Fundamentals of Reinforced Concrete and Prestressed Concrete PDF

FUNDAMENTALS OF REINFORCED CONCRETE AND PRESTRESSED CONCRETE  NATIONAL UNIVERSITY Civil Engineering Department Concrete is a mixture of sand, gravel, crushed rock, or other aggregates held together in a rocklike mass with a paste of cement and w...

FUNDAMENTALS OF REINFORCED CONCRETE AND PRESTRESSED CONCRETE  NATIONAL UNIVERSITY Civil Engineering Department Concrete is a mixture of sand, gravel, crushed rock, or other aggregates held together in a rocklike mass with a paste of cement and water. MacGregor, J. G. & Wight, J. K.,(2012). Reinforced concrete: mechanics and design (Vol. 6). Upper Saddle River, NJ: Prentice Hall.  NATIONAL UNIVERSITY Civil Engineering Department Reinforced Concrete In a reinforced concrete, reinforcing bars are embedded in the concrete in such a way that the tension forces needed for moment equilibrium after the concrete cracks can be developed in the bars. Principles of Reinforced and Prestressed Concrete Introductory Concepts  NATIONAL UNIVERSITY Civil Engineering Department Reinforced Concrete Design A direct application of laws of statics and mechanics of materials to obtain a successful design not only on design rules but is capable of being built in a timely fashion for a reasonable cost and should provide a long service of life. Advantages of Reinforced Concrete 1. Economy 2. Suitability of material for structural and architectural functions Principles of Reinforced and Prestressed Concrete Introductory Concepts  NATIONAL UNIVERSITY Civil Engineering Department Advantages of Reinforced Concrete 3. Fire Resistance 4. Rigidity 5. Low Maintenance 6. Availability of materials Disadvantages of Reinforced Concrete 1. Low Tensile Strength MacGregor, J. G. & Wight, J. K.,(2012). Reinforced concrete: mechanics and design (Vol. 6). Upper Saddle River, NJ: Prentice Hall.  NATIONAL UNIVERSITY Civil Engineering Department Disadvantages of Reinforced Concrete 2. Forms and shoring Principles of Reinforced and Prestressed Concrete Introductory Concepts  NATIONAL UNIVERSITY Civil Engineering Department Disadvantages of Reinforced Concrete 3. Relatively low strength per unit of weight or volume 4. Time dependent volume changes Principles of Reinforced and Prestressed Concrete Introductory Concepts  NATIONAL UNIVERSITY Civil Engineering Department Properties of Concrete 1. Compressive strength 2. Modulus of Elasticity Values ranges from 3000-20000 psi Concrete has no clear-cut modulus of elasticity Principles of Reinforced and Prestressed Concrete Introductory Concepts  NATIONAL UNIVERSITY Civil Engineering Department Properties of Concrete 3. Poisson’s Ratio 4. Shrinkage Values ranges from 0.11 to 0.21 Shrinkage is the decrease in the with average values of about 0.16 volume of concrete during hardening and drying under constant temperature Principles of Reinforced and Prestressed Concrete Introductory Concepts  NATIONAL UNIVERSITY Civil Engineering Department Properties of Concrete 5. Creep Creep is the deformation of a structure under sustained load. Principles of Reinforced and Prestressed Concrete Introductory Concepts  NATIONAL UNIVERSITY Civil Engineering Department Properties of Concrete 6. Tensile Strength A cylinder is placed on its side in the testing machine and a compressive load is applied uniformly along the length. Principles of Reinforced and Prestressed Concrete Introductory Concepts  NATIONAL UNIVERSITY Civil Engineering Department Properties of Concrete 7. Shear Strength Principles of Reinforced and Prestressed Concrete Introductory Concepts  NATIONAL UNIVERSITY Civil Engineering Department Factors Affecting Concrete Compressive Strength 1. Water/cement ratio the ratio of the weight of the water to the weight of the cement for a given volume of concrete. Principles of Reinforced and Prestressed Concrete Introductory Concepts  NATIONAL UNIVERSITY Civil Engineering Department Factors Affecting Concrete Compressive Strength 2. Type of cement 3. Supplementary