What is FormWork in construction?

Formwork is the mould to shape the concrete structure. Good concrete cannot be made from a poor mould; thus formwork is very important in producing good concrete. Besides that, it has to be designed to take the concrete load and the working load generated from workers and plant.

Column Forwork and support

Timber and plywood were generally used Materials in the site for in-situ concrete work. Columns Beams slabs lift walls and staircases were all constructed using Timber and plywood formwork. Steel casing formwork was used for few structures such as round columns.

The following factors were considered when doing form work;

•   Correct position
•   Line and level
•   Accuracy within permitted tolerances
•   Shape of members
•   Verticality (plumb)
•   Correct angles for batters etc.
•   Finishing heights (mark off)
•   Formwork joints flush and tight
•   No nails protruding into the concrete
•   Formwork joints sealed as required
•   Construction joints strutted and supported

All the above formwork was supported with the following false work and other materials   

• GI pipes, concrete & wire nails
• Form ties (to tie the separates and GI pipes)
• Separates (thread bar & P cone)
• Pipe supports and “T”,”U” jacks
• adjustable steel props, mould oil (diesel & grease)

Example Form work Cross section of a Column

Example Form work Cross section of a Column

  What are the accessories/tools used in Formwork

The Factors depend on selection of Roof Materials

An outermost exterior covering part of a building is known as roof. Roof is supported by the beneath layer of structure, Roofing materials commonly provide shelter from natural resources like sun heat and light, air, rain, animals and etc.  When choosing roofing materials, there are some important things we need to consider. They are as follows,

1. Duration and ability of roofing material to withstand 
2. Properties of the material such as weight, thickness, durability, slope and shape
3. Whether the material eco-friendly or not / recyclable or not
4. Cost of the material.

Type of Roofing Materials 

• Thatch is roofing made of plant stalks in overlapping layers
• Shingle is the generic term for a roofing material that is in many overlapping sections, regardless of the nature of the material
• Ceramic tile. High cost, life of more than 100 years
• Membrane roofing. Membrane roofing is in large sheets, generally fused in some way at the joints to form a continuous surface (PVC - roofs)
• Concrete or fibre cement, usually reinforced with fibres of some sort.
• Structural concrete can also be used for flat roof constructions. There are three main categories, precast/prestressed, cast-in-place and shell.

1. Clay & Concrete Tiles

Clay tiles are very heavy, requiring additional roof framing, but they are non-combustible and extremely durable. Clay roofing tiles can come in lighter colors, which adhere to the cool roof standards and can reflect well over 50% of the sun's solar energy. Concrete roofing tiles offer elegant, enduring aesthetics for your home's design and added value. Concrete tiles are very versatile and provide greater protection to the homeowner. These flexible tiles come in so many different hues, shapes, textures and styles that they don't even look like tiles at all. Shingle, shake and slate are just some of the varieties of tile. 

2. PVC roofing material

Polyvinyl chloride (PVC) roofing material exist as leading roofing material at present. Comparatively PVC roofing material is a better one, for its quality, durability, resistant to UV rays, availability of different colours, flexibility, a good heat stabilizer and also for its cost.  A German company produced the PVC roofing material for the first time in 1966. It is a single ply, thermoplastic roofing material which popularized in a short period of time.

3. Asphalt roofing material

A mixture of aggregates, binder and filler are used to form the Asphalt. Asphalt is used as asphalt shingles and asphalt roll in roof construction works.

3.1 Asphalt shingles

The asphalt shingles roofing material is commonly used roofing material which is a good waterproofing material. Strip asphalt roofing shingles, dimensional asphalt roofing shingles and premium asphalt roofing shingles are the three main asphalt shingles roofing material available.

3.2 Asphalt roll roofing

Easiest way of roofing is using roll roofing material. Th same materials used in the production of asphalt roll roofing as in asphalt shingles. Easiest and cheap way of roofing but not suitable for high slope roofing construction.

4. Metal Roofing (Steel, Aluminium )

Metal roofs are some of the coolest roofs around, both in temperature and style for new homes. Metal roofs are available in copper, aluminum, and stainless steel, and often have a high percentage of recycled content. They offer high insulation solar reflectance, and durability, often lasting twice as long as wood or asphalt. Metal shingles typically simulate traditional roof coverings, such as wood shakes, shingles, slate and tile. Aside from its longevity, metal shingles are much lighter than most materials and very resistance to adverse weather.

5. Eco roofing or green roofing material

A best way to reduce global warming is eco roofing. A layer of plants grown above the primary cement layer of a building with necessary barriers and medium ( Root barrier, water proof layer and soil)  is known as eco roofing. Large trees and plants or light plants like mosses are the materials of eco roofing. A good way to reduce heat within the building and provides natural, fresh air. Low cost and environmental friendly way of roofing material. 

