The conventional method of construction is a way of past. The longer period of construction, inconsistent quality delivered and lack of skilled workmanship is giving the method a major setback adapting in the new world where buildings, facilities and infrastructures needs to be in place in the shortest possible time and most importantly without scarifying the quality and also the aesthetical value of own culture and architectural.

For construction industry to cope with other sector, more sophisticated and advanced construction technologies needs to be adapted or practiced. The transformation seems inevitable. Construction sector needs to be industrialized. Industrialized means lessen dependency on manpower. It also means specialization, simplifying details and reduced the risk of mishap. The reliance on foreign workers should be significantly reduce hence we can also shrink the amount of money flowing out from our country. Looking at the current scenario, Precast system way of construction is seen as the perfect solution for the construction industry.

Precast system construction is a system where components for buildings, facilities and infrastructures are cast at a controlled environment either at permanent plant or a temporary off-site plant. They are then transported based on the need of the site, erected piece by piece and joined either through grouting, welding or bolting to make up a complete structure.

This system not only suitable for plain structures but can well accomplished for buildings or structures that requires unique architectural design. The consistency of the quality is guaranteed as it is being produce at a controlled plant where not only quality aspect but also tolerance control and economy can be best achieved.

The myth of Precast system disregard the joint and detailing as per specified in engineering code such as BS8110 is totally absurd. A matter of fact, Precast system practices high level of stability of the structure starting from the design stage, continued at erection stage and till the live loads are being applied. Each detailing and loads are being considered and studied carefully and are being ensured complying with the code of practice.

The different between cast in-situ and precast buildings main structural lies at the structural continuity. For cast in-situ building, the structural continuity is inherent and will automatically follow as the construction proceeds. The opposite goes for construction utilizing Precast. There must be a conscious effort to ensure the continuity in term of structural to be created when Precast elements or components to be connected to each other. The connections act as bridging link between the components.

As the structure need to stand by itself during the construction stage, Precast system is being design more stringent compare to conventional structure. Analysis for the structure was also being conducted thoroughly to ensure its high levels of stability, safety and performance in the face of external forces, other implied and dead loads. Each jointing part not only being design but also being tested to ensure its durability and workability.

Connections form the most vital part of Precast system construction. This is due to structural elements in Precast building will only form a stable structural system after the joints are connected. Structural considerations for stability and safety are required at all stage. A load bearing structure with stabilizing elements which can sustain both vertical and horizontal loads and transmit the loads to foundation is required and essential.

There are two types of precast construction system that are being widely used in Malaysia namely Precast Load Bearing Wall and Precast Framing System. Precast Load Bearing Wall system is widely being used for high rise residential and structural panels. In order to form an integral building framework, the walls are continuously inter-linked perpendicularly from the first floor to the uppermost floor by vertical tie-bars, which are anchored at the transfer floor (refer detail A).

The structure solidity is beyond question as the jointing part between walls, horizontally and vertically are being treated properly. Horizontally walls are being linked by horizontal tie-bars anchored at the top. The tie-bars from each floor are being connected to another through welding plate (refer detail A). Shear keys are being introduced to couple wall together at the side edges (refer detail B). For vertical joints, jointing plates are being applied. The plates are being welded to each side of the wall hence forming a structure that are stable and sound (refer detail C). Shall Precast slab being applied for the wet area, balcony and hood, the slabs are being joint to the walls through welding plate for temporary support (see detail D) and the reinforcement from the slabs will be casted together with the in-situ floor slab to from a stable structure. The process is as being shown on below pictures.

The design and shopdrawing preparation will suit Client’s requirements as there will be no restriction on the size of the room, height and shape. However, suggestion in order to be cost effective, number of repetition for each paneling must be high, streamlining of architectural design must be done during the planning and design stage or before tender stage so to achieve speed, quality and ease of installation and speed.

In precast frame design , the installation and final stage structural elements strength should be considered due to their actual stage of construction.

1) Precast Beam
2) Precast Column
3) Precast Staircase
4) Precast Mid Landing Slab
5) Precast Half Slab / Plank
6) Precast Load Bearing Wall
7) Precast Toilet Module Slab
8) Precast Façade Wall
9) Precast Balcony Slab

Design Stage

The design and shop drawing preparation will suit Client’s requirements as there will be no restriction on the size of the room, height and shape. However, suggestion in order to be cost effective, number of repetition for each paneling must be high, streamlining of architectural design must be done during the planning and design stage or before tender stage so to achieve speed, quality and ease of installation and speed.

Maintaining Structural

The most important step is to identify which walls are to be load-bearing. Partition walls are also precast but structurally they serve no function. Walls length is then sized according to these factors;

1) Crane’s capacity and reach.
2) Sites contour, access and soil conditions.
3) Erection floor cycle.
4) Stability of panels before slab when is functional.

All load bearing walls is designed as a braced slender plain wall. The in-situ floor slab between these walls act as a diaphragm in both direction and thus this combination will behave like a rigid concrete box. The bottom connection of the wall is categorized as pinned joint while the top connection is fixed. At typical units with precast walls as structural members, all provision for ties are met and these joints are mainly transmitting compression load. Progressive collapse are also taken into consideration.

However due to economic of scale, the first floor structure and sub-structure is to be built using the usual in-situ column and beams. However these in-situ works will have to be very precise as its dimension and shape will have to match its precast counter parts at floors above.

M&e Services

All M&E services like PVC conduit for electrical and trenches for plumbing  installation are incorporated into the Precast walls and the location and  type of fixing must be confirmed first before walls are concreted. More stringent  checks and coordination is needed at factories because hacking of Precast walls on site is not advisable. Close attention must be put into sanitary and cold water services especially rain water down pipes as these require big openings both on slab and Precast walls and may require structural reinforcements. Coordination work also must be done with site personal and consultants with regards to fixing of doors to services room as required by building authorities.

In addition lift services and type must also be confirmed much earlier as additional cost can be incurred if lift shaft is too narrow or big. Opening and support for lift motor also must be confirmed and provided at lift motor room. Lift shop drawing must be submitted much earlier and confirmed by consultant before production.

Architectural Finishing

As not to restrict creativity for the architectural design, minimum change is proposed. The layout and external façade remained but proposal was made to the staircase for cost effective production and erection. In fact some design were enhanced and improved as we are able to provide better and more consistent curve. We were able to give more headroom to units without extra costs because it is column and beam free.

Due to the coordination work and study that was done way before construction, we were able to run our sanitary and cold water piping effectively thus saving cost and the need to cover up these services with false ceiling.

However hoods, aluminum windows and door frames must be confirmed earlier before production of precast walls commence. This has always been a problem because decisions are slow and close monitoring is very essential.