Conference PaperPDF Available


M.V. Requena-Garcia-Cruz1, A. Morales-Esteban1, P. Durand-Neyra1, E. Romero-
1Department of Building Structures and Geotechnical Engineering, University of Seville, Spain. Av.
Reina Mercedes, 2, 41012, Seville, Spain
{mrequena1, ame, percy, eromero13}
Most seismic vulnerability analyses do not consider the Soil-Structure Interaction (SSI).
However, it has been proved that SSI does not equally affect all types of structures and all
types of soils. The analysis of the state of the art reveals that SSI especially affects the per-
formance of mid/high-rise buildings under soft/inelastic soil conditions. This leads to overes-
timating the capacity of buildings and to obtaining unreliable results. This paper aims to
assess the soil influence in the seismic vulnerability analysis of a reinforced concrete (RC)
building. Three models of a real case study building have been determined (low-rise (real),
mid-rise and high-rise). A pre-code 1970s case study building, located in Huelva, has been
selected. This building shares typical constructive and structural characteristics with most RC
buildings constructed during that period. The 3D continuum model of the soil has been car-
ried out to simulate its nonlinear behaviour. The most probable soil profile has been defined,
observing a clayey soil. Therefore, the analyses have been performed under undrained condi-
tions. Nonlinear static analyses have been carried out to determine the seismic capacity of the
models through the finite element method (FEM). The damage has been assessed by means of
the local procedure, defined in the European seismic code, and the global fragility procedure.
The results have shown that the soil does not significantly influence the behaviour of low-rise
buildings. However, in the case of mid- and high-rise buildings, the maximum capacity can be
reduced by up to 10% and 30%, respectively.
Keywords: Soil Structure Interaction, Seismic analysis, Reinforced concrete, Buildings,
8th ECCOMAS Thematic Conference on
Computational Methods in Structural Dynamics and Earthquake Engineering
M. Papadrakakis, M. Fragiadakis (eds.)
Streamed from Athens, Greece, 230 June 2021
M.V. Requena-Garcia-Cruz, A. Morales-Esteban, P. Durand-Neyra, E. Romero-Sánchez
Most seismic vulnerability analyses of buildings are carried out without considering the
soil-structure interaction effects (SSI). Despite these notable effects, their consideration in
seismic analysis remains unclear. In fact, SSI was assumed to be beneficial in past research
[1]. This benefit emerges from the reduction of the internal forces and the drifts due to the
soil’s increasing flexibility. Hence, the vast majority of seismic vulnerability analyses consid-
er models with a fixed-based configuration to obtain more conservative results. However, re-
cent studies on the influence of SSI in the capacity assessment of buildings has proved that it
does not positively affect all types of structures and all types of soils [2]. They have conclud-
ed that structures are expected to experience different levels of damage when the soil’s influ-
ence is taken into account [3]. In fact, the Eurocode-8 Part-1 (EC8-1) [4] establishes that the
SSI effects must be born in mind when structures: i) present significant second order (p-Δ)
effects; ii) are slender; or, iii) are medium/high-rise buildings. Moreover, it was proved that
SSI might affect aspects related to the seismic performance of buildings such as the ductility
and the strength [5] or the energy dissipation [6]. Studies have even shown that the SSI can
greatly worsen the performance of buildings due to asymmetrical designs [7]. This suggests
that further research is needed.
The SSI effects can be taken into account by simulating the flexibility of the soil. To do so,
several approaches have been proposed over time. Among others, the most common ap-
proaches used in the behaviour assessment of buildings are the Nonlinear Beam on Winkler
method (NBWM) and the continuum modelling of soil (in 3D). The first approach is mainly
based on simulating the nonlinear behaviour of the soil by adding inelastic springs [8]. These
springs present different characteristics which are applied in certain directions. The NBWM
can simulate the SSI effects very easily and simply. In this way analyses do not become very
tedious [9]. However, this approach presents certain drawbacks: it does not consider the com-
plete behaviour of the soil, the frictional surface between the soil and the foundation and the
effects of deeper soil layers. Therefore, this method might not be applicable for all soil and
structural characteristics.
The continuum modelling of soils can exhaustively capture the soil constitutive behaviour,
obtaining more realistic results [2]. Moreover, this type of analyses has been gaining im-
portance over the past decade due to the availability of new methods and the increase of com-
putational capacity [10]. Some related studies showed that the foundation characteristics and
the soil modulus (shear and bulk) are the parameters that most affect the seismic response of
buildings [2]. Others proved that the SSI are significant when both the structure and the soil
are simulated as inelastic [6]. These parameters cannot be considered in SSI assessment via
the NBWM.
