Creep and thermal response of long span prestressed concrete integral abutment bridge

Abstract

Integral Abutment Bridges (IAB) are getting popular due to significant cost savings in their construction and maintenance. Many countries stipulate the use of IABs in their new bridge construction projects but mostly the span is limited to 60 m. The limit is set considering the concerns on the long-term performance of IAB beyond 60 m span due to complexities in its response to long-term material behaviour, environmental loading and backfill soil conditions. This limitation necessitates the need for research to adequately predict the long-term behaviour of IAB particularly those with span beyond 60 m. A parametric study is carried out by performing non-linear finite element analyses using LUSAS to determine the long-term behaviour of continuous span prestressed concrete IAB. The parameters considered are backfill soil type, bridge total length, thermal loading and creep. Subsoil behind bridge abutment is varied from dense sand, loose sand, stiff clay, to medium stiff clay. The bridge total lengths of 60 m, 90 m, 120 m, and 150 m, with pier-to-pier spans of 20 m, 30 m, 40 m and 50 m are considered respectively. Three dimensional models of IAB are subjected to self-weight, vehicle loading, prestressing force, temperature load ranging from 20 0C to 36 0C and concrete creep. The bridge response at 75 year life is examined in terms of deformations and changes in internal forces in the abutment, prestressed beams and pile foundations. The long term response of the IAB with different backfill soil types and span lengths subjected to all possible loadings was successfully quantified. The results revealed that the variation of the displacement and the internal forces in the abutment and the bridge beam are within the constructable limit where it is possible to design and construct the IAB beyond the length of 60 m. Seventy five years creep and shrinkage loading is found to have significant effect on long term behaviour of the bridge. It causes maximum loss in prestress force by 27 % resulting in reduced moment and shear capacity of girder by 557 kNm and 321 kN respectively and increases the girder deflection by 75 mm (160 %) in 150 m IAB. This also resulted in incremental abutment deflection 25 mm (575 % rise), abutment moment 5410 kNm (95 %), abutment shear 440 kN (41 %), and girder stress 7.53 N/mm2 (378 %) in 150 m long IAB. Soil-abutment interaction is found to have predominant effect in comparison to soil-pile interaction. Bridge length has considerable effect on magnitude of abutment moment causing 5870 kNm (112 %) incremental moment with increase in bridge length from 60 m to 150 m in varying subsoil stiffnesses. Results of the analyses are used in the formulation of long-term response prediction equations for deflection, moment and shear behavior of IAB abutments. The empirical equations have proven to be adequate and time efficient means of predicting deformations and changes in internal forces in the IABs of similar geometry and configurations.