Bar bending process

Bar Bending

Steel bars should cut and bend to the required shape at the bar bending plant located in site. Initially the required bar schedule prepared according to the reinforcement drawings by the structural Engineers is been provided. The bar-benders then they were provided bars with necessary size and will be bent according to the required shape and length.  Then they will be placed as in the drawings.

 Show the process of Bar bending by a bar bender according to the requirements as in the drawings.

Bar bending 

Bar bending

What is reinforcement in construction

Reinforced concrete is one of the most widely used modern building materials. Concrete is an “artificial stone” obtained by mixing cement, sand, and aggregates with water. Fresh concrete can be moulded into almost any shape, giving it an inherent advantage over other materials.

Steel reinforcement is available in the form of plain steel bars, deformed steel bars, cold-drawn wire, welded wire fabric, and deformed welded wire fabric. In Sri Lanka Reinforcing steel must conform to applicable British/ European standard specifications.

The reinforcement in concrete may be simple bar or series of bars, bend to a given schedule which known as bar schedule and tied according to the reinforcement drawings with stirrups.  The normal diameters of bars used at this site are 6, 10,12,13,16, 25 and 32 millimetres.

1. Bar Bending 
2. Bar Notation 
3. Lapping of steel bars
4. Crank Length 
5. Covering 
6. Stool in reinforcement 

Lapping length of reinforcement steel bars

Lapping of Steel Bars

Normally, steel bars have a 6m length. If length of a bar is not enough to keep the reinforcement, we have to lap two steel bars. Normally, lapping position is at where near the minimum shear force is acting. Normally lap length is 50D meaning 50 times the bar diameter if both bars are of same diameter. When lapping two bars of different diameters, the lap length is considered as 50 times the smaller diameter.

50D

Lap length = 50 X Diameter

Stool used in construction

Stools are commonly  used to maintain a cover between top and bottom reinforcements bars. It is used in arrangement of reinforcement bars of slabs. As we are walking on the top reinforcement mesh stools should strength enough to bear the load without changing the gap of two layers. 

there are different types of stool shapes available in the constitutions and also different height it depent on the structure

stool used in reinforcement 

Covering for reinforcement of Concrete

Covering for reinforcement in concrete is very important.  The thickness of cover depends on environmental conditions and type of structural member. The correct cover shall be maintained by
cement mortar cubes (blocks) or other approved means.Concrete coverfor reinforcement in the site was as follows. (This may vary depending on thesite)

Ground Beams	50mm Surface cast against ground 40mm Other face/on blinding 30mm Top face 40mm earth face
Ground Slabs	30mm Top face ;40mm earth face
Suspended Slabs	25mm Internal & external
Beams, Lintels & Capping beams	30mm Internal & external
Columns and Pedestals	30mm Surfaces cast against ground 30 mm Internal & external surfaces in contact with ground cast against shutter
Walls	40mm Surfaces cast against ground 30mm Internal & external surfaces in contact with ground cast against shutter

Cover blocks used in reinforcement

Cover block is  key part of the reinforcement work. It is used to maintain the cover between shuttering boards and the mesh of the reinforcement. In our site 1:2 mortars and binding wire was used for cover block. Cover block size 1.5" x 1.5" and thickness is depending on situation 

cover blocks

What is crank Length of reinforcement

Crank length

Crank is a slight bending in bars at the lap so that maintains the clear cover even at the lap position. The rule that is generally practiced is that the slope of crank 1:10 & minimum length of crank 300 mm.

Crank length of reinforcement

Crank length = (d1+d2+5)*10mm

d1 =diameter of smaller bar                d2 = diameter of largest bar

Cofferdam water retain structure in construction

A cofferdam is a construction structure that retains water and soil that allows the enclosed place to be pumped out and excavated to be dry. Cofferdams are generally used for construction of bridge piers and new desist structures built within water.

Cofferdams are made by driving sheet piling, usually steel in militant works, into the bed to form a watertight fence. The vertical piles are held in area by horizontal framing members that are constructed of heavy timber, steel, or  both of that materials . The sides of a cofferdam must be sturdy and well-braced to withstand the shock of being hit by a heavy weight of bucket; they must as well as be able to withstand the horizontal forces from the surrounding body of water  into account the water inside is pumped from the cofferdam.

Cofferdam in marine 

Types of cofferdams 

• Braced cofferdams
• Cellular cofferdams
• Double-walled sheet pile cofferdams

 Cofferdam shapes

A cofferdam can  be constructed in almost any desirable shape. However, for practical and reasons of economy most cofferdams shapes are circular or rectangular.

Water Proofing and Insulation Roof Slap

Fillet in construction for water proofing

Fillet Between Wall and  Roof Slab

Components of a rubble mound breakwater

Rubble mound breakwaters are used for protection of harbours and beaches against wave action. They are also used for protection of navigation channels and beaches against sediment transportation. The figure below shows the components of a typical Rubble mounted breakwater.

