Strength Evaluation of Deteriorated RC Bridge Columns

Condition-rating methods followed by load rating calculations are used for evaluating existing bridges in the United States. Ratings are assessed visually based on engineering expertise and experience, and in some cases supplemented by nondestructive tests. Good understanding of the effects of deterioration on the structural performance leads to better inspection procedures, planning, and cost-effective rehabilitation methods. This paper presents a bridge pier column strength evaluation method that can be adapted into a currently used bridge condition evaluation method. This method uses damaged material properties, and accounts for amount of corrosion and exposed bar length for each reinforcement, concrete loss, bond failure, and type of stresses in the corroding reinforcement. The proposed evaluation method provides a good estimate of the condition and load-carrying capacity of bridge piers that currently cannot be obtained by normal visual surveys. In addition, the proposed evaluation approach will help reduce repair costs, avoid overconservative condition ratings, and result in a more uniform level of safety of concrete bridge substructure in the United States.     

Case Study: Retrofitting Large Bridge Piers on the Nakdong River, South Korea

The Gupo Bridge crosses the Nakdong River near the city of Busan, South Korea. During Typhoon Maemi in 2003, the old Gupo Bridge collapsed due to excessive pier scour. More recently, the highway construction on the left-bank floodplain required right-bank channel widening to restore the channel flood-carrying capacity. This 7?m deep floodplain excavation is expected to cause significant local scour around the 8–10?m wide and 3?m thick spread footings of Piers 11 and 12 of the Subway Bridge and Piers 15 and 16 of the Gupo Bridge. Three design options are examined for retrofitting floodplain bridge piers with massive spread footings. A solution with sheet piles and riprap was recommended in 2006 as the most appropriate design, but Plan III with a conical riprap structure around the footings was ultimately constructed in 2007 for economic reasons. Laboratory experiments also highlight the need to place gravel and synthetic filters under the designed riprap.     

Bridge Damage and Repair Costs from Hurricane Katrina

Hurricane Katrina caused significant damage to the transportation system in the Gulf Coast region. The overall cost to repair or replace the bridges damaged during the hurricane is estimated at over $1 billion. This paper describes the observed damage patterns to bridges, including damage attributed to storm surge, wind, impact from debris, scour, and water inundation, as well as examples of repair measures used to quickly restore functionality to the bridges and transportation system. Using the data from the 44 bridges that were damaged, relationships between storm surge elevation, damage level, and repair costs are developed. The analysis reveals that, in general, regions with higher storm surge had more damage, although there were several instances where this was not the case, primarily due to damage resulting from debris impact. It is also shown that a highly nonlinear relationship exists between the normalized repair cost and the damage state. The paper concludes with a brief discussion on the efficacy of using typical seismic design details for mitigating the effects of hurricane loads, and potential design considerations for bridge structures in vulnerable coastal regions.     

Effects of Inclination of Bridge Piers on Scouring Depth

For a safe design of a bridge pier footing, it is important to estimate the maximum depth of scour as accurately as possible. The aim of this experimental study is to investigate the effects of inclination of bridge piers on local scour depths around bridge piers. Single circular piers inclined toward the downstream direction were founded in a uniform bed material. Near threshold conditions were employed. The results of this study indicate that the local scour depth decreases as the inclination of the pier increases.     

Application of Riprap and Collar to Prevent Scouring around Rectangular Bridge Piers

Various methods to control scour around bridge piers have been proposed, including application of riprap and installing a collar around piers. In the present study application of riprap alone and a combination of riprap and collar were examined experimentally for scour control around rectangular bridge piers. Piers aligned with the flow and skewed at 5, 10, and 20° to the flow were tested. Piers with three different aspect ratios equal to 1:3, 1:5, and 1:7 were used in this study. A collar three times wider than the piers’ width was installed around the piers at the streambed level. All experiments were conducted at the threshold of motion of the bed material. The size and extent of stable riprap stones for prevention of scouring around the piers was found by experiment with and without the collar. A method previously given for calculating stable riprap size around circular piers is extended for rectangular piers with different aspect ratios and skew angles with and without collar protection. The extent of stable riprap layer in all tests is also presented.     

