Reinforced Concrete Basics 2e Pdf Download

Corrosion of steel in concrete

Lars-Olof Nilsson , in Developments in the Formulation and Reinforcement of Concrete (Second Edition), 2019

5.3.1 Conclusion

Reinforced concrete structures are vulnerable to two types of corrosion—corrosion initiated by carbonation and corrosion initiated by chlorides. A concrete material with w/c ratio below 0.4 will be so resistant to the ingress of the carbon dioxide that would cause carbonation, which the service life of a structure made with that concrete would be a matter of many centuries, assuming that no other deterioration mechanism is at play. As such, carbonation initiation of reinforcement corrosion is not relevant when designing for a 100-year functional service life. As for chloride initiation of reinforcement corrosion, reinforced concrete structures exposed to a freshwater or low-salinity environment where the concentration of chloride ions is low will be much less vulnerable than structures exposed to a high-salinity environment, because the diffusion of chloride ions into the concrete will be much slower.

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Maintenance of aged land-based structures

A VAN GRIEKEN , in Condition Assessment of Aged Structures, 2008

Anodic protection

In reinforced concrete structures, anodic protection is a terminology used for the description of cathodic protection using a sacrificial anode. Anodic protection involves the installation of a metal which is more anodic than the embedded reinforcement, thereby reversing the corrosion process and protecting the reinforcement. This is more commonly used for marine applications. Commercial systems are now available involving anodes which are embedded into repair patches to halt the corrosion of reinforcement. However, the longevity is yet to be established. Systems such as these need to be designed and not installed 'off the shelf as there are many variables to consider, including protective radius, electrical conductivity of the repair mortar and base concrete, reinforcement density and condition, chloride concentration and exposure conditions, amongst others.

Table 16.6 summarises the application of the various electrochemical methods and their advantages and disadvantages.

Table 16.6. Electrochemical treatment

Method	Application/advantages	Suitability/disadvantages
Realkalisation	• Carbonated structures to protect the reinforcement against corrosion • No breakout, noise, dust • Long-term, perhaps permanent solution • Maintains image of uncoated concrete structures	• May not be suitable for prestressed/post-tensioned structures • Risk of starting or accelerating alkali silica reaction in susceptible structures • May require one to two weeks to restore alkalinity
Desalination/chloride extraction	• Extraction of chlorides from concrete to halt or significantly retard reinforcement corrosion • Long-term solution if re-migration of chlorides does not occur • No breakout, noise, dust • Does not alter image of structure	• As for realkalisation • Not suitable where concrete has cracked or spalled due to corroding reinforcement • Not suitable where structure is submerged or in splash zone • Risk of chloride re-migration • May require 4–12 weeks to achieve result
Cathodic protection – impressed current	• Chloride contaminated structures where the reinforcement is corroding or at risk of corrosion • Long-term protection • Remote monitoring and adjustment to changes to exposure conditions or corrosion rates • In some cases also applicable for corroding reinforcement in carbonated concrete • Many anode systems including surface mesh, embedded ribbons, embedded rods, conductive surface coatings	• As for realkalisation with reference to alkali aggregate reaction and post-tensioned, prestressed structures • External wiring/equipment • Need for ongoing monitoring • Limited life of the anodes • Not suitable where it is not possible to achieve electrical continuity of reinforcement and link in all isolated embedded steel elements
Cathodic protection – electro-osmosis	• To protect structures affected by salts from soils • Reverses salt ingress and reduces salt concentrations • Can protect embedded reinforcement against corrosion	• Needs anodes to be embedded into walls • Life expectancy not yet known
Anodic protection	• Protects embedded reinforcement against present and potential corrosion by means of anodes which are embedded in repair patches • No need for wiring or external equipment	• Unknown lifespan • Need to be designed to include the many variable conditions and as-built details • Monitoring is difficult and impractical

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Introduction

Xiaoshan Lin , ... Prabin Pathak , in Nonlinear Finite Element Analysis of Composite and Reinforced Concrete Beams, 2020

1.1.2.3 Effect of cyclic load

Reinforced concrete structures are very often subjected to cyclic loads in their service life, such as traffic and seismic loads. Under cyclic loads, the plastic deformation of a reinforced concrete element increases. The stresses in each constituent material and concrete–FRP interface are likely to increase with the increasing beam plastic deformation, which may promote brittle debonding and unexpected material failures [10]. Therefore, in addition to the strength of reinforced concrete components that have suffered material decay and damage under static load, it is necessary that they have sufficient durability to prevent failure from fatigue [18].

