A Case Study - Life Extension of Offshore Bridge Bearings

Structural bearings of 47 offshore platform-link bridges with average age of 40 years were inspected and recommended for replacements due to their poor condition. Replacement of bridge bearings involves major risk and production interruptions given the structural modifications, and critical piping and E&I disconnections required for safe jacking-lifting activities required during the process. This paper presents the approach adopted to assure the integrity of the bridges and extend their lives without the need to replace the bearings. The approach employed failure mode and effect analysis to identifying and narrowing down areas that need focused efforts while tackling the problem. Scenario based structural assessments were carried out to examine the impact of the level of movement-allowing bearings functionality on the integrity of the bridge and its supporting structures; identify critical locations to be targeted during focused inspections; and establish envelopes for monitoring thermal expansion and contraction of the bridges. Guidelines were developed and implemented for integrated inspection-maintenance and repair campaign, which aimed to tackle corrosion issues and to install movement-monitoring indicators. Indicator seasonal monitoring is employed to establish the functionality of bearings on the long-term. The what-if structural assessments revealed that even in the worst-case scenario (in which the bearing are completely jammed) the option of local strengthening of the bridge and its supporting elements is more attractive than bearing replacement. The integrated inspection-maintenance and repair campaigns revealed that excessive corrosion levels observed from historic visual inspections on external non-critical bearing components (e.g: guide plates, angles, etc.) is not indicative of the condition of the internal load-bearing components (pedestals) which experienced much lower corrosion levels. The seasonal monitoring of bridge movements revealed that the 40+ years old Teflon pads are still functional and allow the bridges expansion and contraction. The developed holistic approach enabled demonstration of the fitness for service of the bearings, and provided means for assuring their long-term performance through monitoring. The results assured safety, integrity and delivered significant cost savings through aversion brownfield modifications, and production loss associated with bridge jacking and bearing replacement operations.

A Simplified Methodology for Condition Assessment of Bridge Bearings Using Vibration Based Structural Health Monitoring Techniques

The mechanical properties of bridge bearings gradually deteriorate over time resulting from daily traffic loading and harsh environmental conditions. However, structural health monitoring of in-service bridge bearings is rather challenging. This study presents a bridge bearing condition assessment framework which integrates the vibration data from a non-contact interferometric radar (i.e. IBIS-S) and a simplified analytical model. Using two existing concrete bridges in Australia as a case study, it demonstrates that the developed framework has the capability of detecting the structural condition of the bridge bearings in real-time. In addition, the results from a series of parametric studies show that the effectiveness of the developed framework is largely determined by the stiffness ratio between bridge bearing and girder ([Formula: see text], i.e. the structural condition of the bearings can only be effectively captured when the value of [Formula: see text] ranges from 1/100 and 100.

Numerical analysis of the spherical bearing geometric configuration with antifriction layer made of different materials

Requirements to critical elements of transport and logistics systems have been increased due urbanization in the territories of Russia and the world. Bridge bearings, which perceive the vertical and horizontal loads from the bridge span, as well as absorb thermal expansion and contraction, shrinkage, seismic disturbances, etc. refer to such elements. Requirements to strength, durability, wear resistance, operation maintenance-free periods, etc., imposed on the bridge bearing are increasing due to a stable growth of loads on the bridge elements and increase in vehicle fleets. Recently, international and Russian companies have been engaged in development of new polymeric and composite materials, which have improved physical and mechanical, frictional, thermo-mechanical and rheological properties and can be used as a thin layer of sliding bearings bridges. A number of problems are outlined in studying material properties and geometric configuration of bridge bearings in order to rationalize the work of its structure. Three topical problems of solid mechanics are reviewed in the work. This is the identification of qualitative and quantitative patterns of the deformation behavior of modern antifriction polymer and composite materials as relatively thin sliding layers of bridge spherical bearings in order to formulate scientifically grounded recommendations for the selection of the interlayer material regarding the study unit operation. This is an analysis of the influence of the sliding layer material physical and mechanical, frictional, thermomechanical and rheological properties on the structure deformation as a whole and the change in the contact zone parameters, in particular. It is an analysis of the influence of the sliding layer geometric configuration on the structure performance. A significant decrease in the area of full adhesions of the contact surfaces, including up to 0, and the occurrence or increase in the area of the divergence of the contact surfaces (no contact) is observed during frictional contact taking into account the lubrication on the mating surfaces. The surface percentage on which the contact surfaces divergence (no contact) is observed decreases, on average by more than 2 times, if the sliding layer thickness is increased.

Basis for Design of Bearings in New the Generation of Eurocodes

A new generation of Eurocodes for structural design is currently being prepared within the Technical Committee CEN/TC 250. The revised Eurocode EN 1990 will be supplemented by the new Annex F for the basis of design of bridge bearings. Harmonised European provisions are still missing with recommended procedures for determination of basis of design and actions on bearings, taking into account various types of uncertainties. In particular, problems can occur where it is necessary to replace bearings at existing bridges according to the new procedures of Eurocodes which can lead to the design of a bigger size of new bearings despite the existing bearings served well for many years. The developed amendment of National Annex to EN 1990 for the basis of structural design should refine the design procedures. The submitted paper describes inconsistencies and main principles of the changes focusing on thermal actions.