|Lindung Zalbuin Mase||Department of Civil Engineering, Faculty of Engineering, University of Bengkulu, WR. Supratman Rd, Kandang Limun, Muara Bangkahulu, Bengkulu 38371, Indonesia|
This paper presents a reliability study of spectral acceleration designs against earthquakes in Bengkulu City. Seismic Hazard Analysis of 1,968 events is performed to define the controlling earthquake event. Furthermore, the controlling earthquake is used as the scale factor to generate five input motions for one-dimensional seismic response analysis. The spectral accelerations resulting from the analysis are then compared to the updated spectral acceleration design. The results show that spectral acceleration designs are still able to cover the spectral acceleration of seismic response analysis. However, for the short period, the spectral acceleration of seismic response analysis exceeds the designed spectral acceleration. This is a matter of concern, since most of the building natural period in Bengkulu City is still categorized as short. In general, this study brings awareness to the design aspect considering earthquakes in Bengkulu City in order to reduce the possible impact on structures in the future.
Earthquakes; Seismic hazard analysis; Seismic response analysis; Spectral acceleration
It is known that earthquakes are a natural hazard which could trigger massive damage to a region such as Indonesia (Kanata et al., 2014; Sukanta et al., 2015). In 2000, a 7.90 Mw earthquake occurred in Bengkulu Province, Indonesia. It resulted in destructive damage, including collapsed buildings, fatalities, and injuries. The earthquake also triggered other catastrophic hazards, such as landslides and liquefactions in mountainous and coastal areas in Bengkulu. Seven years later, another big earthquake with a magnitude of 8.6 Mw hit the area (Mase, 2017a). This earthquake also resulted in structural damage and other geotechnical phenomena, such as ground failure and liquefaction. During both events, Bengkulu City suffered more serious impact than other cities and regencies in Bengkulu Province, due to the fact that the released energy of the earthquakes in 2000 and 2007 was very large (Mase, 2017a). Learning from these earthquake events, this earthquake study of Bengkulu Province is focused on Bengkulu City. Large earthquake events have not only happened in Bengkulu Province, but also in many other provinces in Indonesia, such as Nangroe Aceh Darussalam in 2004, North Sumatra in 2005, and West Sumatra in 2009. Those earthquakes also triggered massive structural damage, which revealed that the seismic design code in Indonesia needs to be evaluated. Considering these earthquake events, the Indonesian Government revised the previous seismic design code (SNI 03-1726-2002) to a new one (SNI 03-1726-2012). The updated seismic design code is now becoming the reference for local engineers in Indonesia for construction design (Mase & Somantri, 2016), and should be considered as design practice for buildings all over Indonesia.
In this study, a seismic response analysis due to earthquakes is presented. The study aims to check the reliability of the updated seismic design code (SNI 03-1726-2012) with regard to earthquakes in Bengkulu. The ground motion is propagated from the surface of engineering bedrock through the soil layer. At the ground surface, it is further transferred to the spectral acceleration curves, which are compared to the updated seismic design code. In addition, the amplification factor between the propagated ground motion and the ground motion analyzed at the ground surface is also presented. In general, the study is expected to provide better understanding of seismic ground response analysis in Bengkulu City, as well as to provide suggestions to local engineers in consideration of spectral acceleration design for construction design in Bengkulu City.
The results show that the designed spectral acceleration is still able to cover the spectral acceleration resulting from the wave propagation of the controlling earthquake. However, for Tn < 0.2s, 0.2s< Tn < 0.7s, the designed spectral acceleration for three site classes (soft soil, medium soil and stiff soil) are exceeded by the spectral acceleration of the seismic response analysis. In addition, the great case needs to be taken when designing earthquake loads for the buildings. This study also brings a recommendation to study liquefaction in the investigated sites, since the sandy soils are generally found in the investigated sites. The numerical analysis as performed by Mase et al. (2017a) and the experimental study as performed by Mase (2017b) can be performed in the future.
The author would be grateful for the earthquake data from National Agency for Meteorology, Climatology and Geophysics, or BMKG, which are used in this study.
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