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.     

Field Testing and Analysis of CRC Deck Girder Bridges

This paper presents findings of field tests and analysis of two conventionally reinforced concrete (CRC) deck girder bridges designed in the 1950s. The bridges are in-service and exhibit diagonal cracks. Stirrup strains in the bridge girders at high shear regions were used to estimate distribution factors for shear. Impact factors based on the field tests are reported. Comparison of field measured responses with AASHTO factors was performed. Three-dimensional elastic finite-element analysis was employed to model the tested bridges and determine distribution factors specifically for shear. Eight-node shell elements were used to model the decks, diaphragms, bent caps, and girders. Beam elements were used to model columns under the bent caps. The analytically predicted distribution factors were compared with the field test data. Finally, the bridge finite-element models were employed to compare load distribution factors for shear computed using procedures in the AASHTO LRFD and Standard Specifications.     

Extending the Fatigue Life of Riveted Coped Stringer Connections

Fatigue cracking occurs at the copes of stringer–floorbeam connections of older, riveted steel bridges. Some cracks are quite long and raise serious questions regarding the remaining fatigue life of the subject bridges. Damage limitation methods (DLMs) have been used to increase the fatigue life of these stringers, but the effectiveness of the DLMs for these riveted connections had never been evaluated by tests. Therefore, tests were conducted to evaluate the fatigue life of coped, riveted stringer–floorbeam connections, and the effectiveness of DLMs. Fatigue cracks in the coped stringer–floorbeam connection were initially developed to establish crack initiation requirements and the rate and extent of crack growth. Once a significant crack was noted, one of several DLMs was applied, and the specimens were retested to determine the effectiveness of the DLM in controlling cracking. These DLMs included the drilled hole, the inserted bolt and the removed rivet methods. The relative effectiveness of the methods is described, and a design procedure is proposed for improving their performance.     

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.     

Investigation of Damaged 12-Year Old Prestressed Concrete Box Beams

An investigation was conducted of unexpected damage to a pair of three-span continuous-spread prestressed box beam bridges after 12 years of service. Routine inspection had revealed cracks in the box beams near the piers and abutments. An investigation was conducted to assess the condition of the beams in the bridges as well as their as-built properties and remaining strength. The investigation showed that the beams were built in accordance with the design drawings and specifications. One beam was tested under a combination of flexure and shear. These tests showed that the effective prestress was lower than standard design estimates. Measurable slip of the strands initiated as shear or flexure-shear cracks developed; however, the bond strength was sufficient for the strands to fail by fracture. The measured ultimate strength exceeded the analytical estimates by 7 to 9%. The conclusion of the investigation is that the cracks in the beams developed from a combination of conditions created by the design, detailing, and production of the beams.     

Assessment of Bridge Remaining Fatigue Life through Field Strain Measurement

With the aging of existing steel bridges and the accumulated stress cycles under traffic loads, assessment of remaining fatigue life for continuing service has become more important than ever, especially for decisions on structure replacement, deck replacement, or other major retrofits. Experience from engineering practice indicates that fatigue analysis based on specification loads and distribution factors usually underestimates the remaining fatigue life of existing bridges by overestimating the live load stress ranges. Fatigue evaluation based on field-measured stress range histograms under actual traffic load proves to be a more accurate and efficient method for existing bridges. This paper describes the application of such a method in assessing the remaining fatigue life of bridge structures. Current AASHTO specifications for fatigue evaluation of existing bridges are reviewed and compared. Case studies of three major highway bridges are discussed. Finally, a procedure is proposed for evaluating fatigue life of existing bridges through field strain measurement.     

Service Life Assessment of Existing Highway Bridges with No Planned Regular Inspections

Safety of a highway infrastructure system depends very much on the proper maintenance of bridges. The level of required maintenance is, typically, determined through a series of regular field inspections with the guidance of safety–economy trade-off. In Turkey, bridge maintenance, repair, and rehabilitation are currently performed on an as-needed basis. Time-dependent reliability analysis cannot be utilized for Turkish bridges for the time being since the majority of the bridges are either not regularly inspected or not inspected at all. The purpose of this paper is to propose a simple method to assess the remaining service life of a bridge by defining a relationship between its current condition rating and its age by evaluating a set of bridges at different ages. In a case study, 28 bridges were inspected for the first time to assess the average life expectancy. The average life of a bridge was predicted to be 80?years, and for this set of bridges, the main body components were found to deteriorate more than earth retaining and serviceability components.     

Effect of Carbonation on Concrete Bridge Service Life

An increase in the number of distressed bridges and the limited financial resources emphasize the need for an efficient bridge management system (BMS) for India. Assessment of the remaining life of bridges becomes an essential step in BMS, which involves modeling of complex deterioration mechanisms in concrete due to chemical attacks, such as carbonation, chloride, sulfate, and so on. Lack of information on material properties used in bridge construction, construction techniques, exposure condition, and maintenance quality adopted make the remaining life assessment of bridges more complicated. Therefore, a parametric study has been carried out to understand the deterioration of concrete bridges due to carbonation. Effect of carbonation on the initiation and propagation time of corrosion was also included in the study. Based on the study, modifications are suggested in the clauses of Indian concrete bridge design standard IRC: 21 (2000) so as to enhance the service life of bridges.     

