Assignment 2B- Site Study (Foundation & Framing)

Introduction

For this assignment, we did the research on multifamily construction located at Taman Sentosa, Klang.

It has only been in the last few hundred years that a significant percentage of housing has been built in the form of multifamily structure. Before the Industrial Revolution, people came together in villages or town for agricultural, defensive and human interaction purposes. During the Industrial Revolution, which started in the mid -18th century, working opportunities drew swarms of people to the cities. Due to the expensive price and limitation of land spaces, multifamily construction is becoming more and more popular. Nowadays, as cities grow ever more crowded, multifamily housing construction is more necessary than ever. Compared to single-family residences, multifamily unit are tightly packed which lead to several issues, such as privacy and structural issues become more extreme.

Before any actual construction, several activities must be carry out from the site. These includes excess vegetation and soil to be removed for the construction of foundation, temporary utilities for workers during construction as well as the water supply, sewer pipes and surface runoff .must be placed. Site preparation is important for the ease of access of routes and storage location. Contractor must establish the locations of the property lines by marking the corners of the building and by using of the batter board system to get the precise location of the building. After the sites has been cleared and identified the approximate location of the corners of the building, excavation can begin. The depth of the excavation is usually the level at which the depth of the building’s footing.

Foundation

After the rough sitework have done, foundation can be construct after that. The purpose of the foundation is to transfer the structural loads from a building safely into the ground. Every foundation should be able to support loads required according to different building construction. The site we chose uses deep foundation types which is the precast concrete piles. A deep foundation is used to transfer load of the structure down through the upper weak layer of top soil to the stronger layer of subsoil below. Precast concrete piles are square, octagonal, or round in section. For the housing we are doing, is the square piles as shown in the picture.

Typical cross-sectional dimensions range from 10 to 16 inches (250 to 400mm) and bearing capacities from 45 to 50 tons. Advantages of precast piles include high load capacity, an absence of corrosion or decay problems and a relative economical cost. Precast piles must be handled carefully to avoid bending and cracking before installation. In order to allow piles to be driven into the earth, a piledriver are used by

hammering piles into earth with repeated blows of heavy mechanical hammer. Pile hammers are usually lifted by either with steam energy, compressed hydraulic fluid or a diesel explosion and either fall by gravity alone or the downward force by the reverse application of the energy source that lifts the hammer. The piles in each cluster are later joined at the top by reinforced concrete pile cap, which distribute the load of the column or wall above among the piles. When piles are used to support loadbearing walls, reinforced concrete grade beams are constructed between the pile caps to transmit the wall loads to the piles.

SITECAST CONCRETE FRAMING SYSTEMS

Constructing Slab Foundation

The foundation type of a multifamily construction is typically a concrete slab on grade for it is the least expensive foundation option. A concrete slab on grade is a level surface of concrete that lies directly on the ground. To prepare for the placement of slab on grade, topsoil is scraped away to expose the subsoil beneath. A 4 inch deep layer of crushed stone is compacted over subsoil as a drainage layer to keep water away from the slab. For interior floor slab, a moisture barrier (usually a heavy sheet of polyethylene plastic) is laid over the crushed stone. A reinforcing mesh of welded wire fabric is then laid over the moisture barrier which aim to help protect the slab against cracking that might be caused by concrete shrinkage, temperature stress, concentrated loads or settlements of ground beneath. For our researching housing instead, it uses reinforcing grids of reinforcing bar which basically serves the same function as the reinforcing welded wire but is stronger. The form for the slab is coated with form-release compound to prevent the concrete from sticking. Concrete is highly conductive of heat, so slab-on-grade foundation usually must be insulated at their perimeter to maintain comfortable indoor temperature. One disadvantages slab is the difficulty of meaning utilities (plumbing, heating and electrical systems) within them. Once these systems have been cast into the concrete, it is impossible to repair or remodel them. Therefore, designer usually keep heating ducts and wiring out of the slab, but there is no way to eliminate underfloor plumbing. Drain lines are set by the plumber in the crushed stone below the slab with more crushed stone to isolate them from concrete to prevent abrasion from thermal expansion and contraction. Control joints must be provided at internals in slab on grade. A control joint is a straight crack that is intentionally formed into the surface of the slab before the concrete has hardened. Alternatively, control joint can also be created by sawing a shallow groove into the top of the slab after it has hardened. The function of control joint is to provide a place where the forces that cause cracking can be relieved without disfiguring the slab.