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.     

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.     

Damage Analysis of Hanshin Expressway Viaducts during 1995 Kobe Earthquake. II: Damage Mode of Single Reinforced Concrete Piers

The damage mode that single reinforced concrete (RC) piers of the Hanshin Expressway Kobe Route suffered during the 1995 Kobe earthquake is discussed. On the Kobe Route, many single RC piers suffered from flexural mode damage; however, some suffered from shear failure, and most shear failure occurred in piers with rectangular cross sections. The flexural and shear capacity of each pier are calculated based on the design documents, and the ratio of flexure to shear capacity, r, is calculated by taking into account the mass of the pier column. It is found that the damage mode (flexure or shear) in the severely damaged single RC piers from P1 to P350 can be explained by the value of r, either >1.0 (flexural mode) or <1.0 (shear mode).     

Bridge Pier Scour in Clay-Sand Mixed Sediments at Near-Threshold Velocity for Sand

Local scour at circular bridge piers embedded in a clay-sand-mixed bed was investigated in laboratory flume experiments. The effects of clay content, water content, and sand size on maximum equilibrium scour depth, equilibrium scour hole geometry, scouring process, and time variation of scour were studied at velocities close to the threshold velocities for the sand in the clay-sand mixture. It was observed that clay content and water content were the key parameters that effect the scouring process, scour hole geometry, and maximum equilibrium scour depth. The bridge pier scouring process in clay-sand mixtures involved different dominating modes for removal of sediment from scour hole: chunks-of-aggregates, aggregate-by-aggregate, and particle-by-particle. Regression-based equations for estimation of nondimensional maximum scour depth and scour hole diameter for piers embedded in clay-sand mixtures having clay content of <40% and water content of <40% were proposed as functions of pier Froude number, clay content, water content, and bed shear strength.     

Reduction of Local Scour around Bridge Piers Using Slots and Collars

The present study examines the use of pier slots and collars for reducing local scour at bridge piers. The efficacy of slots, of different lengths and at different angles of attack, was studied through experiments. The reduction of scour due to the placement of circular collars, of different sizes and at different elevations, was also investigated. Analysis of the data from the experiments as well as data from earlier studies led to an equation for the maximum scour depth around circular bridge piers fitted with collars. The equation applies to local scour of uniform-sized sediment in clear-water flow.     

Investigation and Repair of a Four-Story Building Damaged by Yazoo Clay

Construction of buildings using a slab on grade and belled drilled piers to support column loads in central Mississippi has performed poorly. Similar buildings where the first floor was poured on 15.2 cm (6 in.) cardboard box forms have not fared much better. The first floor of this building was a slab on grade that was dowelled to a grid of grade beams. The grade beams were dowelled to drilled piers. The top of the expansive Yazoo clay varied from 1.8 to 3.66 m (5.9–12 ft) deep. High swell pressures developed under the slab and began to lift the building. A frame analysis showed that foundation movements were significantly changing the stresses of the structural steel frame. About half of the drilled piers of the building were found to be damaged near the connection with the grade beam. Two piers had separations of 10.2 and 8.9 cm (4 and 3.5 in.). During the foundation repair, the building frame was releveled and eight damaged piers were replaced. Recommendations to reduce the risk of this kind of damage were made.     

Seismic Design of Lifeline Bridge using Hybrid Seismic Isolation

This paper presents the merits of a hybrid seismic isolation system used for the seismic design of a major bridge. The bridge is analyzed for two different arrangements of seismic isolation systems. The first arrangement consists of friction pendulum bearings at all substructure locations; the other incorporates a hybrid system where laminated elastomeric bearings are used at the abutments and friction pendulum bearings at the piers. Analysis results have demonstrated that the hybrid seismic isolation system provided a structure with a fundamental period long enough to attract smaller seismic forces, while controlling the magnitude of isolation bearings displacements. It also provided a more uniform distribution of seismic forces among substructure elements. As a result, higher seismic forces on the piers were reduced, allowing for a more economical design of substructures. The hybrid seismic isolation system helped to control the wind-induced vibrations and reduced the sizes of the isolation bearings.     

