Structural Restoration of Masonry Monuments

Arches, Domes and Walls

George Penelis, Gregory Penelis, George G. Penelis, Gregory G. Penelis

• Publisher: CRC Press
• Year: 2020
• eBook ISBN: 9780429656897
• Edition: 1
• Topic: Architecture
• Subtopic: Architecture General

Historic structures need to be restored in line with international guidance and charters developed by architects and archaeologists, but technical understanding of structural engineering and materials is crucial, particularly with respect to response to earthquake loading.

This guide to structural assessment and restoration of masonry monuments and historical buildings outlines the techniques, materials and design procedures used. It begins with principles, theory and practice and then presents case studies.

The assessment focusses on

• 
  
  

• Building materials and construction techniques used in the past

• 
  
  

• The mechanics of masonry

• 
  
  

• The structural behaviour of masonry monuments and historical buildings

• 
  
  

• In-situ investigation and laboratory tests for existing and restoration materials.

The restoration elaborates on

• 
  
  

• Techniques and materials available for structural restoration

• 
  
  

• Structural analysis and design

• 
  
  

• Deciding on the restoration scheme

• 
  
  

• Emergency measures and protective measures.

Chapter 1

Introduction

1.1   General

The conservation of monuments and historical buildings is one of the most important expressions of the contemporary cultural activities. These constructions are all those which merit special care on account of their individual historical or architectural importance or their significance as surviving representatives of earlier tradition (UNDP/UNIDO, 1984).

The structural restoration of monuments and historical buildings, being a part of their conservation, has only been recognised, as a special field of the construction technique, in the last few decades.

Main purpose of this book is to outline the techniques, the materials and the design procedures in use for the structural restoration of masonry monuments and historical buildings generally and particularly in seismic regions.

Both historical buildings and contemporary ones are approached from a structural point of view with the same scientific background, namely the ‘structural mechanics’ (theory of structures, strength of materials and earthquake engineering). In both cases, the structural engineer in charge is concerned primarily with giving the structures the ability to withstand gravity loads and seismic actions without excessive damage, safeguarding primarily the life safety. However, the problem of structural restoration of monuments and historical buildings differs radically from repair and strengthening of conventional contemporary buildings damaged by accidental effects like seismic action. The aim of repair and strengthening of conventional buildings is to keep them in use at a specified safety level (Penelis, G. and Penelis, Gr., 2019). On the other hand, for monumental buildings, emphasis is given to the preservation of their aesthetic and historical values, while the task to remain in use may be considered of secondary importance and, in any case, as consequence of the effort at fulfilment of the main task (Penelis, G., 2002).

More precisely, the features and the values that have to be considered for the characterisation of a building as a monument or historical building may be summarised (UNDP/UNIDO, 1984) as follows:

• A symbolic value that has led to the original construction. A temple, a church or a mosque has such a value from the beginning. Other buildings may have acquired their symbolic value afterwards, as a result of historical events during the life of the structure.
• An aesthetic value, as a work of art deliberately created, or as an important feature in the landscape or the townscape.
• An indirect value based on contents or decorations that are themselves of aesthetic value (mosaics, frescos paintings etc.).
• A ‘documentary value’ of the architectural or structural creativity of a particular time and region.
• A secondary ‘documentary’ value in relation to particular historical or religious events.
• A social function as a focus of community life.
• A value, as part of a group of structures which, together, have one or more of the above values.

The decision for characterising a building or an urban nucleum as a monument or as a historical building is the result of extensive investigation that is carried out by archaeologists, historians and architects, and in this respect is beyond the scope of this book. It should be noted, however, that the final decision for the characterisation belongs to the relevant authorities of each country, or of UNESCO.

1.2   Restrictions Under Consideration for the Structural Restoration

The constraints for a conventional contemporary building that should be taken into account for repair and strengthening are basically the following (Penelis, G. and Penelis, Gr., 2019):

• The specified use function of the building after retrofitting.
• The aesthetics of the building.
• The cost of retrofitting.
• The lifetime of the building after retrofitting.

