shear capacity for the fatigued specimens without stirrup fractures, and shear capacity predictions from computer analysis program Response 2000 were very well correlated with experimental results for fatigued test specimens when the input concrete tensile strength was reduced to nearly zero.     

Probabilistic Capacity Models and Fragility Estimates for Reinforced Concrete Columns Incorporating NDT Data

Knowing the ability of reinforced concrete (RC) bridges to withstand future seismic demands during their life-cycle can help bridge owners make rational decisions regarding optimal allocation of resources for maintenance, repair, and/or rehabilitation of bridge systems. The accuracy of a reliability assessment can be improved by incorporating information about the current aging and deterioration conditions of a bridge. Nondestructive testing (NDT) can be used to evaluate the actual conditions of a bridge, avoiding the use of deterioration models that bring additional uncertainties in the reliability assessment. This paper develops probabilistic deformation and shear capacity models for RC bridge columns that incorporate information obtained from NDT. The proposed models can be used when the flexural stiffness decays nonuniformly over a column height. The flexural stiffness of a column is estimated based on measured acceleration responses using a system identification method and the damage index method. As an application of the proposed models, a case study assesses the fragility (the conditional probability of attaining or exceeding a specified capacity level) of the column in the Lavic Road Overcrossing for a given deformation or shear demand. This two-span concrete box-girder bridge located in Southern California was subject to the Hector Mine Earthquake in 1999. Pre- and postearthquake estimates of the univariate shear and deformation fragilities and of the bivariate shear-deformation fragility are computed and compared. Both displacement and shear capacities are found to decrease after the earthquake event. Additionally, the results show that the damage due to the Hector Mine Earthquake has a larger impact on the shear capacity than the deformation capacity, leading to a more significant increment in the shear fragility than in the deformation fragility.     

Flexural Capacity of Compact Composite I-Girders in Positive Bending

Current American Association of State Highway and Transportation Officials (AASHTO) bridge specifications for compact composite steel girders in positive bending with adjacent compact pier sections limit the allowable maximum strength to a value between the full plastic moment and the hypothetical yield moment of the cross section as a function of the depth of web in compression. The strength prediction equations derived using these methods provide conservative values when compared to the results of the parametric studies used to develop the equations. Recent experimental tests coupled with finite-element analysis and mechanistic evaluations of the cross-section flexural capacity suggest that larger capacities may be achieved than those determined from AASHTO’s prediction equations. This paper presents an assessment of the behavior of composite positive bending specimens. A summary of a comprehensive literature review is provided coupled with results of the analytical and experimental evaluation of the nominal moment capacity of composite girders. Lastly, a less conservative design moment capacity expression developed from this assessment is provided.     

Flexural Reliability of Reinforced Concrete Bridge Girders Strengthened with Carbon Fiber-Reinforced Polymer Laminates

This paper presents the development of a resistance model for reinforced concrete bridge girders flexurally strengthened with externally bonded carbon fiber-reinforced polymer (CFRP) laminates. The resistance model is limited to pure flexural failure and does not address shear failure, laminate debonding, or delamination. The resistance model is used to calculate the probability of failure and reliability index of CFRP-strengthened cross sections. The first-order reliability method is employed to calibrate the flexural resistance factor for a broad range of design variables. The study shows that the addition of CFRP improves reliability somewhat because the strength of CFRP laminates has a lower coefficient of variation than steel or concrete. However, the brittle nature of CFRP laminates necessitates a reliability index that is greater than that generally implied in the AASHTO LRFD for 1998. This leads to a lower resistance factor than is currently accepted for reinforced concrete sections in flexure.     

