Effect of Earthquake-Induced Structural Pounding on the Floor

Accelerations and Floor Response Spectra of Adjacent Building

Structures

PEDRO FOLHENTO1, RUI CARNEIRO DE BARROS2, MANUEL BRAZ-CÉSAR3

1CONSTRUCT, Faculdade de Engenharia da Universidade do Porto,

FEUP, Rua Dr. Roberto Frias, s/n 4200-465, Porto,

PORTUGAL

2CONSTRUCT, Faculdade de Engenharia da Universidade do Porto,

FEUP, Department of Civil Engineering – Structural Division,

Rua Dr. Roberto Frias, s/n 4200-465, Porto,

PORTUGAL

3CONSTRUCT, Instituto Politécnico de Bragança,

ESTiG, Campus de Santa Apolónia - 5300-253, Bragança,

PORTUGAL

Abstract: - The influence of earthquake-induced structural pounding among buildings is paramount in the

seismic analysis and design of structures. The recognition of such a phenomenon has been growing in the last

decades. The search for ways to understand and mitigate the consequences of these structural collisions in

building structures is the primary goal of the investigation of earthquake-induced building pounding. This

phenomenon is known for increasing the floor accelerations, mainly where pounding occurs, implying

significant local damage. These collisions cause short-duration acceleration pulses that may compromise the

building structure and the non-structural elements within the building’s stories. Non-structural elements

supported by the structure’s floors under earthquake-induced pounding instances may present a risk to human

lives and/or human activity. Hence, the influence of earthquake-induced pounding in the floor response spectra

of two adjacent reinforced concrete structures with inelastic behavior is assessed by varying the number of

stories and their separation distance. Pounding greatly influenced the floor acceleration spectra, increasing the

spread of accelerations over a broader period range, particularly exciting low to moderate periods of vibration.

Key-Words: - Seismic analysis, Reinforced concrete structures, Building structural pounding, Non-linear

inelastic behavior, Finite elements, Floor acceleration response spectrum analysis, Non-

structural elements.

Received: April 17, 2023. Revised: February 19, 2024. Accepted: March 15, 2024. Published: April 23, 2024.

1 Introduction

The influence of earthquake-induced structural

pounding among buildings is paramount in the

seismic analysis and design of structures. This

phenomenon leads to unclear patterns or trends of

the colliding structure’s dynamic responses, which

explain contradictions in research results, [1]. The

recognition of such phenomenon has grown in the

last decades, contributing to a better understanding

of building structural pounding and mitigation of its

negative consequences, constituting the main goals

in studying such occurrences in seismic events.

In this context, several mitigation measures and

techniques have been proposed in the literature, [2].

Among them, the interposition of a flexible layer,

bumpers, or shock absorbers between the adjacent

structures, [3], [4], may reduce or soften the

acceleration spikes verified in the colliding floors.

Indeed, this phenomenon is known for increasing

the floor accelerations, particularly where pounding

occurs, implying significant local damage. Floor

acceleration increases caused by pounding can reach

ten times or more than the case with no pounding,

[5], [6], [7], [8]. These collisions cause short-

duration acceleration pulses that may compromise

the building structure and the non-structural

elements within the building’s stories. According to

Eurocode 8, [9], non-structural elements (secondary

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systems) are the appendages (e.g., architectural

components, mechanical or electrical equipment,

partition or curtain walls, etc.) of the buildings, i.e.,

the building’s content without a structural or load-

bearing function, that in case of failure, may pose a

risk to human lives and/or activity, and/or to the

structure (primary system). In addition, Eurocode

proposes an expression as a simplification to

account for the effects of the seismic action on the

structural elements. This expression comprises a

parameter related to the determination of the

pseudo-spectral acceleration acting on a non-

structural component supported by a given floor.

Such simplification would not be appropriate for

essential non-structural elements, [9].

