Simulation and Numerical Modelling of Heritage Stone Masonry

Timber Structure in Seismic Region

Marina D. Traykova

, Alexander V. Traykov

and Raji A. Shouaib

University of Architecture, Civil Engineering and Geodesy (UACEG), 1, Hristo Smirnenski Blvd., 1046 Sofia, Bulgaria

Higher School of Transport “Todor Kableshkov” (VTU), 158, "Geo Milev", 1574 Sofia, Bulgaria

Keywords: Heritage Structures, Simulation, Numerical Modelling, Seismic Performance, Preservation.

Abstract: Numerical modelling of heritage structures is a very challenging task. The difficulties are related to the

adequate computer modelling of the used construction materials and the adequate modelling of the structural

elements and their connection. In the context of the above, it is necessary to specify a lot of input information

and to thoroughly study the output data of the analyses. The paper presents the process of creating and

analysing different numerical models for a heritage stone masonry-timber structure of an ancient church in

Bulgaria. The Orthodox Church "Transfiguration of the Lord" in the city of Pomorie, Bulgaria was built in

the second half of the 18th century. The church is a three-nave building with a timber roof. The combination

of different construction materials – stone and wood and the specific geometry and details of the structure,

impose the creation of several numerical models, especially when studying the seismic behaviour. The final

conclusions for the structure and the structural elements are made using the results from different computer

models. Finally, some more general recommendations for the application of the variant research in modelling

in order to obtain best results are given.

1 INTRODUCTION

Modelling the performance of heritage structures is

important stage for every preservation project (Partov

D and Traykova, 2017., Traykova M and Chardakova

T, 2017., Traykov A, 2017). Numerical modelling is

able to reflect more complex, and hopefully more

accurately, the behaviour of the studied structure,

mainly in terms of its geometry, the behaviour of

various structural components and their interaction.

That stage is part of a bigger plan for investigation

and rehabilitation of structures with historical value.

Methods and approaches for dealing with such tasks

are discussed in (Roca P, 2020., Nowogonska B,

2020., Coïsson E, Ferretti D, Pagliari F, 2020 and

Panto B, et al., 2020). The knowledge of a significant

number of designers is required in order to create

accurate and convincing computer models of intricate

historic buildings. (Traykova M, 2019). It is probably

best to start with the simplest realistic model and then,

if necessary, develop a model that reflects more

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structural features and complexity (Traykova M and

Traykov A, 2021., Maeda T, et. Al., 2020) regardless

the type and the complexity of the analysis. In order

to prolong the life of the structures and preserve them

for the future, it is necessary to develop an

appropriate structural model so that the behavior of

the structure can be evaluated, its vulnerable areas can

be located, and risks can be reduced. In light of the

aforementioned, it is essential to detail a significant

amount of the supplied information. (Traykova M and

Ivanova B, 2021 and Traykova M and Traykov A,

2021) and to thoroughly study the output data of the

analyses (Partov D, Ivanchev I and Traykova M,

2019).

The research that is presented in the paper details the

process of consecutive iterations that were carried out

with the intention of providing the most accurate and

detailed information for the behavior of the structure

as well as the most effective measures that can be

taken to preserve the building Partov D, Ivanchev I

and Traykova M, 2019).

324

Traykova, M., Traykov, A. and Shouaib, R.

Simulation and Numerical Modelling of Heritage Stone Masonry Timber Structure in Seismic Region.

DOI: 10.5220/0012107400003680

In Proceedings of the 4th International Conference on Advanced Engineering and Technology (ICATECH 2023), pages 324-330

ISBN: 978-989-758-663-7; ISSN: 2975-948X

 2023 by SCITEPRESS – Science and Technology Publications, Lda. Under CC license (CC BY-NC-ND 4.0)

2 GENERAL DESCRIPTION OF

THE BUILDING

The Orthodox Church "Transfiguration of the Lord"

in the city of Pomorie (Figure 1), Bulgaria was built

in the second half of the 18th century. The church is

a three-nave building with a timber roof. According

to preserved historical sources, the church was built

on top of an early Christian basilica in 1763-64 and

consecrated in 1765. It is also the oldest building in

the entire city of Pomorie. It houses valuable

examples of iconographic art from the 15th-19th

centuries, with the oldest icon being from the end of

the 15th century, the beginning of the 16th century.

The plan of the church is a rectangle with dimensions

of 24.60 m by 12.10 m (Figure 2). The approximate

thickness of the stone masonry walls in the main part

of the building is about 1m, but it varies within ±5 cm.

Figure 1: Main entrance of the church.

Figure 2: Plan of the church.