Owing to the lack of studies and guidance, this paper aims to analyse the soil’s influence in
the seismic vulnerability analysis of a reinforced concrete (RC) building. To do so, different
models of a real case study building have been simulated (low-rise (real), mid-rise and high-
rise). The EC8-1 statement and past research have been proved. The 3D continuum modelling
of the soil has been carried out to simulate its nonlinear behaviour. Furthermore, the charac-
terisation of the most probable soil profile at the location has been done by considering differ-
ent geotechnical studies. As a clayey soil has been observed, the analyses have been carried
out under undrained conditions. Nonlinear static analyses have been performed to determine
the seismic capacity of models by using the finite element method (FEM). The damage has
been assessed by means of the local procedure established in Eurocode-8 Part-3 (EC8-3) [11]
and the fragility procedure.
M.V. Requena-Garcia-Cruz, A. Morales-Esteban, P. Durand-Neyra, E. Romero-Sánchez
The case study building is a 1970s primary school building located in Huelva (southwest-
ern Spain), which is an earthquake-prone area. This building shares typical constructive and
structural characteristics with most RC buildings of the area. What is more, these buildings
were constructed prior to the applications of seismic codes.
The key contributions of this paper are: i) the analysis of the soil influence in the seismic
vulnerability analysis of RC buildings considering different geometrical characteristics; ii) the
characterisation for the 3D continuum modelling of the most probable soil profile in Huelva;
iii) 3D FEM models in OpenSees to realistically reproduce the entire system’s behaviour
(soil+foundation+structure); iv) the analysis of the seismic damage by means of both local
and global procedures.
2.1 Building configuration
The case study building selected is a primary school building located in Huelva. It has been
defined as an index-building of the typology of RC buildings [12]. This typology represents
27% (75 buildings) of the total (279) of the primary school buildings constructed in the prov-
ince. As they were built during the 1970s, they share constructive and structural characteris-
tics with a major part of the area’s RC buildings: insufficient longitudinal and transversal
rebar ratio, wide beams, short columns, very slender RC columns sections and low-quality
structural materials. Moreover, these buildings have not been designed according to seismic
criteria since they were constructed prior to restrictive seismic codes.
The case study building is a two-story RC frame building (Figure 1). Although it is regular
in height, it presents short columns on the ground floor. This is a typical constructive configu-
ration that can be commonly found in most RC buildings of the 1970s. Short columns are
created due to the elevation of the ground floor from the soil surface to avoid humidity and
water problems. This ground-floor construction often leads to isolated footings (superficial or
deep). In this case, the building was constructed with isolated footings of a depth of 0.80 m.
The structural characteristics of the building are listed in Table 1.
Figure 1: Case study building’s configuration.
Load beams
Tie beams
Dimensions (cm)
Cross-section (cm2)
Longitudinal rebar (cm2)
Top: 0.786
Top: 0.786
Bottom: 3.495
Bottom: 0.786
Transversal rebar (cm2)
Spacing of stirrups (cm)
Table 1. Case-study’s structural elements geometrical characteristics.
M.V. Requena-Garcia-Cruz, A. Morales-Esteban, P. Durand-Neyra, E. Romero-Sánchez
2.2 Soil characterisation
A characterisation of the soil under the building has been carried out to properly model its
constitutive behaviour. The information has been compiled from 8 nearby geotechnical stud-
ies. These studies include information related to laboratory tests done with samples as well as
in-situ geotechnical prospections. Based on the available information, an interpretation of the
soil layering at the site has been performed. In this study, the most probable soil profile has
been considered. To do so, the probability of each stratum according to its depth has been as-
sessed. This determination has considered 17 boreholes. As shown in Figure 2a, four different
geotechnical strata have been identified: tilled, grey clay, brown silt and clay loam. The labor-
atory tests have revealed a predominance of clay. Therefore, only the parameters to perform
undrained analyses have been calculated.
(a) (b) (c)
Figure 2: Soil characterization. (a) Soil profile (b) Nspt and Vs(c) according to depth.
Among other in-situ tests, standard penetration tests (SPT) were executed to determine the
Nspt. In Figure 2b, the Nspt for each soil stratum has been plotted. According to [13], the shal-
low layers can be classified as low-dense soils (Nspt11-30) while the deepest layers are dense
(Nspt31-50) .
The shear wave velocity (Vs) and the Poisson ration (ν) are required to numerically model
the soil in 3D. In [14], several correlations were defined to obtain Vs. However, in this work,
only the Imai equation (Eq.(1)) has been used since it is widely accepted. In Figure 2c, the Vs
values for each soil layer have been defined according to Nspt and depth. Since there are sever-
al values of Vsfor each depth, the most probable value has been used to determine the param-
eters presented below.
Vs=91Nspt0.317 (1)
The soil behaviour is defined according to three parameters: shear (G), elastic (E) and bulk
(B) modulus and the unit weight (γ). The moduli have been calculated according to certain
widely known geotechnical correlations (Eq.(2)(3)(4)). G,Eand Bhave been plotted in Figu-
re 3 for each soil stratum. The soil constitutive behaviour has been plotted considering the
M.V. Requena-Garcia-Cruz, A. Morales-Esteban, P. Durand-Neyra, E. Romero-Sánchez
medium values of each modulus. As can be observed, the shallow layers are weaker than the
deepest ones, which relates to Nspt. The soil stiffness increases at around 5 m depth. The clay
loam’s modulus rises slightly with depth. In order to take the variability of the modulus into
account, four soil layers have been defined following the procedure established in Section 4.2.
