Bridge Construction Technology

bridge construction equipment

The technological aspects of construction influence the modern bridge industry from the very first steps of design. Entire families of bridges such as the launched bridges, the span-by-span bridges and the balanced cantilever bridges take the name itself from the construction method. The full-span method so frequently applied in high speed railway projects is another example.

The bridge industry is moving toward mechanized construction because this saves labour, shortens project duration and improves quality. This trend is evident in many countries and involves most construction methods. Mechanized bridge construction is based on the use of specialized erection equipment.

Beam launchers are used to erect precast beams. Self-launching gantries and lifting frames are used to erect precast segmental bridges. Movable scaffolding systems (MSS) and form travellers are used for in-place casting of spans and segments of prestressed-concrete bridges. Forming carriages are used for segmental casting of the concrete slab of composite bridges. Portal carriers with underbridge and span launchers fed by tyre trolleys are used for transportation and placement of precast spans. Lifting platforms are used to hoist macro-segments for suspension bridges. Alternate configurations of machines are also available for most construction methods.

New-generation bridge construction equipment is complex and delicate. It handles heavy loads on long spans under the same constraints that the obstruction to overpass exerts onto the bridge. Safety of operations and quality of the final product depend on complex interactions between human decisions, structural, mechanical and electro-hydraulic components, control systems, and the bridge being erected.

In spite of their complexity, these machines must be as light as possible. Weight governs the initial investment, the cost of shipping and site assembly, the erection stresses, and sometimes even the cost of the bridge. Weight limitation dictates the use of high-grade steels and the design for high stress levels in different load and support conditions, which makes these machines potentially prone to instability.

Bridge erection equipment is assembled and decommissioned many times, in different conditions and by different crews. It is modified, reconditioned and adapted to new work conditions. Connections and field splices are subjected to hundreds of load reversals. The nature of loading is often highly dynamic, the equipment may be exposed to strong wind, and the full design load is reached multiple times and sometimes exceeded. Impacts are not infrequent, vibrations may be significant, and most machines are actually quite lively because of their high structural efficiency.

Movement adds the very important complication of variable geometry. Loads and support reactions are applied eccentrically, the support sections are often devoid of diaphragms, and most machines have flexible support systems. Indeed such design conditions are almost inconceivable in permanent structures subjected to such loads.

The level of sophistication of new-generation machines requires adequate technical culture in all parties involved in mechanized bridge construction. Long subcontracting chains may lead to loss of communication, the problems not dealt with during planning and design must be solved on the site, the risks of wrong operations are not always evident in so complex and sophisticated machines, and human error is the prime cause of accidents.

Experimenting new solutions without the due preparation may lead to catastrophic results. Several bridge erection machines collapsed in the years with a heavy tribute of fatalities, wounds, damage to property, delays in the project schedule and legal disputes. Technological improvement alone cannot guarantee a decrease in failures of bridge construction equipment, and may even increase them. Only a deeper consciousness of our human and social responsibilities can lead to a safer work environment. A level of technical culture adequate to the complexity of mechanized bridge construction would save human lives and would facilitate the decision-making processes with more appropriate risk evaluations.

In a perfect world, bridge construction equipment would be purchased to meet clear performance requirements, would be designed according to international standards and project-specific technical specifications, would be subject to independent design checking, would be fabricated and commissioned within quality-control procedures, and would be operated by experienced supervisors and trained crews according to procedures issued by the manufacturer.

We are not in a perfect world though. Bridge construction equipment is often purchased by procurement personnel that have just a vague idea on what they are buying and tend to recommend decisions to the management based on the only aspect they can compare: the “cost”. The final cost for the contractor is typically higher than the figure written at the end of the offer, and the overall value of two apparently similar machines may also be pretty different. Inspections may clarify if the machine is in good conditions or is a freshly-repainted bunch of rust; however, other aspects influence the value of a machine. Labour and crane demand of site assembly, for example, may be a bitter surprise if hundreds of field splices are designed with friction bolts and lap plates instead of through pins or stressed bars.

