Bracings For Soft Storey Building Seismic Analysis

Bracings For Soft Storey Building Seismic Analysis

BRACINGS FOR SOFT STOREY BUILDING SEISMIC ANALYSIS

Rohit Kumar B R Department of Civil Engineering

Jain institute of Technology, Davangere, Karnataka, India

Rajesh L Bousle Department of Civil Engineering

Jain Institute of Technology, Davangere, Karnataka, India

Neminath S Department of Civil Engineering

Jain Institute of Technology, Davangere, Karnataka, India

Abstract: Due to residential development, open first stories are particularly common in urban areas. Additionally, it provides continuous defoliated area that has been exploited for convenience in multistory steel buildings. But because of the long story height and decreased rigidity of the earth pressure resisting system, it has been in a very vulnerable state in earthquake zones. This study focuses on the quivering analysis of first-floor soft-storied building frames when two load blending are taken into account. The alternate approach involves installing the proper displacement reduction system in contemplation to provide bracing in the initial soft story in various two arrangements. Ten identical, ten-story steel buildings in three various grouping have been analysed for this aim using ETABS software. The analysis's findings indicate that the bracing in the first soft story greatly lowers the steel building's maximum moment, maximum shear, and story drift.

Keywords: -Soft Story,Displacement, Shear, Moment,Driftetc

INTRODUCTION

An earthquake is the shaking of the Earth's surface caused by a sudden release of energy in the lithosphere of the planet.

Fig1: Failure of soft storey building due to

earthquake.

Sharath V Kumari Department of Civil Engineering

Jain Institute of Technology, Davangere, Karnataka, India

Pranav Kumar M P

Department of Civil Engineering

Jain Institute of Technology,Davangere,Karnataka, India

An earthquake is the shaking of the Earth's surface caused by a sudden release of energy in the Earth's lithosphere, which generates seismic waves. It can also be called a quake, tremor, or temblor. Earthquakes can range in strength from those that are so small that no one can feel them to those that are powerful enough to throw things and people into the air, destroy vital infrastructure, and devastate entire cities. The frequency, kind, and size of earthquakes experienced over a specific time period constitute the seismic activity of a location.

Fig 2: Seismic Zone Map of India -2002.

SOFTST0REYBUILDING

When a shear wall would typically be needed for stability as a matter of seismic engineering design, a soft storey building can also be called as a multi- story structure with windows, broad doors, vastu obstructed or other openings on one or more floors. An ordinary soft story structure is an

Apartment complex with three or more stories that is built above a ground floor with a lot of openings, such a parking garage or a row of big- windowed stores. If a floor is slighter than 70% as stiff as the floor directly above it or slighter than 80% as stiff as the average firmness of the three floors above it, a bui1ding is said to have a soft storey. Soft storey collapse, a phenomenon that can happen in a moderate to severe earthquake, can cause soft storey buildings to collapse. Because it is considerably less resistant to lateral earthquake motion than other floors, the inadequately braced level receives a disproportionate share of the building's overall side-to-side drift.

Methods of Seismic Analysis

A key tool in foreshock engineering is seismic analysis, which is used-up t0 more easily comprehend how buildings react to seismic excitations. Buildings used to just be designed for gravity loads, and seismic analysis is a more modern innovation. Where earthquakes are common, both structural analysis and design are affected.

There are different types of earth quake analysis methods:

1. Equivalent Static Analysis.

2. Response Spectrum Analysis.

3. Time History Analysis.

Fig3: Soft Storey buildings without bracing

BRACIN GS

A braced frame is a type of constructional system frequently employed in buildings that must withstand horizontal loads like air and quivering forces. Usually, the structural steel members used in braced frames are able to function well in both tension and compression. The Earth pressure is carried by the bracing system and the beams and columns that make up the vertical load support frame. 0n the further hand, the placement of the bracing might be difficult since they may obstruct the facade's design or the positioning of apertures. Bracing as a component of internal or external design received a positive response from structures that adopt these high-tech or post-modern styles. different bracing techniques, including only one diagonal brace bracing across, V bracing, Both eccentric and inverted V bracing are used. Placing bracing at angles between 30° and 60° maximises its effectiveness. The end connections may be difficult with steeper bevels.

TYPESOFBRACINGS

Types of bracings based on codebook:

1. VBRACING

2. DIAGONALBRACING

3. X-BRACING

4. K-BRACING

5. ECCENTRICBRACING

6. INVERTEDVBRACING

OBJECTIVES

The main objectives of this study are summarized in few points as follows;

1. To analyse the performance of s0ftst0reybui1ding subjected to seismic forces.

2. To study the quivering behavior of s0ftst0reybui1dingbyprovidingbracings.

3. 2`Tocompare the performance of the structure by providing different types of bracings.

4. To

   findthemostefficienttypeofbracingtobeadoptedi nastructuresubjectedtoseismicforces.

   METHODOLOGYANDSTRUCTURALMOD ELLING

   For the investigation, a G+10 building with typical moment-resisting frames in two orthogonal orientations is chosen. According to IS 1893-2002, it is thought to be situated in Zone IV on medium- stiff soil. ETABS software is used to model and evaluate the buildings, and the proportions of the members are chosen based on how the buildings are designed to withstand gravity loads. The following methodology is used to attain the defined objectives

   • A G+10 building is designed for gravity loadings only, the designed beam and column details such as size sand reinforcement details are assigned for seismic analysis.

   • The equivalent static method ofanalysisiscarriedoutforthebuildingmodelstostu dythestructuralbehaviorwhensubjectedtoseismicf orces, provided with fixed support at the column bases.

