Vulnerability assessment of reinforced concrete structures for fire and earthquake risk - Seismic Risk Analysis and Management of Civil Infrastructure Systems - page 369

in the concrete strength. This simulation was performed for each of the
columns in the fi rst fl oor with recorded seismic damage.
Estimating degradation of concrete strength based on the loss of lateral
load capacity might not be considered an accurate estimation method since
distribution of compression stress, and therefore the concrete strength deg-
radation, on the cross-section of the column, under both axial and lateral
load, is not uniform. Furthermore, for columns that fail in fl exure, yielding
the main steel bars would govern the column response and therefore con-
crete would degrade less than that of the lateral load capacity. However,
this method may be considered as a conservative method, based on a worst
case scenario, and for the sake of safety its application would be reasonable.
Further research is needed to develop a more reasonable and accurate
estimation methodology.
The fi re resistance analysis of the whole building was then carried out
when the above compressive strength degradation was included for the
structural elements that were damaged during the earthquake. It is noted
that in this study, experimental results were available for the seismic
response of the building and its structural elements. In general, when such
data are not accessible, a time history nonlinear analysis of the entire build-
ing subjected to the earthquake input motion can be performed to estimate
the building seismic response.

14.4.4 Heat penetration

Openings, such as crack and spalling, could accelerate heat penetration into
the structural elements and, therefore, increase the heat transfer through
the elements. For instance in the case of concrete or masonry structures
such cracks or spalling could occur as the result of large deformation due
to an earthquake. When the cracks are large enough, these openings would
let the heat and fl ames penetrate deep into the structural elements and
elevate the temperatures rapidly in the elements. This will in turn result in
degradation of material properties and reduction of building load-bearing
capacity. Figure 14.5 shows the temperature distribution of the damaged
and the undamaged cross-sections due to fi re, for a column in the fi rst fl oor
of the building. The results indicate considerable effects of concrete damage
due to the temperature distribution.

14.4.5 Residual drift and P - Δ effects

After an earthquake, a building could experience a large deformation which
could lead to a nonlinear stage that could result in some deformation off-set
or residual lateral deformation. In other words, the building could not
recover its original position after the ground shaking. Such residual defor-