Advances in Reinforced Concrete Integrity and Failure

Abstract

The chapter provides an overview of the advances made in the field of structural integrity and failure with a specific focus on reinforced concrete structures. It begins with a brief history of reinforced concrete and covers its structural properties and characteristics. It then delves into the mechanics of reinforced concrete structures, including the various forces that act on them, and the design and construction of these structures. It delves into the basic mechanics, stressing the concrete’s performance under loading and its inherent material properties. The focus then shifts to the design principles applied to reinforced concrete structures, and the consideration of critical structural elements like beams, slabs, columns, and foundations. Various advances in reinforced concrete technology, including High-Performance Concrete, Fiber-Reinforced Concrete, Self-Compacting Concrete, and the use of nanomaterials, are explored. The chapter provides insights into methods for the analysis and assessment of reinforced concrete structures, discussing non-destructive testing methods, structural health monitoring, and finite element analysis. It examines the causes of failure, including material quality, overloading, design flaws, environmental factors, and construction errors. Several case studies of notable building failures are highlighted, emphasizing lessons learned and the importance of safe construction practices. The chapter concludes by looking at future directions in reinforced concrete, encompassing advanced materials, digital technology, sustainable construction practices, and resilience-based design.

1. Introduction

1.1 Brief overview of reinforced concrete

Reinforced concrete is a composite material where the concrete, possessing high compressive strength but relatively weak in tension, is combined with materials that excel in withstanding tensile stress. The primary objective of such reinforcement is to compensate for concrete’s inherent weakness in tension. When tensile stresses exceed the tensile strength of the concrete, cracks occur. If these stresses persist, the cracks can propagate, potentially leading to the failure of the structure.

The material of choice for reinforcement has been and remains to be steel. The high tensile strength of steel and its exceptional bond with concrete are the main reasons for its widespread use. When encased in concrete, the steel reinforcement acts to counteract tensile stresses, while the concrete resists compressive stresses. This synergetic effect of two materials working together to resist different kinds of stresses is one of the key reasons behind the widespread use of reinforced concrete in the construction industry [1].

Over the years, reinforced concrete has proven to be a versatile, durable, and cost-effective construction material. It is utilized in a wide array of structures including buildings of all types and sizes, bridges, dams, tunnels, roads, and many more. Concrete is the most consumed construction material, and twice as much concrete is used in construction as all other building materials combined [2].

1.2 Importance of reinforced concrete in structural integrity

Structural integrity is a key concept in the field of civil engineering, referring to the ability of a structure to withstand its intended load without experiencing distress or failure. Maintaining structural integrity is a primary concern in the design, construction, and maintenance phases of a structure.

The nature of reinforced concrete—being a composite material that combines the compressive strength of concrete with the tensile strength of the reinforcement—plays a critical role in ensuring structural integrity. The result is a material that exhibits high robustness and resilience under a variety of load conditions, environmental influences, and potential man-made and natural disasters [3].

Structural integrity is particularly critical for structures exposed to dynamic loads and changing environmental conditions. This includes structures like bridges, which must resist the dynamic loads of passing vehicles; skyscrapers, which must withstand wind loads; and coastal structures, which must resist the destructive forces of waves and salt corrosion. The combination of concrete and steel reinforcement creates a material that can effectively resist these and other forces, thereby maintaining the structural integrity of these constructions.

Moreover, the importance of structural integrity extends beyond the avoidance of catastrophic structural failures. It also influences other factors such as the longevity of structures, maintenance costs, and even esthetic appeal. For instance, cracks in concrete not only compromise its structural integrity, but can also accelerate the ingress of harmful substances like water, chloride, and carbon dioxide, leading to further deterioration and higher maintenance costs. Similarly, visible cracks and deflections can detract from the esthetic appeal of a structure, which can be especially problematic for architectural or heritage structures [4, 5].

In this context, the role of reinforced concrete in maintaining structural integrity becomes even more prominent. Advancements in reinforced materials, design methods, and construction techniques are reflected with parallel advancements in the design, assessments, and quality assurance of structural integrity [6, 7, 8].

2. Historical perspective

2.1 Evolution of reinforced concrete

Reinforced concrete’s rich history can be traced back to the mid-19th century. The first widespread use of concrete reinforcement is often credited to the French industrialist François Coignet in 1854. Coignet recognized the potential of embedding iron bars into concrete to create a composite material that capitalized on the strengths of both components [9].

Joseph Monier, a French gardener, took this idea a step further. Looking for a way to create more durable flowerpots, Monier discovered that reinforcing the concrete used to form the pots enhanced their strength and durability. Recognizing the broader implications of his innovation, Monier patented the use of reinforced concrete in 1867 [10].

The evolution of reinforced concrete continued throughout the late 19th and early 20th century, driven by the pioneering work of many visionaries. François Hennebique, a self-taught French engineer and builder, obtained a patent for his groundbreaking system of reinforced-concrete construction in 1892. This system uniquely merged different components of construction, like the column and beam, into a single, unified piece. The Hennebique system was instrumental in paving the way for modern methods of reinforced-concrete construction, being one of its earliest iterations. He developed the technique of systematic reinforcement, optimizing the placement and orientation of the reinforcement within the concrete [11].

Another notable figure, Swiss engineer Robert Maillart, pushed the esthetic and structural possibilities of reinforced concrete. Maillart is particularly known for his revolutionary bridge designs, which combined structural efficiency with artistic elegance [12, 13].

2.2 Key milestones and innovations

The 20th century marked numerous innovations that revolutionized the use and applications of reinforced concrete. A key breakthrough was the development of pre-stressed concrete by French engineer Eugène Freyssinet in the 1920s. By pre-tensioning the steel reinforcement before pouring the concrete, Freyssinet found that it was possible to create long-span concrete structures with reduced depth, opening new possibilities for the design of bridges, roofs, and other large-span structures [14, 15]. Pre-stressed concrete continued its development to play an important role in various sectors of modern construction [16].

The latter part of the 20th century saw the introduction of advanced admixtures that further improved the properties of concrete. By modifying the composition of concrete, these admixtures made it more durable, workable, and adaptable to various applications [17, 18].

