Some vital properties of concrete for mix design

While designing the reinforced concrete structure, the designer should concentrate on the following properties of concrete in its harden state.

COMPRESSIVE STRENGTH: At the time of making the design of the buildings and other structures, the compressive strength of concrete is applied as the most common performance measurement.

Compressive strength of concrete is affected by several factors like water-cement ratio, cement strength, quality of concrete material, quality control throughout production of concrete etc.

Concrete compressive strength for general construction fluctuates from 15 MPa (2200 psi) to 30 MPa (4400 psi) and elevated in commercial and industrial structures.

Compressive strength is a vital factor to evaluate the performance of the material throughout service conditions. The compressive strength of concrete is decided in batching plant laboratories for each batch to retain the optimal quality of concrete throughout casting. The strength of concrete is essential to work out the strength of the members. Concrete samples are casted and tested under the action of compressive loads to find out the strength of concrete.

TENSILE STRENGTH: Tensile strength is an important property of concrete since concrete structures prone to tensile cracking because of different types of effects and applied loading itself. Tensile strength of concrete is very low with regard to its compressive strength.

Because of the complexity in employing uniaxial tension to a concrete specimen, the tensile strength of the concrete is obtained by indirect test methods like split cylinder test and flexure test.

Tensile strength of concrete = 1/10 times of compressive strength
With adherence to IS: 456, the tensile strength of concrete is measured from the compressive strength with empirical relation provided by:
Flexural strength: fcr=0.7√fck N/mm2

MODULUS ELASTICITY: The modulus of elasticity of concrete belongs to a function of the modulus of elasticity of the aggregates and the cement matrix and their relative proportions. The elastic modulus of the hardened paste may come in the order of 10-30 GPa and aggregates about 45 to 85 GPa.

The strength of concrete is mainly based on the relative proportion and modulus of elasticity of the aggregate.

To determine the exact value of elastic modulus of a concrete batch, laboratory test should be carried out. There also exist some empirical formulas which are arranged with different code to get the elastic modulus of Concrete. These formulas are derived on the basis of the relationship among modulus of elasticity and concrete compressive strength. One can easily get an rough value of modulus of elasticity of concrete by applying 28 days concrete strength (f'c) with these formulas.

It can be measured with following formula for normal density concrete:
E = 57,000 (fc’)^0.5
The result will be produced in psi.
fc’ stands for the 28 days cylinder crushing strength in psi.

Modulus of elasticity of concrete is affected by the various factors like type of the aggregates used, type of cement and Mix proportions.

SHRINKAGE OF CONCRETE: It stands for a physical property of concrete. The volumetric variations of concrete structures occur because of the loss of moisture by evaporation is defined as concrete shrinkage or shrinkage of concrete. It is a time-dependent deformation that decreases the volume of concrete devoid of the influence of external forces.

This shrinkage leads to surge in tensile stress, that results in cracking, internal warping, and external deflection, before the concrete has to undergo any type of loading.

Water content in concrete considerably impacts the shrinkage. The IS: 456-2000 suggests the total shrinkage strain as 0.0003 when there is no test data. Drying shrinkage in plain concrete leads to surface cracks. The deflections of reinforced concrete members is also influenced by the shrinkage of concrete.

CREEP OF CONCRETE: Creep is one of the fundamental property of concrete. It is very crucial for designing of concrete structure because in concrete the microstrains of creep fluctuates from 400 to 1000 x 10 -6

Creep is described as the elastic and long-standing deformation of concrete under a continuous load. Normally, a long term pressure alters the shape of concrete structure and the deformation is found along the direction of the applied load.

Creep stands for the time dependent deformations of concrete under permanent loads (self weight), PT forces and permanent displacement.

The creep is affected by the several factors like creep concrete mix proportion, aggregate properties, age at loading, curing conditions, cement properties, temperature, stress level.

COEFFICIENT OF THERMAL EXPANSION: The coefficient of thermal expansion of concrete is impacted by the type of aggregate applied in concrete and it is necessary for making the design of structures like chimneys, water tanks, silos etc. The values provided in IS:456-2000 are as follow :-

Type of Aggregate - Coefficient of Thermal Expansion for Concrete

Quartzite - 1.2 to 1.3 x 10-5
Sandstone - 0.9 to 1.2 x 10-5
Granite - 0.7 to 0.95 x 10-5
Basalt - 0.8 to 0.95 x 10-5
Lime stone - 0.6 to 0.9 x 10-5

For more: http://constructioncost.co/some-vital-properties-of-concrete-for-mix-design.html

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Various types of supports for loads

Roller Supports: Roller Support Example in a CraneRoller supports can be revolved freely as well as translated over the surface upon which the roller is situated.