Fatigue life is defined as the number of cycles that lead to the failure of structural system [19]. The repeated loading would change the fundamental properties of a material, resulting in progressive damage propagation. For reinforced concrete structures, cyclic load typically causes softening behaviour of reinforcing steel and concrete [20]. Similarly, the mechanical properties of FRP are also affected by the cyclic load. Typical damage of FRP composites due to fatigue includes matrix cracking, debonding, and fibre fracture [21].

FRP strengthening plates normally consist of unidirectional fibres and matrix resin, and the fatigue response of FRP composites was reported to be dependent more on the matrix resin than the constitutive fibres [22], as the damage may propagate along the matrix between the unidirectional fibres. However, this is not the case for FRP-strengthened reinforced concrete components. When FRP is bonded on the surface of concrete, the failure of resin seldom occurs as the resin strength is usually greater than that of concrete in tension [19]. As the number of cycles increases, the fatigue damage is accumulated, causing the decrease in the friction between concrete and FRP plate and gradual bond failure, which indicates a progressive delamination of FRP.

The most commonly observed fatigue failure mode of a FRP-strengthened reinforced concrete beam is the rupture of the tensile reinforcing steel, followed by FRP strengthening plate [19]. This is attributed to the fact that, compared with FRP plate, steel reinforcement is more susceptible to fatigue failure. Although the fatigue failure is primarily governed by steel reinforcement, FRP extends the fatigue life of the reinforced concrete beam by reducing stresses in the steel reinforcement. The delamination of FRP often occurs immediately after the rupture of steel reinforcement. Owing to the complex failure mechanisms and the various parameters that may affect the flexural fatigue life, it is still difficult to accurately predict the fatigue behaviour of reinforced concrete beams strengthened with FRP.

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Construction Steel

In Building Materials in Civil Engineering, 2011

8.5.2 Fire Protection of Steel Bars

The reinforced concrete structure refers to the members, such as beams, boards, columns, roof trusses, consisting of concrete and steel bars. In these structures, the steel bars are enwrapped by concrete, but their mechanical properties will still lose due to the fire to destroy the whole structure.

Because the thermal conductivity of concrete is big and the thermal expansion rate of steel bars is 1.5 times of that of concrete after being heated, their elongation strain is bigger than that of concrete. Thus, the thickness of protecting layer should be added accordingly within the allowable range of structure design, which will reduce or delay the elongation strain of steel bars and the losing of pre-stressed value. If the structure design does not allow the adding of thickness, fire retardant coatings can be painted on the surface of the tensile area of the concrete to protect the structure.

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Part 3 Strength and Deformation of Structural Member

Zhenhai Guo , in Principles of Reinforced Concrete, 2014

The reinforced concrete structure used most widely in engineering practice is mainly composed of one-dimensional members, of which the internal forces on the section are singly axial force, bending moment, shear force, or torque and the composition of them. Even the two- and three-dimensional structures are entirely or partly simplified and equivalent to a one-dimensional member. For example, a shear wall of a tall building is considered as a cantilever of narrow but deep section; a core tube of a high-rising building is considered as an eccentrically compressed member with box section; a folded plate structure is composed of eccentrically compressed plates; a diaphragm at the end of a shell structure is simplified to an eccentrically tensed member, etc.

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Supporting Structures

George Antaki , Ramiz Gilada , in Nuclear Power Plant Safety and Mechanical Integrity, 2015

What is the design function of concrete structures, liners, and embedded plates?

