building construction and material

LOAD BEARING CONSTRUCTION &

MATERIALS

Load Bearing Construction

Load bearing masonry is among the oldest and most widespread building techniques in the world.

The earliest load bearing masonry consisted to stones stacked one over the other. Over the passage of time, the stones were chiseled and dressed to make more stable masonry walls.

The firing of earth blocks gave rise to the earliest form of brick masonry.

The key idea with this construction is that every wall acts as a load carrying element.

Load bearing masonry construction was the most widely used form of construction for large buildings from the 1700s to the mid-1900s.

It is very rarely used today for large buildings, but smaller residential-scale structures are being built.

It essentially consists of thick, heavy masonry walls of brick or stone that support the entire structure, including the horizontal floor slabs, which could be made of reinforced concrete, wood, or steel members.

Limitation of Load Bearing Structure

It does not perform very well in earthquakes. Most deaths in earthquakes around

the world have occurred in load bearing masonry buildings.

It is extremely labor-intensive, as it is built mainly of masonry, which is made by hand.

This also makes for very slow construction speeds in comparison with modern

methods that are far more mechanized.

It is extremely material-intensive. These buildings consume a lot of bricks, and are

very heavy. This means that they are not green.

Evolution; Load Bearing Masonry through History To start with, masonry structures were large and

solid, like the pyramids.

With the development of the arch, openings were created in these structures, and large structures like the colosseum in Rome were built.

In India, builders started using horizontal slabs of stone to construct floor plates. This is called trabeate construction. The Taj is built of red standstone masonry walls faced with white marble. Its walls are 6ft (1.8m) thick in some places.Europeans built fine stone walled buildings with floor slabs made of wood beams and planks. The buildings had elaborate arched openings and very finely crafted domes. These buildings have lasted hundreds of years, with limited repair.

the Mondadnock Tower, a 16-storey office building built in 1893 in Chicago. It was made of brick walls 6 feet thick at the base and about 18" thick at the top. It still exists

Foundation Suitable for Load Bearing

Construction Probably the most common form of

modern foundation, this is created

by digging a trench to the pattern of

the load-bearing walls of the

building and then pouring concrete

into the bottom of the trench.

Frequently, the concrete is

reinforced by laying steel bars or

mesh into the wet concrete. Once

the concrete has dried the walls are

then constructed, using the

foundation as a base.

Materials Used for Load Bearing Masonry

Over the centuries, masonry has evolved into a precise science with a myriad of

options in materials and styles.

Some of the more common load bearing masonry used today is brick, stone and

concrete masonry units (CMU) or concrete blocks.

Among these there are several varieties depending on the materials and system of

laying the masonry units. Some of the more recent advancements are aerated

concrete blocks, hollow concrete blocks, etc

Stone & Types of Stone

The term Stone refers to the natural Rocks after their removal from the earth’s crust.

Stone When Derived from rocks are very irregular in shape size; they are dressed for

proper bedding, thin joints & speedy construction.

It has been widely used through out the history, evidences can be seen in Egyptian

civilization, Incas of Peru etc.

Geologically we have three categories of rocks. Igneous, metamorphic &

Sedimentary.

IGNEOUS ROCKS are the oldest & formed by the solidification of molten magma.

Granite & Basalt are the are quarried from igneous rocks.

SEDIMENTARY ROCKS are formed by the erosion of older rocks, that were originally

igneous. Sandstone & Limestone are quarried from Sedimentary Rocks.

METAMORPHIC ROCKS are from by recrystallization of older locks under intense

pressure & heat. Slate, Marble, Quartzite & alabaster is quarried through the

metamorphic rocks.

Stone Masonry & Types of Stone Masonry Stone Masonry is the art of building structures

with stone, Stone is not cheaply available in all

country. They are difficult to handle due to their

heavy weight & they are costly in construction

due to transportation and high dressing

charges.

Stone Masonry is broadly classified in to two

categories; i-Rubble Masonry ii Ashlar Masonry.

Rubble Masonry: The masonry in which undressed stone or roughly dressed stone is laid

in a suitable mortar, in this masonry the joints of

mortar are wider and not uniform.

Ashlar Masonry: The stone Masonry having

finely dressed stones laid in cement and lime

mortar is known as ashlar Masonry.

TYPES OF RUBBLE MASONRY: Rubble masonry is further divided into four categories

1. Un-coursed Rubble Masonry: The stone Masonry in which stones are laid without forming course. Suitable for constructing low walls

2. Random Rubble Masonry: The rubble masonry in which stones are laid to some what level coursed with non uniform joints. Suitable for constructing residential buildings, godowns, boundary walls.

