Structural Design_2012_LFRS.pptx - Chapter 4 u2013 Lateral...

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Chapter 4 – Lateral Force Resisting Systems Dr.-Ing. Girma Zerayohannes Dr.-Ing. Adil Zekaria 1 Dr.-Ing. Girma Z. Dr.-Ing. Adil Z
Chapter 4- Lateral Force Resisting Systems (LFRS) 4.1 Introduction All structures from the simplest to most complex must be provided with suitable LFRS Simple structures such as isolated elevated water tanks, sign boards, simple ware houses, etc. More complex structures buildings, bridges, waterfront structures, ships, etc. 2 Dr.-Ing. Girma Z. Dr.-Ing. Adil Z
Chapter 4- Lateral Force Resisting Systems A cantilever column or a pin supported column with lateral restraint at ground level play the role of LFRS for the similar structures Elaborate LFRS consisting of frames, walls, combinations of frames and walls, and other more complex systems are required for the more complex structures In the latter the vertical elements are rigidly connected with horizontal diaphragms enabling them to act in unison. 3 Dr.-Ing. Girma Z. Dr.-Ing. Adil Z
Chapter 4- Lateral Force Resisting Systems The most commonly used structural systems are: (i) Wall systems(ii) Frame systems(iii) Mixed wall-frame system4Dr.-Ing. Girma Z. Dr.-Ing. Adil Z
Chapter 4- Lateral Force Resisting Systems 4.2Wall System 4.2.1 Stable arrangement of walls (i) There must be at least 3 walls (ii) The axes of the walls should not intersect at a point (iii) All 3 walls should not be parallel 5 Dr.-Ing. Girma Z. Dr.-Ing. Adil Z
Dr.-Ing. Girma Z. Dr.-Ing. Adil Z 6 Chapter 4- Lateral Force Resisting Systems
4.2.2 Avoid high torsion Note: eccentric arrangement of wall is the most frequent cause of collapse during EQ Dr.-Ing. Girma Z. Dr.-Ing. Adil Z 7 Chapter 4- Lateral Force Resisting Systems
Chapter 4- Lateral Force Resisting Systems 4.2.3 Distribution of story shear among the walls 4.2.3.1 Statically determinate wall system Note: the story shear and the forces in the walls are statically equivalent 8 Dr.-Ing. Girma Z. Dr.-Ing. Adil Z
Chapter 4- Lateral Force Resisting Systems 9 Dr.-Ing. Girma Z. Dr.-Ing. Adil Z
Chapter 4- Lateral Force Resisting Systems Note: the story shear and the forces in the walls are statically equivalent V 2x = 100 kN V 1y + V 3y = 0 Torsion exerted by the story shear V x V 2x (5) + V 3y (8) – V 1y (10) = 0 V 3y = -500/18 and V 1y = 500/18 V 3y = -27.78 kN and V 1y = 27.78 kN 10 Dr.-Ing. Girma Z. Dr.-Ing. Adil Z
Chapter 4- Lateral Force Resisting Systems To reduce the magnitudes of the forces, (i) reduce the magnitude of the torsional moment 500 kNm by reducing the distance b/n the story shear V x and and the center of stiffness S that lies on wall axis of Wall 2 and (ii) Increasing the lever arm b/n walls 1 and 3, placing them as far apart from each other as possible ,i.e., at the periphery 11 Dr.-Ing. Girma Z. Dr.-Ing. Adil Z
Chapter 4- Lateral Force Resisting Systems 4.2.3.2 Statically indeterminate wall system More than three walls Additional compatibility conditions are to be considered to determine all shear wall forces 12 Dr.-Ing. Girma Z. Dr.-Ing. Adil Z

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