Some useful tips for machine foundation design

Before starting the detailing work for foundations, the following general needs concerning machine foundations should be fulfilled and the results should be verified.

1. The foundation should have contained the capacity to bear the superimposed loads devoid of producing shear or crushing failure.

2. The settlements should have been inside the allowable limits.

3. The amalgamated centre of gravity of machine and foundation should have been maintained in the equivalent vertical line like the centre of gravity of the base plane.

4. There should have been no resonance, therefore the normal frequency of the foundation–soil system should have been either too big or too small with regard to the operating frequency of the machine. Toward low-speed machines, the natural frequency should have been high.

5. The amplitudes under service conditions should be maintained under allowable limits which are recommended by the machine manufacturers.

6. All rotational and correlating parts of a machine should be well-adjusted efficiently with the purpose of reducing the unbalanced forces or moments.

7. If necessary, the foundation should be planned in an efficient way with the intention of allowing a consequent adjustment of natural frequency by adjusting the base area or form of the foundation as may be essential afterward.

To read the complete article, go through the following link. theconstructor.org

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Published By

Rajib Dey

www.constructioncost.co

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Benefits And Drawbacks Of Flab Slabs Toward Flab Slab Floor System

A flat slab belongs to a one-way or two-way method that is condensed in the slab at the columns and load bearing walls known as ‘drop panels’. Drop panels are used as T-beams over the supports. They improve the shear capacity and the rigidity of the floor system below vertical loads, which consequently enhance the economical span range. Now-a-days, this type of construction is not recommended as the perimeter on economical spans is approximately 9.5 m for reinforced slabs and approximately 12 m for pre-stressed slabs. Reinforced flat slabs should be reasonably pre-cambered (not overdone) to manage deflection.

The primary features of a flat slab floor are a flat soffit, plain formwork and simple construction. The economical span ‘L’ of a reinforced concrete flat slab is roughly D x 28 for simply supported, D x 32 for an end span and D x 36 for an interior span. Prestressing the slab expands the economical span to D x 35, D x 40 and D x 45 correspondingly, where D denotes the depth of the slab exclusive of the drop panel.

Benefits and Drawbacks of Flat Slabs

Benefits :

• Uncomplicated formwork

• No beams—make things easier under-floor services outside the drops

• Lowest structural depth

• Generally no need of shear reinforcement at the columns.

Drawbacks:

• Moderate spans

• Usually not appropriate for supporting brittle (masonry) partitions

• Drop panels hinder in bigger mechanical ducting

• Vertical penetrations should prevent area around columns

• For reinforced flat slabs, deflection at the middle strip becomes complicated.

Ref.: civildigital.com

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Published By

Rajib Dey

www.constructioncost.co

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Categories, Design And Modes Of Failure Of Retaining Walls

Retaining wall is described as a fairly hard wall. It is constructed to give support to the soil mass horizontally to hold the soil at various levels on the two sides.

The following topics are covered in this construction article :-

• Types

• Design

• Modes of Failure

Types of retaining wall:

Usually the retaining walls are categorized as follow :-

Gravity Retaining Wall: Here weight is the key factors for these walls to maintain durability. In general, the walls are developed with plain concrete or masonry. For the structures having long height, these walls may be quite expensive.

Semi-gravity Retaining Wall: The section size regarding a gravity retaining wall is decreased with the placement of the fewer amount of adjacent to the back face. Such walls can be termed as semi-gravity walls.

Cantilever Retaining Wall: The Cantilever retaining walls are mainly developed with reinforced cement concrete. The wall comprises of a lean stem together with a base slab cast monolithically. For the construction that contains a height of 6 to 8 m, this type of wall is cost-effective.

Counterfort Retaining Wall: In Counterfort Retaining walls, there are lean vertical slabs alias counterforts which are positioned over the vertical steam recurrently. The counterforts join the vertical stem by the base slab. Hence, the vertical stem and the base slab extend amid counterforts. Here the counterforts are used to reduce the shear force and bending moments in the vertical stem and the base slab. The structures which contain a height over 6 to 8 m, the counterfort retaining walls are economical.

Guidelines for designing retaining walls: Before developing the realistic design, the soil parameters which can impact the earth pressure and the bearing capacity of the soil, must be analyzed properly. The soil parameters contain the unit weight of the soil, the angle of shearing resistance, the cohesion intercept and the angle of wall friction. The soil parameters are liable for detecting the lateral earth pressures and the bearing capacity of the soil. As soon as the earth pressures are detected, the retaining walls should be verified completely to find out the strength toward sliding, overturning, bearing capacity failure & tension.

Other modes of failure of retaining walls

Besides, three types of failures like sliding, overturning and bearing failure, the following two modes are also liable for collapsing of a retaining wall in case the soil below is feeble.

Shallow Shear Failure: This type of failure takes place along a cylindrical passing with the heel of the retaining wall owing to the extreme shear stresses along the cylindrical surface inside the soil mass. Usually the cause for safety alongside horizontal sliding is reduced contrary to the shallow shear failure. Due to this, if the factor of safety alongside sliding exceeds by 1.5, shallow shear failure will not occur.

Deep shear failure: It happens along a cylindrical surface, if there exists a feeble layer of soil below the wall a depth regarding 1.5 times the height of the wall. The trial and error processes are applied to ascertain the critical failure surface.

Ref : www.civileblog.com

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Published By

Rajib Dey

www.constructioncost.co

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