Luigi Callisto

Seismic Design of Flexible Cantilevered Retaining Walls

In this paper, the seismic behavior of embedded cantilevered retaining walls in a coarse-grained soil is studied with a number of numerical analyses, using a nonlinear hysteretic model coupled with a Mohr-Coulomb failure criterion. Two different seismic inputs are used, consisting of acceleration time histories recorded at rock outcrops in Italy. The numerical analyses are aimed to investigate the dynamic behavior of this class of retaining walls, and to interpret this behavior with a pseudostatic approach, in order to provide guidance for design. The role of the wall stiffness on the dynamic response of the system is investigated first. Then, the seismic performance of the retaining walls under severe seismic loading is investigated, exploring the possibility of designing the system in such a way that during the earthquake the strengths of both the soil and the retaining walls are mobilized. In this way, an economic design criterion may be developed, that relies on the ductility of the system, as it is customary in the seismic design of structures.

A factored strength approach for the limit states design of geotechnical structures

This paper discusses the implications of an approach to the limit states design of geotechnical structures in which the soil strength parameters are factored, as is the one contained in the European construction code. It is shown that a factored strength approach has very different implications for the two customary types of geotechnical analyses; namely, the study of plastic mechanisms and interaction analyses. The relationship between partial safety factors and the reliability of a system is highlighted first, with the aid of approximate reliability calculations relative to two example problems. It is then demonstrated that the method of factoring the soil strength may be regarded as an effective way to assess the distance of a structure from the activation of a plastic mechanism, and to relate this distance to a conventional measure of its reliability. Using the same examples, it is argued that the procedure of factoring the soil strength parameters is not appropriate for the evaluation of the internal...

Capacity Design of Retaining Structures and Bridge Abutments with Deep Foundations

This paper examines a seismic capacity design approach for retaining structures with piled foundations, which assumes full-strength mobilization in the soil and in the foundation piles during the earthquake. The plastic mechanism activated by the seismic forces consists of a horizontal movement of the structure, involving plastic hinging in the piles. This mechanism is triggered when the seismic inertial forces acting within the structure and the soil mass equal the overall strength of the soil-pile foundation system. The paper describes an iterative procedure for evaluating the critical seismic acceleration that activates the plastic mechanism. The seismic performance of the structure is expressed by its permanent displacements and the corresponding curvature ductility demand in the foundation piles. With reference to an idealized bridge abutment, this procedure is expressed in a fully consistent nondimensional form and is applied to a reference case, to show its potentiality and to discuss the influence of a number of key parameters, such as the soil strength and the foundation geometry on the seismic performance of the structure.

Predicting the seismic behaviour of the foundations of the Messina Strait Bridge

This paper presents some of the geotechnical studies carried out for the seismic design of the one-span suspension bridge across the Messina Strait, that is to connect Sicily with mainland Italy. These studies included advanced geotechnical characterisation, through in situ and laboratory tests, estimate of site stability involving both liquefaction analysis and submerged slope stability, evaluation of soil-foundation stiffness for spectral analysis of the superstructure, 3D FE static calculations, evaluation of anchor block performance under seismic conditions, and full dynamic analyses of the soil–structure interaction. The paper summarises the main results obtained from the geotechnical characterisation of the foundation soils, reports the approach adopted for evaluating the seismic performance of the anchor blocks through a modified Newmark-type calculation, and presents the study of the soil–structure interaction carried out through a series of two-dimensional, plane strain numerical analyses. In these analyses, in addition to the embedded foundation elements, the models included a simplified structural description of the bridge towers specifically designed to reproduce their first vibrations modes, that were deemed to have the most significant influence on the system’s dynamic response. The illustration is limited to the foundation systems of the bridge located on the Sicily shore.