Safety Assessment of Existing Highway Bridges and Viaducts

IABSE Symposium Report, 2013

The design codes use safety margins which, in general, exceed those that are reasonable to accept for the assessment of existing bridges. Knowledge about a structure can be improved by further investigations and this can justify modifying partial safety factors. In this context, the Technical Centre for Bridge Engineering (CTOA) of the Technical Department for Roads, Road Safety and Bridges (SETRA) has initiated in 2009 a large study for the calibration of partial factors adapted to the assessment of existing bridges. Based on the reliability theory, its objective is to provide modified partial factors based on tabulated experimental in-situ results. The study is performed on different families of standard bridges but the present paper will only highlight the preliminary results obtained for reinforced concrete slab bridges.

1997

The authors suggest that the work required to strengthen sub-standard bridges needs to be prioritised taking into account costs and risks to the public. A framework is proposed for a risk-based approach for assessment of bridges and simplified methods for risk evaluation. The procedure is most appropriate for bridges which do not satisfy the requirements of a standard assessment of load carrying capacity using current assessment codes. The method is part of an ongoing research project intended to be dovetailed into the strategic research programme being conducted by the Highways Agency. The prupose of the proposed methodology will be to identify the low risk bridges for which traffic disruptive interim measures may not be necessary and to select appropriate remedial actions. For the covering abstract see IRRD 898092.

Structural Engineering International, 2013

The main strategic goal in the assessment of the existing Swiss national road network is to provide a high level of availability of the roads for traffic and reduce interferences caused by construction or repair works. Therefore, renovation works tend to be executed in large maintenance sections for which the complete infrastructure is repaired in order to ensure a period of 15 years without the need for additional construction works. Before 2008, the existing bridges were maintained mostly individually under the responsibility of local cantonal administrations. Entering into the new maintenance strategy requires a careful assessment of the structural conditions. Visual inspections and laboratory testing programs are required in order to bring the structural condition of different structures to a similar level and to fulfil all standards as long as costs are not disproportional to the benefits. Structural safety is evaluated according to the new Swiss code for existing structures, SIA 269, which was published in 2011. For typical short span bridges and overpasses from the early 1970s, which represent the largest number of existing objects, focus has to be set on the shear verifications of slabs without stirrups as well as on the bending capacity of cantilever slabs. Within the structural assessment, actions, material properties, geometrical properties and structural models shall be updated. Partial safety factors can also be updated by means of semi or full probabilistic approaches, in order to verify structural safety.

2012

U.S. engineers need advanced tools and protocols to better assess and assure safety and serviceability of bridges. The Federal Highway Administration, American Association of State Highway and Transportation Officials, and National Cooperative Highway Research Program sponsored a scanning study of Europe to identify best practices and processes to assure bridge safety and serviceability. The scan team found that the European highway agencies expect their bridge programs to not only ensure user safety, but also to meet serviceability expectations and enhance capital investment decisions. The team gathered information on safety and serviceability practices and technologies related to design, construction, and operations. Team recommendations for U.S. implementation include developing a national strategy to increase use of refined analysis for bridge design and evaluation, encouraging States to use refined analysis combined with reliability analysis to avoid unnecessary rehabilitation or replacement of bridges, and encouraging adoption of the concept of annual probability of failure to quantify safety in probability-based design and rating specifications.

In this paper, risk assessment for the activities associated with construction of bridge as part of the risk assessment for the project comprising building of new motorway section from Demir Kapija to the village of Smokvica, Republic of Macedonia is presented. After identified risks and hazards, during activities related with bridge works and after performed risk assessment, control measures are proposed.

The bridge management procedure includes bridge inspection (routine, scheduled, urgent) but the inspection is mostly concerned with damage detection, location and description giving no exact answers for the bridge remining load bearing capacity. However, this answer is the most important outcome in the process of an existing bridge assessment. There are several examples when the bridge inspection is completed, and soon after this inspection, the bridge collapsed. The mentioned clearly indicate the needs for and importance of the existing bridge assessment procedure consisting of the inspection, integrity evaluation, load bearing capacity estimation, and the bridge remining service life prediction. Only fully accomplished mentioned procedure can bring to the bridge owner enough reliable result of the existing bridge assessment.

The Baltic Journal of Road and Bridge Engineering, 2018

Deterioration of bridges due to ageing and higher demands, induced by increased traffic load, require the development of effective maintenance policies and intervention strategies. Such concern should be aimed at ensuring the required levels of safety, while optimally managing the limited economic resources. This approach requires a transversal advance; from the element level, through the system level, all the way to the network level. At the same time intervention prioritisation based on the importance of the system (bridge) inside the network (e.g. highway), or of the single structural element inside the bridge is dependent. The first step in bridge condition assessment is the verification of safety and reliability requirements that is carried out using the traditional prescriptive (deterministic) approach or the current performance- based (probabilistic) approach. A critical issue for efficient management of infrastructures lies in the available knowledge on condition and perform...

Applications of Statistics and Probability in Civil Engineering

The assessment of the structural safety of existing bridges and viaducts becomes increasingly important in many countries due to the age of the structures and an increase in traffic loads. Many structures need to be reassessed in order to find out whether the safety requirements are met. Most existing standards, however, are developed for the design of new structures. This paper summarises the recent developments with respect to the specification of the target reliability levels for existing structures. It appears from total life cost optimisation that application of the same target reliability levels for existing structures as for new structures is uneconomical. Further, in some cases the cost optimisation seems to yield rather low reliability levels and human safety criteria become decisive for specification of the target reliabilities of existing structures. In this paper old concrete slab bridges without shear reinforcement are studied. Probabilistic calculations are performed in order to calibrate partial factors satisfying the target reliabilities under traffic load. These partial factors can be used by engineers in level I probabilistic calculations. In this way the often over-costly application of safety standards intended for new structures can be avoided in the reassessment of existing structures.

Bridge & Structural Engineer, Volume 53, Number 1, March 2023, pp 9-27, 2023

The author believes that the vulnerability to the failure of the structures has a genesis in majority of the cases in the decisions made during the design stage. During the design stage whether it is conceptual or detailed, the design solutions could be such that the probability of the failures could be minimum or the probability of the failure is high despite satisfying all the codes and standards’ requirements. In the ensuing article, the author deliberates and in some cases proposes remedies to obviate the failures at the stages of design, structural calculations for safety, detailing, construction process and construction management.

A numerical procedure for the evaluation of the seismic vulnerability and seismic risk of highway bridges is proposed. It combines elements from the Direct Displacement- based design method and the Capacity Spectrum Method. First, the seismic resistance of each structural subsystem (i.e. pier/abutment + bearing/seismic devices) is determined by conducting a pushover analysis, tracking the formation of flexural plastic hinges or brittle shear failures in the piers, the attainment of the maximum strength/deformation capacity in the bearing/seismic devices, unseating of simply supported spans, degradation due to P-∆ ef- fects, etc.. The contributions of each structural subsystem are then properly assembled to pro- vide the Pushover Curve of the bridge as a whole, both in the longitudinal and transversal direction. A number of performance levels (i.e. damage states) are then identified, for both piers and devices, and reported on the Pushover Curve of the bridge. For each of them, the e...