Lec03 Earthquake Force Using Response Specturum Method (1) (Earthquake Engineering هندسة الزلازل & Assc.Prof Nasser El-Shafey)

1. Lecture (3 )
Prepared by :
Assc. Prof Nasser El-Shafey
2016- 2017

2. When loose, saturated sands, silts, or gravel shaken, the
material consolidates, reducing the porosity and increasing
pore water pressure. The ground settles, often unevenly,
tilting and toppling structures that were formerly supported
by the soil
Liquefaction can cause problems as soil loses it’s ability to
resist shear and flows much like quick sand. Anything
relying on the substrata for support can shift, tilt, rupture, or
collapse.
1-Liquefaction
Damage of Structure As A Result Of Soil Problems

3. Liquefaction-
caused building
failure in Niigata,
Japan.
Liquefaction-
caused building
failure in Niigata,
Japan

4. Liquefaction
Adapazari, Turkey
1999
1995 Kobe, Japan earthquake,
increase pore pressure pushed
quay wall bridge near the west
end toward the river, allowing
the soil and western-most pier
to move one meter Eastward.

5. 2- Landslides
 When a steeply inclined mass of soil is Suddenly shaken,
a slip-plane can form, and the material slides downhill.
 During a landslide, structures sitting on the slide move
downward and structures below the slide are hit by falling
debris.

6.  In 1970 an earthquake off coast of Peru produced a
landslide began 80 miles away from earthquake.
The slide was large (estimated it's height at about
30 meters), killing more than 18,000 people.
Gravity retaining wall pushed
outward by landslide
One of about 75 homes
damaged as a result of the
Turnagain Heights slide.

7. Collapse of Tsu Wei Bridge
due to landslide during the
Ji Ji, Taiwan earthquake.
Slope instability –
Niigata, Japan 2004

8. IMPORTANCE OF GROUND CONDITIONS
Local soil conditions, particularly deep layers of soft soil as may
be found in river valleys or near estuaries, significantly amplify
shaking. They also modify the frequency content of seismic waves
by filtering out higher frequency excitations

9. DAMAGE AS A RESULT OF STRUCTURAL PROBLEMS
Engineers will occasionally design foundations to rock during
earthquakes as a way of dissipating energy and of reducing
the demand on the structure; however, when the foundation
is too small, it can become unstable and rock over
1. Foundation Failure
Large longitudinal
displacements of
bridge span causing
damage to abutment

10. 2. Foundation Connections
Structures need to be well anchored to foundation.
The longitudinal reinforcement did not have sufficient
development length to transfer the force to the footing

11. Soft Story
Soft Story
Soft First Story is
a discontinuity of
strength and
stiffness for
lateral load at the
ground level.
3. Soft Story
Soft Storey at Ground Floor

12. Soft story (stiffening structural elements which are present
in the upper stories are missing at the ground floor)

13. 1) Building Plan
2) Heavy mass at top should be avoided
Smaller water tank at top is preferred
NO YES

14. 3) Large projections not allowed 4) Floating column not allowed

15. Short Column

16. Short Column

17. 4. Torsional Moments
Curved, skewed, and eccentrically
supported structures often
experience a torsional moment
during earthquakes.

18. 5. Shear
Most building structures use shear walls or moment-resisting
frames to resist lateral forces during earthquakes. Damage to
these systems varies from minor cracks to complete collapse.
M. McKinley-ALASKA

19. 6. Flexural Failure
Flexural members are often designed to form plastic hinges
during large earthquakes. A plastic hinge allows a member to
yield and deform while continuing to support its load; however,
when there is insufficient confinement for reinforced concrete
members a flexural failure will occur instead.
Often, flexural damage
is accompanied by
compression or shear
damage, as the capacity
of the damaged area
has been lowered.

20. Flexural damage to
columns
Insufficient transverse
reinforcement to
prevent buckling of the
vertical reinforcement

21. 7. Connection Problems
When a bridge superstructure moves off its expansion joint
or when the connections between building columns and
beams fail, the result is too often the COLLAPSE of the
structure.

22. Special structural systems
 1-Rigid frames
 2-Shear walls
 3-Frames and cores
 4- Coupled framed-shear wall systems
 5- Cores-coupled shear wall
6- Tubular systems
7- Perforated tubes.
8- Tube in tube.
 9- Bundle tube.
Structural system Number of floors
Frames 20
Shear walls 35
Frames & shear walls 50
Cores-coupled shear walls 55
Perforated tube 60
Tube in tube 65
Bundle tube 90

23. The response spectrum is a convenient method for illustrating
and quantifying how natural period of vibration and damping
of a building affects its response to earthquake shaking.
SEISMIC FORCES

24. Natural period of vibration of building has huge effect on maximum horizontal
acceleration, and magnitude. Buildings with T=0.2 to 0.7 seconds are amplifying
ground acc. by almost a factor of 3.0. As natural periods become longer, from 0.7
to 1.7 seconds, peak accelerations reduce towards the same intensity as the peak
ground acceleration. Beyond 1.7 seconds, maximum accelerations continue to
diminish until at T=4.0 seconds building acceleration is only 0.3 of the maximum
ground acceleration.
Earthquake effects on buildings depend on:
Mass of structure Stiffness of structure
Ductility of structures Foundation type
Soil conditions Earthquake zone

25. 1.Symmetry: The structure is almost symmetrical in plan along
two orthogonal directions regarding the lateral stiffness and
mass distribution.
2.Recesses: shall not exceed 5% of the floor area.
3.Aspect Ratio: Lx / Ly <4.0.
4.Torsional regularity: eccentricity between C.M. & C.R.
< 15% Li for each direction (Li=Lx &Ly for x & y directions).
Plan Regularity
Quasi static analysis: Regular buildings; H <100 m & H/B <5.
Response Spectra: Regular buildings; H=100-150 m or H/B >5.
Dynamic analysis: Irregular buildings or H>150m.
Earthquake methods of Analysis

26. Elevation Regularity
All lateral force resisting elements such as cores,
shear walls or frames should be continuous from
foundation up to the last floor or setback or recess
level.
Stiffness and mass regularity: Difference between
two successive floors does not exceed 75% for Lateral
stiffness and 50% for mass.
Capacity Continuity: ratio between actual to
required resistance of columns in framed structures
should sustain for successive floor. The masonry
walls effect should be considered as such.
Vertical geometric regularity.

28. Simplified Modal Response
Spectrum Method