• International Journal of Technology (IJTech)
  • Vol 13, No 1 (2022)

Site Coefficient and Design Spectral Acceleration Evaluation of New Indonesian 2019 Website Response Spectra

Site Coefficient and Design Spectral Acceleration Evaluation of New Indonesian 2019 Website Response Spectra

Title: Site Coefficient and Design Spectral Acceleration Evaluation of New Indonesian 2019 Website Response Spectra
Windu Partono, Masyhur Irsyam, Ramli Nazir, Muhammad Asrurifak, Undayani Cita Sari

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Cite this article as:
Partono, W., Irsyam, M., Nazir, R., Asrurifak, M., Sari, U.C., 2022. Site Coefficient and Design Spectral Acceleration Evaluation of New Indonesian 2019 Website Response Spectra. International Journal of Technology. Volume 13(1), pp. 115-124

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Windu Partono Civil Engineering Department, Engineering Faculty, Diponegoro University, Semarang 50275, Indonesia
Masyhur Irsyam Civil Engineering Department, Faculty of Civil and Environmental Engineering, Bandung Institute of Technology, Bandung 40132, Indonesia
Ramli Nazir Centre for Tropical Geoengineering, School of Civil Engineering, Faculty of Engineering, Universiti Teknologi Malaysia, 81300 Skudai, Johor, Malaysia
Muhammad Asrurifak Faculty of Civil Engineering and Planning, Institut Sains dan Teknologi Nasional, Jakarta 12630, Indonesia
Undayani Cita Sari Civil Engineering Department, Engineering Faculty, Diponegoro University, Semarang 50275, Indonesia
Email to Corresponding Author

Abstract
Site Coefficient and Design Spectral Acceleration Evaluation of New Indonesian 2019 Website Response Spectra

Calculation of site coefficient and design response spectral acceleration are two important steps in the seismic design of buildings. According to Indonesian Seismic Code 2019, two information requirements for site coefficient calculations are the site soil class and Risk-targeted Maximum Considered Earthquake (MCER-SS for short and MCER-S1 for long period) spectral acceleration. Three different hard/SC, medium/SD and soft/SE are typically site soil classes used for building designs. Two different site coefficients (Fa for MCER-SS and Fv for MCER-S1 spectral acceleration) are used for surface and design response spectral acceleration calculations. The Indonesian Seismic Code provides two (Fa and Fv) tables for calculating site coefficients. If the MCER-SS or MCER-S1 values developed for a specific site are not exactly equal to the values in Fa or Fv tables, the site coefficients can then be predicted using straight-line interpolation between the two closest Fa or Fv values within the tables. When the straight-line interpolation is adjusted for Fa or Fv calculation, different results were observed in comparison to the values developed using website-based software (prepared by Ministry of Public Works and Human Settlements). This study evaluates site coefficients and design response spectral acceleration predictions in Semarang City, Indonesia, according to straight-line interpolation method and website software  calculations. The study was conducted at 203 soil boring positions in the study area. The site soil classes were predicted using average standard penetration test values (N-SPT) of the topmost 30 m soil deposit layer (N30). Three different site soil classes were observed in the study area. On average, the largest differences between the two analysis (linear interpolation and website) methods in the site coefficient values and design response spectral acceleration calculation were observed for the SD and SE classes. However, for the SC site soil class, the difference was small, with their values approximately similar.

Design response spectral acceleration; MCER; N-SPT; Site coefficient; Straight-line interpolation

Introduction

    The new National Seismic Code of Indonesia (SNI 1726:2019, 2019) was announced in 2019. Some of the information introduced in this new seismic code was partially adopted from the American Standard Code for Seismic Design ASCE/SEI 7-16, specifically the site coefficient values and design response spectral acceleration calculation methods. Additional information for developing the site coefficients was adopted from Stewart and Seyhan (2013). Due to the improved methods described in ASCE/SEI 7-16 for developing site coefficients for site soil classes SD and SE, not all the information described in the American Code was adopted by SNI 1726:2019. Specifically, the site coefficients for the SD and SE classes presented in SNI 1726:2019 were completely adopted from Stewart and Seyhan (2013).

