The effect of retrofitting high-rise buildings with steel plate shear walls

. The construction of high-rise buildings carries the potential for collapse due to lateral loads, such as wind and earthquake forces. Therefore, the use of lateral force retaining systems need to consider in designing high-rise building. This research provides an overview of how the performance of a high-rise building with stiffened steel plate shear walls (SPSW) as a lateral force retaining systems. The study evaluates the impact of SPSW on a story drift and cross-section capacity of beams and columns high-rise building. The results indicate that SPSW systems enhances the seismic performance of high-rise building. Specifically, the use of SPSW with the thickness 18.7 mm has the most significant effect on the story drift and cross-section capability of columns. Using thicker steel plate shear walls can effectively decrease the story drift experienced in high-rise buildings. Based on the results, the story drift value is reduced by 3-6 mm with a structural system with SPSW. On the other hand, the cross-section capability of the column element is also improved. However, the increasing thickness of SPSW does not have a significant impact on the cross-section of the beam element.


Introduction
High-rise buildings are vulnerable to collapse from lateral loads, including wind and earthquake forces.The risk of collapse increases with the height of the building, and earthquake loads typically dominate these lateral loads.During an earthquake, the ground surface moves horizontally, causing the building to move and resulting in a shear force at the base of the building (ground floor) known as the base shear.This force can be significant and has the potential to cause the building to collapse, highlighting the importance of implementing lateral force retaining systems to improve the building's resistance to these forces.
Over the years, researchers have developed various systems to mitigate the effects of lateral loads on tall buildings.One solution commonly used by planners is the lateral force resistance system, which involves implementing a shear wall structure system [1 -3] .The use of a lateral force resistance system is now mandatory for the construction of tall buildings and has been incorporated into the Indonesian National Standard for earthquake-resistant building and non-building structure planning procedures.This emphasizes the importance of considering lateral force resistance systems during the planning and construction of tall buildings to improve their ability to withstand lateral loads and reduce the risk of collapse.
In recent years, a new type of shear wall system using steel material has been developed, known as a steel plate shear wall (SPSW).SPSW has been utilized in several constructions in countries such as America, Japan, and Canada, leading to the emergence of various theories and experiments on the SPSW system.It is believed that using a steel plate shear wall offers several advantages, including stable hysterical characteristics, high plastic energy absorption capacity, and improved stiffness, strength, and ductility [4][5][6][7][8].These advantages make SPSW a desirable option for improving the resistance of tall buildings to lateral loads, as it can enhance their ability to absorb and withstand these forces [9][10].

Research Methodology
To process the data, it is necessary to ensure that the theory used as a research reference is complete.Once the theory is sufficient, the collected data can be used as material for the research.For this study, data analysis was performed by modelling using the ETABS software.Structural modelling high-rise building was conducted without an SPSW system and additonal SPSW system.Once the analysis process was complete, the research required a conclusion.This conclusion would discuss the effect of SPSW system on the performance of high-rise building.Additionally, some suggestions may be provided to provide additional information related to the research conclusions that have been determined.The research flow chart is shown in Figure 1.

Results and Discussion
The objective of this study is to evaluate the effectiveness of steel plate shear walls as lateral force retaining systems in high-rise building.The study will consider two types of steel plate shear walls: ordinary ones with relatively thin thickness, and those with additional stiffness achieved by increasing the thickness of the steel plate.The primary data used in this research was obtained from working drawings of the project under review.Secondary data used were the standards used in the structural analysis process.Additional data was gathered by conducting a literature search to gather previous journals to be used as references.

Structural Modelling
The modelling and analysis of building structures were conducted using the ETABS software, which includes the modelling of structural elements such as plates, beams, columns, and shear walls.The structural reinforcement elements were also incorporated into the modelling process.For further information on the modelling procedure, please refer to the accompanying Figure 2.

Loading
In this study, the value of self weight, additional dead load and live load was carried out in accordance with SNI 1727 2020.For the lateral forces such as earthquake load was calculated based on SNI 1726 2019.The building structure consists of several elements that support it, such as plates, beams, columns, and SPSW system as lateral force retaining systems.

Dead Load
The elements that support a building structure, such as beams, columns, plates, and other structural elements, all contribute to the dead load of the building.Dead loads are permanent load, and are typically made of materials such as concrete and steel, which act in a vertical direction.In addition to these dead loads, there may also be superimposed dead loads (SiDL), such as brick walls, electrical equipment, and other similar elements as shown in Table 1.

Live Load
Living loads refer to temporary or transient forces that act on buildings or structural elements.These loads are caused by people, furniture, vehicles, and other movable objects within the building.Each structural element, including floors, columns, beams, and roofs, can be assessed to determine the live load, which is considered in calculating the gravity load (Table 2).The unit of measurement used for live load is typically square meters (m 2 ).The living load for hospital buildings is determined in accordance with SNI 03-1727-2020.

