Comparison Analysis of Seismic Base Shear 23 Regencies in Aceh Province Based on SNI 03-1726-2012 and SNI 03-1726-2019

Aceh is one of the most earthquake-prone regions in Indonesia. It is, therefore, essential to design seismic resistance structures according to applicable standards. To reduce damage to building structures, the Indonesian government has updated the seismic-resistant design code for building and non-building structures. The seismic resistant design standard has been updated from SNI 03-1726-2012 to SNI 03-1726-2019 due to a significant change in spectrum response data. The purpose of this study was to evaluate and compare the impacts on the seismic base shear and the cross-sectional area of columns, beams, and tie beams of buildings in 23 regencies in Aceh Province based on SNI 03-1726-2012 and SNI 03-1726-2019. A typical five-story office building with medium-type soil is used in the study. For structural analysis, a particular moment-resistant frame was considered. The determination of the design response spectra is carried out by using coordinates and soil types through the website “indo spectra”. The method used is spectrum response analysis. Some different requirements in the two standards include the spectrum response curve, mass participation, and dynamic base shear. The study’s results revealed that the dynamic base shear in Sabang City had grown by 192.05 percent. Aceh Barat Daya Regency was observed to have the smallest increase in dynamic base shear, which was only 8.16 percent. The required cross-sectional area of structural columns, beams, and tie beams in Sabang City increased by 96%, 40%, and 44.44%, respectively; in the meantime, the required cross-sectional area of columns, beams, and tie beams in several regencies in Aceh province remained unchanged.


Introduction
Indonesia is one of the earthquake-prone countries in the world where mild to high intensity earthquakes might occur in its region [1]. The country is surrounded by four tectonic plates, namely the Eurasian Plate, the Indo-Australian Plate, the Philippine Plate, and the Pacific Plate which is frequently struck by more than 10% earthquakes each year [2], [3]. Earthquake shocks can cause great damage to building structures resulting in many casualties [4]. Structural damages are related with the level of seismic intensity, low material quality and so on [5], [6]. To reduce damages in building structures, the Indonesian government has updated the seismic resistant design code for building and non-building structures in SNI 1726-2019 [7] In 2012, the Indonesian government has issued a seismic design code for building and non-building structures in SNI 03-1726-2012 [8]. However, major seismic events over the decades in Indonesia showed that several issues must be updated and developed to reflect the current development technology used in seismic practice and to consider the latest changes in seismic design codes worldwide. Thus, the government of Indonesia has issued SNI 03-1726-2019 in 2019 [9] to replace the SNI 03-1726-2012 seismic design code. The Sumatera region, including Aceh, is typically driven by two major earthquake sources: the megathrust zone beneath the west Sumatera ocean and the Sumatera Great Fault [10]. Seismic activity in the Sumatera region increased drastically after the great Aceh earthquake and tsunami in 2004 [11]. This is due to the fact that big seismic occurrences continually produce tectonic forces in the surrounding region, causing earthquakes at other epicenters in the region. Numerous earthquakes have occurred since the 2004 Aceh earthquake and tsunami, including the Singkarak, and West Sumatera earthquakes (M6.3 and M6.4), the Padang earthquake (M7.6), and the Kerinci earthquake (M6.7), which happened 12 hours after the Padang earthquake [6]. In the Aceh region, an earthquake occurred in the Takengon Lot Tawar lake area in 2013 with a magnitude of M6.4. This earthquake caused fatalities and extensive damage to structures and infrastructure. The 2016 M6.4 earthquake in Pidie Jaya, Indonesia [12], [13]. The earthquakes in Pidie Jaya have occurred in the past few decades such as in 1967 (M6.1) and 1942 (M6.8). Based on the frequency and intensity of recent earthquakes, Aceh is a highly earthquake-prone region. As there are differences between SNI 03-1726-2012 and SNI 03-1726-2019 regarding the type of spectrum response data, a comparative study of the seismic base shear is required for the analysis of buildings in the Aceh region. Using SNI 03-1726-2012 and SNI 03-1726-2019, this study will analyses the seismic base shear and the required cross-sectional area of columns, beams, and ring beams in low-rise building structures in 23 regencies/cities in Aceh Province.

