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Reinforced concrete design theory & musicmarkup.info This book contains information obtained from authentic and highly regarded Reinforced concrete. Reinforced Concrete: Design Theory and Examples, Third Edition This book contains information obtained from authentic and highly regarded Reinforced. Reinforced concrete is widely used in building industry. Hence, graduates of every civil engineering programme must have basic understanding of the fundamentals of reinforced concrete. This book aims to provide fundamental understanding to the analysis and design of reinforced.
Advancement of softwares is main cause behind comparatively quick and simple design while avoiding complexity and time consuming manual procedure. However mistake or mislead could be happened during designing the structures because of not knowing the proper procedure depending on the situation. Design book based on manual or hand design is sometimes time consuming and could not be good aids with softwares as several steps are shorten during finite element modeling. This book may work as a general learning hand book which bridges the software and the manual design properly. The writers of this book used linear static analysis under BNBC and ACI code to generate a six story residential building which could withstand wind load of kmph and seismic event of that region. For easy and explained understanding the book chapters are oriented in 2 parts.
The design strength or nominal strength is the strength of a material, including a material-safety factor. The value of the safety factor generally ranges from 0. The ultimate limit state is the theoretical failure point with a certain probability. It is stated under factored loads and factored resistances. Reinforced concrete structures are normally designed according to rules and regulations or recommendation of a code such as ACI, CEB, Eurocode 2 or the like.
Analysis and design of RC members can be carried out by using linear or non-linear approaches. When applying safety factors, building codes normally propose linear approaches, but for some cases non-linear approaches.
To see the examples of a non-linear numerical simulation and calculation visit the references:   Main article: Prestressed concrete Prestressing concrete is a technique that greatly increases the load-bearing strength of concrete beams.
The reinforcing steel in the bottom part of the beam, which will be subjected to tensile forces when in service, is placed in tension before the concrete is poured around it.
Once the concrete has hardened, the tension on the reinforcing steel is released, placing a built-in compressive force on the concrete. When loads are applied, the reinforcing steel takes on more stress and the compressive force in the concrete is reduced, but does not become a tensile force. Since the concrete is always under compression, it is less subject to cracking and failure.
Common failure modes of steel reinforced concrete[ edit ] Reinforced concrete can fail due to inadequate strength, leading to mechanical failure, or due to a reduction in its durability. When rebar corrodes, the oxidation products rust expand and tends to flake, cracking the concrete and unbonding the rebar from the concrete.
Typical mechanisms leading to durability problems are discussed below. Mechanical failure[ edit ] Cracking of the concrete section is nearly impossible to prevent; however, the size and location of cracks can be limited and controlled by appropriate reinforcement, control joints, curing methodology and concrete mix design. Cracking can allow moisture to penetrate and corrode the reinforcement.
This is a serviceability failure in limit state design. Cracking is normally the result of an inadequate quantity of rebar, or rebar spaced at too great a distance. The concrete then cracks either under excess loading, or due to internal effects such as early thermal shrinkage while it cures.
Ultimate failure leading to collapse can be caused by crushing the concrete, which occurs when compressive stresses exceed its strength, by yielding or failure of the rebar when bending or shear stresses exceed the strength of the reinforcement, or by bond failure between the concrete and the rebar. Rust has a lower density than metal, so it expands as it forms, cracking the decorative cladding off the wall as well as damaging the structural concrete. The breakage of material from a surface is called spalling.
Detailed view of spalling probably caused by a too thin layer of concrete between the steel and the surface, accompanied by corrosion from external exposure. Main article: carbonation Carbonation, or neutralisation, is a chemical reaction between carbon dioxide in the air and calcium hydroxide and hydrated calcium silicate in the concrete.
When a concrete structure is designed, it is usual to specify the concrete cover for the rebar the depth of the rebar within the object. The minimum concrete cover is normally regulated by design or building codes. If the reinforcement is too close to the surface, early failure due to corrosion may occur.
The concrete cover depth can be measured with a cover meter. However, carbonated concrete incurs a durability problem only when there is also sufficient moisture and oxygen to cause electropotential corrosion of the reinforcing steel. One method of testing a structure for carbonatation is to drill a fresh hole in the surface and then treat the cut surface with phenolphthalein indicator solution. This solution turns pink when in contact with alkaline concrete, making it possible to see the depth of carbonation.
