Performance evaluation of structures with reinforced concrete columns retrofitted with steel jacketing

Reinforced concrete (RC) building construction remains predominant in Northern Cyprus, offering resilience against natural disasters when appropriately designed and implemented. This paper presents a seismic analysis of RC building systems across different stories, configurations, and soil classes, according to three seismic design codes: The Northern Cyprus Seismic Code 2015 (NCSC-2015), Eurocode 8 (EC 8), and Turkish Buildings Earthquake Code 2018 (TBEC-2018). The study compares regular and irregular forms of Moment Resisting Frame (MRF) and MRF combined with Shear Walls (MRF+SW) systems in various configurations: G+3, G+7, and G+11 for regular buildings, and only G+11 for irregular buildings. Pushover analysis using ETABSv18 was employed to assess base shear, displacement, and plastic hinge behavior. The results indicate that structural regularity enhances resistance and longevity compared to irregular configurations, with shear walls augmenting resistance against earthquake loads in both regular and irregular buildings. Furthermore, soil class emerges as a significant factor influencing results across the codes. While variations among the codes were not consistently observed, EC 8 and TBEC-2018 often appeared more conservative, with TBEC-2018 demonstrating greater adaptability to advanced technologies and a more detailed parameter consideration.

Due to the increasing number of high-rise buildings and long-span bridges, high strength concrete (HSC) has been widely used in the infrastructures. Therefore, HSC occupies the same large amount of share in the construction market as normal strength concrete (NSC). In general, fire-exposed reinforced concrete (RC) structure leads to serious structural problems due to the loss of strength and stiffness for both concrete and steel bars. Carbon fiber reinforced polymer composites (CFRP) and steel jacketing are two common methods applied to strengthen RC structure columns. Therefore, it is valued to investigate the structural behavior of fire exposed and retrofitted RC columns with CFRP and steel jackets. This paper presents the compressive behavior of RC columns exposed to ISO834 standard fire for 2 h, cooled by air and retrofitted with CFRP and steel jackets. Total 8 RC columns (\(\upphi\)300 × 1000 mm) with two different concrete strength, normal and high, were tested. Cross-sectional temperature distribution, load-deflection response were investigated in this studied. It was observed that, temperature gradient was developed in each specimen during fire exposure. HSC columns were more susceptible to spall off compared with NSC columns. CFRP and steel jacket can effectively improve the ultimate capacity and the stiffness for fire damaged RC columns. Repaired fire-damaged RC columns with removing loose concrete has large impact on the stiffness improvement for NSC columns.KeywordsFire-damagedCircular columnHSCCFRPSteel jacket

A three-storey half scale Reinforced Concrete (RC) open ground storey building is fixed with yielding type X-shaped metallic (elasto-plastic) damper at the ground storey level, to study the seismic response characteristics. Experimental studies are carried out using the 4m x 4m triaxial shake table facility to evaluate the seismic performance. Initially the reinforced concrete building is tested for different earthquake inputs in the shake table. During the test, the cracks and hinges are formed in various locations of beams, columns, beam-column joints and infill walls. During the seismic testing, the plastic failure cracks (plastic hinges) are formed in the columns and beam-column joints of the ground storey. The seismically damaged RC building is retrofitted. Two types of retrofitting techniques have been developed. Type 1 is the local retrofitting of columns and beam-column joints in the ground storey using Geopolymer concretes. Type 2 is the global retrofitting of RC building with Chevron type steel bracing incorporating X-plate damper in the ground storey. The dual functioning of X-plate damper is to improve the global stiffness of building thereby protecting the building during earthquake. In general, earthquake loading induces large displacements in an Open Ground Storey (OGS) structure. During such large displacements, a yielding type elasto-plastic device made of X-shaped metallic dampers performs better. The supporting steel frame of Added Damping and Added Stiffness (ADAS) is of chevron type, serially contributing stiffness to the system. Free vibration tests on OGS RC building with and without yielding type X-shaped metallic damper is carried out. The natural frequencies and mode shapes of the model with and without yielding type X-shaped metallic damper are evaluated.

