Graziano Leoni

Time analysis of composite beams with partial interaction using available modelling techniques: A comparative study

Abstract This paper presents a comparison of available numerical structural formulations for the short- and long-term analysis of composite beams with partial shear interaction. The finite difference method, the finite element method, the direct stiffness method and the exact analytical model have been considered, and both the instantaneous analysis and the time analysis based on the age-adjusted effective modulus method (AEMM) have been carried out. For modelling based on the first two of these formulations, a spatial discretisation and a discretisation in the time domain are required, while only the time discretisation needs to be specified for the direct stiffness method. The results obtained using these formulations are compared qualitatively and their accuracy is estimated, adopting the exact analytical model as a benchmark reference with the objective of establishing the minimum spatial discretisations required to keep the error within an acceptable tolerance. These comparisons are carried out for simply supported beams, propped cantilevers and fixed ended beams, from which the qualitative behaviour of these formulations in the modelling of continuous beams can also be deduced.

Short- and Long-term Analytical Solutions for Composite Beams with Partial Interaction and Shear-lag Effects

This paper presents an analytical model for the short- and long-term analysis of composite steel-concrete beams with partial shear interaction and accounting for shear-lag effects. The material properties of the concrete have been assumed to be time-dependent and have been modelled by means of the algebraic methods while the remaining materials forming the cross-section have been supposed to behave in a linear-elastic manner. The global balance condition of the problem has been obtained by means of the principle of virtual work and, integrating this by parts, the governing system of differential equations and corresponding boundary conditions have been determined. Analytical expressions for both short- and long-term solutions have been derived and, to outline their ease of use, a number of case studies relevant for bridge applications have been proposed.

Slab Cracking Control in Continuous Steel-Concrete Bridge Decks

This paper presents a study on the effectiveness of various casting techniques used to control slab tensile stresses during the construction of continuous steel-concrete composite bridge decks. The main features describing the early age behavior of concrete are outlined and available modeling options are considered. A practical procedure is presented for the evaluation of the slab stress state taking place at various construction stages based on the modular ratio approach suggested by Eurocode 4. The method, which can be implemented using commercial software, requires the evaluation of suitable modular ratios and creep coefficients to estimate the time-dependent effects of the concrete slab weight and the thermal, endogenous, and drying shrinkage components. This simplified procedure is then applied to a case study to evaluate, for various casting sequences, the contributions of the concrete weight and shrinkage components to the slab early cracking. Finally, the efficiency of various casting techniques in controlling the slab tensile stresses is presented and discussed.

An integrated Survey Experience for Assessing the Seismic Vulnerability of Senigallia’s Fortress (Italy): Documentation for Conservation and FEM Modeling

The paper presents the results of research carried out by an interdisciplinary team at the SAD in Ascoli Piceno in collaboration with MiBACT to verify the seismic safety of national museums. The object of study was the Rocca Roveresca Fortress complex in Senigallia (Marche, Italy), a unique example of a small 14th-century fortress shaped by a series of successive modifications. It currently houses a national museum. An integrated survey based on the acquisition of 3D laser-scanner data and endoscopic investigation was necessary to outline the traces of the stratifications and therefore to obtain different high- and low-poly 3D models useful for different purposes. The main objective was to propose an ideal workflow in developing 3D models that are useful for finite element method (FEM) analysis to detect hidden vulnerabilities in the fortress by evaluating the behaviour of several substructures in the walls.

Dynamic response of composite frames with rubber-based dissipating devices: experimental tests

Publisher Summary The chapter discusses dynamic responses of composite frames with rubber-based dissipating devices. The chapter analyzes composite moment-resisting space frames where lateral stiffness and equivalent viscous damping are augmented by means of dissipating devices, and presents the results of a preliminary experimental campaign carried out on a real scale composite space frame equipped with a dissipating bracing system endowed by high damping natural rubber devices. Moment-resisting frames made of steel-concrete members provide an efficient earthquake resistant system. The efficiency is entrusted to the formation of plastic hinges located at the ends of the beams or at the beam-to-column joints designed as partial strength connections. This design criterion is satisfactory in preventing the structure from collapse against high intensity earthquakes, but it often leads to a very large lateral deformability which brings on excessive inter-storey drift under low intensity earthquakes. The energy dissipation associated with the ductile behavior of dissipating zones induces a large amount of structural damage which usually calls for very expensive and difficult rehabilitation works.