Another significant development was the introduction of fiber-reinforced polymers (FRP) as an alternative to traditional steel reinforcement. Unlike steel, FRP does not corrode, making it particularly suited for use in harsh environments such as marine structures or chemical plants [19, 20].

The 21st century continues to witness numerous advancements in the field of reinforced concrete. Innovations in high-performance concrete, ultra-high-performance concrete [21, 22], self-healing concrete [23], and the use of nanomaterials are pushing the boundaries of what is achievable with this versatile material [24].

As we move forward, the ongoing advancements in the field of reinforced concrete promise to continue transforming our built environment, enhancing its safety, efficiency, and sustainability. The following sections will delve into the fundamental principles, material properties, design considerations, case studies, and recent advancements in the field of reinforced concrete, thereby providing a comprehensive understanding of its critical role in ensuring structural integrity and preventing failure.

3. Fundamental principles of reinforced concrete

3.1 Basic mechanics

The study of reinforced concrete requires a clear understanding of its basic mechanics. This often involves delving into the stress–strain relationships of the materials involved, typically concrete and steel, which display starkly different mechanical behaviors.

3.1.1 Stress: strain characteristics

Stress–strain curves, or relationships, depict how a particular material responds to applied stress. Stress denotes the force exerted per unit area, while strain represents the resulting deformation. Understanding these curves is pivotal to manipulating and predicting a material’s performance under various loading conditions [1].

Concrete, as a material, displays exceptional strength when subjected to compressive loads, but it lacks tensile strength. Consequently, it exhibits a nonlinear stress–strain relationship (Figure 1). Under compressive loading, concrete experiences peak stress at its maximum compressive strength. Any additional stress results in a decrease, signaling material failure.

Figure 1.

Typical stress–strain curve for concrete.

The opposite is true for steel, a material commonly used for reinforcement due to its strong tensile and compressive strengths [2].

The stress–strain relationship for steel is linear up to the yield strength, the point at which steel undergoes plastic deformation. Beyond the yield strength, steel can experience significant strain without an accompanying increase in stress. This key difference underlines the complementarity of concrete and steel in reinforced concrete, leading to its wide usage in construction (see Figure 2).

Figure 2.

Typical stress–strain curve for steel reinforcement.

3.1.2 Flexure, shear, and torsion

Reinforced concrete structures are subjected to a variety of stresses, including flexural, shear, and torsional stresses. Flexural stress is generated when a member is subjected to bending, inducing tension on one side and compression on the other. Shear stress, in contrast, is caused by forces acting parallel to the cross-sectional area, leading to a sliding failure of the material. Torsional stress occurs due to twisting forces [2].

The design of reinforced concrete takes into account these diverse stress types, necessitating the calculation and precise arrangement of reinforcement to counteract these forces effectively.

3.2 Behavior under loading

Understanding the behavior of reinforced concrete under loading is crucial to both its design and analysis. This behavior can be categorized into three main domains: cracking, deflection, and load capacity.

3.2.1 Cracking

Cracking is a fundamental characteristic of concrete, resulting from its brittleness and low tensile strength. Initial cracks often form due to shrinkage as the concrete cures, with further cracks appearing due to applied loads. The reinforcement in reinforced concrete structures serves to tightly bind these cracks, preventing sudden and brittle failure.

The thorough study of cracking patterns and their causative factors can inform construction practices, leading to better control of cracking and the development of more robust and durable structures. This requires a comprehensive understanding of the material properties of both concrete and the reinforcement, along with the environmental and loading conditions the structure is expected to encounter [2]. Correct cracking assessment may require evaluation and consideration of multiple causes and has led to the utilization of Artificial Intelligence and development of expert systems for the crack assessment and recommendations of proper structural integrity solutions for distressed reinforced concrete structures [25, 26].

3.2.2 Deflection

Deflection refers to the displacement of a structural element under a load. It is a critical aspect to monitor, as excessive deflection can lead to a host of serviceability issues. These can range from esthetic concerns, such as cracking in finishes, to functional issues, like ponding on roofs and unpleasant vibrations.

The deflection of a reinforced concrete member depends on its geometry, the properties of the materials, and the nature of the load applied. Careful consideration of these factors during the design process can help to manage deflection and avoid potential problems down the line [1].

3.2.3 Load capacity

Load capacity is the maximum load that a reinforced concrete member can sustain without experiencing failure. It is determined by considering the section’s geometry, the properties of the materials, and the nature of the load applied. In the design of reinforced concrete structures, the load capacity must be calculated for various limit states to ensure that it is never exceeded during the structure’s intended service life [2].

Accurately calculating load capacity requires a thorough understanding of reinforced concrete behavior under different loading and environmental conditions. Additionally, understanding failure modes and recognizing the signs of imminent failure can greatly aid in maintaining the structural integrity of a reinforced concrete structure.

The fundamental principles of reinforced concrete, as outlined in this section, form the basis for understanding its material properties, design considerations, and innovative advancements in the field. The following sections will delve into these topics, providing a comprehensive understanding of reinforced concrete’s role in ensuring structural integrity and preventing failure.

4. Material properties

4.1 Concrete

4.1.1 Composition and strength

Concrete is a composite material that is composed of coarse aggregate (usually gravel or crushed stone), fine aggregate (often sand), and a binder (cement), all of which are mixed with water. The relative proportions of these components play a significant role in determining the final properties of the concrete.

The strength of concrete is primarily a function of the water-to-cement (w/c) ratio, the type of cement used, and the aggregates used. A lower w/c ratio tends to result in a concrete mixture that possesses higher strength but lower workability. Conversely, a high w/c ratio increases the workability of the concrete but at the expense of reducing its strength.

Several other factors, such as the curing conditions and the presence of admixtures, can also influence the strength of concrete. These factors can be controlled and adjusted to produce concrete with specific desired properties.

4.1.2 Durability issues

Durability is a measure of the ability of concrete to resist various forms of deterioration. This could include damage from freeze–thaw cycles, chemical attacks, and abrasion. The durability of concrete is influenced by several factors, including the w/c ratio, the type and quantity of cement used, the type and size of aggregates used, and the use of certain admixtures.