Because of its weight and dimensions, bridge construction equipment is assembled on site. A rule of thumb is that site assembly may take 7-10 hours of labour per metric ton of steel, and two cranes for the entire period. A lot of money – so the contractors frequently take care of assembly labour and cranes to save supplier’s overheads. Identifying what should be assembled in the workshop (paid with the cost of the machine) and what should be assembled on the site (paid by the contractor) may lead to interesting discussions if not specified in the contract. Most of us would guess that primary hydraulic systems should be assembled and tested in the workshop and only the hoses should be applied on site. Dr. Rosignoli witnessed building all the hydraulic systems of an 800ton MSS on site – from bending cold drawn steel tubing to painting – because the contract did not explicitly list that work within the workshop tasks. In addition to the extra cost for the contractor and a two-month delay in the project schedule, a delay penalty was shifted into an accelerated delivery fee.

The absence of comprehensive design standards further complicates the situation. Although construction is the most critical moment in the lifetime of a bridge and poor workmanship may irremediably affect quality and durability, bridge construction equipment does not receive any attention or research funding. Ruling bridge design with state-of-the-art standards is just the first step: assuring quality and durability of the final product requires similar levels of attention and control also during construction.

Safety is another hidden problem. In several industrialized countries the loss of lives during bridge construction is one order of magnitude higher than the loss of lives due to structural failure of bridges in operation. Since bridge construction takes a few years and bridge service covers decades, the risks for the workers are two orders of magnitude higher than the risks for the users. All of this should suggest a deep reflection.

In an imperfect world the operations are uncertain as well. A machine too complex to operate may be so slow to force the supervisor to risky shortcuts to keep the schedule. It may even be so slow to force the contractor to purchase a second machine – being vaguely optimistic on the performance may market a second machine in the next future. Binding the supplier to performance, productivity and labour demand is therefore in the best interest of the contractor.

If the machine is brand-new, procurement may be even more complex. Who will identify performance requirements and technical specifications for such an expensive piece of equipment? Who will review the suppliers’ proposals? Who will be the independent design checker? Where will the machine be fabricated in response to heavy import duties? Who will audit the manufacturer’s quality-control processes during fabrication? Who will supervise load testing and site commissioning? Who will inspect the machine during operations?

Mechanized bridge construction is widespread all over the world. When comparing different proposals, one often notices large cost differences between apparently similar machines. Many aspects should be considered in the comparison: different average quality of steelwork in different countries, different weight resulting from steel grade and structural efficiency, degree of mechanization and access, durability and energetic efficiency, modularity and easy reconditioning for future reuse, and easy shipping and site assembly.

Decisions on bridge construction equipment are trans-disciplinary in nature. Safety is the first concern, performance and productivity govern planning and investments, structure-equipment interaction affects the design of bridge and special equipment, risk mitigation is a major issue for contractors and insurance carriers, and quality control of design, fabrication and operation is strictly related.

Few has been written on these machines in spite of their fundamental role in the modern bridge industry. The purpose of Bridge Construction Equipment (2013, ICE Publishing, 488 pages, ISBN 9780727758088) is conveying trans-disciplinary information on special equipment and bridge construction technologies to the engineering professionals involved in mechanized bridge construction.

  • Bridge owners, architects and engineers will find comprehensive information on how the bridge will be built and will interact with special equipment during construction.
  • Educators will find a solid technology basis for theoretical courses of bridge architecture and engineering.
  • Contractors will find information on procurement, operations, performance and productivity of special equipment and a guide to value-engineering, time-scheduling, risk analysis, bidding, safety planning and the formation of management and site personnel for the risks and the advantages of mechanized bridge construction.
  • Designers and manufacturers of special equipment will find comprehensive information on design loads and load combinations, calibration of load and resistance factors, design for robustness and redundancy, numerical modelling and analysis, out-of-plane buckling and prevention of progressive collapse, human error, failure of materials and systems, repair, reconditioning and industry trends.
  • Construction engineers, resident engineers, inspectors and safety planners will find information on operations, casting cycles, cycle times, loading and structure-equipment interaction.
  • Forensic engineers will find numerous case studies on failed equipment.

The book identifies all the aspects of special equipment: procurement (what you buy); design, fabrication and commissioning (what you get); operations and structure-equipment interaction (what you should do); and things gone wrong and forensics (what you can miss).

The book is schematically divided into three blocks. The first block, from Chapter 2 to Chapter 8, describes the technological aspects of bridge construction and the technical features of related equipment. The structure of the chapters is repetitive: every chapter describes bridge construction technology, details of special equipment, loading, kinematics and typical features, support, launch and lock systems, performance and productivity, and structure-equipment interaction.

