Variation among Working stress method and Limit state method

This construction video shows the variation among working stress method and limit state method.

The basic variance among Working state method (WSM) and Limit State method (LSM) is that WSM stands for an elastic design method while LSM stands for a plastic design method.

In elastic design method, the design strength is estimated in such a manner that the stress in material is controlled with its yield limit, under which the material adheres to Hooke's law, and therefore, the word "elastic" is utilized. This method is used to produce cost-effective design of simple beam, or other structural elements where the standard for evaluating the design is stress (static). But, in case of changing the evaluation standard to other factors like fatigue stress, both the methods will give similar design. Also, WSM substantially reduces the calculation efforts.

In plastic design method the stress in material is permitted to go outside the yield limit and move into the plastic zone to attain extreme strength. Therefore, the "moment-rotation" power of beam, as for instance, is applied for creating more cost-effective design. However, because of the deployment of the non-linear zone, this method comprises laborious calculation.

Given below, some other general differences:

1) Serviceability check if LSM is necessary since after the elastic region strain is greater, it leads to more deformation, therefore a check is required.

2) LSM refers to strain based method while WSM is stress based method.

3) LSM refers to non-deterministic method while WSM is deterministic approach.

4) Partial safety factor is applied in LSM while Safety factor is applied in WSM.

5) Characteristic values (resulting from probabilistic approach) are applied in case of LSM while Average or statistic values are applied in WSM.

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Published By

Rajib Dey

www.constructioncost.co

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How to estimate the quantities of masonry works

In a Masonry work, the cement and delicate aggregates devoid of any coarse aggregates are applied for constructing a structure. There exist various types of masonry work:

1. Brick Masonry

2. Concrete block / brick masonry

3. Stone / rubble masonry

4. Clay tiles, etc.

Masonry works like brick masonry, concrete block, stone or rubble masonry are usually estimated with volume, but in some cases these are computed with regard to area where the thickness of masonry is confined to single brick or single block. Tiling is estimated in area.

To estimate the quantities of masonry work, the wastage of materials like bricks, cement or sand as well as the types and classes of bricks, blocks or tiles are not considered. All types of masonry works are calculated individually into categories to estimate the perfect cost of construction on the basis of its price.

To estimate masonry works, the guidelines given below should be maintained:-

1. Masonry is computed as “net in place” containing deductions for openings like doors, windows, ventilation etc.

2. Various shapes of masonry units are individually estimated which range from rectangular, circular etc.

3. Masonry at various heights is estimated individually as masonry at greater elevation from ground may need scaffolding and hoisting.

4. Masonry work is estimated independently in the following diverse: a. Facings, b. Backing to facings, c. Walls and partitions, d. Furring to walls, e. Fire protection

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Published By

Rajib Dey

www.constructioncost.co

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