Methods
In conducting this research, it begins with data collection including as built drawing of structures and loading data. A five-story office building with medium-type soil is used in the study. A special moment resistant frame is also considered for structural analysis.

Determination of Response Spectra
The location and coordinates of the 23 regencies/cities in Aceh will be utilized in SNI 03-1726-2012 and SNI 03-1726-2019 to calculate the design response spectra. The determination of the design response spectra in SNI 03-1726-2012 is carried out by using coordinates and soil types through the website "indo spectra" [14]. Similarly, using the indo spectra programs that are also available on the website, one can obtain response spectra of SNI 03-1726-2019 [15].

Preliminary Design
According to SNI 2847-2019 article 18.7.2 [16], the smallest cross section's dimensions cannot be smaller than 300 mm, and the smallest dimensions cannot be smaller than 0.4 of the perpendicular dimensions. Meanwhile, Table 9

Structural Modeling
Modeling of building structures is carried out using ETABS 18.1.1 [17]. The following shows floor plans of office building and the 3dimensional view of the building model in Figure 1.

. Loading Input
The types of loads used in this study are dead loads, additional dead loads, and live loads. Based on SNI 1727-2020 [18], the dead load is the weight of all installed building construction materials, including walls, floors, roofs, ceilings, stairs, fixed partition walls, finishing, building cladding, and other architectural and structural components as well as other installed service equipment including tap weight. Additional dead loads used in this study are: a. Additional dead load on beams and tie beams

. Modal Analysis (Modal Participation Mass Ratio)
A significant number of variations must be included in the analysis of the spectrum responses based on SNI 03-1726-2012 in order to obtain mass participation of at least 90% of the total mass. According to SNI 03-1726-2019, the spectrum analysis must take into account a sufficient number of variations to obtain the combined variety mass of 100% of the structure's mass.

. Natural Period
The length of time it takes to reach one vibration is known as the vibrating period. Knowing the structure's natural vibration period will help prevent resonance in the structure [19]. Structural resonance is a state where the natural frequency in the structure is close to the imposed frequency caused by external load so that it can cause a collapse in the structure [20]. Based on SNI 03-1726-2012 and SNI 03-1726-2019 article 7.8.2, there are two limit values for the building period, namely the minimum value of the building period (Ta min ) and the maximum value of the building period ( Ta max ).

. Seismic Base Shear
The seismic base shear is the total of all lateral forces due to the earthquake subjected to the building and so the total of the lateral force subjected to each floor [21]. (1) The value of Cs must be determined by the following equation: The value of Cs calculated above must not exceed the following: The value of Cs must be not less than: Structures located in S1 that are equal to or greater than 0.6g, then Cs should be not less than: Where, Cs = Seismic response coefficient W = Total weight of the building SDS = Short-period design response spectra acceleration parameter R = Seismic reduction factor Ie = Important factor SD1 = response spectra acceleration design parameter at period 1 second T = Fundamental vibrating period of the structure S1 = MCER response spectra acceleration parameter mapped for a period of 1 second

Story Drift
Based on SNI 03-1726-2012 and SNI 03-1726-2019 article 7.8.6, it requires story drift only to determine the performance at the ultimate state. The determination of story drift (∆) should be calculated as the difference in drifts at the center of mass above and below the level of the structure. The deflection of the center of mass at the level of x (δx) in mm, must be determined by, where: Cd = Deflection magnification factor δxe = Deflection at the required location and determined according to the elastic analysis Ie = Important factor

Results and Discussion
The results of the study include the comparison of the seismic shear forces and the required cross-sectional areas of the building structures in 23 Regencies/Cities of Aceh Province using SNI 03-1726-2012 and SNI 03-1726-2019. It has a significant impact on the outcomes of structural analysis, including seismic base shear, mass participation ratio, lateral displacement, and story drift, because there are discrepancies in the response spectra between the two standards.

