1. SEISMIC FORCE RESISTING SYSTEMS AND RESPONSES OF CONCRETE BUILDINGS TO SEISMIC FORCES

2. TOPICS COVERED Building Configuration Response of Concrete Buildings
Seismic Force Resisting Systems
Building Configuration
Response of Concrete Buildings

3. SEISMIC FORCE RESISTING SYSTEMS
Basic structure systems that may be used to resist earthquake forces include
Moment-Resisting Frame Systems
Bearing Wall Systems
Dual System
Building Frame System
Inverted Pendulum System

4. MOMENT-RESISTING FRAME SYSTEMS
A structural system with complete space frame for gravity loads
Lateral forces are resisted by flexural action of frame members
Entire space frame or portion may be designated as seismic-force-resisting system
Three types of detailing of frames are possible based on the effects of seismic forces
Ordinary RC frames
Intermediate moment frames
Special moment frames

5. BEARING WALL SYSTEMS
A structural system without complete space frame for gravity loads
Bearing walls provide support for gravity loads
Lateral loads are also resisted by the bearing walls acting as shear walls
Two types of detailing of walls are possible based on the effects of seismic forces
Ordinary RC shear walls
Special RC shear walls

6. DUAL SYSTEMS A structural system with the following features
Complete space frame for gravity loads
25% base shear resisted by space frames
Resistance to lateral force is provided by the shear walls
Moment frames are either special or intermediate frames
Different combinations of shear walls are possible including
Ordinary RC shear walls
Special RC shear walls

7. BUILDING FRAME SYSTEMS
A structural system without complete space frame for gravity loads
Lateral loads are resisted by the shear walls
No interaction between the shear wall and frames is considered in the lateral load analysis
Two types of detailing of walls are possible based on the effects of seismic forces and building height
Ordinary RC shear walls
Special RC shear walls

8. INVERT PENDULUM SYSTEMS
Structures that have a large portion of mass concentrated near the top
Essentially one degree of freedom
Little redundancy and overstrength
Inelastic behaviour concentrated at the base
Less energy dissipation capacity than other systems

9. BUILDING CONFIGURATION
Buildings having irregular configurations in plan and/or elevation suffered greater damage
Inelastic behaviour concentrates in certain localized regions in irregular structure
Structural elements deteriorate rapidly in these areas
Inelastic demand tend to be well distributed throughout a regular structure
Elastic analysis methods are not capable to accurately predict distribution of seismic demand in an irregular structure
Building with regular configuration are encouraged and highly irregular buildings are prohibited on sites close to active faults

10. PLAN IRREGULARITIES
Five different plan irregularities have been identified
Torsional irregularity
Re-entrant corners
Diaphragm discontinuity
Out-of-plan offsets
Nonparallel systems

11. PLAN IRREGULARITIES
Torsional irregularity

12. PLAN IRREGULARITIES
Re-entrant corners

13. PLAN IRREGULARITIES
Diaphragm discontinuity

14. PLAN IRREGULARITIES
Out-of-plan offsets

15. PLAN IRREGULARITIES
Nonparallel systems

16. VERTICAL IRREGULARITIES
Five different vertical structural irregularities have been identified
Stiffness irregularity-soft story
Weight (mass) irregularity
Vertical geometric irregularity
In-plane discontinuity in vertical lateral-force-resisting elements
Discontinuity in capacity-weak story

17. VERTICAL IRREGULARITIES
Stiffness irregularity-soft story

18. VERTICAL IRREGULARITIES
Weight (mass) irregularity

19. VERTICAL IRREGULARITIES
Vertical geometric irregularity

20. VERTICAL IRREGULARITIES
In-plane discontinuity in vertical lateral-force-resisting elements

21. VERTICAL IRREGULARITIES
Discontinuity in capacity-weak story

22. RESPONSE OF CONCRETE BUILDINGS
A reliable load path is necessary to transfer lateral forces to the foundation
Earthquake forces are resisted by either walls or frame elements
Foundation components transfer the force to the earth
Key elements of the load path through the structure include
Diaphragm
Walls
Frames
Foundations
Connections are also important components of the chain
Resistance of building is as strong as the weakest link in the path

23. DIAPHRAGM RESPONSE
Diaphragms typically span between shear walls of concrete
Respond like deep beams bending in their own plane under lateral forces
Forces produced at the diaphragm edge include
Shear
Tension or compression
Seismic forces acting perpendicular to the long side produce shear forces acting in the opposite direction
Shear forces are transferred to the shear walls
Tension develops in the chord and compression develops on the side on which seismic forces act

24. DIAPHRAGM RESPONSE
Forces similar to chord forces also develop around openings
Openings may need to be reinforced with additional longitudinal steel
Shear forces at the diaphragm edge are transferred through shear-friction
Another mechanism of shear transfer is dowel action
The assumption here is that reinforcement acts as anchor bolt in shear

25. SEISMIC RESPONSE OF SHEAR WALLS
Shear walls resist gravity loads and in-plane lateral forces
They are like vertical cantilever deep beams
Shear force from diaphragm causes bending moment and shear force in the plane of the wall
Tendency to overturn and slide is resisted by the foundation
Bending moment increases from top to bottom of a building and causes tension and compression forces in the wall plane
Seismic response of short stocky shear wall is governed by shear
Response of taller walls is governed by flexure

26. SEISMIC RESPONSE OF SHEAR WALLS
For walls with H/L between 1-2 response depends on several factors including amount of shear reinforcing
Shear dominated response is characterized by inclined (x-shaped) cracking pattern
The wall can loose strength rapidly with little warning

27. SEISMIC RESPONSE OF FRAMES
Response of frames is different than shear walls to lateral forces
Frame resists by being deformed by lateral forces due to the rigidity of the beam-column joints
Beams and columns bend due to this rigidity
Tension stresses caused by the bending must be resisted by the reinforcement
Bending also causes vertical shear forces in beams and horizontal shear forces in columns
Vertical shear reinforcement is needed in beams and horizontal shear reinforcement in columns

28. FOUNDATION RESPONSE Foundations can be shallow or deep
Shallow foundations are supported by vertical pressure of earth
Foundation types include
Square or rectangular spread footings
Continuous strip footings
Deep foundations consists of piles made of
Wood
Steel
Concrete
Piles can be poured in place or driven piles

29. FOUNDATION RESPONSE
Piles are supported by end bearing and skin friction
Connected together by ties, grade beams or slabs on grade
Shear forces are transferred from walls and frames to the foundation
Dowels in foundation must match the vertical reinforcement in walls and frames

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