Following the SNI 1726:2019, the Ministry of Public Works and Human Settlements announced a new website software (online facility) for site coefficient and design response spectral acceleration calculation. Site or building position coordinates (in terms of longitude and latitude) and site soil class are two information requirements for design response spectral acceleration calculations. Risk-targeted Maximum Considered Earthquake (MCER) acceleration, MCER-SS for short and MCER-S1 for long periods, (Luco et al., 2007; Allen et al., 2015; Sengara et al., 2020), and two design response spectral acceleration, SDS and SD1, are four important values calculated by the website facility software. However, no information related to site coefficients Fa for short and Fv for long periods can be obtained from the new website. Thus, these values can be calculated using Equation 1 and Equation 2. All SDS, SS (MCER-SS), SD1, and S1 (MCER-S1) values can be obtained from the website.

                                                                                                                                                        (1)

                                                                                                                                                         (2)

To verify the Fa and Fv site coefficients estimated using Equations 1 and 2, straight-line interpolation can be conducted using the SS and S1 website calculations and applying site coefficient (Fa and Fv) table data provided by SNI 1726:2019. Fa and Fv are then estimated following the procedure described by SNI 1726:2019. Equation 3 shows a simple formula for Fa and Fv site coefficients calculation. Figure 1 shows a diagram of the straight-line interpolation of the Fa and Fv calculation. F and Mw represent the site coefficient to be estimated and the MCER value obtained from the website, respectively; M1S and M2S represent two boundary MCER values close to Mw; F1S and F2S represent the site coefficients for M1S and M2S, respectively; and M1S, M2S, F1S, and F2S are the four values obtained from the SNI 1726:2019 tables. Fa and Fv are estimated separately using Equation 3.

                                                                                                              (3)

This paper describes the site coefficients and design response spectral acceleration verification calculated using the website facility and the straight-line interpolation described in SNI 1726:2019. The objective of the study was to evaluate whether or not the website performed the analysis following the same procedures used by SNI 1726:2019. The study was performed in Semarang City, Indonesia, and conducted at 203 soil boring investigation positions. The study was performed as part of seismic microzonation research of the city. One of the important information requirements for seismic microzonation is the development of soil amplification or site coefficient distribution map at the study area. In this study, the standard penetration test (N-SPT) data observed during boring investigation were used for site class calculation.  All boring investigations in this study were conducted at a minimum depth of 30 m and a maximum depth 60 m. The average standard penetration test (N-SPT) of the topmost 30 m soil deposit layer (N30) of every boring position was used for site soil class interpretation (Moghaddam, 2011; Partono et al., 2019; Syaifuddin et al., 2020). Figure 2a shows the 203 boring positions and the N30 distribution within the study area. Figure 2b shows the distribution of the site soil classes developed based on the N30 data (Partono et al., 2021). The maximum N-SPT data obtained from the boring investigation was 60. Following the procedure described by SNI 1726:2019, the N30 value was estimated using Equation 4, where di and Ni represent the thickness and N-SPT value of any soil layer “i", respectively.

The parameter that can also be used for site interpretation is the average shear wave velocity (VS) of the topmost 30 m soil deposit (VS30) (Naji et al., 2020). The VS30 value can be calculated using the same method as that shown in Equation 4 and replacing the Ni value with VSi. The VS value can be observed using seismic refraction multichannel analysis of surface waves (MASW) or seismometer array investigations. Prakoso et al. (2017) described a comparative study of VS value obtained from MASW investigation and soil boring (N-SPT) data. The VS value developed using MASW was more reliable compared to that developed based on the N-SPT data. Pramono et al. (2020) described the predominant frequency investigation at Lombok Island following the 2018 earthquake event. The greater the VS30 value used, the greater the predominant frequency obtained from the wavelet analysis of the ground motion. Additionally, development of VS30 and predominant frequency correlation was also conducted by Pramono et al. (2017) in the Palu area.

 

                                                                         

 

Figure 1 Straight-line interpolation for Fa and Fv calculations

 

                                                                                                                                      (4)

Conclusion

Evaluations of site coefficients estimated using the website and straight-line interpolation methods were performed for 203 boring positions in Semarang City. No significant differences were found in the Fa and Fv site coefficients between the two methods. The largest difference in the Fa site coefficient calculations was observed for the SD and SE site classes. The difference in site coefficients for the SD and SE site soil classes was less than 0.03, while, for the SC site soil class, the difference was less than 0.01. In terms of site coefficient Fv, the largest difference was observed for the SD and SE site soil classes with a maximum of 0.04. However, the difference in site coefficient Fv for site class SC was less than 0.02. When calculating Fa and Fv site coefficients, the linear interpolation method from SNI 1726:2019 is better compared to the calculated using MCER-SS, MCER-S1, SDS, and SD1 values obtained from the website.