One of the most significant durability issues for reinforced concrete is the corrosion of reinforcing steel. In highly alkaline conditions, concrete can passivate the steel, protecting it from corrosion. However, if the alkalinity is reduced due to processes such as carbonation, or if chloride ions penetrate the concrete and reach the steel, corrosion can occur.

4.2 Reinforcement

4.2.1 Steel reinforcing bars

Steel reinforcing bars, commonly referred to as rebar, are the most frequently used type of reinforcement in concrete. Rebar is available in several grades, with yield strengths typically ranging from 40,000 psi (275 MPa) to 100,000 psi (690 MPa) [2]. To enhance bonding with the concrete, the surface of the rebar is often deformed.

4.2.2 Fiber-reinforced polymers (FRP)

Fiber-Reinforced Polymers (FRP) have emerged as an alternative to steel rebar, especially in environments where corrosion is a significant concern. FRP bars are composed of continuous fibers (such as glass, carbon, or aramid) embedded in a polymer matrix. They are non-corrosive, lightweight, and have a high tensile strength. However, they are also more brittle than steel and have a lower modulus of elasticity [27]. Moreover, researchers have used basalt FRP bars and investigated their bond characteristics with concrete [28].

In the upcoming sections, we will delve deeper into the design considerations for reinforced concrete structures and explore the latest advancements in the field.

5. Design of reinforced concrete structures

5.1 Design approaches

5.1.1 Limit state design

Limit state design is a structured approach used in structural engineering to ensure the safety and functionality of structures under all conceivable conditions. The concept of limit state design revolves around two primary types of limit states: ultimate limit states (ULS) and serviceability limit states (SLS) [29, 30].

The ULS pertains to conditions that would result in the failure or collapse of the structure, such as yielding, buckling, or fracture. These situations usually involve severe loading conditions or structural deterioration that exceeds the structure’s load-bearing capacity. The intent of designing for ULS is to ensure the structure can resist severe or extreme loads without collapse, thereby providing a high level of safety.

The SLS, conversely, relates to conditions that do not cause a structural collapse but can negatively affect the structure’s appearance, durability, and usability. This can include conditions like excessive deflection, vibration, and cracking. While these situations may not immediately threaten the structure’s safety, they can diminish the structure’s serviceability and lifespan.

The overarching aim of limit state design is to ensure that the structure will not reach any of these limit states during its expected service life. This is achieved by applying appropriate safety factors to the loads and material strengths, considering potential variations and uncertainties.

5.1.2 Performance-based design

The performance-based design represents a more contemporary and sophisticated approach to structural design. Instead of strictly adhering to prescriptive code requirements, performance-based design involves specifying the desired performance levels of a structure under different load scenarios [31].

This approach requires a more nuanced understanding of the structure’s behavior and often involves advanced analysis techniques. Despite its complexity, performance-based design can yield more efficient and optimized structures by allowing more flexibility in the design process and better alignment of the design with the intended function and performance of the structure [32].

5.2 Basic structural elements

5.2.1 Beams and slabs

Beams and slabs are integral horizontal structural elements, primarily designed to resist bending. The role of the reinforcement in beams and slabs is to strategically counteract the tensile stresses induced by bending. Meanwhile, the concrete component resists the compressive stresses.

5.2.2 Columns

Columns, being vertical structural elements, are primarily designed to resist axial compression. The design of columns involves ensuring that the column can safely carry the applied load without buckling or crushing. Additionally, columns often need to resist bending due to eccentric loading or lateral forces, which requires additional reinforcement.

5.2.3 Foundations

The role of foundations is to transfer the loads from the structure to the ground effectively. The design of foundations involves assessing the ground conditions to ensure it can safely support the imposed loads without causing excessive settlement or failure. Reinforced concrete is commonly used for various types of foundations, including spread footings, strip footings, and pile caps.

In the subsequent sections, we will explore the recent advancements in the field of reinforced concrete design and discuss the various methods employed for assessing and improving the structural integrity and potential failure of reinforced concrete structures.

6. Advances in reinforced concrete

6.1 High-performance concrete and ultra-high-performance concrete

High-Performance Concrete (HPC) is an advanced type of concrete that has been meticulously engineered to possess superior properties such as exceptional strength, extended durability, or improved workability. The attributes of HPC are typically achieved through a low water-to-cement ratio in conjunction with the inclusion of admixtures and supplementary cementitious materials (SCMs) like fly ash, silica fume, or slag [33, 34].

HPC often exceeds a compressive strength of 6000 psi (41 MPa), significantly higher than the average 3000 psi (20 MPa) for regular concrete. This high strength allows for the design and construction of slenderer and efficient structures. Moreover, HPC’s enhanced durability can contribute to a longer service life and potentially lead to reduced maintenance costs [34].

Ultra-High-Performance Concrete (UHPC) is characterized by its significantly superior strength and durability compared to traditional concrete, UHPC typically surpasses a compressive strength of 21,000 psi (145 MPa). This level of strength makes it suitable for high-stress applications and for constructing structures that are highly resistant to environmental and mechanical stresses [35].

6.2 Fiber-reinforced concrete

Fiber-Reinforced Concrete (FRC) is a unique form of concrete where small fibers are incorporated into the concrete mix to enhance its properties. These fibers can be derived from a variety of materials, including steel, glass, synthetic materials, or natural substances. The fibers serve to enhance the concrete’s tensile strength, ductility, and resistance to cracking and shrinkage. Due to these improved characteristics, FRC has found applications in several areas, including overlays, precast elements, and structures exposed to dynamic or impact loads [35].

6.3 Self-compacting concrete

Self-Compacting Concrete (SCC) is a distinctive type of concrete that possesses the ability to flow and consolidate under its own weight, thereby eliminating the need for mechanical vibration. This property makes SCC especially beneficial for complex forms or densely reinforced structures. The key to achieving self-compacting properties lies in a high content of fine materials and the use of high-range water reducers, commonly known as superplasticizers [36].

