Cover Story

Buildings that will bear the brunt

May 24, 2015 |

NEPAL HAS A LONG HISTORY OF DESTRUCTIVE EARTHQUAKES OWING TO ITS LOCATION IN THE SEISMICALLY ACTIVE HIMALAYAN BELT. OVER THE DECADES, ENGINEERS, ARCHITECTS AND EXPERTS HERE HAVE DECLARED WITH GROWING CERTAINTY THAT IT IS NOT EARTHQUAKES THAT KILL PEOPLE BUT INEFFICIENTLY BUILT HUMAN STRUCTURES THAT DO SO.

Earthquakes have shaken human societies, sometimes devastating entire communities, since the beginning of civilisation. Earthquakes present to us an ominous certainty of sorts. The sudden release of seismic energy beneath the earth’s crust that causes quakes can take place at any moment without the slightest hint.

Nepal has a long history of destructive earthquakes owing to its location in the active quake belt between the Indian and Tibetan plates. Over the decades, engineers, architects and experts here have declared with growing certainty that it is not earthquakes that kill people but human structures that do so. It is the inadequacy of the structural performances of buildings that leads to their collapse. Human casualties and damage to infrastructure and property are a result of such structural failure.

Landslides, liquefaction and tsunamis are a natural outcome of earthquakes. Secondary effects like fi re; blockage of water supply, electricity and transportation; and disruption of communication and communication disruption often prove more disastrous as far as human life in earthquake-hit cities is concerned.

The magnitude of an earthquake and the duration of its occurrence affect its impact. The collapse of buildings, in particular, is directly related to strength of the quake and its duration. Generally, shaking in soft soil is larger and longer than in hard rock. When the ground shakes, buildings respond to these ground accelerations which are transmitted to them by ‘footing’.

The magnitude and the damage done

During an earthquake, the ground seems to move in a random fashion in all directions. These ground motions cause built structures to vibrate, inducing inertial force in them. The most effective way by which to mitigate the damage of earthquakes from an engineering standpoint is to design and construct buildings capable of withstanding strong ground motions. Good construction practice can play a tremendous role in the reducing death toll of an earthquake.

Good construction will save lives

Developing engineered structural designs that are able to resist forces generated by seismic waves can be achieved either by following building codes based on hazard maps or by appropriate methods of analysis. Building codes are prepared to make all design and construction work standard. They are designed to protect fi rst, the lives of occupants, and second, the integrity of the building in question.

The most effective way by which to mitigate the damage of earthquakes from an engineering standpoint is to design and construct buildings capable of withstanding strong ground motions. Poor building performance has been singled out as the major source of Nepal’s ever-increasing earthquake risk.

Nepal has developed its own code for seismic designing of building. The Nepal Building Code (NBC) has classed the country into three zones: Zone A, Zone B and Zone C. In high-hazard areas, engineers and architects have to adhere to more rigorous standards when designing buildings to make sure these withstand the violent shakes of earthquakes. We need different levels of resistance for different classes of structures. Critical structures such as hospitals, schools, public buildings, power plants and watertreatment dams, among others, must not only survive the shaking, but must remain in operation. These structures require the largest investment of resources to insure that they can provide services following an earthquake.

Poor building performance has been singled out as the major source of Nepal’s ever -increasing earthquake risk. Therefore, improving the seismic performance of new structures and improving the same of existing buildings has become a major focus for earthquake safety in Nepal.

Non-engineered buildings

Many residential buildings in the country are constructed under the guidance of local contractors and craftsmen with little or no knowledge of earthquake safety.

Consequently, most of our residential buildings do not have rational design for strength. Local contractors and craftsmen then play a vital role in construction although they do not possess specifi c training on and adequate information regarding safe building practices. Often, they lack information regarding the simplest of earthquake-resistant features that can be incorporated into buildings at nominal extra costs.

Concrete structures built without any consultations with engineers and architects are common in urban as well as rural areas of the country. Though building bylaws exist and must be complied with as per the rules of the municipalities, there is no exact regulation regarding structural design and the effects of earthquakes on these buildings.


The need of the hour

An earthquake may hit any place at any time so adequate preparedness to minimise loss is an absolute requisite. Earthquake risk in Nepal, especially the Kathmandu valley, is increasing due to rapid and uncontrolled urbanization coupled disastrously with poor construction practices.

Despite knowledge of seismic vulnerability, public awareness of earthquake hazard and risk is sill minimal. Programmes and strategies to increase awareness must be devised and implemented. Buildings need to be suitably designed and detailed so as to counteract the force of earthquakes. Building codes need to be strictly followed with the design itself ensuring stability, strength and serviceability all within acceptable levels of seismic safety.

As far as possible, all buildings should be symmetrical so as to distribute seismic force equally through all structural elements. Building components like walls, floors and the foundation should be tied together so as to have the entire structure behave as a single stiff unit that moves with the ground. Structures might also be built to be strong and flexible enough to distort but not break so that they might absorb some of the shaking energy. For load-bearing structures, smaller rooms with properly bonded long and short walls with few opening are ideal.

Buildings designed in such a suitable manners will sustain little damage in small quakes, repairable damage in moderate earthquakes and should not cause loss in life due to collapse in large earthquakes. Technicians and supervisors must be given capacity building training more frequently so that they can adopt and implement earthquake preparedness planning and safe construction practices as effectively as possible. Moreover, locally trained masons should be involved in the construction of earthquake resistant structures under the supervision of relevant technicians so that the required skills are disseminated to a larger workforce.

 


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