     The structural building models are classified into series1 &series2 for the analysis.

     Fig:4 Seismic Hazard Micro zonation Map of

     NewDelhi

     • For the present study New Delhi India is the location selected for zone IV. The key plan of the location is show in the above figure (4.1).

     • Series I, consists of analysis of a G+10 soft storey building in whichever an open storey is provided ground floor for parking purpose.

     • Series II, consists of analysis of G+10 soft storey buildings provided with discrete types of bracings and the most efficient type of bracing is found out.

     • The results from the evaluation of building frames having soft storey, with and without bracings, i.e., Series I and Series II building replicas are scheduled, discussed and ultimately the conclusion is drawn.

   PROCEDURETOBEFOLLOWEDINETABS

   E-TABS2019

   ETABS [EXTENDED 3D ANALYSIS OF

   BUILDING SYSTEM] could be a stay solitary structural research system for a high quality motivation characteristics to structural plan and dissection approximately building frameworks. ETABS is basic to make use of and smooth to apprehend and it's far the first rate in its capability with location those full range from claiming assignments protected inside the remodel for shape investigation what is extra configuration. ETABS may be a suitableness bundle for, Multistoried fabricating examination. the one's whole information may a chance to be produced likely graphically or subsequently, writing truthful English dialect constructed instructions. It is ready with the one's complicated publicizing calculations and the kingdom of the distinctiveness images, dwelling for a significantly smooth to recognize nature's domain.

   Modelling

   The representation of high-rise bui1ding characteristics in the replicas is one of the aim of this mode1 design. High-rise structures today come in a variety of sizes, shapes, and uses. Because of this, each bui1ding has rare qualities. Each type of high-rise bui1ding, inc1uding, residential, government, and commercia1 ones, must adhere to certain criteria. However, key elements inc1uding grid spacing, fl00r shape, floor height, and column section were taken into account when designing replicas.

   FigNo6: View of material property assigned

   (1) (2)

   a)

   (

   (3) (4)

   Fig No 7: (1) Building without bracing (2) Building with inverted V bracing (3) Building with X bracing (4) Building with Diagonal bracing

   RESULTSANDDISCUSSION

   The findings of the structural models' reaction

   4

   0

   3

   5

   3

   Sto Bare

   1 1

   Diagonal InvertedV X

   1

   (b)

   Fig No 8: (a), (b)Maximum Storey displacement along X and Y direction.

   spectrum analysis are tabulated, and graphs are

   0.00

   drawn using the numbers to represent the maximum

   18

   stiffness, maximum displacement, maximum base

   shear, etc. for each storey. shifting of a story.

   Estimating the greatest vertical displacement of the structures caused by a strong earthquake is crucial

   0.00 16

   for seismic design for a number of reasons. Storey displacement, when caused by lateral forces, is the

   magnitude of a storey's absolute displacement with respect to the ground. The outcomes of the storey displacement

   Inter storey drift:

   When a building sways during an earthquake, it is the

   0.00

   14

   (a)

   difference between the roof and floor displacements

   of any particular storey, which is formalised by the storey height.

   0.00

   0.00

   It alludes to how rigid a structural component is. This

   is a reference to the element's resistance to deformation or deflection brought on by an external force.

   Base shear :

   It is a projection of the maximum anticipated lateral strains brought on by seismic ground motion at the base of the structure.

   0.0

   0.00

   0.00

   0.00

   0.00

   Base Story1Story2Story3Story4Story5Story6Bare Diagonal InvertedV X

   (b)

   Fig No 9: (a), (b) Maximum storey Drift along X, Y direction

   6000

   4000

   2000

   F

   F

   F

   M

   Withoutbracing Xbracing

   –

   –

   –

   0.00

   018

   0.000 16

   0.000 14

   Base Story1 Story2 Story3 Story4Story5Story6Bare Diagonal InvertedV X

   1. (a)

6000

F

M

M

(b)

Fig No 10: (a), (b)Base shear for different braced building along X, Y direction.

1

. 8

1

. 6

(a)

1.

8

1.

6

(b)

Fig No 11: (a), (b) Laterala displacement of wind load along X, Y direction.

–

Withoubracing

Xbracing

0.000

0.000

(b)

Fig No 12: (a), (b) Storey drift due to wind load along X, Y direction.

CONCLUSION

• From this study, analyzed the variation of the 1ateral displacement, story drift and shear along X , Y directions. This present study is concluded with the raw wind conclusions. In ESM for the load combinations 1.5(DL+LL+EQX) and 1.5(DL+LL+EQy). The variation of the lateral! Disp1acement of the building is compared with the bare building along X,Y direction. The displacement is minimum in X Braced building and maximum in bare building. The ESM for the load combinations 1.5(DL+LL+WX) and 1.5(DL+LL+WY).

• The variation of lateral Disp1acement of the bui1ding is contrast with the bare building along X and Y direction. The displacement is minimum in X braced building and maximum in bare building.

• The ESM for the load combinations 1.5(DL+LL+EQX)= and 1.5(DL+LL+EQY).The

  Variation of the story drift of bare building is contrast with different types braced building along X, Y direction. The story drift is maximum in bare building and minimum in X braced building.

• The ESM for the load combinations 1.5(0L+LL+WX)and 1.5(DL+LL+WY). The

  variation of the story drift of bare building is compared with different types of braced building along X and Y direction. The story drift is maximum in bare building and minimum in X braced building.

• From the overall result the displacement and story drift are minimum in braced building and base shear is maximum in Braced building compare to bare

building.

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