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AA SSaaffeettyy IInnddeexx ffoorr HHoossppiittaall BBuuiillddiinnggss Aiello

Antonietta

1, Pecce Marisa

2, Sarno

Luigi Di

2, Perrone Daniele

1 and Rossi

Fernando

2*

1. University of Salento, Department of Engineering for Innovation, Lecce, ITALY

2. University of Sannio, Engineering Department, Benevento, ITALY

*fernando@unisannio.it

Abstract Seismic vulnerability assessment is of paramount

importance for existing critical structures, e.g. health

care centers and hospital buildings. Numerous

surveys carried out in the aftermath of recent

earthquakes have shown that the performance of

hospitals is not impaired by the structural damage;

functional breakdowns are instead major threats.

Nonstructural components in buildings are rarely

designed with the same care or with the same degree

of scrutiny used for structural elements.

In the present paper a checking/recording document

is proposed, including the vulnerability of

nonstructural elements and medical equipment; the

overall seismic vulnerability is then estimated by a

vulnerability index referred to both the functional and

structural parts of the buildings. The simplified

methodology, developed on the basis of studies

carried out by Pan American Health Organization

(PAHO) and World Health Organization (WHO),

finally provides a safety index as function of all the

parameters that characterize the seismic risk:

vulnerability, hazard and exposition.

Keywords: Safety Index, Hospital Buildings, Seismic

Risk.

Introduction After a moderate-to-high magnitude earthquake the priority

is to protect lives and assist injured people; as a result

strategic structures are selected to warrant post-earthquake

emergency recovery. Hospital buildings are strategic

structures of paramount importance for civil protection.

Hospitals are highly complex facilities that while providing

care, also function as a hotel (for patients), office buildings

(medical staff and administration), laboratories and

warehouses. Such buildings possess high level of

occupancy (patients, medical and support staff, visitors)

and house expensive medical equipment.

The hospitals must be fully operational in the emergency

after an earthquake this need is demonstrated by the

increasing number of patients that are driven to health

facilities in the first hours after the seismic event1 (Fig.1).

The seismic vulnerability of hospitals does not rely merely

on the vulnerability of structural elements but it is

remarkably influenced by non-structural elements, services

and functional issues. The interaction between all these

aspects makes the hospitals very vulnerable and complex to

be assessed, especially in seismically active zones. While

an ordinary building is properly designed to withstand

strong earthquakes, with limited structural damage,

hospitals should be designed taking into account further

specific performances, as well recognized they cannot lose

their immediate operations due to damage of non-structural

elements, equipments or inadequate training of staff to

manage such situations.

Numerous codes deal with seismic vulnerability of

structures, either ordinary or strategic, notwithstanding

scarce provisions are available to deal with the seismic

vulnerability of non-structural elements and services2-3

.

Damage observed during past earthquakes (e.g. Northridge,

California, 1994; L’Aquila, Italy, 2009; Maule, Chile,

2010) has emphasized the importance of seismic

vulnerability of non-structural elements and components.

Fig.1: Demand for medical services after an earthquake1

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Fig. 2: Typical damage in ceilings and infill of hospitals6

Fig.3: Typical damages to piping and equipment6

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The collapse of infill walls, partitions or ceilings may cause

injuries, can undermine the safe evacuation of the structure

and affect the use of the medical equipments. These are

typical collapses in hospitals. In fact, ceilings are not

generally well anchored to the floor the infill walls are not

connected to the structures with ad-hoc systems to isolate

the infill from the displacements of structures or to prevent

the overturning (Fig.2).

To provide a fully operational environment, damage should

not affect mechanical and medical equipments as well as to

piping and lifelines. Surveys carried out in the aftermath of

several earthquakes world-wide have reported damage to

equipment and piping essentially due to lack of adequate

anchors and connections (Fig.3).

This study has presented the procedure to obtain a safety

index of an hospital in a simply way suitable for large scale

mapping of the seismic risk of hospitals; the procedure is

introduced and applied to two cases of study, then the

detailed structural analysis is developed and the results are

compared with the ones of the simply approach.

A simplified methodology, based on questionnaires, was

developed; it provides a safety index as function of all the

parameters that characterize the seismic risk: vulnerability,

hazard and exposition. The Safety index1 is evaluated

taking into account the aspects reported in fig.4.

