Acivcrete Basics - #2

REINFORCEMENT REQUIREMENT IN COLUMNS

--Minimum % of steel=0.8% of gross cross section area.
--Maximum % of steel=4% of gross cross section area and should not exceed 6%.
--Minimum number of rods in circular and rectangular/square columns are 6 and 4 respectively.
--Minimum diameter of bar=12 mm.
--Bars spacing shall exceed 300 mm along periphery.
--For pedestals minimum area of reinforcement=0.15% of gross cross sectional area.

-Minimum Grade of Concrete for Liquid storage structures is M30.(as per IS 3370(Part 1):2009-Code of practice for storage of liquids)
-Minimum cement content is 320 kg/m3.
-Maximum cement content is 400 kg/m3.


REINFORCEMENT REQUIREMENT IN SLABS:-

-0.15% for Fe 250 grade of steel 
-0.12% for Fe 415 grade of steel.

Acivcrete Civil Site Basics - 1

Clear cover to main reinforcement in 

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Footings : 50 mm
Raft foundation Top : 50 mm
Raft foundation Bottom/ sides : 75 mm
Strap Beam : 50 mm
Grade Slab : 20 mm
Column : 40 mm (d>12mm) 25 mm (d= 12mm)
Shear Wall : 25 mm
Beams : 25 mm
Slabs : 15 mm or not less than diameter of the bar.
Flat Slab : 20 mm
Staircase : 15 mm
Retaining Wall on Earth : 20/ 25 mm
Water retaining structures : 20 / 30 mm
Sunshade (Chajja) : 25 mm

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Hook for stirrups is 9D for one side  

No. of stirrups = (clear span/Spanning) + 1
 
For Cantilever anchorage length for main steel is 69D


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“L” for column main rod in footing is minimum of 300mm

Chairs of minimum 12 mm diameter bars should be used.

Minimum diameter of dowel bars should be 12 mm

Lap slices should not be used for bar larger than 36 mm.

Columns and Lintels

Basic review about Columns and Lintels. For beams, please check our previous post .

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Basic Civil Engineering - Beams

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Basic Civil Engineering Terms

DUCTILITY Ability of a material to deform easily under stress of temperature‚ pressure and Speed; especially‚ ability of a metal to stretch easily. Ductility is characterized by a weak elastic limit and significant lengthening.

WORKABILITY The ability of a mortar or a fresh concrete to fill correctly a mold or a formwork thanks to a well-studied batching of its constituents that give him a sufficient fluidity without harming its strength and its homogeneity. The workability is a factor of the first magnitude because it conditions among other things: good filling, simplicity of placing, good covering of reinforcements.

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BLEED To go up on the surface, speaking of the water contained in a mortar, a concrete. To reject internal water.

BLEEDING The appearance of a film of water or laitance on the surface of a slab or a concrete or mortar screed after troweling or vibration. The vibration, closing between them the various grains of the components of concrete, brings about the expulsion of a part of water that occupies the empties. Water, having lower density than the other components, goes up on the surface. Syn. with BLEED-THROUGH; SWEATING; WATER GAIN

SEGREGATION 1. An imbalance in the chemical composition of the different components of an alloy. 2. A preferential aggregation of the chemically alike components between them during the solidification phase of an alloy; this separation results in a chemically heterogeneous structure. 3. A selective dissociation, in distinct heaps, of different previously mixed bodies as a result of vibration, brewing, etc. 4. A phenomenon of dissociation of the concrete ingredients that can be due to various causes (excessive vibration, carriage, falls from critical height, etc.).

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HYDRATE A chemical body resulting from the combination of a body with water molecules.

HYDRATION Phenomenon of water absorption by a chemically receptive body. The process of chemical reaction between water and cement is also called hydration.


DURABILITY Resistance to weather condition

SHRINKAGE Decrease in volume of Concrete

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COMPACTION Compaction is removing the air from concrete. Proper compaction results in concrete with an increased density which is stronger and more durable.

BITUMEN: Bitumen is a generic name applied to the various mixtures of hydrocarbons. They may be gases, liquid ,semisolid and solid in nature and completely soluble in carbondisulphide.

Paints Paints are used to protect metals, timber, or plastered surfaces from the corrosive effects of weather, heat, moisture or gases etc and to improve their appearance

Basic civil engineering 21

The minimum grades of concrete for prestressed applications are as follows. 
• 30 MPa for post-tensioned members (Ex:slabs)
• 40 MPa for pre-tensioned members. (Ex:sleepers)

Deflection of a simply supported beam for udl is 5 times more than the deflection of a fixed beam for the same loading and beam properties and dimensions.

