        Slide 16 of 24

Notes:

HORIZONTAL FORCE DISTRIBUTION
• How are the horizontal forces distributed within the building?
• Newton’s Second Law of Motion states that force equals mass times acceleration.
• When the earthquake’s sudden movement of the ground accelerates the mass of the building, horizontal forces are created in the building.
• These forces are distributed throughout the building and are concentrated where the weight is: the floors, roofs and walls.
• Discussion of figure
• Two-story building
• Arrows on left of figure are the seismic forces based on the weight of the building.
• Arrow at the roof: represents the seismic force from both the roof weight and one-half of the weight of the walls between the second floor and roofline (F1).
• Arrow at the second floor: represents the seismic force of half the second floor weight and one-half of the weight of the first and second story walls (F2).
• Arrow at the first floor: represents the force at the first floor that is similarly calculated (F3).
• Arrow at the foundation level: Sum of all these forces that must be transmitted safely into the ground. This is why the foundation and cripple wall are so important (FSum=F1+F2+F3)
• Instructor: For clarity draw this out on board if facilities available.