The surface may come in different forms like horizontal, vertical or slopped at any angle. Roller supports are generally situated at one end of long bridges in the sort of bearing pads. This support facilitates bridge structure to stretch and contract as per modifications of temperature and devoid of this expansion the forces can rupture the supports at the banks.

This support does not have the capacity to withstand the lateral forces. Roller support is also utilized in frame cranes in heavy industries, the support can pass on toward left, right and rotate by withstanding vertical loads. In this way, a heavy load can be transmitted from one place to another horizontally.

Hinge Supports: With the hinge support, it is possible to withstand forces which operate in any direction of the plane. This support does not have any resistance capacity against rotation. The horizontal and vertical component of reaction is found with equation of equilibrium. Hinge support is also applied in three hinged arched bridges at the banks supports even as at the center internal hinge is introduced. It is also employed in doors to create only rotation in a door. Hinge support minimizes sensitivity to earthquake.

FIXED SUPPORT: Fixed support has the strength to withstand vertical and horizontal forces as well as moment as they prevent both rotation and translation. They are also called rigid support. To maintain longevity of a structure, a fixed support should exist.

A flagpole at concrete base is the instance of fixed support. In RCC structures, the steel reinforcement of a beam is implanted in a column to create a fixed support. The instances of fixed supports are all the riveted and welded joints in steel structure.

PINNED SUPPORTS: Pinned Supports - A pinned support has the similarity with hinged support. It can withstand both vertical and horizontal forces devoid of a moment.

It facilitates the structural member to rotate, but not to translate in any direction. Many connections are taken as pinned connections although they might withstand a small amount of moment in reality. It is known fact that a pinned connection can facilitate rotation in only one direction by providing resistance to rotation in any other direction.

Ideal pinned and fixed supports are not often detected in practice, but beams supported on walls or simply connected to other steel beams are treated as pinned. The distribution of moments and shear forces is dependent on the support condition.

INTERNAL HINGE: Interior hinges are mostly used to join flexural members at points other than supports.

In some cases, it is purposely introduced with the intension that additional load breaks this weak zone in spite of damaging other structural elements.

Source: aboutcivil.org

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Rajib Dey

www.constructioncost.co

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Different categories of sands and their applications

The sand is mainly applied for rock particles which mainly vary in grain size among 2 mm and 1/16 mm. In composition, they are primarily an oxide of silica SiO2.

Mineralogically, they mostly include broken grains of mineral Quartz (SiO2) that is formed due to the crashing of sandstones and equivalent rocks.

Categorization of Sands: Sands are classified variously on the basis of their Based on the mode of origin, composition, and grain size, the sands are differently categorized.

The mode of origin: With adherence to the mode of origin, there are three types of sands like pit sands, stream sands and marine sands..

The pit sands are generally sharp and angular in outline. Winds generally deposited them and develop accumulations in soils covered by clays. Good quality mortars can be produced from these sands by purifying and cleansing them properly.

The river sands come about large accumulations along the base and banks of all the rivers in plains and semi-hilly areas. The shape of the sand grains in river sands appear almost round (because of significant movement in river waters).

These do not contain clay, salt encrustations, and organic impurities. So, these are frequently utilized to produce mortars, plasters, and concrete.

The marine sands are found on beaches and along the seashores. Similar to river sands, they comprise of rounded grains of quartz. There are some problems with these sands as their grains are mostly wrapped with coatings of salts from sea water.

These salts can’t be separated easily. So, if these salts are utilized with mortars or concrete, a reaction occurs with the binding materials and produce lots of difficulties. Beside, the salt encrustations are often hygroscopic, it means they consume moisture from the atmosphere.

It also leads to delayed setting, dampness. Besides, efflorescence may also happen in mortar or concrete that is formed with these sands. Therefore, the quality of marine sands is substandard and should not be recommended. But, in case of requirements, marine sands should be cleansed perfectly prior to utilize them.

In order to learn how sand is categorized on the basis of composition and grain size, go through the following construction article.

Source: civilseek.com

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Rajib Dey

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Various types of Design Loads on Bridges, Highway & Rail Bridge

While going to deign any bridge, the tasks like computation of Design Loads and loading bridge model are very important. Given below, some crucial loads which should be taken into consideration at the time of creating the design of a bridge.

Dead Load - “Gravity loading because of structural parts of bridge”

Dead load comprises of permanent gravity forces because of structural Elements. It is basically measured as the product of volume and material density. Normally, self-weight is employed in the analysis model with the self-weight option of the analysis software. This makes the calculation step simple.

Superimposed Dead Load - “Dead Gravity loading because of non-structural parts of bridge”

Superimposed dead loads stand for gravity loads that include other permanent items ranging from parapets and road surfacing and other non-structural and architectural attachments to the bridge. Such items last long but should have been modified during the lifetime of the structure. It has similarity with self-weight and it is measured as the product of volume and material density.

