BEHAVIOR AND PERFORMANCE OF STEEL FRAME STRUCTURES WITH X-TYPE CONCENTRIC BRACING SYSTEM DUE TO VARIATIONS IN COMPARISON OF SPAN WIDTH TO STORY HEIGHT (L/H)

. X-type bracing is the strongest bracing. The bigger ratio of the width of the span to the high level (L/H), the slope of the angle on the bracing will be more declivous. The analysis of the structure with the L/H ratio to determine the behavior of the structure using linear analysis of response spectrum and structural performance using the static nonlinear pushover analysis (ETABS 2016) to determine the displacement target that occurred in the structure. Structural modeling is done on 3D portals with levels of 3, 5, 8 and 10 floors with different L/H variations, including L/H=1; L/H=1.25; L/H=1.5; L/H=1.75; and L/H=2. Structural modeling is planned to be in the Surabaya area with moderate soil conditions. This study obtains data such as: (1) The largest maximum drift and floor drift are at type L/H=2, (2) The largest base shear force in the nonlinear pushover analysis at each story occurs at L/H=1, (3 ) In the yield condition type L/H=1 has the smallest percentage of structural stiffness, but in the ultimate condition type L/H=1 has the largest percentage of structural stiffness, and (4) The highest ductility value at each story occurs in type L/H=2 . Based on these results, it shows that the greater the type of L/H in the bracing structure, the greater the displacement target produced. If the angle of bracing becomes more sloping, then the displacement and target displacement that occurs increases.


INTRODUCTION
The area of Indonesia is very vulnerable to earthquakes [1].Indonesia's location is based on its geographical location in the Pacific Ring of Fire region, namely the confluence of three world tectonic plates, the Indo-Australian Plate, the Eurasian Plate, and the Pacific Plate.This makes Indonesia vulnerable to disasters such as earthquakes.Therefore, buildings in Indonesia must take into account the impact that an earthquake will have on building structures [2].The impact of a building structure that gets an earthquake force is to experience a lateral deviation [3].Precise calculations are needed so that the building can withstand earthquake forces.If the calculation is not correct and the structure gets too large a lateral deviation, then the structure will collapse [4].Structural systems in buildings must be designed to resist earthquake forces (lateral forces) [5].In terms of materials also need to be considered in designing a building.The use of steel material is most often used in the construction of high-rise buildings [6].This is because steel has very high elasticity and strength compared to concrete [7].So steel is the most suitable material used in bracing frame systems.
One of the systems that can withstand earthquake forces is the bracing frame system [8].There are several parts in the bracing system, including the eccentric bracing system and the concentric bracing system [9].Furthermore, there are two types of concentric bracing systems, namely Ordinary Concentric Bracing Systems and Special Concentric Bracing Systems.The Special Concentric Bracing System has higher stiffness when subjected to p-ISSN : 1412-114X e-ISSN : 2580-5649 http://ojs.pnb.ac.id/index.php/LOGICearthquake forces compared to the Ordinary Concentric Bracing System [9].Buildings that use a bracing system will minimize the value of deformation that occurs in the building structure because bracing will increase the value of the stiffness of the structure [10].Bracing has several types and X-type bracing is the type of bracing that has the highest structural strength value compared to other bracing types [11].This study aims to determine the ability of a steel frame structure using concentric bracing with the X-type as a result of the variation in the ratio between span width and story height (L/H).Thus, due to the L/H ratio, different bracing angle ratios will be formed.This will cause a difference in angle, so the ability of each X-type concentric bracing of each L/H type will be known.

