Fundamentals Of Concrete Design

This assignment covers all basic concepts of concrete, its history, merits and demerits of concrete construction and methods to design concrete. This report assigned by Dr. Tauqir, civil Engineering deptt. UET, Lahore.

Fundamentals Of Concrete Design 2010-TE-45 Hafiz Syed Rizwan

Fundamentals of Concrete Design

Table of Content Concrete: ..................................................................................................................................... 1 1.

Binding Material: ........................................................................................................................ 1

2.

Filler Materials: .......................................................................................................................... 2

3.

Water: ......................................................................................................................................... 3

4.

Additives:.................................................................................................................................... 3 History of Concrete: ................................................................................................................... 3 Difference b/w Plain & Reinforced Concrete: ............................................................................ 4 Merits & Demerits of Concrete Construction: ............................................................................ 4

Merits: ....................................................................................................................................................... 4 Demerits: ................................................................................................................................................... 4 Concrete Design: ........................................................................................................................ 5 

Self-Weight/ Load: ..................................................................................................................... 5



Imposed Load: ............................................................................................................................ 5

Load Combination: ................................................................................................................................... 5 Steps to Design: .......................................................................................................................... 6 1.

Collect & List all known DATA: ............................................................................................... 6

2.

Select the Trial Section: .............................................................................................................. 6

3.

Perform Strength Checks: ........................................................................................................... 6

4.

Perform Service ability Checks: ................................................................................................. 6

5.

Accept the trial section, if all checks are O.K. ........................................................................... 6

6.

Write Final design Results. ......................................................................................................... 6 Important Terminologies: ........................................................................................................... 6

Limit State:................................................................................................................................................ 6 Design Strength:........................................................................................................................................ 7 Factor of Safety: ........................................................................................................................................ 7

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DTEM, UET, LHR.

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Nominal Strength: ..................................................................................................................................... 7 Design Methods: ......................................................................................................................... 7 Basic Design Equation: ............................................................................................................................. 7 1.

Allowable Stress Design: ............................................................................................................ 7

2.

Load & Resistance for Design (LRFD): ..................................................................................... 8

3.

Plastic Design: ............................................................................................................................ 8 References: ................................................................................................................................. 9

Table of Equations

Equation 1 ..................................................................................................................................................... 7 Equation 2 ..................................................................................................................................................... 7 Equation 3 ..................................................................................................................................................... 8 Equation 4 ..................................................................................................................................................... 8

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Fundamentals of Concrete Design Concrete: Concrete is a composite construction material made primarily with aggregate, cement, and water. There are many formulations of concrete, which provide varied properties, and concrete is the most used man-made product in the worldi The main constituent of concrete is as described under:

1. Binding Material: It is usually a paste of cement in water and is relatively costly constituent of the cement concreteii. Materials that can be used as a binder are discussed as follow:



Portland Cement: Portland cement was developed from natural cements made in Britain in the early part of the nineteenth century, and its name is derived from its similarity to Portland stone, a type of building stone that was quarry Portland cement clinker is a hydraulic material which shall consist of at least two-thirds by mass of calcium silicates (3 CaO·SiO2 and 2 CaO·SiO2), the remainder consisting of aluminum- and iron-containing clinker phases and other compounds. The ratio of CaO to SiO2 shall not be less than 2.0. The magnesium oxide content (MgO) shall not exceed 5.0% by mass ed on the Isle of Portland in Dorset, Englandiii.



Lime: Lime is usually made by burning of limestone. Chemically; lime itself is calcium oxide (CaO) and is maThe main ingredient of this concrete is slaked lime as binding material. The slaked lime is obtained in various forms as hydrated lime powder, lime putty, slaked lime slurry that is prepared by grinding in suitable Grinding Mills. Slaked lime is first mixed with sand to prepare lime mortar which is then further mixed with coarse aggregates, in suitable proportion. For preparation of lime concrete, first hard impervious level base is prepared by stones or brick pitching. Then quantity of sand is spread as the horizontal base. Generally lime & sand are taken in ratio of 1:1 to 1:3 by volume. Measured quantity of slaked lime is then added to sand and then mixing is done. In this mixing, water is sprinkled continuously to make the whole mass plastic.

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Then the whole mass is allowed to mature for 1 to 3 days. After that coarse aggregates of desired type are used to lay on the prepared hard impervious level surface. After that lime mortar which is made with sand & lime is introduced into the base. Sufficient water is sprinkled over the base and it is cut into the layers and then is turned upside down with the help of spade or shovel until the whole assembly has become uniform.de by roasting calcite (CaCO3) to remove carbon dioxide (CO2).iv



Bitumen: Bitumen is also used as binder in concrete. Ancient civilization like Babylon people used bitumen to bind stones for their construction.