•: Reinforced concrete structures are the steel bar (rebar)-reinforced concrete walls, domes, ceilings, and floors that constitute the building structure and its walls.
•: Liners consist of welded steel plates attached to some of the concrete walls to protect the wall and provide leak tightness. The containment liner on the inside of the concrete containment building in a pressurized water reactor (PWR) is meant to maintain the containment leak tightness under normal operation and accidental pressurized release. The liner is the third containment barrier after the nuclear fuel cladding and the reactor coolant system.
•: Baseplates are steel strips, sheet plates, or corner plates that are embedded or bolted to the concrete. They provide a face for welding or bolting to other steel structures and supports to the walls (Figure 5.1). The function of all these embedded or bolted plates is to provide a structural load path from the supported SSC to the reinforced concrete.

Figure 5.1. Bolted baseplate supporting structural steel.

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Introduction

DERIC JOHN OEHLERS , RUDOLF SERACINO , in Design of FRP and Steel Plated RC Structures, 2004

1.1 Introduction

Existing reinforced concrete structures are often in need of strengthening, stiffening, improving the ductility or repair. A common form of retrofitting is to adhesively bond plates or sheets to the surfaces. However, tests have shown that these plates are prone to premature debonding, as has occurred to the tension face plate in Fig.1.1, which can inhibit the use of this retrofitting technique. The aims of this book are to:

•: provide a comprehensive overview of all types and forms of plating
•: provide an insight into the various plate debonding or peeling mechanisms
•: compare, comment and apply the numerous design procedures or guidelines that are currently available in Australia, Europe, Hong Kong and the USA
•: show where adhesively bonded plates can be safely applied, where they should not be applied and where bolted plates should be used instead of adhesively bonded plates
•: clearly distinguish between the behaviours of metal and FRP plated sections
•: provide comprehensive information so that retrofitting by plating can be used with safety and confidence and, hence, extend the use of all types of plating
•: provide engineers with the design tools to develop their own unique plating systems and to decide on appropriate techniques specific to their retrofitting problems

This book covers the mechanics of retrofitting reinforced concrete (RC) beams and slabs using externally bonded longitudinal plates. The plates can be made of FRP, steel, aluminium or any metal; they can have any shape such as flat plates, channels or angle sections; they can be bonded to any surface such as the tension face, sides or compression face; and they can be either adhesively bonded or bolted. Methods of analysis are illustrated and applied to determine the strength, stiffness and ductility of plated structures and design procedures for preventing premature debonding are compared.

In this chapter, the large variety of forms of longitudinal plating available to the designer is first described. This is then followed by a description of the premature failure mechanisms that can occur and have to be designed for, and how these failure mechanisms can affect the choice of plate material and size. Design guides are then compared which shows that there is general agreement on the failure mechanisms.

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Finite element analysis of reinforced concrete beams with bond–slip

Xiaoshan Lin , ... Prabin Pathak , in Nonlinear Finite Element Analysis of Composite and Reinforced Concrete Beams, 2020

5.1 Introduction

In reinforced concrete structures, bond between reinforcing bars and the surrounding concrete plays an important role in transferring stress from the latter to the former and has become one of the thorny issues in the analysis of reinforced concrete structures. In many numerical simulations of reinforced concrete structures, a perfect bond between reinforcing bars and concrete has usually been assumed. Although this assumption can provide a realistic simplification of the real bonding conditions for reinforcing bars with sufficient surface preparation, when there is insufficient surface preparation, especially in FRP-reinforced concrete structures, bond–slip may take place, the effect of which on the structural behaviour should not be ignored [1–3]. In addition, with an increase in load, cracking occurs inevitably, which also results in a reduction in bond strength.