A high percentage of reinforced concrete (RC) buildings in Portugal were designed and built before the introduction of modern seismic codes. This research aims to assess the seismic capacity and vulnerability of RC buildings in the city of Lisbon. For that purpose, nonlinear static procedures have been used and fragility curves have been developed. These buildings are reaching the end of their nominal life. Therefore, ageing effects have been taken into account, as well as the presence of smooth rebar. To do so, a sensitivity analysis has been performed by considering the chloride-induced corrosion of the reinforcement steel rebar and the degradation of the concrete cover. To illustrate the effects of ageing and the procedure adopted for the seismic fragility assessment of old RC structures, three RC buildings with masonry infills have been selected as case studies. They were all built between 1960 and 1980, and they are representative of the current building stock in Lisbon. The seismic capacity of the buildings has been determined by means of nonlinear static analyses of three-dimensional numerical models. The N2 method and its extended version have been considered to determine the target displacement. The seismic safety of the buildings has been estimated in terms of the demand/capacity ratio for each vertical structural element (columns and walls) according to the bending and the shear failures. Then, a set of fragility curves has been developed for all buildings to represent the probability of RC elements reaching or exceeding the significant damage limit state. Results have shown that the concrete strength degradation has had more influence than reduction of the rebar diameter in the seismic capacity. When considering steel corrosion, it has been demonstrated that the corrosion rate has reduced the capacity more than the time of exposure. It can be concluded that ageing affects the seismic behaviour of RC structures, increasing the vulnerability of these buildings.

This paper firstly presents a three-dimensional quasi-phononic crystal model, and then quasi-phononic crystal metaconcrete material for reduction seismic energy is developed. Finally, two scale 4-story reinforced concrete (RC) buildings with different foundations (i.e. one is the common concrete foundation (CCF) RC building, and the other is a quasi-phononic crystal metaconcrete foundation (QPCF) RC building) were designed and tested on the shaking table under seismic waves to compare the dynamic responses of two RC buildings and further evaluate the seismic reduction effectiveness and seismic performance of QPCF RC building. The results show that the quasi-phononic crystal model can obtain multiple low-frequency band gaps within 200 Hz, and the QPCF can effectively attenuate seismic waves. The QPCF RC building exhibits excellent seismic performance.

The 7.7 and 7.6 magnitude Pazarcık and Elbistan earthquakes that struck Kahramanmaraş on 6 February 2023 caused widespread structural damage across many provinces and are considered rare in seismological terms. While many reinforced concrete (RC) buildings designed under current earthquake regulations sustained significant damage, some older RC buildings with outdated designs sustained only moderate damage. This study aims to analyze the seismic performance of such older RC buildings to understand why they did not collapse or suffer severe damage. An 8-story RC building in Adıyaman province, damaged by the earthquake, was considered for analysis. The region’s seismicity and local site conditions were assessed through borehole operations, geotechnical laboratory tests, and seismic field tests. The soil profile was modeled, and one-dimensional seismic site response analyses were performed using records from nearby stations (TK 4615 Pazarcık and TK 4612 Göksun stations) to determine the foundation-level earthquake record. Nonlinear static pushover analysis was carried out via SAP2000 and STA4CAD, utilizing site response analysis and test results taken from the reinforcement and concrete samples of the building. The findings, compared with the observed damage, provide insights into the performance of older RC buildings in this region.

Steel jacketing has become an attractive strengthening technique for reinforced concrete (RC) columns due to ease of construction and less space requirement. The steel cage consists of angle sections placed at corners and held together by battens at intervals along the RC column height. A numerical investigation of the effective use of steel jackets as a strengthening technique in RC columns is presented in this paper. First, the finite element models of the strengthened column were developed and validated using past experimental data. Then, with the validated model, six sets of steel jacket sections with modified cross-sections such as batten spacing, batten thickness, batten width, end batten width, L angle thickness and steel jacket height were tested under constant axial and lateral loading to understand the effectiveness of steel jackets as the strengthening technique. AnunstrengthenRC column were also analysed to compare the performance of a similar column strengthened by steel jackets with modified parameters. It was shown that strengthening RC columns with steel jackets was effective in enhancing the lateral performance of the columns and resulted in a more stable load-displacement curve with lower strength degradations as compared with the un-strengthened ones. Additionally, it was found that the most effective method to increase the lateral strength and ductility is increasing the L angle thickness. On the other hand, increasing the steel jacket height also increases the lateral performance, however, it was identified that increasing the jacket height is effective only up to 1/3rd of the RC column height. Finally, the obtained results for each parameter were compared to study the behaviour of each component of the steel jacket towards lateral strength and ductility improvements.

