Page 25 - Advanced Design Examples of Seismic Retrofit of Structures

Example of a Two-Story Unreinforced Masonry Building Chapter 2 17

evaluation of the effects of building pounding, wherever a portion of an
adjacent structure is located within 4% of the height above grade at the loca-
tion of potential impact [2].

2.3 FACTORS INFLUENCING URM SEISMIC DAMAGE
The extent of damage to URM buildings depends on the parameters below [3].

2.3.1 Seismic Intensity and Other Strong-Motion Characteristics
Seismic structural damage depends mainly on the earthquake record
characteristics, e.g., magnitude, focal depth, fault mechanism, duration, number
of effective cycles, Arias intensity, cumulative absolute velocity (CAV), peak
ground acceleration (PGA), peak ground velocity (PGV), and dominant fre-
quency. However, in some cases, there are researches with contradictory results
which have proven each of these parameters to be the most effective one in
determination of structural damage. For example, Bommer et al. [4] pointed
out that the near-field records which impose considerable energy on the struc-
tures in a short period of time tend to bring about more severe damage compared
to far-field ground motions; however, Kostov and Koela [5] stated that the
opposite is true, as near-field records cause smaller damage compared to far-
field earthquakes, which usually have significant CAVs.

2.3.2 Geometrical Characteristics of URM Buildings
Geometry of URM buildings including dimensions, walls locations, roof sys-
tem, opening location, and also foundation is one of the most influential param-
eters in their seismic performance. IT should be noted that there are strict
regulations in different seismic design codes which necessitate regular plan
in terms of limiting the length to width ratio or any protrusion in the plan. Based
on Iranian National Building Code, Part 8: Design and Construction of Masonry
Buildings [6], the most important geometry regulations of URM buildings are
categorized as follows:

- Geometry of plan
l Length must not exceed width by >3 times;
l Plan should be symmetric in two axis;
l Plan should not have any unusual protrusion or concavity;
- Limitations of height and number of stories
l Maximum number of stories above the ground level is 2;
l Load transfer path to the foundation should be continuous;
l Sudden change in mass and stiffness of adjacent stories should not occur;