On the other hand, for the structural restoration of a monument, basic restrictions that should be taken into consideration may be resumed as follows (UNDP/UNIDO, 1984; Penelis, G., 2002):

• Respect for the original material and authentic documents.
• Respect to the valid contributions of all periods to the building.
• Replacement of missing parts must integrate harmoniously with the whole but, at the same time, must be distinguishable from the original.
• Additions cannot be allowed, except in cases where they do not distract from the interesting parts of the building, its traditional setting and its relations with the environment.
• The use of traditional techniques and materials are clearly preferable for structural restoration.
• Modern techniques and materials are admissible where adequate capacity cannot be ensured by traditional techniques and materials. In this case, durability and compatibility of the interventions should be adequately proven; otherwise the modern techniques and materials should be used only in a manner that will permit easy corrective action at a later date if necessary (reversible interventions).
• Measures are necessary to prevent and safeguard frescos and mosaic decoration. This may exclude the use of some strengthening techniques that may cause damage.

All above restrictions or rather principles or rules are included in Venice Charter, a document which was elaborated at 11th International Conference of Venice, in 1964, an international meeting of experts aiming at the protection of the cultural heritage (Feilden, 2003; UNDP/UNIDO, 1984). Particularly, articles 9, 10, 11, 12, 13 and 16 of this document refer to ‘Restoration’ and include all above-mentioned constraints.

1.3   Authenticity and Life Safety

From what has been presented so far, the preservation of authenticity, in the framework of a restoration, plays a crucial role. However, it is the authors’ opinion that it is also of major importance to ensure many other values, as for example, the use or the visit availability of the monumental building and, most important, the protection of human life, which is directly connected with the safety of a structure against collapse (Penelis, G. and Penelis, Gr, 2019). In this respect, a close cooperation must be established, mainly between archaeologists, architects and structural engineers in charge of the restoration of a monument, so that a common place of understanding may be found, satisfying both main tasks, namely, authenticity and life safety.

The collaboration between the above professionals may be more effective and fruitful, if each has some understanding of the others’ aims, needs and approaches, as well as, the choices open to them. The above constitutes a demanding task that calls for considerable flexibility of mind of all components in defining objectives, seeking, interpreting and assessing evidence and choosing schemes to be put into effect.

It is interesting to note here that the recent publication of ASCE 41-17 (ASCE 41-17, 2017), referring to evaluation and retrofitting of buildings against earthquakes, includes in its scope (see commentary of Chapter 1 – general requirements) the structural evaluation and the retrofitting of historical buildings too. However, it poses serious restrictions for the applicability of the actions that could be taken to evaluate and retrofit conventional contemporary buildings. In this respect, there is, even in this standard, a complete compliance with the concerns presented in detail in the above paragraphs.

1.4   The Structure of THIS Book

As it is already noted above, the purpose of this book is the presentation of techniques, materials and design procedures in use for the structural restoration of masonry monumental and historical buildings.

However, for the accomplishment of this task, it is necessary to precede with a detailed presentation of materials and techniques used in their original construction, the mechanics of masonry, being the basic structural material, their structural forms classified in groups and their behaviour to conventional loads and seismic actions. Furthermore, an insight approach should be made to the philosophy behind of all these for the formation of safe paths for load transfer from the structure to the foundation.

Additionally, before any intervention, it is necessary to obtain a deep knowledge of the texture of a monument under consideration, the materials used for its construction, its pathology and, finally, its residual strength. So, the structure of this book is formatted as follows.

In the first three Chapters (2, 3 and 4), an overview of the main characteristics of the existing historical masonry building stock and its structural response to various loading actions is presented. Particularly a short presentation of the materials and the techniques of the past is made, the masonry mechanics is reviewed and the behaviour of each characteristic structural form under gravity loads and seismic actions is analysed basically.

In the next Chapter (5), the following issues are examined: the restoration philosophy (reversible–irreversible techniques, local–general types of intervention), the intervention techniques and materials in use (Tassios, 2001).

In Chapters 6, 7 and 8, the following procedures are presented: the collection of all necessary information of a monumental building under consideration for structural restoration, i.e. in-situ investigations and laboratory tests, the procedure for static or dynamic analysis and design and the assessment, i.e. diagnosis and safety evaluation together with the choice of the structural restoration scheme.

Finally, in Chapter 9, a series of case studies of some prominent monumental buildings, which the authors have restored during their professional career, is presented.

Chapter 2

Building materials and construction tec...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• List of abbreviations
• Foreword
• Preface
• Authors
• 1 Introduction
• 2 Building materials and construction techniques of monuments
• 3 Masonry mechanics
• 4 Structural behaviour of masonry in monumental buildings
• 5 Techniques and materials in use for structural restoration
• 6 In-situ investigations and laboratory tests
• 7 Structural analysis and design
• 8 Assessment
• 9 Case studies
• References
• Index