Analysis of Internal Forces and Structural Dimensions on the Variations of Courtroom Placement of DPRK Building

The construction of state buildings is caused by the increased mobility of needs. One of them is the DPRK building that wants the placement of the plenary session room to be on the 2nd or 3rd floor. This study aims to evaluate the internal style and behavior of the structure that arises due to variations in the placement of the plenary session room so as to produce the most optimal choice of courtroom for the most effective structural dimensions. Structural analysis was carried out using the ETABS program by carrying out 4 variations of courtroom placement, namely Varian 1 (the courtroom is located on the 1st floor), Varian 2 (2nd floor), Varian 3 (3rd floor), and Varian 4 (4th floor). Variant 2 (DED) is a reference sourced from the DED from the planning consultant. The seismic load analysis used is the method of Dynamic Analysis of Response Spectrum Variety. Parameters reviewed are internal forces (axial, normal, and moment) and structural behavior (story displacement, displacement between floors, nominal base shear forces, and vertical irregularities). The calculation analysis refers to the latest standards, namely SNI 1726:2019, SNI 1727:2020, and SNI 2847:2019. The results of this study indicate that the greatest internal force values occur in Variant 4. The level displacement and the displacement between floors increase in the variant with the smaller structural element dimensions. The level displacement of the X and Y axes has increased in Variant 3 and Variant 4, and has decreased in Variant 1. The nominal base shear force value has decreased for Variants 1, 3, and 4 against Variant 2 (DED) because it has smaller structural dimensions. . All modeling variants experienced soft stiffness irregularity type 1A, excessive soft stiffness irregularity type 1B, and heavy (mass) irregularity type 2. Variant 1 was chosen as the variant with the best courtroom placement, because it met the requirements for earthquake design.


Introduction
Correlation of development is caused by increasing human needs [1].During the planning process, the project owner of the DPRK building wanted the plenary session room to be on the 2nd or 3rd floor.The difference in placement affects the internal style and the amount of pressure on the structure, thus choosing a good courtroom placement is an important thing to do.The plenary session room has a column that reaches 6 meters high, higher than the column in other office spaces in the building which only reaches 4 meters, resulting an uneven distribution of stiffness in the building vertically and causing its stiffness to be smaller.Stiffness of the structure is one of the causes that determine the response of the structure to earthquake loads.Considering that Indonesia is a country with high tectonic earthquake activity because it is located on 4 main tectonic plates, namely the Eurasian, Indo-Australian, Pacific and Philippine plates.The impact of the disaster due to the earthquake that hit Aceh in 2004 resulted in losses in the form of infrastructure damage that disrupted the economic process in Aceh, so building structural elements that are resistant to lateral loads are needed [2].
The difference in demand in the placement of the plenary session room allows changes in the internal forces that arise, besides that the column height which is almost twice can also make the stiffness of the column smaller, so it is necessary to analyze the difference in the placement of the plenary court room so that structural instability does not occur.

Method
The structural analysis application used is ETABS V.18.The loading carried out refers to SNI 2019 and SNI 2020.The building structure is reinforced concrete with a Special Moment Resistant Frame System (SRPMK).The modeling of the structure is 3D modeling.
The building component is a reinforced concrete frame system.The planned material quality is as follows:  The structure being reviewed uses a space frame system.Loading carried out on each structural model uses SNI 2020 and SNI 2019.In the building model designed based on DED (variant 2), the balcony located in the front area of the building with an area <50% floor area.The loading on the 4 model variations follows the building planning regulations of SNI 1727 [3]:2020, SNI 1726:2019 [4] and SNI 2847:2019 [5].

Earthquake Load
According to SNI 1726:2019, to determine the response spectrum, it is necessary to first determine the values of Ss and S1 which are taken through the MCER map [3].This value can also be determined through the Puskim-Ministry of Public Works application at the Meulaboh location with soft soil types.The next step is to determine the response spectrum in the load case.Like in the picture below.

