Bridge Design, Assessment and Monitoring

Airong Chen, Dan M. Frangopol, Xin Ruan

• Publisher: CRC Press
• Year: 2018
• eBook ISBN: 9781351208772
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

Bridges play important role in modern infrastructural system. This book provides an up-to-date overview of the field of bridge engineering, as well as the recent significant contributions to the process of making rational decisions in bridge design, assessment and monitoring and resources optimization deployment for the purpose of enhancing the welfare of society.

Tang specifies the purposes and requirements of the conceptual bridge design, considering bridge types, basic elements, structural systems and load conditions. Cremona and Poulin propose an assessment procedure for existing bridges. Kallias et al. develop a framework for the performance assessment of metallic bridges under atmospheric exposure by integrating coating deterioration and corrosion modelling. Soriano et al. employ a simplified approach to estimate the maximum traffic load effect on a highway bridge and compare the results with other approaches based on on-site weigh-in-motion data. Akiyama et al. propose a method for reliability-based durability design and service life assessment of reinforced concrete deck slab of jetty structures. Chen et al. propose a meso-scale model to simulate the uniform and pitting corrosion of rebar in concrete and to obtain the crack patterns of the concrete with different rebar arrangements. Ruan et al. present a traffic load model for long span multi-pylon cable- stayed bridges. Khuc and Catbas implement a non-target vision- based method for the measurement of both static and dynamic displacements time histories. Finally, Cruz presents the career of the outstanding bridge engineer Edgar Cardoso in the fields of bridge design and experimental analysis.

The book serves as a valuable reference to all concerned with bridge structure and infrastructure systems, including students, researchers, engineers, consultants and contractors from all areas sections of bridge engineering.

The chapters originally published as a special issue in Structure and Infrastructure Engineering.

Conceptual design of bridges

Man-Chung Tang

ABSTRACT

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 finalise 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.

Introduction

The design process of a bridge can be divided into four basic stages: conceptual design, preliminary design, detailed design and construction design (Tang, 2014). 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 finalise 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. Schematically it can be represented by the sketch as shown in Figure 1, which shows that a conceptual design must be able to encompass the preliminary design, the preliminary design must be able to encompass the detailed design and the detailed design must be able to encompass the construction design.

By ‘consider’, we do not mean that we have to actually perform detailed studies on the aforementioned issues during the conceptual design stage, since accumulated engineering experience can help us understand the feasibility of many basic ideas. For example, we do not have to conduct a calculation to ascertain that a 150 m span prestressed concrete box girder bridge is feasible if we can assume the girder depth to be about 7.50 m deep. Rather, our experience accumulated from working on many other bridges tells us that, typically speaking, a medium span prestressed concrete box girder with a depth of 1/20th of the span length can work. By contrast, if we want to build a girder that is only 5.00 m deep, this would require a detailed study during the conceptual design stage because it is far less than the conventional girder depth of 1/20th of the span. Experience is the utmost of importance during the conceptual design stage. For this reason alone, only an experienced engineer should be appointed to perform a conceptual design.

Thus, a conceptual design can be defined as a process that must consider all details of the bridge in all phases from beginning to completion, at least based on experience if not in actual analysis. This is to ascertain that the proposed concept is feasible under the given conditions. Here, ‘feasibility’ should not be restricted merely to structural stability and constructability; it must also satisfy the four basic requirements of a bridge: safety, functionality, economy and aesthetics.

From another view point, the conceptual design stage initiates the design of a bridge. It is a ‘conceiving’ stage that begins with a blank slate – a creative process that tests the innovative abilities of the engineer.

The requirements of a good bridge

A successful bridge must satisfy four basic requirements: safety, functionality, economy and aesthetics. Safety cannot be compromised. A bridge must be safe under all of the loads it is designed for. Otherwise, the bridge can’t be opened to traffic. And, when we talk about safety, we must make sure the bridge is safe not only for a certain limited period of time, but for the entire service life of the bridge. Thus, durability of the structure is equally important and it is contained in the consideration of safety. We have not satisfied the requirement of safety if a bridge designed for a service life of 100 years, for example, becomes unsafe after 50 years.

Figure 1. The four design stages.

Functionality is the reason why we build a bridge in the first place. Functionality should not be compromised. If four lanes are required, for example, it must provide four lanes. But in certain cases, it may still be acceptable if some lane widths are slightly different from the standard width recommended in the specifications, as long as this does not affect safety.

Economy and aesthetics do not have absolute standards. There is no such thing as a ‘correct cost’ of a bridge. It varies from place to place, from time to time and from situation to situation. The cost of a bridge in Florida may be vastly different from the cost of that same bridge if built in New York, or in Shanghai, even though the structures are exactly the same. So what is economical is clearly a relative term. But still, if a bridge is to be built in a certain place, at a certain time and under a certain circumstance, there is a way to judge its economy. However, the first cost of a bridge is not the only cost item we have to consider, the maintenance expense is also a big item to be considered. In other words, the life cycle cost is the real cost of a bridge. If a bridge costs less to build but cost much more to maintain, it is not an economical bridge. Durability again plays a big role in this respect. In summary, economy can be expressed by a ratio of value vs. cost (Tang, 2010), R_vc = value/cost. The higher this ratio, the better the economy of the bridge.

Aesthetics are even harder to define. For example, the Firth of Forth Bridge in Scotland was often criticised as one of the world’s most ugly structures by some and at the same time lauded as a spectacularly beautiful landmark by others. The Eifel Tower in Paris was mercilessly attacked by many architects, engineers, philosophers and other intellectuals alike, as an eyesore of the City at the time of its construction. But now, it has become the most beloved tourist attraction in France. Nevertheless, people do admire the beauty of some bridges and dislike others. If a bridge is deemed beautiful by most people, then we may be allowed to say that it is beautiful. So, at least at a given time and in a given place, it is possible to say whether a bridge is beautiful or not, based on popular opinion.

Purpose of building a bridge

Before we embark on the process of conceptualising a bridge, we must understand why we build the bridge in the first place. The basic purpose of a bridge is to carry traffic over an opening or discontinuity in the landscape. Various types of bridge traffic can include pedestrians, vehicles, pipelines, water and ships, or a combination thereof. An opening can occur over a highway, a river, a valley or any other type of physical obstacle. The need to carry traffic over such an opening defines the function of a bridge. The design of a bridge can only commence after its function has been properly defined. Therefore, the process of building a bridge is not initiated by...

Table of contents

• Cover
• Half Title
• Title
• Copyright
• Contents
• Citation Information
• Notes on Contributors
• Introduction: Bridge design, assessment and monitoring
• 1. Conceptual design of bridges
• 2. Standard and advanced practices in the assessment of existing bridges
• 3. Performance profiles of metallic bridges subject to coating degradation and atmospheric corrosion
• 4. Simplified probabilistic model for maximum traffic load from weigh-in-motion data
• 5. Reliability-based durability design and service life assessment of reinforced concrete deck slab of jetty structures
• 6. Mesoscopic simulation of steel rebar corrosion process in concrete and its damage to concrete cover
• 7. A site-specific traffic load model for long-span multi-pylon cable-stayed bridges
• 8. Computer vision-based displacement and vibration monitoring without using physical target on structures
• 9. Edgar Cardoso: a tribute to a brilliant bridge engineer
• Index