STRUCTURAL RETROFITTING

Earthquakes do not kill but its effects to the buildings and surroundings which kill. Nearly 5,000 earthquakes occur every year, about 1,000 are felt. Minor earthquakes occur nearly constantly around the world in places like California and Alaska in the United States, as well as in Mexico, Guatemala, Chile, Peru, Indonesia, Iran, China, Pakistan, Portugal, Turkey, New Zealand, Greece, Italy, India and Japan, but earthquakes can occur almost anywhere. The energy released on earth’s surface only by the 2004 Indian Ocean earthquake and tsunami was estimated at 26 megatons of TNT (Trinitrotoluene). This energy is equivalent to over 1500 times that of the Hiroshima atomic bomb, but less than that of Tsar Bomba, the largest nuclear weapon ever detonated.

INTRODUCTION

Earthquake creates great devastation in terms of life, money, and failures of structures. We know that earthquake is an important field of study for a long time. Seismic or Structural Retrofitting is a collection of mitigation technique for    Earthquake Engineering. It is utmost importance are for historic monuments, areas prone to severe earthquake and tall or expensive structures. The performance objectives when conducting structural retrofitting are public safety, structure survivability, and structure functionality.

RETROFITTING DEFINED:

Structural retrofitting means making improvements to an existing building.  It is the modification of existing structures to make them more resistant to seismic activity, ground motion, or soil failure due to earthquakes. Addition of any means by which the existing structure may be able to withstand the possible impact of load. The retrofit techniques are also applicable for other natural hazards such as tropical cyclones, tornadoes, and severe winds from thunderstorms.

Retrofitting of the existing structures has become a large part of the construction activity. It is applicable in beams, columns, walls, floors, and foundations. It can make structure resistant to both vertical and horizontal loads. It is an innovative technique, its type; action strategy may vary depending on site condition, and structural pattern. For example, columns are the most authoritative structural element in any structure that transfers the entire loads to the foundation. Strengthening of deficient columns is necessary to increase the load carrying capacity, ductility and energy absorption capacity that can be achieved by external confinement of column. External confinement can be done by retrofitting.

The primary purpose of structural retrofitting to is to keep buildings and or structures from being displaced from its concrete foundation. The purpose is to make the building safer and less prone to major structural damage during and after an earthquake. Existing structures need retrofitting, because understanding of the effects of earthquakes and construction techniques have improved after the buildings are built. The term house bolting, foundation bolting and cripple wall bracing are often used synonymously with structural retrofitting.

WHEN IS STRUCTURAL RETROFITTING NEEDED?

There are two circumstances where existing buildings are needed to be structurally retrofitted. Firstly, when buildings are damaged by an earthquake, and secondly, when buildings are vulnerable to earthquakes but with no severe exposure.

Buildings vulnerable to earthquakes need structural retrofitting when because these structures have been designed according to a seismic code, but the code has been upgraded in later years. Essential buildings must be strengthened like hospitals, historical monuments, and architectural heritage buildings. Essential buildings whose services are assumed to be essential just after an earthquake like hospitals. Buildings that are expanded, renovated, or rebuilt. Building’s use has changed through the years.

By: Arch. Cezar R. Dizon, Jr.