Editor: Professor M C Forde, PhD, FREng, FRSE, FACI, CEng
Carillion Chair, University of Edinburgh
Keynote Papers (K)
EVALUATING SERVICE LIFE OF LONGSPAN BRIDGE CABLES
Dr K Mahmoud, Bridge Technology Consulting Inc, New York, NY, USA
Bridge cables are subject to different degradation processes such as corrosion pitting, stress corrosion cracking, corrosion-fatigue and hydrogen embrittlement. In the last three decades, many suspension bridge cables have demonstrated signs of degradation with different degrees of severity resulting in reduced load carrying capacity. This necessitates a quantitative rationale for the assessment of remaining strength and safe service life of bridge cables. The quantitative methodology must utilize inspection findings and laboratory test results for condition assessment and reliability criteria, similar to LRFD approach. With that in mind, random sampling and reliability-based analytical techniques are required for the assessment of remaining cable service life. The wire mechanical properties and findings of broken and cracked wires must be defined as probabilistic quantities. If an evaluation is conducted using these criteria, the results can be used to establish the tempo of bridge cable inspection and further evaluations in the future. Once probability distributions for wire mechanical properties, such as strength and strain, and loads are established, it’s possible to develop a cable failure mechanism and assess the serviceability of the cable. Use of probabilistic analysis in this approach is similar to the LRFD probabilistic analysis employed in the current AASHTO standards. This paper presents the BTC method, a probability-based methodology for the evaluation of remaining strength and service life of bridge cables. The BTC method is patented and has been published in two reports sponsored by the U.S. Federal Highway Administration (FHWA). Currently, the BTC method is being applied at the Forth Road Bridge in Scotland, and has been applied at the Bronx-Whitestone and Mid-Hudson Bridges in the United States.
SUSPENSION BRIDGES – DESIGN, MAINTENANCE & INSPECTION OF MAIN CABLES
B Colford, Forth Road Bridge, Edinburgh, UK
This paper reviews issues with long span suspension bridges. Two well known and publicised closures of suspension bridges due to cable deterioration, the US Grant Bridge and the Waldo-Hancock Bridge, are salutary lessons for all those involved in long span bridges. They highlight the absolute need for properly funded and well organised maintenance of these assets and that a programme of regular investigations, including internal inspections, of the main cables must be carried over the full service life of the bridges. These investigations cost time and resources but the engineering profession has a duty to ensure they are carried out.
MANAGEMENT OF M4 ELEVATED SECTION SUBSTRUCTURES
CR Hendy & CT Brock, Atkins & ADJ Nicholls, Connect Plus (M25) Ltd Epsom, S El-Belbol, Highways AgencyUK
The M4 Elevated Section in West London is a 1.9 km concrete viaduct structure providing a major arterial route into London. An intervention model bringing together structural assessment and forecast deterioration, corrosion modelling and cracking has been developed to prioritise structural rehabilitation of the substructure crosshead beams. To evaluate residual strength an initial assessment of crossheads was undertaken, which identified a deficiency in tensile capacity at the ends of the crosshead cantilevers compared to current demands. Further assessment has been undertaken, including three dimensional strut and tie, non-linear finite element analysis and plastic analysis, to confirm public safety with continued trafficking of the structure, and to determine the need for strengthening.
Additionally extensive monitoring of the crossheads has been implemented including mapping of all cracks, and remote crack monitoring to safeguard the substructures and allow early interventions. The long term maintenance strategy brings together strengthening and cathodic protection concrete preservation methods with removal and repair of concrete delamination.
This paper discusses the development of the prioritisation process including deterioration modelling, together with the extended structural analysis to formulate a strengthening programme for these substructures.
FLEXIARCH’ – A VERSATILE & SUSTAINABLE BRIDGE SYSTEM
Prof AE Long, Dr S Nanukuttan, Queen's Univ Belfast, A Gupta & D Courtenay, Macrete Ireland, Toomebridge, UK
Concrete bridges built during the 1960s/1970s were largely based on precast girders with an in situ deck slab, as these bridges could be installed rapidly. However, many have deteriorated as a result of corrosion of reinforcement and have had to be replaced. The resulting traffic congestion has cost £ billions. A range of approaches have been adopted to counter the
deterioration caused by the ingress of chlorides including increased cover, surface coatings, cathodic protection but with limited success. One solution is to avoid the use of corrodible reinforcement for elements exposed to aggressive environments.
In this context it has been found that highly sustainable bridges can be developed from the arch concept. Conventional arch bridges have the benefit of being aesthetic, strong and durable as steel reinforcement is not necessary. However, cost and time to prepare the centring and accurate voussoirs render them non competitive against precast girder and slab systems. A
patented system, which uses precast concrete voussoirs and does not require centring, has overcome these problems and over 40 ‘FlexiArches’ have been constructed in the UK/Ireland. These can be installed rapidly, days rather than months, are cost competitive and have all the attributes of masonry arches. They have been extensively tested at full scale, used for short
span bridges and for the rehabilitation/strengthening of deteriorated bridges. Comparative studies have demonstrated that they are significantly more sustainable than alternative systems.