Limited studies have addressed floor spectra

analysis while considering structural pounding

between floors of adjacent buildings, [5], [10], [11],

[12]. An investigation has considered structural

collisions induced by earthquakes between buildings

as multiple degrees of freedom systems to assess,

among other effects, the influence of pounding on

the floor accelerations and floor response spectra,

[5]. The author verified significant increases in the

floor accelerations due to pounding and increases in

the high-frequency range of floor acceleration

spectra. In another study, it was analyzed the

seismic pounding retrofit of adjacent buildings, [10],

verifying the effectiveness of the proposed pounding

reduction devices in the high-frequency content of

floor acceleration response spectra. The use of

different impact models to simulate pounding forces

between three adjacent building structures has been

investigated, concluding that floor acceleration

response spectra are sensitive to the impact model

chosen, [11]. A sensitivity analysis was performed

between adjacent structures considering the

influence of pounding on the floor acceleration

response spectra, [12]. The authors concluded that

the impact impulses govern the floor response

spectra in the case of severe pounding.

This paper investigates the effect of earthquake-

induced structural pounding on the floor

accelerations and floor response spectra of two

adjacent reinforced concrete (RC) structures with

variable separation distances. Pounding is

considered to happen among floors, and five

different configurations for the RC buildings in

terms of the number of stories will be assessed. This

will allow the understanding of how the different

number of stories and the separation of structures

may influence the non-structural elements'

performance, essential for the safety of human lives

and services during a seismic event causing floor

collisions.

2 Problem Formulation

The present section comprises the structural and

dynamic characteristics of the buildings considered

in the five pounding scenarios. The choice of three

recorded seismic signals adjusted to a specific

seismic region also accounts for the seismic effect in

the non-linear analyses.

Finally, the impact model is described to

compute the pounding forces' magnitude.

2.1 Building Structures’ Models

This parametric investigation is based on five

scenarios of adjacent RC structures with variable

separation distances, as depicted in Figure 1.

(a) First scenario (L3R3);

(b) Second scenario (L3R4);

(d) Fourth scenario (L4R3);

(e) Fifth scenario (L5R3);

Fig. 1: Pounding scenarios of RC structures under

investigation

Building 1 is always represented on the left side,

while Building 2 is on the right, as shown in Figure

1 and Figure 2. The plan view of the two buildings

can be seen in Figure 2. Building 1 is intended to

have a more flexible layout, having structural

elements with smaller cross-sections (columns

25x25cm2; beams 35x25cm2) and slender slabs

(15cm). Conversely, Building 2 has bigger cross-

sections (columns: 30x30cm2, beams 40x30cm2) and

thicker slabs (20cm). Every story has 3m of height.

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Fig. 2: Plan view of the adjacent RC building

structures and the impact model

The six different fixed-base RC structures were

designed according to the Eurocode, [9], [13], [14],

using class C25/30 concrete and steel rebars of

S500. The seismic design was performed following

the weak-beam-strong-column philosophy (capacity

design), considering the seismic region of Portimão,

Portugal, assuming a soil type A, class of

importance II, 5% damping, and medium ductility

class. Second-order geometric effects are neglected

in the design and analysis processes.

A live load of 2.0kN/m2 and 0.40kN/m2 was

uniformly distributed over the floors and roof of the

structures, respectively, [13]. Furthermore, a super

dead load of 1.5kN/m2 was applied evenly

distributed over the floors of the structures. A

distributed load of 2.5kN/m on the exterior beams of

the stories (excluding the top story) was considered

to account for the mass of single-leaf exterior infill

walls. Nevertheless, their additional stiffness and

interaction with the main structure in the dynamic

analyses are neglected for simplicity reasons.

For the calculation of the mass per story

(excluding the roof) participating in the dynamic

analyses, only 15% of the floor's live load is

assumed. Hence, Building 1 has 56970kg and

48965kg of story and roof mass, respectively; and

Building 2 has 95788kg and 84476kg of story and

roof mass, respectively.

These scenarios were created from the

configuration of equal heights (L3R3), varying the

number of stories (3 to 5 stories) to understand how

structures with unequal heights are affected by

pounding. Table 1 shows the buildings’ fundamental

periods.

Table 1. Fundamental periods of the buildings.

Sto

ries

Bui

lding

0.5438 s

0.4121 s

0.7195 s

0.5441 s

0.8969 s

0.6778 s

The finite element numerical models are built in

OpenSees, [15], using the fiber model with finite

length lumped plasticity at the critical regions of

plastic hinge formation (Figure 3), i.e., at the ends

of the structural elements. The steel reinforcement

from the design process is applied in these regions,

while an elastic material is assumed at the elements’

center. The constitutive laws of confined and

unconfined concrete with a compressive strength of

33MPa and steel with a yield strength of 500MPa

are exemplified in Figure 4.

