THE ENGINEERING OF FOUNDATIONS A BOOK BY RODRIGO SALGADO POWERPOINT RESOURCES FOR CHAPTER 2 Contains...
Transcript of THE ENGINEERING OF FOUNDATIONS A BOOK BY RODRIGO SALGADO POWERPOINT RESOURCES FOR CHAPTER 2 Contains...
THE ENGINEERING OF FOUNDATIONSA BOOK BY RODRIGO SALGADOPOWERPOINT RESOURCES FOR
CHAPTER 2
Contains copyrighted material
THE DESIGN PROCESS
DESIGN GOALS
• Safety• Serviceability• Economy
The optimum foundation solution transfers the superstructure loads to the ground in a way that minimizes cost (construction and maintenance) over the life of the structures without sacrificing safety or performance
RELIABILITY-BASED DESIGN
LIMIT STATES DESIGN AND WORKING STRESS
DESIGN
TYPES OF LIMIT STATES
• ULTIMATE LIMIT STATES (ULS) : states at which a potentially unsafe/dangerous
condition is reached (typically structural failure, collapse, etc.)
• SERVICEABILITY LIMIT STATES (SLS) : states at which the structure or facility ceases to
perform as intended without loss of safety
Limit State
Nature of Limit State Consequences
IA-1 Classical bearing capacity failure (ULS)
Excessive movement/collapse of foundation causes serious damage, partial collapse or complete collapse of structure
IA-2 Structural failure of foundation element (ULS)
Column is inadequately supported by foundation element, punching through it; this causes serious damage, partial or complete collapse of superstructure
IB Excessive differential foundation settlement (ULS)
Excessive differential settlements create excessive additional loads in the structure, leading to structural damage
II Excessive settlement (total or differential) (SLS)
Excessive settlements lead to serviceability problems, such as access problems, damage to architectural finishings, etc.
III Stability failure of the whole foundation system or a subset thereof
Collapse mechanism develops that encompass the foundations for the building or structure or a part of the foundations (a classical example would be stability failure of a slope on top of which is founded a building)
Limit states for shallow foundation design
Working Stress Design
Ultimate load: the load that would lead to an ultimate limit state
Factor of Safety (FS)
d aQ Q
Ultimate load
ulta
FS
Allowable load
Design load
All load and resistance uncertainities are lumped in this single factor
Design or working load: the sum of the loads under consideration (unfactored)
ULTIMATE LIMIT STATES: LOAD AND RESISTANCE
FACTOR DESIGN
TOLERABLE FOUNDATIONMOVEMENTS
• Uniform Total Settlement
• Non-Uniform Settlement
• Tilting
Types of Settlement
Uniform Total Settlement
• No structural damage
• Damage at interface with utilities
• Access problems
• Drainage problems
Non-Uniform Settlement
• Structural– Cracking of beams/slabs/column
• Architectural– Cracking of panel walls– Door/window jamming– Uneven Floors
• Damage at interface with utility lines
• Access and drainage problems
• Excessive Tilting
Cracks Caused by Foundation Movement
• May have any direction, depending on the direction of the tensile strain (cracks are to the tensile strain)
• At a specific point of the structure, cracks have the same direction (contrast that with the web pattern observed in the case of shrinkage and drying)
• Appear on both sides of an element
Typical Building Structures
• Load Bearing Walls
• Frames