Gypsum: Used as a binder in concrete, the most common form is (CaSO4.1/2H2O) (Calcium sulfate hemihydrate) Similarly there are also other products that can be used as binder like resins & acrylic emulsion etc.v

2. Filler Materials: Filler material required to reduce the cost of the concrete and to provide the natural strength of stone particle. Most commonly filler material is composed of a combination of various sizes crushed stone. Other Materials can be round gravel, bricks, bloated clay and iron fillings may also be used in concrete for filling purposes.vi The stone aggregate should be well graded so that interlocking between all particles should be as good as possible. We get a dense mass also. Depending on the size, we can classify aggregate into course and fine aggregate.



Course aggregate: Course aggregate having particle size greater than 5mm or 3/16 inch



Fine aggregate: Fine aggregate having particle size lesser than 5mm and usually termed as Sand.vii

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3. Water: Water is added according to water to cement ratio (w/c). for example w/c ratio of 0.45 means 45 liters of water will be added in 100kg of cement.

4. Additives: These are added to improve concrete properties like higher strength etc.

History of Concrete: The word concrete comes from the Latin word "concretus" (meaning compact or condensed), the perfect passive participle of "concrescere", from "con-" (together) and "crescere" (to grow).viii 3000 BC Egyptian used mud with straws to bind bricks. They also used gypsum mortars and mortars of lime in the building of the pyramids. On the other hand, Chinese used cementious material in the construction of Great Wall. In 800 BC, The Greeks used lime mortars that were much harder than later Roman mortars. 300 BC, The Babylonians and Assyrians used bitumen to bind stones and bricks together bricks together.ix During the Roman Empire, Roman concrete (or opus caementicium) was made from quicklime, pozzolana and an aggregate of pumice. Its widespread use in many Roman structures, a key event in the history of architecture termed the Roman Architectural Revolution, freed Roman construction from the restrictions of stone and brick material and allowed for revolutionary new designs in terms of both structural complexity and dimensionx. Modern tests show that opus caementicium had as much compressive strength as modern 2

Portland-cement concrete (ca. 200 kg/cm ). However, due to the absence of reinforcement, its tensile strength was far lower than modern reinforced concrete, and its mode of application was also different.

A method for producing Portland cement was patented by Joseph Aspdin on 1824. In 1889 the first concrete reinforced bridge was built, and the first large concrete dams were built in 1936, Hoover Dam and Grand Coolee Dam.Reinforced concrete was invented in 1849 by Joseph Monier.xi

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Difference b/w Plain & Reinforced Concrete: The Plain Concrete consists of Binder, Filler and water only, while Reinforced concrete also embedded with Steel Bars. Basalt rubber, fiber glass etc. can also be used as alternative of steel bars.xii

Merits & Demerits of Concrete Construction: Merits: 

All structures and buildings are subject to everyday wear and tear, and this is where the use of concrete really makes sense. It’s hard, tough surface is extremely resistant to everyday dents and dings.



Concrete is resistant to rain penetration, flood damage and wind-blown debris. It can also withstand many winters of freeze-thaw cycles unlike other materials, which can deteriorate quickly with such regular exposure to expansion and contraction.



Can be formed in any shape, size and texture, it can be designed to deflect or absorb sound. This makes it a good acoustic material for music but also an effective sound barrier along busy roads.



With homes and offices increasingly wired for information technology, it is good news that precast concrete buildings do not interfere with radio signals, local wi-fi or internet networks. This makes precast the most technology-friendly material for homes and places of work.



With a specific gravity of 2.40, precast concrete resists buoyant forces better than any other material.



Concrete buildings from hundreds of years ago are still in use today. Some say concrete can last up to 2,000 years, and there are certainly many structures around that are well on their way to such a ripe old age.xiii

Demerits: 

Concrete is weaker in Tension therefore we have to reinforced it. This increase the cost.



Concrete is a brittle material.



Concrete has a greater self-weight. Some-times it may increase than live load.



Even if the concrete is reinforced but cracks appears on it due to tensile load.xiv

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Concrete Design: To define proper ratio of Concrete ingredients (cement + water + aggregate), size and numbers of steel bars in a member of structure such that it is more economical, durable and feasible is called Concrete Design. As we design our structure against possible loads that a structure to be faced, So, before proceeding we will discuss the type of loads.

 Self-Weight/ Load: The applied by structure due to its weight is called Self-weight.

 Imposed Load: All loads other than self-load is called imposed load. E.g. live load, dead load, wind load etc.

a. Live Load: Loads which are expected to change in context of position and magnitudes are called live load.

b. Dead Load: The loads which are fixed in terms of point of application and magnitude are called dead loads.

c. Wind Load: The force on a structure arising from the impact of wind on it.

d. Factored Load: To consider the uncertainty due to number of factors we increase the load by some factor and resultant load is termed as Factorial load.xv We consider different load combinations for a specific structure. Most commonly combinations are as follow:

Load Combination: 1.4D 1.2D + 1.6L + 0.5 ( Lr or Snow load) 1.2D + 1.6 (L + Lr) + 0.8 W etc.

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Steps to Design: 1. Collect & List all known DATA: To know about the type of structure, uses of structure, spans and loads of structure like shear and bending moments.

