English

4.1 General objectives

As specified in the Inception report (see §1.1), in the Phase A report (see §1.1), and in the previous chapter, here next it is confirmed the main purpose of this assignment: the aim of this design work is to produce all the elaboration required in the ToR following the listed purposes, among which, the most important is to rebuild the bridge as it was before the destruction (see §5.4.1 p.49 of ToR: "This section refers to the part of the reconstruction or remedial works that will be carried out, and the result of which should be a structure identical to the one prior to destruction"). The mentioned design choice has been assumed as the Client request and as Mostar citizen's wish for the future of the Old Bridge with no further analysis and comments.

4.1.1 Additional objectives requirement

Of course, the above mentioned main objective of the assignment, was not enough to complete such a delicate task like the rehabilitation of a monument that doesn’t exist anymore, and by the time that all the issues were analysed it got self evident that a more detailed philosophical consideration was required.

Since Phase A of the works was ongoing, after a preliminary analysis of all the architectural and structural issues concerning this task, it seemed that the Old Bridge of Mostar was not a structure that could be recomposed by the use of its ruins, or at least this could be done only for small portions and with many difficulties of any kind: structural, architectural, practical, historical, technical and conceptual (see the detailed analysis in this report §4.3 §4.3.1 §4.3.2 §4.3.3). At the same time it has been considered that the arbitrary "reconstruction" of a ruined monument is not accepted by the International Principles of Restoration which allow only interventions aimed at the "preservation" of existing monuments and, only exceptionally, allow reassembling of small portions of monuments trough the use of the anastilosis technique (if this may be documented). For the aforesaid reasons the final objectives of the whole project had to be taken into consideration to understand which could be the real purposes of this plan, so that to have a guide during the performing of the main design choices and in respect of the world importance of the monument. A proposal aimed at a better clarification of the finalities, that matched with the main declared objective of the project, (to rebuild the Bridge as it was before destruction), and that examined all the issues concerning this task, have been summarised as follows.

The Bridge of Mostar has been totally destroyed and doesn’t exist anymore as a whole structure, its ruins are the only left portions of it and should be considered the real and the only original Old Bridge of Mostar. The recovered stones are, at the moment, the only valuable elements of a great ancient monument, they have historical value, and they represent an interesting example of the ancient technique of assembling voussoirs and a constructive method which should be studied and investigated. These recovered stones being what is left of the Old Bridge of Mostar should be preserved exactly as they are and should be kept in good condition to ensure their long lasting: they may be settled in a purpose built museum, (see also §1.4.5 of the Inception Report), and they may be organised for exhibition purposes on a steel structure, similar to the bridge shape, on their original positions. The original Old Bridge would be therefore represented by those ruined portions, and this intervention would totally match the International Principles of Restoration: it guarantees complete safeguarding and preservation of the ruins and moreover it would be reversible and absolutely not invasive. At the same time, on the spot where the bridge was, following the willing of the citizen of Mostar and for social, political and symbolical reasons a "new old bridge" may be rebuilt as a declared copy of the previous one. This copy should be built not approximately or just close to the original one, since the value and the meaning of the new structure should be in the "philological" and historical research of the ancient monument as if this were an integration or a preliminary introduction to the visit of the real Old Bridge settled in the museum. This way the project will be at least more correct and clearer in its aims and in its results, and will respect the ancient ruins and will allow any future different solution or study.

For the above reasons one of the main objective is to keep physically, (but not theoretically), divided anything that concerns the ancient original structure from what concerns the new "philological" reconstruction of it; moreover another main objective of the work is represented by the importance of rebuilding the new structure as much close as possible to the original one, since a structure just alike to the ancient bridge would be meaningless and would not even contribute to the ancient monument documentation. During the performing of the design and of the works many difficulties will arise due to these requirements of similarity but if just once, to make it easier, we start performing things differently we would soon loose the limits and our objective, because with the next difficulty we will be much more authorised in making things not identically to the original model since we are already far from the ancient bridge and we may feel it is not worthy to devolve more efforts towards that aim.

