PropertyRisk Glossary


PropertyRisk Glossary (Use the BACK button to return to your previous page.)

BUILDING CONSTRUCTION TYPES
	Steel Frame Buildings of this type have structural systems consisting of a framework of steel columns, beams, and girders. Some may use diagonal braces spanning between floor levels. Exterior walls may be either glass curtain walls, or various kinds of cladding material such as metal or precast concrete panels. Lateral forces are resisted by the steel frame.
	Reinforced Masonry Buildings of this type have exterior walls consisting of either grouted clay brick or concrete block masonry with internal reinforcing steel rods. These buildings may have vertical load bearing frames of concrete or steel. Reinforced masonry buildings are relatively thick walled box-like structures and often have small windows and at least two mostly solid walls. The masonry walls are used to resist lateral forces.
	Concrete Wall Buildings of this type have perimeter and/or interior reinforced concrete walls. These buildings may have vertical-load bearing frames of concrete or steel. Exterior walls may have a veneer finish or may be clad in metal or pre-cast concrete panels. Lateral forces are resisted by the interior and/or exterior concrete walls.
	Concrete Frame Buildings of this type have structural systems consisting of a framework of reinforced concrete columns, beams, and girders. Exterior walls may be either glass curtain walls or various kinds of cladding material such as metal or precast concrete panels. Lateral forces are resisted by the concrete frame.
	Concrete Tilt-Up Buildings of this type are low-rise structures with precast reinforced concrete wall panels that are often poured on the ground and tilted into place. Roofs are often composed of either plywood sheathing or metal decking, and glass curtain walls may exist at the building perimeter. Lateral forces are resisted by the concrete panels.
	Unreinforced Masonry Buildings of this type have perimeter walls, and possibly some interior walls, constructed of unreinforced clay brick or concrete block. These perimeter walls are sometimes used as load bearing walls and have no internal reinforcing steel rods. Anchor plates (square or diamond shaped steel plates with a nut or a bolt at the center) are sometimes used to tie the walls to the floors and roof and are conspicuous from the outside of the structure. Unusual brick patterns may also indicate unreinforced masonry. Lateral forces are resisted by the masonry walls.
	Wood Frame Buildings of this type include low-rise single-family dwellings, multi-family dwellings, and commercial units with structural systems consisting of wood studs and joists, columns, and beams. These structures can have exterior veneers consisting of wood, stucco, brick, or vinyl siding. Lateral forces are resisted by the wooden frame and plywood sheathing attached to the frame.
SITE AND BUILDING ATTRIBUTES
Site Topography This generally characterizes the natural slope of the ground around the site -- basically, is the landscape around the site flat, or not (e.g., hillside property)? Answering this question does not require a specific measurement of slope, and this aspect is not used in calculating the PML. It provides an internal check on the soil mapping by government agencies that is digitally represented in the PropertyRisk system. If "Unknown" the slope is assumed to be flat (a typical setting for commercial property).
Building Plan Shape This is the shape of the building in a "bird's eye view." Generally, simple box-type buildings require fewer and simpler connections to be stable in an earthquake, compared to buildings with more complex or irregular plan shapes. If building plan shape is indicated as "Unknown," it is assumed to have an intermediate level of complexity or irregularity, such as a "Medium rectangle" plan shape. The estimated PML calculated in the PropertyRisk report will reflect the building attributes you indicated. However, if the actual plan shape differs significantly from that assumed for this assessment, the actual PML may differ significantly from that estimated in this report. A more confident PML can be provided with verified building information.
Building Area This is the total square footage of the building. The estimated PML calculated in the PropertyRisk report will reflect the building attributes you indicated. However, if the actual plan shape differs significantly from that assumed for this assessment, the actual PML may differ significantly from that estimated in this report. A more confident PML can be provided with verified building information.
Large Openings in Ground-floor Walls Large openings in a particular level of a building may indicate a weakened condition for some types of structures. A 'large' opening is considered to be one that exceeds 50% of the width of the elevation in which it is contained. Individual smaller openings that, taken together, exceed this 50% criterion can also result in a weakened condition. If the proportion of large openings in ground-floor walls is indicated as "Unknown," it is assumed to be less than 50% of any one elevation. The estimated PML calculated in the PropertyRisk report will reflect the building attributes you indicated. However, if the actual proportion of ground-floor wall openings differs significantly from that assumed for this assessment, the actual PML may differ significantly from that estimated in this report. A more confident PML can be provided with verified building information.