Response Spectra
Based on data analysis, the maximum design acceleration response spectra value (Sa) at the time of occurrence of an earthquake (T) for each Regency/City with a time interval of T = 0 second to T = 4 seconds in both SNI are obtained. The difference in the average Sa maximum value between two standards in all districts/cities are shown in Table 4.

Seismic Base Shear
Based on SNI 03-1726-2012, the seismic base shear force value cannot be less than 85% of static seismic base shear. It cannot be less than 100% static seismic base shear based on SNI 03-1726-2019. The scale factor is used to increase the calculated seismic base shear if it has not met the second condition. For each regency/city, Table 5 shows dynamic base shear in directions x and y for SNI 03-1726-2012 and SNI 03-1726-2019. According to Table 5, the seismic base shear values of direction x and direction y for all districts/cities for SNI 03-1726-2019 are greater than those for SNI 03-1726-2012. This is due to three factors: firstly, an increase in the dynamic seismic shear force of SNI 03-1726-2019 by 25% of the static seismic base shear compared to SNI 03-1726-2012; secondly, an increase in the response spectra value of SNI 03-1726-2019 resulting in a higher load on the structure; and thirdly, the division of the dimensional groups of structural elements based on the response spectra values resulting in the seismic base shear values are different. As shown in Figure 2, the higher increase in the value of seismic shear force is in Sabang (192.05 %). This result is consistent with the increase response spectra value of SNI 03-1726-2019 compared to SNI 03-1726-2012, as well as the difference in the dimensions of the structural elements used in Sabang City based on SNI 03-1726-2012 (e.g., column dimensions of 50x50 cm) and SNI 03-1726-2019 (e.g., column dimensions of 70x70 cm), so that the value of the seismic base shear obtained is significantly different. The smallest increase in the value of seismic base shear was found in Southwest Aceh Regency (8.16 %).

Cross-Sectional Area of Structural Elements
The required cross-sectional area of the structural elements observed is in columns, beams, and tie beams. The difference in the percentage of the required cross-sectional area of structural elements in several regencies / cities representing each group of dimensions of structural elements can be seen in Figure 3 to Figure 5. Based on Figure 3, it can be seen that the higher increase in column crosssectional area obtained in Sabang (96%). Meanwhile, there was no increase in the cross-sectional area of the column in several regencies/cities including South Aceh, Aceh Singkil, Simeulue, Banda Aceh, Nagan Raya, West Aceh, Aceh Jaya, Southwest Aceh, North Aceh, Bireuen, Langsa, Aceh Tamiang, and East Aceh. Based on Figure 4, it can be seen that the largest increase in the cross-sectional area of the beam occurred in Sabang Regency/City, which was 40%. Meanwhile, there was no increase in the cross-sectional area of the beams occurring in several regencies/cities, namely South Aceh, Aceh Singkil, Simeulue, Banda Aceh, Nagan Raya, West Aceh, Aceh Jaya, Southwest Aceh, North Aceh, Bireuen, Langsa, Aceh Tamiang and East Aceh. Figure 5 demonstrates that the highest growth in tie beams cross-sectional area was found in the Sabang (44.44%). Several regencies/cities, including South Aceh, Aceh Singkil, Simeulue, Banda Aceh, Nagan Raya, West Aceh, Aceh Jaya, Southwest Aceh, North Aceh, Bireuen, Langsa, Aceh Tamiang, and East Aceh, exhibited no growth in the required cross-sectional area of the beams.

Conclusion
The dynamic seismic base shear based on SNI 03-1726-2019 compared to SNI 03-1726-2012 increased by 192.05 % in Sabang. The region with the smallest seismic base shear was found in Southwest Aceh (8.16 %). In Sabang, the higher increases in the required crosssectional area of the column elements, beams, and tie beams were 96%, 40%, and 44.44%, respectively. In several regencies/cities, including South Aceh, Aceh Singkil, Simeulue, Banda Aceh, Nagan Raya, West Aceh, Aceh Jaya, Southwest Aceh, North Aceh, Bireuen, Langsa, Aceh Tamaiang, and East Aceh, there was no significant increase in the required cross-sectional area of columns, beams, and tie beams.