SAFETY ASSESSMENT AND SRTENGTHENING OF SHORT SPAN BRIDGES IN CASE OF EXTREME RAINFALLS
Author: Eng. Mario Lucio Puppio Supervisors: Prof. Eng. Phd Mauro Sassu
Prof. Eng. Phd Stefano Pagliara Eng. Phd Linda Giresini Eng. Phd Michele Palermo
Keywords: Short span bridges; vulnerability assessment; erosion; hydraulic thrust; railing collapse; bridge failure; safety index; structural reinforcement.
Abstract.
The present work is a contribution in the field of safety assessment and structural strengthening for short-span bridges, subjected to extreme weather events.
Recent cases occurred in Italy and all over the world caused relevant loss of human life and considerable damage in the territory, often due to unexpected collapse scenarios.
Bridges with short span (with length up to 10 meters) are very common: in Italy alone, there are about 460000 bridges, 75% of which with reduced span. Recurring scenarios of damage are identified: failure of railing; deck collapse and erosion.
The topic is examined from forensic, hydraulic and structural points of view. The defined limit states are useful to define the capacity and demand of a specific infrastructure. They are related to the water level with respect to geometry of the bridge and are: (1) free outflow - FLS; (2) pressurised outflow - PLS; (3)
overtopping - OLS. These are associated with the return period of the rainfall events connected to the corresponding flow rates and allow to determine limit actions on the infrastructure in case of overtopping. In addition, appropriate safety indicators have been established for the following scenarios: (1) submergibility, (2) buoyancy, (3) erosion and (4) dragging.
They allow, through the filling of a specific form, a rapid procedure of survey and classification. It is thus possible to carry out a screening on the territory to identify the most vulnerable infrastructures. Strategies of hydraulic intervention and structural reinforcement are also proposed, aimed at restoring the identified deficits, through the correlation of the four vulnerability indices with the intervention strategies.
It is proposed, for the overtopping bridges, a minimum cost intervention, consisting of an early warning system able to warn the user in case of flood, together with reinforcement measures to protect from dragging the vehicles still on the bridge.
Pisa, May 2018
