Life Cycle Cost Considerations in Seismic Design Optimization of Structures - Structural Seismic Design Optimization and Earthquake Engineering - page 19

Figure 12. (a) Example Pareto-front obtained using TS algorithm, (b) initial and LCC of the building

of LCC oriented seismic design optimization by
the decision makers such as owners and engineers
as well as for its implementation in future seismic
design codes, as the presentation of results in
the Pareto-optimal form gives flexibility in the
decision making process and can accommodate
changes to the performance requirements through-
out the course of design.

Most importantly, for the formulation provided
in this paper, the constants C i in Eqn. (1) which
define the cost of repair for the i th damage state
as a fraction of the initial cost have strong influ-
ence on the LCC. As discussed earlier, it is not
straightforward to determine damage states for
structures and the associated cost of repair. The
effect of other parameters such as the dispersion
in capacity and demand on the LCC should also be
investigated. Eqn. (4) assumes that the structural
capacity is independent of earthquake demand
which is another simplification that is usually
adopted. The evaluation of workmanship cost is
difficult as it is dependent on various parameters
(especially the local cost of labor). Finally, the
cost of non-structural damage after an earthquake
might exceed several times the cost of structural
damage and this also needs to be investigated.

FUTURE RESEARCH DIRECTIONS

There are two major issues in LCC oriented
seismic design of structures that requires further
research. The first one is the application of the
concept developed here to structural models with
significant number design variables. The size of
the search space increases exponentially with
increasing number of design variables and without
a compromise from the accuracy of structural as-
sessment it becomes very difficult to cope with the
computational demand. Although simplified struc-
tural models and analysis techniques are always
an option, these undermine the main objective of
the seismic design optimization by introducing
additional uncertainty into the procedure.
The second issue is sensitivity of the LCC
results to the assumptions made in the derivations.

CONCLUSION

Optimization in structural design is a growing sub-
ject due to increased awareness of the community
regarding the sustainability of civil infrastructure
and the use Earth's nonrenewable resources. And
the recent incidents have shown us once again that
the initial cost of a structure is not a satisfactory