Fig. 3: Fiber model finite-length plasticity for the

example of the three-story structure of Building 1

Fig. 4: Constitutive laws assumed for the materials

used in the fiber model

For the concrete material, the Kent-Park-Scott

model, [16], (Concrete01) was used, and for steel

material, the Giuffré-Menegotto-Pinto model, [17],

(Steel02).

2.2 Seismic Effect

The selection of a set of seismic signals representing

the site characteristics is important to account for

the variability of the seismic effect in non-linear

dynamic analyses. Hence, according to Eurocode 8,

a set of three recorded seismic signals, [18], is

considered and adjusted to match the elastic design

response spectrum of Portimão, Portugal's seismic

[m]4

3.75 [m]

3.75

Gap

m1cimp

kimp

Building 2Building 1

3.75

Impact model

xg(t)

Beam

section

Column

section

Footing rebar

Face rebar Corner

rebar

Top

rebars Top support

rebars

Bottom

rebars

3 legged

hoop

Building 1

(Structure)

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region, following the characteristics previously

described in the design process. Table 2 shows the

characteristics of the original and modified signals.

Table 2. Characteristics of the real and adjusted

seismic signals considered, [19]

Name and station

Loma Prieta,

1989

WAHO-0

RSN811

Northridge,

1994

ArletaNF-360

RSN949

El Centro,

1940

Sta9-180

RSN6

Magnitude, Mw

6.93

6.69

6.95

PGA (m/s2)

Real

3.66

3.02

2.76

Adjusted

2.39

2.82

3.00

Arias intensity

(m/s)

Real

3.70

1.17

1.56

Adjusted

1.20

1.81

2.58

Dominant period

(s)

Real

0.12

0.24

0.46

Adjusted

0.34

0.54

0.46

Significant

duration (s)

Real

10.47

13.46

24.19

Adjusted

10.84

21.40

24.69

Figure 5 graphically shows the adjustment of

the acceleration response spectra to the above-

mentioned target response spectrum.

(a) Original and target response spectra;

(b) Adjusted or matched and target response spectra.

Fig. 5: Response spectra adjustment

The adjustment process is carried out using the

software SeismoMatch, [19], which modifies the

frequency content of the accelerograms using signal

processing techniques. These techniques intend to

reproduce certain response spectra, viz, design

response spectra.

The algorithm used by this software is based on

the addition of wavelets in the time-domain

acceleration signal to attain the desired spectral

result adjusted to the target response spectrum, [20],

[21]. Wavelet addition constitutes a correction more

focused on the time domain, inducing less energy

and preserving the non-stationary features of the

acceleration signal, [8].

2.3 Impact Model

The pounding forces generated from the collisions

between adjacent structures with different dynamic

properties are calculated using the Kelvin-Voigt or

linear viscoelastic impact models, [22], as

represented in Figure 2.

In OpenSees, the ViscoelasticGap material,

[23], is used. However, it was modified to neglect

the unnatural negative pounding force verified at the

end of the impacts.

Impact models are zero-length compression-

only elements, constituted by a massless spring and

a dashpot in parallel having thus, the advantage of

being represented by fewer parameters (Impact

stiffness, kimp, and coefficient of restitution, CR),

although their estimation may be difficult,

constituting the main disadvantage of these models.

The use of these impact elements is generally

based on oversimplified assumptions of the state of

stress of the colliding bodies under the passage of

stress waves, justifying the mass-spring-dashpot

model with reasonable accuracy.

Other impact models have been recently

developed by different authors, presenting great

predictions of the pounding forces between

buildings, [24], [25], [26], [27], [28].

The impact stiffness was assumed to be the

same as the axial stiffness of the stiffer floor. The

coefficient of restitution is taken as 0.65 (usual in

structural applications) and was used to determine

the impact damping constant, cimp, as follows, [22]:

 

 

where

imp imp imp

imp

c=ξk

m +m

- CR

ξ=

π + CR

(1)

In which mi is the lumped mass of one story of a

Building i, and ξimp is the impact damping ratio.

