revised seismic design code for indonesia

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REVISED SEISMIC DESIGN CODE FOR INDONESIA “JAKARTA CAN WITHSTAND MASSIVE QUAKE” This was a headline from The Jakarta Post discussed in an article in the February 2012 edition of UP.DATE. At that time publication of a new seismic design code for Indonesia was expected, and the wait is now over. The previous code SNI 03-1726-2002 has been replaced by SNI 1726:2012. This code provides engineers with up-todate advice concerning the design and construction of buildings in Indonesia to resist the effects of earthquakes. Although Indonesia has not suffered a major damaging earthquake for a few years, it still sits squarely on the “Ring of Fire”, the seismically active zone that encompasses the Pacific rim and heads north via Philippines and Japan, around to the western seaboard of the Americas. Tectonic activity around the Ring of Fire accounts for around 90% of the world’s earthquakes, and Indonesia with about 7,000 km of tectonic plate boundary has a major share of them!! There have been over 20,000 earthquakes of magnitude greater than 5.5 recorded around this “Ring” in the last 80 years. Such earthquakes are described as “destructive”, so if you do your maths quickly, that is one potentially destructive earthquake almost every day! Type www.iris.edu/ seismon into your web browser to see this in action.

the forefront of the development and updating of these “guides”. Indonesia has had an earthquake design code for about 30 years. The first Indonesian code “Guide for Structural Design in Earthquake Areas of Indonesia” was prepared in the early 1980’s based on a combination of the New Zealand and California earthquake design codes. It was soon updated following extensive work carried out by New Zealand engineering consultants in late 1980’s and early 1990’s. National seismic design codes provide advice on methods of design and construction to resist the effects of earthquake shaking, as well as a map of the country which divides it into zones of differing seismic intensity. These maps are generally referred to as “seismic hazard” maps. Most earthquakes in Indonesia occur along the Sunda Arc as a result of subduction of the Indo-Australian tectonic plate under the Eurasian plate,

where the majority of the Indonesian Archipelago is located. Branches of this subduction extend towards Papua to the west and the Philippines to the north. Researchers at the Bandung Institute of Technology (ITB) have carried out detailed studies of recorded earthquakes in this region. The map below shows all the earthquake epicentres of magnitude 5 and greater which have been used for this study, including the tsunami creating 9.2 magnitude quake off Aceh in 2004, the Nias quake in 2005, as well as the 2009 Padang quake. These infamous earthquakes have all taken place since the previous code was published. Part of the work undertaken has been to associate the recorded earthquakes with the main tectonic features, such as the subduction zones and major faults. This has helped the researchers predict where strong seismic shaking may occur in the future, which is a major factor in preparing the seismic hazard maps.

EPICENTRES OF EARTHQUAKES TAKEN INTO ACCOUNT FOR ESTABLISHING THE NEW SEISMIC HAZARD MAPS

Earthquake or seismic design codes are guides which assist engineers and builders to develop buildings and structures in earthquake prone areas, and have been available in a number of countries for many years. California, New Zealand and Japan have been at

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EARTHQUAKE DAMAGE IN PADANG SUMATRA, SHOWING EXAMPLE OF INCORRECT WEAK COLUMN AND STRONG BEAM DESIGN CONTRIBUTING TO DAMAGE

The results of these studies have now been published as part of the new Seismic Design Code for Indonesia. There is no longer a single seismic hazard map, but a series of maps devised to provide a more comprehensive assessment of potential risk and severity of seismic shaking. The recommendations may be applied to a wide range of buildings. In the case of very tall structures, it is recommended that detailed site specific studies are carried out based on the precise location of the proposed building. The code has reinforced some previous design recommendations – for example the principle of building columns being stronger than their beams which helps to prevent buildings from collapsing, as well as the details and form of the steel reinforcement used in the columns and beams. The photographs above illustrate what can happen when these principles are not followed, based on damage observed following the 2009 Padang earthquake. The

study concludes that for low rise structures, good building construction requirements and details will provide adequate protection to inhabitants in most cases. The study and new recommendations prioritise structures in order of “survival importance”. Highest priority is given to lifeline buildings such as hospitals, fire stations and water supply. Very high priority is given to power stations, as well as areas needed for refuge for personnel in cases of a large magnitude earthquake. Secondary levels of importance are assigned to structures such as schools, cinemas, churches and mosques. Kalimantan remains the only area with generally low requirements for earthquake design, although the areas along the east coast have now been given a low level seismic ranking. The revised code is for the design of buildings, and does not address earthquake requirements for civil

ONE OF THE SEISMIC HAZARD MAPS PUBLISHED IN THE NEW SNI 1726:2012 SEISMIC CODE

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Michael Dobie, CEng FICE works for Tensar International Limited, a company which develops and provides solutions to civil engineering problems using reinforced soil techniques. He is a civil engineer specialising in the geotechnical field. He is a Chartered Engineer and the Country Representative of the Institution of Civil Engineers in Indonesia, and has worked in the field of geotechnical engineering for both consulting engineers and geotechnical specialists before joining Tensar International in 1991. Mike has worked in Asia Pacific for a total of 25 years, moving to Jakarta in 1993.

Bob Scouller is engaged as a Consultant in the Mining and Resource Infrastructure areas and serves on the Committee of the Institution of Civil Engineers, (UK), Jakarta Local Association. Bob has been involved in earthquake rectification in Flores, (Maumare) Padang, Bougainville (PNG) and Aceh after the 2004 tsunami. Bob came to Indonesia with Rio Tinto from Australia for the development of KPC Coal and has been active in Indonesia for over 25 years in a variety of senior engineering management and director level roles.

works, roads, embankments, water resources structures, wharves and bridges, etc. It has been suggested this will be the next objective of the Earthquake Study group at ITB. Returning to the conclusion of the February 2012 UP.DATE article, what does the new seismic design code SNI 1726:2012 imply for existing buildings in Jakarta, which were designed to the previous code? There is no one single answer to this question. Design requirements have changed, and have been brought into line with the most upto-date knowledge and practice, accumulated over the last 10 years. Depending on the type of building and its location, seismic design requirements may well have become more onerous, most probably for taller buildings. If building owners or users are concerned, then it would be wise to seek expert advice, in order to check or re-assess their property in the light of the new seismic design code.

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