E=2G(1+ν) (3)
B=E/3(1-2ν) (4)
(a) (b) (c)
Figure 3: G(a), E(b) and B(c) values obtained from correlations according to geotechnical prospections.
3.1 Models defined
The state of the art has revealed that SSI must be considered in the seismic analyses of
mid- and high-rise buildings. Therefore, in order to better understand their influence, different
configurations of the case study building have been determined by varying its height. As
shown in Figure 4, three models have been defined: low-rise (real) (M1), mid-rise (M2) and
high-rise (M3). The total mass and height of each model have been listed in Table 2. Fixed-
base and solid models have been identified with “F” and “S”, respectively. The nodes at the
base of the F-models have been fixed in the 6 degrees of freedom (DOF): X, Y, Z, Rx, Ryand
Rz. The modelling of the soil is presented in Section 4.2. It has also been checked that the
foundationsdimensions are valid for the soil with each model’s configuration.
M.V. Requena-Garcia-Cruz, A. Morales-Esteban, P. Durand-Neyra, E. Romero-Sánchez
Figure 4: Models’ configuration.
Nº of floors
Total height (m)
Table 2. Number of floors, total mass and height of the models analysed.
3.2 Analysis procedure
Nonlinear static analyses have been carried out to determine the capacity of the models by
using the FEM OpenSees software [15]. Since the models are very large, the analyses have
been done using the parallel option available in OpenSees by defying partitions. The outputs
have been handled in PYTHON [16]. A load-control and displacement-control integrator have
been used to perform the gravity and the pushover analyses, respectively. Only the modal load
pattern results have been considered since this has been the most restrictive. Modal analyses
have been carried out to define the load pattern. The -genBandArpack solver has been used
due to the numerous constraints. As models have worked in Mode 1 and 2, torsional effects
can be neglected.
3.3 Damage determination
The N2-method has been used to determine the single-degree-of-freedom (SDOF) ideal-
ised bilinear curves and the target displacement. Its extended version has also been used,
which takes the infills’ effects into account. A 0.1g PGA for Huelva has been used according
to the Spanish updated seismic action values [17]. The response spectrum has been construct-
ed using the EC8-1 procedure.
Two approaches have been considered to determine the damage: the local and the global.
The first one has borne in mind the demand/capacity ratio (DCR) established in EC8-3 and
the local damage of RC structural elements. Three damage states have been determined: dam-
age limitation (DL), significant damage (SD) and near collapse (NC). The NC is calculated
considering the ultimate chord rotation (θum). The SD is determined as 3/4 of θum.The DL is
worked out by means of the yielding chord rotation (θy). The formulae of each parameter are
M.V. Requena-Garcia-Cruz, A. Morales-Esteban, P. Durand-Neyra, E. Romero-Sánchez
established in the EC8-3. Each damage state has been calculated when the demand chord of
one column reaches the capacity values of θum,θum and θy.
The second approach is based on the fragility curves assessment. These curves provide the
probability of reaching or exceeding a certain damage state (ds), given a certain spectral dis-
placement (Sd). They are determined by the well-known lognormal cumulative distribution
(Eq.(5)), where: βds is the dispersion at dsand Sd,ds is the median value of the spectral dis-
placement at which a building reaches the dsthreshold.
P[ds|Sd]=Φ[(1/βds)ln(Sd/S(d,ds))] (5)
Both βds and Sd,ds are statistical parameters that take into account different uncertainties.
They should therefore be determined according to the models analysed. However, in this case
they have not been studied since further research should be carried out considering many
models and including the SSI effects. However, an exhaustive work carried out in [18] has
been used to define these parameters. The authors performed the fragility assessment of typi-
cal Spanish RC buildings and determined the fragility parameters for low-, mid- and high-rise
RC buildings. The values of βds for each building class are listed in Table 5. The values of
Sd,ds have been determined for each of the models analysed and following the provisions es-
tablished in [18], listed in Table 4. This procedure considers the parameters that characterise
the idealised SDOF system curves: Dyand Du, yielding and ultimate displacement.
Damage state/Class
Slight (β1)
Moderate (β2)
Severe (β3)
Complete (β4)
Table 3. βds for each RC building class.
Slight (Sd1)
Moderate (Sd2)
Severe (Sd3)
Complete (Sd4)
Table 4. Sd,ds determination for each damage state threshold.
The different models considered in this study have been modelled with the STKO software
[19], a Graphical User Interface (GUI) for OpenSees.