Stability of Slender Webs of Prestressed Concrete Box-Girder Bridges

Long-span, prestressed concrete, box-girder bridges are haunched and have a span-to-depth ratio of 15 to 20 at the piers. This leads to slender webs, particularly for bridges built with high performance concrete. For girders with sloped webs and constant bottom slab width, the web plate is normally warped, which leads to web curvature in the direction of the principal compressive stresses. It is first shown that buckling is not critical as long as the web is uncracked. But, if the webs have shear cracks, the slenderness ratio of the diagonal compression struts can be very high so that the moments and stability of the curved struts need to be studied. It is shown that the tensile forces in the stirrups—determined according to the truss analogy—will counteract the lateral deformations of the slender compression struts. The procedure, which was developed for the design of the Confederation Bridge in Eastern Canada, will be illustrated by applying it to the slender webs of that bridge.     

New assessment methods for the residual safety of old steel bridges

A great part of existing steel bridges for roads and rails are riveted structures that were built in the last century. Many of these old bridges have undergone several phases of repair or strengthening after damages in the world wars or due to changes of service requirements. For these bridges the question of the actual safety for modern traffic loads and the remaining service life is put forward. This paper describes a procedure to determine the residual safety and service life of old steel bridges and how a basis can be established on which economic decisions for further strengthening or replacement by a new bridge may be made. This procedure has been developed in close cooperation between the Institute for Ferrous Metallurgy and the Institute for Steel Construction of RWTH since 1982. It has been applied to many steel bridges in particular in Eastern Germany and also to other structures susceptible to fatigue, e.g. guyed masts, antennae, machinery parts etc.     

Performance of Coated Reinforcing Bars in Cracked Bridge Decks

The presence of cracks in bridge decks that are reinforced with epoxy-coated reinforcing (ECR) bars has raised some concerns among bridge and maintenance engineers in the state of Iowa. To study the effects of deck cracking on the performance of ECR bars, several concrete cores that contained reinforcing bars were collected from 80 bridges that are located in different counties throughout the state of Iowa. These samples were collected from cracked and uncracked areas of the bridge decks. Concrete powder samples were collected from these cores and were analyzed in the laboratory to determine the diffusion of the chloride in the bridge decks. This study revealed that no sign of corrosion was detected for the ECR rebars that were taken at the uncracked bridge deck locations. In addition, no delamination or spalling was observed for the bridge decks where bars in the core samples, which were taken at the cracked bridge deck locations, exhibited signs of corrosion. The collected ECR rebars samples were rated according to the degree of the corrosion that was observed on each bar. These ratings were used to develop condition/age relationships that were utilized to estimate the functional service life of bridge decks that are reinforced with ECR bars.     

Engineering critical assessment on welding flaws of the X65 UOE girth weld based on CRACKWISE

Focused on the girth weld of a Φ762 × 28. 6 mm( X65) offshore UOE pipe,the fracture toughness properties at different weld joint positions were tested. Meanwhile,the largest size of different cracks under service condition was calculated by using CRACKWISE. The service life of the UOE pipe with postulated crack-like flaws was calculated by considering various fatigue factors,such as vibrations caused by ocean current and fluctuations of inner pressure. The assessment process and results can be used to direct the repair of weld flaws laid in pipes or to assess the reliability of in-serving pipes.     

3#焦炉损坏原因分析及治理措施

针对3#焦炉炉龄增加后,炭化室墙面出现剥蚀、裂纹等问题,分析了出现此现象的原因,并针对剥蚀和裂纹制定了处理措施。     

50-Year-Old Prestressed Segmental Concrete Bridges

The first prestressed segmental concrete bridge in the United States opened to traffic was a small bridge in Madison County, Tennessee. The bridge was constructed using prestressed concrete segments and was opened to traffic in October 1950. Prestressed concrete beams were placed side by side to form the superstructure of the bridge. The construction of this bridge and several other similar prestressed concrete bridges are described herein. The existing condition of eleven prestressed concrete bridges remaining in Tennessee is given. Only minor spalling, leaching, and horizontal cracking are present in the superstructure after fifty years of service. Many of the design features introduced in this design can be found in today’s modern precast segmental concrete bridges.     

Fatigue Strength of Repaired Prestressed Composite Beams

Composite steel-concrete bridges constitute a major portion of the national bridge inventory. Many of these structures are approaching or have passed their service lives and are in need of repair and rehabilitation. External prestressing by means of high-strength bars or cables attached to the steel beams has been used as an effective technique for upgrading the load carrying capacity of composite steel-concrete girders. While several researchers have investigated the static behavior of prestressed composite beams, few have reported on the fatigue strength of this structural system. The writers present the results of the experimental and analytical study of ten composite girders that were prestressed with seven-wire strands and then fatigue tested to failure. Three methods of extending the fatigue life of cracks were then explored: (1) drilling a hole at the crack tip and installing a high-strength bolt; (2) splicing the web at the cracked section; and (3) increasing the prestressing force of the tendon. The efficacy of the three methods is compared.     

