Direct damage to a structure and the structure's contents and vehicles, are calculated as shown in the following equation:


Di=di*vi


where:
Di is the direct damage, where the subscript i is used to represent buildings, contents, or vehicles
di is damage (in percent) as a function of depth and occupancy type
vi is the monetary value


To determine the percent direct damage to a structure and the structure's contents and vehicles, both the depth at the structure and the occupancy type of the structure need to be known. The depth is considered the maximum depth minus the foundation height (FH). The occupancy type is specified as part of the structure inventory and is associated with three individual depth-percent damage relationships, one each for the building, contents, and vehicles. In addition, another option is available to define a fourth depth-percent damage curve for an additional "other" category. Examples of "other" category could include any user specified relationship that relates damage to a computed depth. Therefore, the depth at the structure can be used to determine the percentage that the four components of the structure are damaged. This percent damage can then be multiplied by a structure and the structure's contents and vehicle values (specified in the structure inventory) to determine the total direct damage that occurs at and within a structure.
A schematic of the direct damage computation procedure for a structure is displayed in the figure below. At a maximum depth of seven feet, the structure is 42 percent damaged, based on the depth-damage relationship. Multiplying the structure's value ($100,000) by the damage (42 percent) results in a direct damage of $42,000 for the structure. The direct damage to the structure's contents and vehicles will also need to be added to the structure damage of $42,000 to determine the total damage at and within the structure.

Direct Building Damage Calculation Procedure
Two additional considerations can also affect the direct damage computations. First, direct damage to vehicles may be reduced for structures if the population receives adequate warning time to vacate the structure and clear the flooded area. The value of vehicles that are available to be damaged at a structure (C') is calculated using the following equation:




where:
C' is the total original vehicle value per structure
N is the total number of vehicles per structure
k is the carrying capacity per vehicle (in persons)
P is the population per structure
%clear is the percentage of the structure population that cleared the flooded area
The cleared population is used to estimate the fraction of vehicles that left the structure. The ratio [P * %clear/100]/k is an approximation of the number of vehicles that were needed to carry the cleared population away. The rest of the vehicles are left at the structure to incur flood damage. Multiplying the total original vehicle value (C) by a ratio of the vehicles evacuated to the total number of vehicles (N) gives the value of the vehicles evacuated. The difference between that value and the total original vehicle value is the value of the remaining vehicles (C'), which is the value used in the direct vehicle damage computations. If no population evacuated from a structure, the available vehicle value (C') equals the total original vehicle value (C). Conversely, if all of the vehicles were needed to evacuate the cleared population, the available vehicle value (C') is zero.
The second consideration that can affect the direct damage computations occurs when depth-times-velocity information is entered into HEC-FIA. Prior to any direct damage computations, HEC-FIA will check whether the depth-times-velocity threshold for total damage is exceeded. If the threshold is exceeded, the structure, contents, and vehicles will all automatically be assigned a 100 percent loss.