LIVING WITH EARTHQUAKE RISK (Overview of Structural Aspects of Earthquake Impact Buildings)

Dr. Ir. Ayuddin, IPU., ASEAN Eng., ACPE., APEC Eng.

(Earthquake Resistant Building Structure Analyst)

With this paper, the author does not intend to dispute anyone or any institution in the Majene earthquake in West Sulawesi on Friday, January 15, 2021 at 02.28 Wita in the early morning with a magnitude of 6.2 centered six kilometers northeast of Majene Regency 2.98 LS-118.94 BT at a depth of 10 kilometers (BMKG). This earthquake had a very sharp damage effect by damaging and even knocking down several buildings with floors. Among the buildings that collapsed were the West Sulawesi Governor’s Office, Maleo Hotel, Mitra Manakarra Hospital, Department Offices, and a number of residential houses.

Because the mechanism of a tectonic earthquake is very complex and contains an infinite number of non-linear parameters, the prediction of when (day, hour) and where a particular earthquake will occur has yet to be formulated. Earthquakes are determined based on the probability framework and return period. Thus, to mitigate the loss of life due to earthquakes, the author suggests that before constructing a structure (buildings, bridges, houses, retaining walls, docks, etc.), the concept of earthquake risk should be adopted, as well as only a minimal level of structural strengthening aimed at preventing the occurrence of casualties (life safety). This paper aims to share that a building will always be preceded by the design and analysis of its structure.

Building Structure Models; Design of Earthquake-resistant Building Models The design of earthquake-resistant building models is geared toward choosing simple and symmetrical models. These symmetrical models are stronger in resisting earthquake forces than unsymmetrical models. Unsymmetrical building models have more lateral force displacement due to earthquakes than symmetrical buildings because unsymmetrical buildings are irregular and prone to higher torsion. So, choosing a simple and symmetrical model has lower earthquake risk and can keep the force evenly distributed through the structure. Therefore, it is desirable to avoid unsymmetrical models in construction. Structural damage due to earthquakes generally begins at the location of the building’s structural weak plane, which triggers severe damage that eventually leads to the collapse of the building structure. Furthermore, the positioning of the pillars as support (building columns) must be balanced, accompanied by a unified roof model with strong connections, as well as a foundation with sufficient depth and strong dimensions in accordance with the results of the soil investigation. Not only referring to the structural model, but the selection of concrete mix materials and the size of iron used (for reinforced concrete buildings) must meet the SNI requirements that have been established by Indonesian structural experts. The use of reinforcing steel in the foundation, sloof, column (column connection) and even the begel must be the right size according to the structural calculation.

Structural Analysis Methods; It would be wise to always learn from every earthquake that affects a collapsed building, both domestic and foreign events. The method in analyzing the structure of a building, especially a multi-story building, is decisive in producing structural element detailing. Care in choosing a structural analysis method is very important and can even be fatal if you choose the wrong method. The method that has been used by structural analysts is the strength-based method (in reference to SKBI 87, SKSNI-91, and SNI-2002). This method was popular for several years and even became a powerful weapon of science in analyzing a building structure. However, after the occurrence of several earthquakes that collapsed buildings such as those that had occurred on the west coast of Sumatra, the south coast of Java, Bali, North Sulawesi, Central Sulawesi, Maluku, Irian, Flores and very powerful earthquakes that had occurred abroad such as the 1989 Loma Prieta, 1994 Northridge and 1995 Kobe earthquakes in Japan. These earthquakes have become a source of reflection for structural experts in the world because it seems as if the results of calculations in an applied method are in vain because buildings collapse suddenly and take a very large toll on human life when hit by a strong earthquake. The analysis that was applied was a force-based analysis. Therefore, the author advises against the application of force-based building structure calculations because they have proven to be unsatisfactory and no longer relevant for the current conditions in which many earthquakes occur in earthquake-prone locations because this method is considered unable to achieve the specified level of performance, thus it can be concluded that this classical method is unable to mitigate the effects of earthquakes (collapse of buildings, roads, bridges, casualties, etc.). A very relevant analysis method applied in Indonesia for buildings above 1 floor and areas with high earthquake levels such as the west coast of Sumatra, the south coast of Java, Bali, North Sulawesi, Central Sulawesi, West Sulawesi, Maluku, Irian, Flores is the performance-based method. The performance-based method aims to produce structures that have predictable results in the event of an earthquake. The defining parameter is its performance objective. A building can be designed based on one or more performance objectives e.g. a residential building can be designed for two performance objectives i.e. full occupancy, no damage, continuous service in low and high intensity earthquakes. A further performance objective is to achieve collapse prevention in low and high intensity earthquakes. So, damage to the construction is allowed to occur, but it does not endanger the lives of the occupants and repairs can be made to the construction.

Traditional Bamboo and Wood Buildings; Bamboo and wood buildings can be an alternative solution in areas with high earthquake intensity including West Sulawesi. Bamboo is the fastest growing, readily available and environmentally friendly renewable natural building material and even its mature bark provides strong reinforcement to withstand vertical and horizontal structural loads. Structurally, bamboo material is easy to bend, gives the desired shape and can provide connections to fit the construction. Its exceptional elasticity makes it a building that can withstand the shock of an earthquake. When an earthquake occurs, bamboo and timber constructions experience very little swaying movement compared to reinforced concrete materials or fully reinforced steel constructions because less mass is generated to stress the structure. The properties of bamboo and wood as building materials have been known for centuries. Popular for its lightness, strength, affordability and sustainability, it can provide a solution for construction needs in earthquake-prone areas or locations. However, in utilizing these bamboo and wood materials, it is necessary to design an appropriate, simple construction model and pay attention to the foundation model, connection patterns on columns, beams and roofs. The earthquake-resistant behavior of a structure is also highly dependent on the ability of its connection to withstand lateral earthquake loads. Therefore, the connections in the use of bamboo and timber construction materials play a key role in creating earthquake-resistant construction. So, there is nothing wrong if we switch to making residential houses or simple buildings in places prone to earthquakes in an effort to save lives if an earthquake occurs at any time. These construction structures can perform well in resisting intense ground movements.