Lumped parameter model for the time-domain soil-structure interaction analysis of structures on pile foundations

A lumped parameter model for the time domain inertial soil-structure interaction analysis is proposed with reference to square pile group foundations. Simplified formulas are presented for estimating its parameters. The model is able to reproduce the coupled rotational-translational behaviour of the soil-foundation system. Formulas are calibrated from results of an extensive non-dimensional parametric analysis considering head-bearing pile groups. The closed-form expressions may be readily adopted to define the compliant base restraints of a generic structure for the non linear dynamic analysis carried out with commercial software

Nonlinear response of bridge piers on inclined pile groups: the role of rocking foundation input motion

This paper presents first results of an on-going research focused on the effects of piles layout and inclination on the nonlinear seismic response of bridge piers. The analysis methodology, based on the substructure approach, is firstly presented. The soil-foundation system is studied in the frequency domain according to a numerical model developed by the authors while the inertial interaction analysis of the superstructures is carried out in the time domain to capture the nonlinear structural behaviour. A suitable lumped parameter model is used to approximate the frequency dependent behaviour of the soil-foundation impedances in the time domain analyses. The procedure is applied to some case studies constituted by single bridge piers founded on medium stiff and soft clayed soil deposits. Pile groups with piles of different inclinations are considered, as well as piers with different fundamental periods and yielding bending moments of the base cross sections, to simulate systems with different ductility capacity. Analyses results show the key role of the foundation rocking on the superstructure response and demonstrate that inclined pile foundations may have a significant impact on the superstructure response, reducing the pier head displacements and ductility demand

Numerical and Simplified Methods for Soil-pile Interaction Analysis

The paper presents a review of the analytical and numerical procedures developed by the authors for the dynamic analysis of soil-pile foundation systems subjected to the propagation of seismic waves in the soil. Inclined and vertical single piles and groups constituted by piles with a generic inclination are addressed. For the former, an analytical approach based on the beam on dynamic Winkler foundation approach is adopted; the pile is modelled as a Euler-Bernoulli beam and the soil-pile interaction is captured by defining soil impedances relevant to the harmonic vibrations of rigid disks available in the literature. The coupled flexural and axial behaviour of the pile is solved analytically exploiting exponential matrices. The pile group dynamic problem is similarly formulated but the solution is achieved exploiting the finite element approach. Besides numerical models, simplified approaches based on static equivalent methods and simplified formulas are also addressed to estimate the maximum kinematic stress resultants on vertical piles subjected to lateral seismic excitations. The reliability of the presented tools in capturing the dynamic stiffness and the overall kinematic response of pile foundations is shown by comparing results with those available in the literature or achieved through refined finite element models. From an engineering point of view, the proposed approaches assure a sufficient accuracy and may substitute refined computational demanding numerical models

Finite elements for higher order steel–concrete composite beams

none4noThis paper presents finite elements for a higher order steel–concrete composite beam model developed for the analysis of bridge decks. The model accounts for the slab–girder partial interaction, the overall shear deformability, and the shear‐lag phenomenon in steel and concrete components. The theoretical derivation of the solving balance conditions, in both weak and strong form, is firstly addressed. Then, three different finite elements are proposed, which are characterised by (i) linear interpolating functions, (ii) Hermitian polynomial interpolating functions, and (iii) interpolating functions, respectively, derived from the analytical solution expressed by means of exponential matrices. The performance of the finite elements is analysed in terms of the solution con-vergence rate for realistic steel–concrete composite beams with different restraints and loading con-ditions. Finally, the efficiency of the beam model is shown by comparing the results obtained with the proposed finite elements and those achieved with a refined 3D shell finite element model.openGara F.; Carbonari S.; Leoni G.; Dezi L.Gara, F.; Carbonari, S.; Leoni, G.; Dezi, L

micropile foundation subjected to dynamic lateral loading

Abstract Thanks to their ease of installation, even in access-restricted spaces, micropiles are increasingly adopted for the seismic rehabilitation of existing structures. Moreover, both vertical and inclined micropiles are often used as foundation system for new constructions, ground improvements and many other applications. In order to deepen the knowledge of the dynamic behavior of those systems under horizontal loading, an extensive experimental study was carried out in an alluvial silty soil deposit on two single vertical micropiles and on a group of four inclined micropiles connected at the head by a concrete cap. Several testing procedures are exploited, in order to investigate the dynamic behavior of micropiles under different loading conditions and increasing force level, with special attention on the role of execution techniques and foundation configuration