Earthquake Load
Based on the procedures and provisions stated in SNI 1726-2019, a spectrum response can be generated from several fundamental earthquake parameters, which include: building = hospital risk category = iv earthquake importance factor (ie) = 1.5 ss = 1.085g (short period earthquake acceleration); s1 = 0.393g (long period earthquake acceleration); site class = se (soft soil).By using the basic earthquake parameters mentioned earlier, it is possible to obtain advanced earthquake parameter data, which in turn will generate the design spectral response parameter value (Sa) for a specific period.The Sa value can be observed in Table 3.Thus, a graph of the response spectrum can be formed.The spectrum response graph can be seen in Figure 3 Fig. 3. Spectrum Response

Existing Building Analysis
The lateral load that the reviewed building will receive has already been determined to be the earthquake load.This load will cause the building to have a displacement value between floors, which is in accordance with the provisions of SNI 1726-2019 for both the X and Y axes (Figure 4). Figure 4 indicates that some floors of the building have story drift that exceed the allowable limit.Subsequently, the capability of the beam and column elements in the reviewed building was checked by calculating the demand-capacity ratio, which is based on the regulations stated in SNI 2847-2019.To assess the cross-sectional capability of beam elements, the table below displays the capacity of beam B1 on the 12 th floor or roof (Table 4).The analysis was conducted to assess the cross-sectional capacity of the beam by checking its moment (DCRm), shear (DCRv), and torque (DCRt).Based on the DCR values obtained, it can be observed that the beam section has failed as some of the values exceed 1.The same analysis was conducted for column elements, specifically for columns K2 and K3 on the 4 th floor.The results are presented in Table 5.Table 5 indicates that some columns have failed based on the design, as their DCR values are above 1 (one).

Structural Modelling with Steel Plate Shear Wall (SPSW)
In genaral, the steel plate shear wall (SPSW) system was modeled through three model based on location and the thickness of steel plate shear wall.The thickness of each SPSW type was 4.7 mm and 18.7 mm, respectively.The entire model of steel plate shear wall in high-rise building are six models.The placement locations of the SPSW reinforcement can be seen in Figure 5 -Figure 7. Models 1 to 3 have the same location as models 4 to 6, but with a thickness of 4.7 mm.Models 4 to 6 use a thickness of SPSW are 18.7 mm.

Analysis Results Comparison
The analysis will also include evaluating the story drift and cross-sectional capabilities of steel plate shear wall system in high-rise building.It's important to note that the placement pattern of the SPSW systems involves not only the location but also the thickness of SPSW.A summary of the story drift in the X and Y directions will be presented in Figure 8 -Figure 9. Figure 8 -Figure 9 show the story drift of existing of high-rise building and high-rise building with SPSW system to compare with the allowable limit.Based on the results, some of the floor in model 2 (the thickness of SPSW 4.7 mm), model 3 (the thickness of SPSW 4.7 mm) and model 5 (the thickness of SPSW 18.7 mm), the value of story drift exceed the allowable limit.On the other hand, the value of story drift for model 1 (the thickness of SPSW 4.7 mm) and model 4 (the thickness of SPSW 18.7 mm) and model 6 (the thickness of SPSW 18.7 mm) under the allowable limit.
Based on the analysis, it can be concluded that the most efficient modelling is model 6, where the use of SPSW is medium anf the value of story drift in X and Y axes do not exceed the allowable limit.This indicates that a sufficient amount of SPSW systems is required to ensure the building's stability and safety during earthquakes.However, it is important to note that the selection of the most efficient modeling also depends on other factors, such as cost-effectiveness, construction feasibility, and architectural design considerations.The cross-sectional capability analysis of beams and columns, beam B1 on the 12 th floor or roof was reviewed for the beam element.The summary of beam crosssectional capabilities, based on the DCR values of each load, is presented in Table 6 -Table 9.The tables above provide a summary that the implementation of SPSW systems model 4 has the most significant impact compared to the other models.However, in terms of the cross-sectional capability analysis of the beam, it doesn't seem to show any improvement in the ability as a result of using thicker of SPSW.Table 6, Table 7, Table 8,s and Table 9 summarize the cross-sectional capability analysis of the columns on the 4 th floor, and it can be observed that the use of SPSW systems in entire models has a significant effect on the DCR values of the columns.Model 4, which uses the thickest SPSW, shows the best performance in terms of DCR values compared to other models.The use of SPSW also affects the DCR values differently based on the load type.For instance, in column K2, the DCR values under moment and torque loads decrease significantly with the use of SPSW, while the decrease in DCR value is relatively small under shear load.Similarly, in column K3, the DCR value under torque load decreases the most with the use of SPSW.These results indicate that the use of SPSW can enhance the performance of column elements, especially under moment and torque loads.
The column capability analysis showed some discrepancies in DCR values despite the use of SPSW.This is due to the increased load caused by the placement of SPSW, as seen in column 6 where the DCR value increased from 0.83 in the existing condition to 1 in Model 3 after reinforcement.However, overall, the use of SPSW has a significant effect on the column's capability.

Conclusion
Based on the analysis and calculations, several conclusions can be drawn: a. From the existing conditions, based on the provisions of SNI 2847-2019, it states that there is a story drift and cross-sectional capabilities that do not meet the design requirements or have a value above the allowable limit.b.The use of steel plate shear wall system in highrise building with the thickness 18.7 mm has the most significant effect on the story drift and crosssection capability of columns.c.The story drift value is reduced by 3-6 mm with a steel plate shear wall system in high-rise building.d.The increasing thickness of steel plate shear wall system in high-rise building does not have a significant impact on the cross-section of the beam element.

Table 1 .
Dead Loads of Building

Table 2 .
Live Loads of Building

Table 4 .
Beam Capability on Existing Building

Table 6 .
Beam DCR Recapitulation Towards Bending Moment

Table 7 .
Beam DCR Recapitulation Towards Shear Force

Table 9 .
Column DCR Recapitulation Towards Bending Moment