Structural analysis due to wind speed as static loads on building

. The effect of wind as a dynamic load on structures can vary greatly depending on geographic location, topography, building height, and the characteristics of the building itself. Therefore, careful calculations and an in-depth understanding of these factors are essential in the design of safe wind-resistant structures. For tall buildings, the structural response due to horizontal loads due to wind loads is much greater than vertical loads. This paper reviews the analysis of wind loads as static lateral loads against the internal forces and inter-story drift that occur. A review was carried out of a reinforced concrete structure building with a plan size of 25 x 10 m; the frame height is 32 m, with a total of 8 floors. The speed of the wind is 120 mph. The structural response reviewed compares internal forces, deformation, and inter-story drift under wind loads with variations of wind speed factors based on surface roughness and topographic influence factors (slopes and hills). From the analysis of the effect of wind loads on building structures, it can be seen that wind speeds in flat areas without obstructions (exposure D) and slope areas have more significant wind speeds compared to the city center and hilly regions.


Introduction
Two types of loads can affect structures: static and dynamic.These two loads have their analysis, which must be treated so that the building can function correctly.The Static load is a load that does not change in function of time, while the dynamic load is a load that changes according to a function of time.In applying calculation methods to structural analysis, dynamic loads can be converted into static loads by equivalent the dynamic loads into equivalent static lateral loads.The wind is one of many dynamic loads that can affect building structures [1][2].In structural design, dynamic load calculations such as wind loads need to be taken into account to ensure the safety and stability of the building [3].
In general, understanding performance-based seismic design [4] is beneficial for understanding the dynamic behavior of structures.If this dynamic load is used as a lateral static load, then understanding the performance of the design base in elastic and plastic conditions can help understand the behavior of the structure correctly [5][6][7].
It is important to note that the effect of wind as a dynamic load on structures can vary greatly depending on geographic location, topography, building height, and the characteristics of the building itself.Therefore, careful calculations and an in-depth understanding of these factors are essential in the design of safe wind-resistant structures [8].
Wind as an equivalent static load on buildings refers to a design approach that replaces complex dynamic wind load variations with an equal static load [9][10].In structural design, this method is used to simplify wind analysis and ensure building safety.
For tall buildings, the structural response due to horizontal loads due to wind loads and earthquake loads is much greater than vertical loads.This paper reviews the analysis of wind loads as static lateral loads against the internal forces and inter-story drift that occur.Analysis of wind loads as static wind loads is examined based on the American Society of Civil Engineering (ASCE 7 -02 [11]).

Theoretical background
Indonesia is an archipelagic country with different topographic conditions.Most of the people's territory consists of hilly areas.This condition affects the shape of the building because there are other wind pressures in each room.Wind loads acting on building structures are influenced by topography, building type, and air conditions where the building is located (ASCE 7-02 [11]).
When the wind load hits a building, it will hit all objects in its path.This wind exposure is a horizontal load on the building, which will cause reactions and vibrations.Even though this wind load is sometimes not as big as an earthquake load because the frequency and period are more frequent and longer, occupants will feel discomfort, so it is crucial to consider this.The amount of wind load depends on the wind speed.Meanwhile, wind speed depends on height.Thus, the wind load also depends on the size of the building.

Wind load
The amount of wind load acting on a building structure depends on wind speed, air mass density, geographical location, shape and height, and structure stiffness.Buildings in the wind's path will cause the current to bend or stop.As a result, kinetic energy from the wind will change into potential energy in the form of pressure or suction on the building.
The amount of wind load acting on a building structure depends on wind speed, air mass density, geographical location, shape and height, and structure stiffness.Buildings in the wind's path will cause the current to bend or stop.As a result, kinetic energy from the wind will change into potential energy in the form of pressure or suction on the building.Wind speed is a crucial factor that influences the amount of pressure and suction on a building when the wind is moving.The amount of wind speed varies for each geographic location [9].
Pressure caused by wind is defined as the relationship between climate conditions (air mass density and plain wind speed), exposure coefficient, topographic factors, wind direction factors, and building prominence factors (ASCE 7-02 [11]).This relationship is presented in the following formula: where q z : static wind flow speed at a certain height (Psf) K z : wind pressure speed factor based on terrain roughness K zt : topographic influence factor K d : wind direction factor V : basic wind speed (m/hour) I : building priority factors The wind speed that occurs is greatly influenced by the surface roughness of the terrain where the wind occurs.Especially in winds at low altitudes, wind speed is still affected by friction with the landscape, which slows down the wind speed.However, as size increases, the influence of this friction decreases until it reaches a height where terrain conditions no longer influence wind speed.
In the American Society of Civil Engineers 2002 (ASCE 7-02 [11]), three classifications of terrain are exposure B, C, and D. Exposure B is the areas in the city center, suburbs, and areas where there are lots of trees or other regions with relatively close obstructions.Exposure C is an open area with scattered obstacles, a general height of less than 30 feet, and locations in hurricane-prone territories.Exposure D is a flat, unobstructed area and outside hurricane-prone regions.
In ASCE 7-02 [11], the effect of exposure is formulated as a coefficient, with the equation: For z < 15 ft, � � = 2,01.( 15 where: Z : Height measured from the base of the building Z g : A certain height where friction with the terrain no longer affects wind speed (can be seen in Table 1)