Near Real-Time Scour Monitoring System: Application to Indian River Inlet, Delaware

Scour hole monitoring is widely used by engineers in reaction to bridge scour. Current monitoring methods lack the ability to observe wide areas on operational time scales. It is imperative that wide areas be observed after channel bed armoring countermeasures are taken because the armoring occupies an area larger than can be observed by traditional single-point scour monitors. The present bridge piers within the Indian River Inlet, Delaware, are adjacent to deep scour holes that threaten the bridge. A new scour monitoring system (SM) using two three-dimensional profiling sonars was installed on the Indian River Inlet Bridge to observe more than 19,000??m2 of bathymetry daily. The system components, configuration, and operation are described and example data are presented. Bathymetric data collected by the SM compare favorably with historic high-quality multibeam data from the U.S. Army Corps of Engineers. Quantitative correlations with temporally consistent data from a single-beam personal watercraft survey vessel yield an r2 correlation coefficient of 0.84 with 93% of the absolute value of elevation differences between the two data sets less than 3?m.     

Influence of Wood Debris Accumulation on Bridge Pier Scour

This note deals with the influence of debris accumulation on scour around bridge piers. Clear-water experiments in different hydraulic conditions have been carried out with three wood debris shapes: rectangular, triangular, and cylindrical. A wide range of debris thickness and width were studied in order to determine their influence on the maximum scour hole depth temporal evolution. The ratio of the pier diameter to the channel width was varied between 0.05 and 0.12 with total bridge contractions up to 20%. A proposed relation presents a simple design procedure to predict the increase in scour depth, which mainly depends on the flow contraction due to the debris accumulation.     

Repair of Cracked Steel Girders Connected to Concrete Slabs Using Carbon-Fiber-Reinforced Polymer Sheets

This paper presents the results of an experimental study on the repair of artificially damaged steel–concrete composite beams repaired using adhesively bonded carbon-fiber-reinforced polymer (CFRP) sheets. Eleven, 2 m long, beams composed of W150×22 steel sections with 465×75?mm concrete slabs were tested in four-point bending. Severe damage was first introduced in ten beams by saw cutting the tension flange completely at mid span, to simulate a fatigue crack or a localized severe corrosion. Standard modulus (SM) and high modulus (HM) CFRP sheets were then used to repair nine damaged beams. The length and number of CFRP layers applied to the cracked flange on the underside, or on both sides, were varied. Results showed that the damage had reduced flexural strength and stiffness by 60 and 54%, respectively. Nevertheless, CFRP-repaired beams achieved various levels of recovery, and in some cases, exceeded the original capacities. The strength of beams repaired with sheets, ranging in length from 8 to 97% of the span, varied from 46–116% of the original undamaged strength, whereas the stiffness range was 86–126% of original stiffness. SM-CFRP failed by debonding whereas HM-CFRP was ruptured. Bonding the sheets to both sides of the flange was not very advantageous over bonding to the underside only.     

Flume Tests for Scour in Clay at Circular Piers

Local scour at circular piers founded on clay was studied experimentally in the laboratory to compare the depth of scour in sand and in clay and to investigate the effects of the Reynolds number, Froude number, and approach flow depth on scour depth. The depths of scour in front, at the side, and in the back of the piers were measured as a function of time under steady, gradually varied flow conditions. The measured scour-depth-versus-time curves were fitted with a hyperbola to estimate the equilibrium scour depths. The extrapolated equilibrium scour depths were compared with values predicted by the Federal Highway Administration equation. The results showed that although the rates of scour were much slower in clay than in sand, equilibrium scour in clay was about the same as in sand. It was found that the shape of the scour hole correlates with the pier Reynolds number. At low Reynolds numbers, the depth of scour was about the same all around the piers. At higher Reynolds numbers, the scour holes developed mainly behind the piers with much less scour in front of the piers. It was also found that the extrapolated equilibrium scour depth correlates well with the pier Reynolds number and that the Froude number and relative water depth did not have a significant effect on the scour depth for these experimental conditions.     