6.4 Use of nanomaterials

The potential of nanomaterials in revolutionizing the field of concrete technology has been an exciting recent development. Research has indicated that nanomaterials like nano-silica, nano-titanium oxide, and carbon nanotubes can significantly enhance the properties of concrete. These improvements can span across concrete’s strength, durability, and even grant it self-cleaning properties [37]. However, the application of nanomaterials in concrete is still in its nascent stages. Further research is required to address challenges related to cost, optimal dispersion, and health and safety considerations [38].

6.5 Engineered cementitious composites

Engineered Cementitious Composites (ECC), also known as “bendable concrete,” ECCs are specifically engineered to exhibit strain-hardening and multiple cracking behaviors under tensile stress, unlike traditional concrete which is brittle and prone to cracking. These composites incorporate a high volume of fibers, generally polymer-based, to enhance the ductility and durability of the material. This advanced composite material can significantly reduce maintenance costs and extend the service life of structures, proving to be a promising solution for sustainable infrastructure development [39].

6.6 Eco-concrete

As sustainability becomes a crucial aspect of construction, Eco-Concrete has emerged as a significant advancement. Eco-Concrete refers to any concrete that utilizes recycled aggregate, recycled or waste materials as part or all of its constituents, reducing the consumption of natural resources and CO2 emissions associated with cement production. Examples include the use of fly ash slag [40, 41, 42], recycled concrete aggregates [43, 44], reusing waste shredded tires [45], and waste glass. In addition to being environmentally friendly, research has shown that some forms of Eco-Concrete can also match or even exceed the performance of traditional concrete in terms of strength and durability [46, 47].

6.7 3D printed concrete

3D Printed Concrete has emerged as a radical advancement in the field of reinforced concrete, bringing about a revolution in the construction industry. This technology utilizes robotic arms and extrusion techniques to deposit layers of specially formulated concrete mix, enabling the creation of complex geometric forms that are difficult or even impossible to achieve with traditional construction methods. 3D-printed concrete can offer significant benefits including cost reduction, speed of construction, design flexibility, and the reduction of construction waste [48].

6.8 Bacterial concrete

Bacterial Concrete, also known as Bio-Concrete, is an innovative solution to the issue of concrete durability. Certain types of bacteria, when introduced into the concrete mix, can induce calcium carbonate precipitation, which heals the micro-cracks that form in concrete over time. This self-healing property can significantly improve the durability and lifespan of concrete structures, reduce maintenance costs, and contribute to sustainability in the construction industry. Challenges such as ensuring long-term bacterial survival and minimizing cost remain to be addressed [23].

6.9 Structural health monitoring in concrete structures

Structural Health Monitoring (SHM) technologies are increasingly being integrated into reinforced concrete structures to assess their integrity and predict their performance over time. These technologies involve the use of sensors and data analysis algorithms to detect anomalies and deterioration in structures. With advancements in the Internet of Things (IoT) and machine learning, SHM has the potential to revolutionize the maintenance and inspection process of concrete structures, leading to significant savings in terms of time and costs, as well as enhancing overall safety [38].

6.10 Smart concrete

Smart Concrete is a type of concrete embedded with sensors capable of sensing changes in the material or surrounding conditions. These sensors can detect stresses, strains, temperature changes, moisture content, and even chemical changes, which can be crucial for real-time monitoring and early detection of potential failures. This advancement could pave the way for the development of intelligent infrastructure with greatly improved safety, durability, and maintenance efficiency [49].

7. Analysis and assessment of reinforced concrete structures

7.1 Non-destructive testing methods

Non-Destructive Testing (NDT) methods are crucial for assessing the health and integrity of structures without causing any damage to them. These techniques have evolved significantly over time and have been especially useful for inspecting concrete structures. NDT methods provide invaluable data regarding the condition of the structure, thereby helping identify potential issues before they escalate into serious problems.

Several NDT methods are in regular use, each having unique applications and capabilities. These include visual inspection, the use of a rebound hammer, ultrasonic pulse velocity (UPV), ground penetrating radar (GPR), and core sampling, among others.

7.1.1 Visual inspection

It is the most straightforward method of NDT, relying on the examiner’s expertise to detect anomalies such as cracking, spalling, or signs of corrosion. This method is cost-effective and quick but can only detect superficial defects.

7.1.2 Rebound hammers

In a rebound hammer, a mass is loaded over a spring and can be moved axially along a tubular housing which imparts a defined amount of energy (Figure 3). As the plunger is pressed against the surface to be examined, the spring is extended from a fixed position. The mass rebounds, upon release, from the plunger which remains in contact with the concrete surface, the distance by which the mass rebounds is measured and presented as a percentage of the initial extension (while pressing the hammer) of the spring. This percentage is known as rebound number. They are widely used due to their simplicity and portability. They measure the surface hardness of concrete, which can be correlated to its compressive strength. However, they only provide a qualitative assessment and can be influenced by surface condition and moisture content (Figure 3) [50].

Figure 3.

Rebound hammer for non-destructive testing of compressive strength [50].

7.1.3 Ultrasonic pulse velocity (UPV) tests

They involve sending an ultrasonic wave through a concrete element and measuring the time it takes to travel. This information can help determine the quality of the concrete and detect internal flaws. While effective, this method requires access to both sides of the concrete element (Figure 4) [51].

Figure 4.

Ultrasonic pulse velocity tests [51].

7.1.4 Ground penetrating radar (GPR) tests

They involve emitting electromagnetic waves into the concrete and capturing the reflected signals. This provides details about the location and depth of reinforcement bars, post-tension cables, and the presence of voids or delamination. Although GPR is a versatile tool, it requires skilled interpretation and can sometimes be hampered by interference from metallic objects.

This non-destructive testing (NDT) technique is highly efficient in the detection of metallic objects embedded in concrete or other non-conductive materials because of the high reflectivity of metals and the contrast between the electromagnetic properties of metals and concrete.

The application of GPR to the detection of corrosion and damage as a consequence of corrosion has demonstrated its effectiveness in the detection of corrosion by measuring qualitative changes in the amplitude, even though variation in depth could affect highly the results [52, 53].

