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"Concrete structures"
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The Phenomenon of Cracking in Cement Concretes and Reinforced Concrete Structures: The Mechanism of Cracks Formation, Causes of Their Initiation, Types and Places of Occurrence, and Methods of Detection—A Review
Cracks and cavities belong to two basic forms of damage to the concrete structure, which may reduce the load-bearing capacity and tightness of the structure and lead to failures and catastrophes in construction structures. Excessive and uncontrolled cracking of the structural element may cause both corrosion and weakening of the adhesion of the reinforcement present in it. Moreover, cracking in the structure negatively affects its aesthetics and in extreme cases may cause discomfort to people staying in such a building. Therefore, the following article provides an in-depth review of issues related to the formation and development of damage and cracking in the structure of concrete composites. It focuses on the causes of crack initiation and characterizes their basic types. An overview of the most commonly used methods for detecting and analyzing the shape of microcracks and diagnosing the trajectory of their propagation is also presented. The types of cracks occurring in concrete composites can be divided according to eight specific criteria. In reinforced concrete elements, macrocracks depend on the type of prevailing loads, whereas microcracks are correlated with their specific case. The analyses conducted show that microcracks are usually rectilinear in shape in tensioned elements; in shear elements there are wing microcracks with straight wings; and torsional stresses cause changes in wing microcrack morphology in that the tips of the wings are twisted. It should be noted that the subject matter of microcracks and cracks in concrete and structures made of this material is important in many respects as it concerns, in a holistic approach, the durability of buildings, the safety of people staying in the buildings, and costs related to possible repairs to damaged structural elements. Therefore, this problem should be further investigated in the field of evaluation of the cracking and fracture processes, both in concrete composites and reinforced concrete structures.
Journal Article
Destructive impact of successive high magnitude earthquakes occurred in Türkiye’s Kahramanmaraş on February 6, 2023
Two successive earthquakes with moment magnitudes of M
w
= 7.7 (focal depth = 8.6 km) and M
w
= 7.6 (focal depth = 7 km) occurred approximately within 9 h on February 6, 2023, in Türkiye, respectively. The epicenters were the Pazarcık and Elbistan districts of Kahramanmaraş. Both earthquakes occurred in the East Anatolian Fault Zone, one of Türkiye’s two major active fault systems. Between these two severe earthquakes, there was one more big aftershock with a moment magnitude of 6.6, the epicenter of which was in the Nurdağı District of Gaziantep. Then, on February 20, 2023, another aftershock earthquake with a magnitude of M
w
= 6.4 occurred in Yayladağı district of Hatay. As a result of the earthquakes, severe damage occurred in several provinces and districts with a population of around 15 million, and more than 50,000 people have lost their lives. This study presents on-site geotechnical and structural investigations by a team of researchers after the Kahramanmaraş earthquakes. It summarizes the performance of the building environments as a result of on-site assessments, taking into account observed structural damage, local site conditions, and strong ground motion data. The possible causes of the observed damage are addressed in detail. These earthquakes once again revealed the common deficiencies of existing reinforced concrete structures in Türkiye, such as poor material quality, poor workmanship, unsuitability of reinforcement detailing, and inadequate earthquake-resistant construction techniques. Precast concrete and masonry structures in the region were also severely damaged during the earthquakes due to insufficient engineering service, poor materials, deficiencies during construction, etc.
Journal Article
Using Ground Penetrating Radar Methods to Investigate Reinforced Concrete Structures
This paper provides an overview of the existing literature on the subject of ground penetrating radar (GPR) methods for the investigation of reinforced concrete structures. An overview of the use of concrete and reinforced concrete in civil engineering infrastructures is given. A review of the main destructive and non-destructive testing methods in the field is presented, and an increase in the use of GPR to reinforced concrete structures is highlighted. It was also observed that research in some application areas has been predominantly or exclusively carried out at a laboratory scale, and that similarly, other more application-oriented research has been developed only on real-life structures. The effectiveness of GPR in these areas is demonstrated. Furthermore, a case study is presented on a new methodological and data processing approach for the assessment of reinforced concrete structures using a high-frequency dual-polarised antenna system. Results have proven the advantages of using the proposed methodology and GPR system in order to improve the detectability of rebars, including secondary bottom lines of reinforcement. The horizontal polarisation was proven to be more stable compared to the vertical. Finally, it has been demonstrated that a more accurate location of the rebars in a high-density grid mesh arrangement can be obtained by means of data migration processing with a scan spacing of 5 cm and wave velocity information through the use of the hyperbola fitting method from at least 30% of the targets.
