SEISMIC ENGINEERING DESIGN IN THE PHILIPPINES

SIESMIC ENGINEERING DESIGN

IN THE PHILIPPINES

          “Earthquake for instance is a phenomenon that man has been trying to study for centuries but up to present time is still unpredictable. We, as structural engineers, are faced with the greatest challenge of formulating procedures on how to lessen if not eliminate destruction and casualties due to this. We want to make sure that the intent of our design is carefully followed and carried out in the most professional manner. The burden of setting up and observing rules on how to achieve what has been planned rest upon our shoulders. Design review can be a valuable tool faced with this challenge.”

                   – Introduction for the ASEP Recommended Guidelines on Structural Design Peer Review of Structures (2015).

 

          Earthquake Engineering is now an integrated part of several engineering and scientific disciplines. For structural engineering, particularly in the design of buildings, towers, bridges, piers, and dams, it is probably the most important component.

 

BASIC CONCEPT

          In its early conception, the overall goal of this science is the incorporation of design parameters to make structure “resistant” to earthquakes. The objective is to construct structures that will not be damaged in minor tremors and will avoid serious damage or collapse in a major earthquake.

Hyatt Hotel collapse in Baguio City after the July 16, 1990 earthquake (left),
and a church collapse at the Bohol earthquake in October 15, 2013 (right).

          The basic concepts of earthquake engineering, implemented in most major building codes, assume that a building should withstand code-specified or determined earthquake-induced lateral forces without major damage, and survive a rare, very severe earthquake by sustaining significant damage but without globally collapsing. Prior to the concept of Performance-Based Earthquake Engineering (PBEE), once the specified code requirements are met, the design is already considered sound and applicable. The responsibility is limited to the physical structure and its integrity. No post-earthquake analysis, no environmental impact assessment, no functional or casulaty loss assessment.

 

EXPANDED SCIENCE

Sample seismic tables (PHIVOLCS PEM Atlas p.3)

          Today, the scope of Earthquake Engineering has been broadened and expanded to include not only as mere component of civil, structural, mechanical, nuclear and geotechnical engineering, but also numerous other fields such as applied physics, and natural and social sciences, including environmental dynamics, sociology, economics, political science, psychology and human behavior. In the publication, “Earthquake Engineering: From Engineering Seismology to Performance-Based Engineering” (2004), by Vitelmo V. Bertero and Yousef Bozorgnia, it was pointed out that the scope of Earthquake engineering today is extended to “the scientific field concerned with protecting society, the natural environment, and the man-made environment from earthquakes by limiting the seismic risk to socio-economically acceptable levels.”



          Observation of actual behavior of reinforced concrete buildings after major earthquakes, accumulation and sharing of recorded data between different institutions, experimental research, laboratory simulations, and analytical studies contributed to the advancement in seismic design approaches and code requirements. Today’s building codes for seismic design have evolved from crude treatment of the subject to sophisticated methodology addressing all factors affecting the behavior of the structure under earthquake excitation, and applicable post-eartquake measures.



          Whereas before, the incorporation of the seismic factor in the design of terrestial structures was limited to the analysis and computation of applied forces to enable building and non-building structures to live through the anticipated earthquake exposure up to the expectations and in compliance with the applicable building code, today’s science includes post-earthquake scenarios, investigations and gathering of data. It is no longer limited to the design, construction and maintenance of structures against seismic events, but also include potential consequences, especially in highly populated urban areas. Consequently, a building, for example, is designed to survive applicable seismic loads, but in addition, the designing engineer takes into consideration the eventuality that seismic loads exceed the code requirement. He can, up to a certain level of economics, adjust the factors of safety in his design. Additionally, the “collapse” scenario is also put into perspective. For instance, a 20-storey building within a city block is designed, and constructed, with perimeter setbacks, allowances for that collapse scenario. While it cannot insure non-lost of lives, the primary objective is mitigation of damages to lives and properties.

 

PHILIPPINE SETTING: METRO MANILA IN PERSPECTIVE

          The Philippines is within the Circumpacific Belt, a seismically active region better known as the “Ring of Fire.” The region covers the length of the Philippine and Japan Archipelagos, extending through the Aleutians, Alaska, and the western coasts of the Americas, westward north of the Antarctic, east of Australia and back to the Philippines through the Indonesian Archipelago. It is here where 77 percent of major earthquake epicenters and 82 percent of the active volcanoes in the world are located.

          According to the Philippine Institute of Volcanology and Seismology (PHIVOLCS), the Philippine Archipelago is one of the world’s most tectonically and, therefore, seismically active areas. Statistically speaking, the Philippines host at least five imperceptible to perceptible earthquakes per day.

Ayala Bridge in Manila during its repair and retrofitting
(Picture from www.autoindustriya.com).

