STABILITY OF TOWERS: THE MINARET OF JAM, …prev.enea.it/2015-05-07 Tueor-03-Clemente P.pdf · 2 spiral staircases 6 square vaulted brick platforms Small cupola Wooden staircase

Giornata di Studio

TUEOR ERGO ERO Protezione delle strutture d’interesse storico e artistico dai rischi naturali: alcuni casi di studio nel mondo

ENEA – Roma, 7 maggio 2015

STABILITY OF TOWERS: THE MINARET OF JAM, AFGHANISTAN

Paolo Clemente

ENEA, Prevenzione Rischi Naturali e Mitigazione Effetti

Giornata di Studio TUEOR ERGO ERO ENEA, Roma, 7 maggio 2015

Paolo Clemente – Stability of towers: the minaret of Jam, Afghanistan

JAM AND THE MINARET Jam: Ghur province of western Afghanistan, inaccessible mountainous region about 260 km East of Herat.

Minaret: built on the south bank of the Hari river at the intersection of two canyon-like river valleys.

Site: ancient city of Firuzkuh, capital of the Ghurid dynasty that ruled Afghanistan and parts of northern India, from Kashgar to the Persian Gulf, in 12th and 13th centuries.

Remains of castles and towers of the Ghurid settlement are on the opposite bank of the Hari river and North of the Minaret. Remains of fortifications are East of the Minaret

Ghurid fortunes declined in 1202, and finally the Mongol armies completed the destruction in 1222, under Ghengis Khan.



1962: Architectural survey by Andrea Bruno with proposal for restoration. Then reinforcement of the base with a stone and timber dam (Jam rud and the Hary rud bordering the structure)

1971 – 1975: further surveys to determine the degree of leaning

1978: UNESCO financed the intervention by means of large stone-filled metal gabions

1944: First official record (J.l Anis, Society for Afghan History)

1957: Rediscovered by André Maricq of CNRS, France

1959: Topographical survey by Fischer, Cambridge Univ.

MINARET HISTORY: 1944 – 1999



HISTORY: 1999 – 2007

Reconstruction of the missing parts of the octagonal basement, using bricks similar to the original ones, in terms of form, size, rigidity and strength

2001 – 2007: Technical missions of UNESCO experts (among these Bruno, Margottini and Orlando)

1999: Gabions along the Jam river

2003: UNESCO declared Jam as the Afghanistan’s first World Heritage Site



HISTORY: 2007 – 2008

2007: (end of April) a severe flood occurred at the destroying part of the gabions, very close to the structure

2007: P. Clemente and G. Buffarini were involved in the stability analysis of the tower and in the definition of the necessary interventions

2008: First results were presented in a meeting at ICCROM in Rome (June).

2009 - … The analysis was improved and completed



DESCRIPTION

Materials: bricks and lime mortar

tapered truncated blocks with ring cross-section, one upon the other

tapered blocks with circular cross-section, that ends at the height of 43.50 m.

2 spiral staircases

6 square vaulted brick platforms

Small cupola

Wooden staircase



GEOMETRIC DECORATIONS

Exterior completely covered with geometric decorations

First cylinder the most decorated: the entire Sura of Maryam, the 19th chapter of the Koran, which tells the stories of the prophets.

Further Kufic inscriptions between the first and second balconies and above the latter.



GEOMETRICAL CHARACTERISTICS

D = 2.19 m

D = 9.59 m

D1 = 4.86 m

D2 = 1.72 m

hw = 19.84 m

W = 33.3 MN

H = 65.4 m

* = 0.059 rad

D = 9.74 m

Cross-section of octagonal form for the first 4.0 m

Basement suppose at 2.60 m under the entrance level



SOIL CHARACTERISTICS Geology strongly affected by the mountain environment (Bruno & Margottini): • a bedrock composed by massive granite/granodiorite, and • covered by few orders of alluvial deposit (sediments related to different

alluvial stages, mainly composed by sand and gravel, heteroclastic and heterometric, with abundant presence of sand matrix

Geophysical campaign (georadar, seismic refraction profiles and vertical electric soundings – Orlando): • information about the local stratigraphy and the typology of foundation • buried archeological remains at about 2.0 m from the ground surface

3 layers Soil layer Composition Thickness (m)

Vs (km/s)

1 Clay and sand 2÷10 0.5 2 Sand and gravel 10÷23 2.5 3 Granite - 4.5

• Compression strength: 0.7-1.5 N/mm2 (mean value ft = 1.0 N/mm2) • Elastic-perfect plastic behaviour



PRESENT CONFIGURATION Initial situation = not leaning

Present configuration:

39.19w w

M W h MNm * * *

0.059 rad

33.3N W MN

1.18 8w

e M N m D *

2.06w

T W MN * *

max0.82

minx0.01

m0.44

< 1.0 N/mm2



INELASTIC AND ELASTIC ROTATIONS

0 0

* *

rM k

0

0

1*

wW h

k

Effective values of

Soil

reaction

External

moment

Inelastic rotation 0

Effective value

of the moment

Inelastic rotation 0 < *



INELASTIC ROTATION

3

0 21

E Dk

I 21

w

w

E Dk

I

Iw = 1 I = 6



LIMIT BEHAVIOUR OF THE BASE CROSS-SECTION

2

04

t

DN f0 0

3

DM N

• If N < N0/2 LS1 occurs first

• If N > N0/2 LS2 precedes LS1

3 Limit States



LOADING PATH

0

1

202 0

0 0

8

x N

x D x x x dxD x N

1

0 0

3

8

M N

M N

0

1

22 0

0

8

x N

x D x dxD N

0

1

max 202 0

0 0

8

x

t

Nx D x x x dx

D x f N

0

2

0

0 04

p

p

x x

x op

x x D Nb x dx b x dx

x x N



NON LINEAR ANALYSIS

3

21

E Bk

I

,

(x0, xp) N =W = cost, M, e

d dM k

3

2

2

1

0.233 1

r

w w w

M k E DFS

M W h W h I

E

*

*

3

0 21

E Dk

I



HORIZONTAL FORCE / ACCELERATION

0

H

F m z a z dz

0

0

( )

H

H

m z a z d z dzLd

F m z a z dz

1

w

F

Fe h

W h

F wM F h W h e e

Horizontal F

Rigid model – Horizontal Acc.: gen. F – gen. d



SEISMIC HAZARD (Abdullah, 1981 and 1993; Ambraseys and Bilham 2003).

No large earthquakes have occurred at the site since 25 A.D. (from earthquake

historical and instrumental catalogues (certainly not complete)

Nearest epicenter cited in the literature is located 170 km from Jam

Jam lies in proximity of the Herat fault, a prominent right lateral strike-slip

lineament running along north Afghanistan for about 1100 km, which for

most of its length was not associated with occurrence of earthquakes.

Residents of the neighboring village have

experienced earthquakes;

Earthquakes of moderate intensity cannot

be totally ruled out, as demonstrated by

the recent tectonic uplift in the region

So the region was classified as weak

seismicity area



EFFECT OF COMPRESSION STRENGTH OF SOIL

0

2

0

0 04

p

p

x x

x op

x x D Nb x dx b x dx

x x N

LS2 precedes LS1

Present configuration between LS1 and LS3

Loading path



Compression strength fm = 4.0 N/mm2

Elastic-perfect plastic behaviour

LIMIT BEHAVIOUR OF THE STRUCTURE

Section f N/mm2

N/N0 M/M0 Service

M/M0 LS1

M/M0 LS2

M/M0 LS3

Base 1.0 0.447 0.501 0.527 0.644 0.989

S1 4.0 0.126 0.127 0.158 0.397 0.430

S2 4.0 0.051 0.047 0.067 0.177 0.190

S3 4.0 0.032 0.020 0.047 0.100 0.106



FINITE ELEMENT MODELS Ansys®: linear model, 8 nodes solid brick elements (no planar

cross-sections hypothesys); shell elements for helicoidal stairs

and the vaults

SAP2000®: beam elements (43 with pipe section for the external

ring, 17 with circular cross-section for the core), nonlinear

pushover analysis

Actual geometrical characteristics of the structure

Masonry Young’s modulus E = 3200 N/mm2

Weight per unit volume = 16 kN/m3

Compression strength of masonry fm= 4.0 N/mm2

Compression strength of soil ft= 1.0 N/mm2

fm and ft were varied in order to analyze their influence on the

structural behaviour



MODAL ANALYSIS

Ansys®: solid elements

SAP2000®: beam elements



PUSH-OVER ANALYSIS: LOAD Soil = link element at the base node, with nonlinear moment-rotation curve previously defined

Masonry sections S1 to S3 = moment-curvature relations derived assuming an elastic-perfect plastic behavior (for the link elements the moment-rotation relation was deduced fixing the length of the link)

Case 1: load vector proportional to the first mode

Case 2: multi-mode approach; incremental load vector i-th component

mi = masses

= mass participation coefficients,

= n-th mode vector,

Sa(Tn) = pseudo-acceleration corresponding to the n-th mode, deduced from the spectra.

Total number of seven modes participation mass = 91%.

2

,

1

( )

N

i i n i n a n

n

m S T

Multimodal

Single mode



PUSH-OVER ANALYSIS: RESULTS

• Contribution of higher modes not negligible

• Failure can occur for soil collapse or masonry collapse in the top part, depending on the soil-masonry strength ratio



CONCLUSIONS Stability check

• The Minaret is stable under dead loads

• Check very sensitive to the soil properties

If ft<< 1.0:

• Wide portion of the soil under foundation could be yielded

• The structure could be closer to the collapse point than it appears

Seismic vulnerability

• Very high

• Very sensitive to the soil characteristics

Further investigations:

• Soil characteristics,

• Foundation depth and conditions,

• Masonry characteristics

• Ambient vibration analysis to improve the numerical models



DHARAHARA TOWER, NEPAL



END

THANK YOU

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STABILITY OF TOWERS: THE MINARET OF JAM, …prev.enea.it/2015-05-07 Tueor-03-Clemente P.pdf · 2 spiral staircases 6 square vaulted brick platforms Small cupola Wooden staircase