7.1.5 Core sampling

It involves extracting small cylindrical samples from the structure for laboratory testing. Although it is the most reliable method for determining concrete’s properties, it causes minor damage to the structure. Therefore, it is typically used when other NDT methods indicate potential issues that need further investigation (Figure 5).

Figure 5.

Ground penetrating radar for non-destructive testing of compressive strength [53].

In practice, a combination of different NDT methods is often employed to gain a more comprehensive understanding of a structure’s health. The choice of methods largely depends on the specific objectives of the inspection and the complexities of the structure itself. By providing vital data about factors like compressive strength, depth of cover, location of reinforcement, and the presence of defects or signs of deterioration, NDT methods play a crucial role in ensuring the longevity and safety of our concrete structures.

7.2 Structural health monitoring

Structural Health Monitoring (SHM) is a proactive approach that uses sensors to consistently monitor a structure’s condition and performance over time. These sensors can measure a wide range of parameters, including strain, temperature, vibration, and corrosion rate, among others. The data gathered can be thoroughly analyzed to detect any changes or irregularities that may suggest an issue [38].

SHM has the advantage of providing early warnings of potential issues, thereby enabling timely maintenance or repair. As a result, the service life of the structure can be increased, and lifecycle costs can be reduced [54, 55].

7.3 Finite element analysis

Finite Element Analysis (FEA) is a powerful computer-based method used to predict how a structure will respond to various loads and conditions. FEA involves the division of the structure into small elements and then solving the governing equations for each element. The results are then combined to obtain the overall response of the structure [56, 57].

In the context of reinforced concrete structures, FEA can be used to analyze the complex interactions between the concrete and the reinforcement. This includes the nonlinear behavior of the materials, the bond between the concrete and the reinforcement, the cracking of the concrete, and the yielding of the reinforcement. By accurately modeling these phenomena, FEA can provide valuable insights into the behavior and performance of reinforced concrete structures under various load scenarios, including both service loads and extreme events.

8. Structural loss of integrity and failure of reinforced concrete structures

The main causes of structural integrity and failure in reinforced concrete structures can be grouped into various categories.

The following is what is believed to be the list of the 10 most important categories:

Material Quality and Workmanship: This relates to the quality of materials used in the construction and the skill with which those materials are employed. Poor quality concrete, for example, may have low strength or be prone to shrinkage, which can result in cracks. Similarly, low-quality or poorly placed reinforcement can lead to inadequate resistance to the applied forces, leading to premature failure.

Load and Overloading: This includes factors like dead load (weight of the structure itself), live load (weight of objects and occupants), snow load, wind load, and earthquake load. Overloading beyond the design load can lead to structural failure.

Design Flaws: If the structure has been designed without properly accounting for all loads or has been designed without enough redundancy, it can be susceptible to failure. This includes neglecting to design for shear forces or bending moments, misjudging the weight of materials or the potential live loads, or neglecting potential environmental effects.

Environmental Factors: This includes the impact of weather conditions, temperature changes, moisture (leading to corrosion of reinforcements or freeze–thaw cycles), chemical attacks (such as from chlorides, sulfates, etc.), and seismic activity.

Fatigue and Wear: This occurs due to repetitive loading over time, which can weaken the structure. Even if each individual load is within the design limit, the repetitive nature of the load can lead to fatigue failure.

Corrosion of Reinforcing Steel: This is one of the most common causes of deterioration in reinforced concrete structures. It can be caused by exposure to elements like water and oxygen, leading to the formation of rust. Corrosion expands the volume of the steel, which can cause concrete to crack and spall.

Construction Errors: These are mistakes or inaccuracies made during the construction phase, such as incorrect placement of reinforcement, improper mixing or pouring of concrete, or inadequate curing, which can lead to premature failure.

Deflection and Deformation: Long-term deformation (creep) and short-term deformation (immediate deflection) can lead to serviceability issues, such as cracking or excessive movement.

Foundation Failure: This occurs when the soil beneath the structure is unable to adequately support the load of the structure, leading to settlement, tilting, or even collapse of the structure.

Progressive collapse: It also known as disproportionate collapse, refers to the phenomenon where a localized failure of a primary structural component leads to the collapse of adjoining members which, in turn, leads to additional collapse. Hence, the total damage is disproportionate to the original cause. A primary scenario that can cause progressive collapse in reinforced concrete structures is the sudden loss of a critical load-bearing element, such as a column or a key load-bearing wall. This can be due to extreme events such as explosions, fires, earthquakes, or even design and construction errors. Progressive collapse is particularly dangerous because it can lead to widespread structural damage and loss of life, even from relatively minor initial failures. For this reason, modern design codes often require that buildings be designed to mitigate the risk of progressive collapse [58, 59].

Each of these cases can be mitigated through proper design, high-quality construction methods, regular maintenance, and the use of appropriate materials.

9. Case studies: reinforced concrete building failures

Understanding the failures of the past is crucial for improving the design and construction practices of the future. This section presents several detailed case studies of some notable building failures involving reinforced concrete structures.

9.1 Failure of the L’Ambiance plaza collapse, USA, 1987

The L’Ambiance Plaza was a 16-story residential project under construction in Bridgeport, Connecticut, when it collapsed in April 1987. The collapse resulted in the death of 28 construction workers, making it one of the worst disasters in modern U.S. construction history. The construction method employed was lift-slab, wherein the concrete slabs are cast on the ground and then lifted and placed on top of the columns. The subsequent investigation concluded that the collapse was due to the premature removal of the lifting apparatus before the slabs were adequately secured [58, 59]. The lessons learned from the L’Ambiance Plaza collapse led to increased scrutiny of the lift-slab construction method (Figure 6).

Figure 6.

The L’Ambiance plaza collapse [58].

9.2 Failures in Elazığ earthquake, Turkey, 2020

In January 2020, a magnitude 6.7 earthquake struck the Elazığ province in eastern Turkey, causing significant damage and loss of life. Several reinforced concrete buildings in the region collapsed or were severely damaged, revealing deficiencies in their design and construction (Figure 7). Common issues such as soft-story mechanisms (where the ground floor is weaker and more flexible than the upper floors), inadequate confinement of concrete columns, and poor-quality concrete and reinforcement were discovered in the investigation [60].

