Vulnerability assessment of reinforced concrete structures for fire and earthquake risk - Seismic Risk Analysis and Management of Civil Infrastructure Systems - page 366

used during the shaking table test. For the sake of comparison, the same
fi re load and location, ASTM E-119, as that used in the fi rst analysis, was
assumed for the purpose of this assessment. An analytical method was
utilized to evaluate degradation in mechanical properties of concrete due
to the seismic damage and a numerical analysis was then employed to assess
the effects of heat and fl ame penetration, into the damaged and cracked
concrete elements, on the building fi re resistance. Another effect to include,
in a post-earthquake fi re resistance evaluation, is the effects of residual
lateral deformation of the structures. However, no residual lateral deforma-
tion was observed during the shaking table test of this building; therefore
this was considered in this study. Note that two middle columns in Axis X1
at the fi rst fl oor (see Fig. 14.3), were not included in the analysis, since both
columns collapsed during the earthquake test.
14.4.3 Degradation of mechanical properties of materials
Typically, mechanical properties of materials degrade when they undergo
large deformation. When a building structure is subjected to an earthquake,
large lateral deformation may result in signifi cant damage to the structural
elements and degrade their material mechanical properties. In reinforced
concrete structures, large fl exure, shear and tensile/compression deforma-
tion may lead to the post-peak response of the material, where the materials
incur permanent strength degradations. Therefore, if the deformation
caused by the earthquake to the structural elements is larger than the peak-
strength deformation capacity, those elements are likely to have a perma-
nent change in their mechanical properties. For a post-earthquake fi re
performance assessment of structures, such permanent changes in mechani-
cal properties due to the earthquake need to be taken into account. Although
there are various models available that could estimate degradation of the
material properties for structural elements of a building, there is still a chal-
lenge due to the lack of reliable analytical tools to precisely estimate such
permanent damage. One of the reasons is the irregularity of the damage
distributions in the elements and their cross-sections. In other words, even
in a single cross-section of an element, concrete degrades differently across
the section depending on the induced deformation distributions. For sim-
plicity, in this study, an analytical approach was used to estimate average
values that quantify overall damage of the elements' material properties
due to the earthquake.
For the purpose of heat transfer analysis, location of cracks and crashed
concrete is very important, as it affects the level of heat penetration into
the elements. Since, experimental results were available, locations of cracks
and damage to the concrete in different structural elements were identifi ed
and evaluated based on observations, taken place, after the shaking table