WHY JAVANESE HOUSES WERE SEVERE COLLAPSED IN THE 2006 EARTHQUAKE ?

In general the factors causing the failure of Javanese house can be affected by: the epicenter proximity, the geological formation, high density level, and weak construction of the houses (Idham, N, et.al 2010a)

The epicenter was relatively very close and shallow to the object of Javanese houses

According to USGS, the magnitude was 6.2 Ritcher scale and the epicenter was at 7.96°S, 110.46°E with 10 km depth. The epicenter was located in the Opak river estuary around 20 km from Yogyakarta with shallow depth. It means that the source of the quake was on the site of the houses (Bantul district of Yogyakarta). The magnitude would have less meaning if the proximity to the epicenter is also less by means far away from the energy resource. Some other earthquakes actually stroke later such as the 7.0 SR West Java Province on September 2, 2009 with the epicenter distance 195 km from Jakarta and 46.2 km depth under the sea (USGS 2009a). In this case, it was causing casualties ‘only’ 57 fatalities and 300 injured from about 10000 damaged houses. This earthquake was also felt from Yogyakarta and Central Java but it has no effect or little, if any, to the buildings there. The other earthquake happened in November 13th with 5.4 SR magnitude 360 km away from Jakarta and 41 km depth (USGS 2009b). The last quake has no any casualties and building damage. In this matter, the MMI scale is more useful in measuring the effect earthquake to the buildings since it based on the impact in the area. If the 2006 Java earthquake has VIII-IX, while the September 2, 2009 west Java earthquake only VI-VII.

Geological formation of the sites bolstered up the effect to the buildings

Instead of spreading to the surrounding site in radial way, the 2006 Java earthquake had different effect in some areas related to the local geological condition. Soft soil easily amplifies shear waves transfer from epicenter. MAE recorded that horizontal peak ground accelerations in the region of 0.20~0.34g and vertical ground motion is estimated from structural collapse back-analysis at 0.18~0.30g which was categorized very high (Elnashai AS, et.al, 2007). As a result, buildings located near river line or wet land will be affected more. From the 2006 earthquake data, the nearer area of the epicenter, Gunung Kidul has less effect since the ground is more rigid constituted from limestone. In other hand, farer area as Klaten Regency with most wet agricultural soil has more collapsed houses. Unfortunately, as a consequence of agricultural land, Bantul and Klaten have sit on soft soil and will have more threat from earthquake disaster compared to surrounding areas. The wet areas stretched from Bantul to Klaten are also known as Opak vault.

The affected areas have very high density of houses

Java Island in general is the densest population in the world by 979/km². Among of them, Bantul district where collapsed houses were high is the densest area in Java with population of 831,955 living in 226,777 houses in 506.85 km² area or 1641.4/km² of inhabitants and 447.4 houses in every km² (DEPKES 2007). When the 2006 earthquake stroke, 148,440 out of 218,345 houses (67.9%) in Bantul were non inhabitable or badly damaged and collapsed (BAPPENAS 2006).

The houses structure was very weak and built without earthquake consideration

Eventhough Javanese houses were originally constructed from wood, the modern development shows that brick is the most material used for structural system of the houses. According to Boen (2006), the houses collapsed from Java 2006 were mostly built by masonry either with or without reinforced concrete frame. The weak masonry was the main factor to collapse of the building while for the newer with reinforced concrete; improper connection is the most aspect of structural failures. Those structural failures were mainly because of lack in earthquake consideration since 1943 when big earthquake, for the last time, was causing high casualties before it happen again in 2006.

Figure Javanese House's Changes in Material Structure

The load bearing brick-wall construction has been used widely as preferred house construction system together with timber frame since the Dutch occupied Java Island and started to colonize it in the early 17th century till recent times (Prijotomo,1996). For Javanese, the brick house then has been used as a symbol of social status of family of the owner (Koentjaraningrat, 1984). Unfortunately, this new concept was followed without any consideration in earthquake potential threat. The limitation of their economy and the lack awareness of proper construction of the houses were some of the main problem. As a result, this became one of factors contributing the weakness of the house construction and causing so much loss by recently quakes.