Figure 7.

Damages to adjacent buildings during the Elazığ earthquake [60].

The earthquake served as a grim reminder of the importance of proper seismic design and construction practices, particularly in regions with a high seismic risk. It also underscored the need for enhancing quality control in construction and enforcement of building codes to ensure the safety of the structures and the occupants (Figure 7).

9.3 Collapse of Champlain towers south, USA, 2021

In June 2021, a 12-story condominium building in Surfside, Florida, partially collapsed, leading to a significant number of fatalities. The collapse of the Champlain Towers South is considered as one of the deadliest building failures in U.S. history (Figure 8). While the exact cause of the collapse is still under investigation at the time of writing, preliminary reports suggest that there were serious issues with the building’s foundation and waterproofing, which led to significant corrosion of the reinforcement in the concrete slabs and columns [61, 62].

Figure 8.

Collapse of Champlain towers south [61].

The collapse has prompted a reevaluation of building inspection and maintenance practices, particularly for older buildings situated in corrosive environments. It has also emphasized the importance of promptly addressing any identified structural issues to prevent catastrophic failures.

9.4 Collapse of the CTV building, New Zealand, 2011

The CTV building was a six-story office block situated in Christchurch, New Zealand. During a 6.3 magnitude earthquake in February 2011, the building collapsed, causing 115 fatalities. The collapse was primarily attributed to design deficiencies in the building’s shear walls and the poor layout of vertical structural elements. An eccentric building like CTV would move more at the corners than the middle in an earthquake, and this shape eccentricity has contributed to the building collapse [63, 64].

The CTV building collapse underscored the importance of rigorous seismic design and the potential for disproportionate collapse when key structural elements fail. It highlighted the necessity for robust building codes and standards that consider seismic events, ensuring that buildings can withstand such extreme forces (Figure 9).

Figure 9.

Collapse of the CTV building, New Zealand [63, 64].

9.5 Failures in the Kahramanmaraş earthquake, Turkey, 2023

April 28, 2023 an earthquake measuring 6.5 on the Richter scale hit the city of Kahramanmaraş in Turkey, and caused extensive damage to several structures, among which many reinforced concrete buildings.

The immediate post-event assessment estimated that approximately 120 reinforced concrete buildings in the city either collapsed or suffered severe structural damage that made them uninhabitable. Tremors were felt across the city following the earthquake, leading to more disintegrations and failures of particularly older structures constructed using reinforced concrete which failed to withstand the earthquake’s intense shaking (Figure 10).

Figure 10.

A photo of the building damage from the 2023 Kahramanmaraş earthquake, Turkey [65].

Investigations into the building failures revealed that several factors contributed to the failures, including among other factors: inadequate reinforcement detailing, poor concrete quality, and overall poor construction practices [65].

9.6 Fire-induced partial collapse at the faculty of architecture building at delft university of technology, the Netherlands, 2013

The degradation of reinforced concrete structures due to fire poses a substantial challenge in structural engineering. Under high-temperature conditions, the concrete experiences both physical and chemical modifications, which impair its mechanical characteristics and compromise the overall structural stability. The transformation of the concrete’s inherent moisture into steam results in internal pressures that can provoke explosive spalling. This process not only unveils the underlying reinforcing steel but also diminishes the entire cross-section of the structure, thereby further undermining its load-bearing potential [66].

Moreover, the reinforcing steel within the concrete is prone to losing its strength and rigidity under high temperatures. This loss hampers the structure’s resilience against deformation, steering it toward potential failure. As fire hazards continue to pose a threat to structures, it becomes imperative to understand the dynamics of fire-induced failure in reinforced concrete. This understanding will pave the way toward more fire-resistant materials and structural designs.

Although the complete structural collapse of high-rise buildings due to fire is an uncommon occurrence, large fires leading to localized structural damage or partial collapses are a more regular phenomenon. For instance, on May 13, 2008, a fire-induced partial collapse was reported at the Faculty of Architecture Building at Delft University of Technology in the Netherlands. The fire culminated in the structural collapse of a considerable portion of the building (see Figure 11) [67].

Figure 11.

Fire-induced partial collapse of the Faculty of Architecture Building at Delft University of Technology in the Netherlands [67].

9.7 Progressive collapse of the Ronan point apartment tower collapse in London in 1968

One infamous example of progressive collapse is the Ronan Point apartment tower collapse in London in 1968. A small gas explosion in one of the apartments on the 18th floor led to the failure of a load-bearing wall, which triggered a progressive collapse of the entire corner of the building, resulting in the death of four people and injuries to 17 others. This incident led to significant changes in building codes in the UK and worldwide to prevent similar collapses (Figure 12) [69, 70].

Figure 12.

Progressive collapse of the Ronan point apartment tower collapse in London in 1968 [68].

9.8 Progressive collapse of the Murrah Federal Building in Oklahoma City, USA, in 1995 due to a terrorist attack

Another example is the partial collapse of the Murrah Federal Building in Oklahoma City, USA, in 1995 due to a terrorist attack. It serves as a sobering reminder to structural engineers of the potential consequences of intentional acts of destruction. This tragic incident highlighted the critical need for structural designs that can withstand extreme events and mitigate the propagation of localized failures. The collapse mechanism observed in this case underscored the importance of considering robust security measures and incorporating progressive collapse resistance strategies in building designs. As structural engineers, it is our responsibility to continually improve our understanding of the dynamic behavior of structures under extreme loading conditions and to develop innovative design solutions that enhance the resilience and safety of buildings. The lessons learned from this event have since played a pivotal role in shaping security protocols, risk assessment methodologies, and counterterrorism measures within the field of structural engineering, ensuring that our structures can better withstand intentional acts of destruction and protect the lives and well-being of occupants (Figure 13) [71].

Figure 13.

Progressive collapse of the Murrah Federal Building in Oklahoma City, USA, in 1995 due to a terrorist attack [71].

The key strategy to mitigate progressive collapse is to provide alternative load paths in the structure. If one component fails, the load it was carrying is safely transferred to other, redundant elements. This is often achieved by designing the structure to be ductile, especially at the connections, and by adding reinforcements or using prestressed concrete to enhance structural integrity.

