Effectiveness of Steel Bracings inMultistorey Buildings

Effectiveness of Steel Bracings inMultistorey Buildings

Clydin P A

Department of Civil Engineering Adi Shankara Institute of Engineering

And Technology Ernakulam, India

Muhammed Ansil M A

Department of Civil Engineering Adi Shankara Institute of Engineering

And Technology Ernakulam, India

Denna Babu

Department of Civil Engineering Adi Shankara Institute of Engineering

And Technology Ernakulam, India

Sarath M P

Department of Civil Engineering Adi Shankara Institute of Engineering

And Technology Ernakulam, India

AbstractFor reinforced concrete buildings, the most crucial aspect is ensuring that a multistory structure is stable against lateral load. Steel bracing is a useful tool in RC frame buildings to transfer or reduce these stresses. Steel bracing's remarkable strength, rigidity, and ability to withstand lateral stresses make it an excellent alternative to other materials for high-rise building lateral support. This study presents the analysis of a G+9 building with four different forms of bracing in a structural system: X, V, Inverted V, and Diagonal bracing, using ETABS software. The result of applying lateral loads is a comparison in multiple parameters. It has been observed that the X bracing system outperforms the other two.

Keywords Bracing Systems, ETABS, Storey Displacement, Multistorey Building

1. INTRODUCTION

   Structural aging is a serious global concern because it negatively impacts structural performance by decreasing the structure's seismic resilience. Because of their ability to maximize land use and support a variety of functions, multistorey structures are becoming essential to contemporary urban development. Tall buildings are particularly vulnerable to lateral pressures like wind and seismic loads that compromise their structural integrity. Bracing systems have become essential components in reducing the effects of lateral forces in order to address this. Steel bracing has several advantages, the main ones being its remarkable strength, stiffness, and affordability. For this a G+9 office building in Panampilly Nagar, Kerala building plan is considered and compared with several parameters. A 50 year old multistorey building having structural decay poses a serious risk to occupants and neighboring properties, necessitating thorough inspections and targeted maintenance. Therefore, steel bracing aids in maintaining the structure's structural integrity. After the steel bracing has been installed, the load in an RCC frame

   building is carried to the frame and then to the braces, passing through the weak column and obtaining strength. The load is transferred to the frame and then to the braces in an RCC frame building once the steel bracing is installed, passing through the weak column and gaining strength.

2. OBJECTIVE

   The main objectives include:

   • To analyze the multistorey building using different configuration of steel braces (X, V, Diagonal and Inverted V)

   • To determine storey displacement, time period and storey drift for all four bracing system using ETABS.

3. METHODOLOGY

   Literature Survey

   Identification of Objectives

   Designing

   Modelling And Analysis

   Results and Discussion

4. BUILDING MODELLING

   A G+9 storey RC frame building is modelled in ETABS software. Model is created with four different types of bracing (X, V, diagonal and Inverted-V bracing). Following properties are considered for modeling the building.

   TABLE 4.1 BUILDING CHARACTERISTICS

   Purpose	Office Building
   Number of Floors	G+9
   Building Shape	Rectangular
   Total Building Floor Area	5945.22sq.ft
   Occupying Area	2267.23sq.ft
   Remaining Area	2970.5sq.ft
   Latitude	9°5731.91 N
   Longitudinal	76°1744.52N
   Depth and Type of Foundation	45 m, Under reamed piles
   Floor to Floor Height	3 m
   Ground Floor Height	3.5 m

   TABLE 4.2 MEMBER PROPERTIES

   Beam	0.5×0.35 m, 0.4×0.3 m
   Column	0.59X0.59 m
   Slab Thickness	0.15 m

   TABLE 4.3 MATERIAL PROPERTIES OF CONCRETE AND STEEL

   Column	M 25
   Beam	M 25
   Slab	M 25
   Density of RCC	2500 kg/m3
   Density of PCC	2400 kg/m3
   Main Bars	Fe500
   Confinement Bars	Fe415
   Density of Steel	7850 kg/m3
   Steel Braces	ISA 200X200X25