Many machines share conceptually similar components, which have been discussed along the book instead of in specific chapters. This may complicate searching specific information but should make reading more progressive and interesting. Specific information may be immediately retrieved through the index.

Chapter 1 introduces the reader to the content of the book and identifies the typical features of bridge construction equipment and the symbols used throughout the book. Chapter 2 deals with beam launchers and shifters and Chapter 3 describes the self-launching gantries for span-by-span erection of precast segments. Chapter 4 illustrates the overhead gantries for macro-segmental construction – a hybrid erection method between segmental precasting and in-place casting for medium-span box girders.

Chapter 5 is devoted to the different types of Movable Scaffolding Systems (MSS) for span-by-span in-place casting. Twin-girder overhead MSS, single-girder overhead MSS, modular single-truss overhead MSS for long spans, and underslung MSS are discussed in great detail. Chapter 6 deals with the self-launching forming carriages used for in-place segmental casting of the concrete slab of steel bridges.

The special equipment for balanced cantilever construction is discussed in Chapter 7. Precast and in-place segmental bridges are based on the same design principles and the construction equipment is also conceptually similar. Chapter 7 deals with lifting frames, cable cranes, lifting platforms for suspension bridges, self-launching gantries for precast segmental bridges, form travellers and suspension-girder MSS for in-place casting, and special travellers for arches and cable-stayed bridges. Finally, Chapter 8 deals with SPMT, portal carriers with underbridge and span launchers fed by tyre trolleys for full-span precasting.

The second block of the book deals with the design of bridge construction equipment. Chapter 9 illustrates design loads and load combinations for MSS and heavy lifters, and Chapter 10 deepens specific issues of structural analysis and design such as numerical modelling, analysis of instability, robustness, redundancy, material-related failures and design of connections and field splices.

The third block discusses contractual aspects. Chapter 11 deals with risk analysis and mitigation, procurement and quality control of fabrication and operations, and Chapter 12 discusses the forensic aspects of structural and functional failure of bridge construction equipment through numerous case studies. Finally, Chapter 13 illustrates the terminology, Chapter 14 presents the bibliographic references, and many sources of information are gratefully acknowledged in Chapter 15, which concludes the work.

The book does not deal with the construction equipment for launched bridges. The deck itself works like an erection machine during construction and the design issues related to this construction method are therefore very peculiar. Design and construction of launched bridges are discussed in the second edition of Bridge Launching, also published by ICE Publishing.

Addressing the needs of bridge designers and constructors, equipment manufacturers, resident engineers, inspectors and safety planners, as well as bridge owners, academics and forensics, Bridge Construction Equipment delivers solid professional guidance for the use of special equipment during each stage of the bridge construction process. The book is an excellent technical resource for bridge professionals and the textbook of three courses (1 and 2 days) that Dr. Rosignoli teaches for the Continuing Education Program of the American Society of Civil Engineers and on-demand in the offices of bridge owners, designers and constructors:

  • Mechanized Bridge Construction (2 days). Mechanized bridge construction is based on the use of special equipment. With extensive illustrations and case studies, this course explores configurations, operations, loads, kinematics, performance, productivity, structure-equipment interactions and industry trends for every family of special equipment. The course also explores the design of piers, abutments and superstructures for safe and efficient use of special equipment, and delivers a unique wealth of knowledge, learning and insights extracted from Dr. Rosignoli’s three decades of design, design review, construction and forensic engineering of bridges, bridge construction machines, and their interactions. Addressing the needs of bridge owners, designers and constructors, the course provides an exciting occasion for face-to-face interaction and participating in a true learning experience while earning continuing education credits.
  • Movable Scaffolding Systems (1 day). The course explores the use of MSS for span-by-span and balanced cantilever in-place casting of prestressed-concrete bridges. You will learn under which circumstances is span-by-span casting with MSS a competitive alternative to incremental launching and precast segmental construction, will compare the use of telescopic MSS for macro-segmental balanced cantilever bridges with in-place casting with form travelers, and will explore bridge design and detailing for effective use of MSS. With extensive illustrations and case studies, the course explores configurations, operations, loads, kinematics, performance, productivity, structure-equipment interactions and industry trends of the different types of special construction equipment for in-place casting: overhead and underslung MSS for span-by-span casting; prestressed MSS for four-phase casting of long spans; telescopic MSS for macro-segmental casting of balanced cantilevers; overhead and underslung form travelers for balanced cantilever construction of prestressed-concrete decks, cable-stayed decks and arch ribs; and forming carriages for segmental casting of the concrete slab of steel girders. The course also explains the design of piers, abutments and superstructures for safe and efficient use of MSS.
  • Precast Segmental Bridges (1 day). The course provides exhaustive coverage of span-by-span and balanced cantilever construction of precast segmental bridges. With extensive illustrations and case studies, the course explores the geometric design of precast segmental bridges, the production of standardized atypical segments combined with geometry control with typical segments in short-line molds, the geometry control of short- and long-line casting, and site assembly of precast segmental spans on shoring towers, by strand-jacking from barges, and with self-launching gantries and lifting frames. For each family of special construction equipment, the course explores configurations, operations, loads, kinematics, performance, productivity, the stiffness interactions to consider for the design of piers and superstructures, the progressive instability of tall bridge piers induced by front pendular legs, staged construction of continuous spans, and staged application of post-tensioning to avoid joint decompression and the risk of brittle span failure. You will learn under which circumstances is span-by-span construction of precast segmental bridges a competitive alternative to incremental launching and in-place casting with MSS, will explore bridge design for modularity and effective use of short-line casting cells, and will learn new solutions for balanced cantilever erection of adjacent bridges and the full potential of macro-segmental construction.

