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T.Y. Lin Lecture
Conceptual Design of Bridges
T.Y. Lin International
San Francisco, USA
The design process of a bridge can be divided into four basic stages: conceptual design, preliminary design, detailed design and construction design. The purpose of the conceptual design is to come up with various feasible bridge schemes and to decide on one or more final concepts for further consideration. The purpose of the preliminary design is to select the best scheme from these proposed concepts and then to ascertain the feasibility of the selected concept and finally to refine its cost estimates. The purpose of the detailed design is to finalize all the details of the bridge structure so that the document is sufficient for tendering and construction. Finally, the purpose of the construction design is to provide step-by-step procedures for the building of the bridge. Each of the earlier design stages must carefully consider the requirements of subsequent stages. For example, the detailed design must consider how the bridge is to be built; the preliminary design must consider, in addition, how structural details will look like; and, the conceptual design must consider, in addition to all the above, what information the preliminary design will require. This means that a conceptual design must sufficiently consider what is required to complete the bridge in the given environment, including a general idea of costs and construction schedule as well as aesthetics.
Bridge “Examineering”: How Monitoring and UHPFRC Improve Performance of Structures
Ecole Polytechnique (EPFL)
Examination engineering (short: “Examineering”) of existing bridges comprises accurate determination of structural behaviour and targeted use of advanced materials for improvement of structural behaviour with the ultimate goal of limiting construction intervention to a strict minimum while extending the service life and respecting life cycle costs. “Examineering” thus means leaving beaten paths of currently applied assessment and repair methods.
A novel approach is suggested for structural and fatigue safety verification of bridges based on the determination of updated traffic action effects in the structure by direct use of data from long term monitoring. Monitored data combined with detailed structural analysis allow for accurate determination of relevant stresses in bridge structural elements reducing thus uncertainty in traffic action effects.
If interventions are necessary, their objective must be to improve the structure. An original concept is presented for the durable rehabilitation and strengthening of concrete bridges. The main idea is to use Ultra-High Performance Fibre Reinforced Concrete (UHPFRC) to strengthen those zones that are exposed to severe environmental influences and high mechanical loading. This concept combines efficiently protection and resistance properties of UHPFRC and significantly improves the structural performance of the rehabilitated bridge.
These new methods will be illustrated by case studies and field applications demonstrating that these novel engineering methods and technologies are a step forward towards more sustainable bridges.
Life Cycle Management of Steel-Concrete Composite Bridges
Moe M. S. Cheung
Hong Kong University of Science & Technology
The increasing stock of short and medium span bridges in this region and around the world induces substantial maintenance and rehabilitation costs which result in a significant increase in financial burden to the government and industry. To relieve the long term financial pressure, a whole life cycle cost management concept was introduced in recent decades and is now getting more and more important in engineering design, construction and management. In the whole life cycle cost management model, the mechanism and prediction of structural member deterioration is essential. Among typical short and medium span bridges, such as steel-concrete composite structures, corrosion deterioration and fatigue damages are the most common types of degradation mechanism which are influenced by the environmental conditions, the vehicle loadings and its stress ranges. This paper focuses on the technical review on the typical structural deterioration, such as corrosion and fatigue, on steel bridge girders as well as concrete decks. Thorough discussions on the application of the life cycle cost management concept in dealing with maintenance and rehabilitation of such bridges are illustrated with examples.
The Future of Ageing Metallic Bridges
Marios K Chryssanthopoulos
University of Surrey
During their service lives, metallic structures are susceptible to degradation through corrosion and cracking, particularly when loading and environmental demands increase over time. In the UK, as in many other countries, the transport infrastructure network relies on a large number of metallic bridges which require careful performance management under tight budgetary constraints in order to keep them in service for longer than planned, or to overcome deficiencies revealed during operation. Over the past decade, significant progress has been made in understanding many facets of the problems associated with ageing metallic bridges, including better appreciation of loading histories and future loading trends, refined approaches for structural response modeling, the potential benefits of health monitoring data, and the availability of new repair techniques using fiber reinforced composites. Lessons learned from a variety of projects undertaken in conjunction with infrastructure owners and other stakeholders will be reviewed, with particular emphasis on the implications for new construction, whose future will depend on the knowledge that we can acquire and transfer successfully from a previous generation of structures.
Assessment of existing structures in France: standard and advanced practice
Technical Centre for Bridge Engineering
In recent years, the state of deterioration of the bridges' stock has been such that the volume of necessary works has reached un-manageable proportions in many countries. As budgets for maintenance, repair and rehabilitation are always limited and demands are constantly increasing, to find an optimal balance between cost and safety is today a new trend in bridge maintenance. Optimizing bridge maintenance and management is a strong expectation for owners and stakeholders facing aging bridge stocks and increasing aggressive traffic. In this context, the assessment of the structural performance may be necessary for various reasons thorough its lifetime.
