How to Decide Thickness of Different Masonry Walls in Buildings?

Thickness of masonry walls in a building is designed based on loads and other factors. Various requirements for suitable thickness of masonry walls are discussed

Fig.1: Masonry Wall and Masonry Structure

Requirement for Thickness of Masonry Walls in Buildings

There are various requirements regarding the thickness of masonry walls that needs to be considered at the design stage.

For example, it is recommended to use constant masonry wall thickness between lateral supports. The lateral support for masonry is provided by cross walls, pilasters, and structural frame members as shown in Figure-2.

Fig.2: Lateral Support of Masonry Wall

Regarding variation of masonry in vertical direction, the distance between floors, structural frames and roofs should be considered when the thickness of masonry wall is varied.

Masonry wall thickness changes between floor and roof and between different floors is usually enforced to reach thermal, sound and fire requirements.

Fig.3: Vertical support of masonry wall considered for making changes in masonry thickness

If masonry wall thickness is changed, it is recommended to extend the thicker wall to the lower support level.

Building code requirements and specifications for masonry structure (ACI 530-11) states that, when the thickness of masonry wall constructed from hollow masonry units is changed, then it would be required to provide a layer or several layer of solid masonry units or completely grouted hollow masonry units between thicker masonry wall and the thinner masonry wall.

The aim of providing solid masonry course between thicker and thinner masonry wall is to properly transfer loads from the above wall (thin wall) to the wall below (thick wall).

There are several limitations and restrictions which should be considered for masonry walls except in the case where the walls are designed for reinforcements based on the engineering principles.

The limitation associated with masonry thickness for different masonry walls types are discussed below.

Thickness Requirements for Load Bearing Masonry Wall

The thickness of load bearing masonry wall should be at least 304.8 mm (1 ft.) thick for maximum wall height of 10.668m (35 ft.).

Moreover, the thickness of masonry wall need to be increased by 101.6 mm (4in.) for each successive 10.668m (35 ft.) height or fractions of this height measured from the top of the masonry wall.

There are several cases in which the above conditions may not be applied for load bearing masonry walls.

These exceptional cases involve stiffened masonry wall, top storey masonry wall, residential masonry wall, masonry wall of penthouses and roof structures, plain concrete and grouted brick masonry wall, hollow masonry wall, faced masonry wall, nonbearing masonry wall.

Stiffened Masonry Wall

If load bearing masonry wall is strengthened or stiffened by reinforced concrete floors or masonry cross walls at a distance not greater than 3.65m (12 ft.), then it is possible to adopt thickness of 304.8mm (1 ft.) for maximum wall height of 21.33m (70 ft.).

The thickness of masonry wall should be increased by 101.6mm (4 in.) for each successive 21.33m (70ft.) height or fractions of this height measured from the top of the masonry wall.

Top Storey Masonry Wall

It is permitted to use a thickness of 203.2mm (8 inch) for top storey bearing masonry of a building with ultimate height of 10.668m (35 ft.).

The wall should not experience lateral loads and its height should not exceed 3.65m (12 ft.) otherwise such thickness cannot be considered.

Residential Masonry Wall

The thickness of bearing masonry wall of in residential building with maximum three storeys can be assumed to be 203.2mm (8 inch).

This thickness should not be employed if the building is higher than three storeys, or the height of the wall exceeds 10.668m (35 ft.), or the wall subjected to lateral forces.

Additionally, the wall thickness can be decreased to 152.4mm (6 in.) for one storey building if the maximum wall height is 2.74m (9 ft.).

Masonry Wall of Penthouses and Roof Structures

The thickness of bearing wall masonry with a height of 3.65m (12 ft.) above roof level or penthouses can be assumed to be 203.2mm (8 inch).

Plain Concrete and Grouted Brick Masonry Wall

It is possible to adopt 152mm (6 ft.) thickness of plain concrete and grouted brick masonry wall.

Hollow Masonry Wall

It is advised to restrict the height of cavity or bonded hollow masonry wall to a maximum of 10.668m (35 ft.).

Added to that, the height of cavity wall should not be greater than 7.62m (25 ft.) above the support if its thickness is equal to 254mm (10 inch).

Thickness Requirements of Rubble Stone Walls

The thickness of stone wall should not be smaller 406mm (16 in.) in any case.

Thickness of Non-Load Bearing Masonry Walls

The minimum thickness of parapet wall can be assumed to be 203mm (8 inch) and its height should not be larger than three times the wall thickness.

Nonetheless, it is possible to use smaller thickness for parapet wall if it is reinforced to resist earthquakes.

Regarding thickness requirements of exterior nonbearing masonry wall, the same specifications provided by ACI 530-11 for bearing masonry wall should be used which is 152mm (6 inch) for single storey building and 203mm (8 inch) for more than one storey building.

Residential Buildings – Types and Site Selection for Residential Building

What is a residential building?

A residential building is defined as the building which provides more than half of its floor area for dwelling purposes. In other words, residential building provides sleeping accommodation with or without cooking or dining or both facilities

Types of residential building

Residential buildings are divided into following types

• Individual houses or private dwellings
• Lodging or rooming houses
• Dormitories
• Apartments
• Hotels

Individual houses or private dwellings

Individual houses or private dwellings are generally owned by members of a single family only. If more than one family residing in that building then it is called as multiple family private dwelling.

Lodging or rooming houses

Lodging or rooming houses are multiple or group of buildings which come under one management. In this case, Accommodation is provided for separately for different individuals on temporary or permanent basis.