METHODS
This research will conduct research on behavior and performance in each structure.The research aims to determine the behavior of the structure using a linear response spectrum analysis.Meanwhile, to determine the performance of the structure will use a non-linear static pushover analysis using the help of the 2016 ETABS application.
The steps taken for this research began with determining the cross-sectional dimensions used in each structure.Structural data worked on in this research were typical steel structures with 3, 5, 8, and 10 stories which the dimensions for each story are 4 m.The election for those total of the stories is mostly classification that we can find at the site consisting of a special concentric bracing system model made with five different types of L/H, namely L/H=1, L/H= 1.25, L/H=1.5, L/H=1.75, and L/H=2.So that the total models to be made are 20 models, of which 1 type of L/H consists of 4 models.The modeling was carried out using the 2016 ETABS application.The structure to be modeled is assumed to be in the Surabaya area with moderate soil conditions.The function of the building that will be used in each building is an office.Here are the materials and load used in each structure: The dead load has been calculated by the 2016 ETABS application, the additional dead load on the floor slab is 166 kg/m 2 , and the additional dead load on the roof plate is 142 kg/m 2 .e) Live Load The structure is assumed to be used as an office building, so the live load on the floor used according to SNI 1727:2013 [12] is 2.4 kN/m 2 and the live load used on the roof is 0,96 kN/m 2 .f) Earthquake Load The earthquake load used on the structure is class D in the Surabaya area.The place choices in Surabaya are because Surabaya is an industrial city also the classification of class D is the current primary situation at the site.After the structural data is determined, then the criteria are checked for each structure with a stress ratio.Next, calculate the deviation between floors based on the classification from SNI 1726:2012.The structure studied is in risk category II (office).Then a nonlinear pushover static analysis is carried out which will produce a curve due to the base shear force and displacement which is called the capacity curve.After obtaining the capacity curve for each type of L/H, the value of the stiffness of the structure can be determined.Stiffness of the structure can be seen from the slope of the capacity curve in yielding and ultimate conditions.If the displacement values at the time of melting and ultimate conditions are known, then the value of the ductility of each structure can be known.Next determine the displacement target by determining the assumption that there is a maximum displacement that may occur as a result of the earthquake load.The displacement target in this study used the ASCE 41-13 NSP (Nonlinear Static Procedure) method which is available in the ETABS 2016 software application.Determination of the displacement target based on the nonlinear static procedure is carried out by constructing an idealization curve from the capacity curve resulting from the static nonlinear pushover analysis.With the idealization curve, it will be known the target displacement that occurs from the structural model.After knowing the target displacement of the structure, it can also be known the level of performance of each structure.

RESULTS AND DISCUSSION Cross Section Dimensions
Determining the cross-sectional dimensions used in each structure is carried out by checking the criteria for each structure with a stress ratio of less than 0.95.The dimensions used in the structure are the dimensions obtained for the largest L/H type (L/H=2).Dimensions and stress ratios in the 3-floor, 5-floor, 8-floor and 10-floor models can be seen in Table 1 to Table 4

Pushover Nonlinear Static Analysis
In this pushover analysis it will produce a curve due to the base shear force and displacement which is called the capacity curve.With the existence of a capacity curve it will also be known the capacity of the structure including the stiffness of the structure and the ductility of the structure.The results of the day's pushover analysis can be seen in Figure 5

Structure Stiffness
After obtaining the capacity curve for each type of L/H, the value of the stiffness of the structure can be determined.The magnitude of the structural stiffness value is the result of the comparison between the base shear force (V) to the displacement (δ), both in yield (y) and ultimate (u) conditions.The results of structural stiffness can be seen from the slope of the capacity curve in yielding and ultimate conditions.Based on the data in Table 5 to Table 12, it can be seen that in the melting condition, the L/H=1 type is the L/H type which has the smallest percentage of stiffness at each level.Meanwhile, in the ultimate condition the greatest structural stiffness at each level occurs in the L/H=1 type.So that it can be said that in the ultimate condition, the greater the L/H type, the smaller the stiffness value of the structure.The relation between the structural stiffness and the shear force is the bigger of the structure stiffness in the building, it will resist with the bigger shear force.

