Abutment Piles Research Articles

Capacity Evaluation of Exterior Sacrificial Shear Keys of Bridge Abutments

Shear keys are used in bridge abutments to provide transverse support for the superstructure. The damage observed on bridge abutments in the aftermath of the 1994 Northridge Earthquake prompted the revision of the design of shear keys. As part of this revision, experimental and analytical work was conducted to investigate the seismic behavior of exterior shear keys in bridge abutments designed in accordance with current guidelines and to investigate shear keys designed for damage control. The latter work was aimed at providing guidance for seismic design of shear keys to act as structural fuses that would limit the input force in the abutment piles. Ten shear keys were designed and built at 1:2.5 scale of a prototype abutment design provided by Caltrans. The study concluded that a smooth construction joint should be considered at the interface of the shear key–abutment stem wall to allow sliding shear failure. A mechanism model was developed for capacity evaluation of shear keys with sliding shear failure. The results of the experimental program and development of the simple analytical model for capacity evaluation of exterior shear keys are presented in this paper.

Field Monitoring of Integral Abutment Bridge in Massachusetts

Integral abutment bridges are increasingly being used to eliminate undesirable bridge joint effects on the long-term performance of bridges. Although many states use this type of construction, common design guidelines are lacking, and nonuniform limitations on integral abutment design are imposed by different agencies. Data from the field monitoring of an existing three-span integral abutment bridge in central Massachusetts are presented. Resulting data are valuable in evaluating existing design provisions and understanding structural behavior. The results presented for a 16-month period of monitoring include recorded ambient temperature from -4°F to 99°F (-20°C to 37°C). Longitudinal movements induced by thermal expansion and contraction of the bridge are consistent with temperature changes. However, earth pressure cell data indicate that the maximum pressures generated behind the abutment walls occur in early spring. Lower pressures measured in the summer indicate some dissipation of soil pressures with time. Longitudinal displacement measurements taken during 2-week periods included variations that approached the magnitude of seasonal changes. Although fairly significant abutment movement has been recorded to date, there is no clear indication that the abutment piles have yielded. Field monitoring will continue, and the results from this study will be used to calibrate a detailed finite element model of the bridge to validate current integral abutment bridge design practices.

Field Performance of Integral Abutment Bridge

The behavior of an integral abutment bridge near Rochester, Minnesota, was investigated from the beginning of construction through several years of service by monitoring more than 180 instruments that were installed in the bridge during construction. The instrumentation was used to measure abutment horizontal movement, abutment rotation, abutment pile strains, earth pressure behind abutments, pier pile strains, prestressed girder strains, concrete deck strains, thermal gradients, steel reinforcement strains, girder displacements, approach panel settlement, frost depth, and weather. In addition to determining the seasonal and daily trends of bridge behavior, live-load tests were conducted. All of the bridge components performed within the design parameters. The effects from the environmental loading of solar radiation and changing ambient temperature were found to be as large as or larger than live-load effects. The abutment was found to accommodate superstructure expansion and contraction through horizontal translation instead of rotation. The abutment piles appeared to be deforming in double curvature, with measured pile strains on the approach panel side of the piles indicating the onset of yielding.

Approximate computer analysis of pile groups subjected to loads and ground movements

This paper describes the development of an approximate approach for the analysis and design of piles subjected to axial and lateral loading and also to vertical and horizontal ground movements. The analysis involves a number of simplifications in order to make it feasible to implement. For example, it considers the behaviour of a ‘representative’ pile in a group to characterize the behaviour of all piles in the group, and adopts approximations to derive free-field interaction factors from the conventional interaction factors for direct loading. The analysis has been implemented via a computer program called EMbankment PIle Group (EMPIG) and has the ability to incorporate the following features: 1. single piles or pile groups, 2. applied vertical, lateral and moment loading on the pile cap, 3. the effects of axial and lateral soil movements caused by embankment construction, 4. a layered soil profile, 5. non-linear axial and lateral response of the piles. Comparisons between solutions from EMPIG and other independent programs suggest that it is capable of providing results of adequate accuracy for practical design purposes. The analysis has been used to investigate the effects of pile rake on a typical bridge abutment group. The presence of raked piles can have a detrimental effect on group behaviour, especially in the presence of ground movements. Large lateral deflections can be generated and axial forces and moments in the piles are increased. Comparisons are also made with the results of centrifuge model tests on abutment pile groups. Copyright © 1999 John Wiley & Sons, Ltd.

Abutment Pile Design for Jointless Bridges

Abutment piles for a jointless bridge are subjected to lateral displacement as the bridge superstructure expands and contracts. The piles must be designed to satisfy the strength criteria of a structural member and the load transfer requirements and support resistance of the surrounding soil. Two design alternatives for the pile capacity are presented. Results for both design alternatives are shown to be conservative when compared with the solutions obtained from a previously developed finite element model. Alternative one, involving elastic behavior, is recommended for piles with insufficient moment‐rotation capacity, while alternative two, involving inelastic behavior, is recommended for piles having a moment‐rotation capacity that exceeds the moment‐rotation demand at plastic hinge locations. Specific expressions for the ductility requirements for alternative two are specified for both uniaxial and biaxial bending conditions. When the piles have sufficient ductility, alternative two will permit the saf...