Mechanical properties of building materials

All the building structures are developed with various types of materials. These materials are either known as building materials or materials of construction. The cost of material in a building varies from 30 to 50 percent of entire building cost.

Given below, the detail mechanical properties of materials :-

Strength:

a. Strength is defined as the strength of material to resist the load.
b. Strength of materials – Capacity to resist an applied stress devoid of failure.
c. Compressive strength – Capacity to resist axially directed pushing forces.
d. Tensile strength – Highest stress at the time of being expanded or dragged prior to necking.
e. Shear strength – The capacity to resist shearing.
f. Elasticity – In a material if exterior load is employed it experiences deformation and on elimination of the load, it gets back to it’s actual shape.

Plasticity: If a material fails to retrieve it’s actual shape while eliminating the exterior load, it is defined as plastic materials.

Ductility: When a material experiences a significant deformation devoid of rupture, it is known as ductile materials.

It experiences a large deformation throughout tensile test. It is considered as the most perfect material for tension member. Steel, copper, wrought iron, aluminum alloys belong to ductile materials.

Elongation is in excess of 15%

Brittleness:

a. If a material can’t experience any deformation if some external force functions on it and it collapses with rupture.
b. Brittleness means powerful in compression and poorer in tension.
c. Brittleness is found in C.I, glass, concrete, bricks etc.
d. Elongation remains under 5%

Malleability: Malleability is the capability of a material to distort under pressure (compressive stress). After being malleable, a material is flattened into thin sheets through hammering or rolling. Several metals with high malleability also contain high ductility.

Malleable materials are gold, silver, copper, aluminum, tin, lead steel etc.

Toughness: Toughness means the capability of a material to consume energy prior to rupture is known as toughness.

Toughness is found in mild steel, wrought iron etc.

Hardness: Hardness means the resistance of materials against abrasion, indentation, wear and scratches.

C.I is stronger material.

Stiffness: Stiffness refers to force that is necessary to create unit deformation in a material.

Creep: Creep means inelastic deformation because of sustained load.

Physical properties of materials

Bulk density = ρ = M/V
Water absorption
Permeability
Stability

Specific gravity (G): Mass of solids of specified volume / Mass of equal volume distilled water

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Published By
Rajib Dey
www.constructioncost.co
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Some useful information on detailing of beam

Detailing is one of the most crucial basic features of any construction. The architect should evaluate and place different elements of RCC members with proper care.

Proper detailing of reinforcements with accurate drawings is necessary at the construction site to maintain perfect construction process. Normally, these drawings comprises of a bar bending schedule. The bar bending schedule defines the length and number, location as well as the shape of the bar.

The detailing of beams is normally related to the followings :-

a. Size and number (or spacing) of bars
b. Lap and curtailment (or bending) of bars
c. Development length of bars
d. Clear cover to the reinforcement
e. Spacer and chair bars

The steel that is applied in beams pertains to various categories on the basis of the following objectives :-

i) Longitudinal reinforcement at tension and compression face (at least two 12 mm diameter bar should be arranged in tension) in single or multiple rows should be supplied.

ii) Shear reinforcements in the type of vertical stirrups and or bent up longitudinal bars should be arranged. (The bar bent round the tensile reinforcement and delivered to the compression zone of an RCC beams is known as stirrups).

iii) Side face reinforcement in the web of the beam is placed when the depth of the web in a beam remains in excess of 750 mm. (0.1% of the web area and allocated consistently on two faces at a distance not surpassing 300 mm or web thickness whichever is lower).




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Published By
Rajib Dey
www.constructioncost.co
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Stress Control by Deflecting & Debonding Tendons in PSC Design

If precast beams contain straight, fully bonded tendons, they can be easily detailed and manufactured. The main benefit of pre-stressing is that it can apply the dead toad of the unit to minimize the transmission of the tensile stresses in the concrete.

