BridgeLCC

Tools for Designing Cost-Effective Building Systems

The Office of Applied Economics develops economic methods and software to aid industry in evaluating the cost effectiveness of new-technology construction materials, "green" building materials, building energy systems, and other construction/building processes. BridgeLCC 2.0 supports this effort by helping engineers to evaluate bridge-related design decisions, including

• what bridge designs are life-cycle cost-effective;
• whether to repair an existing bridge or replace it;
• whether to use a new construction material or process in a bridge design; and
• what are acceptable levels of cost risks associated with earthquakes, river flooding, or other disasters.

Figure 1. BridgeLCC Cost Summary Window

BridgeLCC 2.0 uses an economic methodology based on the ASTM Standard Practice for measuring the life-cycle costs of buildings and building systems (E 917). The software includes a cost classification scheme that helps insure that all costs are accounted for and are well organized so that useful comparisons can be made quickly between project alternatives. Analyses are carried out in discrete steps, which are now listed on the left side of the BridgeLCC Cost Summary Window (Figure 1).

Basic Mode: Deterministic Analyses

So as to accommodate two types of analysis --- relatively basic estimations of life-cycle cost and comprehensive life-cycle cost that include uncertainty and risk assessments --- BridgeLCC 2.0 can operate in two alternate modes: (1) a Basic Mode where the amounts and timings of costs are best-guess values without any uncertainty, and (2) an Advanced Modewhere uncertainty in amounts and timings of costs can be taken into consideration. The analyst can switch back and forth between the two modes without any loss of data.

Sensitivity Analysis

Within the Basic Mode, after inputting and computing the life-cycle costs of the alternative designs, materials, or processes, the analyst can use the Sensitivity Analysis window (Figure 2) to see what effect changes in individual parameters and costs can have on the overall life-cycle cost effectiveness of particular alternatives. Likewise, the analyst can have BridgeLCC compute and compare the relative sensitivity of all parameters and costs and then view them in one table.

Figure 2. Sensitivity Analysis Window

 

 

Advanced Mode: Uncertainty and Risk

In the Advanced Mode, the analyst can assign one of four probability distributions (uniform, normal, triangular, lognormal) to quantity, unit cost, and timing of individual costs. The analyst then runs Monte Carlo simulations to see how these uncertainties in individual costs create uncertainty in the overall life-cycle cost effectiveness of each alternative (Figure 3).

Figure 3. Analysis of Results Window

 

 

 

 

Supporting Tools

BridgeLCC includes several important tools that support comprehensive life-cycle cost analysis of bridges. The Workzones window (Figure 4) allows the user to estimate the per-day cost of road construction and repair to drivers on and under a bridge, in terms of driver delay costs, vehicle operating costs, and accident costs. These user costs are then applied to alternatives to see how these costs affect the overall life-cycle cost effectiveness of each alternative.

Figure 4. Workzones Window

 

 

 

 

BridgeLCC 2.0 also includes an expanded Concrete Service Life Prediction Tool for estimating bridge damage caused by exposure to road salts.

 

 

Improvements over BridgeLCC 1.0

BridgeLCC 2.0 offers significant features compared with BridgeLCC 1.0, including:

• analyzing up to 6 alternatives at a time;
• creating life-cycle 'events' that affect many agency, user, or third-party costs;
• creating and using multiple workzones (with driver delay, vehicle-operating costs, and accident costs);
• improved sensitivity analysis of interest rates, life-cycle events, and costs;
• improved Monte Carlo simulation, in which most parameters can be modeled with probability distributions;
• unified reporting designed for direct submission to stakeholders and clients;
• online, context-sensitive help;
• select non-U.S. currencies (British, Japanese, Euro, General).

 

 

 

Interest Rates

The following inflation and discount rates are recommended for use in BridgeLCC.

Inflation Rate
	Length of Study Period
Base year	3-year	5-year	7-year	10-year	30-year
2003 and beyond	1.5%	1.7%	1.7%	1.7%	1.8%

 

 

 

 

Real Discount Rate
	Length of Study Period
Base year	3-year	5-year	7-year	10-year	30-year
2003 and beyond	1.6%	1.9%	2.2%	2.5%	3.2%

 

 

 

 

 

 

 

 

Source:

Office of Management and Budget, Guidelines and Discount Rates for Benefit-Cost Analysis of Federal Programs, Appendix C, OMB Circular A-94, Washington, D.C., January, 2003.