cementitious materials Principles of Reinforced and Prestressed Concrete Introductory Concepts  NATIONAL UNIVERSITY Civil Engineering Department Factors Affecting Concrete Compressive Strength 4. Aggregate The strength of concrete is affected by the strength of the aggregate, its surface texture, its grading, and, to a lesser extent, by the maximum size of the aggregate. Principles of Reinforced and Prestressed Concrete Introductory Concepts  NATIONAL UNIVERSITY Civil Engineering Department Factors Affecting Concrete Compressive Strength 5. Mixing water There are no standards governing the quality of water for use in mixing concrete. In most cases, water that is suitable for drinking and that has no pronounced taste or odor may be used. 6. Moisture and temperature conditions during curing The development of the compressive strength of concrete is strongly affected by the moisture conditions during curing. Prolonged moist curing leads to the highest concrete strength. Principles of Reinforced and Prestressed Concrete Introductory Concepts  NATIONAL UNIVERSITY Civil Engineering Department Factors Affecting Concrete Compressive Strength 7. Age of concrete Effect of type of cement on strength gain of concrete (moist cured, water/cement ratio = 0.49). 8. Rate of loading H. F. Gonnerman and W. Lerch, Changes in Characteristics of Portland Cement as Exhibited by Laboratory Tests over the Period 1904 to 1950, ASTM Special Publication 127, American Society for Testing and Materials, Philadelphia, PA, 1951.  NATIONAL UNIVERSITY Civil Engineering Department Tangent and Secant Moduli of Elasticity The slope of a line that is tangent to a point on the stress–strain curve, such as A, is called the tangent modulus of elasticity, ET, at the stress corresponding to point A. The slope of the stress–strain curve at the origin is the initial tangent modulus of elasticity. The secant modulus of elasticity at a given stress is the slope of a line from the origin and through the point on the curve representing that stress. The modulus of elasticity of normal concrete is frequently taken as 𝐸! = 4700 𝑓′! MacGregor, J. G. & Wight, J. K.,(2012). Reinforced concrete: mechanics and design (Vol. 6). Upper Saddle River, NJ: Prentice Hall.  NATIONAL UNIVERSITY Civil Engineering Department The stress–strain curves show five properties used in establishing mathematical models for the stress–strain curve of concrete in compression: 1. The initial slope of the curves (initial tangent modulus of elasticity) increases with an increase in compressive strength. 2. The rising portion of the stress–strain curve resembles a parabola with its vertex at the maximum stress. 3. The strain, 𝜖! , at maximum stress increases as the concrete strength increases. 4. The slope of the descending branch of the stress– strain curve results from the destruction of the structure of the concrete, caused by the spread of microcracking and overall cracking. 5. The maximum strain reached, 𝜖"# , decreases with an increase in concrete strength. Stress–Strain Curve for Normal-Weight Concrete in Compression MacGregor, J. G. & Wight, J. K.,(2012). Reinforced concrete: mechanics and design (Vol. 6). Upper Saddle River, NJ: Prentice Hall.  NATIONAL UNIVERSITY Civil Engineering Department Steel reinforcing bars are basically round in cross section, with lugs or deformations rolled into the surface to aid in anchoring the bars in the concrete. They are produced according to the following ASTM specifications, which specify certain dimensions and certain chemical and mechanical properties. 1. ASTM A 615: Standard Specification for Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement. This specification covers the most commonly used reinforcing bars. 2. ASTM A 706: Standard Specification for Low-Alloy Steel Deformed and Plain Bars for Concrete Reinforcement. This specification covers bars intended for special applications where weldability, bendability, or ductility is important. 