although this construction type was permitted in some jurisdictions having moderate or high seismicity until the late 1940s or early 1950s (in some jurisdictions URM may still be a common type of construction, even today). These buildings usually range from one to six stories in height and typically function as commercial, residential, and industrial buildings. The construction varies according to the type of use, although wood floor and roof diaphragms are common. Smaller commercial and residential buildings usually have light wood floor/roof joists supported on the typical perimeter URM wall and interior wood load bearing partitions. Larger buildings, such as industrial warehouses, have heavier floors and interior columns, usually of wood. The bearing walls of these industrial buildings tend to be thick, often as much as 24 inches or more at the base. Wall thicknesses of residential buildings range from 9 inches at upper floors to 18 inches at lower floors.

Unreinforced masonry structures are recognized as perhaps the most hazardous structural type. They have been observed to fail in many modes during past earthquakes. Typical problems are

1. Insufficient Anchorage-Because the walls, parapets, and cornices were not positively anchored to the floors, they tend to fall out. The collapse of bearing walls can lead to major building collapses. Some of these buildings have anchors as a part of the original construction or as a retrofit. These older anchors exhibit questionable performance.

2. Excessive Diaphragm DeflectionBecause most of the floor diaphragms are constructed of wood sheathing, they are very flexible and permit large out-ofplane deflection at the wall transverse to the direction of the force. The large drift, occurring at the roof line, can cause the masonry wall to collapse under its own

weight.

3. Low Shear Resistance-The mortar used in these older buildings is often made of lime and sand, with little or no cement, and has very little shear strength. The bearing walls will be heavily damaged and collapse under large loads.

4. Wall Slenderness-Some of these buildings have tall story heights and thin walls. This condition, especially in nonload bearing walls, will result in buckling out-of-plane under severe lateral load. Failure of a non-load-bearing wall represents a falling hazard, whereas the collapse of a load-bearing wall will lead to partial or total collapse of the

structure.

2.4 Configuration Problems

Configuration, or the general vertical and/or horizontal shape of buildings, is an important factor in earthquake performance and damage. Buildings that have simple, regular, symmetric configurations generally display the best performance in earthquakes. The reasons for this are (1) non-symmetric buildings tend to twist in addition to shaking laterally, and (2) the various "wings" of a building tend to act independently, resulting in differential movements, cracking, and other damage. Rotational motion introduces additional damage, especially at re-entrant or "internal" comers of the building. Figure 2-20 shows some symmetric and asymmetric building plans.

The term "configuration" also refers to the geometry of lateral load resisting systems as well as the geometry of the building. Asymmetry can exist in the placement of bracing systems, shear walls or moment-resisting frames that are used to provide earthquake resistance in a building. This type of asymmetry can result in twisting or differential motion, with the same consequences mentioned in the previous

paragraph. Some examples of symmetric and non-symmetric placement of lateral load resisting systems are shown in Figure 2-21. The situation shown in Figure 2-21(a) is

common in corner buildings that have two walls that are mostly glass on the street sides and two concrete or brick walls facing the alley or adjacent buildings.

3.1 Survey Implementation Sequence

There are several steps involved in collecting data, planning and performing a rapid screening of potentially seismically hazardous buildings. As a first step, the community, through its local governing body and local building officials, should formally approve of the general procedure. Second, the members of the community should be informed about the purpose of the survey and how it will be carried out. Then there are many decisions to be made such as use of the survey results, responsibilities of the building owners and the community, and actions to be taken. These decisions are very specific to each community and therefore are not discussed in this handbook.

The general sequence of implementing the survey methodology presented in this handbook consists of:

• Budget development and cost estimation • Selection of area to be surveyed

• Development of mapping system for survey area

Selection of supplementary data to be included in survey and used in decision making

• Development of record keeping system

Many of the decisions that are made about the level of detail of the rapid visual screening procedure will depend upon budget constraints. It is important to realize that although the RSP is designed so that field inspections of each building should take no more than 15 to 30 minutes, time and funds should be allocated for pre-field data collection. Pre-field data collection can be time consuming (10 to 30 minutes per building depending on the type of supplemental data available). However, it can be extremely useful in reducing field time and can increase the reliability of data collected in the field. A good example of this would be the age, or design date, of a building. This might be readily available from building department files but is