However, there are no standards and regulations on the subject in France but also in other countries. The studies upon a new Eurocode for the "Evaluation and rehabilitation of existing structures" are just starting and it will not be available before several years. Bridge assessment is very similar to bridge design. The same basic principles lie at the heart of the process. An important difference nevertheless lies in the fact that when a bridge is being designed, an element of conservatism is generally a good thing that can be achieved with very little additional costs. When a bridge is being assessed, it is important to avoid unnecessarily conservative measures because of financial implications that may follow if a bridge is designated as sub-standard without good cause.
For this reason, the French Ministry of Transport has initiated a set of studies to develop recommendations for the assessment of the structural performance of existing bridges. The keynote will present today's practice as well as the development of new approaches based on the calibration of appropriate partial safety factors for existing structures when investigation results are available.
The outstanding legacy of Edgar Cardoso: An audacious and visionary Portuguese bridge engineer
Paulo J.S. Cruz
University of Minho
Edgar Cardoso (1913-2000) was a brilliant bridge designer and an enthusiastic pioneer of experimental analysis of bridges and of the development and use of high precision instruments to measure the critical parameters affecting the structural behavior of reduced models.
In his long and proficuous career Professor Edgar Cardoso was very committed to the use of high performance materials, to develop new structural concepts and innovative construction techniques, and to propose inexpensive and effective processes for bridge retrofitting.
He was the designer of some outstanding audacious elegant bridges in several continents. Some of them were world records and deserved a worldwide diffusion and recognition. In the construction of the Arrábida Bridge (1963) it was the first time ever that such a large arch was cast over a single-span steel formwork and that a structure of approximately 2.200 tones was moved into place exerting force only on the abutments, which were 260 m apart. The São João railway bridge (1991), with very simple lines, was a record for the largest span of this type.
The holistic vision of such inspiring bridge engineer will be emphasized and part of its valuable legacy will be shared through a detailed presentation of several examples.
Durability of Steel Orthotropic Bridge Decks
John W. Fisher
Co-author(s): Sougata Roy
Prefabricated modular steel orthotropic deck panels can provide effective solution for accelerated construction of highway bridges. This deck form has been widely used as new design and rehabilitation of long span signature bridges and movable bridges, as temporary structures in battle zones and large urban construction projects, and as emergency bridge replacements in the aftermath of natural disasters. The light weight redundant deck form helps in increasing the longevity of a bridge by reducing dead load stresses on the main supporting elements. In addition, a thin overlay reduces the imposed stresses, improves riding quality and allows flexible maintenance. In-service performance and limited laboratory tests have demonstrated that if adequately designed and properly fabricated, the orthotropic deck is the only system likely to provide a service life exceeding 100 years, enhancing life cycle costs. Despite the advantages, widespread implementation of orthotropic decks has been limited, primarily due to lack of robust standards, increased efforts required for advanced analysis and design, relatively high initial cost owing to intensive fabrication, and most importantly due to concerns regarding higher possibility of in-service fatigue cracking from a large number of welded connections and often less than desirable performance of wearing surfaces that were prevalent in ubiquitous orthotropic decks. Modern orthotropic decks are usually designed with relatively thin closed ribs and thicker deck plates that reduce the local stresses in the overlay and improve its durability. The ribs are passed continuously through matching cut-outs in the floor beams, often with an additional cut-out in the floor beam under the rib soffit, and with internal bulk head plates or stiffeners. Particularly sensitive in the deck system are the rib-to-floor beam and the rib-to-bulkhead plate connections, which depending on the connection flexibility are subjected to a complex combination of local in-plane and out-of-plane bending stresses. Nominal stress based fatigue design provisions are not readily applicable to these design situations. The commonly referenced fatigue design guidelines based on advanced analyses and local stresses lack uniformity in application, and are not applicable to infinite life. As such, fatigue performance of orthotropic decks is often evaluated by full scale laboratory testing, where the boundary conditions are adequately reproduced. Because of the sheer length, the rib-to-deck plate welded connection (twice the length of all the ribs in a deck) is the major contributor to the increased initial cost of fabrication of orthotropic decks. This connection is often specified as 75~80% partial joint penetration (PJP) groove weld. To ensure consistent weld penetration over the entire length, often a joint preparation is specified that requires beveling the relatively thinner rib walls to a smaller landing, which is too susceptible to weld melt through and blow-through conditions. Fabrication of this weld without a joint penetration requires larger heat input, which may result in hot-cracking if not carefully controlled. In addition, the gap opening at the weld root affects the success of this weld. Use of Phase Array Ultrasonic Testing (PAUT) during fabrication can non-destructively ensure the joint quality.
