Development of corrosion hazard maps for reinforced concrete bridges

Infrastructures in coastal areas are often prone to several hazards, and thus the elaboration of effective risk management plans in such zones are possible if all relevant threats are considered and analyzed. In this context, the assessment of the corrosion hazard attributable to airborne chlorides is of utmost importance since the resulting deterioration phenomena can heavily jeopardize both reliability and resilience of the infrastructures. Therefore, this contribution aims at proposing the preliminary version of a possible framework for the elaboration of corrosion hazard maps at regional scale for coastal areas, with focus on reinforced concrete bridges. The proposed approach encompasses three main steps. First, the relevant stock of infrastructures vulnerable to chloride-induced corrosion is identified and quantified. This requires the collection of relevant features, such as construction type, position, and age. Environmental conditions are examined next, including data about sea waves and salinity, wind, temperature, humidity, rainfall, and chloride deposition rate. Finally, the corrosion hazard is estimated in probabilistic sense. The proposed methodology is presented together with the preliminary results obtained from a relevant case study

Effects of Near-Fault Ground Motions on Civil Infrastructure

Near-fault earthquakes (NFEs), characterized by high peak ground velocity (PGV) and long period pulses, show different properties from far-field ones. The input motions from NFEs are usually composed of a small number of sinusoidal large waves in addition to significant vertical components. These specific characteristics of NFEs strongly influence the seismic response of civil infrastructure and may reduce the effectiveness of the adopted protection devices

Nonlinear static analysis by finite elements of a Fujian Hakka Tulou

Hakka Tulous are massive circular earth constructions of the Fujian Province, China, included in the UNESCO World Heritage list. They are subjected to earthquakes of medium magnitude, but their response to the seismic action is not yet investigated in depth. The seismic response of Fujian Tulous was herein investigated through pushover analysis modelling the Tulou structure by finite elements. Although the Tulou is a big construction with a circular earth wall of about fifty meters in diameter, a micromechanical approach was used to model the earth nonlinear behaviour. Even if no binder is added to the earthen material, the Concrete Damaged Plasticity model can be adopted and has shown to be effective in modelling its nonlinear behaviour, as well as the nonlinear response of the Tulou earth wall. Performing pushover analysis of a big earth structure using a micromechanical approach seems to give reliable results, that must be proved by future research

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

Experimental tests on existing RC beams strengthened in flexure and retrofitted for shear by C-FRP in presence of negative moments

Abstract The shear strength of reinforced concrete beams extracted from existing buildings often reveals insufficient transversal steel reinforcement, mainly due to design or construction defects or increased design load requirements. FRP wrapping is one of the best solutions to improve beam shear strength as the retrofitting intervention is fast and the cost is modest. Design codes provide clear indication about the retrofitting design of simply supported beams, while the case of a beam with negative moments at the end is not considered, although this is in the case of a beam in a framed structure. One of the main uncertainties lies in the effectiveness of the FRP U sheet anchorage behavior in the area of negative bending moments with cracked concrete. This may limit the shear strength of the retrofitted beam. In this study, two beams extracted from an existing building constructed in the 1930s in Rome and retrofitted by carbon fiber-reinforced polymer (C-FRP) U strips placed at beam ends, where also negative bending moments were present, and have been evaluated with experimental tests at the laboratory of the Department of Architecture of Roma Tre University. Beam steel and concrete characteristics were evaluated by means of different tests. The experimental results are discussed considering the final results in terms of maximum shear resistance in the presence of negative bending moments. Load deflections at different points along the beam, shear-C-FRP deformation along the reinforcement strips and the damage state for different load levels, are presented. The importance of avoiding possible fragile mechanisms in the sections retrofitted with FRP is clearly shown

Ultra-High performance concrete (UHPC) with polypropylene (Pp) and steel Fibres: Investigation on the high temperature behaviour

Ultra-high performance concretes (UHPC) are advanced cement-based materials characterised by superior me-chanical properties with respect to normal and high-strength concretes; however, their dense and compact matrix can facilitate the onset of spalling at high temperatures. This problem is often coped up by adding polypropylene (PP) fibres to the mix design, alone or with other types of fibres; steel fibres enhance the material’s tensile ca-pacity. The paper presents a series of tests on two UHPC types (150 and 180 N/mm2) with PP fibres (0.27% of volume) and variable content of steel fibres (0% to 1.92%), aimed at investigating the residual mechanical properties of the material after high temperature exposure. The experimental results are compared to available research on small UHPC specimens exposed to high temperatures, with dosages in PP fibres from 0.03% to 2%, and in steel fibres from 0 to 3%. The results of this research demonstrate that UHPCs need hybrid fibre rein-forcement (PP +steel) to withstand high temperatures, and that the residual strength increases after 200 ◦C exposure, at all steel fibre dosages; this is in line with literature. Available research also shows that strength loss is possible in hot conditions, as found in the present research, while PP fibres alone do not always prevent the occurrence of spalling in small UHPC sample