4.1 Superstructure
The nonlinear behaviour of the RC elements has been simulated though the distributed
plasticity approach. This can automatically compute deformations and curvatures, reducing
the modelling time. The RC beams and columns have been discretised into different fibres
with the fibre section aggregator. In order to take p-delta (p-Δ) effects into account, force-
beams elements have been applied to the RC frames. “Concrete01” has been considered to
simulate concrete. The concrete’s core has been defined by increasing its strength and strain
according to [20]. “Steel02” has been used to model steel. In this case, the smooth rebars have
been considered by decreasing the steel elastic modulus as in [21]. The effects of infills have
been taken into account by means of the two-diagonal truss approach defined in [22]. Due to
the rigidity of the concrete slabs, rigid diaphragm interactions have been applied to the nodes
of each floor. Masses have been applied to each structural member considering the gravita-
tional loads and the self-weights. Gravitational loads have also been applied to each structural
element bearing in mind: dead (self- weight and the weight of constructive elements) and live
M.V. Requena-Garcia-Cruz, A. Morales-Esteban, P. Durand-Neyra, E. Romero-Sánchez
loads. The characteristics of the structural materials considered in this study are listed in Table
ƒcu (MPa)
τcr (MPa)
ɛcu (%)
Table 5. Values of the structural materials’ parameters.
Where: concrete compressive (ƒc) and crushing strength (ƒcu); concrete strain at maximum (ɛc) and ultimate
strength (ɛcu); steel yielding strength (ƒy); steel modulus of elasticity (Es); infills shear modulus (Gw); post-
capping degrading branch coefficient (α); shear cracking stress (τcr); masonry elasticity modulus (Ew).
4.2 Continuum modelling of the soil
The underlying soil of the building has been modelled with a mesh of 125x40x21 m (X, Y
and Z directions). The mesh has been defined according to the Vsand to the frequency (ω) of
the models. “SSPbrick” brick elements have been applied to the solid elements to capture the
soil small deformation (Figure 5). The mesh is characterised by 51,954 nodes and 120,040
brick elements. The lateral boundaries have been fixed in the corresponding direction and the
base in all directions.
According to the different test results (Section 2.2), the soil beneath the building is clayey.
Therefore, the analyses have been performed under undrained conditions since this is the most
restrictive. Hence, the soil constitutive behaviour has been simulated by means of the “Pres-
sureIndependMultiYield” (PIMY) material. This has been implemented in OpenSees to model
elasto-plastic undrained clay-type soils, which are independent from pressure. The soil’s fail-
ure criterion is based on Von Misesmulti-surface plasticity theory (Figure 5) determined in
[23]. “EqDOF” has been applied to the interaction between the soil’s and the foundation’s
surfaces. Four soil layers have been defined according to the characterisation performed in
Section 2.2, which can be observed in Figure 4.
Figure 5: “PressureIndependMultiYield” soil material’s failure criterion.
The results obtained from the analyses appear in this section. In Figure 6, the deformed
shape of each model after the application of the gravity loads is shown. As can be observed,
the settlement of the structure is higher when the height increases. The displacement in the Z
M.V. Requena-Garcia-Cruz, A. Morales-Esteban, P. Durand-Neyra, E. Romero-Sánchez
direction of the control node (in the rooftop) increases 220% and 323% when adding 2 floors
(M2) and 4 floors (M3), respectively. Therefore, this increase is not linear.
Figure 6: Deformed shape of models analysed after the application of gravity loads.
In Figure 7, the SDOF capacity curves for each of the models have been plotted. Also, the
damage states (Section 3.3) and the target displacements (demand) have been determined. In
order to compare the results, the multi-degree-of-freedom (MDOF) curves have been normal-
ised by dividing the base shear (Vb) by the weight (W) and the displacement (d) by the total
height (Ht).
M.V. Requena-Garcia-Cruz, A. Morales-Esteban, P. Durand-Neyra, E. Romero-Sánchez
Figure 7: SDOF normalised capacity curves for each of the models assessed.
It can be observed that the higher the structures’ height, the higher the soil effects. In the
case of the low-rise model (M1), the SSI just decreases the initial stiffness of the systems. In
the X direction, the difference between the demand and the NC displacement is higher for the
S models. In the Y direction, for the F model, the demand is located between the LD and the
SD. However, when considering the SSI, the demand is after the SD; therefore, it will not
comply with the EC8 requirements like in the X direction. Mid-rise buildings are more affect-
ed by the SSI than low-rise buildings due to the considerable modification of the initial stiff-
ness. The maximum capacity has been reduced by around 10%. In the Y direction, the
demand displacement is considerably higher for the S model. High-rise models are the most
affected by the SSI, the maximum capacity being reduced by up to 30%. In terms of damage,
the models behave worse due to the failure of columns located in the irregularity of the
ground floor.