Impact of climate change on the life cycle greenhouse gas emissions of cross-laminated timber and reinforced concrete buildings in China

This study assesses performance objectives defined in the Turkish Earthquake Code (TEC) in order to make a realistic evaluation related to heavy damage and collapse reasons of reinforced concrete (RC) buildings that experienced severe earthquakes in Turkey. A series of three-dimensional RC buildings with different characteristics and representing low-rise structures damaged and collapsed in the earthquake areas is designed according to Turkish codes (Turkish Design Standards and Turkish Earthquake Code). Pushover analyses are carried out to determine nonlinear behavior of the buildings under earthquake loads. Building performances are determined by using the displacement coefficients method, which is a commonly used nonlinear static evaluation procedure for different seismic hazard levels defined in the TEC. The stipulated performance objectives in the TEC are checked in terms of plastic rotations and maximum story drift. From the results of this research, it can be concluded that low-rise RC buildings designed according to Turkish codes sufficiently provide for the performance objectives stipulated in the TEC. Reasons for the heavy damages and collapses of RC buildings during severe earthquakes are explained by commonly occurring themes (i.e., project errors, poor quality of construction, modifications of buildings, etc.).

To quantify the post-earthquake residual seismic capacity of reinforced concrete (RC) column members, experimental data for 6 column specimens with flexural, flexural–shear and shear failure modes are used to derive residual seismic capacity of damaged RC column members for specified damage states in this work. Besides of the experiment data, some related researches are also investigated to suggest the reduction factors of strength, stiffness and energy dissipation capacity for damaged RC column members, respectively. According to the damage states of RC columns, their corresponding seismic reduction factors are suggested herein. Taking an RC column with the flexural–shear failure for an example, its reductions factors of strength, stiffness and energy dissipation capacity are 0.5, 0.6 and 0.1, respectively. This work also proposes the seismic performance assessment method for the residual seismic performance of earthquake-damaged RC buildings. In the case study, this work selects one actual earthquake-damaged school building to demonstrate the post-earthquake assessment of seismic performance for a damaged RC building.

Assembly technology using prefabricated reinforced concrete (RC) members can effectively improve the seismic performance of existing masonry buildings. In this study, an existing masonry wall is enhanced by two pieces of prefabricated RC panels bonded on both surfaces of the wall. In order to guarantee the co-action between RC panels and the masonry wall, three techniques are employed, specifically, RC dowelling keys, grouting agent, and post-cast concrete bands. To investigate the interaction and force transmission between the two components, this study builds sophisticated finite element models and conducts nonlinear analyses to simulate the quasi-static cyclic tests. It is demonstrated that the proposed retrofitting technology effectively improves the seismic performance of existing masonry walls. The strength of existing walls increases 3-4 times and the stiffness increases 2-3 times, so that the requirement of current seismic design code is satisfied.