          Metro Manila, on the other hand, is the world’s 11th most populous metropolis with over 12 million residents. It is very much susceptible to multi-hazard natural disasters such as earthquakes. Since the revelations about the Marikina Valley Fault System (MVFS) came to public knowledge in the 1990s, Metro Manila's vulnerability with regards to major seismic events has been highlighted in the last three decades. Information about and the facilitation of new technologies with regards to advance seismic engineering, updated performance-based design of new structures, and seismic retrofit programs for vulnerable existing structures have become vital for public safety and in the mitigation of damages and casualties in the event of a major earthquake.

The Metropolitan Theater.
Designed by Architect Juan M. Arellano and formally inaugurated in December 10, 1931,
gravely damaged during the Battle for the Liberation of Manila (1945), partially restored in 1946,
and completely restored in 1978 through the patronage of First Lady Imelda R. Marcos.
After the EDSA Revolt (1986), vindictive politics marred the very existence of this national heritage,
and by 1996 it was forced to close down and the art works on its walls left to rot.
It is currently undergoing another restoration through the initiative of the
National Commission for Culture and Arts (NCCA).

          As it is, most of the buildings in Metro Manila, especially the low and medium-rise designed and constructed using the older codes and standards; buildings older than three decades or more that are still currently in use, are generally considered extremely vulnerable to supertyphoons and very strong earthquakes. The same holds true with public infrastructures such as dams, bridges, school buildings, hospitals and other government facilities more than three decades old. While government is addressing this concern, retrofitting, rehabilitating and upgrading these public facilities and infrastructures, very little is known with regards to actions taken by private entities. Economics has always been the prevalent reason as the cost of structural rehabilitations maybe beyond their capacity. The dilemma lies in post-earthquake scenarios where the damage or collapse of one structure affects another, and another, and so on. There should be a government agency specifically tasked to handle this eventuality.

 

MIS-APPLIED CONTINUING PROFESSIONAL DEVELOPMENT

          Philippine engineering information and technology is at far with the rest of the world. Knowledge-wise of new concepts, analysis, and design supplements, materials evaluations, continuously practicing engineers – “professionals” – are constantly updated through releases from international engineering bodies like the American Concrete Institute (ACI), American Institute of Steel Construction (AISC), American Society for Testing of Materials (ASTM), International Code Council (ICC), and other institutions and committees involve in engineering and construction. There is really no problem with regards to this so-called “continuing professional development” (CPD) as far as practicing engineers are concern. With online videos and correspondences, today’s engineers are well-informed and updated by the international engineering communities, far superior than attending local sit-in class seminars. This is contrary to the ignorant assumptions of Senator Antonio Trillanes IV, the author of Republic Act 10912 (CPD Law). He was definitely misinformed with respect to the local engineering profession. Local seminars, as proposed, for this continuing professional development, in all practicality, should be for newly-graduates; those engineers who do not consistently practice their profession; and those who failed to renew their licenses continuously, and it should be voluntary, and not compulsory to the point of using it as a prerequisite in renewing professional licenses. Any new information should, instead, be available online freely accesible to interested parties. Commercialization should not be a priority in this endeavor. As such, the CPD Law should be entirely revised or otherwise totally scrapped!

          The real problem, one need to mention, lies in the approval and issuance of building permits by local goverment authorities, and in the Philippines’ existing building codes, especially in the aspect of seismic engineering.

 

THE REAL PRIORITIES: POLICIES AND CODES

          Although lessened by the current government strict policies, there are still corruption and laxity in the issuance of building permits, implementation of contruction guidelines, evaluation of the quality and strength of materials, and determination of the soundness of the completed structure. Furthermore is non-compliance of property owners to adhere to setback and zoning requirements imposed in the Civil Code and the National Building Code (NBC), and the non-vigilance of building officials with regards to this matter. That is why, in Metro Manila, we see tall buildings erected just barely a meter or two from a river, houses and apartments constructed on sloping grounds without gravity wall protections, pollution-causing factories built in the middle of residential areas, subdivisions established directly on top of existing faults, etc. There is also a glaring lack of overall planning in the metropolitan development and management, especially in disaster preparedness and post-disaster measures. These are the ones that should be address with priority. Subsequently, the priority in professional development should be focused on the mandates, services and actions of government personnels – building officials – and not on the practicing professionals.

          With regards to the status of codes, both the National Building Code (NBC) and the National Structural Code of the Philippines (NSCP) lack provisions, guidelines and specifics with regard to seismic engineering, and the updating of data from real-time sources are slow.

          The provisions and guidelines set forth in the Philippines’ first NBC (Republic Act 6541) is more than half a century old. Though it was revised by President Marcos, through PD 1096 in February 19, 1977, most of the provisions, both general and specific, are outdated and needs further updating to conform with today’s building and construction standards and models. The 2015 NSCP (Seventh Edition) Volume 1, on the other hand, of which most of its contents pertaining to seismology and seismic engineering were culled from the 1997 Uniform Building Code (UBC), while it has been updated several times, many of its provisions related to seismic design and safety factor are arguably still not in line with the fast-updating international standard. Both codes should also, now, incorporate current provisions with regards to performance-based seismic and structural design standards.

