Prefabrication for high rise

Finding the reasons why modular and high rise are not gelling

Horst Brandstaedter.
Horst Brandstaedter.

 

Many articles about prefabrication were written already, but when it comes to high rise the literature is decreasing to only a few books or comments.

Especially for high rise the idea of prefabrication, I am talking here about modular cell systems, would be the ideal market and a perfect construction method.

But let’s find out why modular and high rise (over 30 floors) is still not going very well together.

Besides the usual pros and cons of prefab with modular systems, a few major issues are to be considered when there is the intention to combine prefab with high rise. Critical issues are structural systems, wind load, fire life & safety precautions, acoustic, MEP and construction methods.

Modularisation and structural decisions have to be made right at the beginning of the design process. Does the structural design prefer load bearing systems, staging systems or a mix of structural framework with the modular elements?

The core has to take a higher function and responsibility against deflection because mostly the bracing wall systems will be in conflict or influence the modular system. The entire building system is going to be more separated into elements and research must be done on how they will interact together. Therefore the wind load plays a more important role than in usual traditional structural designs.

Fire life safety for the structural frame and the modular cells needs to be determined by their type of construction and materials. Structural steel frames and staged modular systems require a high fire protection while concrete structural systems are commonly without any fire protection. Modular cells of steel must have fire protection while concrete wall modular cells would not require fire protection. In general for modular building systems the amount of fire protection is much higher and becomes a bigger position in building costs.

Acoustics can be handled within the modular cells. They have to be separated acoustically to avoid sound transmissions. A major item of concern will be the right balance of weight impact for any modular element to omit acoustical problems against construction methods.

 

 

Construction methods is the major critical issue for high rise. The construction of modular cells with solid walls like concrete walls will create a major weight issue. Site cranes usually will not be able to lift the heavy load of i.e. entire modular cells of hotel rooms with weights of more than 20 tons on the crane. Special cranes and lifting systems to lift these cells and units to bring them into position would be required.

Therefore modular cells are commonly in light weight systems consisting of steel frames with i.e. cement boarding and fire protection layers. They can be lifted up easily with cranes and brought into position within the building's structural framework. There is no restriction in building heights for the towers.

However, for load bearing staging systems with modular cells the construction would be more difficult as they take the structural load. Structural elements changing sizes will influence the cell system. Consequently load bearing staging systems of modular cell types, especially for high rise buildings over a certain height, would not really be recommended.

Conclusions:
By not going into too many details we can say that a few critical issues are to be considered for pre-fabricated modular cell systems in high rise buildings of more than 30 floors i.e. for hotels and residential towers. These are structural frame, fire protection and construction method. If these items are developed and solved at the early design stage between stakeholders, designers, consultants and contractors a good chance for pre-fabricated high rise buildings is given.

Horst Brandstaedter is a German national, RIBA registered Project Director and Business Developer, who has worked for design companies, consultants, real estate developers, governments and various public and private clients. He has more than 20 years international and Middle East professional experience in the building and construction industry for large scale projects, infrastructure, mixed use, residential, banks, commercial, retail, shopping malls, industrial, high rise towers, luxury 5-star hotels & hospitality buildings and resorts.

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