This document analyzes the seismic behavior of structures during pounding. Pounding occurs when adjacent structures collide during earthquakes due to insufficient separation distance and differences in their dynamic characteristics. Three cases were modeled: 1) Two equal buildings, 2) Buildings of different heights but equal floor levels, 3) Equal height buildings but different floor levels. Results showed pounding increases displacements and accelerations, and causes large inertial forces. Irregular positioning or small separation distances risk inaccurate seismic design by ignoring pounding effects. Proper separation is needed to allow free movement and accurate structural design.

1. SEISMIC BEHAVIOR ANALYSIS OF
STRUCTURES DURING STRUCTURAL
POUNDING
ARSIOLA KAPRI
AGIM SERANAJ
Date:October12,2017

2. Agenda
Introduction
The phenomenon
“Pounding Effect”
o Case I
o Case II
o Case III
Results
o Case Analysis
o Modelling and inputs
Methods
Conclusions

3. Introduction
In metropolitan areas, but not only, where the cost of land is very high, structures are built very close to each
other. Due to this closeness, they collide with each other when subjected to earthquake or any vibration.
So, analysing the behaviour of structures during the impact, because of a powerful seismic action, in cases
of an insufficient separation distance between them, considering different configurations and possibilities of
occurrence of the phenomenon caught our attention and become the objective of our study.
(Northern California, 1989) (Mexico City,1985) (L’ Aquila, 2009)

4. Pounding Effect
During earthquakes, structures’ mass and rigidity affects its behaviour. As result, it is nearly impossible to
construct buildings with similar seismic behaviours, and during the vibration, with different modes and
periods, they enter in contact with each other.
Kinetic energy transfer, in the moment of impact, from one structure
to the other, leads to great inertial forces.
These additional forces can cause either architectural and structural
damages or collapse of the whole structure.
Pounding Effect refers to collision between adjacent structures during earthquakes. It is
induced when structures with different dynamic characteristics, having insufficient
separation distance enter in contact.

5. Pounding Effect
Factors behind this complex phenomenon:
o structure heights and their differences;
o separation distance between structures;
o collision’s points location;
o used ground acceleration;
o lateral load resisting system;
o fundamental periods of structures;
o type of structural material and the material that fills the space
between them, (if it is used);
o floor elevations;
o used damping mechanism;
o type of inducted vibrations, (in or out of phase);
o the positioning of the structures (standalone or in row);
o the lateral eccentricity and twisting motion (if any), etc.

6. Methods
Time history analysis, (FNA)
The model was accepted:
o With a predetermined
number of nonlinear
elements;
o Initially linear-elastic;
o The nonlinear
behaviour was
identified through link
elements.

7. Methods
Case analysis
Case I: Two adjacent
buildings, (5+1) floors,
with equal heights and
floor levels
(a)
(b)
Case II: Two adjacent
buildings with different
heights but with equal
floor levels
(a)
(b)
Case III: Two adjacent
buildings with equal
floor heights but
different floor levels
(a) (b)

8. Methods
Modelling and Inputs
o For modelling the space between two buildings was used an element called: “Gap element”
• nonlinear element;
• it is placed between two adjacent buildings;
• it is activated when two buildings move toward each other;
o Seismic acceleration of the
ground was applied on the
model as time function, (El
Centro earthquake).
o Ritz vectors
were used.
o We considered three load combinations:
• 1.35 Dead+ 1.5 Live
• 1 Dead+ 0.4 Live+ 1 Earthquake load
• 1 Dead+ 0.4 Live-1 Earthquake load

9. Results
Case I
(a) Two adjacent buildings, (5+1) floors, with equal structural and dynamic characteristics
(b) Two adjacent buildings, (5+1) floors, with different structural systems
• At subcase (Ia) structures do not enter in
contact.
• For close characteristics the differences in
values are smaller.
• For different structural and dynamic
characteristics, differences in values are clearly
noticed.
• At subcase (Ib) it is noticed the increase of
displacements and accelerations for both
structures.
• Smaller increase is noticed for the structure
with dual structural system.

10. Results
Case I
• As a result of kinetic energy transfer, in the moment of contact, large inertial forces are created.
• The graphics of pounding forces and the number of contacts preserve the same shape but increase
significantly in values.
• The biggest force was achieved at the highest connection and the smaller force at the lowest one.
• The largest number of contacts is noticed in the upper floors.

11. Results
Two adjacent buildings with different heights but equal floor levels, (same structural system or not)
• Displacements for both structures are decreased.
• Immediate pulsing of acceleration in the opposite direction of movement it is noticed.
Case II

12. Results
• Graphics of pounding force and the number of contacts change shape for the two last floors.
• The lower structure is pounded from the adjacent one in the whole height.
• The opposite happens with the highest structure, the two last floors of which are not pounded directly,
but manifest changes in behaviour as result of pounding in lower floors.
Case II

13. Results
Case III
Two adjacent buildings with equal heights but different floor levels, (same structural system or not)
• Great shear forces are created in the middles of floor columns, (most dangerous case).
• Displacements and accelerations of one of the structures decrease and with the same scale
the displacements and accelerations of the other structure are increased.

14. Results
Case III
• A great number of contacts were noticed not only at the highest level but also at the lower ones.

15. Conclusions
• In cases when for different reasons we are obligated to place objects close to each other, with small
dividing space or equal to zero, must be studied the impact that pounding may have in seismic reaction
of the structures and measures need to be taken for proper designing.
• For an irregular positioning, (and other cases), of the structures, without providing the necessary
separation distance between them, ignoring the Pounding Effect would risk the accuracy of seismic
design.
• The comparison of the behaviours between them in terms of displacements, accelerations and other
parameters can be helpful in a more accurate design of the structures.
• During the Pounding effect are noticeable changes in displacements, accelerations of floors and forces
in the columns.
• It is very important the dividing space necessary to allow the free displacement movement of adjacent
structures in order to evolve an expected seismic reaction and a correct design of the structures.

16. Thank you!