II. CONVENTIONAL BRACING SYSTEM AND BUCKLING RESTRAINED BRACING SYSTEM

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1 ANALYTICAL COMPARISION OF UNBRACED, BRACED AND BUCKLING RESTRAINED BRACED STRUCTURES WITH COST COMPARISON OF CONVENTIONAL BRACING AND BUCKLING RESTRAINED BRACING SYSTEMS Harshal Chavan 1, Nikita Mane 2, Tushar Mali 3 1, 2, 3 UG Student, Department of Civil Engineering, Kit s College of Engineering, Kolhapur, Maharashtra I. INTRODUCTION Earthquake is a natural calamity which is very much unpredictable and causes a large damage to the structures even resulting in the failure of the entire structure. Thus, the buildings and structural frames must be designed such that they can withstand a large earthquake force and maintain its stability for its entire life period. Thus, there is a need of earthquake resistant design for the maintaing the stability of the structure. However there a no. of ways for making the buildings earthquake proof, the method considered and analysed in the project deals with Bracing Systems. Firstly, the conventional bracing systems are introduced and then the Buckling Restrained Bracing Systems (BRB) are explained. Buckling Restrained Braces (BRB) are a recently developed structural system, and consist of Steel Frames encased in concrete and covered with thin casing. BRB s are characterised by almost equal capacity in compression and tension, and a high degree of post-elastic reliability. BRB s are proposed to be adopted for the buildings to act as a stiff, reliable structural system that limits nonstructural damage, and in which structural damage is concentrated in discrete, replaceable elements. II. CONVENTIONAL BRACING SYSTEM AND BUCKLING RESTRAINED BRACING SYSTEM Conventional bracings provide stability and resist lateral load from diagonal steel. Conventional steel frames undertake large level of lateral deformation when subjected to strong ground motion or wind forces.if this deformation is excessive, structural and non structural damage is evident compromising the structural integrity. Damage becomes stronger as P-delta actions takes place, product of large deformations. Conventional braces have limited deformation ductility capacity, and exhibit unsymmetrical hysteretic cycles with marked strength deterioration when loaded in compression. Also, they are weak in sustaining compression and thus heavy sections are needed to be provided. BRB s are proposed to be adopted for the buildings to act as a stiff, reliable structural system that limits nonstructural damage, and in which structural damage is concentrated in discrete, replaceable elements. The buckling restrained frame is seen as follows : 334 P a g e

2 Fig.1 : Buckling Restrained Brace Fig.2 : c/s of Buckling Restrained Brace Fig.3 : Image Showing Conventional Bracings(left) and Buckling Restrained Bracings(right) II. OBJECTIVES OF PROJECT 1. Analysis of unbraced, conventionally braced and buckling restrained braced G+14 storied RC frame which will be done by seismic coefficient method on ETABS Design of Conventional bracing systems and buckling restrained bracing systems. 3. Cost analysis of conventional bracing systems and buckling restrained bracing systems. 335 P a g e

3 III. MODELING 1. Modelling Parameters : Description Size Dimensions 28m x 28m No of bays in X-direction 7 No of bays in Y-direction 7 Spacing of bays in X-direction 4m Spacing of bays in Y-direction 4m Height of Storey 1)bottom 2)typical 3m 3m Beam 230X500mm Column 1050X350, 400X230,300X230,400X230,500X230,550X X300,650X300,750X300,750X350,900X350 Thickness of slab 0.150m Thickness of wall 0.230m Thickness of glass 0.065m 2. Material Properties : Properties Concrete Fe415 Mass per unit volume Weight per unit volume(kn/m 3 ) Modulus of elasticity (KN/m 2 ) X10 5 Coefficient of thermal expansion (/Oc) 1.2X X Loading Consideration : Types Of Load Intensity Of Load Dead loadself weight of the structural element Calculated lumped mass of respective storey e.g. floor load,glass load, wall load Live load On top floor On typical floor 3(KN/m 2 ) 3(KN/m 2 ) 4. Seismic coefficient parameters : Parameters Specification Seismic loading Zone 5 Soil type 2 (medium) Response reduction factor 5 Importance factor 1.5 Damping 5% Type of frame SMRF 336 P a g e

