The use of ultrahigh-performance fiber-reinforced concretes (UHPFRC) improves the structural response and extends the durability of concrete structures. Three basic configurations for structural elements combining UHPFRC and reinforced normal strength concrete are proposed with regard to typical demands on rehabilitation projects. They fulfill a protection function and the resistance can be increased if required. The flexural response of these composite UHPFRC–concrete elements is investigated with an original analytical cross-sectional model in a parametric study: UHPFRC increase stiffness and resistance and delay the formation of localized cracks. For this, a minimum magnitude of strain-hardening of 0.2% is necessary. Additional reinforcement in the UHPFRC layer is the most efficient way to increase the bending resistance. The investigation demonstrates how to use UHPFRC and reinforcing bars best in rehabilitation of existing concrete structures.

‘Structural UHPFRC’ stands for Ultra-High Performance Fibre Reinforced Cementitious Composite material, that is, complemented by reinforcing steel bars forming a R-UHPFRC layer with the goal to enhance the resistance and durability of structural elements in reinforced concrete. This technical paper is intended to serve for the design of enhancement of reinforced concrete bridges. After summarizing the properties of UHPFRC and R-UHPFRC in terms of structural performance, analytical design rules are presented to calculate the increase in structural resistance of structural elements strengthened with a layer of R-UHPFRC. Three applications related to the design and execution of the enhancement of three existing concrete bridges including the three most common cross sections, that is, box girder, multiple beam girder and massive slab, are described with emphasis of conceptual design aspects, main results of design and main features of execution of the UHPFRC work.

In January 2011, the Swiss Society of Engineers and Architects (SIA) published a series of standards for existing structures. The standard entitled ‘existing structures—bases for examination and interventions’ specifies the principles, the terminology and the appropriate methodology for dealing with existing structures. This standard is complemented by a series of standards which treat specific items regarding ‘actions on existing structures’, ‘existing concrete, steel, composite, timber and masonry structures’ as well as ‘geotechnical aspects of existing structures’. It is expected that these standards will provide effective solutions on questions such as higher live loads, accidental actions or the restoration and improvement of the durability of existing structures. This paper highlights major principles, in particular those related to risk-based safety, proportionality of interventions and updating of variables. Methodological aspects of the main activities, that is, examination of structures ...

The visual inspection of existing infrastructure is a critical step for asset management, as the detection and quantification of damage must be useful to prioritise maintenance. In Switzerland, main inspections are made every five years for all road bridges. For each bridge, a condition value ranging from 1 to 5 is given. As only element-based degradations are currently taken into account in bridge-condition evaluations, inaccurate assessments of global structural safety are often provided by bridge inspectors. In this paper, a risk-based methodology is introduced to evaluate bridge conditions based on visual-inspection data. Degradation states of bridge elements are coupled with element-failure consequences on the global structural safety in risk analysis to accurately assess the bridge condition. A case study of a strategic road involving sixty bridges is used to assess bridge-condition evaluations using the risk-based methodology based on recent visual inspections. The study reveals that including element-failure consequences in bridge-condition assessments supports more accurate evaluations of the impacts of damage on the global structural safety, leading to more objective decisions on asset management actions. Analyses of four damaged bridges show that inspection reports are often over-pessimistic in terms of structural damage, and this can lead to unnecessary rehabilitation interventions.

Located in Switzerland, Chillon viaducts are two parallel highway posttensioned concrete bridges built in the late 1960s. The concrete of the deck slabs of these bridges shows signs of early stages of the alkali-aggregate reaction (AAR), which will induce, in time, a decrease of the concrete strength. To insure structural safety for future traffic demands, it was decided to strengthen the slab by adding a layer of 40 mm of an Ultra High Performance Fiber Reinforced cement-based Composite (UHPFRC) material, reinforced with steel rebars. Strain-hardening UHPFRC, with its low permeability, is used as a waterproofing layer protecting the slabs from the water to reduce the rate of AAR. UHPFRC has excellent mechanical properties and also acts as an external tensile reinforcement for the slab, increasing its bending and shear resistance and extending the fatigue life. To investigate this increase in structural resistance, an analytical calculation is done using models previously developed based on extensive experimental campaigns. Finally, the choice of UHPFRC for strengthening was also the most efficient in terms of intervention duration and cost.