REINFORCEMENT REQUIREMENT IN SLABS:-

-0.15% for Fe 250 grade of steel 
-0.12% for Fe 415 grade of steel.

REINFORCEMENT REQUIREMENT IN COLUMNS

--Minimum % of steel=0.8% of gross cross section area.
--Maximum % of steel=4% of gross cross section area and should not exceed 6%.
--Minimum number of rods in circular and rectangular/square columns are 6 and 4 respectively.
--Minimum diameter of bar=12 mm.
--Bars spacing shall exceed 300 mm along periphery.
--For pedestals minimum area of reinforcement=0.15% of gross cross sectional area.

-Minimum Grade of Concrete for Liquid storage structures is M30.(as per IS 3370(Part 1):2009-Code of practice for storage of liquids)
-Minimum cement content is 320 kg/m3.
-Maximum cement content is 400 kg/m3.

PINNED SUPPORT- The beam rods terminate at the end of the beam and are not anchored into the columns.

SAFETY CURVE 

ACCELERATORS

->Accelerators are admixtures used in cold weather to increase the rate of hardening and thereby reduce the failure of concrete.
->They accelerate the hardening of cement & increase the rate of evolution of heat;hence the temperature of concrete is raised.
->CaCl2 is the most commonly used and reliable accelerator.
->Used upto a maximum of 2% by weight of cement.

Basic Civil Engineering - 20

Allowable settlement for a pile foundation is 12mm.

->Minimum grade of concrete for RC Structures as per IS 456:2000 is M20.
->Minimum grade of concrete for Water Retaining RC Structures as per IS 3370:2008 is M30.

Lateral Sway/Drift at the top of a RC structure should not exceed H/300.

Types of Beam-Column Connections

(a) Simple – transfer only shear at nominal eccentricity
Used in non-sway frames with bracings etc.Used in frames upto 5 storeys

(b) Semi-rigid – Transmits both shear and moment . Practically this type of connection is most found.

(c) Rigid – transfer significant end-moments undergoing negligible deformations. Used in sway frames for stability and contribute in resisting lateral loads and help control sway.

Minimum Grade of Concrete for Liquid storage structures is M30.(as per IS 3370(Part 1):2009-Code of practice for storage of liquids)
-Minimum cement content is 320 kg/m3.
-Maximum cement content is 400 kg/m3.

REINFORCEMENT REQUIREMENT IN SLABS:-

-0.15% for Fe 250 grade of steel 
-0.12% for Fe 415 grade of steel.

THIXOTROPHY--the process by which soil particles re-orient themselves closely and thereby gains strength over a gradual period of time!!!

DO YOU KNOW ??
CIRCULAR columns are the most efficient when compared to rectangular/square as they possess equal radii of gyration in both the axes!!

Basic civil engineering Part 19

Question-1: What is the FM(Fineness Modulus)?
Answer: FM( Fineness Modulus is an empirical figure obtained by summing up the cumulative percentage of materials retained on each of the sieve excluding 0.075 mm sieve and dividing the sum by 100.

Question-2: What is the FM value for Sand and Stone?
Answer: For sand the FM value varies from 2.5-4.0 and for stone FM value varies between 6.5-8.0.

Question-3: What is LAA?
Answer: LAA means Los Angeles Abrasion Test which represents the strength of stone to withstand with the abrasion that occurs during the life cycle of the stone.

Question-4: If the W/C cement ration is less what will be the strength of concrete?
Answer: If W/C ratio decreases concrete strength will rise up.

Question-5: What is Compaction?
Answer: Compaction is a process by which the volume of the soil decreases by using any mechanical devices and by pulling out the available air in the soil.

Question-6: What is Consolidation?
Answer : Consolidation is a natural process by which the soil volume reduces and it becomes in compacted form by pulling out the water and decreasing the pore spaces between the particles    

Question-7: Say name of the compaction test methods?
Answer : 1. Standard Proctor Test
2. Modified Proctor Test

Question-8: How can you measure workability of the concrete on field?
Answer: Workability can be measured by slump test.

Question 9: What is the normal slump value for concrete?
Answer: Normally slump vale varies between 50 mm-100 mm for normal concrete.

Question 10: What is the dimensions of Slump Mold?

