“LIVING WITH EARTHQUAKE RISK : An Overview of the Structural Aspects of Buildings Affected by Earthquakes”
Dr. Ir. H. Ayuddin, S.T., M.T., IPU., ASEAN Eng., ACPE., APEC Eng.
(Earthquake-Resistant Building Structure Analyst)
With this paper, the author does not intend to dispute any individual or institution regarding the Majene earthquake in West Sulawesi, which occurred on Friday, January 15, 2021, at 02:28 WITA in the early morning. The earthquake had a magnitude of 6.2, with its epicenter located six kilometers northeast of Majene Regency at coordinates 2.98°S–118.94°E and a depth of 10 kilometers (BMKG). This earthquake caused severe damage, destroying and even collapsing several multi-storey buildings. Among the buildings that collapsed were the West Sulawesi Governor’s Office, Maleo Hotel, Mitra Manakarra Hospital, various government offices, and a number of residential houses.
Because the mechanism of a tectonic earthquake is highly complex and involves an infinite number of non-linear parameters, it is currently impossible to predict the exact time (day or hour) and location of a particular earthquake. Earthquakes are assessed based on probabilistic frameworks and return periods. Therefore, to mitigate loss of life due to earthquakes, the author suggests that, before constructing any structure (such as buildings, bridges, houses, retaining walls, docks, etc.), the concept of earthquake risk should be incorporated, along with a minimal level of structural reinforcement aimed at ensuring life safety. This paper emphasizes that the construction of any building should always be preceded by careful structural design and analysis.
The design of earthquake-resistant building models focuses on selecting simple and symmetrical configurations. Symmetrical models are more effective at resisting earthquake forces than unsymmetrical ones. Unsymmetrical building models experience greater lateral displacement during earthquakes because their irregular shape makes them more prone to torsion. Therefore, choosing a simple and symmetrical model reduces earthquake risk and allows forces to be distributed more evenly throughout the structure. Consequently, it is recommended to avoid unsymmetrical models in construction.
Structural damage due to earthquakes generally begins at the building’s weak structural planes, which can trigger severe damage and eventually lead to structural collapse. Additionally, the placement of pillars (building columns) must be balanced, complemented by a unified roof system with strong connections, and a foundation with sufficient depth and dimensions according to soil investigation results.
Beyond the structural model, the selection of concrete mix and the dimensions of reinforcing steel used in reinforced concrete buildings must comply with the Indonesian National Standard (SNI) as established by structural experts. The use of reinforcing steel in the foundation, sloof, columns (including column connections), and even in stirrups (begel) must conform to the appropriate sizes calculated in the structural design.
It is wise to learn from every earthquake that affects collapsed buildings, both domestically and internationally. The method used to analyze a building’s structure, especially multi-storey buildings, is decisive in producing accurate structural detailing. Careful selection of a structural analysis method is crucial, as using the wrong method can have fatal consequences.
A method historically used by structural analysts is the strength-based method (referencing SKBI 87, SKSNI-91, and SNI-2002). This method was widely applied for many years and became a cornerstone in structural analysis. However, after several earthquakes that caused building collapses—such as those on the west coast of Sumatra, the south coast of Java, Bali, North Sulawesi, Central Sulawesi, Maluku, Irian, Flores, as well as major international earthquakes like the 1989 Loma Prieta, 1994 Northridge, and 1995 Kobe earthquakes, it became clear that the force-based calculations often failed to prevent catastrophic damage. These events demonstrated that, despite careful calculations, buildings could still collapse suddenly, resulting in severe human and material losses.
Force-based analysis is therefore no longer recommended, as it has proven insufficient for modern earthquake-prone conditions. This classical method cannot reliably achieve the desired level of performance, and it fails to mitigate the effects of earthquakes, including building and infrastructure collapse and loss of life.
A more relevant and effective method for buildings above one floor, especially in high seismic zones in Indonesia such as the west coast of Sumatra, south coast of Java, Bali, North and Central Sulawesi, West Sulawesi, Maluku, Irian, and Flores is the performance-based method. The performance-based method aims to produce structures with predictable behavior during earthquakes, defined by specific performance objectives.
A building can be designed according to one or more performance objectives. For example, a residential building may have two performance objectives: full occupancy with no damage, ensuring continuous service during low and high-intensity earthquakes, and collapse prevention in low and high-intensity earthquakes. In this approach, some structural damage is acceptable, but occupant safety is guaranteed, and the building can be repaired after the event.
Bamboo and wood buildings can serve as alternative solutions in areas with high earthquake intensity, including West Sulawesi. Bamboo is one of the fastest-growing, readily available, and environmentally friendly renewable natural building materials. Even its mature bark provides strong reinforcement to withstand both vertical and horizontal structural loads. Structurally, bamboo is flexible, can be shaped as desired, and allows for connections that fit the construction. Its exceptional elasticity enables buildings to withstand the shocks of an earthquake.
During an earthquake, bamboo and timber constructions experience minimal swaying compared to reinforced concrete or fully steel-reinforced buildings, as they generate less mass, reducing stress on the structure. The properties of bamboo and wood as building materials have been recognized for centuries. Their lightness, strength, affordability, and sustainability make them practical solutions for construction in earthquake-prone areas.
However, to utilize bamboo and wood effectively, it is essential to design an appropriate and simple construction model, paying careful attention to the foundation, as well as the connection patterns of columns, beams, and roofs. The earthquake-resistant behavior of a structure heavily depends on the ability of its connections to withstand lateral earthquake loads. Therefore, proper connections in bamboo and timber constructions play a critical role in creating earthquake-resistant buildings.
Thus, using bamboo and wood for residential houses or simple buildings in earthquake-prone areas is a viable approach to save lives, as these structures can perform well in resisting intense ground movements.