Timber-concrete composite bridges: Three case studies

During the last years, timber-concrete composite (TCC) structures have been extensively used in Europe both in new and existing buildings. Generally speaking, a composite structure combines the advantages of both materials employed: the strength and stiffness of the concrete in compression and the tensile strength, lightweight, low embodied energy, and aesthetical appearance of the timber. The concrete slab provides protection of the timber beams from direct contact with water, which is crucial to ensure the durability of the timber beams, particularly when used for bridges. Different types of connectors can be used to provide force exchange between the concrete slab and the timber beam. The choice of a structurally effective yet cheap shear connection between the concrete topping and the timber joist is crucial to make the TCC structures a viable solution that can compete with reinforced concrete and steel structures. In this paper, the possibilities offered by TCC structures for short-span bridge decks are discussed. The technology of TCC structures and the general design rules are illustrated. Three case studies are reported, including a short-span bridge tested in Colorado, USA, with the timber layer being constructed from recycled utility poles and notch connection; a TCC bridge with glulam beams and triangular notches with epoxy-glued rebar connectors built in Portugal; and a TCC bridge with glulam beams and rectangular notches built in Germany. All the solutions were found to be structurally effective and aesthetically pleasing. They can all provide a sustainable option for short-span bridges. Keywords: Timber-concrete composite, Bridge, Design, Connection syste

Seismic performance of spherical liquid storage tanks: a case study

Abstract Spherical storage tanks are widely used for various types of liquids, including hazardous contents, thus requiring suitable and careful design for seismic actions. On this topic, a significant case study is described in this paper, dealing with the dynamic analysis of a spherical storage tank containing butane. The analyses are based on a detailed finite element (FE) model; moreover, a simplified single-degree-of-freedom idealization is also set up and used for verification of the FE results. Particular attention is paid to the influence of sloshing effects and of the soil–structure interaction for which no special provisions are contained in technical codes for this reference case. Sloshing effects are investigated according to the current literature state of the art. An efficient methodology based on an "impulsive–convective" decomposition of the container-fluid motion is adopted for the calculation of the seismic force. With regard to the second point, considering that the tank is founded on piles, soil–structure interaction is taken into account by computing the dynamic impedances. Comparison between seismic action effects, obtained with and without consideration of sloshing and soil–structure interaction, shows a rather important influence of these parameters on the final results. Sloshing effects and soil–structure interaction can produce, for the case at hand, beneficial effects. For soil–structure interaction, this depends on the increase of the fundamental period and of the effective damping of the overall system, which leads to reduced design spectral values

Aerodynamics of bridge hangers in smooth and turbulent flow and implications on aeroelastic stability

The risk of large amplitude vibrations of bridge hangers due to galloping instabilities has posed a challenge to the engineering and research community. Galloping vibrations can lead to serviceability problems and reduce fatigue life. A number of aeroelastic models have been developed to predict the unstable behavior and to design counteracting measures, i.e. shape modifications and increase of structural damping. In particular, the majority of such models is based on the application of the quasi-steady theory to a 2-D model of the cable vibrating in 1 DoF, in-plane, out-of-plane and torsional. Three key issues are relevant to the sectional galloping stability assessment of dry bridge hangers: (i) the complex aerodynamics depending, on the flow conditions (smooth or turbulent), (ii) the deviation of the cable geometry with respect to that of a perfect circular cylinder, and (iii) the choice of a proper stability criterion. In this paper, aerodynamic force coefficients of a real HDPE plain cable cover were measured in the wind tunnel in smooth and turbulent conditions are presented. Cable irregularities (surface roughness, section distortion and axis curvature) are characterized and correlated to the measured aerodynamics. Then, the aerodynamic coefficients are used to investigate aerodynamic stability using different models from the literature. A comparison of the results has highlighted that the use of MDoF models is not justified, as 1-DoF models are sufficient to predict instability; furthermore, it was found that cable irregularities and flow conditions can have a strong influence on the prediction of aerodynamic stability

To compute or not to compute?

