AllSteel-SRetrofit · All-steel external frame for the non-disruptive seismic retrofit of existing reinforced concrete buildings

All-steel external frame for the non-disruptive seismic retrofit of existing reinforced concrete buildings

A significant challenge in high seismic regions is that a large proportion of existing reinforced concrete (RC) buildings were constructed without adhering to modern seismic design standards. This lack of seismic consideration makes these structures inherently vulnerable to strong earthquake forces. Compounding this issue is the presence of architectural and structural irregularities, such as an uneven in-plan distribution of structural elements or height-wise inconsistencies in infill wall layouts. These irregularities can significantly amplify deformation demands during seismic events, leading to increased structural stress. Moreover, deficiencies in reinforcement detailing—such as inadequate design of columns, beams, and beam-column joints—exacerbate these vulnerabilities. Such poor detailing compromises the ductility and energy dissipation capacity of the structure, making it more prone to severe damage and even collapse under strong ground shaking. The consequences are devastating, often resulting in significant loss of life, injuries, and economic disruption. Recent earthquakes have also highlighted another critical issue: the high repair costs associated with damage to non-structural components. Drift-sensitive elements and acceleration-sensitive components are particularly susceptible to damage. These damages not only impair the functionality of the building but also represent a substantial financial burden, underscoring the need for improved design and retrofitting strategies that address both structural and non-structural vulnerabilities. This project aims to develop a retrofit technology that is non-disruptive and easy to implement, achieves simultaneous control of drifts and accelerations, and overcomes major issues related to low concrete strength, poor reinforcement details, and vulnerable RC columns, has never been described in the literature or in seismic design codes. The ambitious main objective against the background of the state-of-the-art of the project is to develop such a retrofit technology. Buckling-restrained braces (BRBs) have been widely used in engineering practice in recent years due to their excellent energy dissipation capability. However, the property of the low post-yield stiffness observed in BRBs may result in inter-story drift concentration, accompanied by large residual drifts when used in moment-resisting frames. To address this issue, a novel multi-stage yielding energy dissipation brace is proposed to improve the limitations mentioned above of the BRBs. During the first period of the project, the Fellow in collaboration with the Supervisor performed an extensive literature review on the state-of-the-art of multi-stage yielding energy dissipation brace and of the use of dissipative devices in buildings. This study showed the significant lack of knowledge in the behavior of such kind of braces. A new configuration of the brace has been developed, which uses the multi-stage yielding mechanism. The core energy dissipation part comprises 12 U-shaped dampers (UDs). The UD consists of a half-circle section with two straight sections on either side. The two UDs are arranged with openings opposite each other and parallel. The upper and lower straight portions are elongated and shortened when the UDs are subjected to external forces, respectively. The rolling deformation of the UDs provides energy-dissipation capacity. The load-transfer part is a H-shaped steel with a special mechanical mechanism. Three rectangular slotted holes are cut respectively on both sides of the upper flange, and different types of bolt holes are provided on the lower flange. The special mechanical mechanism is obtained utilizing bolted connections with different types of bolt holes. H-shaped steel moves under the action of external forces. As the force increases, when the displacement reaches a certain limit value, the special mechanical mechanism is activated to realize the multi-stage working mechanism. A series of tests were conducted in this study to understand the seismic performance of UDs. To further investigate the multi-stage working mechanism, the finite-element numerical simulation of the three specimens was established by ABAQUS. A parallel work focusing on retrofit and performance assessment of existing buildings was conducted. Given the response databank, probabilistic economic seismic loss estimation studies was carried out by developing vulnerability functions, which consider uncertainties in earthquake ground motion, structural response, and repair costs. Both the probability of collapse and the probability of demolition due to excessive residual drifts will be taken into account to qualitatively and quantitatively assess the effectiveness of the proposed retrofit solution. Comparison of the different retrofit solutions on the basis of economic loss will offer a realistic evaluation of the competitiveness of the proposed technology in practice and market.

Data: CORDIS, © European Union