These parameters are then included in the piecewise

function that computes the pounding force

depending on the interpenetration depth δ (=x1-x2-

Gap), the condition of impact,

       

 

for 0

0 for 0

imp imp

kδ t + c δ t , δ t >

f t = δt 











(2)

A relatively small time step must be undertaken

to capture an impact between adjacent building

structures. However, very small time steps condition

the feasibility of parametric studies since these are

incompatible with computationally demanding

simulations. To address this, a condition of

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proximity was included in the non-linear dynamic

time history analyses. A fraction of the gap size

triggers this condition of proximity of the adjacent

buildings. The normal time step was assumed to be

5×10-3 s, and when a collision is approaching or

happening, the time step is reduced to 2×10-4 s.

The simulation time is considerably reduced,

and the accuracy in capturing and calculating the

pounding forces is maintained. Still, care should be

taken for discrepancies between these time steps,

which may lead to convergence problems.

3 Results and Discussion

A series of non-linear time-history analyses were

carried out.

The results of these analyses will be presented

and discussed in terms of the number and magnitude

of collisions, floor accelerations, and floor response

spectra for the five pounding scenarios considered

and across all the values considered for the gap size

or separation distance.

The gap size values were assumed to vary

between the nearly zero gap (5 mm, here referred to

as “zero-gap”) until no collisions were verified.

3.1 Number and Magnitude of Pounding

Forces

Figure 6 presents the number of impacts verified for

the three adjusted seismic signals and pounding

scenarios over the gap sizes considered. Similarly,

Figure 7 shows the results regarding the magnitude

of pounding forces.

The number of collisions and their magnitude

naturally depends on the separation distance.

Nevertheless, a zero-gap size does not always

present the highest magnitude of pounding force,

though it is always the case with a greater number of

impacts.

A scenario that presents a greater difference in

the number of stories will be more susceptible to

more collisions and of a larger magnitude than a

scenario with an equal number of stories and the

same height. In particular, scenario L5R3, an RC

structure with a more flexible layout and a greater

number of stories (L5) than the adjacent structure

that has a stiffer structural configuration and fewer

stories (R3), performs worse than the opposite

scenario, L3R5.

Fig. 6: Number of impacts per story for the different

scenarios studied

Fig. 7: Maximum pounding force per story for the

different scenarios studied

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The top story consistently exhibits the highest

magnitude and number of collisions since it

experiences the largest relative displacements.

The number of impacts decreases significantly

with the increase of the gap size. The magnitude of

the pounding forces also decreases with the

increasing gap size. However, it is not as evident as

with the number of impacts.

Overall, the adjusted seismic signals tend to

present a similar trend with gap size variation. Loma

Prieta earthquake shows a smaller number and

magnitude of impacts, due to the reduced duration

and different dominant periods of vibration (Table

2).

Figure 8 presents the case with the biggest

number of collisions and higher magnitude of the

pounding force. Figure 9 shows the first scenario

that presents the highest magnitude of pounding

force. Moreover, Figure 10 shows the pounding

cycles, typical of the Kelvin-Voigt impact model

without the tensile force, corresponding to Figure 8

and Figure 9.

Fig. 8: Displacements and pounding forces time

history of the colliding stories in scenario L5R3

with zero-gap size under the modified Northridge

earthquake

Fig. 9: Displacements and pounding forces time

history of the colliding stories in scenario L3R3

with 2.5 cm of gap size under the modified El

Centro earthquake

Fig. 10: Pounding cycles of the cases presented in

Figure 8 and Figure 9, respectively

These collisions are thus associated with a steep

variation of the adjacent buildings’ velocity

corresponding to acceleration spikes, to which

significant local damage is implied.

The following two subsections will address how

these acceleration spikes influence each structure

and non-structural elements supported by the floors.

3.2 Floor Accelerations

The acceleration spikes’ values are proportional to

the pounding forces’ values, as seen in the

comparison of Figure 9 and Figure 11. Hence, the

same conclusions regarding the gap sizes can be

derived from the previous sub-sections. Figure 11

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and Figure 12 present examples of the floor

acceleration time histories in two of the scenarios

studied. In these figures, it is possible to witness the

sudden increases in acceleration due to building

pounding. A zero-gap size scenario will present a

higher number of acceleration spikes, and of

significant amplitude, constituting one of the worst

scenarios in pounding.