2. Select the Trial Section: Based on experience, make a structure for trial. We select it by thumb rule.

3. Perform Strength Checks: Check whether our trial structure is according to load or not.

4. Perform Service ability Checks: Perform all serviceability checks on a designed structure and select appropriate one.

5. Accept the trial section, if all checks are O.K. 6. Write Final design Results.

Important Terminologies: Limit State: A limit state is a condition of a structure beyond which it no longer fulfills the relevant design criteria. The condition may refer to a degree of loading or other actions on the structure, while the criteria refer to structural integrity, fitness for use, durability or other design requirementsxvi Limit State is divided into two Categories:

Strength/ Safety Limit State: Means conditions of loading corresponding to maximum ductile flexural strength like fatigue, fracture, overturning etc.

Serviceability State: Concerned with occupancy of building, such as excessive deflection, undesirable vibration etc.xvii

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Design Strength: The design strength of structural steel is assumed to be equal to the yield stress. The structural properties of different materials are conveniently expressed in terms of their design strength. This does not necessarily correspond directly to failure of the material, but rather to some point at which the structural performance becomes unacceptable. In the case of structural steel this is defined as the yield stress of the material. The quality of structural steel is carefully controlled with a high degree of quality assurance, and its design strength, py, is expressed as a guaranteed minimum yield stressxviii

Factor of Safety: Factor of safety is the ratio between internal resistance and load effects. FOS = Internal resistance ÷ Load effects Equation 1

Nominal Strength: Strength of section/ member determined using design codes is called nominal strength.

Design Methods: There are three different design methods. 

Allowable Stress Design. (ASD)



Load & resistance for Design. (LRFD)



Plastic Design

Basic Design Equation: In design, the applied forces and moments due to external loads are equated to the maximum resistive forces and moments that can be developed within the material of a member with factor of safety one or greater. External Forces due to loads × FOS = Max internal resistance offered by Material Equation 2

1. Allowable Stress Design: For this method, the FOS is taken on right side of the basic design equation.

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Forces per unit area due to load = Material resistive force ÷ FOS Equation 3

If the factor of safety is applied by reducing the material strength and service loads are considered as such without any increase, the design method is called Allowable Stress Design (ASD) or working stress design.xix

2. Load & Resistance for Design (LRFD): In this method, FOS is divided into two parts. Major part of FOS is applied on load and minor part on material strength. In LRFD by which loads are increased is termed as Overload factor and material strength part is called resistance factor.xx In this method, the engineer uses the Load and Resistance Factor Design (LRFD) load combinations (below) to determine the required strength of a member and arranges for the allowable strength to satisfy this equation:

Equation 4

where: 

Ru = required strength,



Rn = nominal strength, specified in Chapters B through K of the AISC SCM,



φ = resistance factor, specified in Chapters B through K of the AISC SCM,



φ·Rn = allowable strength.

3. Plastic Design: This method is similar to LRFD but we also consider inelastic behavior of material in design and analysis.

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References:

i

Lomborg, Bjørn (2001). The Skeptical Environmentalist: Measuring the Real State of the World. p. 138. ISBN 978-0-52180447-9. ii

Concrete Structures Part-I by Zahid Ahmed Siddique Gillberg, B.; Jönsson, Å.; Tillman, A-M. (1999) (in Swedish). Betong och miljö [Concrete and environment]. Stockholm: AB Svensk Byggtjenst. ISBN 91-7332-906-1. iv http://www.enggpedia.com/civil-engineering-encyclopedia/dictionary/engineering-materials/329lime-concrete v Alternative of concrete other than cement by Jame SK Yeung Honk Kong Concrete Institute. vi Concrete Structures Part-I by Zahid Ahmed Siddique vii Concrete Structures Part-I by Zahid Ahmed Siddique iii

viii

"concretus". Latin Lookup. Retrieved October 1, 2012

ix

Alternative of concrete other than cement by Jame SK Yeung Honk Kong Concrete Institute x Lancaster, Lynne (2005). Concrete Vaulted Construction in Imperial Rome. Innovations in Context. Cambridge University Press. ISBN 978-0-511-16068-4 xi Herring, Benjamin. "The Secrets of Roman Concrete". Romanconcrete.com. Retrieved 1 October 2012. xii Smarter Building Systems, Newport, Rhode Island USA xiii A little book of concrete by British Precast and NPCA xiv Concrete Structures Part-I by Zahid Ahmed Siddique xv Class notes by Dr. Tauqir, UET, LHR. xvi

EN 1990:2002 E, Eurocode - Basis of Structural Design, CEN, November 29, 2001

xvii

Concrete Structures Part-I by Zahid Ahmed Siddique

xviii

http://www.tatasteelconstruction.com/en/reference/teaching_resources/architectural_studio_reference/el ements/introduction_to_design_codes/design_strengths/ xix Concrete Structures Part-I by Zahid Ahmed Siddique xx Class notes by Dr. Tauqir, UET, LHR

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