Structural Ductility
After knowing the value of the displacement during the melting condition and the ultimate condition, it can be known the value of the ductility of each structure.The ductility value of the structure is the result of a comparison between the displacements in the melting state (δy) and the ultimate condition (δu).Based on data from Tables 13 to 16, the type L/=1 is used as a comparison for the structural ductility of each type of L/H.The greatest structural ductility at the 3 story level in the X direction and Y direction occurs in the L/H=2 type with a value of 9.3.The greatest structural ductility at the 5 storey level in the X and Y directions occurs in type L/H=2 with values of 9.7 and 9.4 respectively.The greatest structural ductility at the 8 storey level in the X direction and Y direction occurs in the L/H=2 type with values of 8.9 and 8.2 respectively.The greatest structural ductility at the 10 story level in the X and Y directions occurs in type L/H=2 with values of 11 and 10.6 respectively.So at each level, the greatest ductility occurs at type L/H=2.

Displacement Target
Then determine the displacement target, namely the assumption that there is a maximum displacement that may occur as a result of the earthquake load.The displacement target in this study used the ASCE 41-13 NSP (Nonlinear Static Procedure) method which is available in the ETABS 2016 software application.Determination of the displacement target based on this nonlinear static procedure is carried out by making an idealization curve of the capacity curve resulting from a static nonlinear pushover analysis.So, with the idealization curve, it will be known the displacement target that occurs from the structural model [14].Based on data from Table 17 to Table 20, it is known that the largest displacement target for each type occurs at type L/H=2.So that the greater the type L/H in the bracing structure, the greater the displacement target produced.24, it shows that the highest level of performance is in the 3-story structure model in the X direction and Y direction with type L/H=2, which is at the Collapse Prevention (CP).The level of Collapse Prevention (CP) occurs when 0% -0.5% = IO ; 0.5%-1.5% = LS ; > 1.5% = CP level which if 0%-0,5% = IO ; 0,5%-1,5% = LS ; > 1,5% = CP.

CONCLUSION
The conclusions that can be drawn from this research are: (1) The greater the increase in the type of L/H, the greater the deviation generated by the structural model, (2) After performing a nonlinear pushover analysis, the largest shear and displacement forces on each story occur in the type L/H=1, (3) In the melting condition, type L/H=1 is the type L/H which has the smallest percentage of stiffness at each level.However, in the ultimate condition, the greatest structural stiffness at each story occurs in the L/H=1 type.So that it can be said that in the ultimate condition, the greater the L/H type, the smaller the stiffness value of the structure, (4) The greatest value of structural ductility at each story occurs in the L/H=2 type in both the X and Y directions, (5) Based on ASCE 41-13 NSP model displacement targets L/H=2, all level models experience the largest displacement targets in the X and Y directions when compared to the other 4 types of L/H, (6) The highest level of structural performance occurs in the 3-floor structure model with type L/H=2, namely at the Collapse Prevention (CP) level, while for other structural models all are at the Life Safety (LS) level.
a) Steel profile material The steel material used in all steel profiles is ASTM A992, with the following data: -Yield Stress (Fy) = 344,74 MPa -Ultimate stress (Fu) = 448,16 MPa -Modulus of elasticity of steel (E) = 200.000MPa b) Corrugated steel deck material -Melting stress (Fy) = 550 MPa -Steel deck thickness (td) = 0,70 mm -Steel deck weight = 7,35 kg/m 2 -Sliding link (@90 mm) = 19 mm c) Concrete materials -Compressive strength (f'c) = 25 MPa -Modulus of elasticity of concrete (Ec) = 23.500MPa -Concrete slab thickness = 120 mm d) Dead Load Deviation between floor levelsDetermination of the deviation between floors based on the classification of SNI 1726: 2012[13] the structure studied is in risk category II (office).So that the requirements of the deviation between floors of the design level should not be more than 0,020 hsx.The level height of each structure is 4000 mm, then the allowable deviation of each structural model is 80 mm.The results of the deviations between storey levels on floors 3, 5, 8 and 10 along with the X and Y directions can be seen in Figure1−4.

