Failure evidences of reduced span bridges in case of extreme rainfalls The case of Livorno

Abstract

The heavy rainfalls occurring in Italy in the last few years focused the attention on the vulnerability of the land and the related infrastructures. Critical situations involving losses of human life and deterioration or failure of relevant structures are frequent. These events were due to: (1) improper land-use; (2) aging of infrastructures, (3) insufficient maintenance and protection; (4) climate changes causing rainstorms similar to tropical events. The failure of small bridges in road networks plays a key role in this sense. The present paper aims to analyse the behaviour of small bridges during rainfalls or floods. In particular, the recent case of Livorno is analysed. The Italian territory has about 460.000 small bridges, mostly designed without the support of technical codes or a proper interaction between the hydraulic and structural aspects. A large part of them can be submerged by water flows during rainfalls and pushed by unexpected actions. The failure scenarios allow identifying the hydraulic and structural vulnerabilities through a specific survey. A classification of small bridges on the basis of submergibility indexes is eventually proposed. KEYWORDS. Small bridges; Structural and hydraulic assessment; Road network safety; Livorno flood. Citation: Puppio, M. L., Novelli, S., Sassu, M., Failure evidences of reduced span bridges in case of extreme rainfalls, The case of Livorno, Frattura ed Integrità Strutturale, 46 (2018) 190-202.

Fragility of bridge decks exposed to hydraulic and driftwood actions

“…The uplift mechanism is generated by the balance between the deck self-weight and the algebraic sum of dynamic and static upward components of the hydraulic force. One further underlying assumption is that no vehicles are crossing the bridge at the failure time; unfortunately, this was not always the case, as reported by previous disasters (Puppio et al, 2018), but any additional load would result in more unsafe predictions of the collapse probability due to the additional weight. Uplift LS is assessed as:…”

“…However, overtopping water forces combined with debris lead to the collapse of steel parapets before any of the investigated limit states would occur. On the contrary, reinforced concrete parapets play a major role in adding a fictitious thickness to the deck that should not be neglected (Puppio et al, 2018). The bridge of Figure 3 As per hydrologic model it is used MOBIDIC, having the two mentioned calibrated datasets as inputs for the discharge computation.…”

Risk management for bridges: a case study of unforeseen failure mode

“…Although the analysis can be also performed by simplified methods [9], the buoyancy action is very sensitive to the bridge's boundary conditions.…”

Seismic Analysis of Historical Urban Walls: Application to the Volterra Case Study

“…Analysis of these failures highlights that the presence of moisture is a common denominator in many cases [2,8]. Water induced by flooding and rainfall threatens civil infrastructure [9][10][11][12], especially those placed in urban and sub-urban contexts, such as HUW and bridges of reduced span [12][13][14][15][16]. This evidence indicates the need to introduce the weakening effect of water into the failure mechanism.…”