## 4 Results of Analysis  
Figure 3 exhibits the computational result of B/C under various conditions (analysis periods and discount rates) of 10 \"collapse hazard zones\" disaster recovery and reconstruction projects (Table 9). The B/C estimates of this study utilize the damage risk zones and damage estimating methods suggested by \"natural disaster hazard zone management guidelines [14]\" for its damages estimating method. To calculate the cost, the actual operating expense was applied.  
Figure 3: _Cont._The benefit/cost analysis results of 10 target zones showed that the analysis periods and discount rates affected the analysis. For instance, in the 30- and 50-years analysis periods, without considering the return period (i.e., recurrence interval), all B/Cs were found to be more than one (Figures 3 and 4).  
Figure 4: B/C distribution of project sites.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Classification** & **Analysis Period** & **Discount Rate** & **Classification** & **Analysis Period** & **Discount Rate** \\ \hline B/C\_1 & & 5\% & B/C\_9 & & 5\% \\ B/C\_2 & 30 years & 4\% & B/C\_10 & & 4\% \\ B/C\_3 & & 3\% & B/C\_11 & & 3\% \\ B/C\_4 & & 2\% & B/C\_12 & & 2\% \\ \hline B/C\_5 & & 5\% & B/C\_13 & & 5\% \\ B/C\_6 & & 4\% & B/C\_14 & Considering return & 4\% \\ B/C\_7 & & period (total & 3\% & B/C\_15 & period (total & 3\% \\ B/C\_8 & & period, 30) & 2\% & B/C\_16 & period, 50) & 2\% \\ \hline \end{tabular}
\end{table}
Table 9: Evaluation condition.  
Figure 3: Benefit/cost (B/C) results of project sites.  
It is seen that as the duration of the analysis periods increases, the cost/benefit ratio also increases. This is because the periods applied to the estimation of benefits have been increased, even though the total operating expense is fixed.  
When the cost/benefit ratio of a certain project is one or more, the project could be regarded as economically feasible as the benefit of the project exceeds the cost. In case of Wolmyeong zone, its cost/benefits ratio was estimated to be nine or more. However, the cost/benefit ratio could be easily overestimated if the benefits are set to occur every year.  
When the return period was considered, the analysis period was reduced according to the frequency of the damages that occurred in the past; this, in turn, reduced the benefits and consequently, lowered the cost/benefits ratio. However, since the return period is estimated by using the losses from the past ten years in this research, it is difficult to conclude whether this value is representative of the return period of the region. However, it is best to apply an analysis period that takes the return period into account to derive the appropriate estimation of cost/benefits ratio.  
Additionally, as shown in Figure 3, the B/C ratio decreased as the discount rates increased. This is because the benefits that occur after the completion of the projects are greatly discounted and the present value is estimated to be small. The total operating expense is also evaluated by dividing it into project execution periods; hence, it is affected by discount rates, but the period is relatively short. On the other hand, when the return period was considered, the B/C values were similar due to the low impact of discount rates. This could be because the benefits that are affected by discount rates are small.  
It is difficult to determine the investment effects of the \"collapse hazard zone\" disaster recovery and reconstruction projects with only 10 target zones analyzed for the cost/benefit analysis in this study. However, when the analysis period of 50 years and 5% discount rates are applied as the criteria for analyzing the investment effects of the zones for the projects, the average B/C for the ten target zones is 2.5 or more, and this is definitely more than 1. These results suggest that the \"collapse hazard zone\" disaster recovery and reconstruction projects will be more cost-effective.