Erratum to: Implications of non-synchronous excitation induced by nonlinear site amplification and of soil-structure interaction on the seismic response of multi-span bridges founded on piles

This work investigates the effects of soil-structure interaction and spatial variability of seismic motion due to nonlinear site amplification on the seismic behaviour of long multi-span bridges founded on piles. An analysis framework able to include the spatial variation of ground motion induced by specific geological and geomorphological scenarios in the seismic soil-structure interaction analysis of long bridges is adopted, exploiting advantages of the substructure approach. The methodology is applied to a case study constituted by a pile-supported multi-span bridge founded in a soft clay deposit overlaying a stiff bedrock with three different configurations: horizontal, inclined and wedge-shaped. The reference input motion at the outcropping bedrock is represented by a set of real accelerograms and different seismic response models are used to compute site amplification effects, discussing the contribution to the free-field ground motion of both the two-dimensional configuration of the deposit and the nonlinear soil behaviour. The ground motions obtained from the different models are then used for computing the foundation input motion accounting for the pile–soil kinematic interaction; thereafter, inertial interaction analyses are performed on structural models with either fixed or compliant base, considering the non-synchronous seismic actions at the piers foundation. The results, compared in terms of piers head displacements, ductility demand and deck transverse bending moments, finally show the relative importance of bedrock morphology, soil nonlinearity and soil-structure interaction on the structural response.

Assessment of seismic vulnerability of historical defensive walls

Abstract. This paper presents a study on the behaviour of the walls of the Rocca Roveresca of Senigallia in Italy built in the XIV century on the ruins of a former Roman defensive struc-ture. This is a peculiar example of a small fortress that had undergone in the XV century im-portant modifications of the plant in order to enhance its defensive performances. A linear finite element model is first developed in order to understand the dynamic behaviour of a ge-neric portion of the wall and to detect the probable incipient failure mechanisms. A subse-quent static nonlinear analysis is carried out, with the same finite element model, to investigate the formation of the cracking layout and to detect the position of plastic hinges. The last analysis level is carried out with a tailored macro-element constituted by three bod-ies, namely the two external curtains and the inner fill for which a degradation of the behav-iour is considered. The results obtained demonstrates the efficiency of the wall against earthquakes characterized by return times typical for ultimate limit states. Same issues that deserve further investigation are highlighted.

A beam finite element for the shear-lag analysis of steel-concrete composite decks

Publisher Summary The chapter presents a beam model for the analysis of composite decks, considering the warping of a slab cross-section and the partial shear interaction between the slab and girders. Slab shear-lag is considered by means of the product of a known function, describing the shape of the slab cross-section warping, and an intensity function measuring the magnitude of warping along the beam axis. The numerical solution is obtained by means of the finite element method with a new 13-dof beam element. The results of a number of applications of the proposed model to a realistic bridge deck are compared with those obtained by means of shell finite elements, showing the accuracy of the proposed element.

Influence of shear connection distributions on the behaviour of continuous steel-concrete composite beams

For this purpose a finite element model specifically developed for the nonlinear analysis of steel-concrete composite beams is adopted. This finite element model includes material nonlinearity of slab concrete, reinforcement steel, beam steel as well as slabbeam nonlinear partial interaction due to the deformable shear connection. The inclusion of the partial interaction in the composite beam model provides information on the slab-beam interface slip and shear force and enables to model the failure of the shear connectors.

A Comparative Study on the Time-Dependent Analysis of Composite Beams Using Available Modelling Techniques

This paper presents a comparison of available numerical structural formulations for the short-and long-term analysis of composite beams with partial shear interaction. Four methods of analysis are considered and these include the finite difference method, the finite element method, the direct stiffness method and the exact analytical model. The results obtained using these formulations are compared qualitatively and their accuracy is estimated, adopting the exact analytical model as a benchmark reference with the objective of establishing the minimum spatial discretisations required to keep the error within an acceptable tolerance. These comparisons are carried out for two static configurations, i.e. simply-supported beams and propped cantilevers, from which the qualitative behaviour of these formulations in the modelling of continuous beams can also be deduced.