Many existing reinforced concrete structures were constructed with substandard characteristics. Low quality concrete, poor transverse reinforcement details and insufficient flexural strength are among the most common deficiencies. While substandard structures are in need of retrofitting, particularly in seismic areas, problems such as high costs and disturbance to occupants are major obstacles for retrofit interventions. Fiber reinforced polymers can provide feasible retrofit solutions with minimum disturbance to occupants. In this study, the basic aim is to investigate the flexural seismic performance of substandard reinforced concrete columns retrofitted with embedded longitudinal fiber reinforced polymer reinforcement without increasing the original dimensions of the columns. In the experimental study, the reference and retrofitted columns were tested under constant vertical and reversed cyclic lateral loads. Three different connection methods of aramid fiber reinforced polymer reinforcement to the footing were investigated experimentally. A significant enhancement was obtained in lateral flexural strength through the proposed retrofitting method. Furthermore, it was observed that the cyclic lateral drift capacities of the retrofitted columns were as high as 3%, which can be deemed as quite satisfactory against seismic actions. The comparison of the experimental data with analytical calculations revealed that a conventional design approach assuming composite action between concrete and fiber reinforced polymer reinforcement can be used for flexural retrofit design. Experimental results also demonstrated that strain limit for longitudinal fiber reinforced polymer (FRP) reinforcement should be remarkably lower in case of reversed cyclic loading conditions.

No abstract

The aging building stock is turning to be an urging problem for Europe, and it costs even human lives in some cases. Significant part of this building stock along with infrastructure were constructed with substandard characteristics such as poor-quality material, insufficient flexural strength, wrong reinforcement details and improper design of structural system. On the other hand, Europe has highly seismically active zones where devastations are inevitable after even moderate earthquakes. In the light of these facts, countless structures are in need of retrofitting, particularly in seismic areas, while high costs, disturbance to occupants, historical heritage and environmental restrictions are major obstacles for retrofit interventions. Many substandard reinforced concrete (RC) and masonry structures should be seismically retrofitted to reduce their vulnerabilities against earthquakes. Financial constraints, disturbance to the occupants and disruption of functions of the structures are the main obstacles for proper seismic retrofitting of these substandard existing structures. Traditional retrofitting methods such as concrete and steel jacketing, are not applicable in many cases due to high disturbance to occupants and long duration of retrofitting, which may be very critical for commercial, industrial and public buildings. Besides, these methods are also not preferred for historic structures due to the incompatibility of the concrete with traditional lime-based mortars (e.g. Roman cement) and the heavy visible impact to the architectural design. In the last two decades, use of fiber reinforced polymers (FRP) in construction industry has become quite common. Academic researches go back even a decade earlier. FRPs offer practical and innovative solutions for seismic retrofitting due to their lightweight, high tensile strength and noncorrosive character. Besides, the disturbance to the architectural design of the structures are quite limited when they are retrofitted with FRPs. This opens new possibilities for masonry buildings and historic structures belonging cultural heritage.