Analysis of Non-Linear Static Procedure Based on Fema 356 to Evaluate Structural Performance in the Alton Apartment Building

ABSTRACT


Introduction
Seeing the development of the city of Semarang, a destination for higher education and tourist attractions, the need for housing or housing is increasing (Lalo, 2023).The city of Upper Semarang, especially the Banyumanik and Tembalang sub-districts, is the center of the crowd as the place where many universities are located.Seeing the increasing population and decreasing land is a challenge to developing vertical housing.The Alton Apartment is located on Jalan Prof. Sudarto no.10 Pedalangan, Banyumanik District.The residence in the apartment has two basement floors, five podium floors, and 25 floors for each of the 3 towers.The total height of the building is 96.7 m from the basement floor (Suwandi, 2019).
With the condition of the building, which is a category of high-rise buildings, it is necessary to review the reliability of the structure from the earthquake side and the elements that hold the earthquake force.The city of Semarang, within a radius of 500 km, has several faults as follows (Masbudi, Purwanto, & Supriyadi, 2015).The first fault, the Pati fault, has a strike-slip mechanism with a value of 6.8 magnitude.The second fault, the Lasem fault, has a strike-slip mechanism with a value of 6.5 magnitude.Another earthquake source is the Java megathrust subduction, which has a reverse mechanism of 8.3 magnitude (Muttaqin & Afifuddin, 2020).The overall data collection is used to find out each potential source that can produce energy for soil movements heading to the city of Semarang.Data collection was recorded by the Meteorology, Climatology, and Geophysics Agency/BMKG, then the international institution National Earthquake Information Center, and the U.S. Geological Survey/NEIC-USGS.Earthquake data was collected from 1900 to 2013 with a minimum of 5 Mw and a maximum magnitude (Mmax) of 8.3 Mw (Partono, Irsyam, & Wardani, 2017).
At the time of planning, Alton Apartments used old regulations, including SNI 1726-2012 for earthquake resistance, SNI 1727-2013 for minimum load design, and SNI 1729-2015 for structural steel buildings.Seeing the high level of operational buildings and the need to adapt to earthquake resistance rules for buildings, damage mitigation is needed through pushover analysis or non-linear static analysis procedures.Pushover Analysis is a method of evaluating the structure contained in a new concept for earthquake engineering based on Performance Seismic Evaluation (PBSE) (Nabhilla & Hayu, 2020).This analysis method includes a specific static load with a lateral direction that is increased gradually until the collapse of the structural element is achieved due to the presence of plastic joints or reaching a specific displacement target (Andrio & Masagala, 2022).
Previous research related to the evaluation of building structure performance using pushover analysis, such as those conducted at RSGM UGM Prof. Soedomo Building, Faculty of Law, Sam Ratulangi University Manado, podium-type multi-story building structures, buildings with soft first stories, Postgraduate Building of the Faculty of Mathematics and Natural Sciences UGM, and the University of Indonesia Teaching Hospital Building, as well as the Graha Wiyata UNTAG Building Surabaya, the research has similar objectives and analysis methods.Namely to evaluate the performance of building structures against earthquake loads using pushover analysis.The results showed that the structure's performance was at a certain level of performance, such as Immediate Occupancy, which indicates the ability of the building to be reused after an earthquake without significant structural damage (Nabhilla & Hayu, 2020).
This study uses FEMA 356 rules with a non-linear static procedure method to assess the performance level of buildings, especially in meeting the drift value and strength ratio (μstrength) requirements.The formulation of the problem includes evaluation of performance point values, compliance with the requirements of the Non-Linear Static Procedure according to FEMA 356 rules, calculation of ductility values from pushover results, checking the boundaries between levels, calculation of P-delta stability, the need to adjust horizontal irregularities, and when the structure can be said to meet the requirements of vertical irregularities.The objectives of the study include understanding the performance level of the structure, verification of Non-Linear Static Procedure requirements, assessment of ductility, checking the difference of deviation at the center of mass, calculation of P-delta stability, adjustment of horizontal irregularities, and verification of vertical irregularities.The limitations of the problem include the building being studied, the type of structure, the source of earthquake data, the evaluation procedure, the earthquake resistance regulations used, and the performance evaluation method of the structure applied.

