T.Y. Lin & Keynote Lectures

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  T.Y. Lin Lecture

Precast Cantilever Bridge Construction in Seismic Zones
The San Francisco - Oakland Bay Bridge

Frieder Seible
University of California
San Diego, La Jolla, CA, USA

Following the inspiration and pioneering work of Professor T.Y. Lin, California is finally embarking on segmental precast concrete construction for major bridges in areas of high seismicity. For many years, uncertainty of the behavior of matchcast joints between precast concrete segments in bridge superstructures during seismic excitation prohibited the use of precast concrete segmental bridge construction in California. While prestressed concrete is widely used in cast-inplace multi-cell box-girders and in cast-in-place segmental construction, the Skyway of the new San Francisco-Oakland Bay Bridge East Bay spans constitute the first modern concrete segmental bridge erected in precast segmental cantilever construction.
Prior to the skyway construction, an extensive research and proof-testing program at the University of California at San Diego into the behavior of matchcast and epoxy bonded joints between precast segment under simulated seismic loads was conducted.
The test showed that not only the desired seismic response can be achieved with precast segmental construction but that less severe damage patterns can be achieved. Furthermore, this seismic segmental bridge research showed that the correct use of external and internal unbonded tendons can significantly improve the seismic bridge response.
A summary of this precast segmental bridge construction research for seismic zones will be presented together with the example of the new San Francisco - Oakland Bay Bridge design and construction.

  Keynote Lectures

Renewal and Rehabilitation of the Brazilian Railway Bridge Infrastructure

Túlio N. Bittencourt
University of São Paulo
São Paulo, Brazil

Nowadays Brazil is facing many challenges in order to improve its transportation infrastructure to set the grounds for a continuous development and economic growth. Among these challenges, the renewal and rehabilitation of the railway network is one the most important priorities. The modernization of the railways, and specifically of bridges and tunnels, is very important in this context. This paper presents the plans for the expansion of the Brazilian railway system and its impact on the new and existing bridges. Bridges will face an increasing axle load to attend the internal and global demands for commodities, specially crops, sugar, oil, ethanol and minerals. Therefore, more resistant structures will have to be designed, while the existing ones will demand more constant maintenance and some retrofit. Examples describing the structural integrity assessment of some existing steel and reinforced-concrete bridges are presented. Short term monitoring campaigns have been used to assess the performance of such bridges under controlled and service load conditions. Analyses are concentrated so far to fatigue problems, but other deterioration phenomena, like corrosion, carbonation, alkali-aggregate reaction and chloride attack, will have to be addressed in the near future. To conclude the need for implementation of long term monitoring programs for emblematic or critical bridges is described. These programs will allow for the application of more reliable Structural Health Monitoring techniques, resulting in a better estimate of service life and more realistic and efficient maintenance schemes.

Operational Deformations in Long Span Bridges

James Brownjohn
University of Sheffield
Sheffield, UK

Being among the most flexible of civil engineering structures, long span bridges deform both dynamically and quasi-statically under a range of operational conditions including wind, traffic and thermal loads, in varying patterns, with different timescales and at different amplitudes. While external loads and internal forces can only rarely be measured, there are well developed and emerging technologies for measuring deformation. It is well known that some of these technologies can be used to validate or improve numerical simulations, which can then be used to estimate the external loads and internal forces.
Changes in response patterns and relationships can also be used directly as a diagnostic tool, signal unusual loading or structural changes, but excessive deformations themselves are a concern in terms of serviceability and allowable operational limits (e.g. of vibration, and bearing movement).
This paper discusses the challenges of deformation measurement and applications in structural identification, performance diagnosis and load estimation, including observations of response to the largest or most extreme loads.

Wind Tunnel: A Fundamental Tool for Long Span Bridges Design

Giorgio Diana
Politecnico di Milano
Milan, Italy

In the last years many very long suspension bridge and cable stayed bridge projects have been developed and some bridge has been already built or is at the construction stage. The wind action on a very long suspension bridge represents one of the main issues affecting the bridge feasibility and design. In this view, tests in the wind tunnel are mandatory to verify the bridge behaviour.
The wind tunnel tests are made on sectional models of the deck, the tower and the cables.
Wind tunnel tests on the tower full aeroelastic model are mainly devoted to the definition of the tower response to vortex shedding. Wind tunnel tests on the full aeroelastic model of the whole bridge are generally used to have a final check of the design.
However wind tunnel tests alone are not sufficient to fully identify the bridge response to the wind action. Numerical models based on wind tunnel results have been developed: these models reproduce the bridge response to the wind action and are the instrument used to design the bridge.
There is a strong interaction between numerical approach and wind tunnel testing in the sense that some wind tunnel test is just finalized to give data for the numerical approach.
The lecture deals with the problems related to the wind action on a bridge, the numerical approach to predict the bridge response, the different types of wind tunnel tests and the validation of the numerical approach.