In Figure 8, the fragility curves for each of the models analysed are plotted considering the
demand displacement. It can be noted that the fragility curves for the models with SSI are
worse than the F-model’s curves. Therefore, the probability of reaching higher damage in-
creases in models that bear the soil influence in mind. This probability also increases with the
height. As can be seen, the S-models fragility curves are worse than the F-models curves
when the height increases. This results in the high-rise models being the most affected. More-
over, the fragility curves of high-rise buildings are worse than the rest due to the statistical
M.V. Requena-Garcia-Cruz, A. Morales-Esteban, P. Durand-Neyra, E. Romero-Sánchez
Figure 8: fragility curves considering fixed-based and solid models and low-, mid- and high-rise models.
This paper aims to analyse the SSI in the seismic vulnerability analysis of RC buildings.
The state of the art has revealed that SSI must be considered in the seismic analyses of mid-
and high-rise buildings. Therefore, different configurations of a case study RC building have
been defined by varying the height: low- (real), mid- and high-rise. The characterisation of the
location’s soil profile has been carried out. This characterisation has revealed that the soil is
Nonlinear static analyses have been performed to assess the models’ capacity. The seismic
damage has been determined by means of the European seismic code (local damage of ele-
ments) and the fragility procedures (global damage). 3D nonlinear models considering the soil
as a continuum have been modelled using the FEM to simulate the soil nonlinear behaviour.
The results have shown that the soil does not significantly influence the behaviour of low-
rise buildings. However, in the case of mid- and high-rise buildings, the maximum capacity
can be reduced by up to 10% and 30%, respectively. Moreover, according to the local damage
assessment, structural elements might collapse due to considering the soil, even for low-rise
In the light of the fragility assessment results, it can be concluded that the probability of
reaching higher seismic damage increases when considering the SSI. Moreover, this probabil-
ity increases with the height.
This work has considered the most probable soil profile that can be found in the area.
However, further research should be carried out in order to consider several soil profiles since
softer layers could worsen the building’s seismic capacity. This research has considered statis-
M.V. Requena-Garcia-Cruz, A. Morales-Esteban, P. Durand-Neyra, E. Romero-Sánchez
tical parameters from other works in the fragility assessment. Yet, further research should be
assessed to properly determine these values according to the modelscharacteristics and the
type of soil. This research has not considered the element contact between the soil and the
foundation’s surfaces, which can capture the soil behaviour better, leading to more accurate
[1] Kwag, S., Ju, B.S., & Jung, W., Beneficial and Detrimental Effects of Soil-Structure
Interaction on Probabilistic Seismic Hazard and Risk of Nuclear Power Plant.
Advances in Civil Engineering,2018, 2018.Epub ahead of print 2018. DOI:
[2] Anand, V., & Satish Kumar, S.R., Seismic Soil-structure Interaction: A State-of-the-
Art Review. Structures,16, pp. 317326, 2018.
[3] Rajeev, P., & Tesfamariam, S., Seismic fragilities of non-ductile reinforced concrete
frames with consideration of soil structure interaction. Soil Dynamics and Earthquake
Engineering,40, pp. 7886, 2012.
[4] European Union., Eurocode 8: Design of structures for earthquake resistance. Part 1:
General rules, seismic actions and rules for buildings. Belgium, 2004.
[5] Miranda, E., & Bertero, V. V., Evaluation of strength reduction factors for
earthquake‐resistant design. Earthquake Spectra,10(2), pp. 357379, 1994.
[6] Karapetrou, S.T., Fotopoulou, S.D., & Pitilakis, K.D., Seismic vulnerability assessment
of high-rise non-ductile RC buildings considering soil-structure interaction effects. Soil
Dynamics and Earthquake Engineering,73, pp. 4257, 2015.
[7] Badry, P., & Satyam, N., Seismic soil structure interaction analysis for asymmetrical
buildings supported on piled raft for the 2015 Nepal earthquake2016.Epub ahead of
print 2016. DOI: 10.1016/j.jseaes.2016.03.014.
[8] Boulanger, R.W., Curras, C.J., Kutter, B.L., Wilson, D.W., & Abghari, A., Seismic
Soil-Pile-Structure Interaction Experiments and Analyses. Journal of Geotechnical and
Geoenvironmental Engineering,125(9), pp. 750759, 1999.
[9] Harden, C.W., & Hutchinson, T.C., Beam-on-Nonlinear-Winkler-Foundation Modeling
of Shallow, Rocking-Dominated Footings. Earthquake Spectra,25(2), pp. 277300,
[10] Cayci, B.T., Inel, M., & Ozer, E., Effect of Soil-Structure Interaction on Seismic
Behavior of Mid-and Low-Rise Buildings. International Journal of Geomechanics,
21(3), pp. 04021009, 2021.
[11] European Union., Eurocode-8: Design of structures for earthquake resistance. Part 3:
Assessment and retrofitting of buildings. Belgium, 2005.
[12] Morales Esteban, A. et al., Schools: seismicity and retrofitting (PERSISTAH project).
Universidad de Sevilla, 2020.
[13] Spanish Ministry of Public Works [Ministerio de Fomento de España]., Spanish
Technical Code of Buildings [Código Técnico de la Edificación (CTE)]. Spain, 2006.