Seismic reliability of the Abruzzo hospital system and upgrading strategies

SUMMARY A model for the regional hospitals system behavior in case of a seismic event is developed. The aim is the evaluation of the vulnerability of the system as well as the selection of the best intervention strategy for the retrofitting of the hospitals so as to minimize the cost benefit ratio and to evaluate the effect of different post-earthquake emergency measures like the use of camp hospitals. The efficiency of the system is measured in terms of mean distance to be cured for persons injured by the earthquake. In a previous work by the authors [Nuti and Vanzi, 1998c] a common fragility law had been assumed for all the hospitals in Abruzzo because of lack of information. This information is now available, since the vulnerabilities of the Italian hospitals have been computed and presente

Asynchronous earthquake strong motion and RC bridges response

The dynamic response of long structures (e.g., bridges) is sensitive to the spatial variability of strong ground motion (asynchronous motion). Ground motion differences increase from point to point with increasing foundation distance. This latter is due to two physical phenomena: soil-wave interaction, that causes the loss of coherence and local amplification; wave traveling with finite velocity, that causes signals time lag. This ground motion variability produces a different structural demand compared to the synchronous one, which is the only one considered by designers in the majority of cases. A few codes consider this type of actions, therefore further research efforts are necessary. In this study, asynchronous ground motions are generated by means of a new generation procedure implemented in the software GAS 2.0 using as input the simultaneous strong motion records from the April 6th, 2009, L'Aquila (Italy) at the seismic stations AQA and AQV, located in the Aterno River valley. These records are used to calibrate the generation model and to produce sets of asynchronous earthquake sampling. The asynchronous earthquake sets are applied on a typical highway reinforced concrete bridge to study its dynamic response considering two different configurations: non-isolated with traditional supports and isolated bridge with lead rubber bearings. The bridge is placed in two positions along the wave propagation direction: a position near one recording station and a position between the two stations to consider local soil effects. The response parameters investigated are the maximum relative displacements of soil and deck. The results show that there is an important variation of relative displacement along the direction of wave propagation due to asynchronous motion with effects that designer should consider for the structural details design of isolated and non-isolated bridges. Keywords: Asynchronous motion, Bridges, Seismic response, Earthquake spatial variabilit

Damage patterns in the town of Amatrice after August 24th 2016 Central Italy earthquakes

The impact of the two seismic events of August 24th 2016 on the municipality of Amatrice was highly destructive. There were 298 victims, 386 injured, about 5000 homeless, and the historical center of the town suffered a great number of partial and total collapses. The 260 strong motion records obtained for the first event were analyzed and plotted in a shakemap, comparing them with the macroseismic damage surveys made in 305 localities. On the basis of an inspection survey made in September 2016, a map of the damage patterns of the buildings in the historical center was elaborated according to the EMS 98 classification. The damage level resulted very high with more than 60% of the inspected buildings showing partial or total collapse. The elevated level of destruction was mainly caused by the high vulnerability of the masonry buildings, mostly due to specific vulnerability factors such as the poor quality of masonry, the lack of connections between walls and the poor connection between external walls and floors

Time-dependent cyclic behavior of reinforced concretebridge columns under chlorides-induced corrosion andrebars buckling

This study presents the results of a refined numerical investigation meant at understanding the time-dependent cyclic behavior of reinforced concrete (RC) bridge columns under chlorides-induced corrosion. The chloride ingress in the cross-section of the bridge column is simulated, taking into account the effects of temperature, humidity, aging, and corrosion-induced cover cracking. Once the partial differential equations governing such multiphysics problem are solved through the finite-element method, the loss of reinforcement steel bars cross-section is calculated based on the estimated corrosion current density. The nonlinear cyclic response of the RC bridge column under corrosion is, thus, determined by discretizing its cross-sections into several unidirectional fibers. In particular, the nonlinear modeling of the corroded longitudinal rebars exploits a novel proposal for the estimation of the ultimate strain in tension and also accounts for buckling under compression. A parametric numerical study is finally conducted for a real case study to unfold the role of corrosion pattern and buckling mode of the longitudinal rebars on the time variation of capacity and ductility of RC bridge columns