Using an existing hole does not suffice because the exposed surface will already be carbonated. Chlorides[ edit ] Chlorides , including sodium chloride , can promote the corrosion of embedded steel rebar if present in sufficiently high concentration.
Chloride anions induce both localized corrosion pitting corrosion and generalized corrosion of steel reinforcements. For this reason, one should only use fresh raw water or potable water for mixing concrete, ensure that the coarse and fine aggregates do not contain chlorides, rather than admixtures which might contain chlorides. Rebar for foundations and walls of a sewage pump station. The Paulins Kill Viaduct , Hainesburg, New Jersey, is feet 35 m tall and 1, feet m long, and was heralded as the largest reinforced concrete structure in the world when it was completed in as part of the Lackawanna Cut-Off rail line project.
The Lackawanna Railroad was a pioneer in the use of reinforced concrete. It was once common for calcium chloride to be used as an admixture to promote rapid set-up of the concrete. It was also mistakenly believed that it would prevent freezing.
However, this practice fell into disfavor once the deleterious effects of chlorides became known. It should be avoided whenever possible.
The use of de-icing salts on roadways, used to lower the freezing point of water, is probably one of the primary causes of premature failure of reinforced or prestressed concrete bridge decks, roadways, and parking garages.
The use of epoxy-coated reinforcing bars and the application of cathodic protection has mitigated this problem to some extent. Also FRP fiber-reinforced polymer rebars are known to be less susceptible to chlorides.
Properly designed concrete mixtures that have been allowed to cure properly are effectively impervious to the effects of de-icers. Another important source of chloride ions is sea water. Sea water contains by weight approximately 3. These salts include sodium chloride , magnesium sulfate , calcium sulfate , and bicarbonates.
In the s and s it was also relatively common for magnesite , a chloride rich carbonate mineral , to be used as a floor-topping material. This was done principally as a levelling and sound attenuating layer. However it is now known that when these materials come into contact with moisture they produce a weak solution of hydrochloric acid due to the presence of chlorides in the magnesite. Over a period of time typically decades , the solution causes corrosion of the embedded steel rebars.
This was most commonly found in wet areas or areas repeatedly exposed to moisture. Poorly crystallized silica SiO2 dissolves and dissociates at high pH The soluble dissociated silicic acid reacts in the porewater with the calcium hydroxide portlandite present in the cement paste to form an expansive calcium silicate hydrate CSH.
The alkali—silica reaction ASR causes localised swelling responsible for tensile stress and cracking. This reaction occurs independently of the presence of rebars; massive concrete structures such as dams can be affected. Conversion of high alumina cement[ edit ] Resistant to weak acids and especially sulfates, this cement cures quickly and has very high durability and strength. It was frequently used after World War II to make precast concrete objects.
However, it can lose strength with heat or time conversion , especially when not properly cured. After the collapse of three roofs made of prestressed concrete beams using high alumina cement, this cement was banned in the UK in Subsequent inquiries into the matter showed that the beams were improperly manufactured, but the ban remained.
The most typical attack of this type is on concrete slabs and foundation walls at grades where the sulfate ion, via alternate wetting and drying, can increase in concentration. As the concentration increases, the attack on the Portland cement can begin.
For buried structures such as pipe, this type of attack is much rarer, especially in the eastern United States. The sulfate ion concentration increases much slower in the soil mass and is especially dependent upon the initial amount of sulfates in the native soil. A chemical analysis of soil borings to check for the presence of sulfates should be undertaken during the design phase of any project involving concrete in contact with the native soil. If the concentrations are found to be aggressive, various protective coatings can be applied.
This type of cement is designed to be particularly resistant to a sulfate attack. Steel plate construction[ edit ] Main article: Steel plate construction In steel plate construction, stringers join parallel steel plates. The plate assemblies are fabricated off site, and welded together on-site to form steel walls connected by stringers.
The walls become the form into which concrete is poured. Steel plate construction speeds reinforced concrete construction by cutting out the time-consuming on-site manual steps of tying rebar and building forms.
The method results in excellent strength because the steel is on the outside, where tensile forces are often greatest. Main article: Fiber reinforced concrete Fiber reinforcement is mainly used in shotcrete , but can also be used in normal concrete. Fiber-reinforced normal concrete is mostly used for on-ground floors and pavements, but can also be considered for a wide range of construction parts beams, pillars, foundations, etc.