Journal Article
Design deficiencies, failure modes and recommendations for strengthening in reinforced concrete structures exposed to the February 6, 2023 Kahramanmaraş Earthquakes (Mw 7.7 and Mw 7.6)
After two major earthquakes centred in Kahramanmaraş on February 6, 2023, in Türkiye, there was significant destruction of the building stock. More than fifty thousand people lost their lives, and many people lost their comfort of life even though they were rescued from the wreckage. Researchers have emphasized that this catastrophic consequence is generally caused by design and production errors and low material quality in almost all building types, especially reinforced concrete, steel, masonry, and prefabricated structures. Within the scope of this study, damage patterns and the design flaws of reinforced concrete structures in Malatya, which is one of the provinces affected by the Kahramanmaraş earthquakes, were examined via a field study. During the fieldwork, it was determined that inadequate longitudinal reinforcement and stirrup reinforcement, in-depth reinforcement, and concrete quality, design errors in the column‒beam junction area, ignoring the structure‒soil interactions, short columns, torsional irregularity, and soft stories were the main factors that led reinforced concrete buildings to be heavily damaged or collapse. After the root causes of damage to reinforced concrete structures were examined, the measures and applications that should be taken to ensure that reinforced concrete structures can maintain their services in the event of earthquakes that are likely to occur in the future was discussed.
Journal Article
Mechanical behaviors of 3D printed lightweight concrete structure with hollow section
A practical revolution in construction could be realized by combining the potential of 3D concrete printing with lightweight cementitious materials to fabricate adeptly hollow structures. In this study, five concrete mixtures with different replacement rates of lightweight ceramsite sand to silica sand are prepared for extrusion-based 3D printability evaluation. To reduce the water absorption induced shrinkage and micro-cracks, the ceramsite sands were coated with polyvinyl alcohol. An optimized cementitious material was identified by harmonizing the fresh properties to the continuous printing process. Cubic and beam elements with four different types of interior hollow structures were designed and 3D printed based on the optimized lightweight mixture. The interior structures include cellular-shaped structure, truss-like structure, lattice-shaped structure with a square topology, as well as gridding shaped structure with triangle topology. The mechanical capacities of the printed samples were measured and evaluated by compressive tests for the cubic samples and four-points flexural bending tests for the beam specimens. Basing on the results, the rectangular lattice hollow structure demonstrates the best mechanical resistance to compression and the truss-shaped prism structure ensues the highest flexural properties. The stress distribution and failure process were also explored through discrete element method.
Journal Article
Finite Element Analysis of the Influence of End Grouting Defects in Grouted Sleeve on the Structural Performance of Precast Reinforced Concrete Columns
Precast concrete structures have gained popularity due to their advantages. However, the seismic performance of their connection joints remains an area of ongoing research and improvement. Grouted Sleeve Connection (GSC) offers a solution for connecting reinforcements in precast components, but their vulnerability to internal defects, such as construction errors and material variability, can significantly impact performance. This article presents a finite element analysis (FEA) to evaluate the impact of internal grouting defects in GSC on the structural performance of precast reinforced concrete columns. Four finite element models representing GSC with varying degrees of defects were used to investigate the effects on mechanical properties, including bearing capacity, stress-deformation behavior, and stiffness degradation. The study highlights the significant impact of internal grouting defects on the mechanical performance of GSC, with findings indicating a decrease in stiffness, increased plastic deformation, and reduced energy dissipation as the proportion of internal defects rises. The analysis reveals that the internal defects in GSC act as stress concentration points, leading to early crack formation and accelerated damage under cyclic loading. By improving construction quality and reducing the prevalence of grouting defects, the adverse effects on the performance of GSC can be mitigated. Compared to defect-free specimens, those with defects of 30% exhibited a 31.23% reduction in horizontal bearing capacity, highlighting the importance of minimizing defects in practical engineering applications.
Journal Article
24 January 2020 Sivrice-Elazığ, Turkey earthquake: geotechnical evaluation and performance of structures
The January 24, 2020 Sivrice-Elazığ (Mw = 6.8) earthquake occurred on the East Anatolian Fault zone. Main shock of this earthquake was occurred 20:55 at local time. The Peak Ground Acceleration was equal to 0.3 g at the epicenter (Sivrice district) of the earthquake. Even though the main shock was moderate, its effects on the structures were rather serious. The main shock caused significant damage and resulted in 41 casualties. 1540 buildings were damaged moderately, while 8519 buildings were damaged heavily and collapsed. This main shock effected four cities surrounded the epicenter due to its shallow earthquakes. The purpose of this paper is to summarize past and present seismic characteristics of the earthquake region. In addition, the aim of this paper is to summarize the seismotectonic of the region, the general characteristics of the earthquake and more specifically to report on the structural damage, and structural damage caused by the earthquake, observed during the site investigation. The damages were classified for reinforced concrete structures, masonry dwellings and non-residential structures. All distinguished earthquake induced failures and damages were discussed. Moreover, lessons learned were presented in this study.
Journal Article
Modelling of reinforced concrete structures and composite structures with concrete strength degradation taken into consideration
Because of the properties of the material (concrete), computer simulations in the field of reinforced concrete structures are pose a challenge. As opposed to steel, concrete when subjected to compression exhibits nonlinearity right from the start. Moreover, it much quicker undergoes degradation under tension. All this poses difficulties for numerical analyses. Parameters needed to correctly model concrete under compound stress are described in this paper. The parameters are illustrated using the Concrete Damaged Plasticity model included in the ABAQUS software.
Journal Article