No significant differences in the design response spectral acceleration SDS and SD1 values were found for any of the site classes. The largest design response spectral acceleration difference in SD between the two methods was less than 0.02 g, while, for the SC and SE site classes, the differences were less than 0.005 g.

Acknowledgement

    This study was funded by the Directorate Research and Community Service, Deputy of Research Empowerment and Development, Ministry of Research and Technology/National Research Council and Innovation, through its 2021 research grant (Contract Number: 187-12/UN7.6.1/PP/2021). The authors also appreciate the Centre for Housing and Settlement Research and Development for supporting data and information collection during the development of this study.

Supplementary Material
FilenameDescription
R2-CVE-4132-20210820110617.pdf Supplementary File
References

Allen, T.I., Luco, N., Halchuck, S., 2015. Exploring Risk-Targeted Ground Motions for the National Building Code of Canada. In: The 11th Canadian Conference on Earthquake Engineering, Canadian Association of Earthquake Engineering, Canada, July 21–24

ASCE/SEI 7-16., 2017. Minimum Design Loads and Associated Criteria for Buildings and Other Structures. American Society of Civil Engineers (ASCE)

Luco, N., Ellingwood, B.R., Hamburger, R.O., Hooper, J.D., Kimball, J.K., Kircher, C.A.,
2007. Risk-Targeted Versus Current Seismic Design Maps for the Conterminous United States. In: Structural Engineers Association of California 2007 Convention Proceedings, pp. 163175

Moghaddam, A.N., 2011. Significance of Accurate Seismic Site Class Determination in Structural Design. In: 2011 Pan-Am CGS Geotechnical Conference, Ontario, Canada, October, pp. 2–6

Naji, D.M., Akin, M.K., Kabalar, A.F., 2020. A Comparative Study on the VS30 and N30 Based Seismic Site Classification in Kahramanmaras Turkey. Advances in Civil Engineering, Volume 2020, pp. 1–15

Partono, W., Asrurifak, M., Tonnizam, E., Kistiani, F., Sari, U.C., Putra, K.C.A., 2021. Site Soil Classification Interpretation based on Standard Penetration Test and Shear Wave Velocity Data. Journal of Engineering and Technological Sciences, Volume 53(2), pp. 272–284

Partono, W., Irsyam, M., Sengara, I.W., Asrurifak, M., 2019. Seismic Microzonation of Semarang, Indonesia, based on Probabilistic and Deterministic Combination Analysis. International Journal of Geomate, Volume 16(57), pp. 176182

Prakoso, W.A., Rahayu, A., Sadisun, I.A., Muntohar, A.S., Muzli, M., Rudyanto, A., 2017. Comparing Shear-Wave Velocity Determined by MASW with Borehole Measurement at Merapi Sediment in Yogyakarta. International Journal of Technology, Volume 8(6), pp. 9931000

Pramono, S., Prakoso, W.A., Cummins, P., Rahayu, A., Rudyanto, A., Syukur, F., Sofian., 2017. Investigation of Subsurface Characteristics by using a VS30 Parameter and a Combination of the HVSR and SPAC Method for Microtremors Arrays.  International Journal of Technology, Volume 8(6), pp. 983992

Pramono, S., Prakoso, W.A., Rohadi, S., Karnawati, D., Permana, D., Prayitno, B.S., Rudyanto, A., Sadly, M., Sakti, A.P., Octantyo, A.Y., 2020. Investigation of Ground Motion and Local Site Characteristics of the 2018 Lombok Earthquake Sequence. International Journal of Technology, Volume 11(4), pp. 743753

Sengara, I.W., Irsyam, M., Sidi, I.D., Mulia, A., Asrurifak, M., Hutabarat, D., Partono, W., 2020. New 2019 Risk-Targeted Ground Motions for Spectral Design Criteria in Indonesian Seismic Building Code. In: 4th International Conference on Earthquake Engineering & Disaster Mitigation (ICEEDM 2019), Padang, September, pp. 26­–27

SNI 1726:2019., 2019. Seismic Resistance Design Codes for Building and Other Structures. National Standardization Agency of Indonesia

Stewart, J.A., Seyhan, E., 2013. Semi-Empirical Nonlinear Site Amplification and Its Application in NEHRP Site Factors, PEER Report 2013/13, November

Syaifuddin, F., Widodo, A., Warnana, D.D., 2020. Surabaya Earthquake Hazard Soil Assessment. In: E3S Web of Conferences 156, 02001 4th ICEEDM 2019 Conference, Padang, Sept. 26–27