The external jacketing method using cement-based matrices and textile reinforcement has gained popularity for the enhancement of strength and ductility characteristics of reinforced concrete members. In this study, glass fiber–reinforced mortar (GFRM) with or without basalt textile reinforcement was used for external jacketing of low-strength concrete prisms. An innovative spraying method was used during the application of the cement-based matrix to the specimen’s surface. Investigations were carried out on a large number of concrete prisms with five different cross-sectional geometries (circular, square, and rectangular, with cross-sectional aspect ratios of 1.5, 2, and 3). At the end of the tests, it was shown that the proposed retrofit methodology is effective for the enhancement of performance of low-strength concrete members. The spraying technique is practical and feasible, particularly for the cases in which access to the structural members that are destined to be retrofitted is limited. Furthermore, a simple analytical approach based on the effectively confined concrete area concept is also presented for predicting the peak strength and the ultimate strains of the retrofitted specimens.

Brittle failure of lightly reinforced concrete columns is one of the primary reasons for partial or total collapse of substandard existing buildings subjected to earthquake loading. This study presents collapse performance of a full-scale building that was performed to gain insight into the seismic behavior and the collapse mechanisms of nonductile buildings with lightly reinforced concrete columns. The three-story building was tested under displacement-controlled quasi-static reversed cyclic loading followed by a lateral pushover loading up to realization of the total collapse. In addition to the poor reinforcement details, columns had high axial load–to–axial capacity ratios as also observed in many existing substandard buildings. During the test, severe structural damage was observed at 0.9% first-story drift ratio in the cyclic part of the lateral loading and the brittle total collapse of the building took place during the pushover loading at 1.45% first-story drift ratio. In this paper, after the introduction of the test campaign, the formation of structural damage and collapse mechanisms are discussed. In addition, an attempt to predict the behavior and performance of the test building is made by using a column model that considers flexural, slip, and shear deformations. Finally, the obtained analytical results are compared with the experimental observations and results.

This research aims to address a post-earthquake urgent strengthening measure to enhance the residual seismic capacity of earthquake-damaged reinforced concrete wall structures with coupling beams. The study consists of a series of tests on half-scale prototype coupling beams with various detailing options, including confined with reduced confinement, partially confined, and unconfined bundles, under cyclic loading conditions. The methodology employed involved subjecting the specimens to displacement-controlled reversal tests, and carefully monitoring their response using strain gauges and potentiometers. The main results obtained reveal that GFRP wrapping significantly enhances the seismic performance of earthquake-damaged coupling beams, even in cases where specimens experienced strength loss and main reinforcement rupture. The strengthened beams exhibit commendable ductility, maintaining high levels of deformation capacity, and satisfying the requirements of relevant seismic design codes. The significance of the study lies in providing valuable insights into the behavior and performance of damaged coupling beams and assessing the effectiveness of GFRP wrapping as a rapid and practical post-earthquake strengthening technique. The findings can be particularly useful for developing urgent post-earthquake strengthening strategies for high-rise buildings with structural walls. The method may be particularly useful for mitigating potential further damage in aftershocks and eventual collapse. In conclusion, this study represents a significant advancement in understanding the post-earthquake behaviors of coupling beams and provides valuable guidance for practitioners in making informed decisions regarding post-earthquake strengthening projects. The findings contribute to the overall safety and resilience of structures in earthquake-prone regions.

Our research aims to address the urgent need for retrofitting measures to enhance the resilience of damaged coupling beams in real-life scenarios. We conducted a series of tests on scaled-down prototype coupling beams, carefully adhering to similarity theory requirements to ensure accurate representation. The test results showed that the chord rotation capacities of different specimens with the same diagonal bundle varied significantly due to the difference in the confinement levels. The specimens with lower level of confinement were found to have less displacement capacity. When the specimens were strengthened by wrapping with GFRP after damage, it was observed that the increase in confinement level significantly increased the chord rotation capacities of all specimens. In addition, in the tests before the strengthening, the elongation behavior of the specimens is observed until the damage development reaches approximately 2% chord rotation. With the in-crease in chord rotation, the elongation behavior of the specimens stops with increasing damage and then shortening behavior is observed. After retrofitting, it was observed that the axial elongation continued in a limited manner depending on the location and size of the concrete separated from the beam core in the case of collapse before strengthening, and then the beam showed a shortening behavior predominantly. After strengthening studies, our findings contribute valuable insights into the behavior and performance of damaged coupling beams, emphasizing the potential of urgent GFRP wrapping as a viable solution to enhance the seismic resilience of middle- and high-class buildings with structural walls after seismic events.