۱٫ Introduction

۲٫ Case study

۳٫ Proposed optimization framework

۴٫ Results of the optimization for the case study

۵٫ Conclusions

References

Steel jacketing (SJ) of beams and columns is widely employed as retrofitting technique to provide additional deformation and strength capacity to existing reinforced concrete (RC) frame structures. The latter are many times designed without considering seismic loads, or present inadequate seismic detailing. The use of SJ is generally associated with non-negligible costs depending on the amount of structural work and non-structural manufacturing and materials. Moreover, this kind of intervention results in noticeable downtime for the building. This paper presents a new optimization framework which is aimed at obtaining minimization of retrofitting costs by optimizing the position and the amount of steel jacketing retrofitting. The proposed methodology is applied to the case study of a 3D RC frame realized in OpenSEES and handled within the framework of a genetic algorithm. The algorithm iterates geometric and mechanical parameters configurations, based on the outcomes of static pushover analysis, in order to match the optimal retrofitting solution, intended as the one minimizing the costs and, at the same time, maintaining a specified safety level. Results of the proposed framework will provide optimized location and amount of steeljacketing reinforcement. It is finally shown that the use of engineering optimization methods can be effectively used to limit retrofitting costs without a substantial modification of structural safety.

Introduction

Steel jacketing is a widely employed technique to improve strength and deformation capacity reinforced concrete (RC) elements presenting critical conditions with respect to seismic and gravity loads condition Steel jacketing of columns is arranged in two possible ways. The first provides a full connection between the steel cage and the slab. In this case, besides the confinement effect, additional flexural strength is provided. For the cases in which full connections are not simple to be realized, steel jacketing is arranged by simply providing the cages. Also in this case a some additional flexural resistance is provided because of friction [1], but the most significant effect is related to the increase of column deformation capacity as consequence of confinement. Experimental and numerical investigations have been carried out by researches for both for the first typology of arrangement (e.g. [2-4]) and for the second one (e.g. [1,6-9]). Despite the effectiveness, it must be also said that steel jacketing is an invasive strengthening technique. In fact, its application to columns provides demolition and reconstitution of portions of masonry infills and plaster. Structural optimization is widely recognized as a valuable computational tool allowing engineers identifying cost-effective design solutions controlling design parameters, and several seismic design optimization applications for steel and RC structures are available in the literature (e.g. [10-17]). At the same time, the issue of the optimization of retrofitting interventions for RC structures has not been investigated many times in the past.