For more details about all this matters and about the use of the ancient stones see §4.3 in this report and specially §4.3.3.

The reconstruction of the "new Old Bridge" is not an easy task, and the thing that is more important to point out is that the reconstruction works will not be identical to the constructive methods used at the time for that bridge and for any other ever built. Anything will be much more complex due to the requirement of making all things identical, stone by stone, to the previous one.

The Old Bridge of Mostar was probably built following a design of the global shapes, sections, and structures but the stones were put on site following average dimensions and depending on the quarried blocks. In other words the quarried blocks were of different sizes, and they were cut as voussoirs on site, making them all alike for the face dimensions and using the different thickness with few rules, making only sure that intrados joints were not on the same position. As final result we have that each voussoir is different from the others and that, being the north and south spans different, each arch row changes its sizes in the bridge thickness. All these irregularities were, on the ancient yard, absolutely caused by the working procedure, the morphological characteristics of the site, the arch centering, the stone cutting instruments, and by the original stone blocks as they were quarried.

Nowadays, if we want to rebuild a bridge identical to the previous one, we have to face, first of all, a technological problem because on the design side it is possible to control and determine each stone size, shape and position but on the stone cut side it is not an easy task to perform the exact design indications. Knowing all the 3d co-ordinates of the intrados and extrados curves, all the dimensions, all the deviations from the plans, all the diagonals and all the joint tolerances it is possible to give more then 200 dimensions for each row but this dimensions would be useless for the stone cut workers. It would be different if we were talking of steel but here we have to manage stone: the design of the reconstruction of the Old Bridge had therefore mainly a technological problem to face that has never been faced.

General Engineering has proceeded in facing the above mentioned limits and has worked out, [see chapter 7 of this report], a new design system to allow the performing of the exact stone cutting trough the use of simple and practical on site methods. This way workers, without being even aware, will reproduce, following some procedures and a little number of dimensions, the stone row exact dimensions of the load bearing arch.

On the other side it is important to respect and perform a control method at predefined steps: one inaccuracy on one row may even be difficult to be surveyed but every five or ten rows there should be reference points and control systems so that to check the proceeding of the works.

This design for the bridge reconstruction couldn't be easily represented only by plans, sections and elevations, but it has been necessary to produce a sort of on-site manual containing all the necessary assembling procedures to guarantee the exact performing of the works.

As specified even in the Inception report (see §1.2), here next it is confirmed the methodology that has been followed for the performing of this assignment: the design has followed scientific methods, existing documentation and restoration procedures; the design procedure has taken also into consideration any evolution during the developing and the performing of the assignment: many details have been discussed by the time they got self evident. For the above reasons, and since the plan was quite complex and linked to many investigation results, not all of the design choices could be specified in advance, but only at this final stage; nevertheless still some matters will have to be finalised while works are ongoing.

The methodology that has been adopted for the design in each step is the following:

first to determine which were the ideal architectural solutions of each matter and then to verify them with all the technical parameters of resistance and feasibility.

Methodology has referred, first of all, to the requirements asked by the PCU TA, by the ICE, by UNESCO and, as much as possible, to the international principles of restoration; for what concerns this assignment we have in detail:

• Restoration should be performed trough documented phases
• Any integration should be documented and recognisable.
• For the strengthening aim of the structure modern techniques may be used only for static reasons and only when the ancient constructive method would not be adequate.

Moreover methodology has referred to the additional principles:

• Preservation and special care should be taken for the interior interventions, even if they are not visible.
• Structure and technological solutions should be maintained.
• Interventions should be as less invasive as possible.
• Interventions should be as much reversible as possible.

During the several stages of on site surveys and design processing, it has been used exclusively instrumental systems and computer systems. The procedures adopted guarantee the following:

• precise diagnostic and measurements
• constant control and updating of the designing stage

long-lasting, ready-to-hand and duplicable data for records

CREDITS:

Intellectual property of this report and of the design drawings is owned by General Engineering s.r.l.

© - General Engineering Workgroup -

SOURCE:

Final Design Report