Method
This study was conducted in Pedalangan, Banyumanik, focusing on the Alton Apartment, which has two basement floors, five podium floors, and 25 floors for three towers, totaling 96.7 m.The research is divided into several stages, from preparation, to data collection and analysis.Data collection consists of secondary data from direct surveys and literature studies.The data includes images, test reports, and maps of earthquake acceleration.The analysis process involves a pushover method using the ETABS V 18.1.1program.The analysis steps include defining the mass source, gravity load, and pushover load.The analysis results are evaluated to determine the performance category of the structure, such as Immediate Occupancy, Life Safety, or Collapse Prevention.The analysis also considers aspects such as ductility, boundaries between levels, P-delta influence, and horizontal and vertical irregularities.All of these steps are important to ensure the structure's performance against earthquakes.

Earthquake Risk Categories and Priority Factors
Alton Semarang Apartment is an apartment function building, so the risk category based on Table 3 of SNI 1726-2019 is II.The Ie earthquake's priority factor is 1.0 according to Table 4 of SNI 1726-2019.

Categories Seismic Design and Seismic Force Bearing System
If a 1000-year reage earthquake map is used by the point of the research location, it is known that the SMS value = 0.792 and SM1 = 0.600.It can be known that the value of the seismic design category is according to Tables 8 and 9 of SNI 1726-2019.As a calculation of short periods, 0.5 ≤ 0.792 SMS are included in type D. For a period of 1 second, 0.20 ≤ 0.600 are included in type D.
The seismic force-bearing system is regulated in Table 12 of SNI 1726-2019, where it is determined based on the results of the selection of seismic design categories and the selection of frames to withstand seismic forces.In the structure of the Alton Apartment building, reinforced concrete walls are chosen as the seismic style carrying frame.Then, it is determined that particular reinforced concrete sliding walls can be allowed.The value of the specified factor is R = 7; Ω = 2,5, and Cd = 5.5.

Structural Modeling
The modeling is based on the results of the as-built drawings, which were issued by the contractor PT.PP (Persero) Tbk with the approval of PT's construction management.Maksi Engineering Solutions.Here is the application of modeling to ETABS and as-built drawings.

Earthquake Response Spectrum Map
The map used is sourced from the results of a study by the National Center for Earthquake Studies on May 1, 2021, to retrofit and seismic evaluation of existing buildings.The types of maps used are 250-year and 1000-year periods.The following is the map used.

Entering Earthquake Data
On the earthquake map, 2 data were obtained: the Short-Period Acceleration Spectrum of 0.2 seconds (Ss) and the Period Acceleration Spectrum of 1.0 seconds (S1).Then, the site coefficients Fa and Fv are looked for; the soil site class also determines this at the project site (Dalo, Handono, & Wallah, 2019).The Alton Semarang Apartment Project is determined by the medium soil site (SD) class.For the sake of the 250-year and 1000-year earthquake recurrence periods, the 2/3 multiplier is not used.The following are the results of the earthquake data input.

Entering the Block Repeating Area
The beam repetition area and effective height (d') need to be entered according to the results of the implementation and installation drawings.These results are needed to consider the moment yields and test a block's level of vitality.The following are the results of the block repetition input.

Enter the Repetition Area
The repetition input is intended to check the size, diameter, number of repetitions, and quality of the repetitions.The following are the results of the input on ETABS.

Entering the Shearwall Repeating Area
The sliding wall's repetition is divided into a special boundary element area and a body area.The following is the sliding wall's repetition on ETABS.

Mass Source Analysis and Gravitational Load Cases
In the non-linear analysis, the live load is calculated at 25% without reducing by ASCE rule 7 but not less than the actual live load.

Pushover Load Case Analysis
The performance target in the Alton Apartment project is determined, namely Life Safety, with a drift of 1% according to the function of the structural concrete wall.To control the magnitude of displacement, the formula 150% x drift performance target x building height is used.This is by FEMA 356 Table C1-3 rules.