The structure of the church is massive,

constructed from an insignificant amount of worked

stones used for the corners of the building, as well as

from roughly cut stones with a very heterogeneous

petrographic composition, arranged with wide lime

joints. The petrographic origin of the rocks used for

stone blocks differs significantly, predominating the

specimens of sedimentary rocks, but metamorphic

rocks, mainly marble, have also been found. Stone

blocks of sandstones were found as individual

specimens. A significant part of the stone blocks has

a wet surface with a depth of 10-15 mm from the

surface, and some are even cracked as a result of loads

or operational impacts. The connection is made by

means of lime mortar, and the joints during the last

renovation works of the church were locally surface

treated with cement mortar.

In the longitudinal direction of the stone walls,

internal connections are made with solid timber

elements (Figure 3).

Figure 3: Timber elements used for masonry structure.

3 NUMERICAL MODELLING

There is a large volume of literature devoted to

computer modelling of structures. While some of the

books have a more general nature (Feng Fu, 2015)

and a significant volume, a significant part of the

publications present specific methods related to the

numerical modelling of buildings and facilities with

historical and cultural value (Panto B, 2020., López

López D, 2020., Hassanieh A, Gharib M, King M,

2020), and some of them present a methodology

related to the analysis of specific buildings or bridges

(Gobbin F, et. Al., 2009 and Mentese V, Celik O,

2020). Comprehensive study and practical approach

for numerical analysis and assessment of masonry

Simulation and Numerical Modelling of Heritage Stone Masonry Timber Structure in Seismic Region

325

structures is presented in (Iannuzzo A, et al., 2020).

For the purpose of the preservation project considered

in the present paper, 3D computer computational

models of the church were created with the software

SAP2000 (CSI software). The geometry of the

structure, the characteristics of the used materials, as

well as the geotechnical data for the ground base,

defined during the “on site” investigation, were taken

into account in the models.

The following construction materials

characteristics are defined in the computer models for

modelling the structure (all characteristics are defined

“in situ” or on specimens in the Laboratory of

University of Architecture, Civil Engineering and

Geodesy, Sofia, Bulgaria):

• Timber – Modulus of elasticity

E = 3000 MPa

(1)

Characteristic compressive strength:

c,90,

= 7,25 MPa (2)

Characteristic tensile strength:

t,0,

= 14,53 MPa (3)

The weight per unit volume is 8 kN/m

;

• Masonry – Modulus of deformation E

1626 MPa;

= 1626 MPa (4)

The weight per unit volume is 18 kN/m

The limited level of knowledge for the

construction materials requires the reduction of the

characteristics with a confidential factor

KL1

= 1,35 (5)

according to EN 1998-3 (European Standard – part 3,

2005).

Concerning the checks for the bearing capacity

and the deformations, the requirements of the

standards Eurocode are followed.

3.1 Numerical Modelling of the Timber

Roof (Model 1)

This model aims to provide information about the

elements of the timber roof structures. According to

the location of the city, the specific loading for wind

and snow are considered.

Figure 4: 3D model of the timber roof structure.

The elements of the timber roof are checked.

Special attention is provided for the deformations

because of many real damages in the roof found

during the site investigation (Figure 5).

Figure 5: Deformation of the most unfavourable timber

truss from: a) permanent loading; b) wind loading.

Based on the structural analysis carried out and

the results obtained after the analysis, it was found

that one part of the timber elements need

strengthening. A special project was developed with

specific details for strengthening of the roof elements.

This local 3D model of the roof was very useful for

the realistic assessment of the condition of the

analyzed structure. The reactions of the roof

subsequently are applied in one of the next models.

ICATECH 2023 - International Conference on Advanced Engineering and Technology

326

3.2 Numerical Modelling of the

Building Structure (Model 2)

Modelling and linear static analysis of the structure is

carried out according to Eurocode (European

Standard – part 1-3, 2005). Two 3D computational

models have been developed using the finite element

method in the SAP2000 software product

environment. All elements of the structure, including

the roof, are presented in the first model (Variant 1,

Figure 6). That model is analyzed for load

combinations: seismic, in order to obtain the

maximum horizontal displacements, and also the

main (fundamental) load combination to obtain

internal forces from ultimate limit states. Due to the

fact that the timber roof structure is "softer" compared

to the stone masonry structure and in order to specify

the real behavior of the structure, a second model was

created (Variant 2, Figure 7) where the timber roof

structure was replaced with the loads from its support

reactions. The following types of finite elements (FE)

were used in the models: for the planar elements –

two-dimensional shell finite elements, elements with

smaller cross-sections and less linear bending

stiffness are modeled with one-dimensional frame

finite elements. The elements at the edge are modified

in a way to reflect the performance of the supporting

structure as accurately as possible.

