As a general presentation of the calculation tool’s possibilities and to get an idea of the general economic competitiveness of the different deck designs the total LCC’s of the three alternative bridge designs have been calculated over different bridge spans with equal life cycles of 100 years.
While the design calculations of GFRP bridge decks showed that GFRP road bridges with a span of about 24 meters are currently the limit (based on fabrication restrictions), GFRP bridge decks above this limit have been calculated for the sake of completeness. The results are shown in Figure 21.
Figure 21, Total LCC for design alternatives at different spans for a life cycle of 100 years
Keeping in mind that the results above are based on the assumption that the input variables are static and accurately represent reality, a few things can be observed.
The first thing that can be noticed is that - using these inputs – concrete has the lowest LCC, GFRP second lowest and CFRP has by far the highest LCC. The difference in total LCC between GFRP and CFRP is caused almost entirely by the difference in ICC. The other costs are either completely the same (MC, UC) or just a little lower (SC). This means that CFRP will always be way less economically competitive than GFRP. It is therefore decided that further analyses will focus only on GFRP and concrete bridge decks. The second thing that can be observed from Figure 21 is that the AC (ICC+MC) makes up the largest part of the total LCC. Of the AC the ICC makes up the largest part. This is a very interesting result because it directly influences the overall differences between the alternative bridge designs. The differences in MC, UC and SC between the different alternative designs have nearly no effect on the total LCC. One of the reasons
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for this is that the discount factor reduces the effect of future expenses (MC and UC) on the total LCC. The other reason is that most of the maintenance activities (and their accompanying MC and UC) are unrelated to the type of bridge deck (concrete or FRP) used in the design. Most of the maintenance costs are made up by maintenance activities that are necessary for both concrete bridges and FRP bridges. These activities are calamity maintenance (maintenance after calamity or inspection) and the replacement of bridge expansion joints.
This can be seen well in Figure 22 where the MC and UC have been displayed along the life cycle of the object. The UC and MC for the different design alternatives are very similar. The most notable differences between the two take place on the 15 and 25 year intervals. These are the intervals on which the replacement of the different pavements are scheduled. The rest of the costs are nearly identical.
The effects of discounting can also be seen well in Figure 22 by looking at the costs that take place on 30 year intervals. These costs are mainly caused by the replacement of the bridge expansion joints. At year 60 these costs are discounted to almost half of what they were on year 30, at year 90 it is only about a quarter of the costs compared to year 30.
Figure 22, Comparison of user costs and maintenance costs of a 10 meter concrete and GFRP bridge
Figure 23 shows the total cumulative LCC for a 10 and 30 meter concrete bridge and a 10 and 30 meter FRP alternative. The increases to the total LCC are the result of the costs incurred during the lifecycle of the bridge as depicted in Figure 22. In Figure 23 it can be clearly seen that the similarities between the two maintenance schedules of a bridge with a concrete deck and an GRFP deck (and thus the similar UC and MC) make it that the total LCC increases rather equally during the lifespan of the different design alternatives.
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Figure 23, Total cumulative LCC displayed along the lifespan of the bridge
A third observation from Figure 21 is that – as can be expected - the total LCC increases when the span of the bridge increases. The rise in LCC has a weak exponential relation to the span of the bridge. This is explained by the fact that the deck not only increases in surface area but the deck also increases in thickness when spans become larger. Therefore the costs of the decks exponentially grows with span increase. This in turn means the ICC grows exponentially with span increase. Because of the large share that the ICC makes up of the total LCC this exponential trend is also present in the total LCC.
Combining the above observations of higher ICC of GFRP in comparison to concrete decks, the large contribution of ICC on the total LCC, and the exponential rise in ICC when the span increases, it can be seen that: while at 10 meters concrete and GFRP are relatively competitive, the difference in LCC becomes increasingly bigger. Thus at bigger spans it becomes increasingly more difficult for other costs (UC, MC, and SC) to compensate for the difference in ICC.
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