Tangible costs in risk-based design

Hydrosystems Engineering Reliability Assessment and Risk Analysis

Design of a hydrosystem infrastructure, by nature, is an optimization prob­lem consisting of an analysis of the hydraulic performance of the structure to convey flow across or through the structure and a determination of the most economical design alternative. The objective function is to minimize the sum of capital investment cost, the expected flood damage costs, and operation and maintenance costs. The relevant variables and parameters associated with the investment cost and the expected damage costs of a hydraulic structure, i. e., a highway drainage structure, are listed in Tables 8.1 and 8.2, respectively. The maintenance costs over the service life of the structure generally are treated as a yearly constants. Based on Tables 8.1 and 8.2, the information needed for the risk-based design of hydraulic structures can be categorized into four types:

1. Hydrologic/physiographic data include flood and precipitation data, drainage area, channel bottom slope, and drainage basin slope. These are needed to predict the magnitude of hydrologic events such as streamflow and rainfall by frequency analysis and/or regional analysis.

Pipe culverts

Box culverts

Bridges

Parameters

Unit cost of culvert

Unit cost of concrete Unit cost of steel

Unit cost of bridge

Variables

Number of pipes Pipe size Pipe length Pipe material

Number of barrels Length of barrel Width of barrel Quantity of concrete Quantity of steel

Bridge length Bridge width

SOURCE: After Tung et al. (1993).

TABLE 8.1 Variables and Parameters Relevant in Evaluating Capital Investment Cost of Highway Drainage Structures

2. Hydraulic data include flood-plain slopes, geometry of the channel cross sec­tion, roughness coefficients, size of the structural opening, and height of the embankment. These are needed to determine the flow-carrying capacities of hydraulic structures and to perform hydraulic analysis.

TABLE 8.2 Damage Categories with Related Economic Variables and Site Characteristics in Risk-Based Design of Highway Drainage Structures

Подпись: Floodplain property damage: Losses to crops Losses to buildingsПодпись: Damage to pavement and embankment: Pavement damage Embankment damage Подпись: Traffic-related losses: Increased travel cost due to detour Lost time of vehicle occupants Increased risk of accidents on a flooded highway

Подпись: Location of crop fields Location of buildings Physical layout of drainage structures Roadway geometry Flood characteristics Stream valley cross-section Slope of channel profile Channel and floodplain roughness Flood magnitude Flood hydrograph Overtopping duration Depth of overtopping Total area of pavement Total volume of embankment Types of drainage structure and layout Roadway geometry Average daily traffic volume Composition of vehicle types Length of normal detour paths Flood hydrograph Duration and depth of overtopping Подпись: Types of crops Economic value of crops Types of buildings Economic values of buildings and contents
Подпись: Material cost of pavement Material cost of embankment Equipment costs Labor costs Repair rate for pavement and embankment
Подпись: Rate of repair Operational cost of vehicle Distribution of income for vehicle occupants Cost of vehicle accident Rate of accident Duration of repair

Damage category Economic variables Site characteristics

SOURCE: After Tung and Bao (1990).

3. Structural data include material of substructures and layout of structure.

4. Economic data include (a) type, location, distribution, and economic value of upstream properties such as crops and buildings, (b) unit costs of structural materials, equipment, operation of vehicles, accidents, occupancy, and labor fee, (c) depth and duration ofovertopping, rate ofrepair, and rate ofaccidents, and (d) time of repair, and length of detour.

In the design of hydrosystem infrastructures, the installation cost often de­pends on environmental conditions, such as the location of the structure, ge — omorphic and geologic conditions, the soil type at the structure site, type and price of construction material, hydraulic conditions, flow conditions, recovery factor of the capital investment, and labor and transportation costs. In reality, these cost-affecting factors would result in uncertainties in the cost functions used in the analysis. However, a practical way to incorporate economic uncer­tainties in the risk-based design of hydrosystem infrastructures remains to be developed.



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Updated: 25 ноября, 2015 — 2:59 дп