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Failures of structures are often tragic events, however represent an opportunity to improve the understanding of phenomena. In this paper, after the review of Bridge collapses, on August 14, 2018, the history of Polcevera Bridge is presented, starting from aging considerations done by its designer Riccardo Morandi in 1981, analyzing the outcomes of inspections in the years from mid ‘80s with references to Italian Regulations on inspections, the interventions done during bridge life, and finally some considerations on its collapse. The case is certainly a reference for reinforced concrete bridges built just after the 2nd world war in a highly corrosion-prone environment due to nearby sea and industrial as well as chloride pollution. Large reference is done to data included into the Report of the Commission of Italian Ministry of Infrastructures for the failure of Polcevera Bridge. Monitoring for assessment of performance decay due to corrosion is discussed with reference to the meaningful example considered.

The bridge over the Basento river in Potenza, Italy, designed by Sergio Musmeci, is supported by a continuous double-curvature RC shell optimized to reduce bending forces. This 300 m long bridge can be considered as a unique representative example of pioneering research on the design and construction of optimized structures. First, the design process employed for determining the form of the shell and the relevant constructive issues are described. A refined 3D geometric model of the shell is then obtained through an aerial survey carried out by a commercial UAV and a photogrammetric image-based reconstruction. A recent formulation of the Force Density Method allowing for non-isotropic stress state is exploited to numerically derive the form of the supporting shell; it is validated versus the surveyed geometry of the shell by employing a nonlinear optimization procedure in order to identify forces and stresses to be used as input parameters. Finally, the derived form of the shell is tested by a Finite Element analysis to verify its funicular efficiency, i.e., whether it is capable to withstand design loads by pure membrane actions.

This paper presents a smooth hysteresis model for reinforced concrete (RC) structural elements based on the differential equation of the Bouc–Wen model. Stiffness degradation and strength degradation are defined by introducing a damage index that includes both dissipated energy and maximum displacement. The pinching effect acts directly on the stiffness of the system and is controlled by an activation energy. The degrading functions are connected to the actual processes with which the damage occurs, thereby giving each parameter a physical meaning. The simple formulation of the model allows a straightforward identification of the best-fitting parameters and an easy interpretation of the results. Applications to the cyclic behaviour of RC structural elements demonstrate that the model is well capable of describing complex hysteretic behaviours involving degradation and pinching effects.

The development of new digital design tools and fabrication technologies stimulated a large research interest in the design and construction of free-form architecture. Free-form architecture indicates the symbolic act of freeing architecture from the limitations of pure form. During the form-finding process, the priority is on identifying the geometry that enables the optimum force flow within the structure. This study focuses on the problem of the form-finding problem of concrete double-curved surfaces. First, a suitable form-finding optimization framework to optimize shell surfaces based on the surface Stress Density method is established. This framework is based on the use of different software such as Rhinoceros, Grasshopper, and Matlab. The stress density method is chosen because it allows obtaining an optimized shape starting by few parameters: the geometric characteristics of the model, the surface density factor and the magnitude of the load. In a second step, the study is focused on a single panel of the structure. Structural analyses of this panel are carried out using the commercial finite element software SAP2000 to demonstrate that it is a shape resistant structure. Finally, a new production process for concrete double-curved surfaces is presented showing a prototype at a small scale. This process is trying to satisfy the needs of new shapes within architectural design. The proposed solution is the improvement of an existing flexible mould formwork technology and represents the first attempt to reach a reusable, reconfigurable and affordable procedure.

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 minimization

Due to the superior mechanical properties and durability, the ultra-high performance concrete (UHPC) has been widely used for the design of various types of structures, while research on its performance has been rapidly growing in the last five years. While the application of UHPC in bridge engineering is limited due to its higher cost, relatively little is known about the mechanical behavior of UHPC in different bridge components. In order to inform future research needs, this paper provides a comprehensive review of the properties of UHPC and its application in bridge engineering. Applications in various bridge components, such as the piers, girders, decks, and link slabs used for jointless bridges have been summarized. This review also discusses future research on optimized UHPC mix designs considering economic cost and its applications in both jointed and jointless bridges.

This paper discusses the seismic behavior of reinforced concrete (RC) bridge structures, focusing on the shear&ndash, flexure interaction phenomena. The assessment of reinforced concrete bridges under seismic action needs the ability to model the effective non-linear response in order to identify the relevant failure modes of the structure. Existing RC bridges have been conceived according to old engineering practices and codes, lacking the implementation of capacity design principles, and therefore can exhibit premature shear failures with a reduction of available strength and ductility. In particular, recent studies have shown that the shear strength can decrease with the increase of flexural damage after the development of plastic hinges and, in some cases, this can cause unexpected shear failures in the plastic branch with a consequent reduction of ductility. The aim of the research is to implement those phenomena in a finite-element analysis. The proposed model consists of a flexure fiber element coupled with a shear and a rotational slip spring. The model has been implemented in the OpenSEES framework and calibrated against experimental data, showing a good ability to capture the overall response.

The purpose of this article is to describe the Bouc–Wen model of hysteresis for structural engineering which is used to describe a wide range of nonlinear hysteretic systems, as a consequence of its capability to produce a variety of hysteretic patterns. This article focuses on the application of the Bouc–Wen model to predict the hysteretic behaviour of reinforced concrete bridge piers. The purpose is to identify the optimal values of the parameters so that the output of the model matches as well as possible the experimental data. Two repaired, retrofitted and reinforced concrete bridge pier specimens (in a 1:6 scale of a real bridge pier) are tested in a laboratory and used for experiments in this article. An identification of Bouc–Wen model's parameters is performed using the force–displacement experimental data obtained after cyclic loading tests on these two specimens. The original model involves many parameters and complex pinching and degrading functions. This makes the identification solution unmanageable and with numerical problems. Furthermore, from a computational point of view, the identification takes too much time. The novelty of this work is the proposal of a simplification of the model allowed by simpler pinching and degrading functions and the reduction of the number of parameters. The latter innovation is effective in reducing computational efforts and is performed after a deep study of the mechanical effects of each parameter on the pier response. This simplified model is implemented in a MATLAB code and the numerical results are well fit to the experimental results and are reliable in terms of manageability, stability, and computational time.