29
Chapter 2
Inappropriate design
DOI: 10.1201/b12914-2
2.1 IntroductIon
Completing a structure starts with an appropriate design, based on structural requirements. As already mentioned in Chapter 1 (Figure 1.5), the
design stage includes dimensioning, detailing, and material selection based
on properly defined environmental conditions, duly considering both
mechanical loading and potential degradation processes. Structural engineers are well-trained in estimating the external loading, as well as in determining the resulting internal forces and stresses in structural elements. To
do so, many tools can be considered, going from hand calculations to estimate order of magnitudes to very complex computer models giving accurate numbers for complex geometries under combined loading effects.
The fundamental theories behind structural behaviour are well known
and can be translated into sound mathematical language. In this way, the
calculation of the internal forces in a structural element can be obtained
by solving fourth order partial differential equations linking deformations
with external loading. Different material models can be considered to
finally calculate stress distributions, going from simple linear elastic behaviour to more complex behaviour including visco-elasticity, plasticity, cracking, and anisotropy.
Dimensioning the structure can finally be based on the concept of allowable stress levels (as typically done in elastic design methods) or on the
definition of (partial) safety factors relative to the failure condition of the
structural element (as typically done in ultimate limit state design methods,
ULS). Especially for slender structures, due attention should also be paid
to allowable deformations (as defined in the so-called serviceability limit
state, SLS). These concepts are well documented in literature or in design
codes, and will not be dealt with in the framework of this book on damage
to concrete structures.
Although design engineers are well acquainted with these concepts, due
to the complexity of the structure, often in combination with uncertainties
regarding the external loading, things can go wrong. Fortunately, structural
Chapter 2
Inappropriate design
DOI: 10.1201/b12914-2
2.1 IntroductIon
Completing a structure starts with an appropriate design, based on structural requirements. As already mentioned in Chapter 1 (Figure 1.5), the
design stage includes dimensioning, detailing, and material selection based
on properly defined environmental conditions, duly considering both
mechanical loading and potential degradation processes. Structural engineers are well-trained in estimating the external loading, as well as in determining the resulting internal forces and stresses in structural elements. To
do so, many tools can be considered, going from hand calculations to estimate order of magnitudes to very complex computer models giving accurate numbers for complex geometries under combined loading effects.
The fundamental theories behind structural behaviour are well known
and can be translated into sound mathematical language. In this way, the
calculation of the internal forces in a structural element can be obtained
by solving fourth order partial differential equations linking deformations
with external loading. Different material models can be considered to
finally calculate stress distributions, going from simple linear elastic behaviour to more complex behaviour including visco-elasticity, plasticity, cracking, and anisotropy.
Dimensioning the structure can finally be based on the concept of allowable stress levels (as typically done in elastic design methods) or on the
definition of (partial) safety factors relative to the failure condition of the
structural element (as typically done in ultimate limit state design methods,
ULS). Especially for slender structures, due attention should also be paid
to allowable deformations (as defined in the so-called serviceability limit
state, SLS). These concepts are well documented in literature or in design
codes, and will not be dealt with in the framework of this book on damage
to concrete structures.
Although design engineers are well acquainted with these concepts, due
to the complexity of the structure, often in combination with uncertainties
regarding the external loading, things can go wrong. Fortunately, structural