Fig.4: Aspects influencing vulnerability of hospitals

1

A Safety Index for hospital buildings A detailed study of seismic risk for hospitals requires the

definition of an adequate level of knowledge of material

properties and structural details3 as well as the formulation

of complex structural models. It is evident as an advanced

study of the buildings involves time-consuming

computational efforts due to the size of the investigation to

be performed to obtain desired level of knowledge.

Moreover, it is not straightforward to develop models

taking into account the non-structural elements and

systems.

Nationwide, there are several hospitals, so it is unrealistic

to assess, in short time, the seismic vulnerability by

advanced analysis. It is, however, essential to evaluate a

safety index for all structures. This index should include

all facets of the seismic risk.

The methodology is based on the Hospital Safety Index

proposed initially by Pan American Health Organization7.

In the formulated methodology a number of changes were

introduced by the authors to improve the safety index.

Emphasis is on the Italian seismic hazard and the different

influences that each parameter has on the overall response

of the structure. In the implementation of the form, an

additional document by a Norwegian geo-scientific

research foundation (NORSAR) for seismic risk of

hospitals and schools8, was also used as reference.

The questionnaires comprise three principal sections; the

first section is related with structural elements, the second

with non-structural elements and facilities and the last

section takes into account the organizational aspects. The

formula adopted for the evaluation of the Safety Index is as

follows:

In the proposed methodology, Hazard (HAZ) is a function

of the seismicity of the area where the structures are built

and the soil type. Exposition (EXP) is a function of the

importance of the sample structures. For hospitals, the

exposition is related with the typology of hospital

departments located in the structures.

Vulnerability (VULN) is evaluated considering the

vulnerability of structural and non-structural elementsas

well as the organizational aspects. It was defined an index

for structural elements (ISTR), an index for non-structural

elements (INSTR) and finally an index for organizational

aspects (IORG); from the combination of these indexes,

called primary indexes, it is defined the vulnerability

(VULN).

The value of primary index is estimated through the

answers given in the questionnaires, separately for each

sections of the form. For each question, three answers are

given, as a function of the level of risk: low, medium and

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high. Different values express different levels of risk. Each

question assumes a different importance in the calculation

of the primary index, this value is called Unit Risk Index.

Two hospital buildings are considered as case studies in the

present work. The structures are located both in South of

Italy in areas with different seismic hazard. In particular,

RC_1 is located in an area with low seismicity. The second

structure, RC_2, is located in Apennines of Campania; it is

characterized by high seismic hazard. The investigated

buildings are multi-storey RC structures, designed in the

‘70s with the typical beam-column frame configuration.

RC_1 was built in the 70’s according to Italian codes in

force at the time (R.D.L. 2229 of 1039 and D.L. n°1086 of

1071). It can sustain only gravity load since at that time the

location was not classified as seismic area. The building is

composed by 15 blocks (fig.5) connected each other by an

expansion joint, i.e. approximately 7 cm.

The additional sample structure, RC_2, was built in the

early 70’s.The structure was designed for gravity loads and

seismic (moderate seismicity) actions. The hospital is

composed by 11 blocks. Thorough in situ surveys were

carried out to fill the forms and to evaluate the safety index.

Table1 provides the results obtained for the two case

studies, for the primary indexes.

For all primary indexes RC_1 presents higher levels of risk

than RC_2. The highest value of risk is related with ISTR of

RC_1 (0,78); this follows from the irregularity of the

structure, both in elevation than in plan and in the lack of

structural seismic details. ISTR for RC_2 assume a medium

value because the structure was designed to sustain not

only gravity load but also seismic action according to the

Italian seismic classification of that time (medium level of

seismicity).

For both the structures, the section dealing with non-

structural elements and services was not straightforward.

The difficulty stems from the needs to survey all facilities

in the buildings. The most important deficiencies are

related to anchorages of equipment and piping. A

INSTRvalue of 0,74 and 0,49 was founded for RC_1 and

RC_2, respectively; these values correspond to a high and

medium level of risk.

The index related to the organization of emergency is the

index with minor level of risk; in particular IORG assumes a

value of 0,64 for RC_1 and 0,41 for RC_2. In both

structures emergency plans are present even not directly

related with seismic emergency.

In fig.6, the histograms related to the percentage of answers

associated with different levels of risk are shown, for each

primary index. The plots are directly connected with the

values assumed by the primary indexes, with the difference

that in the indexes all questions are weighted as a function

of their importance in the final vulnerability.