Fig. 11: Acceleration time-histories for the first

scenario with a 2.5 cm gap size under the modified

El Centro earthquake

Fig. 12: Acceleration time-histories for the last

scenario with zero-gap size under the modified El

Centro earthquake

Figure 13, Figure 14, Figure 15, Figure 16 and

Figure 17 present the maximum absolute

acceleration ratio between the case with and without

pounding for every scenario under the modified El

Centro earthquake and for some of the gap sizes.

Conclusions, however, will be reflected for

every seismic signal studied and gap size. The

positive and negative signs reflect the inbound and

rebound directions of each building, as can be

confirmed by Figure 8, Figure 9, Figure 11 and

Figure 12, e.g., a negative acceleration in Building 1

corresponds to its rebound direction.

Fig. 13: Maximum absolute acceleration ratios for

the first scenario under the modified El Centro

earthquake

Results from every seismic signal show that

absolute accelerations can suffer sudden and

momentary increases due to pounding forces that

can achieve 80 times those without collisions.

Fig. 14: Maximum absolute acceleration ratios for

the second scenario under the modified El Centro

earthquake.

The absolute acceleration ratios reveal that

Building 1, possessing the most flexible layout, is

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significantly more vulnerable to pounding forces.

Building 1 presents increases in the maximum

absolute acceleration concerning the case without

pounding that are higher (scenarios L3R3, L3R4,

L4R3, and L5R3) or approximately equal (L3R5) to

the ones verified in Building 2.

Fig. 15: Maximum absolute acceleration ratios for

the third scenario under the modified El Centro

earthquake

Accelerations are significantly affected in the

stories where pounding occurs and have little

influence in the stories without pounding, evident

when buildings have unequal heights (Figure 14,

Figure 15, Figure 16 and Figure 17).

Fig. 16: Maximum absolute acceleration ratios for

the fourth scenario under the modified El Centro

earthquake

The scenarios related to pounding between

buildings with different numbers of stories show

higher increases in absolute acceleration compared

with the L3R3 scenario. The exception is scenario

L3R4, which presents the smallest increases in

absolute accelerations compared with the cases

without pounding. This is justified by the

observation of the fundamental periods of the

structures (Table 1) that are nearly identical,

producing an almost in-phase response, which also

explains the reduced magnitude and number of

impacts (Figure 6 and Figure 7).

Fig. 17: Maximum absolute acceleration ratios for

the fifth scenario under the modified El Centro

earthquake

Regarding the effect of gap sizes, generally for

the different ground motions, one can verify that the

smallest separation distances do not always result in

the highest increases (Gap 2.5 – 6.0 cm) in absolute

acceleration, as can be verified in the scenarios

where the difference in the number of stories is

greater (scenarios L3R5 and L5R3).

Similar results were obtained among the seismic

signals. However, the El Centro earthquake

generally provided higher increases in story absolute

accelerations over a wider gap size range.

3.3 Floor Acceleration Response Spectra

The floor acceleration response spectra, or just floor

response spectra, are now derived for the different

scenarios, gap sizes, and ground motions mentioned

previously.

In addition to the threat to human lives and

activity, damage to non-structural elements during

seismic events may result in substantial economic

losses.

Several non-linear time-history analyses were

performed to assess the influence of pounding

forces in the adjacent building structures' floor

acceleration response spectra. The process

undertaken is now explained in the following

paragraphs, and conclusions are then withdrawn

based on the observation of graphic results.

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Following the non-linear time-history analyses,

the accelerations of the various floors of the primary

structures (Buildings 1 and 2) are computed and

recorded. A non-structural component is now

considered (the secondary element) as a single

degree of freedom (SDOF), supported by a floor of

the primary structure and characterized by a period

of vibration and a damping ratio. By subjecting the

SDOF component to a certain floor acceleration for

different values of the period of vibration and

recording the maximum acceleration value, the floor

acceleration response spectrum can be constructed.

The seismic demand of a non-structural element on

a certain floor is now known, assuming that the

dynamic interaction between the primary and

secondary components is insignificant.

