Table 8 shows what engineers expect in the performance-based seismic design. The highest expectation was to “make design rational by appropriately choosing the performance criteria depending on bridge” (40.5%), followed by “determine the design force appropriately depending on the site condition” (16.5%) and “introduce probabilistic concept in the determination of design force, analysis and evaluation” (12.5%). On the other hand, little expectation was directed to “use of the most favorable analytical models and tools” (1%). It seems that extensive use of nonlinear static analysis (pushover analysis) and linear and nonlinear dynamic response analysis
Table 8. What do you expect in the performance-based seismic design? What do you expect in the performance-based seismic design? Choose 2
maximum from below.
Number and percentage (1) Make design rational by appropriately choosing the performance
criteria depending on bridges
81 (40.5%) (2) Determine the design force appropriately depending on the site
condition
33 (16.5%)
(3) Use the most favorable analytical models and tools 2(1%)
(4) Want to propose new structural type not yet ever constructed 18 (9%) (5) Eliminate unnecessary sections and members to have well balanced
bridges
16 (8%) (6) Introduce probabilistic concept in the determination of design force,
analysis and evaluation
25 (12.5%) (7) Want to declare the copy right of design and construction 4 (2%)
(8) Other 4 (2%)
(9) No answer 17 (8.5%)
Total 200 (100%)
Table 9. Use of dynamic response analysis in performance-based design How do you want to use dynamic response analysis in the performance-
based seismic design?
Number and percentage (1) Want to use dynamic response analysis more extensively, because
input data for pushover analysis are the same with the input data for dynamic response analysis. Furthermore, pushover analysis is inconvenient because it cannot be used for some types of bridges with predominant higher modes, while dynamic response analysis can be used to all bridges regardless of the types.
28 (28%)
(2) Want to use dynamic response analysis more extensively for bridges to which pushover analysis provides poor application. Want to use pushover analysis for bridges to which the equivalent static analysis provides good application.
46 (46%)
(3) Current level of balance between pushover analysis and dynamic response analysis is appropriate
9 (9%) (4) Want to use pushover analysis more, because dynamic response
analysis is inconvenient for determination of sections
9 (9%)
(5) Others 8 (8%)
(6) No answer 0
Total 100 (100%)
after the Kobe earthquake is one of the reasons why limited expectation was directed to this goal.
Table 9 shows how the engineers regard dynamic response analysis compared to pushover analysis. A majority opinion is that they intend to “use dynamic response analysis more extensively for bridges to which pushover analysis provides poor application. They intend to use pushover analysis for bridges for which the equivalent
Table 10. Problems of performance-based design What do you think the barriers for performance-based seismic design? Choose from the followings based on the assumption that necessary cost- up of design by increasing steps and times is paid by clients.
Number and percentage
(1) It is trouble because many decisions have to be made 7 (7%)
(2) Time for design increases 2 (2%)
(3) Current technology is insufficient to meet realistic and practical demands and requirements
10 (10%) (4) Require engineers with higher engineering background, knowledge
and skill
30 (30%) (5) Design is controlled by a designer or a design group with high
technical background, and the design cannot be approved by others
21 (21%)
(6) Risk and responsibility increase 20 (20%)
(7) Others 10 (10%)
(8) No answers 0
Total 100 (100%)
static analysis provides good application” (46%). Subsequent opinion is that they intend to “use dynamic response analysis more extensively, because input data for pushover analysis are nearly the same to the input data for dynamic response analysis. Furthermore, pushover analysis is inconvenient because it takes more man-power and it cannot be used for some types of bridges with predominant higher modes, while dynamic response analysis can be used for all bridges regardless the types” (28%). On the other hand, few opinions were directed to “current level of balance between pushover analysis and dynamic response analysis is appropriate” (9%) and “use pushover analysis more, because dynamic response analysis is inconvenient for determination of sections” (9%).
Table 10 shows problems which the engineers are concerned about in the performance-based seismic design. The largest problem was that “engineers with higher engineering background, knowledge and skill are required” (30%). This is followed by “design is controlled by a designer or a design group with high technical background, and the design cannot be approved by others” (21%), “risk and responsibility increase” (20%), and “current technology is not matured to meet realistic and practical demands and requirements” (10%). On the other hand few pointed out “it is trouble for having several decisions” (7%) and “it increases time for design” (2%).
CONCLUSIONS
Seismic performance criteria and levels were clarified based on a questionnaire survey to 100 civil engineers. The following conclusions may be deduced based on the results presented herein:
(1) Experience of a damaging earthquake makes the engineers to set higher seismic performance levels. The group who experienced 1995 Kobe earthquake recognized the importance of strong involvement in determination of the seismic performance levels including appropriate investment level, instead of only doing their best within a given boundary conditions.
(2) The experience of Kobe earthquake affects the estimate of actual period of repair. The group who experienced Kobe earthquake estimated the actual repair period longer than the group who did not experience Kobe earthquake.
(3) Based on the current technology, it is not possible to take account of the difference of demands for accessible time between “within a week” and “within 3 weeks” in design. We need a breakthrough technology which enables to incorporate realistic demands in design.
(4) There exist large scatterings in the estimate of cost increase which is required to construct bridges which are free from any closure to traffic (damage-free bridges). How much cost can be validated for repair had large scattering in replies from the engineers. Realistic evaluation on the initial cost and repair cost is important to set clearer performance goals.
(5) In the performance-based seismic design, the engineers expect to make design rational by setting the performance criteria depending on bridges. Little expectation was directed to use the most favorable analytical models and tools. (6) The engineers intend to use dynamic response analysis more extensively in the
performance-based seismic design. About a half engineers want to use dynamic response analysis for bridges to which pushover analysis is poor, while approximately a quarter engineers intend to use dynamic response analysis instead of pushover analysis because the input data for dynamic response analysis are nearly the same with the input data for pushover analysis
(7) The engineers pointed out that higher engineering background, knowledge and skill required for engineers is the largest barrier for the seismic performance- based design. They also pointed out problems that design is controlled by only a designer or a design group with high technological background, and risk and responsibility increase in the performance-based seismic design.
REFERENCES
Arakawa, T., and K. Kawashima. (1986). Dependence of construction cost of bridges on the lateral force coefficient. Civil Engineering Journal. 28(2): 64-69.
Japan Association for Earthquake Engineering. (2004). Current state and future problems of the performance-based seismic design of structures, Research Committee on Performance-based Seismic Design.
DEVELOPMENT OF NEXT-GENERATION PERFORMANCE-BASED