A few finite element models have been developed for analysing steel-reinforced concrete beams with bond–slip effect. In several studies, 1-D beam elements were developed based on fibre models. For example, a refined beam element proposed by Manfredi and Pecce [4] included an explicit formulation of bond–slip relationship, and each beam element was divided into subelements defined by two consecutive cracks determined by either semiempirical formulations or the spaces between stirrups. Oliveira et al. [5] presented a layered beam model based on Manfredi and Pecce's model [4], in which the bond stress–slip relationship was applied to the domain of a finite element delimited by two successive cracks. Monti and Spacone [6] developed a reinforced concrete beam finite element that combined a force-based fibre section model with a finite element model of a rebar with continuous slip. Whereas it provided the solution within a single beam element only, the determination of the force-based element state was complex. Later, a displacement-based reinforced concrete beam fibre model was presented by Spacone and Limkatanyu [7], in which the element was composed of a two-node concrete beam and several two-node bars for reinforcing steel to allow slip. It should be mentioned that the Euler–Bernoulli beam theory was applied in all these fibre model-based beam elements in which the shear effect was neglected.

In the existing 2-D and 3-D models, a separate bond element has often been used to account for the slip between reinforcing bars and the surrounding concrete. In the study reported by Kwak and Filippou [8], eight-node quadrilateral elements and 1-D truss elements were used to model the concrete and reinforcing steel, respectively, and bond-link elements were employed to consider the bond–slip effect. This method is suited for cases with no significant bond–slip and associated bond damage. Khalfallah's finite element model [9] was built using eight-node serendipity plane stress elements for concrete, three-node truss elements for reinforcing bars and imperfect bond elements for bond–slip. In a 2-D model proposed by Rabczuk et al. [10], a bond element consisting of two double nodes was used to connect elements for concrete and steel. In Jendele and Cervenka's model [11], continuum elements (2-D or 3-D) were used to model concrete, truss elements with constant strain to model reinforcing bars and bond elements to model constant slip.

The existing 2-D and 3-D models for steel-reinforced concrete beams with bond–slip effect are usually complex in geometry and modelling and computationally expensive due to their large numbers of nodes and degrees of freedom. In 1-D models, inaccuracies may be introduced by using simplified methods. Therefore, a simple and effective 1-D finite element, which accounts for the effect of bond–slip, is required to enable more efficient analysis.

In this chapter, the 1-D layered composite beam element introduced in Chapter 4 is further extended for modelling reinforced concrete beams, in particular FRP-reinforced concrete beams, with bond–slip effect. In this element, the concrete is divided into a number of concrete layers and the reinforcing bars represented by equivalent smeared reinforcing layers. By using the layered method, not only can material nonlinearity be accounted for, but also the bond–slip between reinforcing bars and concrete can be simulated. In addition, both concrete and reinforcing bars can be modelled simultaneously in the integrated element, so that different types of elements are not required in numerical simulation. Apart from the degrees of freedom for transverse displacement and rotation, the composite beam element has two additional degrees of freedom to represent the axial displacements of the equivalent tensile and compressive reinforcing layers. Thus, the nodal degrees of freedom for concrete and reinforcing bars are different, allowing the reinforcing layers to slip with respect to concrete. The bond stress–slip relationships suggested in the CEB-FIP Model Code 1990 [12] and the BPE modified model [13] are used to describe the bond performances of steel and FRP reinforcing bars, respectively. As this element has only two nodes and four degrees of freedom per node, it is computationally efficient.

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Design and specification of marine concrete structures

P.E. Smith , in Marine Concrete Structures, 2016

3.7.8.4 Construction joints

Most reinforced concrete structures have construction joints between casts, with reinforcement passing through these joints. The intention of the joints is to allow a monolithic structure to be broken down into a series of casts of manageable size or a logical component assembly sequence (such as connection of a precast pile to the superstructure beams and the beams to the slab). It is important for the second or subsequent casts to bond onto the previous casts to create a monolithic structure without any weaknesses that could compromise the structure's durability. As a minimum, therefore, construction joints should be specified to have an exposed aggregate finish in order to be rough enough to assist the bond. The critical part of the joint is the cover zone outside of the reinforcement, and it is essential that this is prepared correctly so that the next cast is able to bond to the first and not compromise the durability by the formation of a crack between the two casts.