In summary, the threat of progressive collapse in reinforced concrete structures is a significant design consideration. It involves understanding potential weak points in a structure and designing them to either be robust enough to withstand abnormal loads or flexible enough to redistribute the loads to other elements should failure occur. Awareness and careful consideration of progressive collapse can result in safer, more resilient structures.

10. Future directions in reinforced concrete

The realm of reinforced concrete is perpetually in flux, guided by developments in material science, design methodologies, and novel construction technologies. This comprehensive section delves into potential future directions in the field, exploring advanced materials, digital technologies, sustainability efforts, and resilience-based design strategies.

10.1 Advanced materials

The future of reinforced concrete is intertwined with advancements in material science. The next generation of concrete and reinforcement materials promises superior properties and better structural integrity.

10.1.1 Ultra-high-performance concrete (UHPC)

Characterized by its superior properties compared to traditional concrete, UHPC offers exceptional strength and durability. Regular concrete usually has a compressive strength of about 3000 psi, but UHPC surpasses this sevenfold, with strengths exceeding 22,000 psi (150 MPa).

Furthermore, UHPC boasts excellent durability, with high resistance to corrosion, abrasion, and impact. However, it is important to note that the complex mix design and associated high cost currently restrict its widespread use.

10.1.2 Shape memory alloys (SMAs)

Shape Memory Alloys (SMAs) present a revolutionary concept for reinforced concrete. These materials possess the ability to regain their original shape after deformation—a property known as the shape memory effect (Figure 14) [72, 73].

Figure 14.

Diagram illustrating the shape memory effect in SMAs [71].

The integration of SMAs into reinforced concrete structures holds immense promise for mitigating damage, improving structural integrity, and facilitating self-repair after calamitous events like earthquakes. This application remains largely experimental but offers considerable potential for future development [73].

10.2 Digital technology

The integration of digital technologies into the field of reinforced concrete provides valuable tools for more precise and efficient design and construction processes.

10.2.1 Building information modeling (BIM)

Building Information Modeling (BIM) is an innovative method that harnesses digital technology to create, manage, and manipulate a virtual representation of a building’s physical and functional characteristics. Within the context of reinforced concrete structures, BIM provides a platform to collaboratively explore, evaluate, and optimize design choices, thus ensuring the integrity of the structure.

BIM is more than just a detailed 3D model of the building; it is an intelligent information repository that includes data about every component of the structure. For reinforced concrete, this might include data about the concrete mix design, the size and placement of the reinforcement bars, and the expected load-bearing capacity. This comprehensive information allows engineers to perform detailed analyses and make informed decisions about the design and construction process.

Through BIM, architects, engineers, and contractors can collaborate effectively, visualizing and addressing potential structural, architectural, and construction issues early in the design phase. This collaborative approach results in better-coordinated projects, reducing the likelihood of costly errors and rework during construction.

In the maintenance phase, BIM can contribute to the structural integrity of reinforced concrete structures by providing a detailed, readily accessible database of the building’s components. This can inform maintenance activities and provide valuable data in the event of a required intervention or rehabilitation process. BIM could even integrate with Structural Health Monitoring (SHM) systems, providing a platform to visualize, interpret, and act upon the data gathered by these systems [74].

In conclusion, BIM stands as a revolution in the field of reinforced concrete design and construction [74, 75]. It is not only a tool for creating detailed 3D models but also a comprehensive database, a collaborative platform, and an advanced analysis environment. By reducing errors, enhancing collaboration, and enabling sophisticated analyses, BIM significantly contributes to reinforced concrete structural integrity.

10.2.2 Artificial intelligence: from expert systems to machine learning

Artificial Intelligence (AI) has significantly evolved in its application to the field of structural engineering, specifically for reinforced concrete structures. This progression can be traced from the early use of expert systems, followed by the adoption of neural networks, and culminating with the latest innovations involving machine learning. Each phase of this evolution has brought about remarkable changes and improvements in how we understand, design, analyze, and manage reinforced concrete structures.

In the early days of AI, expert systems were developed to harness the knowledge and expertise of human experts in a rule-based system. These systems were used to guide less experienced engineers in making design and construction decisions related to reinforced concrete structures. Expert system can be used to provide recommendations for appropriate concrete mix design or reinforcement layout based on input parameters such as load requirements, environmental conditions, and project constraints. Examples of early expert system applications in structural concrete include: A system for concrete mix design in normal and hot climates an expert system for the preliminary design of earthquake-resistant buildings [76, 77], and a knowledge-based approach for the maintenance of reinforced concrete buildings in hot climates [78], and an advisory graphical system for crack diagnosis and assessment (Figure 15) [25].

Figure 15.

Sample of an early AI expert system for the diagnosis of cracks in reinforced concrete [25].

With the advent of neural networks, AI in the field of reinforced concrete structures took a leap forward. Neural networks, inspired by the human brain’s workings, enabled more sophisticated analysis of complex structures and phenomena. Neural network come up with solutions based on its training [79].

In the most recent phase of AI evolution, machine learning has emerged as a powerful tool for reinforced concrete structures. Machine learning algorithms, unlike traditional rule-based systems, improve their performance iteratively as they are exposed to more data. They have found applications in a variety of areas in structural concrete.

In summary, the use of AI in reinforced concrete structures has grown from simplistic rule-based expert systems to sophisticated machine learning models capable of learning from data and improving their performance over time. This evolution continues to open new possibilities for the design, analysis, and management of reinforced concrete structures.

10.3 Sustainable construction

Sustainability has become a key driving factor in the construction industry, urging professionals to devise methods to create structures that minimize environmental impact while maximizing efficiency and performance. The realm of reinforced concrete is no exception, as researchers and professionals in the field actively seek to imbue sustainability into every aspect of the process, from material selection to production methods and even end-of-life disposal.

10.3.1 Green concrete

At the forefront of sustainable concrete construction is the concept of Green Concrete. More than a specific type of concrete, Green Concrete encompasses an approach to concrete construction that prioritizes environmental sustainability. The development and use of Green Concrete involve careful selection of materials and optimized production processes aimed at minimizing environmental impact [80, 81].