The most crucial item of superimposed dead load belongs to the road pavement or surfacing. It is not atypical for road pavements to become gradually thicker over a number of years since every new surfacing is just placed on top of the one before it. Therefore, specifically high load factor is employed to road pavement.

Imposed traffic Loading - “Because of road or rail vehicles”

Imposed traffic loads contain those forces which are produced with road or rail vehicles on the bridge. Bridge traffic can be vehicular, rail or pedestrian/cycle or genuinely any combination of these. The type and strength of the design vehicle alters on the basis of the design code. As for instance, HL-93 is used in AASHTO design code.

Bridge traffic loading is frequently monitored by trucks whose weights significantly surpass the maximum legal. Bridge traffic loading is used with the notional lanes which do not depend on the actual lanes. Eurocode normal loading comprises of invariable loading and a pair of four wheels in a single lane.

To examine the dynamic effects of traffic, the vehicular loads are multiplied with an impact factor frequently.

Pedestrian and cycle track - “Gravity loading because of non-vehicular traffic”

Bridge codes normally indicate a basic intensity for pedestrian loading. Again intensity is based on the design code, it is 5 kN/m2 in the Eurocode and the British standard and 4 kN/m2 in the American code.

To get more detail information, go through the following link. engineeringcivil.org

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Published By

Rajib Dey

www.constructioncost.co

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How to make the design of a Foundation

Foundation is the portion of structure underneath plinth level up to the soil. It is directly connected with soil and it transfers the load of super structure to soil. Normally, it is located under the ground level.

If some portion of foundation is situated over ground level, it is also enveloped with earth filling. This part of structure is not in touch with air, light etc, It is considered as the concealed part of the structure.

Depth of Foundation: Depth of foundation is based on the following points-

1. Sufficient bearing capacity should exist
2. Depth of shrinkage and swelling for of clay soils, because of change in climate that may lead to appreciable movements.
3. Depth of frost penetration for fine sand and silt.
4. Chances of availability of excavation
5. Depth of ground water table
6. Practical lowest depth of foundation should not be under 50 cm. to facilitate subtraction of top soil and deviations in ground level.
7. So, the desired depth of foundation should vary from 1.00 meter to 1.5 meter from original ground level.

Footing: Footing belongs to a structure that is built up in brick work, masonry or concrete under the base of a wall or column for dispersing the load over a extended area.

Width of Foundation/Footings

The width of footings is based on the structural design. For light loaded buildings like houses, flats, school buildings etc which do not contain over two stories, the width of foundation is provided below :-

1. The width of footing should not be under 75 cm for one brick thick wall.
2. The width of footing should not be under 1 meter for one and half brick wall.

Various methods in Foundation Work: The following methods are involved in the foundation works -

1. Excavation of earth work in trenches for foundation.
2. Work out cement concrete.
3. Set the footing for raft or column construction.
4. Arrange Anti termite treatment.

5. Set Brick work up to plinth level.
6. Set Damp proof course on the walls.
7. Refilling of earth around the walls
8. Refilling of earth in the building portion up to the desired height as per plinth level.

For more: http://constructioncost.co/how-to-make-the-design-of-a-foundation.html

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Rajib Dey

www.constructioncost.co

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Structural Design of ASDIP Concrete

ASDIP Concrete is a set of modules which are fully devoted for the design of concrete members like beams, columns and walls depended on the newest ACI 318 specifications.

These specifications can explain the time wasting calculations in any type of structural engineering office; while this ASDIP Concrete 3.1.7v is developed by ASDIP Structural Software and can perform well with Windows. This is a trial version and the file size of the downloaded version is about 4.85 MB.

Here is the list of things which are found under this ASDIP Concrete:

Modules of ASDIP Concrete: This concrete is a unified, merged system that has a combination of flexibility of a fill-in-the-blanks format with the power of Windows Forms and both of them can easily develop either an optimal design or a fast investigation. ASDIP Concrete uses a screen with tabbed pages to enter the users’ data directly onto the forms and allow seeing the results instantly which helps to control the design process, to get the detailed results and the graphics easily.

User Interface: The software uses pull-down menus, dialog boxes and in-field editing as the primary user interface, all these components help to manage and control the difficult design algorithms easily and transparently to the end user in a simple way. It also approves the input data to stop wrong format and users can automatically develop their design with the text-with-values output messages which are updated with every change.

Project Manager: It is a very important thing in the ASDIP Concrete System which takes care of both the calculations and files management from where anyone can create, copy, delete or print calculations, create and save projects and arrange the work.

Reports: The concrete creates high quality previously formatted reports with particular information of any design and optimize the design with the graphical interface, then print preview the results and finally print the report.

