Page 356 - Advanced Design Examples of Seismic Retrofit of Structures

Example of a Steel Frame Building Retrofitted Chapter 5 331

Based on ASCE 41, soil actions are considered as deformation-controlled
actions which are determined according to Section 5.5.5.1. The results indicate
the vulnerability of the foundation of the main building in terms of soil pressure
and foundation uplift as the example contours of two load combinations shown
in Figs. 5.16 and 5.17. Neither soil nor the foundation in the sports building
show any form vulnerability (see Fig. 5.18 as an example). The required rein-
forcement for the foundation derived from modeling (Fig. 5.19) is also less than
the existing reinforcement found in the field observations.

5.9 RETROFIT OPTIONS
Based on the results of the evaluation of the building, apart from the fact that
both buildings, at least in one direction, lack any lateral load-bearing element,
different structural elements are vulnerable, and hence the building should
undergo retrofit. The approaches of the retrofit measures can be as follows:

5.9.1 Local Retrofit of the Vulnerable Structural Elements

Although there are several vulnerable structural elements including columns,
infill walls, braces, and foundation, because the buildings lack any lateral
load-bearing element, local retrofit of the vulnerable structural elements cannot
be regarded as the final solution.

5.9.2 Elimination or Reduction in the Building’s Irregularity
The results of the studies in Section 5.5.1 indicate both buildings are irregular in
plan but regular in height. As previously stated, the buildings lack lateral load-
bearing elements, and adding a new lateral load-bearing system is thus neces-
sary. It is imperative to arrange the lateral load-bearing elements with the aim
more uniform demand forces distribution on these elements which per se orig-
inated from reduction of the irregularity of the building to as little as possible.

5.9.3 Providing Lateral Stiffness to the Building
The lateral stiffness in the main building is provided by masonry infill walls
only. In the sports building in the transverse direction, the lateral stiffness of
the building is provided by braces. As a result, a system should be added to both
buildings to provide lateral stiffness. This can be done by one of the following
methods.

5.9.3.1 Concentric Braces
One of the main problems in adding braces to the building is architectural con-
cerns. In the example buildings, there are few bays that can be considered for
adding concentric braces without conflict to a lesser degree with the view and