Performance Evaluation of Short Span Reinforced Concrete Arch Bridges

In this paper, the static and seismic performance of some short span reinforced concrete arch bridges, before and after strengthening interventions, are evaluated. To verify whether retrofit strategies for the considered arch bridges, which were designed for resisting under permanent and service actions, were adequate for earthquake resistance, seismic analyses of the as-built model of the structures have been undertaken. To account for multiple input effects on arches, induced by out-of-phase motions at foundation levels as well as different boundary conditions at structural supports, the seismic response of the structures under correlated horizontal and vertical multiple excitations is calculated. The effects on arch bridges of conventionally used uniform input and partially correlated multiple inputs with phase shifts are compared. In all cases, the results are discussed with particular reference to the influence of structural configuration, secondary systems, cross-section thickness of the arch, and retrofit interventions.     

Parametric Study of Posttensioned Inverted-T Bridge System for Improved Durability and Increased Span-to-Depth Ratio

Rehabilitation of the existing bridges is one of the most pressing needs in maintenance of the transportation infrastructure. As an example, more than 2,000 bridges in Kansas alone need to be replaced during the next decade. The majority of these bridges have spans of 30 m (100 ft) or less, and shallow profiles. The inverted-T (IT) bridge system has gained increasing popularity in recent years due to its lower weight and relatively larger span-to-depth ratio compared to the prestressed I-girder bridges. However, there are some limitations in replacing the existing cast in place (CIP) bridges with IT system. Implementation of posttensioning, which is the focus of this paper, is a promising solution for these limitations. This leads to a higher span-to-depth ratio and reduces potential transverse cracks in the CIP deck which is a major concern for corrosion of the reinforcement. An analytical research was conducted to identify the major parameters influencing the performance of a posttensioned IT bridge system. This was followed by a parametric study to explore the scope of these parameters and specify the design limits in terms of posttensioning stages, timing scenarios, and posttensioning forces. Concrete strength and different methods for estimating time-dependent restraining moments were addressed in this parametric study.     

In-Service Diagnostics of a Highway Bridge from a Progressive Damage Case Study

Development of diagnostic and prognostic routines for application to in-service measurements from highway bridges necessitates analysis of experimental measurements from in-service highway bridges under natural or prescribed induced damage. This is generally limited to the unique opportunity of investigating end-of-service life bridges prior to reconstruction and consequently only a limited library of such case studies exist. This paper documents a field test of an end-of-service bridge span with prescribed progressive damage to a bearing as well as several diaphragm connections. Thirty dual-axis accelerometers were distributed across the bridge span with data acquisition and transmission facilitated by a real-time lossless wireless sensor network. A highway department service truck applied traffic excitation to the structure through routine passes on a consistent lane of traffic. Output-only system identification was applied to the baseline time history response to develop a state-space model of the bridge dynamics used for forward prediction in the form of a Kalman filter. Simple statistical evaluation of the prediction error in the model demonstrates the variance can be used to localize and generally quantify the degree of damage in the structure. The case study additionally illustrates the potential importance of monitoring lateral acceleration along the girders to permit identification of damage to elements, such as the diaphragms, that contributing primarily to the lateral and torsional response of primary structural members.     

Life prediction based on the propagation of short cracks

The growth of short and long fatigue and creep-fatigue cracks was examined in various steels. The experiments were carried out to test if recent models for creep-fatigue crack growth can be applied to describe the influence of strain rate on the growth of large and small cracks. Damage parameters were derived from these crack-growth laws for the life prediction under complicated loading. These parameters were applied to predict the life of smooth specimens cycled at different temperatures and deformation rates. Compared to conventional life predictions better predictions were obtained presumed the growth mechanism of the short cracks did not change for the range of temperature and strain rates in question.     

Behavior of Split Timber Stringers Reinforced with External GFRP Sheets

A large number of timber bridges are at the end of their service life in North America and the prohibitive costs of replacement make owners face the challenge of developing efficient rehabilitation techniques. This paper presents the results from an experimental program of testing old full scale timber stringers with longitudinal splits. Stringers were reinforced for shear and bending using glass fiber-reinforced polymer (GFRP) sheets. A total of nine full-scale Douglas-fir beams were tested in three-point bending after strengthening for flexure and shear with GFRP sheets. Horizontal shear forces in shear reinforcement were calculated using a simplified model. Beams that failed by debonding of shear reinforcement, failed at horizontal shear forces within the range of 150–266?kN. Design charts were constructed on the basis of these calculated forces to simplify the design of shear reinforcement for different sizes and locations of splits.