Material selection often involves the use of recycled or waste materials as part of the aggregate or as supplementary cementitious materials (SCMs). SCMs could include by-products from other industries, such as fly ash from power plants or slag from metal processing industries. Utilizing these materials not only reduces the need for raw materials but also prevents these by-products from ending up in landfills.

Reducing cement content is another strategy employed in Green Concrete, as the production of cement is a significant contributor to global CO2 emissions. Instead, other binding materials like lime or SCMs may be used. Research and development are ongoing in the field to find alternative binding materials that can match or even surpass the performance of traditional cement.

Green Concrete can also involve the use of carbon capture technologies during cement production. These technologies can significantly reduce the carbon footprint of cement production, making the entire process more sustainable.

10.3.2 Life-cycle assessment (LCA)

LCA is a method used to evaluate the environmental impacts of a product or system from its inception to its end of life. This includes the extraction and processing of raw materials, the manufacturing process, the use and maintenance of the product, and its final disposal or recycling [65].

In the context of reinforced concrete structures, an LCA would include the extraction and processing of raw materials like aggregate and cement, the production and transport of the concrete, the construction process, the service life of the structure (including maintenance and potential repairs), and the eventual demolition and disposal or recycling of the structure.

By employing LCA in the design and construction process, professionals can identify areas where environmental impact can be reduced. This might involve choosing more sustainable materials, optimizing production and construction processes, extending the service life of the structure, or planning for efficient demolition and recycling at the end of the structure’s life [81].

10.3.3 Sustainable use of water in concrete production

Water plays a vital role in the production of concrete, but the construction industry is one of the largest consumers of freshwater resources. Recognizing this, sustainable water management in concrete production is becoming a priority [82].

Recycling and reusing water from concrete production, known as wash water, is a key strategy in this area. Wash water, typically high in pH and containing trace amounts of cement, can potentially be reused in the concrete production process itself, thereby reducing the demand for freshwater.

10.3.4 Reducing, reusing, and recycling concrete waste

Construction and demolition waste constitutes a significant portion of total solid waste produced globally, and concrete waste forms a large part of this. Sustainable management of concrete waste is thus a crucial aspect of green construction [80].

Concrete structures at the end of their lifecycle need to be effectively managed. One such strategy is the recycling of concrete waste into Recycled Concrete Aggregates (RCA) [42, 44], which can be used in the production of new concrete. While there are challenges to overcome regarding the potentially variable properties of RCA, it offers a valuable route to reducing the demand for virgin aggregate and reducing landfill waste.

Finally, reducing concrete waste in the first place is paramount. This can be achieved through accurate calculation and optimization of concrete quantities required for a job, minimizing over-ordering, and effective management of leftover concrete. Employing these strategies helps move the reinforced concrete construction industry toward a more circular economy model, promoting sustainability.

10.4 Resilience-based design

The concept of resilience-based design is a holistic approach gaining significant traction in the realm of structural engineering, especially within the field of reinforced concrete. Resilience-based design goes beyond the traditional focus on the safety and serviceability of structures, aiming to create systems that not only withstand but also recover quickly from extreme events like earthquakes, floods, or hurricanes.

Resilience-based design takes into consideration the broader societal, economic, and environmental implications of structural failure. This includes the direct and indirect costs associated with structural repair and replacement, as well as the economic impact of disruptions to services and facilities housed within the structures. It also takes into account potential environmental impacts associated with structural damage or failure [81].

One important principle of resilience-based design is the notion of designing structures to exceed the minimum standards specified by codes. This “code-plus” approach involves designing structures to perform well under loads exceeding those prescribed by design codes, essentially preparing structures for worst-case scenarios.

In addition to this, resilience-based design involves proactive planning for the entire lifecycle of the structure. This includes careful consideration of the materials used, the construction methods, operation and maintenance, and even end-of-life deconstruction or recycling of the structure. By considering the entire lifecycle of the structure, the resilience-based design approach aims to reduce the overall environmental impact and promote sustainability.

A major aspect of resilience-based design is the integration of Structural Health Monitoring (SHM) systems. SHM involves the incorporation of advanced sensors and data analysis algorithms that can monitor the structural performance of the building over time. This allows for early detection of potential issues, enabling timely intervention and repair, thus minimizing downtime and disruption in the event of an extreme event [38].

Furthermore, the use of advanced modeling and simulation tools is a crucial part of resilience-based design. These tools enable engineers to predict how structures will respond under various scenarios, allowing for design optimization and proactive preparation for potential events. This includes seismic modeling for earthquake-prone regions, hydrodynamic modeling for structures exposed to potential flooding, and even aerodynamic modeling for buildings exposed to high wind loads.

11. Conclusion

The dynamic nature of reinforced concrete as a material, and its integral role in the construction industry, is indisputable. This chapter has provided an overview of the history of reinforced concrete, its fundamental principles, the progress made in the understanding of its behavior under various loads, and recent advances that have led to the development of stronger, more durable, and more versatile concrete structures.

Significant advancements have been made in the types of concrete available, including High-Performance Concrete, Fiber-Reinforced Concrete, and Self-Compacting Concrete. These developments allowed for more robust and efficient designs, reduced maintenance costs, and longer service life. Other recent advances in reinforced concrete look promising, including advanced materials like ultra-high-performance concrete and shape memory alloys, and smart concrete.

The chapter also highlighted some notable reinforced concrete building failures. These case studies serve as reminders of the consequences of inadequate design, poor construction practices, and failure to adhere to building codes. The lessons learned from these failures are invaluable in promoting safer construction practices and informing revisions to building codes.

The future of reinforced concrete is one of exciting possibilities, driven by the relentless pursuit of knowledge and the ambition to build structures that are not only strong and durable, but also contribute positively to our societies and the environment.

In conclusion, the field of reinforced concrete will continue to evolve, driven by innovation, research, and the imperative to learn from past failures. As we move forward, it is crucial that we continue to push the boundaries of what is possible, while always prioritizing safety, reliability, structural integrity, and sustainability.