4 5. Properties of BRB S : Properties M20 Fe250 Mass per unit volume Weight per unit volume(kn/m 3 ) Modulus of elasticity (KN/m 2 ) Coefficient of thermal expansion (/Oc) 1.2X10^-5 1.2X10^-5 6. Tentative Sizes of BRBs for analysis : Storey Casing I Section Filler Material 1, 2 300X300X2 ISSC 250 M20 7, 8, 9 270X270X2 ISSC 220 M20 14, X250X1.5 ISWB 200 M20 7. Tentative Sizes of Conventional Bracings for analysis : Storey I Section 1, 2 ISHB 600 7, 8, 9 ISHB , 15 ISWB 250 Fig.4 : 3D View of Unbraced Building 337 P a g e

5 Fig.5 : 3D View of Configuration of Ordinary and Bucling Restrained Braced Building IV. ANALYSIS RESULTS 1. Comparison of Displacement : 338 P a g e

6 2. Results for Storey Drift : 3. Results for Mode Period : 339 P a g e

7 V. DESIGN OF BRACES Here in the design of sections the sections are designed as per the Indian Standards. DESIGN OF CONVENTIONAL BRACING TENSILE FORCE COMP. FORCE SECTION PROVIDED ISWB ISWB600* ISWB ISHB450* ISHB450* ISWB ISWB225 DESIGN OF BRB TENSILE FORCE COMP. FORCE CASING PROVIDED SECTION X275X1.1 ISHB X300X1.3 ISHB250* X300X1.1 ISHB X275X1.1 ISHB X275X1.1 ISHB X150X3 ISSC X150X1.5 ISMC P a g e

8 VI. COST ANALYSIS COSTING OF CONVENTIONAL BRACING NOS. SECTION WT OF SECTION TOTAL WT. OF PROVIDED IN KG. SECTIONS IN TONNES 56 ISWB ISWB600* ISWB ISHB450* ISHB450* ISWB ISWB COST OF TOTAL QTY. BRACING OF STEEL IN SYSTEMS TONNES (40000) P a g e

9 Fig.8 : Comparisionof Steel Consumption for Conventional Bracing And Buckling Restrained Bracings Fig.7 : Cost comparision of Conventional Bracing and Buckling Restrained Bracings VII. CONCLUSIONS 1. The software analysis shows that for conventional bracing as they are weak in taking compressive forces, heavy bracing sections are required, thus they become uneconomical. 2. The project shows that buckling restrained braces which sustain tension as well as compression effectively by using less amount of steel. 3. The results show that the displacement of braced models is nearly 39% less than that of unbraced model. 4. The steel quantity reduces by 44% when BRBs are used instead of conventional bracing systems. 5. From the cost analysis it can be seen that BRBs are more economical than conventional bracing and reduce the cost upto 43%. 342 P a g e

10 6. It can be seen that the response of the structure can be greatly altered beneficially by using the bracing systems and especially by BRBs. 7. Thus, from the overall paper it can be seen than BRBs are more effective, efficient and economic than conventional bracing systems. REFERENCES [1]. Comparison of Different Bracing Systems for Tall Buildings(2014),Z.A.Siddiqi,Rashid Hameed,Usman Akmal [2]. Advances in design requirements for Buckling Restrained Braced frames (2014), K. S. Robinson, Star Seismic, Park City, UT, USA. [3]. Buckling Restrained Braces For Vibration Control Of Building Structure(2010), W. N. Deulkar, C. D. Modhera & H. S. Patil [4]. Design Procedure For Buckling Restrained Braces To Retrofit Existing R.C. Frames.T. Albanesi, A. V. Bergami and C. Nut [5]. Buckling restrained braces research and implementation in Taiwan (2013) K. C. Tsai1, P. C. Lin, A. C. Wu, and M. C. Chuang 343 P a g e