3. Coursed Rubble Masonry: The stone Masonry in which face stones are squared on all joints and bedded by chisel or hammer dressing before laying. Suitable for Residential and Public buildings

4. Dry Rubble Masonry: the stone Masonry in which stones are laid with mortar.it is used for compound walls, retaining walls; height should not exceed 6ms.

TYPES OF ASHLAR MASONRY:

Course Ashlar Masonry: Stone block of same height is used. Every stone is fine tooled

on all sides. Thickness of mortar joint is uniform.

Random Course Ashlar Masonry: This type of Ashlar Masonry consist of course of

varying thickness.

Rough Tooled Ashlar Masonry: Sides of stones are rough in each course but mortar

joints are uniform.

Block-in-course Masonry: its an intermediate between rubble and ashlar Masonry. All

stones are properly dressed and squared but edges of the stones are rough and of

varying length.

Above all are suitable for Retaining walls, sea walls. But it is also used for Large Public

Buildings.

Ashlar Facing: It is the best type of Ashlar Masonry. Since this type of Masonry is very

expensive. It is not used through out the wall except in work of great importance. In

this wall is made of rubble masonry back with Ashlar Facing.

GENERAL CONSTRUCTION ASPECTS FOR LOAD BEARING CONSTRUCTION

The height of the construction may be

restricted to four story of category, Where

light sheeted roof is used, an attic floor may

also be used.

The height of a story may be kept as low as

2.5 m but not more than 3.5m.

The wall thickness should be used as small as

feasible, say 300 to 450mm.

Openings should be as small and as

centrally located as practicable

Stone Masonry in Abbottabad (A Case Study)

Non-engineered construction is very common in many parts of Pakistan. Most such

buildings are unreinforced masonry (URM) structures with walls constructed from

either stone, brick or concrete block masonry, depending on which material is

locally available. These masonry walls are brittle and often cannot resist the lateral

forces which are generated during a seismic activity. In the Kashmir 2005

earthquake, an estimated 19,000 children died due to the collapse of masonry

school structures.

The case-study school is situated in the seismically active Abbottabad region. The

school has been built using a design template which is the same for most of the

schools in the area.

The school consists of four classrooms which have been divided into 3 blocks.

The structural system of the building consists of load bearing walls which have been

constructed using random rubble stone masonry with a cavity in the middle. The

roof is constructed of timber trusses topped with metal sheets.

RETROFITTED SOLUTIONS Lateral load resistance of individual masonry

walls have been increased by providing both

horizontal as well as vertical metal strips (50 x 6

mm). These strips have been provided on both

the internal and external faces of the walls and

well connected with each other.

All the four walls have also been connected

together at their junctions using steel angles (75

x 75 x 3 mm) from inside as well as outside to

enable closed box action and provide a

stronger lateral load resisting system.

Weak areas within the walls such as openings

for doors and windows were additionally

strengthened using metal strips around the

openings from both inside and outside.

Individual and isolated members, such as stone

masonry columns, were tied together by tie

beams both at plinth and lintel levels

Application of Stone

Due to the Advancement in construction techniques and structure evolution. And due to its availability , high transportation and dressing charges Application of stone as main building material for construction is suitable to heavy and monumental works. Although its application as cladding material for floor and walls is widely used.

I. GRANITES are hard and dense and are very stable and durable material. Its virtually impermeable to water. It is available in variety of color and texture. But the highly polish granite is effective at displaying colors and crystalline texture. But because its high cost of quarrying and finishing . It is used as cladding material for floors for hard landscape and also in countertop material in kitchen.

II. CAST BASALT is a fine grained stone nearly as hard as granite. It is used in tile units or as worktops.

III. SANDSTONE may be fine or coursed in texture depending on the nature of the original sand deposit. It ranges in Color from white, grey, brown and shades of red. It can be used as main building material but is normally used for wall cladding (thickness is 75 to 100mm)

SLATE is typically used as cladding material for roof it can also be used at walls. Its

available in variety of colors blue, grey, green, silver grey. Slate is strong acid and

frost resistant and lasting up to 400 years as a roofing material.

MARBLE is metamorphosed limestone and its appearance of marble is associated

with the impurities in lime stone. Its extensively used as cladding material. For

external cladding above 1st floor its thickness should be 40mm while for internal and

lower level it could be 20 mm in thickness