CHECKLIST: Will your house survive a major earthquake?

The Philippine Institute of Volcanology and Seismology and other concerned government agencies have prepared a "self-check" questionnaire to help Filipinos quickly whether their houses can stand a strong earthquake.

The test—initially devised for one to two-storey "concrete hollow block" houses, shops, and offices—will verify whether the structure "was properly built and have followed appropriate construction procedures and recommended measures."

However, PHIVOLCS still recommends "that the state of your house be consulted to the proper authorities," with engineers from the local government able to recommend methods to strengthen the house, especially its walls.

Interest in earthquake readiness picked up recently after PHIVOLCS released its the Valley Fault System (VFS) Atlas, which mapped the areas affected by earthquake faults in Metro Manila and nearby provinces.

PHIVOLCS has previously warned about possible impending activity from the West Valley Fault.



Here are some notes about the checklist that may help homeowners in their assessment of their houses:

- It is assumed that building construction standards were most likely observed if authorized people took charge of the construction.

- It rates the chance that your house was built compliant to the recent earthquake-resistant building standards similar to special seismic detailing introduced in 1992.

- If damaged by previous earthquakes and disasters and not repaired, the structure is weakened making it vulnerable to a partial or total collapse during a strong ground shaking.

- The shape of the house influences its behavior during strong ground shaking. Box-type or rectangular-shaped houses behave better than those with irregular or unsymmetrical configurations.

- It is assumed that supervised expansion or extension leads to safer and stronger structures.

- The use of standard 6” CHB for external walls produces more stable and stronger structures. This was realized in the Full Scale Shaking Table Test conducted for CHB houses on two models on Feb 2011 in Tsukuba, Japan.

Avoid using sand and gravel taken from the shorelines and beaches as materials for CHB, mortar, plaster and concrete mix for foundation for they are known to corrode the steel bars over time resulting to thinner diameter and loss of bond.

- Steel bars embedded in CHB walls, concrete columns, floors, and foundation resist the impact of ground shaking.

The use of the standard 10 millimeters diameter steel bars spaced at 40 centimeters from side to side and properly connected and tied to steel bars laid every 3 layers of CHB (~60 centimeters) prevent collapse of walls during earthquakes.

- Walls wider than 3 meters span without any perpendicular walls or supports are susceptible to collapse in a strong ground shaking.

- The shaking table test for CHB Houses exhibited that the unanchored gable part of the wall show larger horizontal movement during strong ground shaking. It is recommended that well reinforced and well-anchored CHBs or light materials be used for the gable wall.

- Reinforced concrete wall foundation resists shaking, slipping and tilting better than stone-foundations.

- Rock or stiff-soil provides better support. Soft soils usually amplify strong ground shaking and tend to spread and subside the ground which may worsen damage to the structure. For houses on slopes, tie beams or continues wall foundation prevent uneven settlement during strong ground shaking.

- It is important to observe the state of our house over time. Regular house maintenance must be done to prevent deteriorations like sagging roof, chipped-off plasters and cracks on walls. -NB, GMA News