January 19, 2018
by Archian
PHIVOCS Guide 2: Earthquake Proofing your Building
In the first installment of the Article, we discussed the Characteristics of Earthquake proof buildings.
Earthquake Attacks a City and its Buildings
Why is it important for homes and buildings to meet standards set in the Structural Code?
The code prescribes requirements which, if followed, ensure that homes and buildings will not sustain major structural damage when an earthquake strikes. In effect, it protects homeowners and building occupants.
It is developed and updated regularly by the ASEP and is approved by the Department of Public Works and Highways (DPWH), the national government agency mandated to enforce structural standards in the Philippines.
The code derives its mandate from the National Building Code of the Philippines, which was enacted by Congress in 1972, years after the Casiguran Earthquake destroyed the Ruby Tower in Manila. It was later revised by former President Ferdinand Marcos in 1977 through Presidential Decree No. 1096, which allowed updating of structural standards without a need for new legislation.
Updates are integrated by the ASEP when hazard scenarios, which are not yet factored in when the previous versions of the code were drafted, crop up. Since 1972, the Structural Code has been updated 6 times.
The present NSCP was written in an “ultimate strength basis.” This means structures following the code should be able to withstand earthquakes with magnitudes 8 to 9 on the Richter scale, according to engineer Cesar Pabalan, National Director of Philippine Institute of Civil Engineers and former ASEP President.
Devastation damage on 2 storey building Earthquake
High-risk buildings
The SEAOC developed an earthquake-resistant design for buildings. The newest requirement added was the assessment of the structures’ nearness to the fault line. Included with it is the structural response mechanisms that help structures withstand vibration from earthquakes.
For 2015, a new edition will be made in response to the country’s experience with 315-kilometer per hour winds during Typhoon Yolanda (international code name: Haiyan). The current code can only withstand 250-kilometer per hour winds.
The big problem in the Philippines, is that a big percentage of the houses and structures are non-engineered – they were built without the benefit of engineers and structural codes. “Building owners still need to consult experts,”.
Structural integrity
Following the code does not necessarily guarantee a totally “earthquake-proof” house. This is because a house can still sustain non-structural damage during shaking. Windows, for instance, may still break as a result of the shaking. The goal of the code is to ensure low probability of structural collapse.
In the “How Safe is My House” project for instance, PHIVOLCS, ASEP, and JICA outline the features of a properly-built Concrete Hollow Block (CHB) house that follows the current structural code. See the table that lists the “characteristics” of earthquake proof houses. Features of Earthquake-proof houses
Where is it safe to build?
All said and done, where is it safe to build homes?
The PHIVOCS Director noted that the code mandates a “no-build zone” which is 5 meters from both sides of the fault line. This is to make sure that buildings will not be affected by ground fissure. Beyond the “no-build zone,” the height of the building and the distance from the source of the earthquake can affect the level of risk.
Low-rise structures near the fault are more at risk when the West Valley Fault line moves.
LOW-RISE BUILDINGS VULNERABLE. Low-rise structures are more vulnerable to shaking when the source is nearer. Graphic by Alejandro Edoria and Nico Villarete/Rappler
High-rise buildings near the fault, on the other hand, can withstand the shaking better because they are more flexible.
Away from the epicenter, tall structures are more vulnerable as the ground moves slower, making high-rise buildings sway more slowly.
TALL BUILDINGS VULNERABLE. High-rise buildings are more vulnerable to swaying when the source of the shaking is far as the ground moves left and right. Graphic by Alejandro Edoria/Rappler
Cutting Costs can put Lives at Risk
Whether you build near a fault line or not, the design of the building is important to ensuring safety during earthquakes.
We all want to build a house and cut the cost so we don’t get engineers and architects. But what is the price of losing family to accident or worse, death? It is priceless. Is it worth losing family members for a few thousand pesos?
The right process is to consult an engineer, get a building permit, and have a responsible person at the site during construction. These may add to costs, but it could spell the difference between safety and danger in case an earthquake strike.
Read Fears in Constructing a House in Iloilo City.
Archian Designs Architect Studios , Philippines
Archian Designs Architect Studios is a Collaboration of Architects, Urban Planners, Interior Designers, Landscape Designers and Engineers in the Philippines. To see the contact information, email to archiandesigns@yahoo.com, call 0907 7240452 or contact us.