For RC_1, total vulnerability (VULN) is equal to 1. This

results is connected with the decision to assume equal to 0

the functionality (FUNZ) if ISTR>0,67. Despite the

vulnerability and exposure are maximum, the overall

seismic risk is equal to 0,50. This value, in accordance with

established thresholds, corresponds to a medium level of

risk (Fig.7).

a)

b)

Fig.5: Case studies a) STR1, b) STR2

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a) b)

Fig.6: Histogram of the primary index a)Primary index for RC_1, b)Primary index for RC_2

Fig.7: Safety index RC_1

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Fig.8: Safety index RC_2

Model RC_1 Model RC_2

Fig.9: 3D view of two hospitals.

For RC_2 total vulnerability (VULN) assumes a value of

0,48, while functionality (FUNZ) is equal to 0,5. Despite

these percentages are better than those reported for RC_1,

the Safety Index is still medium (Fig.8). The reason is to be

found in the hazard; in RC_2 the seismic hazard has a

weight twice that of RC_1.

Effectiveness of ISTR index: Evaluation form

versus pushover analyses To obtain realistic seismic evaluations of existing structures

and to evaluate the results of the formulated simplified

methodology, advanced analyses are needed. Modal and

push-over analyses were performed. The analysis was

carried out in compliance with EC83 by SAP2000

9.

Relatively simple three-dimensional mathematical models

were chosen (Fig.9); the models consist of plane frames

connected by means of rigid diaphragms at the floor levels

as shown in figure 9.

Beam and column flexural behavior was modeled by

lumped plasticity i.e. inserting two inelastic rotational

hinges at both ends of elastic beam elements both for

beams and columns. The ultimate plastic rotation was

determined according to EC8-3.The elastic and inelastic

demand spectra are defined according to EC8, considering

the data of the locations where the hospitals are built.

Values in table 2 demonstrate the two structures are located

in two areas with very different seismic hazard (Table 2).

Table 2

Seismic Hazard

Limit State

agvalues DL SD NC

Structure ID [g] [g] [g]

RC_1 0.029 0.077 0.083

RC_2 0.171 0.442 0.486

The results of free vibration analysis for RC_1 and RC_2

are summarized in table 3, where T is the period of the

given mode; Ux and Uy are the participation masses of

each mode in X and Y direction, respectively; Uz is the

participation mass related with rotation in the plane of

diaphragms.

Table 3

Modal analysis

Case

Study

Mode T

(s)

Ux(%) Uy(%) Uz(%)

RC_1 1 2,28 0 74 53

2 1,61 0 2 13

3 1,33 79 0 13

RC_2 1 1,06 0 68 37

2 0,88 26 1 6

3 0,79 47 0 27

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The period of vibration of the first mode, for RC_1, is

2,276 sec. This elongated period is due to the structural

configuration of the analyzed block in the Y direction; in

fact the absence of frames in that direction causes a

cantilever behavior. The period of the first mode, for RC_2,

is 1,06 sec. This result shows that RC_2 is stiffer than

RC_1 because of the presence of frames in both principal

directions. In both structures torsional effects are evident

related to relevant participation masses for rotation in the

plane. These effects are due to the irregularity both in

height that in plant of the structures.

To evaluate the seismic performance, push-over analyses

were carried out according to EC8. Three limit states were

examined: DL (limit state of Damage Limitation), SD

(limit state of Significant Damage) and NC ( limit state of

Near Collapse). The non-linear static analysis was

performed with respect to the two main directions of the

construction even if independently.

The behaviour of the structures is characterized by a

capacity curve that represents the relationship between the

shear base force and the displacement at the top of the

buildings; these capacity curves for RC_1 and RC_2 are

shown in fig.9 for both the principal directions of the

seismic action (X and Y). In these figures the displacement

demands for the three limit state considered (NC, SD, DL)

are also marked.

The capacity curves of RC_1 show that the maximum base

shear force is different for the two principal directions; in

particular the shear capacity in X direction is 160% greater

than that in Y direction.

Furthermore the analysis of hinges rotation proves that the

structure is not compliant with the code at NC and SD limit

states. In fact, with an NC seismic demand, all columns of

the ground floor and some of the first and second floors

reach the limit rotation. The collapse of the structure occurs

by a soft-storey mechanism involving the columns of the

ground floor. The highest demand of plastic rotation for the

columns of the first three floors is due to the already

mentioned irregularity in height.