          Before the publication of the first edition of the International Building Code (IBC) in 2000, by the International Code Council, replacing the more than two-decade old UBC, seismic risk and subsequently seismic design criteria in building codes depended only on the level of the earthquake ground motion. The concept of seismic zone was used. For its part, according to the UBC, regions are divided into five seismic zones 0 through 4. Zone 0 is where the earthquake ground motion the weakest and zone 4 the strongest. The method of analysis, height limits, seismic constants, and level of detailing depended on the seismic zone in which a structure is located.

          With computer-aided technology, recent seismic events have been studied more closely and definitively. Scientists and engineers now acknowledge that structure performance during an earthquake depends not only on the energy level of the earthquake ground motion, but also on the nature of the soil on which the structure is founded, the current IBC 2018 established the Seismic Design Categories (SDC) as a measure for the seismic risk for a certain structure. The SDC is a function of the level of the earthquake ground motion, the soil nature at the site, and the intended usage of the structure. The IBC contains procedures in determining the SDC for every structure. That is, the allowed method of analysis, height limits, seismic constants, and level of detailing.

 

THE CALL FOR NATIONAL STANDARD

           For all purposes and intents, the Philippines should have its own seismic design categories manual apart from the NBC and NSCP, which should contain tables for Earthquake Magnitude, Intensity (based on distance from epicenter), Peak Ground Acceleration, Spectral Acceleration, Mean Spectra, Maximum Induced Laterial Force, Maximum Induced Vertical Uplift, Allowable Fault Proximity Distance, Soil Bearing Capacity (in relation to seismic induced liquefaction), Minimum/Maximum Base Shear, etc.

          The Philippines, being on a very seismically active zone, should have its own standards, models and guideless, for design. Our neighboring countries are proceeding to this objectives. We should, we must, do the same,

          PHIVOLCS had recently released the Philippine Earthquake Model (PEM) atlas. This is a valuable tool that designing engineers can use as basis/reference for peak ground acceleration and spectral acceleration. It is this kind of progressive “continuing (professional) development” tool, which can be locally applied, that are useful to engineers and not seminar informations which are readily available online. It is initiative like this that engineers really need. 

Three-column test specimen on earthquake simulator (PEER Center).
The Philippines should have laboratories for seismic research and studies such as this,
based on local seismic experiences.

          We need to have our own national standard based on local experiences and events applicable to prevailing factors and conditions. For this to happen, we need to do our own seismic engineering research, investigations, and model experiments. This could be done by the Department of Science and Technology (DOST), in joint understaking with the Philippine Institute of Civil Engineers (PICE) and Association of Structural Engineers of the Philippine (ASEP), with the aid or in conjunction with other international bodies on the subject, like the Pacific Earthquake Engineering Research (PEER) Center, the Japan International Cooperation Agency (JICA), the China Earthquake Networks Center (CENC), or the US Earthquake Engineering Research Institute (EERI), etc.

 

REFERENCES:

ACI-318-19, “Building Code Requirement for Structural Concrete” (2019), American Concrete Institute (ACI).

ACI-HB-12, “Compilation of Performance-Based Seismic Design Recommendations and Standards” (2017), American Concrete Institute (ACI).

Applied Technology Council (ATC) and Federal Emergency Management Agency (FEMA), “Expected Seismic Performance of Code-Conforming Buildings” (2018), FEMA P-58-5, Seismic Performance Assessment of Buildings Vol. 5

Association of Structural Engineers of the Philippines (ASEP) Inc., National Structural Code of the Philippines (NSCP) 2015, Volume 1, Seventh Edition.

International Code Council, International Building Code (IBC) 2018.

International Conference of Building Officials, Uniform Building Code (UBC) 1997.

Japan Society of Civil Engineers (JSCE), “Comparative Performances of Seismic Design Codes for Concrete Structures” (1999), The Concrete Committee of JSCE.

H. Kit Miyamoto and Amir SJ Gilani, “Comprehensive Seismic Risk Reduction Program for Public Buildings in Metro Manila, Philippines” (2015).

Naveed Anwar, Jose A. Sy, Thaung HtutAung, and Deepak Rayamajhi, “Performance Based Seismic Design, State of Practice in Philippines” (2012), Conference Paper, CTB UH 9th World Congress.

Pacific Earthquake Engineering Research (PEER) Center, “Tall Building Initiative: Guidelines for Performance Based Seismic Design of Tall Buildings” (2010).

Vitelmo V. Bertero and Yousef Bozorgnia, “Earthquake Engineering: From Engineering Seismology to Performance-Based Engineering” (2004).

 

WALL ILLUSTRATION:

By John Richards, from the book, Earthquakes and Volcanoes (Reader’s Digest Pathfinders, 2000), pp. 22-23.