Durability and service life 5
the safety of the structure might no longer be at a very high level, or that
high maintenance or repair costs will have to be expended in order to keep
the performance of the structure at an acceptable functional level. Quite
often it is a matter of economical and profit calculations in order to decide
whether to maintain and repair or to demolish and reconstruct. Another
option is to give a new destination to the structure, with possibly a reduced
required minimal quality level.
The service life of a structure can be studied from at least three different
points of view: technical or structural, functional, and economical.
Depending on the point of view, a technical, functional, or economical
service life can be defined. Technical or structural requirements are linked
with the strength of materials and the load bearing capacity of structures.
These requirements are commonly considered in design standards and
model codes.
Functional requirements are related to the normal use of a building
or a structure. The width of a bridge and the height underneath must be
in accordance with the dimensions of the vehicles crossing the bridge or
driving under the bridge. The functional service life is not determined by
load bearing capacity or other technical issues, but rather by the evolution
in traffic. As an example, the Walnut Lane Bridge (which was the first
prestressed concrete bridge in the United States of America, designed by
G. Magnel, and built in 1949 in Philadelphia) was replaced by a larger
bridge in the 1990s. At that time, the Walnut Lane Bridge was still in very
good shape and showed no problems with load bearing capacity. It was
rather the intensified traffic, needing more lanes, which caused the replacement of this famous bridge. Other examples are the many office buildings
Time
Service life
Minimal
Initial
Quality
Repair
Figure 1.4 Schematic representation of the service life and the effect of repair.
the safety of the structure might no longer be at a very high level, or that
high maintenance or repair costs will have to be expended in order to keep
the performance of the structure at an acceptable functional level. Quite
often it is a matter of economical and profit calculations in order to decide
whether to maintain and repair or to demolish and reconstruct. Another
option is to give a new destination to the structure, with possibly a reduced
required minimal quality level.
The service life of a structure can be studied from at least three different
points of view: technical or structural, functional, and economical.
Depending on the point of view, a technical, functional, or economical
service life can be defined. Technical or structural requirements are linked
with the strength of materials and the load bearing capacity of structures.
These requirements are commonly considered in design standards and
model codes.
Functional requirements are related to the normal use of a building
or a structure. The width of a bridge and the height underneath must be
in accordance with the dimensions of the vehicles crossing the bridge or
driving under the bridge. The functional service life is not determined by
load bearing capacity or other technical issues, but rather by the evolution
in traffic. As an example, the Walnut Lane Bridge (which was the first
prestressed concrete bridge in the United States of America, designed by
G. Magnel, and built in 1949 in Philadelphia) was replaced by a larger
bridge in the 1990s. At that time, the Walnut Lane Bridge was still in very
good shape and showed no problems with load bearing capacity. It was
rather the intensified traffic, needing more lanes, which caused the replacement of this famous bridge. Other examples are the many office buildings
Time
Service life
Minimal
Initial
Quality
Repair
Figure 1.4 Schematic representation of the service life and the effect of repair.