Improving Global Quality of Life

9.9.2 Hot topics
Raising and enforcement of building code standards in emerging countries to a global standard.
Training, qualification and certification of personnel to ensure industry’s ability to design and
implement steel construction in all countries.
Research and development of robust field welding automation.
Improved welding, training and inspection for concrete construction.
Continued research and development of seismic and blast resistant structures.
9.10 Bridge sector
Bridges are essential links in the transportation system, whether used by trains, trucks, buses or cars. Besides
the obvious functional differences, bridges are differentiated from other structures such as buildings by
the nature of loading: bridges are subject to “live loads” created by moving traffic. This loading results in
the potential for fatigue cracking in the structure. When fatigue cracks grow to a critical size, fracture of
structural elements can occur, leading to collapse of the structure.
Bridges are exposed to the environment where ambient temperatures affect material properties, as well as
to fog, rain, snow and industrial pollutants that challenge paint systems and cause corrosion to unprotected
materials that rust. In climates where salt is applied to control ice on roadways, and where bridges cross
waterways with salt water, corrosion is even a greater problem.
Major bridges today are made of steel or concrete. Significant amounts of welding are done on steel bridges,
allowing the engineer to choose from a variety of material thicknesses and strengths for optimal design.
Concrete construction typically involves pre-tensioning cables and little welding on the primary structural
members is involved, although miscellaneous components such as cable anchors may be welded.
In developed countries, the inventory of bridges typically includes many that are structurally or functionally
obsolete. These structures may carry greater loads than ever anticipated, or have already done so for longer
than planned, or simply cannot handle the current volume of traffic. Many of these structures are riveted
and may have been made with unweldable or difficult-to-weld steel.
9.10.1 Needs and Challenges
Avoidance of fatigue crack initiation is critical for bridge safety, and welded connections have an unfortunate
history of such cracking. The art and science of fatigue crack avoidance is well developed and understood
by experts in the field. In practice, however, errors are still made in the design and detailing of bridges.
The cracking that results from such error typically takes years to occur, and may be discovered only after
the problematic detail was been incorporated into many other bridges. Thus, the challenge is to improve
the process by which such structures are designed, detailed, reviewed and approved, as well as in the
training of the professionals involved.
Closely related to the preceding, in-service inspection of such structures for fatigue cracking is an ongoing
challenge. Today, most inspection is visual, since economics and practicality preclude non-destructive
inspection of each and every fatigue sensitive location. Visual inspection is difficult, however. Access to all
the various connections is often restricted. Peeling paint, corroded surfaces, bird droppings and other foreign
material may hide such cracks. The challenge is for quick, economic and reliable methods of identifying the
onset of fatigue cracks.
130 Improving Global Quality of Life Through Optimum Use and Innovation of Welding and Joining Technologies