Analysis of Internal Force and Behavioral Structure
Determination of the structural system is determined based on the level of vulnerability to earthquakes (Seismic Design Category Function) [7], based on SNI 1726:2019 and ACI 318-14 [8], Meulaboh City is classified as a D design concept, including the special moment resisting frame system (SRPMK), like in the picture below.Structural analysis of the maximum loading combination will produce internal forces and support reactions [9].The results of the analysis will then be compared to the internal forces that arise.Internal forces consist of moment, normal (axial) force, and transverse (shear) force [10].The internal force that will be used to design the dimensions of the structure is the internal force with the maximum value.

Structural Element Redesign
In the results of the structural analysis, if unsafe elements are found, the steps to be taken are to redesign the structural elements so that the strength of the building structure exceeds the safe limit in accordance with the provisions of SNI [11].Based on the tables above, there are changes in the dimensions of the beam and column structural elements used.The modeling carried out in this study consisted of 4 variations of the placement of the plenary court room, with reference to Variant 2, namely the placement of the court room on the 2nd floor as a DED model.Varian 1 (the courtroom is located on the 1st floor), Varian 3 (3rd floor), and Varian 4 (4th floor).

Displacement
The table below describes the displacement values on the X-axis and Y-axis which are the outputs of the ETABS analysis.Table 5 shows the change in the mass of the structure from each modeling variant, so that the nominal base shear force decreases with respect to Variant 2 (DED), the decrease that occurs in Variant 1 is 11.04%, Variant 3 is 4.95%, and Variant 4 is 8.51%.The difference in the mass of the structure occurs because of the optimization carried out on Variants 1, 3, and 4. Variants 1, 3, and 4 are planned with smaller structural dimensions.Variant 3 has a larger mass due to the occurrence of over strength (excess pressure) which is marked in red on the beam element so that to overcome this, dimension enlargement is carried out.The picture above explains the value of the deviation between these different floors due to the different placement of the plenary session room.For example, when looking at the deviation on the 2nd floor between Variant 1 and Variant 3, it is certainly different because of the different floor heights so that the resulting displacement is different.However, it can be seen that the 2nd floor in Variant 1 has a larger deviation value of 84.805 mm, while for Variant 2 (DED) it is 31.966mm, Variant 3 is 35.217mm, and Variant 4 is 35.849mm.

Internal Forces
The output results of internal forces for each beam and column element in each variant are as presented in the table below respectively.Determining the Amount of Reinforcement Needs

Determining the Amount of Reinforcement Beams
The following is a recap of the number of beam reinforcement requirements for the elements in each variant, which are presented below.

Suggestion
Based on the conclusions above, the suggestions for future research are: 1. Conduct a time history dynamic analysis method using local earthquake records in order to be able to see the behavior of the structure based on the characteristics of the local earthquake, and to compare the results of the analysis that has been carried out 2. Evaluation and review of the foundation structure due to variations in the placement of the plenary session room with a high column structure, in order to obtain a safe foundation structure

Figure 4 .Figure 5 .
Figure 4. Input Scale Factor Response Spectrum Direction X

Figure 11 .
Figure 11.Graph of X-Axis Interfloor Deviation The picture above shows that the largest value of the deviation between floors in each modeling in the X axis is on the 4th floor of Variant 3 with a maximum deviation value of 73,942 mm.The value of the deviation between these floors is different due to the different placement of the plenary session room.The 2nd floor of Variant 1 has a larger deviation value of 66,237 mm, while for Variant 2 (DED) it is 23,276 mm, Variant 3 is 32,808 mm, and Variant 4 is 33,187 mm.

Figure 12 .
Figure 12.Graph of Y Axis Interfloor Deviation

Table 1 .
Changes in Sloof Dimensions

Table 2 .
Changes in Beam Dimensions

Table 3 .
Changes in Ring Beam Dimensions

Table 4 .
Changes in Column Dimensions

Table 10 .
Results of Calculation of Irregularity 1a X Axis

Table 11 .
Results of Calculation of Irregularity 1a Y Axis

Table 12 .
Calculation Results of Irregularity 1b X Axis

Table 13 .
Calculation Results of Irregularity 1b Y Axis

Table 15 .
Output Forces in Beam Structural Elements

Table 16 .
Force Output in Column Structural Elements

Table 18 .
Amount of Reinforcement Beam