One of the most important decisions in design is the levels of seismic performance. Six goals and levels as shown in Table 2 were shown to engineers to select two per engineer. Since there were engineers who did not reply or replied only one level, those were classified “no answer” in Table 2. Number of replies as well as cross correlation with the experience of 1995 Kobe earthquake, which will be described later, are presented in Table 2.
Among six levels, Level 1 and Level 2 are a pair of questions. Level 2 intends that “it is allowed for engineers to design bridges so that collapse can be avoided no matter how extensive damage which results in long suspension of traffic occurs because it is not economically feasible to design bridges so that they do not suffer damage under a rare earthquake such as the Kobe earthquake.” On the other hand, Level 1 intends that “since the roads and railways are essential infrastructures in urban areas, socio-economic damage (indirect damage) resulted by bridges damage must be extensively larger than the direct damage. Furthermore, it takes weeks even to arrange materials and human resources once an urban area is extensively deteriorated by an earthquake. Therefore it is required to design bridges so that they do not suffer extensive damage to an extent that they require emergency repair even under a rare earthquake such as the Kobe earthquake.”
Excluding “no answer” (23.5%), Level 2 had the highest support of 23% from the engineers. This may be reasonable because Level 2 is now widely accepted in the engineering community worldwide. On the other hand, Level 1 had support of 14.5%. It is noted that the higher level of seismic performance in Level 1 had support of nearly 2/3 of the support of Level 2.
It is interesting to note that the support rate of Levels 1 and 2 depends on whether they experienced 1995 Kobe earthquake or not. If one classifies 100 engineers into two groups, i.e., the group who experienced Kobe earthquake (personally experienced the Kobe earthquake, involved in rescue and repair, or involved in design and analysis of damage bridges) and the group who did not experience Kobe earthquake, the support ratio for Level 1 was 17.9% in the group who experienced the Kobe earthquake, but it was only 10.6% in the group who did not experience the Kobe earthquake. This may be regarded that the engineers who have experienced Kobe earthquake intend to set higher seismic performance level than the group who did not experience Kobe earthquake.
The second highest support (15%) was directed to Level 6, i.e., “the seismic performance level depends on the amount of investment. However it is civil engineers
Table 2. Seismic performance goals Choose two among the following six goals which are close
to your professional opinion on the seismic performance levels (1) Experienced the Kobe earthquake （2） No experience to Kobe earthquake (3) Total
(1) Since the roads and railways are essential infrastructures in urban areas, socio-economic damage (indirect damage) resulted by damage of bridges must be extensively larger than the direct damage. Furthermore, it takes several weeks even to arrange materials and human resources once an urban area is extensively deteriorated by an earthquake. Therefore it is required to design bridges so that they do not suffer extensive damage in an extend that they require emergency repair even under the Kobe earthquake.
19(17.9%) 10(10.6%) 29(14.5%)
(2) It is not economically feasible to design bridges so that they do not suffer damage under a rare earthquake such as the Kobe earthquake. It must be thus allowed for engineers to design bridges so that collapse can be avoided no matter how extensive damage which results in long term suspension of traffic occurs. Saving lives must be the goal.
25(23.6%) 19(20.2%) 46(23.0%)
(3) It is not meaningful for bridges to be functional when an urban area is extensively and widely deteriorated. Consequently, Sustaining extensive damage on bridges is acceptable. 2 (1.9%) 3 (3.2%) 5 (2.5%)
(4) Criticism was raised by public after the 1995 Kobe earthquake on the collapse of bridges. Public expects that bridges are so designed that they do not collapse. The philosophy that only collapse should be prevented with allowing extensive damage to occur is realized only among engineers.
10(9.4%) 10(10.6%) 20(10.0%)
(5) The seismic performance depends on the amount of investment. Engineer’s mission is to do their best within given investment and boundary conditions. Because budget is limited, it is difficult to prevent extensive damage during destructive earthquakes such as the 1995 Kobe earthquake.
14(13.2%) 13(13.8%) 27(13.5%)
(6) The seismic performance level depends on the amount of investment. However it is civil engineers who decide the design force levels and the performance goals. We make design calculations according to design codes, but are we really trying to design bridges so that damage can be avoided? We should deliver our engineering knowledge for preventing damage.
19(17.9%) 11(11.7%) 30(15.0%)
(7) No answer 17(16.0%) 26(27.7%) 47(23.5%)
who decide the design force levels and the performance goals. We make design calculations according to design codes, but are we really trying to design bridges so that damage can be avoided? We should deliver our engineering knowledge for preventing damage.” This Level 6 was in pair of Level 5, i.e., “the seismic performance depends on the amount of investment. Engineer’s mission is to do best within a given investment and boundary conditions. Because budget is limited, it is difficult to prevent extensive damage during destructive earthquakes such as the 1995 Kobe earthquake.” Level 6 had slightly higher support than Level 5.
It is interesting to note that the selection of Levels 5 and 6 also depends on the experience of Kobe earthquake. Similar to the comparison of Levels 1 and 2, if we classify into the group who experienced Kobe earthquake and the group who did not experience the Kobe earthquake, the support ratio was 13.8% and 11.7 % for Levels 5 and 6, respectively, in the group who did not experience Kobe earthquake, while it was 13.2% and 17.9%, respectively, in the group who experienced Kobe earthquake. The fact that the support ratio for Level 6 is higher by 6.2% in the group who experienced Kobe earthquake than the group who did not experience Kobe earthquake shows the importance of strong involvement in determination of the seismic performance levels including appropriate investment level, instead of only doing our best within a given boundary condition.
EXPECTED AND ACTUAL REPAIR PERIODS