An exposed aggregate construction joint finish that is formed by application of a retarder chemical on to the construction joint surfaces immediately after casting is preferred to a surface that is roughened by mechanical means. Nonvisible cracks or loose aggregate may be caused by the mechanical roughening that could become a weak point for chloride ingress.

In precast beam construction, such as the examples in Section 3.7.6.2, it should be specified that the top and ends of the part-height precast beam or the inner surfaces, and the ends and top of the U beam, are given a construction joint finish. Similarly, the inner surfaces of precast pile caps and headstock boxes also need to be prepared.

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Finite Element Analysis of the Loading History for Structures

Zhenhai Guo , Xudong Shi , in Experiment and Calculation of Reinforced Concrete at Elevated Temperatures, 2011

12.3.3 Calculation Procedure

The NARCSLT computer program is compiled for nonlinear finite element analysis of the mechanical history of a reinforced concrete structure under common actions of temperature and load, and the calculation procedure is as follows:

1.: The temperature and load are divided into a certain number of increment steps according to the time step, and the increments of temperature, load, and time within each increment step are not zero simultaneously. The increment vector of load {ΔP} at the nodes of the structure is not zero in any increment step, so Eqn (12.66) is a series of nonlinear equations at the kth iteration within the ith increment step, and the incremental vector of displacement at the nodes of the structure is not zero in any increment step.
2.: Each member of the structure is divided into a certain number of beam elements along its length, and each beam element is divided again into a certain number of prism elements along its section. The areas of the cross sections of the concrete and reinforcement of each prism element are calculated.
3.: The initial conditions of the structure are given.
4.: The temperature field on the cross section of each beam element is calculated using the HTARC program (see Chapter 6). However, this is not needed if the temperature increment within the current increment step is zero.
5.: The vector of the stress–strain point on the section of every beam element obtained from the previous increment step is transformed into that under the temperature condition within the current increment step, and the vector of the yield limit of the section of every beam element under the current condition is found. This is not needed if the temperature increment within the current increment step is zero.
6.: The tangential moduli, related to the strain, temperature, and time, of concrete and reinforcement on the section of a prism element of each beam element are calculated using Eqns (12.4) and (12.9).
7.: The stiffness matrixes of the load, temperature, and time, and the total stiffness matrix of the section of a beam element are formed using Eqns (12.27)–(12.30).
8.: The incremental load vectors of the temperature and time at the nodes of a beam element are calculated using Eqns (12.38)–(12.42).
9.: The calculated result of Eqn (12.24) is added to the vector of the unbalanced force (the coordinates of which have been transformed) at the nodes of a beam element after the last iteration within the previous increment step, and the incremental load vector at the nodes of the beam element is obtained.
10.: The equivalent stiffness matrix of every beam element is calculated using Eqn (12.65).
11.: The local coordinates of every beam element are transformed into the integral coordinate of the structure for the equivalent stiffness matrix and the incremental vector of the load at the nodes.
12.: The incremental vector of the load at the nodes of the structure is collected.
13.: The total stiffness matrix of the structure is collected and the boundary condition of its displacement is introduced.
14.: The vector of the unbalanced force is calculated using Eqn (12.67).
15.: If the norm of the vector of the unbalanced force is smaller than the convergence tolerance given, the vector of the displacement at the nodes of the structure within the current increment step is calculated using Eqn (12.68), and the current condition of deformation of the structure is recorded. These are taken as the initial conditions for calculating the next increment step, which is started again from step 4 above and conducted until failure of the structure or the end of the last increment step given. If the norm of the vector of the unbalanced force is greater than the convergence tolerance given, the iteration is continued within the current increment step.
16.: The incremental vector of the displacement at the nodes of the structure is calculated using Eqn (12.66).
17.: The incremental vector of the displacement at the nodes of every beam element is determined.
18.: The strain vectors caused by stresses of concrete and reinforcement on the section of every beam element are calculated.
19.: The vector of the yield limit of the section of every beam element under the current temperature conditions is calculated and then return to step 6 above.