M.V. Requena-Garcia-Cruz, A. Morales-Esteban, P. Durand-Neyra, E. Romero-Sánchez
[14] Naik, S.P., Patra, N.R., & Malik, J.N., Spatial Distribution of Shear Wave Velocity for
Late Quaternary Alluvial Soil of Kanpur City, Northern India. Geotechnical and
Geological Engineering,32(1), pp. 131149, 2014.
[15] McKenna, F., Fenves, G.L., & Scott, M.H., OpenSees: Open system for earthquake
engineering simulation2000.
[16] Python Software Foundation., Python2021.
[17] Spanish Ministry of Public Works [Ministerio de Fomento de España]., Update of the
seismic hazard maps [Actualización de mapas de peligrosidad sísmica de España].
Spain, 2012.
[18] Barbat, A.H., Pujades, L.G., & Lantada, N., Seismic damage evaluation in urban areas
using the capacity spectrum method: Application to Barcelona. Soil Dynamics and
Earthquake Engineering,28(1011), pp. 851865, 2008.
[19] Petracca, M., Candeloro, F., & Camata, G., \"STKO user manual\". ASDEA Software
Technology. Pescara Italy, 2017.
[20] Mander, J.B., Priestley, M.J.N., & Park, R., Theoretical Stress‐Strain Model for
Confined Concrete. Journal of Structural Engineering,114(8), pp. 18041826, 1988.
[21] Couto, R., Requena-García-Cruz, M., Bento, R., & Morales-Esteban, A., Seismic
capacity and vulnerability assessment considering ageing effects. Case study: Three
local Portuguese RC buildings. Bulletin of Earthquake Engineering2020.Epub ahead of
print 2020. DOI: 10.1007/s10518-020-00955-4.
[22] Celarec, D., Ricci, P., & Dolšek, M., The sensitivity of seismic response parameters to
the uncertain modelling variables of masonry-infilled reinforced concrete frames.
Engineering Structures,35, pp. 165177, 2012.
[23] Mazzoni, S., McKenna, F., Scott, M.H., & Fenves, G.L., OpenSees command language
manual. 2006.
... The soil behaviour has been defined according to three parameters: shear (G), elastic (E) and bulk (B) modulus and the unit weight (γ). These have been obtained according to the widely-known geotechnical correlations available in [41]. In Fig. 3(d), the shear modulus has been plotted as a function of depth to represent the rigidity of the soil. ...
Existing reinforced concrete (RC) structures might not comply with current seismic codes due to their aseismic design and construction date. By seismically retrofitting them, it is possible to improve their seismic performance to resist the expected seismic loads. However, selecting the best solution is challenging since social and economic issues can affect the choice. Multi-criteria decision making (MCDM) provides an opportunity to overcome the challenge but there are some drawbacks in the available MCDM techniques. This paper reports an improved MCDM-based seismic retrofit: Additional criteria have been included and weighted according to their importance (ductility improvement and damage reduction); Finite element modelling of the case study building has been carried out instead of following methods based on different simplifications; iii) Structural performances have been assessed by determining the damage in local elements instead of following global assessment procedures; Effects of soil-structure interaction (SSI) have been taken into account to ultimately compare different structural and ground-improvement techniques. Consistency and sensitivity analyses have proved the stability of the results and the robustness of the method. It is shown that SSI can increase the seismic damage up to 17%, and regarding the seismic safety verification, the building needs to be retrofitted. Adding fibre reinforcement polymers and steel bracings are the best solutions due to the minimum architectural impact and the outstanding structural improvement, respectively. Nevertheless, the solution preferred is the addition of single steel braces in beam-column joints despite its high maintenance costs. The sensitivity analysis indicates that the most sensitive criteria are the functional compatibility and the reduction of the collapse risk.
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The present book aims to present the work developed in the European research project PERSISTAH (Projetos de Escolas Resilientes aos SISmos no Território do Algarve e de Huelva, in Portuguese), which has been developed cooperatively by the University of Seville (Spain) and the University of the Algarve (Portugal). This research project focuses on the study and assessment of the seismic risk of primary education buildings in the territory of the Algarve (Portugal) and Huelva (Spain). To this end, the objectives established by the National Platforms for Disaster Risk Reduction (PNRRC) of the National Civil Protection Commissions of Portugal and Spain have been taken into account.
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This study investigates the effect of soil-structure interaction (SSI) on seismic behavior of mid- and low-rise residential buildings considering linear and nonlinear behavior of structural members. For this purpose, four- and seven-story buildings representing a majority of existing building stock were used. The outcomes indicate that there are significant variations in displacement demand estimates depending on ground motion records, modeling approaches (linear/nonlinear structural modeling and fixed-base or SSI), and soil types. The findings in this study evidently indicate that linear fixed-base models are highly sensitive to dynamic amplification. Therefore, their use may result in inappropriate displacement demand estimates. If the soil amplification and nonlinear modeling are considered, the differences in the average displacement demand estimates of both the fixed-base and SSI models are negligible. Besides, the displacement demand estimate for stiffer soils is independent of modeling. This study underlines that the linear structural modeling includes SSI or the fixed-base model has to be used with nonlinear structural modeling in order to have acceptable demand estimates for the seismic evaluation of the reinforced concrete residential buildings.