3. ASTM A 996: Standard Specification for Rail-Steel and Axle-Steel Deformed Bars for Concrete Reinforcement. This specification covers bars rolled from discarded railroad rails or from discarded train car axles. MacGregor, J. G. & Wight, J. K.,(2012). Reinforced concrete: mechanics and design (Vol. 6). Upper Saddle River, NJ: Prentice Hall.  NATIONAL UNIVERSITY Civil Engineering Department MacGregor, J. G. & Wight, J. K.,(2012). Reinforced concrete: mechanics and design (Vol. 6). Upper Saddle River, NJ: Prentice Hall.  NATIONAL UNIVERSITY Civil Engineering Department The initial tangent modulus of elasticity, Es , for all reinforcing bars can be taken as 200000 MPa. MacGregor, J. G. & Wight, J. K.,(2012). Reinforced concrete: mechanics and design (Vol. 6). Upper Saddle River, NJ: Prentice Hall.  NATIONAL UNIVERSITY Civil Engineering Department Objectives of Design 1. Appropriateness Arrangement of spaces, spans, ceiling heights, access and traffic to complement the intended use. The structure should fit its environment and be aesthetically pleasing. 2. Economy A function of the cost of materials. The overall cost should not exceed the client’s budget. https://www.belfasttelegraph.co.uk/news/uk/classrooms-in-new-schools-too-small-for-number-of-pupils-conference-hears-36763979.html  NATIONAL UNIVERSITY Civil Engineering Department Objectives of Design 3. Structural Adequacy Must be strong enough to support anticipated loadings safely. Must not deflect, tilt, vibrate, or crack in a manner that impairs its usefulness. 4. Maintainability Require a minimum amount of simple maintenance procedures. Principles of Reinforced and Prestressed Concrete Introductory Concepts  NATIONAL UNIVERSITY Civil Engineering Department Limit States A limit state is a state of impending failure, beyond which a structure ceases to perform its intended function satisfactorily, in terms of either strength or serviceability. 1. Ultimate limit states involve a structural collapse of part or all of the structure. 2. Serviceability limit states are those conditions that are not strength based but still may make the structure unsuitable for its intended use. 3. Special limit states involves damage or failure due to abnormal conditions or abnormal loadings. Principles of Reinforced and Prestressed Concrete Introductory Concepts  NATIONAL UNIVERSITY Civil Engineering Department Limit-States Design Limit-states design is a process that involves 1. the identification of all potential modes of failure (i.e., identification of the significant limit states), 2. the determination of acceptable levels of safety against occurrence of each limit state, and 3. structural design for the significant limit states. Principles of Reinforced and Prestressed Concrete Introductory Concepts  NATIONAL UNIVERSITY Civil Engineering Department UNCERTAINTIES IN DESIGN “Structural analysis and design involves the prediction through imperfect mathematical theories of the performance of structural systems constructed by fallible humans from material with variable properties, when these systems are subjected to an unpredictable natural environment.” - Cornell Principles of Reinforced and Prestressed Concrete Introductory Concepts  NATIONAL UNIVERSITY Civil Engineering Department DESPITE UNCERTAINTIES… Manhattan Bridge, New York City https://wallpaperaccess.com/4k-bridge  NATIONAL UNIVERSITY Civil Engineering Department However, poor engineering design can lead to disasters… https://www.hindustantimes.com/india/chennai-building-collapse-death-toll-at-61-rescue-operations-end/story-yYLhuMcharjA9AmkPtWF7J.html  NATIONAL UNIVERSITY Civil Engineering Department STRUCTURAL SAFETY There are three main reasons why safety factors, such as load and resistance factors, are necessary in structural design: 1. Variability in strength MacGregor, J. G. & Wight, J. K.,(2012). Reinforced concrete: mechanics and design (Vol. 6). Upper Saddle River, NJ: Prentice Hall. Mattock A., Kriz L., and Hognestad, E., “Rectangular Concrete Stress Distribution in Ultimate Strength Design,” ACI Journal, Vol. 32, No. 8, February 1961, pp. 875–928.  