Figure 6: Variant 1 3D model of the masonry structure and

the timber roof.

The presence of cracks in the walls was accounted

for in the computer model by forming a critical zone,

with a height of about 1/6 of the height of the wall, in

which the elastic stiffness is reduced by 50%.

Figure 7: Variant 2 3D model of the masonry structure

without the timber roof.

The seismic analysis of the building is carried out

by means of the response spectrum method. The first

natural period of the structure is T1=0,1166 s, the

activated masses are more than 90% in horizontal and

vertical directions. Maximum displacement at the top

of the wall under seismic loading is 15 mm.

According to the seismic map of Bulgaria

(European Standard – part 1, 2004) ground

acceleration

g,R

= 0.11g

(6)

g,R

= 0.11g is adopted. The soil is category D

According to (European Standard – part 1, 2004)

and after the special geotechnical investigation on

site. A very weak backfilling with low bearing

capacity was found as a soil layer under the building.

According to the geotechnical report a value of ks is

5000kN/m

for the soil area stiffness is adopted in the

computer model. The importance factor is

= 1,2 (7)

as the church is a specially protected heritage

building. A behaviour factor

q= 1,5

(8)

It is adopted according to (European Standard –

part 1, 2004) as the structure is one of a limited

ductility. Horizontal and vertical design response

spectrum according to (European Standard – part 1,

2004) is used for the calculation of the accelerations.

A comparison between the results of the two

variants are made for the different internal forces:

F11, F22, M22, V23 (Figures 8, 9).

Simulation and Numerical Modelling of Heritage Stone Masonry Timber Structure in Seismic Region

327

Figure 8: F11 – Comparison between Variant 1 and Variant

Figure 9: M22 – Comparison between Variant 1 and

Variant 2.

Due to the predominant effect of vertical loads,

the stresses in the walls are mainly compressive. The

analysis of the two combinations (fundamental and

seismic) shows the occurrence of local tensile forces

with minimum values in the areas around the

openings. Local tension also appears in the areas of

the triangular walls on the east and west facades at the

points where the timber structure is supported. This is

found in both combinations, as for the seismic one,

the values are slightly higher compared to the

fundamental combination.

The main conclusion that can be drawn from the

actual comparison of the two variants of Model 2 is

that the addition of the roof structure leads to some

redistribution of forces in limited-sized and localized

areas of the walls, but the forces do not change as

values. As expected, the stress concentration zones

are local and concentrated around the openings. In

connection with the results obtained from the

numerical analyses of the models, it can be assumed

that in practice the zones in the walls, in which there

are locally significant stresses, are present in very

small areas. Given the status of the church and the

need for preservation of its authentic vision, it is

appropriate to recommend taking measures to repair

the cracks in the walls and improve the spatial

performance of the masonry structure by improving

the connection between the walls/facade walls and the

connection between the roof structure and the walls.

4 CONCLUSIONS

The numerical modelling provided for the

preservation project of the church "Transfiguration of

the Lord" in the city of Pomorie, Bulgaria led to the

following particular as well as more general

conclusions and recommendations:

1. The analysis of the numerical results obtained as

a result of the simulation of the behaviour of the

building shows that the structure is able to resist

the provided by Eurocode vertical and

horizontal loads acting on it.

2. Usually creating one numerical model is not

sufficient to cover the specific features of the

structure and its elements and to reflect all

details and complexity of the structure. The two

numerical models discussed in the paper provide

better information about the structural

behaviour and the specifics of the contribution

of the different elements of the building to its

overall response to actions.

3. Based on the numerical models provided in the

research, it was possible to prepare a special

preservation project that includes three groups

of activities: 1) Rehabilitation and strengthening

of the roof structure; 2) Rehabilitation and

strengthening of the stone masonry structure; 3)

Rehabilitation and strengthening of the

foundations. There is many construction

solutions reported in the scientific literature and

implemented by the professionals for

rehabilitation, strengthening and conservation

of structures of historical value.

4. The numerical modelling of heritage structures

presents increasing challenges to structural

engineers – complex structural geometry,

specific structural schemes, different types of

existing damages, necessity to find the real

characteristics of specific old construction

ICATECH 2023 - International Conference on Advanced Engineering and Technology

328

materials, etc. The option to analyse different

models brings the opportunity to select easier

the different techniques and structural solutions

for each specific part of the structure. That

approach allows for the optimization of the

structural design and for minimizing the

construction cost. Future work envisages

monitoring the behaviour of the building, as

well as developing computer models for the

analysis of the non-linear structural behaviour

based on the available data.

ACKNOWLEDGEMENTS

This work was supported by AVT Consult Ltd,

Bulgaria.

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