TILT-UP CONSTRUCTION

Tilt up is an extremely versatile method of construction offering a cost effective solution to many challenges it is presented with. Initially used to create simple wall panels, tilt up has itself evolved to the point where the benefits of working at ground level and lifting a completed element are being applied to a variety of applications:

Ideally, panels are cast on the surface bed of the project or on final concrete hardstand areas around the building. If project conditions dictate the use of sacrificial casting beds, 75mm thick unreinforced beds are prepared and later demolished and carted off site. This is only done as a last resort in order to minimise unnecessary costs.

Panels are set out in accordance with a predetermined casting layout drawing.

Simple perimeter formwork is erected outlining the shape of the panel as well as any openings required. Decorative relief work can then be prepared where necessary. Should space constraints prevail, similar panels can be stack-cast one on top of another.

  

A chemically reactive bondbreaker is then applied to the casting surface to ensure that there is no adhesion between the panels. The bondbreaker is non membrane forming and has no effect on applied finishes to either the walls or the surface bed.

Reinforcing is either tied in place or prefabricated and placed in position depending on the size and complexity of the panel. Lifting inserts are tied in place and the panel is cast and floated.

Panels must cure for between 5 and 9 days before being lifted, depending on the concrete strength used. On larger projects phased lifting allows panels to be lifted periodically once sufficient panels have been prepared. A balance needs to be struck between optimising crane establishment costs and programming requirements.

Panels are then lifted using a mobile crane, placed in their final position and temporarily braced. Braces have an 450mm long adjustable thread, thus allowing the panels to be adjusted and lined at any stage prior to them being finally connected into the structure.

Connections are designed by the project engineer, in consultation with the tilt up supplier to suit the specific requirements of the project. Cast in plates, chemical and expansion anchors, or in-situ concrete stitching are all used, depending on performance requirements.

Once integrated into the final structure the temporary braces are removed and panel joints are sealed internally and externally using a polycord backing and a polyurethane sealant before the final applied finish is added to the panel.

In competitive tender situations, tilt up has repeatedly proven itself to be the most effective method of construction.

The system does not sacrifice quality for cost. Instead, it provides a finished product which is superior to most other alternatives, as it offers the strength and durability of reinforced concrete walls. Simultaneously it is possible to economically achieve aesthetic effects which are either not possible or cost effective with other methods of construction. This ensures attractive, aesthetically pleasing buildings.

 

Tilt Up is a fast method of construction. Time savings of up to 15% can be achieved over conventional methods due to the following reasons:

• Fast tracking: - the sequential relationship between activities in conventional construction need not apply to a tilt up alternative. For example, with tilt up it is possible to begin forming and casting wall panels whilst still excavating foundations. This allows overlapping of activities not possible with conventional construction.
• Increased productivity - by virtue of the fact that with tilt up most of the work is done at ground level, without the need to hoist materials and work at elevated positions, labour is far more productive than is the case conventionally.
• Reduction in number of trades - since a tilt up panel combines the structures, external envelope and final finish to the building in one operation, there is an obvious reduction in the number of building trades required to achieve the finished product. This reduction in the number of sequential trades automatically results in time savings on the project.

The aesthetic possibilites of a tilt up alternative are virtually endless and may be limited only by the architect's imagination. Shapes and designs not possible conventionally can easily be formed and cast to a high degree of accuracy using tilt up.

A tilt up panel is virtually a blank canvas ready to receive any aesthetic the architect requires. Since there are no restrictions due to brick coursing or set module sizes of a cladding system, relief in large panels is not limited to horizontal and vertical bands as tends to be the case conventionally. Instead, a whole range of shapes and effects now become possible. For example, a company logo can easily be incorporated into a tilt up panel simply by forming the logo out of timber or polystyrene and casting the panel over it, thereby recessing the logo within the panel.

Similarly, decorative precast panels can be laid face down and the tilt up panel cast over them, thereby bonding them to the panel, which when lifted, incorporates the decorative panels without any additional fixing requirements.

Tilt up is an extremely flexible system, able to accommodate changes to a building envelope with minimal disruption to the construction programme, or occupants of the building in the case of a completed project.

Openings can be cut into a tilt up panel if required. No lintels are required above new openings as the panel creates a concrete "column and beam" arrangement.

Panels can also be designed to allow for future expansion. Connection details to the main structure are simply detailed allowing the panel to be disconnected from the main structures at a later date. The panel can then be removed and reused in a new position if required.

Tilt up buildings are extremely durable and long lasting. There are examples of such buildings that date back to the 1940's, which have recently been given a cosmetic "facelift" and look as good as new.

A tilt up panel is hard and durable. Able to withstand heavy impact loads without any major damage, it is ideal for high wear and tear areas such as warehousing and manufacturing facilities where forklifts are used. Since walls cannot be damaged by forklifts, product can be stored hard up against them, thereby increasing useable space within the structure.

With tilt up one does not have the problem of plaster cracking over time and the high quality finish remains unchanged for decades.

Full height, reinforced concrete walls to the building external envelope provide a virtually impenetrable envelope to even the most determined intruder.

150mm thick tilt up panels have an excellent fire rating over 3 hours. Case studies have shown that even in the event  of a fire, tilt up panels often suffer only cosmetic damage and any remedial work was of a purely decorative nature.

Due to the fire rating achieved with tilt up, as well as the non-combustible nature of the reinforced concrete walls, a reduction in insurance premiums has often been negotiated by the owners of tilt up buildings.

Clearly one can see that tilt up has evolved to address weaknesses in traditional construction methods, solving problems and challenges faced, whilst delivering a high quality finished product within the tight time and monetary constraints common to modern day projects.

The sytem has only recently started to gain more widespread acceptance within South Africa, but as it continues to meet the demands of our challenging industry, it seems destined to become the construction method of choice.

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