Four Decades of Inspecting a Suspension Bridge Cable
Barney T. Martin, Jr.
Modjeski and Masters, Inc.
The New York State Bridge Authority manages and maintains six long span crossings of the Hudson River consisting of four truss bridges and two suspension bridges. It has always been the policy of the New York State Bridge Authority to take a proactive approach to the maintenance of their bridges. Therefore, in 1969 a decision was made by the Authority to begin a limited inspection of the interior of the main cables of the Mid-Hudson Bridge located in Poughkeepsie New York. A decision was initially made to just take a "peak" at the outer wires of the parallel wire cable in order to gather some idea regarding the condition of the main cables. In 1969 the bridge was just about to celebrate its 40th birthday. This initial inspection began what is believed to be one of the oldest main cable inspection programs in the world.
These limited inspections continued in 1981 and again in 1982. The purpose of the inspections remained to gather limited information regarding the condition of the entire cable by observing only the condition of short lengths of the exterior wires. The general conclusion at the time was this level of inspection was sufficient since there was no indication of severe deterioration.
In the early 1980's, increasing traffic volumes on the bridge resulted in the consideration of placing a second deck on the bridge. The projected total load resulting from this second deck dictated that more definitive information regarding the cable condition and strength be established. To determine the cable condition and strength, three preliminary investigations were performed; Phase I, performed in 1986; Phase IIA, performed in 1987; and Phase IIB conducted in 1989. Phase III, a detailed investigation of 20% of the length of the main cables was begun in early 1990 and a cable rehabilitation contract, designated as Phase IV, was begun in 1991. Since the completion of Phase IV, there have been three, five-year follow up inspections of selected lengths of the cable; one performed in 1998-99, one in 2003-04 and the most recent in 2009-2010.
This paper will present a general summary of the evolving methods of cable inspection used, the findings of those inspections, the results of the laboratory-testing program that have been performed to date and the colclusions regarding the remianing strength of the cables.
Life-Cycle Performance Monitoring and Evaluation of Long-Span Bridges
Harbin Institute of Technology
Dalian University of Technology
Co-author(s): Xigang Zhang, Hui Li, Minshan Pei, Na Li
A large number of long-span bridges in mainland China have been constructed. There are largest number of longest-span suspension bridges, longest-span cable-stayed bridges, longest-span arch-bridges and longest-span girder bridges in mainland China over the world. The total number of the highway bridges and railway bridges in China has ranked No.1 over the world, too. These longest-span bridges become the motivation of applications of structural health monitoring technology. A number of bridges have been implemented with advanced structural health monitoring systems in mainland China and Hong Kong. Recently, the structural health monitoring technology has been extend to life-cycle performance monitoring and evaluation, including long-term actions of loads and environment, responses and performance deterioration (fatigue, durability, etc), natural hazards (including wind, wave, current, ice, rain, earthquake, tsunami, and geotechnical disaster), and man-made disasters (including ship crash, truck crash, explosion, etc).
Based on the experience of research and practice on structural health monitoring technique for long-span bridges, it is recognized that the structural health monitoring technique is a powerful tool to develop the methodology of life-cycle performance design, evaluation, maintenance and management of bridges. It is also a tool for developing new structural analysis methodology through validation and feedback from structural health monitoring results. It is also a powerful tool to rapid assess the disaster and loss of engineering structures in large region post-earthquake and strong wind/typhoon. In addition, it is an experimental technique and testbed for scientific research of bridge engineering. Structural health monitoring technique has shown bright perspective. The challenge issues on the structural health monitoring and future trends are recognized.
Performance enhancement of bridges and other structures through the use of fibre-reinforced polymer (FRP) composites: some recent Hong Kong research
The Hong Kong Polytechnic University
Hong Kong, China
Due to their various advantages including excellent corrosion resistance and high strength-to-weight ratios, fibre-reinforced polymer (FRP) composites have been widely used as bonded external reinforcement to enhance the performance of bridges. In addition, FRP composites have attracted increasing attention for use in the construction of high-performance new bridges. This lecture will examine the role of FRP composites in both areas.
The successes and limitations of FRP composites in bridge maintenance will first be analyzed, with particular attention to the prestressing and long-term performance of FRP reinforcement. Based on this analysis, areas that require further research are identified.
A large variety of possibilities exist for the use of FRP composites in the construction of new bridges, including FRP decks, FRP cables and the hybrid use of FRP with concrete and steel to form various structural components. These possible uses will be critically reviewed to assess their potential and to demonstrate how FRP composites can be used to maximize their benefits. The lecture will conclude with an examination of the further research needed to bring these structural forms into wide practical use.