The period of vibration is varied over a range of

values suitable to the structural and non-structural

components applications, and a damping ratio of 5%

is assumed.

Many factors influence the floor acceleration

response of building structures, viz., the structural

system, the building’s height, the fundamental

period of vibration of the structure, the dominant

period of the earthquake excitation, damping,

inelastic behavior, etc. [29]. Structural pounding

between adjacent buildings is another factor that

significantly influences the floor response spectra.

Figure 18 shows the comparison of the floor

response spectra for the first scenario without

pounding under the modified El Centro earthquake,

revealing the influence of the structures’ inelastic

behavior. Inelastic behavior tends to increase the

dominant period of the structures’ stories,

particularly true for the upper stories. In addition, it

reduces the magnitude of accelerations.

Fig. 18: Comparison of response spectra

Since the earthquake signals were adjusted to a

seismic region and the seismic effect was not

significant, the mean floor response spectra of the

three ground motions were obtained for the different

scenarios, and for most of the gap sizes considered.

The mean floor acceleration response spectra were

obtained for different gap sizes, accounting for

pounding until the gap size, where the absence of

pounding was verified. Figure 19, Figure 20, Figure

21, Figure 22 and Figure 23 show the graphic results

in a logarithmic scale.

The first and foremost conclusion that can be

withdrawn is the evident and expected increase of

story accelerations for higher modes (smaller

periods of vibration) due to pounding. This increase

becomes more pronounced for smaller gap sizes,

and as concluded in the previous results, the zero-

gap size is not always the worst-case scenario.

Depending on the scenario, gap sizes between 1 and

3 cm provided higher accelerations than the zero-

gap size (second and third stories of L3R3 and third

stories of L5R3).

Building pounding slightly reduced the

magnitude of floor accelerations for moderate, but

especially larger periods (from 0.5s and 1.0s), more

evident in Building 1 in scenarios L3R5, L4R3, and

L5R3.

Non-structural elements in the colliding stories

characterized by higher frequencies or low periods

(mostly in periods between 0.01s and 0.25s) will

thus be very susceptible to events of structural

pounding, particularly true for scenarios in which

Building 1 is the tallest structure.

The shape of the floor acceleration response

spectra is completely changed in the range of low

periods when pounding occurs. Not only the stories

under impacts are affected, but the stories above are

also influenced by acceleration rises of twice the

magnitude of the case without pounding (fourth

story of scenarios L3R5 and L4R3, and the fourth

and fifth stories of scenario L5R3). For the same

reasons explained in the previous subsection,

scenario L3R4 leads to a phase synchronization of

both buildings, resulting in only a slight influence in

the stories above and below the collisions. However,

substantial increases in floor acceleration at the

colliding stories are still verified.

Scenarios in which the buildings have different

numbers of stories generally presented higher floor

accelerations across the various gap sizes

considered. The gap size plays a vital role in the

floor response spectra. An adequate separation

distance may reduce substantially the floor

accelerations and hence reduce damage.

Nevertheless, a gap size close to the no-pounding

case still presented high floor accelerations on the

colliding stories that are susceptible to causing

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damage to non-structural components, e.g., the gap

size of 9cm in the third to fifth scenarios.

Comparing the floor response spectra between

the two building structures, one can verify that a

building with a more flexible layout (Building 1)

will be more susceptible to pounding instances than

a structure with a stiffer layout (Building 2).

Fig. 19: Floor response spectra of the first scenario

(L3R3) for different gap sizes

Fig. 20: Floor response spectra of the second

scenario (L3R4) for different gap sizes

This can be verified by comparing the two

buildings in the first scenario (Figure 19) and the

opposite scenarios of an unequal number of stories,

i.e., L3R4 with L4R3 (Figure 20 and Figure 22), and

L3R5 with L5R3 (Figure 21 and Figure 23).

Fig. 21: Floor response spectra of the third scenario

(L3R5) for different gap sizes

Fig. 22: Floor response spectra of the fourth

scenario (L4R3) for different gap sizes

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Fig. 23: Floor response spectra of the fifth scenario

(L5R3) for different gap sizes

Building 1 will be more vulnerable to pounding,

presenting increases in the floor acceleration for a

wider range of periods of vibration (low to moderate

periods), as can be verified in scenarios L4R3 and

L5R3.