Beam Hinge Analysis
The beam hinge was determined based on the distance between the plastic joints, which is 0.05 from the left edge and 0.95 from the right edge.Then, the degree of freedom is determined using the M3 value.The repetition distribution in this study is considered conforming because, in past work practice, reinforcing the beam structure was very concerning.Beam hinge parameters are based on ASCE 41-17 rules with table 10-7.

Column Hinge Analysis
For hinge columns based on ASCE rules 41-17 with tables 10-8 and 10-9.The degree of freedom in the column is determined using P-M2-M3.The repetition of the columns is considered adequate based on the drawings as-built drawings.The axial force P is determined based on the case of gravity and gravity plus lateral load in the form of pushover load in the x and y directions.

Hinge Shearwall Analysis
This is in contrast to columns and beams, which apply sliding walls using hinge properties in the form of fiber.The following are the results of the sliding wall shell hinge assignment on ETABS.

Performance Point Analysis
The following are the results of analyzing the performance level of buildings for pushover in the x and y directions on the 250-year and 1000-year earthquake maps.It is known that the height of the building is 96100 mm, with two basements and 30 floors that function as apartment occupancy (Nugroho, 2015).If you look at Table 2.1 ASCE 41-17 regulations, the risk category is II.On the 250-year earthquake map, the specified performance requirement is life safety (LS) if you look at Table 2.1 ASCE 41-17 with a 1% drift according to Table C1-3 FEMA 356.Meanwhile, in the 1000-year earthquake map, the specified performance requirement is collapse prevention (CP) if you look at Table 1 ASCE 41-17 with a drift of 2% according to Table C1-3 FEMA 356.The results of the breakdown are described in the form of a table.The results above show that the Alton Apartment building still meets the life safety and collapse prevention performance level.

Analisis Syarat 1 Non Linear Static Procedure
The purpose of this check is to determine whether the Non-Linear Static Procedure (NSP) analysis results can be used if the strength ratio (μstrength) is less than μmax.

Analisis Syarat 2 Non Linear Static Procedure
Checking this condition is to compare story forces of the first model structure with capital participating mass ratios of 90% and not more significant than the second model in analysis of one variety only and by taking into account 130% x Vstory forces model 2. The primary purpose of checking one variety for the second modeling is not significant for the higher mode of the first modeling (Kurniati, 2019).

Structural Ductility Calculation
The greatest is the calculation of ductility to see the level of the structure's ability to experience post-elastic deviation when it reaches the condition on the verge of collapse.The ductility value was achieved based on calculating the R-value from the pushover analysis with the formula μstrength, μmax, and RR factor.The result of the ductility value R must be achieved according to the seismic force-bearing system.

Calculation of Inter-Tier Limits
The diaphragm in the Alton Apartment research is divided into two types: diaphragm 1 (D1) and diaphragm 2 (D2).The diaphragm 1 (D1) division includes basement floors 1 to the rooftop floor with podium area, towers 1 and 2. The division of diaphragm 2 (D2) covers the 8th floor to the rooftop floor with a tower area of 3.An example of calculation is taken for the 1st floor with diaphragm 1 (D1).

Horizontal Irregularity Calculation
In this calculation, horizontal irregularities are calculated based on several types, namely torque irregularities, excessive torque irregularities, inner angle irregularities, diaphragm discontinuity irregularities, irregularities due to perpendicular shifts to the plane, and nonparallel system irregularities.

Conclusion
Based on the results of the analysis carried out, it can be concluded that this building can withstand the earthquake force that occurs well.The requirements for Non-Linear static procedure analysis have been met, indicating that the building has adequate strength.In addition, the ductility of buildings against earthquakes has also been fulfilled and safe.All deviation values and calculations of P-delta values show that the building remains stable and safe against the effects of earthquakes.Although horizontal irregularity adjustment is necessary, the building is safe from vertical collapse failure in the event of an earthquake.Suggestions for the next research include the addition of Linear Dynamic Procedure (LDP) analysis, review of displacement points, maintenance of the shape and function of existing spaces, and checks by earthquake maps and the latest building evaluation rules.