In a previous paper "to retrofit or not to retrofit?" (Nuti and Vanzi, 2003) a straightforward procedure able to forecast the economic return of seismic structural upgrading was presented. More recently, the authors realized that the final mathematical results can be much simplified so as to allow back-of-an-envelope computation. The title of this paper tries to highlight precisely this aspect, namely that for many a regular seismic structural upgrading cases, nearly no computation is needed (apart from one subtraction and one multiplication) to assess their economic convenience. These findings are presented and discussed in this paper, together with a state of the art on the cost-studies available in literature and technical codes. The mathematical formulation leading to the proposed approximation is suitably explained, underlining its applicability field and comparing it with the rigorous solution. Also a table and a formula are furnished that alternatively allows to calculate the maximum estimation errors, in order to obtain an upper and lower bound for the maximum amount of money which should be allocated for seismic structural upgrading.Finally an application example is described, dealing with retrofitting of reinforced concrete viaducts, a widespread bridge typology in Italy. The adopted upgrading solution consists of a concrete jacket at the base of some piers, particularly suitable in order to increase their ductility. Keywords: Seismic retrofitting, Structural reliability, Safety, Optimization, Cost minimizatio

Aerodynamics and aeroelastic behaviour of ice-accreted bridge cables

This dissertation investigates the effects of ice accretion on the aerodynamics and aeroelastic stability of bridge hangers and stay cables. First, a review of the state of art on the aerodynamics of nominally circular cylinders is given. Then, the aerodynamic behavior and accretion characteristics of ice accreted bridge cables were experimentally studied by climatic wind tunnel tests. The aerodynamic stability was investigated using the models proposed by different authors. Furthermore a novel 3D 3-DoFs quasi-steady aeroelastic model is proposed

Low-LOD code-driven identification of the high seismic risk areas for industrial buildings in Italy

The identification of the areas with high seismic risk for industrial buildings is of paramount importance for decision-makers to implement risk reduction policies. In this context, this study aims at performing a low-LOD (Level of Detail) code-driven identification of areas in Italy where industrial buildings face high seismic risk. Firstly, the hazard, vulnerability, and exposure models are introduced. Then, such input data are validated by comparing the predictions of the proposed framework with the observational data obtained after the Emilia-Romagna earthquakes of 2012. The validated framework is used to predict the conditional (to a certain return period) and unconditional risk in terms of elements-at-risk and economic losses. The unconditional risk in terms of economic losses expressed in terms of Expected Annual Losses (EAL) is used to rank areas in Italy in terms of seismic risk for industrial buildings. As expected, the area hit by the Emilia-Romagna earthquakes in 2012 is included among those with the highest seismic risk, indicating the predictability of large damage occurred on industrial buildings during the seismic event. Finally, some conclusions are drawn about the implications for future policies and studies for seismic risk reduction of industrial buildings in Italy

Pressure modes for hyperbolic paraboloid roofs

This paper presents a study on Singular Value Decomposition (SVD) of pressure coefficients hyperbolic parabolic roofs. The main goal of this study is to obtain pressure coefficient maps taking into account spatial non-uniform distribution and time-depending fluctuations of the pressure field. To this aim, pressure fields are described through pressure modes estimated by using the SVD technique. Wind tunnel experimental results on eight different geometries of buildings with hyperbolic paraboloid roofs are used to derive these pressure modes. The truncated SVD approach was applied to select a sufficient number of pressure modes necessary to reconstruct the measured signal given an acceptable difference. The truncated pressure modes are fitted through a polynomial surface to obtain a parametric form expressed as a function of the hyperbolic paraboloid roof geometry. The superpositions of pressure (envelopes) for all eight geometry were provided and used to modify mean pressure coefficients, to define design load combinations. Both symmetrical and asymmetrical pressure coefficient modes are used to estimate the wind action and to calculate the vertical displacements of a cable net by FEM analyses. Results clearly indicate that these load combinations allow for capturing large downward and upward displacements not properly predicted using mean experimental pressure coefficients

Prediction of the aerodynamic instability of ice-accreted bridge cables using different stability criteria

The aerodynamic force coefficients of iced bridge cables were recently obtained by the authors through a series of static wind tunnel tests on a full-scale vertical and inclined bridge cable section model, under typical climatic conditions of incloud icing. The availability of these data allows the application of quasi-steady stability criteria. During the last decades, a number of stability models were derived to investigate the galloping phenomenon, with different levels of detail. In this paper, an attempt is made to compare background hypotheses and results obtained using different quasi-steady sectional aerodynamic stability criteria, applied to ice-accreted bridge cables. Not existing a benchmark, the research is not aimed at judging the quality of each approach, but rather at pointing out the differences they bring