Soil-structure interaction effects on the seismic response of multi-span viaducts

The paper focuses on the effects of soil-structure interaction in the seismic response of multi-span viaducts on pile foundations. Analyses are performed by means of the substructure approach: the soil-foundation systems are studied in the frequency domain to obtain the foundation input motion and the dynamic impedance functions; inertial interaction analyses are carried out in the time domain accounting for the material nonlinear behaviour. Suitable lumped parameter models are introduced to simulate the frequency dependent behaviour of the soilfoundation system. A specific procedure for selecting and scaling real ground motions is proposed and used for the definition of the spatial seismic input. The seismic response of bridges on compliant base is compared with that obtained from fixed base analyses discussing the significance of soil-structure interaction effects

Slab cracking influence in the fatigue assessment of continuous composite decks

The paper analyzes the influence of the slab cracking in the fatigue assessment of continuous composite decks by considering the effects of slab casting sequences and the shrinkage components (thermal, endogenous and drying). A numerical procedure for the stress calculation accounting for the tension stiffening of the slab longitudinal rebars is presented. The long term effects of casting sequences and concrete shrinkage are analysed with a simplified procedure based on the application of the modular ratio method. With reference to a realistic continuous twin girder composite deck the fatigue verification of the longitudinal girders is carried out by considering three different casting modalities. The obtained results show the important role of the slab casting sequences in the stress range calculation and the remarkable influence of the slab cracking in the fatigue assessment

Seismic Response of Bridges Accounting for Soil-Structure Interaction effects and the Non-Synchronous Ground Motion due to 1D and 2D site analysis.

This work focuses on the effects of soil-structure interaction and the spatial variability of seismic motion due to site effects on the seismic response of a multi-span viaduct on pile foundations. In particular, site effects induced in a soft clay deposit by an inclined bedrock layout are evaluated through different models, characterised by an increasing level of accuracy, which allows determining the free-field motion that is adopted to perform soilstructure interaction analyses in the frame of the substructure approach. The seismic input is represented at the outcropping bedrock by a set of suitably selected and scaled real accelerograms. After a brief presentation of the adopted numerical procedure, analyses results are presented focusing on both site and structural response. Amplifications effects obtained from simplified linear equivalent 1D and nonlinear 2D site response models are compared, discussing the applicability of the simplified approach. Structural responses, obtained by considering the non-synchronous motion resulting from the local stratigraphic conditions, in conjunction with soil-structure interaction effects, are shown in terms of piers displacement and ductility demands. Furthermore, the role of soil structure interaction is clarified comparing results with those obtained from fixed base bridge models, proving that its contribution is more significant if the simplified model for site response is adopted

Simultaneous effect of spatial variability of ground motion due to site conditions and SSI on the seismic response of multi-span viaducts

This work focuses on the effects of the spatial variability of the seismic motion due to site effects on the seismic response of multi-span viaducts on pile foundations. A methodology is proposed to include the effects of both soil-structure interaction and non-synchronous seismic actions in the nonlinear response of bridges. Then, some results of nonlinear dynamic analyses performed on a multi-span bridge founded on soft soil are presented. The deposit is characterized by an inclined layout of the bedrock and the seismic input is represented by a set of suitably selected real accelerograms. Comparisons with results obtained considering synchronous seismic motions demonstrate the influence of site effects on the response of long bridges