4 Conclusion

The present study investigated the influence of

earthquake-induced structural pounding on the floor

accelerations and floor acceleration response spectra

of two building structures with a varying number of

stories and separation distances. Different scenarios

were derived based on the number of stories. It was

verified that adjacent buildings with a different

number of stories led to a higher number and

magnitude of pounding forces, which will influence

their floor acceleration response significantly. It was

observed that the peak absolute acceleration

suffered sudden increases due to pounding forces of

approximately 80 times the peak acceleration

without pounding. Pounding forces significantly

altered the shape of the floor response spectra in the

low period range (between 0.01s and 0.2s).

Substantial damage in non-structural elements may

thus be expected, particularly in the colliding

stories. Building 1, characterized by a more flexible

layout than Building 2, was more vulnerable to

pounding forces, revealing increases in floor

acceleration for a broader range of periods of

vibration (low to moderate periods). Generally, a

very small gap size or no separation distance led to

the highest increases in floor accelerations due to

pounding. Although a gap size close to the case

without pounding offered similar results to the

smaller gap sizes in some cases, since only one

collision may generate a sudden acceleration

response of the buildings’ stories.

Hence, buildings adjacent to smaller structures

presenting a stiffer structural layout can be

particularly vulnerable to earthquake-induced

structural pounding. Non-structural elements

supported by colliding stories in these conditions

must be carefully designed to withstand sudden and

large acceleration spikes.

Future studies should address additional

pounding scenarios, i.e., more variations of the

number of stories, pounding between floors and

columns, and the consideration of more ground

excitations, assessing both near-field and far-field

ground motions. Further developments and

directions will also include the assessment of floor

accelerations and floor response spectra in the case

of adjacent buildings equipped with solutions to

mitigate earthquake-induced structural pounding,

such as rubber bumpers and/or passive and semi-

active vibration control devices.

Acknowledgments:

This paper is within the scope of the first author’s

Ph.D. degree in progress, financially supported by

the Portuguese Foundation for Science and

Technology (FCT) through the PhD grant reference

SFRH/BD/139570/2018, finished in April 2023,

under the program POCH (N2020 – P2020) and

subsidized by the European Social Fund (FSE) and

national funds from MCTES. This work was

financially supported by: Base Funding -

UIDB/04708/2020 with DOI:

10.54499/UIDB/04708/2020

(https://doi.org/10.54499/UIDB/04708/2020) of the

CONSTRUCT - Instituto de I&D em Estruturas e

Construções - funded by national funds through the

FCT/MCTES (PIDDAC).

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Manuel Braz-César

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Contribution of Individual Authors to the

Creation of a Scientific Article (Ghostwriting

Policy)

The authors equally contributed in the present

research, at all stages from the formulation of the

problem to the final findings and solution.

Sources of Funding for Research Presented in a

Scientific Article or Scientific Article Itself

This paper is within the scope of the first author’s

Ph.D. degree in progress, financially supported by

the Portuguese Foundation for Science and

Technology (FCT) through the PhD grant reference

SFRH/BD/139570/2018, finished in April 2023,

under the program POCH (N2020 – P2020) and

subsidized by the European Social Fund (FSE) and

national funds from MCTES. This work was

financially supported by: Base Funding -

UIDB/04708/2020 with DOI:

10.54499/UIDB/04708/2020

(https://doi.org/10.54499/UIDB/04708/2020) of the

CONSTRUCT - Instituto de I&D em Estruturas e

Construções - funded by national funds through the

FCT/MCTES (PIDDAC).

Conflict of Interest

The authors have no conflicts of interest to declare.

Creative Commons Attribution License 4.0

(Attribution 4.0 International, CC BY 4.0)

This article is published under the terms of the

Creative Commons Attribution License 4.0

https://creativecommons.org/licenses/by/4.0/deed.en

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WSEAS TRANSACTIONS on APPLIED and THEORETICAL MECHANICS

DOI: 10.37394/232011.2024.19.4

Pedro Folhento, Rui Carneiro De Barros,

Manuel Braz-César

E-ISSN: 2224-3429

Volume 19, 2024