Final Report Summary - LONG LIFE BRIDGES (Long Life Bridges) -PROJECT DESCRIPTIONThe Long Life Bridges project ran from the 1st September 2011 to the 31st August 2015. The consortium consists of two academic institutes, Kungliga Tekniska Högskolan (KTH) from Sweden and Aalborg University (AAU) from Denmark, and two SMEs, Roughan & O' Donovan (ROD) from Ireland and Phimeca from France. The technical goal of the project is to extend the safe working lives of bridges.-PROJECT OBJECTIVESThe research objectives of the project are described under 3 core headings/tasks;• Task 1.1: Railway Bridge Dynamics;• Task 1.2: Life Cycle Evaluation;• Task 1.3: Fatigue Evaluation.• Task 1.1: Railway Bridge DynamicsThis element of the project deals with railway bridge dynamics and has two main objectives: 1. To accurately quantify the ‘true’ dynamic allowance for railway bridges for a specified (very low) probability of exceedance, using a probabilistic evaluation.2. To develop a semi-active damping system to reduce the risk of dynamic excitation.• Task 1.2: Life Cycle EvaluationThe purpose of this element of the project is to:Develop a framework for probabilistic life cycle evaluation of bridges, particularly new large cable stayed bridges.• Task 1.3: Fatigue EvaluationIn this task the aim is to:Develop a probabilistic framework for fatigue design of steel bridges, including stochastic models for significant uncertainties.-WORK PERFORMED TO DATEThe research tasks are directly linked to a series of secondments between the participating organisations, as indicated below. All secondments are now complete. The last secondment, Secondment 1.1a was completed at the end of February 2015. The Period in which the secondments took place is indicated below;Task 1.1 Railway Bridge DynamicsSecondment 1.1a ROD to KTH (Period 2)Secondment 1.1b KTH to ROD (Period 1)Task 1.2 Life Cycle EvaluationSecondment 1.2a (recruitment) ROD to AAU (Commenced Period 1, Completed Period 2)Secondment 1.2b ROD to AAU (Period 2)Secondment 1.2c KTH to Phimeca (Period 1)Task 1.3 Fatigue EvaluationSecondment 1.3a Phimeca to AAU (Period 1)Secondment 1.3b AAU to Phimeca (Period 1)In Task 1.1 the research associated with quantifying the ‘true’ dynamic allowance for railway bridges was completed in February 2015 and focused primarily on railway bridges subjected to high speed train passage (v > 200km/h). Though the use of the Assessment Dynamic Ratio (ADR) was found to be not applicable for railway bridges, useful observations were made in relation to the importance of including dynamics in the analysis of railway bridges. In the other activity undertaken in this task, a two-frequency tuned mass damping system has been developed. The prototype damper developed by KTH and ROD, was tested on a real bridge in Sweden, the hangers of which are susceptible to fatigue damage. Comparisons were made between the damping capability of the prototype damper and the existing dampers on the bridge.In the Probabilistic load modelling aspect of Task 1.2 associated with Secondment 1.2b more accurate load models for traffic loading alone and traffic plus wind load interaction were developed, by considering the actual traffic and wind as a coupled system. In the Structural Health Monitoring aspect of Task 1.2 associated with Secondment 1.2c a monitoring system was implemented on the Skidträsk Bridge in Sweden to assess the influence of temperature effects on ballast stiffness which in turn affects the natural frequencies of the bridge. In secondment 1.2a the recruited Exploitation Manager identified exploitable results, managed the project throughout its duration and coordinated the various dissemination, training, knowledge sharing and outreach activities that took place.In Task 1.3 as part of Secondment 1.3a a global methodology was developed to assess system reliability which considers cables as a parallel system. The methodology utilised real Weigh-in-Motion traffic data for the loading and included the effect of corrosion. In the second strand of this work, Secondment 1.3b a probabilistic fatigue model was developed for welded plate details using fracture mechanics. The models developed consider both crack width and depth and include for the effect of bending stresses arising from misalignments.-RESULTS ACHIEVED TO DATEThe following are lists of results achieved to date within the various research tasks.Task 1.1 - Railway Bridge Dynamics• Simulations showed that the existing passive damping system in place on the case study bridge may be partly inefficient, due to changes in the dynamic response during train passages;• A prototype damper has been designed to account for the bridge response both during and after train passages;• The prototype damper was shown to attenuate the fatigue-related stresses by about 20% compared to the previous condition (existing dampers);• The likelihood of resonance occurring increases as train speeds increase;• Deck acceleration is typically the predominant load effect; • Including vehicle-bridge Interaction in the analysis can result in lower maximum accelerations (i.e. less conservative design);• When accounting for vehicle-bridge interaction and velocity, the maximum load effect is not necessarily located at the same position as the maximum static load effect (e.g. simply supported single span structure - max. moment not located at span/2);• Wavelet analysis is potentially a powerful tool for signal processing.Task 1.2 - Life Cycle Evaluation• Ballasted bridges were found to show a step like variation on the eigenfrequencies as the temperature rises. Temperature dependence of measured first and second eigenfrequencies for a number of train passages over a case study bridge was demonstrated;• Long span bridges are governed by stationary congested traffic rather than dynamic free-flowing conditions;• The Eurocode deterministic loading models are conservative when used for long span bridges;• The traffic and wind loads can be reduced considerably from that given in the Eurocode, even for a bridge subject to repeated daily congestion and considerable heavy truck traffic;• The complementary method of prediction of stochastic bridge loads proposed in this work is recommended for predicting the performance of long and complex bridge structures under various combined loading conditions;• The overall procedure developed is flexible enough to allow the development of accurate site-specific multi-lane traffic and instantaneous multi-component wind load models. This is significant for the design of new bridges and has great importance for detailed fatigue analyses and bridge assessments.Task 1.3 - Fatigue Evaluation• A global methodology was developed, considering the cables as a parallel system of wires, the effects of corrosion and length of the cable;• Reliability level decreases as a result of longer cable lengths;• Corrosion level has a significant impact on reliability of the cable;• A probabilistic model was developed for fatigue crack growth estimation;• The probability of failure in fatigue is approximately one order of magnitude lower than the probability of failure in the ultimate limit state;• Misalignments and bending stresses reduce the reliability level;• Reliability can be increased with regular inspections.-EXPECTED FINAL RESULTS, POTENTIAL IMPACT and USE• Damping system for railway bridges to minimise the effect of harmful vibrations;• Importance of including dynamics in the assessment/design of high speed railway bridges;• More accurate load models for long span bridges, considering both traffic and wind loading;• Method to monitor and assess the effects of seasonal variation on bridge dynamic behaviour;• Global method to assess the reliability of steel cables on cable stayed bridges;• Probabilistic method for assessing fatigue-critical welded steel details;• Framework for an optimised inspection and maintenance plan;• The deregulation of the transport industry also means that control over railways is no longer the responsibility of one organisation and hence it could be argued that overloading and speed limits on railway lines will be harder to control and monitor.Work performed in the project will facilitate the identification of old bridges that are safe to remain in service and those that need maintenance plans, incorporating structural control and health monitoring, to optimise their remaining life. Coupled with reduced spending on infrastructure, this is particularly important, ensuring the maximum return possible from the existing bridge infrastructure as opposed to undertaking expensive and carbon-intensive new projects. Long Life Bridges will deliver:• More road and rail bridges being proven to be in a safe state;• Higher speeds on our (non-high-speed) railway lines;• With less demand for non-renewable and carbon intensive resources and• For less cost.-Contact DetailsCoordinator: Professor Eugene OBrienEmail: eugene.obrien@rod.ieTel: +353-1-2940800