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A high percentage of reinforced concrete (RC) buildings in Portugal were designed and built before the introduction of modern seismic codes. This research aims to assess the seismic capacity and vulnerability of RC buildings in the city of Lisbon. For that purpose, nonlinear static procedures have been used and fragility curves have been developed. These buildings are reaching the end of their nominal life. Therefore, ageing effects have been taken into account, as well as the presence of smooth rebar. To do so, a sensitivity analysis has been performed by considering the chloride-induced corrosion of the reinforcement steel rebar and the degradation of the concrete cover. To illustrate the effects of ageing and the procedure adopted for the seismic fragility assessment of old RC structures, three RC buildings with masonry infills have been selected as case studies. They were all built between 1960 and 1980, and they are representative of the current building stock in Lisbon. The seismic capacity of the buildings has been determined by means of nonlinear static analyses of three-dimensional numerical models. The N2 method and its extended version have been considered to determine the target displacement. The seismic safety of the buildings has been estimated in terms of the demand/capacity ratio for each vertical structural element (columns and walls) according to the bending and the shear failures. Then, a set of fragility curves has been developed for all buildings to represent the probability of RC elements reaching or exceeding the significant damage limit state. Results have shown that the concrete strength degradation has had more influence than reduction of the rebar diameter in the seismic capacity. When considering steel corrosion, it has been demonstrated that the corrosion rate has reduced the capacity more than the time of exposure. It can be concluded that ageing affects the seismic behaviour of RC structures, increasing the vulnerability of these buildings.
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The purpose of this study is to investigate the soil-structure interaction (SSI) effect on the overall risk of a PWR containment building structure with respect to two failure modes: strength and displacement. The precise quantification of the risk within the seismic probabilistic risk assessment framework depends considerably on an accurate treatment of the seismic response analysis. The SSI effect is one of the critical factors to consider when accurately predicting structural responses in the event of an earthquake. Previous studies have been conducted by focusing more on the positive side of the SSI effects and the effects mainly on the seismic fragility result. Therefore, this paper presents the results of a study of the SSI effect on the overall risk. Also, the study relies on an emphasis on revealing a beneficial and a detrimental effect of the SSI by utilizing an example of the containment structure in three soil conditions and two main failure modes. As a result, the consideration of SSI shows a complete conflicting effect on the seismic fragility and risk results depending on two failure modes considered in this study. This has a positive effect regarding the strength failure mode, but this brings a negative effect regarding the displacement failure mode. The risk fluctuation width is particularly noticeable in the site having a considerable change in seismic hazard information such as Los Angeles on the western site of the US. Such results can be expected to be utilized in a future study for investigating the pros and cons of the SSI effect associated with various failure modes in diverse conditions.
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Seismic damage surveys and analyses conducted on modes of failure of structures during past earthquakes observed that the asymmetrical buildings show the most vulnerable effect throughout the course of failures (Wegner et al., 2009). Thus, all asymmetrical buildings significantly fails during the shaking events and it is really needed to focus on the accurate analysis of the building, including all possible accuracy in the analysis. Apart from superstructure geometry, the soil behavior during earthquake shaking plays a pivotal role in the building collapse (Chopra, 2012). Fixed base analysis where the soil is considered to be infinitely rigid cannot simulate the actual scenario of wave propagation during earthquakes and wave transfer mechanism in the superstructure (Wolf, 1985). This can be well explained in the soil structure interaction analysis, where the ground movement and structural movement can be considered with the equal rigor. In the present study the object oriented program has been developed in C++ to model the SSI system using the finite element methodology. In this attempt the seismic soil structure interaction analysis has been carried out for T, L and C types piled raft supported buildings in the recent 25th April 2015 Nepal earthquake (M = 7.8). The soil properties have been considered with the appropriate soil data from the Katmandu valley region. The effect of asymmetry of the building on the responses of the superstructure is compared with the author’s research work. It has been studied/observed that the shape or geometry of the superstructure governs the response of the superstructure subjected to the same earthquake load.