Concrete reinforced with fibers which are usually steel, glass , plastic fibers or Cellulose polymer fibre is less expensive than hand-tied rebar. A thin and short fiber, for example short, hair-shaped glass fiber, is only effective during the first hours after pouring the concrete its function is to reduce cracking while the concrete is stiffening , but it will not increase the concrete tensile strength.
Fiber reinforcement is most often used to supplement or partially replace primary rebar, and in some cases it can be designed to fully replace rebar. Steel fibers can only be used on surfaces that can tolerate or avoid corrosion and rust stains.
In some cases, a steel-fiber surface is faced with other materials. Glass fiber is inexpensive and corrosion-proof, but not as ductile as steel. Recently, spun basalt fiber , long available in Eastern Europe , has become available in the U. Basalt fibre is stronger and less expensive than glass, but historically has not resisted the alkaline environment of Portland cement well enough to be used as direct reinforcement.
New materials use plastic binders to isolate the basalt fiber from the cement. The premium fibers are graphite -reinforced plastic fibers, which are nearly as strong as steel, lighter in weight, and corrosion-proof.
The introduction of non-steel reinforcement of concrete is relatively recent; it takes two major forms: non-metallic rebar rods, and non-steel usually also non-metallic fibres incorporated into the cement matrix. For example, there is increasing interest in glass fiber reinforced concrete GFRC and in various applications of polymer fibres incorporated into concrete. Although currently there is not much suggestion that such materials will replace metal rebar, some of them have major advantages in specific applications, and there also are new applications in which metal rebar simply is not an option.
However, the design and application of non-steel reinforcing is fraught with challenges. For one thing, concrete is a highly alkaline environment, in which many materials, including most kinds of glass, have a poor service life.
Also, the behaviour of such reinforcing materials differs from the behaviour of metals, for instance in terms of shear strength, creep and elasticity. These rebars are installed in much the same manner as steel rebars.
There are uncertainties in the design process both in the estimation of the loads likely to be applied on the structure and in the strength of the material.
Moreover, full guarantee would only involve more cost. Thus, there is an acceptable probability of performance of structures as given in standard codes of practices of different countries. The designed structure should sustain all loads and deform within limits for construction and use: Adequate strengths and limited deformations are the two requirements of the designed structure.
The structure should have sufficient strength and the deformations must be within prescribed limits due to all loads during construction and use. The structure having insufficient strength of concrete which fails in bending compression with the increase of load, though the deformation of the structure is not alarming. In another situation where the structure, having sufficient strength, deforms excessively.
Both are undesirable during normal construction and use. However, sometimes structures are heavily loaded beyond control. The structural engineer is not responsible to ensure the strength and deformation within limit under such situation.
The staircases in residential buildings during festival like marriage etc. Though, the structural designer is not responsible for the strength and deformations under these situations, he, however, has to ensure that the failure of the structures should give sufficient time for the occupants to vacate.
The structures, thus, should give sufficient warning to the occupants and must not fail suddenly. The designed structures should be durable: The materials of reinforced concrete structures get affected by the environmental conditions. Thus, structures having sufficient strength and permissible deformations may have lower strength and exhibit excessive deformations in the long run.
The designed structures, therefore, must be checked for durability. Separate checks for durability are needed for the steel reinforcement and concrete. This will avoid problems of frequent repairing of the structure.
Fire may also take place as accidents or as secondary effects during earthquake by overturning kerosene stoves or lantern, electrical short circuiting etc.
Properly designed structures should allow sufficient time and safe route for the persons inside to vacate the structures before they actually collapse. How to fulfill the objectives? All the above objectives can be fulfilled by understanding the strength and deformation characteristics of the materials used in the design as also their deterioration under hostile exposure.
Out of the two basic materials concrete and steel, the steel is produced in industries. Further, it is available in form of standard bars and rods of specific diameters. However, sample testing and checking are important to ensure the quality of these steel bars or rods.
The concrete, on the other hand, is prepared from several materials cement, sand, coarse aggregate, water and admixtures, if any. Therefore, it is important to know the characteristic properties of each of the materials used to prepare concrete.
These materials and the concrete after its preparation are also to be tested and checked to ensure the quality. The necessary information regarding the properties and characteristic strength of these materials are available in the standard codes of practices of different countries.