NATIONAL UNIVERSITY Civil Engineering Department STRUCTURAL SAFETY 2. Variability in loadings MacGregor, J. G. & Wight, J. K.,(2012). Reinforced concrete: mechanics and design (Vol. 6). Upper Saddle River, NJ: Prentice Hall. Ong-Cherng Pier and C. Allan Cornell, “Spatial and Temporal Variability of Live Loads,” ASCE, Journal of the Structural Division, Vol. 99, No. ST5, May 1973, pp. 903–922.  NATIONAL UNIVERSITY Civil Engineering Department STRUCTURAL SAFETY 3. Consequences of failure National Structural Code of the Philippines (NSCP2015) MacGregor, J. G. & Wight, J. K.,(2012). Reinforced concrete: mechanics and design (Vol. 6). Upper Saddle River, NJ: Prentice Hall.  NATIONAL UNIVERSITY Civil Engineering Department Loads on Structures The objective of a structural engineer is to design a structure that will be able to withstand all the loads to which it is subjected while serving its intended purpose throughout its intended life span National Structural Code of the Philippines (NSCP2015) MacGregor, J. G. & Wight, J. K.,(2012). Reinforced concrete: mechanics and design (Vol. 6). Upper Saddle River, NJ: Prentice Hall.  NATIONAL UNIVERSITY Civil Engineering Department TYPES OF LOADS DEAD LOADS Dead Loads are gravity loads of constant magnitudes and fixed positions due to the weight of the structural system itself and any other material permanently attached to it. Unit Weight of Common Construction Materials Materials Unit Weight (kN/m3) Aluminum 25.9 Brick 18.8 Reinforced Concrete 24.0 Structural Steel 77.0 Wood (Timber Material) 6.3 National Structural Code of the Philippines (NSCP2015) MacGregor, J. G. & Wight, J. K.,(2012). Reinforced concrete: mechanics and design (Vol. 6). Upper Saddle River, NJ: Prentice Hall.  NATIONAL UNIVERSITY Civil Engineering Department NSCP Chapter 2 – Dead Loads National Structural Code of the Philippines (NSCP2015) MacGregor, J. G. & Wight, J. K.,(2012). Reinforced concrete: mechanics and design (Vol. 6). Upper Saddle River, NJ: Prentice Hall.  NATIONAL UNIVERSITY Civil Engineering Department LIVE LOADS Live Loads are gravity loads of varying magnitudes and/or positions caused by the use of the structure. These may include weights of objects temporarily placed on a structure, moving vehicles, or natural forces. Minimum Floor Live Loads for Buildings Type of Occupancy Live Load (kPa) Residential 1.90 Other Offices (Basic Office Floor Load) 2.40 Library (Reading Rooms), Hospitals (Operating Rooms) 2.90 Restaurants, Gymnasiums 4.80 Light Storage Warehouses 6.00 Heavy Storage Warehouses 12.00 National Structural Code of the Philippines (NSCP2015) MacGregor, J. G. & Wight, J. K.,(2012). Reinforced concrete: mechanics and design (Vol. 6). Upper Saddle River, NJ: Prentice Hall.  NATIONAL UNIVERSITY Civil Engineering Department NSCP Chapter 2 – Live Loads National Structural Code of the Philippines (NSCP2015) MacGregor, J. G. & Wight, J. K.,(2012). Reinforced concrete: mechanics and design (Vol. 6). Upper Saddle River, NJ: Prentice Hall.  NATIONAL UNIVERSITY Civil Engineering Department WIND LOADS Although the procedures described in the various codes for the estimation of wind loads usually vary in detail, most of them are based on the same basic relationship between the wind speed V and the dynamic pressure q induced on a flat surface normal to the wind flow, which can be obtained by applying Bernoulli’s principle and is expressed as. ! q = ρV2 " ρ is the mass density of the air National Structural Code of the Philippines (NSCP2015) MacGregor, J. G. & Wight, J. K.,(2012). Reinforced concrete: mechanics and design (Vol. 6). Upper Saddle River, NJ: Prentice Hall.  NATIONAL UNIVERSITY Civil Engineering Department WIND MAP OF THE PHILIPPINES National Structural Code of the Philippines (NSCP2015) MacGregor, J. G. & Wight, J. K.,(2012). Reinforced concrete: mechanics and design (Vol. 6). Upper Saddle River, NJ: Prentice Hall.  