5. LOAD CALCULATION

   1. Dead Load

      The values of the unit weights of the materials are specified in IS 875:1987 (Part-1). The self- weight of structural member auto calculated by software (self-weight multiplier given as 1 in load pattern). The sample manual computation for dead load

      Beam 1 = 0.5 x 0.35 x 25

      = 4.375 kN/ m2

      Beam 2 = 0.4 x 0.3 x 25

      = 3 kN/ m2 Column = 0.59 x 0.59 x25

      = 8.702 kN/ m2

      Slab = 0.15 x 25

      = 3.75 kN/ m2

   2. Live Load

      The values of the imposed loads depend on the functional requirement of the structure. The standard values are stipulated in IS 875:1987 (Part II) is 2.5 kN/ m2

   3. Seismic Load

      The design base shear is computed in accordance with the IS: 1893 (Part-I): 2016

      TABLE 5.1 SEISMIC DATA

      Seismic Zone	III
      Zone Factor	0.16
      Importance Factor	1
      Response Reduction Factor	5

   4. Wind Load

   As per IS 875 Part III-2015, wind load is determined using following parameters

   Basic wind speed in Kerala= 39m/s Risk factor k1= 1

   Topography factor k3=1 Terrain category= 3

   Value of k2 varies as per building height, k2 = 1.062 Design wind speed, = × 1 × 2 ×3

   Design wind pressure, = 0.62

   TABLE 5.2 WIND PRESSURE

   Height (m)	Vb	k1	k2	k3	Vz (m/s)	Wind Pressure
   30.7	39	1	1.062	1	41.418	1029.270

6. LOAD COMBINATION

   Various load combinations as per the partial safety factors given in IS 456:2000 and IS 1893 (Part I) 2016 stipulates the combination of the loads to be considered in the design of the structures.

   1. 1 DL

   1. 1.5 (DL+LL)

   2. 1.5 (DL+EQX)

   3. 1.5 (DL+EQY)

   4. 1.5 (DL+EQ-X)

   5. 1.5 (DL+EQ-Y)

   6. 1.5 (DL+WLX)

   7. 1.5 (DL+WLY)

   8. 1.5 (DL+WL-X)

   9. 1.5 (DL+WL-Y)

   10. 1.2 (DL+LL+EQX)

   11. 1.2 (DL+LL+EQY)

   12. 1.2 (DL+LL+EQ-X)

   13. 1.2 (DL+LL+EQ-Y)

   14. 1.2 (DL+LL+WLX)

   15. 1.2 (DL+LL+WLY)

   16. 1.2 (DL+LL+WL-X)

   17. 1.2 (DL+LL+WL-Y)

   18. 0.9DL+1.5EQX

   19. 0.9DL+1.5EQY

   20. 0.9DL+1.5EQ-X

   21. 0.9DL+1.5EQ-Y

   22. 0.9DL+1.5WLX

   23. 0.9DL+1.5WLY

   24. 0.9DL+1.5EQ-X

   25. 0.9DL+1.5EQ-Y

   All these load combinations are built in ETABS. Analysis result from the critical load combinations are used for the design of structural members.

   Fig 6.1 Unbraced Frame

   Fig 6.2 X Braced Frame

   Fig 6.3 V Braced Frame

   Fig 6.4 Inverted V Braced Frame

   Fig 6.5 Diagonal Braced Frame

7. RESULTS AND DISCUSSION

After analysis of G+9 storey building in ETABS software. Results are in form of Storey displacement, storey drift and time period . Storey drift and displacement were determined for each building separately in every instance. The parameters obtained for the unbraced system are compared to the bracing systems of the X, V, Inverted V, and diagonal braced frames. Upon comparing all of these systems, it is found that when the steel bracing system is modeled, there is the least amount of building drift. Storey displacement decreased as well when steel bracing was installed. Find out that the X braced frames are most effective one by comparing all of the data to resist the lateral load caused by the seismic load. Below are graphs and tables for each of the several scenarios

1. Storey Displacement

   Fig 7.1 Storey Displacement in X Direction

2. Storey Drift

   Fig 7.3 Storey Drift in X Direction

   Fig 7.4 Storey Drift in Y Direction

3. Time Period

Fig 7.2 Storey Displacement in Y Direction

TABLE 7.1 TIME PERIOD

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