3R’S APPROACH TO BRIDGE MANAGEMENT: RETAIN, REPAIR & REPLACE
D Dunne, AECOM, P McKenna, D Barnett & A White, CH2M HILL, Glasgow & Worcester, UK
Deterioration of reinforced concrete structures, such as bridges, is over time a normal and to a certain degree an expected process. When these processes become abnormally advanced before a structures design life is attained, this poses challenges both economically and technically. As a result, the condition of such structures and the cause of any deterioration must be accurately determined by visual assessment, monitoring and testing, for safety and operational requirements are to be achieved. Ombersley Bridge carries the A449 over the A4133 approximately 6 miles north of Worcester in the UK. The bridge was originally constructed in 1974. A regular inspection programme established that the bridge abutments were cracking and that the bridge was moving. This paper, from a consultant’s perspective, outlines aspects of the investigation and subsequent retention, repair and replacement intervention works. Findings of the experimental investigations are presented. Thereafter, overviews of the works which were undertaken are discussed. The paper ends with conclusions taken after the works concluded.
BALANCING EXTENDED SERVICE LIFE AND SUSTAINABLE CONCRETE MATERIAL USAGE IN MISSOURI BRIDGE A7957
E.S. Hernandez, A. Griffin and Prof J.J. Myers, Missouri Univ of Science & Technology, Rolla MO, USA
Because of its unique nature, self-consolidating concrete (SCC) has the potential to significantly reduce costs associated with transportation-related infrastructure, benefiting both MoDOT and the residents of Missouri. SCC is a highly flowable, non-segregating concrete that can be placed without any mechanical consolidation, and thus has the following advantages over conventional concrete:
decreased labor and equipment costs during concrete placement,
decreased potential for and costs to repair honeycombing and voids,
increased production rates of precast and cast-in-place (CIP) elements, and
improved finish and appearance of cast and free concrete surfaces.
In addition to SCC, innovative materials such as High Volume Fly Ash Concrete (HVFAC) also provide a significant potential to produce more cost effective mix designs for CIP concrete. Since the 1930’s, fly ash – a pozzolanic material – has been used as a partial replacement of portland cement in concrete to improve the material’s strength and durability, while also limiting the amount of early heat generation. From an environmental perspective, replacing cement with fly ash reduces concrete’s overall carbon footprint and diverts an industrial by-product from the solid waste stream (currently, about 40 percent of fly ash is reclaimed for beneficial reuse and 60 percent is disposed of in landfills). The objective of this research is to provide an implementation test bed and showcase for the use of sustainable and extended service life concrete. In this implementation study for Missouri Bridge A7957, a level of 50% fly ash to cement proportions was utilized as well as SCC and high-strength self-consolidating concrete (HS-SCC) in the load carrying elements to showcase the use of these innovative materials.
OPTIMIZING A BRIDGE RESPONSE MODIFICATION APPARATUS
A Schultz, Univ of Minnesota, Minneapolis, A Gastineau, KPFF Engineers, Seattle & SF Wojtkiewicz, Clarkson Univ, Potsdam, NY, USA
Given the plurality of bridges in the United States that are classified as deficient and in need of replacement or repair, methodologies to help avoid the substantial costs of replacing these bridges simultaneously are important. This paper presents a synthesis of work conducted to develop a structural response modification approach employing a mechanical amplifier and supplemental stiffener and damper to extend the fatigue life of existing steel bridge structures. The optimal cross-sectional area for apparatus members and response modification device stiffness and damping characteristics for these apparatuses are investigated to reduce local stresses as a means to increase bridge life. A reduced order numerical model of an existing finite element bridge model is developed for the purpose of optimizing the apparatus. The study indicates that for the apparatus employing the mechanical amplifier, small dampers are optimal for maximal safe life extension. The study also suggests that improvements in performance can be obtained from the apparatus using semi-active control.
ANALYSIS & FATIGUE TESTING OF FULL SIZE BRIDGE HANGER CONNECTION TO DEVELOP INSTRUMENTATION SYSTEM & DETECTION CRITERIA FOR IN SERVICE MONITORING
P Plemic & R E Lindenberg, Wiss, Janney, Elstner Associates Inc, Northbrook, IL, USA
To address the complex in-service behavior of a bridge platform welded hanger connection, modeling and laboratory studies were conducted to develop an instrumentation plan for monitoring and detecting of crack initiation and propagation. The purpose of the work was to understand the anticipated test behavior and to robustly measure the accelerated 400,000 lbf (1700kN) cyclic fatigue test to failure.