Answer: Height=12 inch, Top width=4 inch and bottom width= 8 inch

Basic civil engineering - Part 18

Mechanics of Solids

Definition: It is the combination of physical, mathematical, and computer laws and techniques to predict the behavior of solid materials that are subjected to mechanical or thermal loadings. It is the branch of mechanics that deals with the behavior of solid matter under external actions. The external actions may be: External Force Temperature Change Displacement BUY THE BEST CIVIL ENGINEERING BOOKS HERE -- http://goo.gl/8PVgzL LIKE US NOW  -- https://www.facebook.com/Acivcrete Applications of Solid Mechanics This field has a wide range of applications, laws and concepts of solid mechanics are used: In Civil Engineering to design foundations and structures In Geo-Mechanics to model shape of planets, tectonics and predict earthquakes In Mechanical Engineering to design load bearing components for vehicles, power generation and transmission

Some Important Definitions in Solid Mechanics Stress When an external force is applied on a body, it undergoes deformation which is resisted by the body. The magnitude of the resisting force is numerically equal to the applied force. This internal resisting force per unit area of the body is known as stress. Stress = Resistive Force/Area In equation form: σ = P/A, Units are – N/m2, kN/m2 MPa (Mega Pascal) – Psi (lb/in2), psf (lb/ft2) – Ksi (kips/in2), ksf (kips/ft2) BUY THE BEST CIVIL ENGINEERING BOOKS HERE -- http://goo.gl/8PVgzL LIKE US NOW  -- https://www.facebook.com/Acivcrete Strain When a body is subjected to an external force, there is some change of dimension in the body. Numerically the strain is equal to the ratio of change in length to the original length of the body. Strain = Change in length/Original length In equation form: ε= δL/L Units m/m, mm/m In/in, in/ft Primary Strain/Longitudinal Strain/Direct Strain It is the ratio of the change in longitudinal length (dimension parallel to the direction of applied force) to the original longitudinal length. Longitudinal Strain = δL / L Secondary Strain/Lateral Strain/indirect Strain It is the ratio of the change in lateral dimension (dimension not parallel to the direction of applied force) to the original lateral dimension. Lateral Strain = δW / W Shear Stress(τ) and Shear Strain(G) The two equal and opposite forces act tangentially on any cross sectional plane of the body tending to slide one part of the body over the other part. The stress induced is called shear stress and the corresponding strain is known as shear strain. BUY THE BEST CIVIL ENGINEERING BOOKS HERE -- http://goo.gl/8PVgzL LIKE US NOW  -- https://www.facebook.com/Acivcrete Hooke’s law This law states that when a material is loaded, within its elastic limit, the stress is directly proportional to the strain. Stress α Strain σ α ε σ = Eε E = σ/ε Its unit is same as that of Stress Where, – E is Young’s modulus – σ is Stress – ε is Strain Poisson Ratio It is the ratio of the lateral strain to the longitudinal strain and is constant property of each material. Poisson’ ratio (μ or 1/m) = Lateral strain /Longitudinal strain Young’s Modulus: It is the ratio of the normal stress to the normal strain. E = σ/ε Rigidity Modulus: Its is the ratio of the shear stress to the shear strain. N = Shear stress/Shear strain N = τ/G Elastic Limit: The maximum stress that can be applied to a metal without producing permanent deformation is known as Elastic Limit – When stress is applied on a body its dimensions change, these changes can be reversed if the stress applied do not cross a certain limit. – This certain limit within which the material when unloaded will re-gain its original dimensions is known as Elastic Limit. – Beyond the elastic limit the changes will be permanent and cannot be reversed without an external force. Brittle materials tend to break at or shortly past their elastic limit, while ductile materials deform at stress levels beyond their elastic limit. Stress-Strain Relation Yield Point or Yield Stress It is the lowest stress in a material at which the material begins to exhibit plastic properties. Beyond this point an increase in strain occurs without an increase in stress which is called Yielding. Ultimate Strength It is the maximum stress that a material can withstand while being stretched or pulled before necking. Strain Hardening It is the strengthening of a metal by plastic deformation because of dislocation (irregular) movements within the crystal structure of the material. Any material with a reasonably high melting point such as metals and alloys can be strengthened by this method. Strain Energy: Whenever a body is strained, some amount of energy is absorbed in the body. The energy that is absorbed in the body due to straining effect is known as strain energy. Resilience: The total strain energy stored in the body is generally known as resilience. Proof Resilience: The maximum strain energy that can be stored in a material within elastic limit is known as proof resilience. Modulus of Resilience It is the ratio of the proof resilience of the material to the unit volume • Modulus of resilience = Proof resilience /Volume of the body

