Many existing reinforced concrete buildings in developing countries located in seismic areas do not possess sufficient strength and ductility characteristics to resist the effects of severe earthquakes. Among other deficiencies, improper detailing of reinforcement and poor quality of materials are major causes of poor seismic performance. More specifically, inadequate lap splice lengths provided at floor levels on plain column longitudinal bars, particularly when concrete strength is low, is a widespread deficiency that has not been investigated in detail to date. Information on the behavior of such columns under earthquake actions is extremely important for reliable assessment of the seismic safety of many existing structures with detailing deficiencies and poor construction quality. In this study, the effect of lap splice length on the cyclic lateral load behavior of low-strength RC columns with plain longitudinal bars (14 mm diameter) was investigated experimentally. The specimens were designed to represent columns with low axial loads. The geometric ratio of the longitudinal reinforcement and the volumetric ratio of the lateral reinforcement of the columns are 1% and 0.8%, respectively. The test program included five RC columns with lap splice lengths of 25, 35, 44 and 55 times longitudinal bar diameter, as well as a reference specimen with continuous longitudinal bars. Test results clearly demonstrated that presence of 180-degree hooks at the ends of the lap splice reduces the negative influence of the inadequate lap splice length on RC member performance, even in the case of low-strength concrete. All specimens reached their flexural strengths and did not experience considerable strength degradation until large drift levels. Test observations were supported with findings of a fiber-based analytical model, which also demonstrated the influence of hooks on improving the bond slip behavior along inadequate lap splices.

Many existing reinforced concrete (RC) substandard structures in seismically active regions, designed and/or constructed improperly or constructed before up-to-date seismic design codes, are in urgent need of seismic retrofitting. Beside financial issues, disturbance to the occupants and functions of the structures are among obstacles for seismic retrofitting. Utilization of fiber reinforced polymer (FRP) composites can reduce disturbance to the occupants and hindrance of the functions of the structures remarkably. In this study, the applicability of flexural seismic retrofitting using carbon FRP precured laminates and rods is investigated experimentally. In seismic retrofitting, the key issue is the effect of reversed cyclic actions, which impose cycles of compression and tension stresses on the FRP reinforcement. Two major issues examined in the study are (1) the anchorage of FRP precured laminates/rods used for cyclic flexural strengthening to the low-strength concrete support (foundation) and ...

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.

Corrosion is one of the major problems for the existing structures and may cause significant decrease in drift capacity and strength of RC (reinforced concrete) columns due to reduction of effective cross-section of reinforcing bars, alteration of bond characteristics between reinforcing bars and concrete, and cover cracking along the reinforcing bars. Therefore, rehabilitation of corrosion-damaged columns is extremely important, particularly in seismic regions and if a substandard construction methodology is used. In this paper, an experimental work is presented on the seismic performance of rehabilitated/retrofitted substandard RC columns, which were damaged due to corrosion of reinforcing bars. For this purpose, four substandard columns were tested under high axial load and reversed cyclic lateral loads. The columns were constructed with extremely low quality concrete and plain round bars. The spacing and details of transverse reinforcing bars did not comply with the code regulations as well. Then, the specimens, except the reference one, were subjected to accelerated corrosion process. One of the corrosion-damaged specimens was tested before rehabilitation/retrofitting procedure, while the other two specimens were tested after rehabilitation/retrofitting procedure. The test results clearly demonstrated the efficiency of the applied rehabilitation/retrofitting procedure, both in terms of strength and ductility. Furthermore, analytical predictions about strength and failure modes of the specimens are compared with experimental findings.