Pouring and Finishing the Slab on Grade

Start with the placing of concrete into the formwork. Next, using handheld hook, workers will reach into the wet concrete to raise the welded wire fabric to the mid height of the slab so that it will be able to resist tensile forces caused by forces acting either upward or downward. For the finishing of the slab, the nest step is to stiff off or straightedge the concrete by drawing a stiff plank of wood or metal across the top of the slab. When straightedging has been completed, the top of the slab is level but rather rough. The slab is next floated to produce a smoother surface. This process is done when the watery sheen has evaporated from the surface and smoothen using a flat tool called a “float”. For a completely smoothen surface, the slab must also be done by hand with a smooth rectangular steel trowel or with a rotary power trowel. Troweling is done several hours after floating. To reach the area where the mason (worker) cannot reach from around the edges, knee boards are placed on the surface of the concrete to distribute weight of the mason without making indentation. Marks left by the kneeboard will be removed by trowel later. When the finishing operations have been completed, the slab should be cured for at least a week.

Constructing a Concrete Wall

A reinforced concrete wall at ground level usually rest on a poured concrete strip footing. The footing is formed and poured similar to a concrete slab on grade. A key, a groove that will form a mechanical connection to the wall, is sometimes formed in the top of the footing with strips of wood that are temporarily embedded in the wet concrete. Vertically projecting steel dowels (steel reinforced bar) are usually installed in the footing before pouring. The usage of the dowel is to

connect by overlapping it with vertical bar in the walls to form a strong structural connection. At wall corners, L-shaped horizontal bars are installed to maintain full structural continuity between the two walls. The first step of constructing a concrete wall is first to wired the vertical reinforcing bars to the dowels that project from the footing, and horizontal bars are wired to the vertical bars. Next step is to assemble and erect the temporary wall forms into which the concrete will be poured. These forms are reusable panels of plywood or metal that should be placed on top of the completed footing. The panels for one side of the form are coated with form-release compound, align carefully and temporary braced with vertical wood studs, walers, rod ties and diagonal braces. The rod ties or form ties are small diameter steel rod that function to hold the formwork panels. It pass straight through the concrete wall from one side to the other and remain embedded permanently in the wall after it is poured. Then, the workers will stand on the top of the forms deposit the concrete into the forms. After the form is filled to a certain level, hand floats are used to smooth and level the top of the wall. After 1 to 2 days of curing, the bracing is taken down.

Constructing a Concrete Column

A column is usually form constructed on isolated column footing, a pile cap (in this case) or caisson. First, the column footing was poured with concrete with dowels projecting upwards. The dowel is to connect the reinforced bad for the column. The cage of column reinforcing is assembled with wire ties and hoisted into place over the dowels. The form for the column may be a rectangular box of plywood or composite panels, a cylindrical steel or plastic tube bolted into halves so that it can later be removed. The vertical bars project from the top of the column supposed to be longer and extend to the top of the column in order to overlap or splice to the bars in the column for the story above.

Two-Way Solid Slab System

Two-way s;abs are the s;abs that are supported on four sides and the ratio of longer span to shorter span is less than 2.  In two way slabs, load will be carried in both the directions,  perpendicularly and parallelly. It starts with the form for the girders and beams and then the slab. The forms are supported on temporary joists and metal or wood, and temporary beams are supported on temporary shores (adjustable- length columns). A form release compound is applied to all formwork surfaces that will be in contact with the concrete. The girder and beams are reinforced by bottom bar, top bars, and stirrups which are installed in the forms, supported on chairs and bolters to maintain the required cover of concrete. The girders, beams and slab are then poured in single operation to become a single piece. One way slab depths are typically 4 to 10 inches (100-250mm), depending on the span and loading intensity. The top of the slab is finished in the same manner as a slab on grade, usually to a steel trowel finished in the same manner as a slab on grade and the slab is sealed or covered for damping curing. When the slab and beams have attained enough strength to support themselves safely, the formwork is stripped. The slabs and beams are reshored with vertical props to relieve them of loads until they have reached full strength, which could take several weeks.

  

Backfilling

After the foundation has been water-proofed or damp-proofed, the insulating boards and the drainage features have been installed, the area around the foundation is backfilled to restore the level of the ground. Backfilling involve placing soil back against the outside foundation, taking care not to damage drainage or waterproofing components or to place excessive pressure on walls.