Survey and Evaluation of Damaged Concrete Bridges

It is well known that the U.S. bridge inventory stands in need of repair. For a rational allocation of U.S. investment resources to bridge maintenance, life cycle cost and probabilistic methods must be used. This requires a quantitative estimate of the remaining strength over the intended lifespan for a given bridge. Although nondestructive evaluation methods are becoming established for bridge inspection purposes, specific recommendations for the application of these methods for individual bridges do not exist. This study focuses on reported damage and damage modeling for concrete bridges, with particular attention to Colorado bridges. A survey on degradation mechanisms is briefly presented. Bridge damage is reviewed for a variety of concrete bridges based on information in the literature and from field studies performed by the Colorado Department of Transportation. A catalog of damages and examples that illustrate the variety and severity of damage in these bridges are presented. For the bridges considered in the survey, the most common source of damage is water leaking through deck joints. A method for predicting strength loss is applied to a typical bridge in Colorado. It is shown that corrosion initiation occurs more quickly and normalized strength loss is much greater for shear than for flexure. It is also shown that many reinforced concrete bridges under corrosion attack may be more vulnerable to shear than to bending failure. The results can be used to identify critical elements for inspection and repair, and to assist in the development of rational maintenance planning strategies for concrete bridges.     

Assessment of Fire Damage to a Reinforced Concrete Structure during Construction

This article summarizes an engineering evaluation of the extent of fire damage to a concrete structure under construction. The fire occurred in a portion of the reinforced concrete structure and visibly damaged a load bearing exterior foundation wall. The purpose of the assessment was to promptly evaluate the in situ condition of the wall and recommend necessary repair or replacement options prior to commencement of backfilling and the concrete construction to be supported by the subject wall. The engineering assessment of the damaged wall included a nondestructive evaluation phase consisting of ultrasonic pulse velocity testing and a laboratory testing phase on the concrete cores removed from the damaged wall. Dynamic Young’s modulus of elasticity and an air permeability index of 25?mm (1?in.) thick disks sawed from the cores were determined. Analysis of properties of 25?mm (1?in.) concrete specimens permitted assessment of the presence and degree of any damage in smaller depth increments compared to the size of a compressive strength core. Significant differences were not indicated by compressive strength of cores, however, the in situ nondestructive testing and laboratory testing of the disks were effective in determining the depth of damage, as a result of the fire. The results of the nondestructive and laboratory evaluation indicated that the distressed zone of the concrete was limited to a near-surface layer. Repair recommendations were based on removal and replacement of the affected concrete sections identified by the testing program.     

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.     

Analysis and Testing of Piles for Ship Impact Defenses

This paper deals with analyses and reduced scale tests carried out to validate the design of flexible protection structures for bridge piers against ship impact. The protection system analyzed is part of the fixed link currently under construction across the Parana River between the cities of Rosario and Victoria in Argentina, and it will protect a cable-stayed bridge and parts of the approach viaduct against impact of aberrant vessels with sizes up to 100,000 DWT. The protection system was designed on the basis of dissipated energy and consists of groups of steel-encased large diameter concrete piles connected at the top by a reinforced concrete platform. The impact energy is to be absorbed by large horizontal displacements of the pile caps that involve large deformations of the surrounding soil and geometrically and material nonlinear response of the pile shafts themselves. The paper focuses on modeling the nonlinear characteristics of the response of the structure, and on its assessment by means of 1:15 scale model tests performed in both the laboratory and in the field to account for the displacements and deformations undergone by the pile shafts.