NATIONAL UNIVERSITY Civil Engineering Department EARTHQUAKE LOADS Earthquake Loads produced loadings on a structure through its interaction with the ground and its response characteristics. lateral loads produced by the flow of wind around the structure. National Structural Code of the Philippines (NSCP2015) MacGregor, J. G. & Wight, J. K.,(2012). Reinforced concrete: mechanics and design (Vol. 6). Upper Saddle River, NJ: Prentice Hall.  NATIONAL UNIVERSITY Civil Engineering Department SEISMIC MAP OF THE PHILIPPINES National Structural Code of the Philippines (NSCP2015) MacGregor, J. G. & Wight, J. K.,(2012). Reinforced concrete: mechanics and design (Vol. 6). Upper Saddle River, NJ: Prentice Hall.  NATIONAL UNIVERSITY Civil Engineering Department OTHER ENVIRONMENTAL LOADS ON STRUCTURES 1. Impact Loads – the dynamic effect of the load (usually live load) that causes the increase in stress when the loads are rapidly applied to a structure. 2. Snow Loads – these are loads due to snow which are considered in other countries that can cause a possible failure of the structure. 3. Hydrostatic Loads – loads on a structure used to retain water such as dams and tanks as well as coastal structures designed to resist hydrostatic pressure. 4. Soil Loads – loads from soil pressure resisted by retaining walls, underground structures, and basement walls and floors. 5. Thermal Loads – loads on a structure caused by stresses due to temperature changes, shrinkage of materials, fabrication errors, and differential settlements of supports. National Structural Code of the Philippines (NSCP2015) MacGregor, J. G. & Wight, J. K.,(2012). Reinforced concrete: mechanics and design (Vol. 6). Upper Saddle River, NJ: Prentice Hall.  NATIONAL UNIVERSITY Civil Engineering Department LOAD COMBINATIONS An engineer must consider all loads that might act simultaneously on the structure at a given time. Based on past experience and probability analysis, there are various load combinations to be considered when designing structures. It is important to note that the structure must be designed to have adequate strength to resist the most unfavorable of all the load combinations. National Structural Code of the Philippines (NSCP2015) MacGregor, J. G. & Wight, J. K.,(2012). Reinforced concrete: mechanics and design (Vol. 6). Upper Saddle River, NJ: Prentice Hall.  NATIONAL UNIVERSITY Civil Engineering Department LOAD COMBINATIONS The following are the commonly used load combinations in the design of structures: Ø 1.4 x DL Ø 1.2 x DL + 1.6 x LL + 0.5 x SL Ø 0.9 x DL + 1.0 x WL Ø 0.9 x DL + 1.0 x EL where: DL = Dead Load, LL = Live Load, SL = Snow Load, WL = Wind Load, and EL = Earthquake Load National Structural Code of the Philippines (NSCP2015) MacGregor, J. G. & Wight, J. K.,(2012). Reinforced concrete: mechanics and design (Vol. 6). Upper Saddle River, NJ: Prentice Hall.  NATIONAL UNIVERSITY Civil Engineering Department DEALING WITH UNCERTAINTIES Deterministic Approach - analysis: ignore uncertainties - design: rely on “factor of safety”(strength and load factors) Probabilistic Approach - analysis: probabilistic analysis - design: reliability based design Principles of Reinforced and Prestressed Concrete Introductory Concepts  NATIONAL UNIVERSITY Civil Engineering Department Design Procedures Working-Stress Design - Design is based on working loads, also referred to as service loads or unfactored loads. The structural material behaves in linear elastic manner and the ratio of the strength of the material to the permissible stress is often referred to as the factor of safety. Limitations - The assumptions of linear elastic behavior and control of stresses within specially defined permissible stresses are unrealistic due to several reasons. Uses the concept of modular ratio which is variable. - The degrees of uncertainties of different types of load acting simultaneously are not considered - Does not account for behavior under loads that exceeds service loads. Principles of Reinforced and Prestressed Concrete Introductory Concepts  NATIONAL UNIVERSITY Civil