Based on Paper:

Idham, N; Mohd, M, and Numan, I (2010a) ”Why The Javanese Houses Have Failed In The 2006 Earthquake”, in proceeding of the International Conference on Sustainable Built Environment (ICSBE 2010) pp.121-128. Faculty of Civil Engineering and Planning, Islamic University of Indonesia, August 2010.

Is the CONCRETE FRAME HOUSE MOST SECURE for EARTHQUAKE RESISTANT HOUSE (2)

In the midst of my routine busyness (and bored to!) to wrote my PhD thesis, I tried again to fill this blog just in order not to neglect and fills my saturated time since being away from my wife and kids this (... ehem). My topic now is not far away from the theme of my thesis, traditional Javanese house and its relation to earthquakes.

STIFFNESS, STRENGTH, and DUCTILITY

As a result of the earthquake in Bantul 2006, many buildings whether it is called traditional or modern building, mostly badly hit by the devastated earthquake. Soon after, the government and hundreds of donors rebuilt shelters in the Bantul and surrounding areas with new houses through a reconstruction program. The popular reconstruction house types were built from bricks wall altogether with reinforced concrete frame. Those new houses are considered the safest or most appropriate to anticipate the future earthquake. Previous homes, especially the traditional houses, are considered less suitable for earthquake resistant buildings. So the people in Bantul and surrounding communities then build their homes with this type of reinforced concrete which was previously not widely used, especially by rural communities who had still familiar with the house bricks or wooden house using 'gedhek' or 'gebyok'. Now it can be ascertained when you come to the Bantul, old style house ‘tempo doeloe’ such as Javanese Limasan, is rarely used anymore in Bantul, and just as a memory.

Just to note, that houses by framework of concrete bricks indeed be one solution to the earthquake-safe building houses but not the safest one. The nature of the framework of concrete brick wall relies on the principle of stiffness and strength rather than ductile. The principles of earthquake resistant buildings are supposed to cover all three issues. Stiffness is the principle of building to resilience the shocks so that the building does not change in shape, while building strength is the principle of maximum load of an earthquake can be accommodated, so it is always associated with load resistance. Ductile in the other hand more to do with building endurance to change its shape (flexible, plastic), or absorb the force, according to the existing burden. The principle stiffness in buildings is by applying heavy materials such as bricks and concrete that is rigid or rigid and not flexible. While ductile is more suitable when using a material like wood and steel.

Unfortunately, the principle of prioritizing the stiffness first in building only fit for the area that have small earthquake risk since consideration to resist shocks will be relatively low. This is worst by the burden of building by using materials such as bricks and concrete slabs. High load in addition to relatively low plasticity are also vulnerable to the dangers of rolling for lateral or horizontal forces caused by the earthquake. It's also very dangerous if used as a residential building since it element will ruins the occupants under yet of lightweight materials such as wood. Furthermore, if the quality of implementation is also low, the risk of earthquake will be very-very high.

This is what bothered over my mind. New houses in Bantul were completely been built using bricks and concrete slabs. Regardless of whether its implementation is right or not, the use of this material type is still worrying for earthquake prone areas such as in Bantul. The houses with a high ductile principle should be more secure and less stressed rather than the reinforced concrete which is more rigid and brittle. Although some opinions said it would be very expensive for using wood, but the reinforced concrete building materials are also not that expensive now? And probably should not be forgotten, the potential use of local wood or bamboo or palm-coconut wood also still can be improved. And another thing, by building houses made of wood we will also return to preserve the Javanese traditional house which previously been widely used (in the future we will discuss why many traditional houses collapsed in the quake of 2006 in Java).

Why Javanese Houses were Easily Collapsed on the 2006 Earthquake?

Introduction:
This topic is the initial thought of my study, why Javanese houses were so easily collapsed in the 2006 earthquake and caused a lot of casualties?

