Saturday, 10 December 2016

Avoiding Building Collapse: If the Foundation of Your Building is Weak Don't Panic, Just Underpin

Most building collapse scenarios across the world have been attributed to faulty, weak or unstable foundations/sub-structures or issues of overloading of some structural members within it. Some others are a consequence of partial or total failure of a member or several members, elements or components of the building/structure occasioned by several forces. 

Many people wonder if there is ever any remedy to damaged or poorly-constructed foundations and defective buildings. The good news is -Yes there are. For buildings or other structures with poor, faulty or weak foundations, underpinning operations can be carried out to correct such defects without aesthetic distortion or demolition. Similarly, in buildings for which extra-loading is intended to be introduced (due to remodeling or change of use) beyond the original design, underpinning is also recommended. In the later case, it is important to first carry out an in-depth assessment of the strength of the foundation in order to ascertain if it can sufficiently sustain the additional load and safely transmit it to the ground on which it rests. 
Generally when a major renovation, repair, addition, alteration or conversion work is to be performed on an existing building of one-storey or more, a structural integrity test on its load-bearing elements and components should be carried out by a structural engineer to ascertain current structural needs or deficiencies. This assessment should form an essential part of the condition survey of the existing building from which the schedule of dilapidation will be prepared and submitted for the purpose of measurement/valuation and subsequent work.

The structural integrity test aims to determine the mechanical properties of the soil stratum just beneath and at the sides of the building’s foundation as well as the current strength/stability status of all its structural members e.g. foundation members, beams, columns, load-bearing walls, shafts, floors and roof and the restrictions imposed during this operation.

If the foundation is not strong enough to sustain the new load you want to add to the building (for example an extra floor), additional weights may be introduced to the foundation. However if its strength is ok but will deflect largely when transmitting the entire load to the subsoil on which it rests, the foundation can be taken to a safer depth using micro-piles, pre-stressed connections, jet grouting, etc. or by simply improving the supporting soil’s mechanical properties, its stiffness or bearing capacity in what is known as an underpinning operation. 
Underpinning operation on an existing foundation of a building 

However, only a competent professional foundation or structural engineer must be allowed to manage this high-risk operation to avoid any disaster ranging from underground trappings/caving-in, structural disintegration, to uncontrolled failures or collapse which may pose a huge threat to adjoining structures and facilities, losses and avoidable injuries or death especially in medium and high-rise buildings or structures above 7m from natural ground level.

In Nigeria, most building owners are ignorant of the existence of this cost-effective technique and would rather pull down the entire structure and put up a new one. Research has shown that apart from saving time, the cost of underpinning foundations is generally much lower than the cost of demolish-and-rebuild. In addition, underpinning operations saves time and retains the structure’s original efficiency or even gives it a greater efficiency throughout its life span. 

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