The analysis of shear capacity was performed in the post-

analysis stage. The analysis showed that shear is much

more critical than flexure, especially because it is a fragile

mechanism of collapse. Evaluating the shear capacity

according to EC8, shear failure occurs in all columns of

ground floor for NC limit state, before reaching limit

rotations corresponding to the flexural collapse mechanism.

For RC_2 a lot of plastic hinges form in the beams giving

an high ductily level albeit is not enough to satisfy the

demand; furthermore some beams and columns reach the

shear strength before the flexural one and all the joints are

not reinforced with stirrups and non verified at the ultimate

condition of the capacity curve.

The results of push-over analysis were used to study the

effectiveness of results obtained by simplified

methodology. The Safety Index, derived by simplified

methodology, was compared with an index of risk

evaluated by push-over analysis. The push-over index

proposed is the ratio between the capacity and demand in

condition of near collapse limit state (NC):

Fig.9: Pushover curve for the two case studies

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IPush-overis equal to 0,74 and 0,47 for RC_1 and RC_2,

respectively; and these values are structural safety

indexesobtained by detailed analysis.

With reference to simplified methodology, the safety

indexes result equal to 0,5 and 0,51 for RC_1 and RC_2,

respectively, since INSTR and IORG are set to 0 and only the

structural indexes (ISTR) are taken into account to evaluate

the vulnerability (VULN).

As can been seen, there is a good match for the results of

RC_2, while for RC_1 a higher scatter has been obtained.

This result seems mainly related to the different HAZ

valuesassigned to the two case studies. In particular, for

RC_2 both the hazard and the exposure parameters are the

highest, for RC_1 the exposure assumes the highest value

while the HAZ value is halved with respect to the RC_1

one, resulting in an over reduction of the whole safety

index when compared to that given by the pushover

analysis. Therefore the performed applicationswould

suggest a revised calibration of the HAZ parameter aiming

to better comply with the variation of the seismic hazard

maps of the Italian national territory.

Conclusion A simplified methodology, based on questionnaires, has

been developed aiming to map the seismic risk of critical

constructions, as hospital buildings, on a territorial scale.

The proposed methodology is based on the Hospital Safety

Index assessed by Pan American Health Organization,

modified by the authors to comply with specific national

features influencing the seismic risk.

The proposed methodology takes into account not only the

structural vulnerability but also the vulnerability of non-

structural elements and services as well as the

organizational aspects. In addition parameters depending

on Exposition and Hazard are also considered to finally

evaluate the Safety Index of the hospital buildings. The

form has been applied to two Italian hospitals built in the

same period but in areas with different seismic hazard.

Push-over analysis has been carried out to check the

effectiveness of the structural index derived from the

simplified procedure.

It does not show a satisfying agreement between the

structural index evaluated by the simplified methodology

and the index obtained by the push-over analysis for both

the examined cases, since the influence of the hazard index

is probably not well calibrated.

References 1. WHO (World Health Organization), NSET (National

society for earthquake technology-Nepal), Guidelines for

seismic vulnerability assessment of Hospitals (2004)

2. FEMA 396. Incremental Seismic Rehabilitation of

Hospital Buildings; Federal Emergency Management

Agency, (2003)

3. CEN, Eurocode 8: Design of Structures for Earthquake

Resistance; European committee for standardization (2004)

4. D.M. Infrastrutture 14 gennaio Nuove norme tecniche

per le costruzioni (2008)

5. ASCE 7-10, Minimum Design Loads for Buildings and

Other Structures, American Society of Civil Engineers,

(2010)

6. FEMA E-74 Reducing the risks of nonstructural

earthquake damage, Practical Guide, January (2011)

7. WHO (World Health Organization), PAHO (Pan

American Health Organization), Hospital Safety Index,

Guide for evaluators (2008)

8. Lang D.H., Verbicaro M.I., Wong Diaz D. and Gutierrez

M., Structural and non-structural seismic vulnerability of

schools and hospitals in Central America, Final Report,

NORSAR, Kjeller, Norway (2009)

9. SAP, Analysis reference manual, Computers and

Structures, Inc., Berkeley (2000) (Received 9

th April 2012, accepted 8

th August 2012)

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