Proem

Yesterday I was able to read the draft “DRR and CCA” manual that is issued to Municipal Engineers in Bohol for their comments.  It is prepared by hired consultants from Australia.

I was not able to find the meaning of DRR and CCA.  Since its introduction statement says that it was in compliance to the instruction of President P-Noy to rebuild better, stronger, and more disaster resilient buildings I presume that DRR would mean “Disaster and Risk Resilient”.  I do not know what is CCA.

The DRR manual contains recommendations how to design structures and where to build.  The problem is who will implement the recommendations because it encompasses almost all government agencies.

There is a recommendation that I find strange.  It says that a CHB (Conrete Hollow Blocks) building is more resistant to earthquake than a wooden building.  Concrete has a damping factor of 5%, which is lower that the 10% damping factor of wood.

Shape Is The Determining Factor

In structural design the greatest determining factor is the moment of inertia or “I”.  The “I” is determined by the shape of the material.  If it has a rectangular shape, the formula is “I = bd³/12” or “Moment of Inertia = width times the depth to the exponent 3 and divided by 12.  You will notice that the particular material used, like wood, concrete, or steel do not matter.

The Bohol Experience

In Bohol the most common public buildings are the church, the municipal building, and the cockpit.  Did you not wonder why the town churches and the municipal buildings were destroyed by the Bohol Earthquake of Oct. 15, 2013 and the cockpits were not destroyed?  In all the towns it was only the cockpit of Antequera, Bohol that was destroyed because its shape did not follow the traditional cockpit design.  The same situation also occurred during the Feb. 8, 1990 earthquake in eastern Bohol.

Roman Catholic Churches has a “T” floor plan.  The altar is at the top of the “T” and the entrance is at the bottom of the “T”.  During earthquakes the bottom of the “T” or entrance portion will sway more because it is less rigid than the altar portion.  It will be the first to be damaged as seen in the Dauis, Baclayon, and Loay Churches.  When the front of the church is damaged and there will be more vibrations, the other parts of the church will also collapse.

Municipal Buildings and regular buildings in Bohol has a rectangular floor plan.  Depending upon its structural design to resist earthquake forces, some buildings collapsed and others did not.

Cockpits in Bohol have a circular floor plan.  A circle has a large moment of inertia compared to a rectangle.  The formula is “I= (Ï€R⁴)/4” or moment of inertia = 3.1416 times the radius to the exponent 4 divided by 4.  Take note that a radius is only from the edge until the center of the circle.  In a rectangle the “d” is already the whole length of the long side.  The divisor “12” in a rectangle is bigger than the divisor “4” of a circle, so the rectangle will have a lesser quotient.

Another advantage of a circular shape is that the “earthquake forces” will just flow along the side of the circle until the forces are dissipated.  It can also “split or deflect” the wind forces and lessens the impact of the wind.

Recommended Octagonal Shape

It is not easy to construct a circular house.  The nearest shape is an octagonal or eight-sided house.  The floor plan is just like two squares crossing its other.  It will be a star with eight (8) points.

For a low cost house, just see to it that the eight points of the star will have a distance of eight (8) feet.  It can be covered by the long side of a plywood sheet with “four feet by eight feet (4’ x 8’)” dimension.  If the flooring can be elevated, it can also resist floods.

There are hundreds of Architects and Engineers in Bohol.  The Provincial or Municipal Governments can make a contest how to design a beautiful and functional octagonal house.

If our people will construct and use an octagonal house, all the requirements of the DRR Manual will be satisfied.  The Municipal Engineer will now have the sole authority and responsibility for the octagonal buildings.

The draft DRR Manual involves so many government agencies like the DENR, MGB, DSWD, etc.

An octagonal house is very resistant to earthquake forces, typhoons and even floods.  It will solve the recurring situation of destruction, evacuation, and rebuilding.  The money of the people and the government can be used for other equally important infrastructures.

An example of a circular building is the old 1912 concrete water tank of the “Rocha-Mendoza Waterworks” of Tagbilaran.  It was converted by the Late Arch. Venerando Dumadag into an office for the Phil. National Red Cross.  It is located at Marapao Street just above the PNB Building and the Tennis Court.  It has existed for more than 100 years already.

If someone can design an octagonal school building, it will be a “game changer” in our community life. (By Jes B. Tirol)