Free Civilengineering subject Tutorial
Learn civil engineering online
R.C.C. Structure design :a combination of concrete and steel reinforcement that are joined into one piece and work together in a structure. The term “reinforced concrete” is frequently used as a collective name for reinforced-concrete structural members and products. The idea of combining in reinforced concrete two materials that are extremely different in properties is based on the fact that the tensile strength of concrete is significantly lower (by a factor of 10–20) than its compressive strength. Therefore, the concrete in a reinforced-concrete structure is intended to take compressive stresses, and the steel, which has high ultimate tensile strength and is introduced into the concrete as reinforcement rods, is used principally to take tensile stresses. The interaction of such different materials is extremely effective: when the concrete hardens, it adheres firmly to the steel reinforcement and protects it from corrosion, since an alkaline medium is produced during the process of hydration of the cement. The monolithic nature of the concrete and reinforcement also results from the relative closeness of their coefficients of linear expansion (7.5 × 10−6 to 12 × 10−6 for concrete and 12 × 10−6 for steel reinforcement). The basic physicomechanical properties of the concrete and steel reinforcement are virtually unchanged during temperature variations within a range of –40° to 60°C, which makes possible the use of reinforced concrete in all climatic zones.
In R.C.C. Structure design :The basis of the interaction between concrete and steel reinforcement is the presence of adhesion between them. The magnitude of adhesion or resistance to displacement of the reinforcement in concrete depends on the mechanical engagement in the concrete of special protuberances or uneven areas of the reinforcement, the frictional forces from compression of the reinforcement by the concrete as a result of its shrinkage (reduction in volume upon hardening in air), and the forces of molecular interaction (agglutination) of the reinforcement with the concrete. The factor of mechanical engagement is decisive. The use of indented bar reinforcement and welded frames and nets, as well as the arrangement of hooks and anchors, increases the adhesion of the reinforcement to the concrete and improves their joint operation.
R.C.C. Structure design : Structural damage and noticeable reduction of the strength of concrete occur at temperatures above 60°C. Short-term exposure to temperatures of 200°C reduces the strength of concrete by 30 percent, and long-term exposure reduces it by 40 percent. A temperature of 500°-600°C is the critical temperature for ordinary concrete, at which the concrete breaks up as a result of dehydration and the rupture of the cement stone skeleton. Therefore, the use of ordinary reinforced concrete at temperatures exceeding 200°C is not recommended. Heat-resistant concrete is used in thermal units operating at temperatures up to 1700°C. A protective layer of concrete 10–30 mm thick is provided in reinforced-concrete structures to protect the reinforcement from corrosion and rapid heating (for example, during a fire), as well as to ensure its reliable adhesion to the concrete. In an aggressive environment the thickness of the protective layer is increased.
R.C.C. Structure design :The shrinkage and creep of concrete are of great importance in reinforced concrete. As a result of adhesion, the reinforcement impedes the free shrinkage of concrete, leading to the emergence of initial tensile stresses in the concrete and compressive stresses in the reinforcement. Creep in concrete causes the redistribution offerees in statically indeterminate systems, an increase in sags in components that are being bent, and the redistribution of stresses between concrete and reinforcement in compressed components. These properties of concrete are taken into account in designing reinforced-concrete structures. The shrinkage and low limiting extensibility of concrete (0.15 mm/m) cause the inevitable appearance of cracks in the expanded area of structures under service loads. Experience shows that under normal operating conditions cracks up to 0.3 mm wide do not reduce the supporting capacity and durability of reinforced concrete. However, low cracking resistance limits the possibility of further improvement of reinforced concrete and, particularly, the use of more economical high-strength steels as reinforcement. The formation of cracks in reinforced concrete may be avoided through the method of prestressing, by means of which concrete in expanded areas of the structure undergoes artificial compression through mechanical or electrothermal prestressing of the reinforcement. Self-stressed reinforced-concrete structures, in which compression of the concrete and expansion of the reinforcement are achieved as a result of the expansion of the concrete (manufactured with so-called stretching cement) during specific temperature-moisture treatment, is a further development of prestressed reinforced concrete. Because of its high technical and economic indexes (profitable use of high-strength materials, absence of cracks, and reduction of reinforcement expenditures), prestressed reinforced concrete is successfully used in supporting structures of buildings and engineering structures. A basic shortcoming of reinforced concrete, high weight per volume, is eliminated to a considerable extent by the use of lightweight concrete (with artificial and natural porous fillers) and cellular concrete.