Pathology, Appraisal, Repair and Management of Old Prestressed Beam and Slab Bridges

Bruno Godart
Université Paris-Est, IFSTTAR
Paris, France

The prestressed beam and slab bridges (named in France VIPP) are viaducts with multiple single spans made of prestressed concrete beams that are precast on site and post tensioned, and then assembled transversely by a prestressing which can, according to cases, be installed either in the crossbeams, either in the slab, or in both crossbeams and slab. Their span length are generally ranging between 30 and 50m.
A great number of those bridges were built in France at the beginning of the development of the prestressing technique: approximately 250 between the years 1945 and 1957, and 450 between 1957 and 1967). Some of them present strong losses of prestress related to the corrosion or the rupture of tendons that are not detected during traditional examinations, because there is no external sign allowing to reveal them. It is particularly the case of the prestressing steels sensitive to stress corrosion cracking or to hydrogen embrittlement, and more particularly the case of the KA-type steels.
After a presentation of the pathology and its various causes, the paper presents the difficulties of the appraisal and the methodology that has been developed to assess the residual load carrying capacity of this type of bridges. The appraisal method is based on several levels of investigations and re-calculations. Then, the paper reviews different solutions of repair that has been used with success to maintain or to strengthen the capacity of these structures; such solutions include the use of re-injection of prestressing ducts, FRP, additional prestressing tendons, and a coupling of passive and active strengthening. Finally, the paper addresses the problem encountered with the management of such structures by emphasizing the interest of the risk analysis for helping owners to optimize the management of their patrimony of beam and slab bridges, with respect to safety.

Assessment and Retrofitting of Existing Bridges

Claudio Modena
University of Padua
Padua, Italy

The existing stock of road and railway bridges in Italy and in most European countries frequently exhibits insufficient performances, both in terms of structural safety and functionality, compared to the current demands coming from modern structural codes, transportation systems and necessity of reducing the costs of maintenance. Quick and reliable methodologies are then needed to assess the specific vulnerability of any bridge typology, in any possible environmental and operating conditions. In the first part of the lecture the application of such type of methodologies to both road and railway transportation infrastructure in Italy is described showing that, e.g., masonry arch bridges are usually quite robust structural systems, r.c. bridges generally present durability problems and are vulnerable to seismic actions, steel bridges, other than presenting durability problems, are particularly vulnerable to fatigue. Typical retrofitting interventions considered in these studies are also briefly presented. In the second part of the lecture significant case studies of retrofitting interventions are in more detail described, focusing on four existing r.c. bridges, which represent an homogeneous set, all of them being part of the post-IInd World War reconstruction on the Adige River (the second longest river in Italy). These bridges are examples of some of the most usual typologies adopted in that historic period, and the defects they evidenced after fifty years of service life were typical of these kind of structures, being often the consequences of a poor maintenance and the lack of durability rules in the original design. The refurbishment interventions are presented outlining a methodological approach, which takes into account the typological characteristics of the structure, the state of maintenance, the functional requirements and the environmental aspects connected to the repair and strengthening system.

Innovative Steel Bridge Girders with Tubular Flanges

Richard Sause
ATLSS Center, Lehigh University
Bethlehem, PA, USA

I-shaped steel girders with tubular flanges have been studied for application in highway bridges because of their large torsional stiffness relative to conventional I-shaped steel plate girders (conventional I-girders). For straight girder bridges, the large torsional stiffness of a tubular flange girder (TFG) results in significantly greater lateral-torsional buckling (LTB) strength compared to a corresponding conventional I-girder. For horizontally curved girder bridges, the large torsional stiffness of a TFG results in much less warping normal stress, vertical displacement, and cross section rotation compared to a corresponding conventional I-girder.
The lecture presents experimental and finite element analysis results for straight and horizontally curved TFG bridges. These results are compared to similar results for corresponding conventional I-girder bridges. The results are used to show the practical advantages of TFGs in comparison to conventional I-girders. In particular, the significant LTB strength of TFGs enables the amount of bracing required for straight girder bridges to be substantially reduced. The large torsional stiffness of TFGs enables curved girder bridges to be erected with much less (perhaps no) temporary support (i.e., falsework or temporary shoring) within the spans. Practical design methods and criteria for TFGs are outlined. Results from a TFG demonstration bridge constructed in the U.S. are summarized.

