Assessment of steel load-bearing structures - Assessment and Refurbishment of Steel Structures - page 59

Figure 3.1 Kinds of assessing
inspection
ment can monitor those physical quantities, such as shifts, deformations and opening of
cracks, etc. by which it is possible to establish the technical condition of the structure.
Destructive and non-destructive methods are used to determine the crucial properties
of a material. Non-destructive methods are designed to assess both the basic properties of
material, and the extent of damage without destroying a part or the whole of a structure.
Non-destructive methods for determining material properties include hardness testing,
dynamic and ultrasound methods, and radiometric and radiographic methods. The
properties of a material, in particular its strength characteristics, are determined indirectly
by means of physical-mechanical quantities such as hardness, elasticity, speed of
propagation of acoustic signal in the material tested, diminution of gamma radiation
while transiting or being reflected by the atoms of the material, etc. Destructive methods
are used to determine in particular the strength characteristics of materials by testing
samples taken from the completed structure. Using destructive methods on a structure
while it is in operation reduces the strength of the structure or part of it, so they are rarely
used on steel structures.
Among methods of assessment, a special role is played by the loading test. This test is
used on the steel structures of ground constructions, particularly steel bridges. The
method uses the results of all partial methods of assessment and together with the results
of the loading test, this give a more comprehensive view of the overall condition of the
structure, particularly of its behaviour under loading. Loading tests also provide basic
information about the appropriateness and validity of the chosen model of calculation
with respect to further assessment of the structure. The tests are usually performed when
new bridges are commissioned, but they can also be done as control tests during the
lifetime of the structure particularly after important interventions in load-bearing
structures, such as example when they are refurbished.
Loading tests are divided into static and dynamic kinds. Under currently valid
standards, static loading tests are prescribed for all new permanent bridges with span