Fabrizio Gara

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.

Simple Physical Models to Simulate the Behavior of Buckling-Type Marine Fenders

AbstractThis paper presents a simple physical model for the numerical simulation of the behavior of buckling-type marine fenders. The proposed model is characterized by four parameters and is derived starting from similarities between the unstable behavior of marine fenders and shallow arches. In this model, the large displacements solution expressing the relationship between the model displacements and reaction force is determined in a nondimensional form, and the model parameters are calibrated to minimize residuals between real and predicted normalized reaction force–deflection curves. By considering an in-series arrangement of two elementary physical models, the approach can be also used to simulate the behavior of parallel-motion fenders. The proposed model can be directly implemented in commercial computer programs for structural analysis to study interactions arising between buckling-type marine fenders and flexible berthing structures. In this paper, the model effectiveness in capturing the behavi...

Dynamic monitoring of an isolated steel arch bridge during static load test

This paper describes the dynamic monitoring carried out by means of vibration measurements during the standard static load test of a half-through steel arch bridge on the Potenza river. The structural design of the bridge is characterized by some notable aspects: the river crossing is obtained by two coupled steel arches, having a span length around 115 m, and a steel-concrete composite deck sustained by thirty couples of steel hangers; the approaching spans are realized with continuous girders on intermediate supports, having cross section with variable height; the arches are supported on rubber bearing seismic isolators. The vibration measurements were nearly continuously acquired during the loading tests to detect the occurrence of anomalies in the structural behavior. In particular, the global dynamic characteristics of the structure, in terms of modal parameters, were determined using the data set of measurements at specific phases of the load test: first on the unloaded configuration, then on two different loaded configurations and finally after the bridge unloading. Measurements of vibrations due both to the ambient and to the impulse produced by a fully loaded truck passing over a bump, were carried out. The experimental results, in terms of modal parameters of the bridge, are in agreement with the theoretical results obtained with the predictive finite element model developed for design purposes and opportunely modified to account for the real conditions of the bridge during the tests.

Operational modal analysis on a r.c. building for the evaluation of the dynamic changes due to retrofitting

The paper deals with the changes of the modal parameters of a r.c frame building sited in Camerino, Italy. Operational modal analysis were performed before and after the seismic retrofitting of the building achieved with an innovative system that uses external steel towers equipped with dissipative devices. Before retrofitting, ambient vibration tests were carried out with the aim of evaluating the actual linear dynamic behavior of the building including the contribution of non-structural components (e.g. external and internal walls); modal parameters, i.e. natural frequencies and mode shapes determined by means of experimental modal analysis, allowed the calibration of a predictive f.e. model of the building which was crucial for the final design of the retrofitting system. Tests were repeated after the retrofitting works, with the main objective to verify that changes of modal parameters are in agreement with those predicted by the f.e. model. Results and comparisons between the modal parameters obtained before and after the retrofitting works demonstrate that the ambient vibration tests and the data processing techniques used allow the identification of the dynamic behavior of r.c. few-storeys buildings under operating conditions and, then, the identification of dynamic changes due to seismic retrofitting works performed with external steel “dissipative towers”. A model updating procedure is carried out to identify the value of the elastic modulus of the different materials constituting structural and non-structural elements.

Linear and Nonlinear Dynamic Response of Piles in Soft Marine Clay

AbstractThis paper presents the results of free vibration tests carried out at different load levels on a system of three near-shore steel pipe piles vibro-driven into soft marine clay. Piles are arranged in an L-shaped horizontal layout and are free at the head. The instrumentation consists of strain gauges placed at selected levels along the shaft of the loaded pile and accelerometers at the head of the receiver piles. The aim of this experiment is to analyze the dynamic soil–water–pile and pile-to-pile interaction and to investigate the development of nonlinearities at increasing load levels. The results of experimental modal analyses, in terms of natural frequencies and damping ratios of the system, are presented and the complex dynamic behavior of the vibrating soil–water–pile system and the pile-to-pile interaction are discussed. For a better reliability assessment of the system response in the range of linear behavior, the results of free vibration tests at the lowest level of the applied loads are...

Stochastic Seismic Analysis and Comparison of Alternative External Dissipative Systems

This paper deals with the seismic retrofit of existing frames by means of external passive dissipative systems. Available in different configurations, these systems allow high flexibility in controlling the structural behaviour and are characterized by some feasibility advantages with respect to dissipative devices installed within existing frames. In particular, this study analyzes and compares the performances of two external solutions using linear viscous dampers. The first is based on the coupling of the building with an external fixed-based steel braced frame by means of dampers placed horizontally at the floor levels. The second is an innovative one, based on coupling the building with a “dissipative tower,” which is a steel braced frame hinged at the foundation level, and activating the dampers through its rocking motion. The effectiveness of the two solutions is evaluated and compared by considering a benchmark existing reinforced concrete building, employing a stochastic dynamic approach, under the assumption of linear elastic behaviour for the seismic performance evaluation. This allows efficiently estimating the statistics of many response parameters of interest for the performance assessment and thus carrying out extensive parametric analyses for different properties of the external systems. The study results provide useful information regarding the design and the relative efficiency of the proposed retrofit solutions.

Experimental study on instrumented micropiles

In the present work, first steps of an extensive experimental study carried out on two vertical micropiles in alluvial silty soil are presented. One of the vertical micropiles is injected throughout valves a-manchèttes placed along the steel core of the shaft, while the other one is grouted with a unique global injection. Both of them are instrumented with several strain gauges along the shaft and an accelerometer at the head. The protection technique adopted to prevent damages on the strain gauges during micropile installation and high-pressure injections is also discussed. The main objectives of this experimental campaign are the monitoring of the modifications in the dynamic characteristics of the complex soil-micropile system due to execution techniques and construction stages, and the investigation of the dynamic response considering different kind of cyclic and dynamic loading. In particular, the effect of the high-pressure injections on the dynamic response of vertical micropiles is here investigated, by means of series of ambient vibrations and lateral impact loading tests. Experimental data of impact load tests are finally compared with results obtained from an analytical model.

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.

Fatigue Assessment of Continuous Composite Bridges Accounting for Slab Casting Sequences

Abstract The paper presents a procedure for the fatigue assessment of continuous steel–concrete composite bridges which accounts for concrete slab casting sequences. Cracking, tension stiffening, creep and shrinkage (thermal, endogenous and drying) effects are included in the analysis in order to correctly evaluate the stress state of steel girders. The purpose of the paper is to present a method that, based on the analysis of a number of models developed according to the structure’s evolution, leads to a more effective and realistic fatigue assessment than that usually performed in practice. The method proposed is applied to a case study of a continuous, twin-girder, composite bridge deck, showing the influence of three different slab casting modalities on fatigue assessment.