Optimized seismic retrofit of steel-concrete composite buildings

• Published in: Engineering structures Vol. 213; p. 110573
• Main Authors: Papavasileiou, Georgios S., Charmpis, Dimos C., Lagaros, Nikos D.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 15.06.2020; Elsevier BV
• Subjects: Building codes; Building frames; Buildings; Composite columns; Composite materials; Concrete; Concrete construction; Concrete jacket; Cost analysis; Cost-effectiveness; Eigenvalues; Frame structures; Horizontal loads; Optimization; Reinforced concrete; Reinforcing steels; Retrofitting; Seismic engineering; Steel; Steel beams; Steel bracing; Steel cage; Strengthening; Structural optimization; Steel bracing; Strengthening; Steel cage; Structural optimization; Cost-effectiveness; Concrete jacket
• ISSN: 0141-0296; 1873-7323
• DOI: 10.1016/j.engstruct.2020.110573

•Objective assessment of different retrofit approaches is achieved using structural optimization.•Steel cage retrofit is the most tractable for lightly under-designed composite buildings.•For higher requirements on column capacity, RC jackets provide cost-effective solutions.•Installation of bracings is required for overly under-designed buildings.•Bracings installation does not necessarily alleviate the deficient composite columns. This work is focused on comparatively assessing the cost-effectiveness of three seismic retrofit approaches for non-code-conforming frame buildings with steel-concrete composite columns. The first two of the assessed retrofit approaches aim in indirectly enhancing structural system performance by strengthening individual composite columns using reinforced concrete jackets or concrete-covered steel cages. The third retrofit approach considered aims in upgrading the composite building frame at hand by installing steel bracings at selected bays. A specially developed structural optimization procedure is used to perform an objective comparison of the cost-effectiveness of the three retrofit approaches. The objective of the optimization procedure is to minimize the total retrofit material cost, while constraints are imposed to ensure the satisfaction of design requirements for the retrofitted structure regarding member capacities (according to Eurocodes 3 and 4 for steel beams and composite columns, respectively), structural system performance under horizontal loading (based on interstorey drifts calculated by pushover analyses) and fundamental periods (obtained from eigenvalue analyses). By defining 30 cases of under-designed 2-storey, 4-storey and 6-storey composite buildings (i.e. buildings with steel-concrete composite columns), an extensive numerical investigation involving 120 retrofit optimization runs was conducted. The results obtained provide insight into the relative cost-effectiveness of the three seismic retrofit approaches and reveal certain conditions under which each approach is economically most viable.