But dead load is lost in such members since this tension remains most critical at the ends of the beams, where the alleviating effect owing to dead load is zero. The methods of deflecting and debonding tendons are frequently applied in pre-tensioned beams to obtain a pre-stress distribution much like that is obtained by the draped profiles of post-tensioned systems. It maintains some of the dead-load benefits, which lead to fewer tendons in the beams or a slightly smaller depth of beam than would be feasible with straight, fully bonded tendons.

Stress Control by Deflecting Tendons: The method of deflecting some of the tendons upwards towards the ends of a beam at a proper position along the span transfers the important section at transfer to this position, where vital relieving stresses as beam dead-load bending moment is accessible. Based on the stress computations for the end regions of the beam, the design engineer set the number of tendons to be deflected and the position of the deflection point.

The deflection point normally remains in the neighborhood of the quarter-span position, where three-quarters of the mid-span value of dead-load moment is accessible to neutralize the tensile stress (top fibre) because of pre-stress at transfer.

The angle of deflection of these tendons are placed in such a manner that the effective eccentricity and the pre-stressing force of the tendons do not generate a tensile stress of more than N/mm2 at transfer at the important sections, a limit set in the Code.

This method of deflecting tendons is specifically effective where continuity for live loads should be set in the finished structure since by deflecting some of the tendons upwards towards the ends of a beam, some compressive stresses are produced in the top fibre at the ends. This is useful for withstanding tensile stresses occurred because of the hogging moments caused by the passage of live loads on the superstructure. It also minimizes the formation of compressive stress in the bottom fibre because of prestress and live loads or any other loads at the ends of the beam.

Another benefit of deflected tendons is that the Code allows the vertical component of the tendon force to be applied in withstanding the imposed shear force on the beams in areas which stay flexurally uncracked at the ultimate limit state. This component is also suitable for the flexurally cracked regions and for examining the maximum shear stress condition in the member. Due to some limited test evidence, however, the Code does not allow relief against shear in these later conditions. Actually, the shear resistance of any section is decided in both flexurally cracked and uncracked modes and the lower value is selected. The shear links are then designed to bear the rest of the enforced shear force. Because only the tendons which are situated within the web width are deflected, the strand pattern for the whole unit should be cautiously chosen so that sufficient strands are available for deflecting upwards towards the ends to meet the stress conditions during the length of the beam.

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



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Published By
Rajib Dey
www.constructioncost.co
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The 7 Major Highway Cross Sectional Elements of a Road

Given below, the details of cross sectional components of a road

1) Right of way: Right of way or permanent land stands for the area of land obtained and conserved for construction and formation of a road along its alignment. The width of right of way is termed as permanent land width or road land width.

2) Road way / Formation width: The top width of a highway embankment or bottom width of highway cutting exclusive of the side drain is known as roadway width or formation width. It belongs to the sum of width of carriageway and the shoulders.

3) Carriageway: Carriageway or pavement or crust is defined as the segment of roadway developed for movement of vehicular traffic

4) Shoulder: The segments of roadway among the exterior edges of the pavement and edges of the top surface of the embankment or inside edges of the side drains in cutting are termed as shoulders.

The objective of shoulders

i) They offer lateral strength to the carriageway.
ii) They function as parking place for vehicle for emergency purpose.
iii) They arrange space for constructing road signals.
iv) They arrange space for animal drawn vehicles, cyclists, pedestrians.

5) Berm: The segments of land width kept among the toe of road embankment and the inner edges of borrow pits or the segments amid the top edges of road in cutting and the adjacent edges of spoil banks on either side are described as berm.

6) Building Line: It refers to the line, on either side of the road, among which and the road; no building activity can be done at all.

7) Control Line: It refers to the line which shows the nearby restraint of future unrestrained building activity concerning a road. It implies that though building activity is not entirely combined among the building line and control line, the nature of building allowable here is restricted.



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Published By
Rajib Dey
www.constructioncost.co
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