Components of a typical Rubble mounted breakwater

Core -The purpose of the core is to prevent wave transmission into harbour; hence the core material is not too coarse.

Toe -The Toe functions as the foundation for the armour layer. It also may catch armour units displaced from armour layer; The Toe is normally constructed of large stones of quarry run or the most coarse filter layer.

Filter layer -The objective of the filter layer (under layer) is to prevent the core material from being washed out through armour layer. It is built of quarry run.

Armour layer -The purpose of armour layer is to protect the core from direct wave attacks by the dissipation of wave energy. Armour layers are built of large rocks or larger concrete armour units.

Superstructure -The superstructure is used either in order to reduce the crest elevation or to reduce wave overtopping, or as a roadway for traffic or pipelines. The superstructure is usually constructed of concrete.

Primary armours used in marine structures

There are various types of concrete armour units, that are currently been used for the construction of marine structures. Throughout the past few decades various types and shapes of primary armour units have been invented and used in the construction industry. These have the advantage of being interlocked with high permeability and porosity as armour layer, which make them more stable and more effective in dissipating wave energy. Figure below show some of the concrete armour units that are been used in the current construction Industry.

(Source: www. www.researchgate.net)

Different types of armour units have been invented throughout the past few decades, and they too have been undergone evolution. Out of the following we have selected three primary armour units that have been used from time to time for a simple comparison.
Cube

	Cube	Tetrapod	Accropode
Shape	Cubical	Tetrahedral	Combined bard 2D
Structural strength	Massive/ Blocky	Slender	Bulky
Stability factor	Own weight and Friction	Own Weight and Interlocking	Interlocking
Number of layers	2	2	1
Placement method	Random and/or Uniform	Random	Random
Cost (relative to accropode)	200%	191%	100%
Relative volume of concrete	220%	208%	100%
Standard average Mass (tons) considering equal total volumes of concrete	2.2	3.2	11.8
Effectively	Less effective	Moderately effective	Very effective

Column and Beam system in construction

This article gives a brief introduction about the column and Beam system of a typical building or structure.

Introduction

The System of Columns and Beams have been used in Construction since Ancient Egypt (Which lasted from about 3100BC until it was finally absorbed in to the Roman Empire in 30 BC) Ancient Greece and Ancient Rome. In modern day construction, Column-Beam-Slab System is been used in all superstructures with new technology, and construction materials. Generally the load of the slab is transferred to the columns or walls through the beams, down to the foundation, and then to the supporting soil beneath.

Column

Columns (Image Source Wikipedia)

Columns (Image Source Wikipedia)

A column can be defined as a vertical structural member designed to transmit a compressive load. A Column transmits the load from ceiling/roof slab and beam, including its own weight to the foundation. Hence it should be realized that the failure of a column results in the collapse of the entire structure. The design of a column should therefore receive importance.

In the modern construction industry, Columns are mostly constructed by concrete; apart from that materials such as Wood, Steel, Fibre-reinforced polymer, Cellular PVC, and Aluminium too are been used. The type of material is been decided on the scale, coast and application of the construction.

Types of Columns

Columns can be classified bases on its Shape, Slenderness ratio, type of loading and Pattern of lateral reinforcement.

Classification based on Slenderness ratio

Long Column or Slender [The length is greater than the critical buckling length and it fails by buckling.]

• Short Column [The length is less than the critical buckling length and it fails by shearing.]
• Intermediate Column

Based on shape

•  Rectangle
• Square
• Circular
• Polygon

Based on type of loading

• Axially loaded column
• Axial load and un-axial bending column
• Axial load and biaxial bending column

Based on pattern of lateral reinforcement

• Tied columns
• Spiral columns

RCC Columns (Reinforced Concrete Columns)

A reinforced concrete column can be defined as a structural member with a steel frame (reinforcement bars) composed of concrete that is been designed to carry compressive loads.


Figure Shows the Reinforcement of a Column with cross-section 500x500.

Reinforecement of Column sections

Beams

A beam is a structural member which spans horizontally between supports and carries loads which act at right angles to the length of the beam. They are small in cross-section compared with their span. The width and depth of a typical beam are "small" compared with its span. Typically, the width and depth are less than span/10.

Generally a beam is subjected to two sets of external forces and two types of internal forces. The external loads are the loads applied to the beam and reactions to the loads from the supports. The two types of internal force are bending moments and shear forces. The internal shear force and the internal bending moment can be represented as pairs of forces. The Figure below shows a Typical Beam with Internal and external forces acting on it.

Beam With Internal and external forces 

There are several types of beams

• Simply supported Beam
• Fixed Beam
• Cantilever Beam
• Continuous Beam
• Overhanging Beam

Written By : Nilantha Perrera