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Empirical correlation between standard penetration resistance (SPT-N) and shear wave velocity measured by seismic downhole techniques are prepared of the alluvial soil of quaternary age for the Kanpur city. The Kanpur city is having seismic threat from Himalaya and it falls in seismic zone III according to seismic zones of India. Standard penetration test as well seismic downhole test has been carried out up to 30 m at twelve different locations of Kanpur city. The measured SPT-N values and shear wave velocity values are used to develop empirical correlation between SPT-N and shear wave velocity. The proposed correlations have been compared with the existing regression equations by various other investigators. It is found that the proposed correlation exhibit good performance (10 % error bar). Also the measured shear wave velocity has been used to prepare spatially distributed contour map of 50, 75 and 100 m/s using ArcGIS-9 software. It is observed that the shear wave velocity values for the northern part of Kanpur city vary from 125 to 825 m/s. In southern part, it is varying from 125 to 500 m/s where as in the central part of the city the shear wave velocity varies from 125 to 375 m/s. The eastern part of the city also shows some variation in shear wave velocity which ranges from 250 to 625 m/s. The western part of the city shows the variation of shear wave velocity from ≤125 to 500 m/s. The soil type of the study area are classified as per NEHRP and new Italian O.P.M.C classification system as B, C and D type soil with having site period of 0.1–0.9 s and Poisson’s ratio varying from 0.1 to 0.4.
The process of soil response influencing motion of the structure and vice-versa is termed as soil-structure interaction (SSI). SSI has been traditionally considered to be beneficial to seismic response of a structure. It has been suggested that ignoring SSI in design practice leads to a conservative design. It is evident from the design codes which either allow a reduction of the overall seismic coefficient on account of SSI or suggest it to be ignored altogether. However observations from some of the past seismic events such as 1989 Loma Prieta earthquake and 1995 Kobe Earthquake show evidences of detrimental nature of SSI in certain circumstances. Recent studies have also been able to justify such possibilities. As a consequence of this dissent among the research fraternity, there is a lack of adequately formulated design guidelines. Though advances have been made in developing methods to solve an SSI problem, incorporating SSI in design practice has been a rarity. The present paper attempts to summarize various approaches to include SSI in analysis of structures and guidelines outlined in prominent seismic codes. The significance of such a study lies in the need for selection of appropriate approach. A review of contemporary research in field of SSI is also presented at the end.
Traditionally fragility curves of reinforced concrete (RC) buildings are estimated with the assumption of fixed base structures. The objective of the present research is to study whether soil-structure interaction (SSI) and site effects may affect the seismic performance and vulnerability of reinforced concrete moment resisting frame (MRF) buildings and consequently modify the fragility curves. SSI is modeled applying the direct one-step approach considering either linear elastic or nonlinear soil behavior while site effects are inherently accounted for. To further examine the contribution of site and SSI effects, a two-step uncoupled approach is also applied, which takes into account site effects on the response of the fixed base structure, but neglects SSI effects. Additional analyses are performed investigating the influence of the soil depth and stratigraphy under nonlinear soil behavior on the seismic response and fragility of RC buildings. A 9-story RC MRF designed with low seismic code provisions is adopted as a reference structure. A comparative dynamic analysis is performed highlighting various trends in the seismic response of the considered SSI and fixed base systems. Fragility curves are derived as a function of rock outcropping peak ground acceleration for the immediate occupancy and collapse prevention limit states for the fixed base and SSI models based on the statistical exploitation of the results of incremental dynamic analysis (IDA) of the given structural systems. Results show the significant role of SSI and site effects under linear or nonlinear soil behavior in altering the expected structural performance and fragility of high-rise fixed base structures.
The sensitivity of the seismic response parameters to the uncertain modelling variables of the infills and frame of four infilled reinforced concrete frames was investigated using a simplified nonlinear method for the seismic performance assessment of such buildings. This method involves pushover analysis of the structural model and inelastic spectra that are appropriate for infilled reinforced concrete frames. Structural response was simulated by using nonlinear structural models that employ one-component lumped plasticity elements for the beams and columns, and compressive diagonal struts to represent the masonry infills. The results indicated that uncertainty in the characteristics of the masonry infills has the greatest impact on the response parameters corresponding to the limit states of damage limitation and significant damage, whereas the structural response at the near-collapse limit state is most sensitive to the ultimate rotation of the columns or to the cracking strength of the masonry infills. Based on the adopted methodology for the seismic performance assessment of infilled reinforced concrete frames, it is also shown, that masonry infills with reduced strength may have a beneficial effect on the near-collapse capacity, expressed in terms of the peak ground acceleration.
The nonlinear behavior of shallow foundations under large amplitude earthquake-induced loading can result in dissipation of seismic energy through the mechanism of soil yielding beneath the foundation. In addition, foundation uplifting may shift the period of the soil-foundation-structure system away from the damaging energy content of most earthquakes. However, this yielding and uplifting may lead to excessive transient and permanent deformations (settlement, rocking, and sliding). Therefore, modeling procedures that account for foundation nonlinearity and uplift are needed before these benefits can be realized in performance based earthquake engineering (PBEE) practice. This paper adopts a beam-on-nonlinear-Winkler-foundation (BNWF) simulation methodology for modeling shallow foundation-structure systems, where seismically-induced rocking plays a predominant role in their response. Numerical results demonstrate that reasonable comparison between the nonlinear Winkler-based approach, and experimental response in terms of moment-rotation, settlement-rotation, and shear-sliding displacement can be obtained, given an appropriate selection of model and soil properties.