Allegation:
Several reasons for this issue are given below with the expectations to conduct of study to prove it by the scientific method. At least there are two main factors causing this 'failure' of the Javanese house from the earthquake, the environment as external factors and the house itself as an internal factor that will significantly influenced by several things:

1. The epicenter of the May 27, 2006 earthquake was occurred in very close to the settlement
Although the earthquake was ‘only’ with the power of magnitude 5.9 (BMG) or 6.2 (USGS) Richter Scale, but the epicenter was close to the settlement of the population. It was also relatively shallow with a depth of 10km. If the earthquake source close to the object, it will have greater intensity as VIII-IX MMI (Merchali Modified Intensity). This measurement is applied to level the impact on the local influence of the earthquake, rather than in the center such as the Ritcher scale.

2. Local geology conditions that support the spread of the earthquake energy easily.
Bantul and Klaten districts are located in a relatively fertile compared with Gunung Kidul. If we draw a line from the Klaten to Bantul districts, the area was actually on top of the fault of Opak which is identified by loose soil conditions. Unfortunately, these conditions produce relatively more fertile soil when compared with Gunung Kidul district which the land consists of layers of limestone rocks (karts). So, it is not wonder if dense settlements located on it. In the event of an earthquake, buildings in this area would be easier to get a bigger influence. That is why in Klaten and Bantul regions have high number collapsed buildings more compared to other regions.

3. The Javanese houses are not in accordance with natural conditions anymore
Javanese houses are always changing in accordance with the time. Unfortunately the change is more influenced by external factors such as changing in life outlook and economic conditions. Traditionally, the Javanese houses are wooden houses (gebyok) which consists of several types such as Joglo, Limasan, or Kampung. Along to successive age, changes in materials such as replacing wooden wall by brick wall, replacing wooden columns by reinforced concrete and so on. These changes will directly affect the performance of the home from natural phenomena such as earthquakes.

4. The earthquake was long time not happened before 2006.
If an earthquake occurs periodically, according to the theory of geology would not produce a big earthquake. Unfortunately prior to 2006, it almost never happened since 1943. Time span of 60 years was enough to gather enough potential energy to produce a large earthquake.

From the human side, which has long been an earthquake does not occur has lowered the level of their awareness of their occupancy in save buildings. Not only for economic reasons alone, the application of construction also because of lack awareness of the people to potential threat of earthquake hazards.

So, for that reasons Javanese houses were easily down by the earthquake in 2006. Any other views?

Earthquake, Traditional Javanese House, and Newton Law

Even though Java Island is located in near Sunda Trench, the meeting continental boundaries of Australian and Eurasian plates, earthquakes were very rarely before the year of 2006. Several quakes may happen in the ancient time without a significant number of casualties. It can be understood that the population density was lower and most of buildings were constructed from wood. This assumption is based on the fact that big fatalities in 2006 Java earthquake was caused by collapsed houses which are constructed by weak masonry.

Earthquake history in Java Island:
1867 : 372 houses collapsed, 5 fatalities
1943 : 2.800 houses collapsed, 213 fatalities, 2.096 injured
1981 : no casualties 2006 May 27 Central Java: 5.9 (BMG) 6.2 (USGS) 6.234 fatalities, > 50.000 injured, >70.000 houses collapsed
2006 Jul 17 West-Central Java: 7.7 (USGS) 500 fatalities, 9299 injured, 68 houses damaged
2009 Sept 2 West Java: 7.4 (BMG) 7.0 (USGS) 57 fatalities and 300 injured , >10.000 houses damaged
2009 Nov 13 Central Java: 5.4 (USGS) No casualties

When we look back to ancient traditional Javanese houses, wooden based structures are mostly used for houses where stone and brick construction were for temples. Lateral forces from earthquake were easily dissipated by light wooden building since wooden post and beam has flexible adaptability to deal with the forces while heavy (masses) building will be affected more. The simplest form of the equation which expresses the Second Law of Motion is:

F = MA

Beside masses, acceleration has this important influence on damage, because, as an object in movement, the building obeys Newton' Second Law of Dynamics.

This states the Force acting on the building is equal to the Mass of the building times the Acceleration. So, as the acceleration of the ground, and in turn, of the building, increase, so does the force which affects the building, since the mass of the building doesn't change.

The greater the force affecting a building, the more damage it will suffer; decreasing F is an important goal of earthquake resistant design. When designing a new building, for example, it is desirable to make it as light as possible, which means, of course, that M, and in turn, F will be lessened. Various techniques are now also available for reducing A.