Dormitories

Dormitories are another type of residential buildings, in which sleeping accommodation is provided together for different individuals. School hostels, military barracks come under this category.

Apartments

Apartments or flats are big buildings which consists separate dwellings for different families. Apartment will resides minimum three or more families living independently of each other.

Hotels

Hotels are just like lodging houses and also managed by single management but they provide accommodation primarily on temporary basis. inns, motels etc come under this category.

Site Selection for Residential Buildings

Selection of site for any building is a very important and experts job and should be done very very carefully by an experienced engineer. The requirements of site for buildings with different occupancies are different.Following are some of the important factors which should be considered while selecting site for any residence.

1. The site should be in fully developed area or in the area which has potential of development.
2. There should be good transport facilities such as railway, bus service, for going to office, college, market, etc.
3. Civic services such as water supply, drainage sewers, electric lines, telephone lines, etc. should be very near to the selected site so as to obtain their services with no extra cost.
4. Soil at site should not be of made up type as far as possible. The buildings constructed over such soils normally undergo differential settlement and sometimes become the cause of collapse. Cracks in buildings in such conditions, are quite common
5. The selected site should be large enough; both to ensure the building abundant light and air to prevent any over dominance by the neighboring buildings.
6. The ground water table at the site should not be very high.
7. Nearness of schools, hospitals, market, etc. are considered good for residential site but these facilities do not carry any significance in the selection site for other public buildings.
8. Good foundation soil should be available at responsible depth. This aspect saves quite a bit in the cost of the building.
9. The site should command a good view of landscape such a hill, river, lake, etc.
10. Residential house site should be located away from the busy commercial roads.
11. Residential site should not be located near workshops, factories, because such locations are subjected to continuous noise.
12. Orientation of the site also has some bearing on its selection. Site should be such in our country that early morning sun and late evening sun is accepted in the building in summer and maximum sun light is available in most of winter.

Testing of Sand Quality at Construction Site for Concrete

There are different methods for testing of sand quality at construction site for concrete construction. Quality of sand is as much of importance as other materials for concrete.

Aggregate most of which pass through 4.75 mm IS sieve is known as fine aggregate. Fine aggregate shall consists of natural sand, crushed stone sand, crushed gravel sand stone dust or arable dust, fly ash and broken brick (burnt clay).

It shall be hard, durable, chemically inert, clean and free from adherent coatings, organic matter etc. and shall not contain any appreciable amount of clay balls or pellets and harmful impurities e.g. iron pyrites, alkalis, salts, coal, mica, shale or similar laminated materials in such form or in such quantities as to cause corrosion of metal or affect adversely the strength, the durability or the appearance of mortar, plaster or concrete.

The sum of the percentages of all deleterious material shall not exceed 5%. Fine aggregate must be checked for organic impurities such as decayed vegetation humps, coal dust etc.

Testing of Sand Quality at Construction Site

Following are the tests for sand at construction site:

1. Organic impurities test – this test is conducted at the field, for every 20 cum or part thereof.
2. Silt content test – this is also a field test and to be conducted for every 20 cum.
3. Particle size distribution – this test can be conducted at site or in laboratory for every 40 cum of sand.
4. Bulking of sand – this test is conducted at site for every 20 cum of sand. Based on bulking of sand, suitable water cement ratio is calculated for concrete at site.

1. Test for Silt Content Test of Sand

The maximum quantity of silt in sand shall not exceed 8%. Fine aggregate containing more than allowable percentage of silt shall be washed so as to bring the silt content within allowable limits.

2. Test for Grading of sand

On the basis of particle size, fine aggregate is graded into four zones. Where the grading falls outside the limits of any particular grading zone of sieves, other than 600 micron IS sieve, by a total amount not exceeding 5 percent, it shall be regarded as falling within that grading zone.

IS Sieve	Percentage passing for
	Grading Zone I	Grading Zone II	Grading Zone III	Grading Zone IV
10mm	100	100	100	100
4.75mm	90 – 100	90 – 100	90 – 100	90 – 100
2.36mm	60 – 95	75 – 100	85 – 100	95 – 100
1.18 mm	30 – 70	55 – 90	75 – 100	90 – 100
600 micron	15 – 34	35 – 59	60 – 79	80 – 100
300 microns	5 – 20	8 – 30	12 – 40	15 – 50
150 microns	0 – 10	0 – 10	0 – 10	0 – 15

3. Test for Deleterious materials in sand

Sand shall not contain any harmful impurities such as iron, pyrites, alaklies, salts, coal or other organic impurities, mica, shale or similar laminated materials, soft fragments, sea shale in such form or in such quantities as to affect adversely the hardening, strength or durability of the mortar.

The maximum quantities of clay, fine silt, fine dust and organic impurities in the sand / marble dust shall not exceed the following limits:

(a) Clay, fine silt and fine dust when determined in accordance within not more than 5% by mass in IS 2386 (Part-II), natural sand or crushed gravel sand and crushed stone sand.

(b) Organic impurities when determined in colour of the liquid shall be lighter in lighter in accordance with IS 2386 (Part –II) than that specified in the code.

4. Test for Bulking of sand

Fig: Bulking of sand test

Fine aggregate, when dry or saturated, has almost the same volume but dampness causes increase in volume. In case fine aggregate is damp at the time of proportioning the ingredients for mortar or concrete, its quantity shall be increased suitably to allow for bulkage.

Table below gives the relation between moisture content and percentage of bulking for guidance only.

Moisture content (%)	Bulking percentage (by volume)
2	15
3	20
4	25
5	30