Construction Type and Number of Stories Certain construction types typically are not consistent with certain story heights. Hence, your selection of construction type for a building may require consideration of the number of stories it has. Two examples of inconsistencies to watch out for: Wood frame structures are typically not more than 4 stories high. Tilt-up buildings are typically not more than 3 stories high. The estimated PML calculated in the PropertyRisk report will reflect the building attributes you indicated. However, if the actual construction type or number of stories differs significantly from that assumed for the assessment, the actual PML may differ significantly from that estimated in the report. A more confident PML can be provided with verified building information.
Construction Type and Year Built Certain construction types typically are not consistent with certain vintages of construction. Hence, your selection of construction type for a building may require consideration of the building's age. A few examples of inconsistencies to watch out for: Tilt-up buildings generally were not constructed before about 1950. Reinforced masonry buildings generally were not constructed before about 1935. Unreinforced masonry (URM) buildings generally were not constructed after about 1940 in California. The estimated PML calculated in the PropertyRisk report will reflect the building attributes you indicated. However, if the actual construction type or year built differs significantly from that assumed for the assessment, the actual PML may differ significantly from that estimated in the report. A more confident PML can be provided with verified building information.
Seismically Strengthened Has the framework of the building ever been retrofitted to resist earthquake damage? In answering this question note that the vintage indicated for retrofitting may be inconsistent with the evolution of seismic design. Generally, prior to the 1971 San Fernando earthquake, very few buildings had been retrofitted for earthquakes. Those that had been retrofitted during that early period were probably retrofitted to standards well below modern standards and, typically, gain little, if any, advantage in an earthquake over an unretrofitted building of the same type, age and location. For this reason, if retrofit status is indicated as "Unknown" it is assumed to be "No." The estimated PML calculated in the PropertyRisk report will reflect the building attributes you indicated. However, if the actual retrofit status differs significantly from that assumed for this assessment, the actual PML may differ significantly from that estimated in this report. A more confident PML can be provided with verified building information.
LOSS OR LENDER CRITERIA
Hazard Exposure Period This is the time span considered in assessing maximum earthquake ground shaking intensity at a particular location. Expected maximum shaking intensity generally increases as the exposure period increases.
Non-exceedance Confidence Level This is the level of confidence that the reported PML will not be exceeded during the specified Hazard Exposure Period.
Probable Maximum Loss (PML) The seismic risk of a structure is the combination of the seismic hazard at the site and the seismic vulnerabilities of the building. The Probable Maximum Loss (PML) is a financial measure of the seismic risk of the building. The PML is an estimate of the cost to restore the structure to pre-earthquake condition, expressed as a percentage of the replacement value. The PML anticipated over the span of 475 years is a common measure of the seismic risk. Two opinions of the PML may be provided in this report. The PML-50 is our best estimate of the likely loss to be experienced over the designated time duration. The PML-50 has a 50% confidence level, meaning that as much as 50% chance exists that actual losses experienced over the time duration would be more than this amount. A more conservative PML-90 estimate is also provided to represent the likely worst case scenario. This estimate has a 90% confidence of not being exceeded, or there is only a 10% chance that actual losses experienced over the designated time duration would be exceeded.
UBC Seismic Zone The Uniform Building Code (UBC) contains a Seismic Zone Map of the United States (including the island territories of Puerto Rico, Guam, and Tutuila). The map is intended to serve as a guide to the level of expected earthquake ground shaking. Each mapped zone is assigned a hazard level that ranges from 0 (lowest) to 4 (highest), and these designations are part of the basis for seismic design criteria for new construction and earthquake retrofitting projects. The seismic zone designations as mapped in the UBC are generalized and subject to modification by local Building Officials as may be warranted for their building regulations. In addition, the 1997 UBC introduced a "near-source" factor for seismic design criteria in order to account for stronger shaking expected close to hazardous faults than may be reflected by the conventional UBC seismic zone designations. As a result, the hazard level designated on the UBC Seismic Zone Map may differ from the hazard level that is assumed and actually applied at the local level. The actual hazard level for a specific location must consider the activity of all hazardous faults in the region across the spectrum of earthquake magnitudes possible on those faults, which can only be done through a probabilistic seismic hazard analysis such as that provided by the PropertyRisk^TM analysis.
EARTHQUAKE INTENSITY
Modified Mercalli Intensity (MMI) Unlike earthquake "magnitude," which is a measure of total energy released at the source of the earthquake, earthquake "intensity" is a measure of shaking strength at different locations in the region where a quake is felt. Earthquake intensities are characterized in terms of how the shaking affected people and buildings. There are several "shaking scales" in use internationally. In this website we use the Modified Mercalli Intensity (MMI) Scale. For a description of the damage states represented by the levels of the original (1931) MMI levels, and a "modernized" description of those damage levels, click here.
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