Shear Strengthening of Reinforced Concrete Beams Using Carbon-Fiber-Reinforced Polymer Laminates

Shear failure is catastrophic and occurs usually without advance warning; thus it is desirable that the beam fails in flexure rather than in shear. Many existing reinforced concrete (RC) members are found to be deficient in shear strength and need to be repaired. Externally bonded reinforcement such as carbon-fiber-reinforced polymer (CFRP) provides an excellent solution in these situations. To investigate the shear behavior of RC beams with externally bonded CFRP shear reinforcement, 11 RC beams without steel shear reinforcement were cast at the concrete laboratory of the New Jersey Institute of Technology. After the beams were kept in the curing room for 28?days, carbon-fiber strips and fabrics made by Sika Corp. were applied on both sides of the beams at various orientations with respect to the axis of the beam. All beams were tested on a 979?kN (220?kips) MTS testing machine. Results of the test demonstrate the feasibility of using an externally applied, epoxy-bonded CFRP system to restore or increase the shear capacity of RC beams. The CFRP system can significantly increase the serviceability, ductility, and ultimate shear strength of a concrete beam; thus, restoring beam shear strength by using CFRP is a highly effective technique. An analysis and design method for shear strengthening of externally bonded CFRP has been proposed.     

Interface Shear Connection Analysis of Ultrahigh-Performance Fiber-Reinforced Concrete Composite Girders

The purpose is to analyze the interface shear connection behavior for ultrahigh-performance fiber-reinforced concrete (UHPFRC) and normal concrete (NC) composite girders. The shape and dimension of the shear stud in the conducted tests are referenced from the traditional interface connection design and engineering experiences. The interface shear connection parameters, i.e., initial stiffness and slippage capacity of a single shear stud, are measured from three groups of lateral direct push test specimens with different numbers of studs. Based on the UHPFRC tensile failure characteristics and cracked section rotational mechanisms of the UHPFRC-NC composite structures with flexural, or flexural and shear failure, the limit state is defined as a full pullout from the bottom fiber of the UHPFRC girders. Pseudostrain hardening behavior of the UHPFRC is simplified as an equivalent rectangular stress block. From this mechanism, the interface equilibrium equations are constituted and the interface shear connection degree of the UHPFRC-NC composite girders is derived. It is recommended that the interface shear connection degree may be used as minimum design standard for UHPFRC-NC composite interface shear connection design.     

Wire Gabion for Protecting Bridge Piers

As a new alternative countermeasure to riprap for scour protection around bridge piers, wire gabions were investigated experimentally for failure mechanisms, effects of significant parameters on failure and its sizing in a clear-water condition. The dominating failure mechanism was found to be a shear failure. Based on the experimental data, the controlling factors for the stability of wire gabions as a scour countermeasure at the pier are flow depth relative to pier diameter, length to thickness ratio, coverage, alignment and placement depth of wire gabions. An equation for sizing of a wire gabion is proposed in terms of Froude number and factors reflecting both the effect and limit of significant parameters. Comparison of the equation with those of ripraps shows that smaller wire gabions than ripraps provide an equivalent protection implying cost effective and improved stability.     

Repair of New Long-Span Bridges Damaged by the 1995 Kobe Earthquake

The 1995 Hyogo-ken Nanbu (Kobe), Japan earthquake provided the world’s first experience with earthquake damage to new long-span bridges designed to 1990s seismic standards. This paper reviews damage and describes techniques used to repair three major steel bridges along the Wangan route (Bayshore route) in Kobe—the 885 m Higashi-Kobe Bridge, the 217 m Rokko Island Bridge, and the 252 m Nishinomiya Port Bridge. These bridges, in service for less than three years, were essential components in the highway transportation system in the Kobe region. Extremely large ground motions, and failure of bearings, connections, and seismic restrainers were principal contributors to the damage sustained by these bridges. Repairs utilized heavy-lift floating cranes (up to 4,100 ton capacity) and various jacks to stabilize the structures and to realign spans. In one case, reconstruction of a collapsed span was required, with lifting weight a prime concern. Significant constraints on the repair included confined working space and requirements for maintaining maritime navigational clearances. The closure times for the repair of the bridges ranged from three to nine months.     

