The 2008 earthquake in L’Aquila, Italy, shocked many people across the Mediterranean. Can we can design buildings in Malta that would be more resistant to earthquakes?

A large office block in Malta was designed to withstand an earthquake- David Grima

There are various possibilities, though one must understand that seismic forces are inertia forces, so when an object such as a building experiences acceleration (as caused by an earthquake), an inertia force is generated when its mass resists the acceleration.

The single most important factor determining the inertia force in a building is its weight. The force is proportional to the mass or weight and the heavier an object, the greater the inertia force. Therefore it is ideal to build as light a structure as is practicable.

When designing larger buildings such as office blocks or hospitals, it is important for an engineer to carefully plan out the building. Examples of this are the positioning of the services cores and stairwells. These provide the most resistance to lateral forces; so they should be positioned with the centre of mass, so that the building is as stiff as possible.

Smaller buildings that are well constructed and light will easily survive a moderate earthquake. The fact that these smaller buildings are well tied together using concrete slabs or beams will add to the rigidity and hence overall resistance to an earthquake.

What is perhaps more worrying are the larger apartment buildings. A common structural system in Malta is to support apartment blocks on concrete ‘planki’. These ‘planki’ are used because basement garages are often constructed beneath the apartment floor levels with a different wall layout being used.

‘Planki’ consist of separate concrete elements that are not adequately tied into the supporting wall structure (or even into each other sometimes). This lack of continuity and support prevents adequate load transfer which could be catastrophic during an earthquake. Today, various large buildings are being constructed using reinforced concrete transfer slabs instead of ‘planki’, which offer far better protection in case of earthquakes and are also cheaper to construct as they are specifically designed for each building.

Vertical wall systems that support ‘planki’ or transfer slabs should also be tied together using steel and concrete to prevent any sliding in case of an earthquake.

Framed buildings always perform better and abroad it has become common to construct residential buildings out of concrete or steel frames. The floor slab is normally designed as one continuous whole and the walls are then constructed out of gypsum.

This creates a lighter structure as well as a more flexible one which performs very well in the case of an earthquake. This system allows the client to be more versatile with his building and allows a prospective buyer to position walls wherever he deems fit without the hassles of creating openings in masonry walls.

Foundations are also very important. It is crucial that a building is well supported if it is to respond well to any seismic activity.

An interesting and popular structural system is adopted in Japan and other seismic zones where earthquakes are common. The buildings are mainly constructed out of frames and designed with the view of directly minimising the loss of life.

The engineer always ensures that the supporting columns would be the last elements to fail, as their collapse would lead to the whole building collapsing and hence a larger loss of life. One would ensure that the horizontal slabs or beams would fail prior to the vertical column and wall elements in the case of a powerful earthquake.

This concept was used when designing a large office building block in the south of Malta. It was designed to withstand an earthquake and the vertical elements were protected so they would be the last to fail.

All horizontal beams were also designed to fail gradually rather than in a sudden brittle manner. This was made possible by making full use of the ductility of reinforced concrete. By designing a stiff but considerably lightweight building one can ensure that it will respond well in the case of an earthquake.

Through careful design and detailing, the loss of life and even overall damage could well be minimised.

Mr Grima is a chartered civil engineer and conservation architect.