The existing Reinforced Concrete (RC) buildings stock is often characterized by a significant seismic vulnerability, due to the absence of capacity design principles, even in regions with high seismic hazard, such as Italy. Approximately 67% of existing RC buildings in Italy have been designed without considering seismic actions (GLD), resulting in very low transverse reinforcement amount in beams and, particularly, in columns. Additionally, beam-column joints typically totally lack stirrups. Consequently, shear failures under seismic actions are very likely for this pre-code building typology, often limiting their seismic capacity. However, the assessment of shear failures in beams/columns or joints varies significantly from code to code worldwide. The main goal of this work is to quantify the impact of different code-based brittle capacity models on the seismic capacity assessment and retrofit, focusing on GLD Italian pre-1970 RC buildings. This comparative analysis is carried out by first considering three current codes, emphasizing their, even significant, differences: European (EN 1998-3-1. 2005), Italian (D.M. 2018), and American (ASCE SEI/41 2017) standards. Then, shear capacity models prescribed by the current drafts of the next generation of Eurocodes are implemented and compared to the current models. The assessment includes: (i) a parametric comparison among models; (ii) the evaluation of case-study buildings capacity in their as-built condition and after shear strengthening interventions. The latter is performed on 3D “bare” models, due to the lack of practical guidance in most codes on modelling masonry infills.

Two large‐scale, single‐storey, single‐bay reinforced concrete (RC) moment frames, designed as per an outdated seismic code to represent a typical framing detail of a four‐storey building, have been tested under displacement‐controlled quasi‐static loading protocol as per ACI 374.1‐05. The RC frames include a plinth beam with brick infill underneath, a slab monolithically cast with the top beam and provision for applying axial load to the column to simulate real construction scenario. One of the frames has been tested as a bare frame, and the second one has been retrofitted with conventional steel braces designed to undergo in‐plane buckling. The size of the brace has been selected based on the result of a nonlinear time history analysis of representative low‐ to mid‐rise open‐ground storey RC buildings. Post‐installed chemical anchors have been utilized to connect the steel braces to the narrow RC frame members following the outcomes of an experimental investigation by the same authors. Local‐level retrofitting by steel jacketing using adhesives has been designed and utilized on columns and beams to achieve the desired seismic response. The seismic performance of the retrofitted frame has been compared with the bare frame in terms of strength, stiffness, ductility, energy dissipation and hysteretic damping. The tests provide insight into the role of the plinth beam, effect of RC slab on the strong‐column weak‐beam aspect and the achievement of the desirable hinge mechanism through a precise design and detailing of global and local level retrofitting technique.

The seismic vulnerability of reinforced concrete (RC) buildings has prompted structural engineers to incorporate lateral load-resisting systems that enhance structural stability and performance. Among these, shear walls have proven to be highly effective in controlling lateral displacements and increasing energy dissipation. This study investigates the effect of shear walls on the seismic behavior of 3D RC buildings with different heights—10, 20, and 30 stories—through detailed finite element analysis using LUSAS FEA 14.03 software. A total of six models were analyzed: three without shear walls and three with shear walls symmetrically placed around the elevator core. Time-history analysis was conducted using the El Centro 1940 earthquake record over a 10-second interval. Peak displacement in the Y-direction was reduced from 0.1263 m to 0.0571 m in the 10-storey model (54.7% reduction), from 0.4666 m to 0.2669 m in the 20-storey model (42.7% reduction), and from 0.6466 m to 0.3033 m in the 30-storey model (53.1% reduction). Validation against ETABS software showed results within a 1.8–3% margin for displacement and modal frequencies. The Modal analysis further revealed that shear walls significantly influence dynamic characteristics by increasing stiffness and shifting critical mode participation to higher frequencies. For instance, in the 10-storey configuration, mass participation exceeding 90% occurred at Mode 5 without shear walls and at Mode 35 with shear walls. These findings confirm that shear walls substantially improve seismic performance and are essential for RC buildings in earthquake-prone regions

A large number of existing reinforced concrete (RC) buildings have surpassed their anticipated service life and show signs of degradation due to aging; this degradation is a function of the construction practices adopted in the past as well as environmental conditions. This paper discusses seismic fragility and the risk assessment of RC structures, emphasizing the impact of corrosion due to concrete aging and the associated deterioration mechanisms. The literature on this topic is critically reviewed, and a methodology for studying the seismic fragility of deteriorated RC buildings is proposed. As a case study, a four-story RC building designed according to contemporary code provisions is examined. The investigation encompasses the derivation of fragility curves, considering critical parameters such as the corrosion rate, the initiation time, and the cover depth. The proposed approach enables the evaluation and quantification of the impact of corrosion mechanisms on the seismic performance of buildings.