Abstract 
     
    PAYÁ ZAFORTEZA, IGNACIO. (2007). Heuristic optimization of reinforced concrete 
buiding frames. Doctoral thesis. School of Civil Engineering. 295 pages. igpaza@cst.upv.es. 

     The objective of this thesis is to design robust and flexible algorithms that allow to 
automate the optimal design of reinforced concrete frames, commonly used in building 
construction, as well as to draw general conclusions about the optimized structures. This 
work outlines a general framework for the single-objective (economic cost) and the multi-
objective optimization of these structures which is applied to planar frames with a maximum 
of 153 variables. Among them we find six different types of concrete grades.

     Five heuristic methods are tested in order to minimise the economic cost: Random 
Walk Strategy (RW), First Best Gradient (FB), Simulated Annealing (SA), Threshold 
Accepting (TA), and Genetic Algorithms (GA). These techniques are used in a first phase in 
order to optimise a portal frame made up of two bays and four floors subject to vertical and 
horizontal forces. The SA version developed provides the highest quality design, whose cost 
is 3473.06 €. The best projects obtained through the created versions of TA, FB, GA and RW 
have minimum costs exceeding it by 0.52%, 5.74%, 8.69% and 124.6%, respectively. For 
this reason, SA is chosen to economically optimize other building frames made up of two 
bays and two, six and eight floors. 

     The results obtained allow to suggest rules for the pre-dimensioning of the optimized 
structures and to automate the selection of parameters for the SA algorithm, thus avoiding 
long trial-and-error processes. Besides, it is verified that the limit states usually checked in 
this structural typology are also enough in order to guarantee the safety of the optimized 
structures. 

     Likewise, the research comprises an analysis of the economic impact derived from the 
use of a single type of concrete (HA-25 with characteristic compressive strength of 25 MPa), 
as well as of the use of flat beams instead of overhanging beams. Regarding the eight-floor 
portal frame, the exclusive use of HA-25 implies a cost increase of 3.02% and, in case flat 
beams are also employed, it raises by 46.7%. 

     Finally, the thesis includes a study of the simultaneous optimization of the cost of the 
structure and of the objectives related to its ease of construction, environmental sustainability 
and safety. For this, the Suppapitnarm Multi-objective Simulated Annealing (SMOSA) 
method is used. The results show that the different criteria come into conflict, and so it is not 
possible to find an optimal design for all three objectives simultaneously. Nevertheless, the 
SMOSA method provides the project designer with a sufficiently wide set of alternatives 
among which to choose a compromise solution.