Remote Monitoring; Concept and Pilot Study

Masanobu Shinozuka
University of California
Irvine, CA, USA

This presentation introduces the concept of remote monitoring of civil infrastructure systems, and demonstrates pilot applications of the concept using laboratory and field experiments. The remote monitoring system is expected to be capable of long-term, offsite, and real time monitoring of a spatially distributed large scale civil infrastructure network subjected to various types of hazard. The monitoring is not only for damage and other anomalies of local components of the network, but also for the resulting malfunction of the network performance. It is envisioned that the remote monitoring system can be equipped with active control devices to minimize the level of such network malfunction. In this context, the remote monitoring system proposed here, particularly if active control devices are installed, conceptually represents the next generation SCADA System (Supervisory Control and Data Acquisition system). Conventional SCADA systems are widely deployed in utility industry for continuous monitoring of vital operational parameters and for control of anomalous perturbation of these parameter values and hence of operational performance. These parameter values are in turn acquired by monitoring electro-mechanical equipments installed at a number of nodal locations of the network. A conventional SCADA system usually does not directly monitor the damage or other anomalies in links of the network. If it does, it is a next generation SCADA.

The Art of Arches

Man-Chung Tang
T.Y. Lin International
San Francisco, CA, USA

An arch is a very efficient form of structure to carry high loads. There have been many varieties of arch forms used for bridge construction. The lecture explores how arches can be used to support a bridge.

System Design and Implementation of Structural Health Monitoring System and Maintenance Management System for Marine Viaduct Bridges

Kai-Yuen Wong
The Government of the Hong Kong Administrative Region
Hong Kong, P.R.C.

The service life of marine viaduct bridges will be decreased due to the occurrence of degradation mechanisms in their structural components. These degradation mechanisms are results of the combined actions arising from environmental attacks, operational loads and aging effects. In order to maintain the designated service life, routine inspection and maintenance works on marine viaduct bridges are usually required for reinstating their performance, strength and durability as designed. Modern inspection and maintenance works of marine viaduct bridges are normally composed of works in seven aspects, namely, inspection, monitoring, evaluation, rating, maintenance, enquiry and management. In conventional maintenance approach, these works are executed in discrete and ad hoc forms and therefore result in lacking of data continuity for maintenance management decision making. Furthermore, the conventional inspection and maintenance works of marine viaduct bridges are heavy relying on visual inspection approach, such approach is however impossible to identify structural deterioration at the early stage, i.e. the depassivation of the embedded steel reinforcement before the formation of cracks. As deterioration of structural concrete will significantly reduced the load-carrying capacity of the structure, any late discovery of deterioration in structural concrete by appearance of cracks and spalling of concrete cover will certainly not only result in downgrading the structural performance (or safety margin), but also induce maintenance difficulties hence the cost in subsequent maintenance works.
For reasons of improving/enhancing/upgrading the conventional inspection and maintenance to modern inspection and maintenance, a system named as "structural health monitoring and maintenance management system or SHM&MMS" is therefore devised to standardize and/or unify the seven aspects of works in continuous and systematic manner so that the maintenance management works of marine viaduct bridges can be executed efficiently and semi-automatically. This paper introduces the system design and implementation works in eight aspects: (1) relationship between structural health monitoring and maintenance management, (2) similarities between structural health monitoring and durability health monitoring, (3) limitations of previous structural health monitoring systems designed and installed during 1995-2007, (4) improvements on structural health monitoring system for Stonecutters Bridge, (5) further improvements on structural health monitoring systems for marine viaduct bridges, (6) system design of structural health and maintenance management system for marine viaduct bridges, (7) implementation of structural health and maintenance management system for marine viaduct bridges, and (8) conclusions on structural health monitoring systems regarding future applications.

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