Engineering Department Design Procedures Strength Design The design is based on factored loads and resistances. The loads are amplified or reduced by load factors depending on the type and sense of the load, while the strengths are reduced by resistance factors less than or equal to unity. The stress condition at the state of impending collapse of the structure is analyzed, and the non- linear stress-strain curves of concrete and steel are made use of. Limitations - Satisfactory performance at ultimate loads does not guaranty serviceability at working loads. - The use of non-linear stress-strain behavior for the design of sections becomes truly meaningful only if appropriate non-linear limit analysis is performed on the structure. Principles of Reinforced and Prestressed Concrete Introductory Concepts  NATIONAL UNIVERSITY Civil Engineering Department Design Procedures Working Strength Design VS Ultimate Strength Design WSD attempts to ensure adequate safety under service loads, while USD attempts to ensure adequate safety under extreme loads. WSD does not investigate behavior beyond service loads, ULM does not guaranty serviceability under service loads. Principles of Reinforced and Prestressed Concrete Introductory Concepts  NATIONAL UNIVERSITY Civil Engineering Department Design Procedures Limit State Design Strength Design strategy is adopted for which members are designed such that materials reach its ultimate point. Since the plastic limit is considered in the design, chances are the development of more cracks and deflection. So the serviceability of structure has to be checked against working stresses. Serviceability includes drifts, deflections and cracks widths. Plastic Design Also referred to as limit design or capacity design, is a design process that considers the redistribution of moments as successive cross sections yield, thereby forming plastic hinges that lead to a plastic mechanism. Principles of Reinforced and Prestressed Concrete Introductory Concepts  NATIONAL UNIVERSITY Civil Engineering Department TYPES OF DESIGN 1. Balanced Design A designed so proportioned that maximum stresses of concrete and steel are reached simultaneously. 2. Underreinforced Design A designed in which the amount of steel is lesser than what is needed in the balanced design. In this design the steel fails first but failure is gradual with the steel yielding. 3. Overreinforced Design A designed in which the amount of steel is more than what is required in the balanced design. In this design the concrete fails first in crushing and the steel will not yield before failure. Principles of Reinforced and Prestressed Concrete Introductory Concepts  NATIONAL UNIVERSITY Civil Engineering Department Stress and Strain Compatibility and Section Equilibrium Two requirements are satisfied throughout the flexural analysis and design of reinforced concrete beams and columns: 1. Stress and strain compatibility. The stress at any point in a member must correspond to the strain at that point. Except for short, deep beams, the distribution of strains over the depth of the member is assumed to be linear. 2. Equilibrium. Internal forces must balance the external load effects. Principles of Reinforced and Prestressed Concrete Introductory Concepts  NATIONAL UNIVERSITY Civil Engineering Department Two different types of problems arise in the study of reinforced concrete: 1. Analysis. Given a cross section, concrete strength, reinforcement size and location, and yield strength, compute the resistance or strength. In analysis there should be one unique answer. section load 2. Design. Given a factored design moment, normally designated as Mu ,select a suitable cross section, including dimensions, concrete strength, reinforcement, and so on. In design there are many possible solutions. load possible sections Principles of Reinforced and Prestressed Concrete Introductory Concepts  NATIONAL UNIVERSITY Civil Engineering Department Principles of Reinforced and Prestressed Concrete Introductory Concepts