Figure 1 .
Figure 1.Deviation between Floors at Level 3 Floor X and Y Direction.

Figure 2 .
Figure 2. Deviation between Floors at Level 5 Floor Y Direction

Figure 3 .
Figure 3. Deviation between Floors at Level 8 Floor Y Direction

Figure 4 .
Figure 4. Deviation between Floors at Level 10 Floor Y Direction Based on the results from Figure 1−4, the deviation between storey floors at each level in the X direction and Y direction occurs at type L/H=2.This is due to the smaller the resulting bracing angle, the less resistance of the bracing in resisting the deformation received by the structure. −8.

Figure 5 .
Figure 5.Comparison of Capacity Curves in X and Y Directional 3 Storey Structures.

Figure 6 .
Figure 6.Comparison of Capacity Curves in X and Y Directional 5 Storey Structures.

Figure 7 .
Figure 7.Comparison of Capacity Curves in X and Y Directional 8 Storey Structures.

Figure 8 .
Figure 8.Comparison of Capacity Curves in X and Y Directional 10 Storey Structures.Based on the results obtained, for a 3-storey building the largest base shear force occurs in the L/H=1 type in the X direction of 12,263 KN with a displacement of 151 mm, while the Y direction is 12,124 KN with a displacement of 150 mm.Furthermore, in a 5-storey building the largest base shear force occurs in type L/H=1 in the X direction of 15,316 KN with a displacement of 275 mm, while in the Y direction of 15,937 KN with a displacement of 262 mm.Then, in the 8-storey building the largest base shear force occurs in the L/H=1 type in the X direction of 16,173 KN with a displacement of 334 mm, while the Y direction is 16,168 KN with a displacement of 343 mm.In the 10storey building the largest base shear force occurs in the L/H=1 type in the X direction of 18,221 KN with a displacement of 561 mm, while the Y direction is 18,236 KN with a displacement of 563 mm.

Table 1 .
. Dimensions and Stress Ratio on the 3 Floor Model

Table 2 .
Dimensions and Stress Ratio on the 5 Floor Model

Table 3 .
Dimensions and Stress Ratio on the 8 Floor Model

Table 4 .
Dimensions and Stress Ratio on the 10 Floor Model

Table 5 .
Structural Stiffness with 3 Storey Levels in Melting Conditions

Table 7 .
Structural Stiffness with 5 Storey Levels in Melting Conditions

Table 8 .
Structural Stiffness with 5 Floor Levels in Ultimate Condition

Table 9 .
Structural Stiffness with 8 Storey Levels in Melting Conditions

Table 10 .
Structural Stiffness with 8 Floor Levels in Ultimate Condition

Table 11 .
Structural Stiffness with 10 Storey Levels in Melting Conditions

Table 12 .
Structural Stiffness with 10 Floor Levels in Ultimate Condition

Table 13 .
Structure Ductility with Level 3 Floors

Table 14 .
Structure Ductility with Level 5 Floors

Table 15 .
Structure Ductility with Level 8 Floors

Table 17 .
Target Displacement and Basic Shear Force of 3 Floor Structure Model

Table 18 .
Target Displacement and Basic Shear Force of 5 Floor Structure Model

Table 19 .
Target Displacement and Basic Shear Force of 8 Floor Structure Model

Table 20 .
[15]et Displacement and Basic Shear Force of 10 Floor Structure Model After knowing the target displacement of the structure, it can be known the level of performance of each structure.Based on FEMA 273, the determination of the performance level of the structure is based on the calculation between the target displacement and the total height of the building.The structure performance level grouping is divided into 3, namely: Immediate Occupancy (IO), Life Safety (LS), and Collapse Prevention (CP)[15].The performance level of each structure can be seen in table 21 to table 24.
So, based on data from Tables 21 to Table