High-Cycle Fatigue of Diagonally Cracked Reinforced Concrete Bridge Girders: Field Tests

Large numbers of conventionally reinforced concrete deck–girder (RCDG) bridges remain in-service 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. RCDG bridges with diagonal cracks were inspected and instrumented. Strain and crack displacement data were collected under ambient traffic conditions and controlled test trucks. Results indicated relatively small stirrup stresses and diagonal cracks exhibited opening and closing under truck loading.     

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.     

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.