Construction Site Preparations

On successful completion of this course, students will be able to:

1. Identify the function of, and desirable performance attributes required for, primary structural building elements
2. Identify the function of, and desirable performance attributes required for, secondary structural building elements
3. Qualitatively describe the forces and environmental agents incumbent upon building structures
4. Qualitatively describe the link between structure and form
5. Identify/Describe a range of design details.

Temporary Fencing

All construction sites are temporary fenced or hoarded for purposes of safety and security. In most cases, temporary fences are erected around the project as per the range of the set Standards for fencing. Specific policies and regulations regarding to the type of fence to be erected around the construction site include how the fencing should be done, the strength of the fence, height, influence to traffic, and where the fence should be put up.

A majority of the fences are constructed using portable aluminum cyclone fence – open fencing. In most cases, the erection is done with a construction wrap attached either during the demolition process, or excavation process.

Solid fencing or hoarding is done using self-supporting panels erected either by use of their own supports or overhead structure or scaffolding. This type of fencing is used in larger construction sites and those in the middle of busy cities and urban centers.  

Signs informing people on various aspects of construction are and should always be put at all construction site and projects. Construction warning signs are used to show safety hazards and dangers the workers and other people the risks they are exposed to within the construction area. Building site and other construction sites are potentially dangerous areas to be. Therefore, it is the responsibility of those running the construction site to take precautionary measures by installing sufficient safety signs that can be viewed fully by the workers and the visitors on site.

Signage has a range of signs that range from health and safety, warning/hazard signs, signs indicating new development, and general site hoarding signs. Signage pays a closer attention to placement and clarity for maximum coverage and awareness.

Controlling of sedimentation and erosion on construction sites should be done prior, during and after the construction process to prevent problems such as uneven settlement. Sedimentation control can be done temporarily or permanently depending on the nature of construction taking place. Controlling sedimentation also limits the amount of sediments carried into lakes and streams.

Sedimentation control can be done through several methods including erection of silt fences, use of fiber logs, rock construction entrances, grade breaks, erosion control blankets, temporary sedimentation blankets, filter bags, etc. All these methodologies work through the mechanism of holding or acting as a barrier to the soil particles and thus preventing erosion and down-wash of the soils.

Once the plans and structural drawings of the building are completed, the paperwork is transferred to the ground in a process known as setting out. The process is complex yet simple. At times, the services of a land surveyor are necessary, especially for large buildings. Surveyors use equipment such as total stations and theodolites to accurately locate the position of the building. The most common method of setting out a building is simple pegging or use of bricks.

Signage

Setting out of buildings is objectively done to accurately define where the excavation will take place. Also, it is done to determine the centerline of the walls of the structure.

Before any site excavation work begins, site preparation must take place and this includes removal of trees. Preparation of a construction site is usually a two-step process: first, vegetation clearance and second, removal of surface soil layer.

Removal of trees and other woody vegetation clears obstructions within the construction site. However, the contractor and all involved parties should keep in mind that preserving nature is important and therefore removal of trees should be done with a lot care and keeping sustainability in mind.

Bulk excavation in any project basically involves hauling of large quantities of land and debris from the construction site to where the material is deposited. Bulk excavation is done mainly to reach soils with good bearing capacity, create level grounds or to specifications.

Bulk excavations are done using heavy construction machinery because of the large quantities of earth that need to be moved. The type of bulk excavation done depends on the type material being excavated or the purpose of the excavation.

Detailed excavation includes the precise removal of earth so as to meet specifications for construction elements such as drainage and footings. In detailed excavations unlike bulk excavations, small sized construction plants are used. Smaller equipment allows access to limited areas of the excavation to meet the detailed scale of work.

The primary areas of detailed excavations include site leveling, foundations and relevant footings, services and trenches.

Concrete slab floors are of various forms including ground, suspended or a combination of both. Conventional concrete used for the slabs has high embodied energy.  Conventional ground floor slabs have deep excavated beams and waffle pod slabs. They are located near the Ground Level (GL) and can be made up of expanded polystyrene foam pods. Ground slabs are insulated beneath floor panels to reduce heat loss.