Riprap Failure at Circular Bridge Piers

Riprap of bridge piers is placed to prevent scour and to secure the pier from failure. Riprap is therefore an addition to a pier to increase its performance against scour. The present research intends to present three basic scour mechanisms associated with circular-shaped bridge piers in rivers first, to introduce then a number of selected experiments for a range of hydraulic, geometric, and sedimentologic conditions, and finally to describe a novel procedure for assessing the safety of these river elements against failure. This procedure is based on the Shields diagram relating to sediment entrainment in a uniform and flat sediment bed subjected by a water flow. The Shields approach is extended for the presence of a circular-shaped pier that is protected by a circular-arranged riprap layer of equal size elements. The design procedure presented in the following thus reduces to the entrainment condition of a pier for equal riprap and the sediment sizes and to the Shields entrainment condition when the pier diameter degenerates to 0.     

Seismic Performance Assessment of Damage-Controlled FRP-Retrofitted RC Bridge Columns Using Residual Deformations

Despite the improved performance of fiber-reinforced plastic (FRP)-retrofitted bridges, residual deformations in the event of an earthquake are inevitable. Little consideration is currently given to these deformations when assessing seismic performance. Moreover, important structures are currently required not only to have high strength and high ductility but also to be usable and repairable after high intensity earthquakes. This paper presents a definition of an FRP-RC damage-controllable structure. An intensive study of 109 bridge columns, extracted from recent research literature on the inelastic performance of FRP retrofitted columns with lap-splice deficiencies, flexural deficiencies, or shear deficiencies, is used to evaluate the recoverability of such retrofitted columns. The residual deformation, as a seismic performance measure, is used to evaluate the performance of 39 FRP-retrofitted RC columns from the available database. Based on this evaluation, a requirement for the recoverable and irrecoverable states of FRP-RC bridges is specified. Finally, the Seismic Design Specifications of Highway Bridges for RC piers is adapted to predict the residual deformations of FRP-RC columns.     

侧向冲击荷载下钢筋混凝土墩柱的性能

采用数值仿真技术建立了足尺钢筋混凝土墩柱精细有限元模型, 分析了侧向冲击荷载下墩柱的动态响应和抗冲击性能, 提出了一种基于截面损伤因子的损伤评估方法, 讨论了不同碰撞参数对钢筋混凝土墩柱破坏模式和损伤机理的影响.结果表明: 冲击荷载下钢筋混凝土墩柱的耗能主要分为接触区域局部耗能和构件整体耗能; 当冲击体的初始动能恒定时, 冲击质量和冲击速度的不同组合会导致钢筋混凝土墩柱损伤破坏机理的显著差异; 基于截面损伤因子的损伤评估方法可以比较准确地描述墩柱的破坏状态.轴压力对墩柱抗撞能力的有利贡献比较有限, 且墩柱随着轴力的增大更易发生剪切破坏; 冲头刚度对碰撞力和墩柱动态响应的影响十分显著.      

Probability of Exceedance Estimates for Scour Depth around Bridge Piers

Scour at a bridge pier is the formation of a hole around the pier due to the erosion of soil by flowing water; this hole in the soil reduces the carrying capacity of the foundation and the pier. Excessive scour can cause a bridge pier to fail without warning. Current predictions of the depth of the scour hole around a bridge pier are based on deterministic models. This paper considers two alternative deterministic models to predict scour depth. For each deterministic model, a corresponding probabilistic model is constructed using a Bayesian statistical approach and available field and experimental data. The developed probabilistic models account for the estimated bias in the deterministic models and for the model uncertainty. Parameters from both prediction models are compared to determine their accuracy. The developed probabilistic models are used to estimate the probability of exceedance of scour depth around bridge piers. The method is demonstrated on an example bridge pier. The paper addresses model uncertainties for given hydrologic variables. Hydrologic uncertainties have been presented in a separate paper.