Learn : Design of singly reinforced rectangular section for flexure, factored moment, ultimate moment of resistance, limiting moment of resistance factor, fixing dimension of the section, Area of tension steel. Design of singly reinforced rectangular section for flexure The design problem is generally of determining dimensions (cross-sectional) of a beam (b X D) and …
Continue reading "Design of singly reinforced rectangular section for flexure"
Learn About design of beams, effective span, effective depth, reinforcement, nominal cover to reinforcement, curtailment of tension reinforcement BASIC RULES FOR DESIGN OF BEAMS While designing R.C.C. beams, following important rules must be kept in mind: Effective Span (CI. 22.2, IS 456) The effective span of the beams are taken as follows : (a) Simply …
Learn : Stress Strain relationship for concrete, Stress Strain relationship for steel,Design Strength Values for Steel Design Stresses at Specified Strains. fe 415 and fe 500 Stress Strain relationship for concrete and Stress Strain relationship for steel Stress Strain relationship for concrete Stress Strain relationship for concrete : The experimental or actual stress strain curve for …
Continue reading "Stress Strain relationship for concrete and Stress Strain relationship for steel"
Learn Assumptions in limit state of collapse in flexure (Bending),relationship between the stress strain distribution in concrete,stresses in the reinforcement are taken from the stress-strain curve Assumptions in limit state of collapse in flexure (Bending) (REFER CL. 38, IS 456) The design of reinforced concrete sections for limit state of collapse in bending, is based …
Continue reading "Assumptions in limit state of collapse in flexure (Bending)"
Design Strength of Materials : Partial Safety Factors for Materials (rm), and Design Loads : Values of Partial Safety Factor (rf) for Loads(Refer Clause 36, IS Code) DESIGN VALUES (REFER CLAUSE 36, IS CODE) Design Strength of Materials The strength of any material obtained in a structure is always less than the characteristic strength of the …
Continue reading "Design Strength of Materials and Design Loads(Refer Clause 36, IS Code)"
Types of shear reinforcement : Vertical stirrups, Bent up bars along with stirrups, Inclined stirrups, contribution of bent up bars TYPES OF SHEAR REINFORCEMENT The following three types of shear reinforcement are used : Vertical stirrups. Bent up bars along with stirrups. Inclined stirrups. Vertical Stirrups These are the steel bars vertically placed around the tensile reinforcement at suitable …
Learn : Effects of Shear Diagonal Tension, maximum bending tensile stress, tensile stress (σ) as well as shear stress (τ),crack pattern for a simply supported beam, The maximum bending moment in this beam will be at midspan and the maximum shear force, at the supports. EFFECTS OF SHEAR DIAGONAL TENSION Consider a beam AB subjected …
Shear Stresses in R.C.C. beam (Reinforced cement concrete beam), Stress Based Approach (Elastic Theory), IS Code Approach SHEAR STRESSES IN R.C.C. BEAMS Stress Based Approach (Elastic Theory) R.C.C. is a composite materials so the exact shear distribution as per elastic theory is very complex. It is shown in Fig. 5.2(b) by the hatched portion of the curve.It …
Learn : Characteristic Strength of Materials :Characteristic Strength of Concrete, Characteristic Strength of Steel. and Characteristic Load or ultimate load CHARACTERISTIC VALUES (REFER CLAUSE 36, IS CODE) Characteristic Strength of Materials The characteristic strength is based on the statistical analysis of the test results because there are variations in the strength of the material used. In …
Continue reading "Characteristic Strength of Materials Characteristic Load or ultimate load"
Learn : comparison of working stress method and limit state method, working stress method,Drawbacks of the working stress method, Limit state method : Limit state of collapse, Limit state of serviceability. COMPARISON OF WORKING STRESS METHOD AND LIMIT STATE METHOD Working Stress method and Drawbacks of the working stress method Working Stress method This method of design …
Continue reading "comparison of working stress method and limit state method"