Footings of a foundation are vital for any structure under construction. They are made of rebar reinforcement and concrete poured into the trench. Concrete footings are also important parts of projects such as decks, pergola, and retaining walls. Footings act as support parts of the foundation and minimize settling.

In construction sites with soils that have good bearing capacity, strip foundations are the most suitable. Strip foundations have same sizes as the concrete cavity walls or the timber frame cavity walls. The width of the wall and the strip size and position are directly related. While concreting strip foundations, steel reinforcement is included to strengthen the foundation.

Sedimentary Control

Raft or mat foundations are essentially continuous slabs on the foundation soil that extend over the entire area where the building is to be built. Raft foundations transfer the loads and weight of the buildings into the ground.

Raft foundations are the best for weak soils because they distribute the loads of the building over the entire covering unlike other types of foundations such as pile, which transmit loads to a single individual point. The action of raft foundations reduces stress on the soil.

Concrete is usually chosen to suite and adapt to specific development and desired requirement. The different types of concrete available show different performances and have specific sustained durability.

Concrete types differ depending on mix design, applications, reaction to water, and method of construction being carried out. The following are the main types of concrete used;

1. Normal Concrete – This is the most commonly used concrete which is a mix of cement and aggregate, water acts as a solvent. It is also known as normal strength concrete. The normal setting period is half an hour to one and half hours. The concrete is estimate to set fully in about 28 days, attaining a strength of 10MPa to 40MPa.
2. High Strength Concrete – This type of concrete has a compressive strength greater than 6000 pounds/sq inch. The water cement ratio is significantly low to 0.35 or lower. Silica fume is used as an additive to prevent free calcium hydroxide crystals that reduce strength in the bonds. The strength values are greater than 40 Mpa.

• High Performance Concrete – Prepared by mixing concrete with super plasticizers to attain high workability. W/C ratios are lowered below 0.25 and hydration content only left. Ash and silica are added to modify cement mineralogy and attain high durability, and enhance compatibility of ingredients. Strength values range from 1000 psi – 15000 psi.

1. Air Entrained Concrete – Used in construction regions where concrete is subject to freezing and thawing. Air entraining admixture added to lower water surface tension and prevent coalescing.
2. Light Weight Concrete – Mixed with ordinary ingredients but has substantially lower mass per unit volume. Strength varies from 7 MPa to 40 MPa.
3. Self Compacting Concrete – Compacts itself due to weight. No vibration is required to compact.

(Jamal, 2017).

Steel reinforcement is used to reinforce concrete. Reinforced concrete is has been one of the most common construction materials in buildings. Reinforcement steel can be in form of plain bars, deformed steel bars, welded wire, cold-drawn wires or fabric (Basic Civil Engineering, 2015).

The reinforcement drawings/structural drawings give a guideline or bar schedule to which the reinforcement in concrete is bend. Normal bar diameters are 6, 10, 12, 16, 18, 20, 22, 25, and 32mm.

The English Bond is a brickwork formation with alternating courses of headers and stretchers. The vertical joints in the header courses align to one another, and those in the stretcher course also align to one another.

The brickwork formation has the headers and stretchers in each course placed with alternating bricks. Each header is put in the central area between the stretcher just above and below to maintain an even bond.

It is also known as the running bond. This bond is used to facade the main structural buildings.  It is a plain bond that is often used in garden walls.

The heading bond is a form of brickwork with all bricks laid as a header with the 4-5 in 112mm face breaking joints above or below. The bonding is used in footings and corbellings.

This is a rare type of bonding used in construction. The English Garden Wall Bond has three rows of stretchers and one row of headers, while the Flemish Garden Wall Bond has only one header in each row with three stretchers.

Not so common type of bond. Was used sometimes in the 19^th century and the early 20^th centuries. The bond has two stretchers to one header.

Set Out

This is a building maintenance technique that involves the repair of the mortar joints in bricks and other masonary elements. The process involves the removal of defective mortar by hand or power tool and replacing it with fresh mortar with the same mix as the original. Pointing is done for whole building or entire wall because defective points are not easily located. Pointing is done by packing the mortar tightly in thin layers and tooling it to a smooth concave finished surface.

