Enzo Siviero

The Footbridge over the River Adige at Legnago in Italy Part 1: The Role of Modal Analysis in Design:

Weight reduction, achieved through the use of materials with high mechanical strength and, in terms of shape, by adopting visually light structures, gave rise to the design of constructions with low self-weight, which were therefore sensitive to the effects of live loads. This sensitivity is particularly acute in the case of footbridges, where pedestrian traffic translates into dynamic forces that can lead to resonance, since pacing frequencies would be similar to the natural frequencies of the structure itself. In general, the problem is one of serviceability. The footbridge over the River Adige at Legnago (Northern Italy), designed by some of the authors(1) of this paper, showed a marked sensitivity to repeated horizontal forces that tended to cause transversal and torsional vibration around its longitudinal axis. This paper examines how an analysis of Natural Frequencies (NF) and modal response revealed the excessive deformability of the piers to be the key reason for the structure to behave in this way. As a result, a design solution was adopted that involved a more sound connection between the heads of the new and existing piers. In regard to the serviceability behaviour with respect to vibrations caused by human-induced dynamic loads, the NF analysis showed that the added links improved the behaviour of the structure. However, some natural frequencies remained close to the range of typical human pacing frequencies (walking, running or jumping). A dynamic analysis was therefore performed, the results of which are presented in the second part of the work - with the aim of ensuring that comfort conditions are verified. Finally, the experimental frequency determination enabled the design solution to be checked, demonstrating the excellent ability of the Finite Element Model used to predict dynamic structural behaviour.

Footbridges as elements for urban rehabilitation and renewal

When a bridge is designed, we start from the basis that it is visible in all its parts. In actual fact, due to the position and speed of the observer, the bridge can be perceived partially and for a limited period of time. The area and time within which the bridge can be perceived are entities that can be quantified and, therefore, measured (Perceptive quantity). Italian legislation about infrastructures distinguishes between two forms of quality: internal, also referred to as technical performance and, more general, work function apply; and external, namely connected with the social-economic, environmental and landscape impact of the work. Footbridges make it possible to create closer relations between the user and the work, as walking on them implies moving at a slower pace. The aim of this paper was to understand how the perception of a footbridge can prove to be an effective knowledge base for planning, and an instrument for urban rehabilitation. This paper will also explore the ways in which existing footbridges can change the perception and the meaning of a place. It will also investigate the connection between the design of footbridges and planning tools. The results involve the study of the effects that a footbridge may have on the urban landscape, taking the relationship between the internal and external quality of the work into consideration.

Technical Plan for the Realization of Five Footbridges in the Ring Road of Catania

This article analyzes the design of five footbridges in functional adjustment of the ring road of Catania, in Sicily. In case of earthquake are necessary planned interventions: for this reason some flyover will be demolished to restore the road system with the creation of ring junctions. However, when the project will be ended, the city will be divided in two areas for the lack of pedestrian links between the south and the north of the road system. The goal of our study is to create a link between these two areas of the city that will be separated with the creation of the new ring road.

Re-establishing the functionality of older bridges - two case studies, Italy

For historical reasons, centuries of development in the Italian region have led to a multitude of flourishing but small urban centres. In this context, it is obvious that communication in the form of roads, canals and rivers have been of fundamental importance to the culture and lifestyle of the region. The continuous change that these centres of habitation have seen from the viewpoint of economic, social and urban growth has made the regions communication system even more complex, forcing infrastructure to adapt to a variation in demand on a regular basis. It is quite understandable that in such a context, bridge building has been a frequent stimulus to engineering genius. No wonder then that, apart from some examples of large-scale engineering, the region can also boast an extremely large number of minor river management and bridge works all over the region, characterised by an inventiveness engendered by incredibly varied and sometimes quite unusual requirements. On top of the obvious functional requirements, in many cases, the physical characteristics of the surroundings and the region in general played a major role in conditioning the shape and form of the finished work. The limitations they dictated, choices they forced and environmental conditions they imposed combined to create a modus operandi that over time led to a characteristic style of public works, of which the bridge is the noblest form. The period in which we ourselves are living is equally affected by perpetual change: new safety requirements have emerged together with new means of transport, and new road layouts are requiring the functional adaptation of works designed and constructed to satisfy needs that have long been superseded. If we are to respect tradition, our approach to the modernisation of existing works must be based on a firm understanding of the needs and conditions that led to their construction in the first place. Unfortunately, in the name of modernisation, in recent decades many projects have been little more than acts of vandalism, irremediably destroying the heritage that ancient works could have preserved for future generations. The attitude behind these interventions was not only lacking in respect for the past and for the value of tradition but also ignorant of the factors driving change in the landscape of the locality involved. Nevertheless, exceptions to this rule, in the form of works performed under the guidance of heritage conservation bodies, are slowly bringing about a change of heart, so much so that nowadays modernisation projects based on a thorough understanding of the local area and its history are becoming increasingly widespread. The inability of bridges to fulfill their original purpose has become increasingly manifest in recent years, amplified by an increase in through traffic in addition to local traffic. The speed of such traffic has also impacted negatively on road safety and led to an increase in the number of accidents. On top of this, the cyclists and pedestrians who use older bridges do so not only without specific protective structures in place but often without the most elementary guarantees of safety. This article examines two cases of modernisation of older main road bridges achieved by the construction of cyclist and pedestrian bridges alongside. (A)