The primary objective of the laboratory testing was to develop the detection criteria, to demonstrate the effectiveness of Acoustic Emission (AE) sensors for potential crack detection and to optimize the number of required sensors and AE system for the detection and monitoring of the crack growth. The secondary objective of the experimental testing was to estimate the fatigue resistance life cycle of the fillet weld between the hanger connection and kicker gusset plate. Testing was conducted on four samples, two simple plate connections models and two full-scale hanger connection using Universal Test Machine with a 400,000 lbf (1700kN) capacity equipped with a controller that allows cyclic or fatigue testing of samples. During testing a visual examination as well as Magnetic Particle Testing of the test specimen was conducted. At the conclusion of the cycling, Ultrasonic Testing was performed on each test specimen. The testing was performed at the structural laboratory of the Jack R. Janney Technical Center at Wiss, Janney, Elstner Associates, Inc. (WJE) in Northbrook, Illinois
Prior to testing a finite element analysis (FEA) was performed to identify high stress locations for each test sample, and to allow for visualization and animation of the sample response to the applied loads.
REVIEW OF "ADA BRIDGE" LOAD TEST PROJECT
D Kovacevic, V Radonjanin, M Malešev & D Lađinović, Univ of Novi Sad, & S Ranković, Univ of Niš, Serbia
This is brief presentation of "Ada Bridge" load test project. Things that stand out this project are scale, status and importance of the structure. In this sense, this load testing is, if not the biggest, probably until now, the most complex structure testing in this (ex-YU) region. This fact emphasizes the amount and type of load used for testing, number and type of load configurations, number and type of performed measurements and assortment of used measuring equipment.
Load test of "Ada Bridge" was done according to our SRPS U.M1.046 regulation respecting the special demands set by investor, contractor and manager in corresponding parts of the technical documentation.
The goal of testing was to get experimental proof of bridge's capacity for taking and transferring design loads and actions, namely the proofs that bridge structure satisfies the criteria of bearing capacity, stability and serviceability.
PRACTICAL STRUCTURAL MONITORING OF LONG-SPAN BRIDGES - THE STRAINSTALL 2014 UPDATE
J St Leger, S Babin, M Anderson, A Scullion, Strainstall Monitoring, Royston, UK
This paper considers the following from a practical perspective:
1. Bridge management - how appropriate structural health monitoring systems help the bridge owner.
2. Current effective monitoring systems and how new sensor technology and future developments will help.
3. The fast moving world of web based applications for the delivery of structure information – the changing picture.
4. Derivation of meaningful and timely information from structural health monitoring systems to enable effective bridge management and informed decision making.
5. An overview of state-of-the-art structural health monitoring systems for bridges.
NEW TEST METHODS FOR STAY CABLE SYSTEMS
AW Gutsch, M Laube, T Nolte, TU Braunschweig, Germany
In cable bridges the cables are subjected to different kind of loading scenarios during their lifetime. Before the installation of stay cables the systems have to proof their sustainability in tests. The different types of tests are mentioned in several national and international accepted recommendations [1 – 5]. Up to now the most common loading tests for stay cable systems are the axial fatigue loading test and subsequently a static loading test to determine the ultimate breaking load (UBL).
Experience showed that bending effects due to installation tolerances of the anchorages and other sources of bending like sag, wind-rain induced vibration or flexural deformation of the bridge deck are fatigue relevant in practice, too. For the investigation of these effects in tests the anchorages are usually installed with a specific angle in the axial test set-up or recently specific bending fatigue tests were performed. Here different test set-ups for bending fatigue tests with constant axial forces and with synchronized axial dynamic forces will be shown.
Saddles must be designed such as to ensure a safe transfer of vertical forces and of differential forces of stay cables from opposite sides of the pylon. The simulation of a saddle in a stay cable test results in a complex test set-up. Here a modified test set-up for a saddle test with fatigue load will be presented.
Finally the test set-up for fire resistance tests for qualification test of stay cables with fire resistance characteristics will be shown here.
Access provision to undertake construction and remedial works to structures is an increasingly demanding consideration for the execution of bridge projects worldwide. Both temporary and permanent access solutions provide engineers with opportunities to undertake projects in challenging locations whilst satisfying the concerns of multiple stakeholders, not least the bridge users. With many structures operating above capacity and subsequently demanding regular maintenance and enhancement, options to limit or mitigate disruption to the infrastructure whilst utilising cutting edge construction and maintenance techniques frequently demand extensive innovation in access provision alone, just to allow staff and equipment safe and adequate passage to the final work site.
Regardless of the structure type, age, usage and location, access provision to undertake construction, remedial, maintenance and enhancement projects is a constant consideration for Bridge Engineering globally. With ongoing changes to intended maintenance plans, design life and asset management technologies, few structures were designed and built with adequate access to facilitate the types of projects typically seen around the world today, as such facilitating access alone can occupy a disproportionate amount of the design and construction approach to any bridge project.
The paper will discuss current issues in today’s industry and how new-build bridge projects can be designed with future-proof access in mind, whilst of course considering the capital expenditure implications of such provisions. The paper will focus upon the project-specific requirements for some typical and specialist remedial & maintenance projects and why access alone frequently becomes the pinnacle consideration in today’s market. Finally the paper will consider variations in the working cultures and legislation of international markets and how this can impact upon the chosen access methodology for a given scheme.