1. Common Burnt Clay Bricks Sand Lime Bricks (Calcium Silicate Bricks)

  iii. Engineering Bricks iv. Concrete Bricks

1. Fly ash Clay Bricks

Common burnt clay bricks are made from pressed molds. A kiln is used to dry and fire the bricks. Used in general works with no aesthetic beauty or attractiveness. Require plastering and rendering.

Sand lime bricks are made from fly ash, sand and lime mixture. A chemical process is introduced during wet mixing, and then the mix is molded under pressure to form bricks.

Engineering bricks are made under very high temperature conditions, to form dense and strong bricks. The bricks limit strength and water absorption. They have good load bearing damp-proof characteristics and are chemical resistance.

Concrete bricks are made from solid concretes. They are placed in facades, fences and are good in aesthetics. The bricks can be produced in different colors.

Fly ash clay bricks are made with clay and fly ash. They are fired at temperatures of about 1000^oC. Studies show that the bricks tend to fail poor produce pop-outs when hydrated, causing them to expand.

Flushing is striking off even with the face of the brick to create a smooth wall.  The measurements for the joints used in flushing are often but not always larger than ¾ joint.

Cavity ties hold together (tie) the internal and external walls made up of bricks or cement blocks.  The two parts of the wall are now made to act homogenously as one unit. Ties are put in the cavity walls during construction and they span the cavity. Means of preventing water enter the ties are also put.

Often in construction pieces of timber are fitted together to give the structure support and shape in a process called framing. Materials commonly used for framing include wood, structural steel, and timber. There are two types of framing, heavy frame construction, and light-frame construction. In both categories, material elements are used for walls, corners, lintels, exterior wall studs, interior partitions, etc.

The common timber species used for framing include: white pine, red and white oak, Douglas fir, cypress and cedar.

1. White Pine Red Oak

Tree Removal

iii. White Oak iv. Douglas Fir

Douglas fir is used for framing because of its structural strength characteristics. The species is good for construction of posts and beams. The wood does not easily crack or check when dried making it a suitable species for framing.

White pine is a soft wood that tends to check. The checking and cracking when dried gives the wood a rustic, weathered appearance. However, it is easy to work with and does not twist or deflect if treated properly.

The oak is the fastest growing hardwood tree. The white oak is decay resistance; however, it is hard and difficult to work in frame construction.

Timber species commonly used for external works include: (1) the western red cedar – a durable softwood that has excellent natural weathering properties; (2) European redwood – a common species for windows and door construction; (3) Iroko – has durable properties making suitable for door and window construction, Idgbo – high strength hardwood used for internal purposes.

Timber species common for interior linings are the bleugum, blue mallet, bunya pine, and the blue leaved stringybark.

Cladding involves the application of waterproof layers on the roof to prevent moisture from building up on the roof and within the building. There are different types of roof cladding and most of them add aesthetic value to the building such as renewed appearance and increased water tightness. Cladding is normally done by overlapping large shets of corrugated metal to form seals that are waterproof.

Plasterboard is the inner layer of gypsum put in between two layers of lining paper including additives in gypsum layer and different weights and strengths of inner lining paper. The finished boards have different properties. Plasterboard is used for interior finishes.

Tiling is done by accurately laying tiles on high finishes in a number of materials both residential and commercial buildings. Tiling includes laying ceramics, mosaic, natural stone or other granites on floors, stairs, swimming pools, outside installations etc.

Openings in a building (windows and doors), are framed to various dimensions by different manufacturers. Framing can either be metal or timber. Frames transfer the window or doors weight down the house to the walls and finally to the foundation. Frames also hold the window or door in position.

Timber framed window Metal Framed window

Timber Framed Door Metal Framed Door

Services provide shelter take care of heat and cold, effects of the sun and rain, and also provide comfortable and conducive working environment where people can live i.e safety, efficiency and comfort. Building services include, energy generation, distribution and supply, escalators and lifts, façade engineering, and fire safety and detection. Others include gas supply, telecom and lighting.

References

Basic Civil Engineering. (2015). What is reinforcement in construction. Retrieved April 21, 2018, from Basic Civil Engineering: https://www.basiccivilengineering.com/2015/05/what-is-reinforcement-in-construction.html

Jamal, H. (2017). Common Types of Concrete and their Characteristics. Retrieved April 21, 2018, from aboutCivil.com: https://www.aboutcivil.org/types-of-concrete.html