Trial Limitations:
• Report- Print disabled
• File- Save Disabled
• 15 day assessment period

ASDIP Concrete has the design of following types of concrete elements:

• Concrete Columns: The design of a concrete column under the action of axial loads and bending moments; while this module can calculates the enlarged moments for slimness of ASCE 7 load combinations and creates the column strength interaction diagram.

• Concrete Beams: The design of a concrete multi-span regular beam under the action of uniform and concreted loads while this module specifically calculate the bending and crop strength for various types of beams and load combinations per ASCE 7.
• Bearing Walls: The design of a concrete wall under the action of vertical and out-of-plane literal loads; the module calculates the magnified moments for slimness of ASCE 7 load combinations and creates the wall strength interaction plan.

Here is some similar software of ASDIP Concrete:

ASDIP Foundation: It is a set of modules certainly dedicated to the design of concrete footings depended on the newest IBC/ACI 318 specifications that simplify calculations of the wasted time in any structural engineering office.
ASDIP Retain: It is a set of modules dedicated fully to the design of retaining walls depended on the new IBC/ACI 318 specifications to simplify the time consuming calculation in any structural engineering office.
ASDIP Steel: It is a set of modules dedicated fully to the design of structural steel members depended on the new AISC 360 for simplifying the time taking calculations in any structural engineering office.
ASDIP: It is a 13-module structural ser with a board of design solutions for new structural engineers.
Advance Concrete: It is totally designed for engineers and structural draftsmen for total and easy to use software fully integrated into AutoCAD.
ASTRUTTIE: It is a strut-tie model design software for concrete members with disturbed stress regions.

Download Free 15 days Trial: asdipsoft.com/asdip-concrete

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Published By

Rajib Dey

www.constructioncost.co

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How concrete is mixed in different ways

Concrete belongs to a composite material formed by cement, sand, coarse aggregate, water and chemical admixtures (if necessary). To maintain the superior quality of concrete, the materials of the concrete should be blended properly so that the quality of concrete is not impacted.

A well-mixed concrete is formed on the basis of the following conditions:

• The color of the concrete should be consistent.
• Admixture of all concrete materials like cement, fine aggregate, coarse aggregate and water should be uniform.
• Cement paste should wrap all the surface of the aggregate.
• Segregation should not happen as soon as the mixing of concrete is completed.

Mixing concrete is dependent on the following three options:

• Hand mixing (Mixing concrete devoid of a mixer)
• Machine mixing (Mixing concrete with a mixer)
• Ready mix concrete

Hand mixing (Mixing Concrete without a Mixer): Hand mixing stands for the method of mixing the different materials of concrete by hand. Mixing concrete devoid of a mixer is suitable for small works. Mixing of materials is executed on masonry platform or flat iron sheet plates.

The hand mixing concrete is performed as follow:

• Expand the measured quantity of sand on the platform, and then unload the cement on the sand.
• The sand and cement should be blended thoroughly with the help of shovels in the dry state.
• The measured amount of coarse aggregate should be extended, and the mixture of sand & cement should spread on it and mixed in an exact manner.
• Depression is provided at the centre of the mixed materials.

• Include 75% of the required quantity of water in the depression and blend well by the shovels.
• Include the leftover amount of water and the mixing method should be carried on unless a uniform colour and consistency of concrete is procured. Time of mixing concrete should not be in excess of 3 minutes.
• The mixing platform should be washed at the end of the day’s work.

Machine Mixing (Mixing Concrete with a Mixer): Machine mixing is mostly suitable for bigger projects where huge masses of concrete are necessary. The machine mixing can retain the persistent uniformity of concrete. Besides, the machine mixing can significantly reduce the mixing time. In recent times, different types of concrete mixers are available which run with petrol/diesel or electricity.

The machine mixing is performed in the following ways:

• Initially, the concrete mixer should be drenched inside of the drum.
• After that Cement, sand and coarse aggregate should be arranged in the portable concrete mixer in desired ratio.
• The dry materials should be blended in the mixing machine. After this, exact quantity of water should be added slowly when the machine is running.
• The concrete should be blended for minimum two minutes after placing all materials in the drum.
• If segregation occurs, the concrete should be remixed after unloading from the mixer.

Ready Mix Concrete: Ready Mixed Concrete (RMC) is developed in the factory or in a batching plant and supplied in a ready-to-use manner. The quality of the consequential concrete is superior as compared to the site-mixed concrete.

Less time is necessary for ready mix concrete as compared to site mixing (hand or machine mixing) and quality of concrete is also greater than the site mixing.

For more: http://constructioncost.co/how-concrete-is-mixed-in-different-ways.html

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Rajib Dey

www.constructioncost.co

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