Α
: Coefficient of influence of plain exposure (can be seen in Table 1).Topographic factors are taken into account for greater wind speeds if the structure is located on a hill or slope (escarpment).To determine topographic values, you can refer to Figure 1.For structures in a relatively flat area, the value of K zt = 1.The site is relatively flat if (a) H/Lh < 0.2, or (b) H < 15' for exposures C and D, and H < 60' for exposure B. For structures located in hilly or sloping areas, the K zt value can be determined using the following equation: The K1, K2, and K3 grades follow the standards ASCE 7-02 set.

External pressure coefficient (Cp)
The building surface, structural configuration and wind direction influence the external pressure coefficient.This coefficient also depends on the force that will be used for design/analysis, namely where the main wind forceresisting systems are structural elements that resist wind over a reasonably large area, and components and cladding are structural elements that resist wind over a small space.
The parts that become the Leeward Wall (L) and Windward Wall (B) in the structure are influenced by the side of the building that is viewed against the incoming wind so that the Cp values for the x and y directions are different (Table 2).The L and B values can be seen in the following Figure 2.

Wind load design
Based on ASCE 7-02 [11], wind loads acting on a building are divided into four cases, namely: • Case 1: Full design wind pressure acting on the planned area perpendicular to each principal axis of the structure and considered separately along each principal axis • Case 2: 0.75 of the design wind pressure acting in the planned area perpendicular to each principal axis of the structure together with the twisting moment (torque) that occurs, considered separately along each principal axis • Case 3: 0.75 of the design air pressure in case 1 • Case 4: 0.75 of the design air pressure in case 2 In this research, the first type of case was used.In case 1, the design is full of wind pressure acting on the planned area perpendicular to each principal axis of the structure and is considered separately along each principal axis.

Research Methodology
As equivalent static loads on buildings, an analysis was carried out on an 8-story office building located in a highrisk zone for earthquake loads, represented by the city of Padang.This reinforced concrete building is located on medium ground with a building height above the floor of 32 m.The size between the columns is 8 meters, while the span of each beam is 5 meters.From Figure 3. it can be seen that the building area is 10 x 25 meters.The structural elements to be reviewed can be seen in Figure 4.  Wind loads and earthquake loads are dynamic loads that can affect buildings.Both loads can be used as static loads equivalent to the actual dynamic loads on the building.The direction of this load is lateral to the structure axis.
For equivalent static earthquake loads' loading modeling in the x direction can be seen in Figure 5.The equal static lateral earthquake force pair when modeling is if the load is given at 100% in the x direction, then in the y direction, the load is offered at 30%.Vice versa, if the equivalent static lateral earthquake force is provided 100% in the y direction, then in the x direction, it is given 30% For static wind loading, the pair of lateral static forces that hit the building become a suction wind and a pressure wind, as seen in Figure 6.If seen from the top view, the pair of forces can be seen in Figures 7 and 8

Loads on buildings
The dead load calculation is taken from the weight of building materials and building components, as shown in Table 3.The specific gravity of concrete is taken as 2400 kg/m 2 as the input material in the program.The live load used is adjusted to the regulations in force in Indonesia, namely 250 kg/m 2 on the building floor and 100 kg/m 2 on the roof.

Statics wind loads
There are two variations of wind load as a static load in this research, namely variations in surface exposure and topography, as presented below.