The second edition of Bridge Launching (2014, ICE Publishing, 376 pages, ISBN 9780727759979) is the textbook of other two courses that Dr. Rosignoli teaches for the ASCE Continuing Education Program and on-demand in the offices of bridge owners, designers and constructors:

  • Launched Bridges (2 days). With extensive illustrations and case studies, this course provides exhaustive coverage of the design, construction, technology and industry trends of steel and prestressed-concrete bridges built by incremental launching. You will learn under which circumstances is bridge launching a competitive solution, will explore the other construction methods for medium-span prestressed-concrete bridges, and will compare alternatives in preparation of successful value engineering sessions. The course explains how to control self-weight bending and shear with launch noses, temporary piers and front cable-stayed systems, and how to optimize their interaction with the deck. It discusses the Reduced Transfer Matrix method for parametric launch stress analysis, the global and local launch stability of steel girders; and launch post-tensioning, deck segmentation and different organizations of the casting facility for prestressed-concrete bridges. The course also explores geometric launchability criteria, launch bearings and guides for steel and prestressed-concrete bridges, thrust systems, and how to control the deck movements during uphill and downhill launching. Richly illustrated with dozens of photographs and case studies, the course is constantly top-rated for material and presentation.
  • Launched Bridges (1 day). Originally prepared for the Structural Engineer Association of Illinois, the course explores the design, construction, technology and industry trends of steel and prestressed-concrete bridges built by incremental launching. It explains the use of launch noses, temporary piers and front cable-stayed systems, web stability and lateral torsion-flexure buckling of steel girders, and launch post-tensioning, deck segmentation and different casting yard organizations for prestressed-concrete bridges. For both types of bridges, the course also explores launch bearings and guides, thrust systems and how to control the deck movements during uphill and downhill launching.

The bridge engineering eManuals of BridgeTech expand the discussion in depth and breadth to provide exhaustive coverage of their topic. Some of the readers of Dr. Rosignoli want to excel as bridge designers. Others want to foster training and innovation within their agencies and firms. Others want to win bridge projects and construct them safely and cost-effectively, and others want to boost their own career and emerge from the team. For all of them, the eManuals deliver a unique wealth of knowledge, learning and insights.

The Bridge Engineering eManuals Project is modular and scalable. You may purchase a couple of eManuals to learn about a specific construction method, or the entire collection to become the Means & Methods guru in your firm or agency and enjoy a 20% discount. You may also study eManuals to deepen the knowledge earned during one of Dr. Rosignoli's courses of modern bridge design and construction technology.

In less than two years, bridge owners, designers, constructors, educators and providers of materials, technology and services have downloaded eManuals from 46 countries on five continents. We do encourage you to discover the full potential of the eManuals Project and the wealth of knowledge and learning it can bring to your firm, agency and professional career.

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The titles below are a selection for further reading on the topic. BridgeTech offers courses, books, eManuals and a rich collection of exclusive articles and free publications. Our Newsletter reaches thousands of bridge owners, designers and construction professionals in every corner of the world. Enjoy the offer of BridgeTech and the wealth of knowledge, learning and insights that it can bring to your firm, agency and professional career.

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