The Response Modification Factor for Seismic Design of Integral Abutment Bridges

The response modification factor (R factor) is a crucial parameter for calculating the design seismic forces applied to a bridge structure. This factor considers the nonlinear performance of bridges during strong ground motions. Conventional bridge structures rely on the substructure components to resist earthquake forces. Accordingly, there are R factors available in the design codes based on the type of bridge substructure system. Lateral load resisting system of Integral Abutment Bridges (IABs) in the longitudinal direction is more complex than ordinary bridges. It involves the contributions from soils behind the abutments and soil/structure interaction (SSI) in addition to existing rigid connection between the superstructure and abutments. There is no R factor available in any design code throughout the world for IABs in the longitudinal direction that considers all these parameters. In this research, the Federal Emergency Management Agency publication FEMA P695 methodology has been applied to estimate the R factor for IABs. It is found that 3.5 could be a safe and valid R factor in the longitudinal direction for seismic design of such bridges.

Study of Horizontally Curved Slab-on-Steel I-Girder Bridges with Integral Abutments Under Thermal Loading

Integral abutment bridges have started to become part of the construction industry worldwide. However, they present challenges arising from the monolithic connection between bridge deck and the abutment. Thermal loading induced by daily cycles superimposed on seasonal cycles result in complex soil-structure interaction. Due to uncertainties in integral abutment bridge performance, there is no consensus among different codes on the bridge maximum length limit. A parametric study was carried out, using SAP2000 software, to examine the behavior of horizontal curved concrete slap-on-steel Igirders, under the effect of thermal loading conditions (±65°c). The self-weight of the bridge was considered. Spatial variables, including abutment height, radius of curvature, bridge span length, stiffness of backfill and types of foundation soil, were considered. The numerical analysis results were used to drive equation relating abutment height and bridge span with the maximum bridge length limit, which produces 40 mm horizontal displacement on pile head.

Study of Horizontally Curved Slab-on-Steel I-Girder Bridges with Integral Abutments Under Thermal Loading

Integral abutment bridges have started to become part of the construction industry worldwide. However, they present challenges arising from the monolithic connection between bridge deck and the abutment. Thermal loading induced by daily cycles superimposed on seasonal cycles result in complex soil-structure interaction. Due to uncertainties in integral abutment bridge performance, there is no consensus among different codes on the bridge maximum length limit. A parametric study was carried out, using SAP2000 software, to examine the behavior of horizontal curved concrete slap-on-steel Igirders, under the effect of thermal loading conditions (±65°c). The self-weight of the bridge was considered. Spatial variables, including abutment height, radius of curvature, bridge span length, stiffness of backfill and types of foundation soil, were considered. The numerical analysis results were used to drive equation relating abutment height and bridge span with the maximum bridge length limit, which produces 40 mm horizontal displacement on pile head.

Influence of Construction Joint and Bridge Geometry on Integral Abutment Bridges

Although integral abutment bridges (IABs) have become a preferred construction choice for short- to medium-length bridges, they still have unclear bridge design guidelines. As IABs are supported by nonlinear boundaries, bridge geometric parameters strongly affect IAB behavior and complicate predicting the bridge response for design and assessment purposes. This study demonstrates the effect of four dominant parameters: (1) girder material, (2) bridge length, (3) backfill height, and (4) construction joint below girder seats on the response of IABs to the rise and fall of AASHTO extreme temperature with time-dependent effects in concrete materials. The effect of factors influencing bridge response, such as (1) bridge construction timeline, (2) concrete thermal expansion coefficient, (3) backfill stiffness, and (4) pile-soil stiffness, are assumed to be constant. To compare girder material and bridge geometry influence, the study evaluates four critical superstructure and substructure response parameters: (1) girder axial force, (2) girder bending moment, (3) pile moment, and (4) pile head displacement. All IAB bridge response values were strongly related to the four considered parameters, while they were not always linearly proportional. Prestressed concrete (PSC) bridge response did not differ significantly from the steel bridge response. Forces and moments in the superstructure and the substructure induced by thermal movements and time-dependent loads were not negligible and should be considered in the design process.

Seismic Response of Skewed Integral Abutment Bridges under Near-Fault Ground Motions, Including Soil–Structure Interaction

Studies on the seismic response of skewed integral abutment bridges have mainly focused on response under far-field non-pulse-type ground motions, yet the large amplitude and long-period velocity pulses in near-fault ground motions might have significant impacts on bridge seismic response. In this study, the nonlinear dynamic response of an skewed integral abutment bridge (SIAB) under near-fault pulse and far-fault non-pulse type ground motions are analyzed considering the soil–structure interaction, along with parametric studies on bridge skew angle and compactness of abutment backfill. For the analyses, three sets of near-fault pulse ground motion records are selected based on the bridge site conditions, and three corresponding far-field non-pulse artificial records are fitted by their acceleration response spectra. The results show that the near-fault pulse type ground motions are generally more destructive than the non-pulse motions on the nonlinear dynamic response of SIABs, but the presence of abutment backfill will mitigate the pulse effects to some extent. Coupling of the longitudinal and transverse displacements as well as rotation of the bridge deck would increase with the skew angle, and so do the internal forces of steel H piles. The influence of the skew angle would be most obvious when the abutment backfill is densely compacted.