The bridge industry is moving toward mechanized construction because this saves labor, shortens project duration and improves safety and quality. This trend is evident in many countries and involves most construction methods. Mechanized bridge construction is based on the use of special equipment.
New-generation bridge erection machines are complex and delicate structures. They handle heavy loads on long spans under the same constraints that the obstruction to overpass exerts onto the final structure. Safety of operations and quality of the final product depend on complex interactions between human decisions, structural, mechanical and electro-hydraulic components of machines, and the bridge being erected.
Despite their complexity, the bridge erection machines must be as light as possible. Weight governs the initial investment, the cost of shipping and site assembly, and the transient stresses in the machines due to varying geometry during self-launch. Weight limitation dictates the use of high-strength steels and designing for high stress levels in different load and support conditions, which makes these machines potentially prone to vibrations and instability.
The bridge erection machines are assembled and dismantled many times, in different conditions and by different crews. They are modified and adapted to new work conditions. Structural nodes and field splices are subject to hundreds of load reversals. The nature of loading is often highly dynamic, and the machines may be exposed to impacts and strong wind. 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 subject to such loads.
The level of sophistication of new-generation bridge erection machines requires adequate technical culture to all parties involved. 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 structural systems, 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 fatalities and huge delays in the project schedule. 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.
Dr. Rosignoli wrote Chapter 6.37.40 Bridge Erection Machines (51 pages in full A4/letter format) of the UNESCO Encyclopedia of Life Support Systems in 2012 upon invitation from the United Nations Educational, Scientific and Cultural Organization. The fact itself that the United Nations commissioned a report on bridge construction equipment highlights the social relevance of safety and quality of mechanized bridge construction.
Chapter 6.37.40 introduces the special equipment for bridge construction and its design, loading, kinematics, performance, productivity, structural modeling and analysis, instability, fabrication, site assembly, commissioning, load testing and inspections during operations.
- Introduction to Bridge Construction Methods
- Main Features of Bridge Erection Machines
- Beam Launchers
- Self-Launching Gantries for Span-By-Span Precast Segmental Erection
- Movable Scaffolding Systems (MSS) for Span-By-Span Casting
- Self-Launching Machines for Balanced Cantilever Construction
- Carriers and Gantries for Full-Span Precasting
- Design Loads of MSS and Form Travelers
- Design Loads of Heavy Lifters
- Modeling and Analysis
- Instability of 3D Trusses
- Instability of Vertical Support Members
- Load Testing
The eManual Introduction to Mechanized Bridge Construction (44 pages in full A4/letter format), the bestseller Bridge Construction Equipment (2013, ICE Publishing, 488 pages) and other bridge engineering eManuals of BridgeTech expand the discussion in depth and breadth to provide exhaustive coverage of the topic.
These publications are indispensable sources of information and guidance for bridge owners, designers and construction professionals interested in the design and construction of modern bridges. Feel free to download Chapter 6.37.40 Bridge Erection Machines of the UNESCO Encyclopedia of Life Support Systems: it is totally free.