Wind static load due to exposure type
The coefficient values used are: K zt is 1, K d is 0.85, and I is 1.15, so the C p value is obtained 0.8.The P external for each floor on the windward wall for exposure B can be seen in Table 4.For the leeward wall, the coefficient values used are: K zt is 1, K d is 0.85, I is 1, q z 36.11; the P external for each floor can be seen in Table 5 for exposure B on x and y direction.The coefficient values used are: K zt is 1, K d is 0.85, and I is 1.15, so the C p value is obtained 0.8.The P external for each floor on the windward wall for exposure C can be seen in Table 6.For the leeward wall, the coefficient values used are: K zt is 1, K d is 0.85, I is 1, q z 46 Psf.The P external for each floor can be seen in Table 7 for exposure C in the x and y directions.The coefficient values used are: K zt is 1, K d is 0.85, and I is 1.15, so the C p value is obtained 0.8.The P external for each floor on the windward wall for exposure D can be seen in Table 8.For the leeward wall, the coefficient values used are: K zt is 1, K d is 0.85, I is 1, q z 52.07 Psf, and the P external for each floor can be seen in Table 9 for exposure D on x and y direction.

Static wind load with variations in topographic influence factors
In this research, the calculated wind load due to topographic variations is only at exposure B for the windward and leeward walls.The coefficients used are the same as the coefficients used in exposure B. For 2dimensional conditions on a slope, the windward wall wind force can be seen in Table 10, while the leeward wall can be seen in Table 11.For 2-dimensional conditions on the ridge, the leeward wall wind force for exposure B on x and y can be seen in Table 12.Next, the wind load on each floor will be included in the program model as area or area load.

Results and discussion
Static wind pressure at a certain height is influenced by external stress and internal stress.In this thesis, the Case 1 wind load design is used, so the wind load due to the acting external pressure is analyzed separately for P wx (windward wall in x direction) and P Lx (leeward wall in x order) as well as P wy (windward wall in y direction) and P Ly (leeward wall y direction).The wind pressure analyzed is only that which comes from external wind pressure.
A comparison of the loading values due to variations in the wind pressure speed factor based on the roughness of the terrain can be seen in Table 13 and Table 14.

Internal forces
The moment force in this study was only on beam B 1 by considering exposure variations B, C, and D, as seen in Figure 9.These exposure variations were also seen in the exterior (C 1 ) and interior (C 4 ) columns, as seen in Figure 10.The two pictures show that exposure variations increase from A to D according to those grouped in ASCE 7-02 [11].This condition also occurs for shear forces in beam B1 (Figure 11) and column C 1 C 4 (Figure 12).This behavior also happens in beam B1 (Figure 13) and column C1 C4 (Figure 14) for axial force conditions. .

Inter-story drift
Interstory drift is one of the crucial parameters in designing building structures to measure the extent to which a building can withstand deformation due to lateral loads.In this study, the lateral load is caused by the equivalent wind load.The inter-story drift considered is on exposure B with variations in slopes and ridges in the x direction (Figure 15) and y direction (Figure 16).

Conclusion
Based on the results of internal forces and inter-story drift resulting from static wind loading with variations in factors that influence the magnitude of wind speed, it can be concluded that for plains that are in open areas, without barrier areas (exposure D) and slope areas have a strong wind influence more significant than exposure B, exposure C, 2-dimensional ridge.

Fig. 2 .
Fig. 2. Determination of L and B Values in a Building according to ASCE 7-02.

Fig. 4 .
Fig. 4. The sections considered in the X direction and the beams and columns under.

Fig. 5 .
Fig. 5. Static earthquake load modeling on building sections in the x direction. .

Fig. 6 .
Fig. 6.Wind load modeling in the x-direction section.

Fig. 7 .
Fig. 7. Top view of the wind load model in the x direction.

Fig. 8 .
Fig. 8. Top view of the wind load model in the y direction.

Tabel 5 .
Wind loads of a leeward wall for exposure B on x and y direction.

Fig. 9 .
Fig. 9. Moment that occurs in beam B1 due to exposure variations.

Fig. 13 .
Fig. 13.Axial force that occurs in beam B1 due to exposure variations.

Table 1 .
Coefficient values for terrain exposure.

Table 3 .
Dead load on structures

Table 4 .
Wind loads on a windward wall for exposure B.

Table 6 .
Wind loads on a windward wall for exposure C.

Table 7 .
Wind loads of a leeward wall for exposure C on x and y direction.

Table 8 .
Wind loads on a windward wall for exposure D.

Table 9 .
Wind loads of a leeward wall for exposure D on x and y direction.

Table 10 .
Wind loads on a windward wall for exposure B on a slope.

Table 11 .
Wind loads of a leeward wall for exposure B on x and y direction on a slope.

Table 12 .
Wind loads of a leeward wall for exposure B on x and y direction on ridge.

Table 13 .
Comparison of loading values due to variations in wind pressure speed factors based on terrain roughness.

Table 14 .
Comparison of loading values for variations in topographic influence factors.