Soil Basics - #1

Classification of Soil is based on 3 Methods
MIT System of soil classification

AASHTO classifications of soils

Unified soil classification system (USCS)

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ATTERBERG LIMITS

Liquid limit: The boundary between the liquid and plastic states; Plastic limit: The boundary between the plastic and semi-solid states; Shrinkage limit: The boundary between the semi-solid and solid states. These limits have since been more definitely defined by A. Casagrande as the water contents which exist under the following conditions: 1. Liquid limit The water content at which the soil has such a small shear strength that it flows to close a groove of standard width when jarred in a specified manner. The Liquid Limit, also known as the upper plastic limit, is the water content at which soil changes from the liquid state to a plastic state. OR It is the minimum moisture content at which a soil flows upon application of very small shear force. Liquid Limit (LL or wL) ‑ the water content, in percent, of a soil at the arbitrarily defined boundary between the semi‑liquid and plastic states.
Liquid limit is defined as “ the moisture content at which soil changes from liquid state to plastic state” Or According to Casagrande Liquid Limit Test it is also defined as “ the moisture content at which two sides of a groove come close together for a distance of 12.7 mm under the impact of 25 number of blows” Or According to fall cone test method Liquid Limit is also defined as “the moisture content at which the cone( fall cone test) penetrates with in the soil for 1 cm when falls freely for 5 seconds. 2. Plastic limit The water content at which the soil begins to crumble when rolled into threads of specified size. The Plastic Limit, also known as the lower plastic limit, is the water content at which a soil changes from the plastic state to a semisolid state. Plastic Limit (PL or wP) ‑ the water content, in percent, of a soil at the boundary between the plastic and semi‑solid states. It is defined as “The moisture content at which the soil behaves like a plastic material is called plastic limit” Or It may also be defined as “The moisture content at which the soil changes from plastic state to semi solid state" Or “The moisture content at which the soil begins to crumble when rolled up into a thread of 3 mm in diameter” 3. Shrinkage limit: Shrinkage limit is defined as “the moisture content at which the soil change from a semi solid state to a solid state” Or “The maximum water content at which the reduction in water content will not cause decrease in total volume of soil but the increase in moisture content will cause an increase in moisture content” Or It is also defined as “the lowest water content at which the soil are still completely saturated” 4. Plasticity Index (PI) ‑ the range of water content over which a soil behaves plastically. It is defined as “the range of consistency with in which the soil exhibit plastic properties”. Or It is also defined as “the numerical difference between the liquid limit and plastic limit”. Mathematically, Plasticity index = Liquid Limit – Plastic Limit It is denoted by Ip and Ip = LL – PL 5. Liquidity index: Its advantage is that The liquidity index (LI) is used for scaling the natural water content of a soil sample to the limits. How to find Bearing Capacity of Soil Methods of bearing capacity determination §  Analytic method i.e. through bearing capacity equations like using Terzaghi equation, Meyerhof equation, Hansen equation etc §  Correlation with field test data e.g. Standard penetration test (SPT), Cone penetration test (CPT) etc §  On site determination of bearing capacity e.g Plate load test, Pile load test Presumptive bearing capacity (recommended bearing capacity, in various codes) Following are the methods: Analytical Method of Bearing capacity determination Analytical Method Lower Bound Failure Lower bound failure states that “If an equilibrium distribution of stress can be found which balances the applied load and nowhere violates the yield criterion, the soil mass will not fail or will just be at a point of failure i.e. it will be a lower bound estimate of capacity. Consider the equilibrium conditions in soil under the footing load. When the foundation pushes into the ground, stress block 1 has principal stresses, as shown. The push into the ground however, displaces the soil on the right side of the line OY laterally, resulting in the major principal stress on block 2 being horizontal as shown. When the two blocks are adjacent to each other at the vertical line OY, then Some Formulae Upper Bound theorem Upper bound theorem states that “If a solution is kinematically admissible and simultaneously satisfies equilibrium failure must result” i.e. it will be an upper bound estimate of capacity. For a possible upper bound, consider failure surface as semicircle. Taking moment about O Terzaghi’s bearing capacity equation (1943) Terzaghi developed a general formula for ultimate bearing capacity of spread footing foundation under the following assumptions: The depth of the footing is less than or equal to its width (D, B) The foundation is rigid and has a rough bottom The soil beneath the foundation is homogeneous semi-infinite mass Strip foundation with a horizontal base and level ground surface under vertical loads. The general shear mode of failure governs and no consolidation if the soil occurs (settlement is due only to shearing and lateral movements of the soil) The shear strength of the soil is described by s = c + σ tan