English

Preface In the year 1999, when still everything was very much undefined about the reconstruction design, General Engineering was asked to provide preliminary technical documentation about the studies that could be worked out for the Old Bridge of Mostar. On that occasion some tentatives were performed although the source data available were still very scarce and not in final formats. The results and comments are contained in the following technical report: of course most of the contents are  not anymore updated any many things are innacurate, but this report let us understand, on one side, how difficult it was to start a work of the kind, and on the other, how many design strategies were correctly started from the very beginning. By the right side there are some pages of the report in its original layout. Preliminary studies for the Old Bridge have been developed by General Engineering during the years 1996-1999 on its own, with no help, few data and no resources. Authors of the text: Manfredo Romeo - Bernardo Rossi - Giovanni Checcucci. In this first part of the document there are the following paragraphs: introduction - working procedure available data sources analysis

INTRODUCTION - WORKING PROCEDURE

Required Survey Elaborations:

Preliminary Design:
Photogrammetry of the previous condition
Photogrammetry of the current condition

Dectailed Design:
Digitalization of the 1950 survey of the bridge
Three dimensional drawing of the stone arc
Tematic drawings of the elevations

Existing Data Sources:
A 1950 survey with local numerical dimensions - scale 1:50
A 1980 photogrammetric survey - scale 1:200
Aerial photogrammetry of the bridge - scale 1:200
Ancient Photographs of the bridge as it was

Available Data Sources:
A north side elevation of the 1950 survey plus an intrados view.
Elevations, intrados, and abutments of the 1980 survey
Ancient photographs where stone connections are not visible everywhere
A photogrammetric current condition survey (to be completed)

Planimetry with the representation fronts involved in the survey plus all the others of the towers and buildings near by.

The first step of the survey of the Old Bridge of Mostar has been the accurate analysis of the available data sources: anything related to the metric documentation of the Bridge has been checked and verified both compared with the other surveys information, and compared with themselves, to ensure also an internal coherence.

This preliminary inquiry has found a fairly incompleteness of each survey source taken by itself, and this has brought to start a compare plan of all the data available in a single main elaboration, (that will become a sort of data base), from which all the drawings should get trough. Therefore, next to all the required elaborations, there will be a sort of numeric differences table to prove any anomaly from the mediated survey.

The main elaboration of this survey program, is the result of the accurate mediation of all the metric data related to the Bridge. Any of the differences found has been documented in numeric tables, and those ones which came from the numeric survey have been located also because, most of the times they were among other data similar to each other.

The first sources that have been compared were the two surveys from the '50's and from the '80's. The method followed has been to evaluate the global shape and metric data from the photogrammetric survey, while the local measures have been taken from the numeric survey, but this has been only a staring step: anything have been digitalized and inserted in a computer aided drawing system for a contemporary numeric and graphic check. Data from the numeric survey have been remounted in a numerical way, while the photogrammetric elaborations have been referenced to the working scale.

Other inquiry systems have been those related to the geometric and modular analysis of the bridge. One of the most important research for a correct drawing of each stone of the arc has been the seek of the point of the radial direction of the vault. This point has been found trough a mathematic analysis focused on a minimalization of the error, the radial geometric references as been essential for a direct comparison of the local data and for the identification of any anomaly.

Other references have been constituted by the arsin modularity (taken from historic research and drawings led previously by Prof.Arch.Blasi). These references integrated by new considerations have been successfully compared with the results coming from the mathematic analysis. All this represents, anyhow, a precious instrument of comparison of the real situation of the bridge as it was before destruction, and the supposed geometry of the bridge as it should have been in the design, denouncing both survey inaccuracies, and structure yeldings during time.

Planimetry with the shots taken for the photogrammetric survey of the ‘80’s.

AVAILABLE DATA SOURCES ANALYSIS

The numeric survey of the '50's is affected by an internal incoherence, which has been proved by a numeric remounting of the whole north elevation. The values of the x,y location of every single stone connection at the intrados, are sometimes in contrast with the local stone length been probably measured on site. While the total amount coming from both the sources is fairly the some. This has brought to suppose that inaccuracies are to be found as local events to be mediated, each with the nearby ones, also because a difference wich is not taken in consideration brings inevitably to invalidate all the following metric data.
Moreover all the x,y values dimensioned in the botton of the elaboration are affected by the growing distances taken from the origin and from the reference level: so that an error of a 0.5-1% (which is the standard for this kind of surveys) on a distance of ten or twenty meters brings a considerably high error on the location of the stone connection and on the global geometry of the arc curve.

Survey of the 1950 - with details of the two dimensioning systems

The photogrammetric survey of the '80's is a precious support for determining the shape, geometry and stone locations of the bridge, but the original scale of this elaboration was too high: 1:200, which makes it not really sharp in details and in stone dimensioning. Main indeterminateness are found on radial directions of stone connections, since lines are too thick. The survey has already been referenced with the metric collimators points in a computer aided drawing system with the support of raster and vectorial management.

Survey of the 1980 - with details of the reachable stone connections

The photogrammetric survey trough the use of ancient pictures of the bridge is one of the most important data source since it is the only one which allows current surveys with known errors and methods on a structure that doesn't exist anymore.
Nevertheless the sharpness of those elaborations are related to the quality of the source photographic shoots: the ones available are fairly good, but in many areas stone connections are not visible, and vegetation sometimes covers important areas.
Anyway other photo documentation of better quality may be found in the next future, and in any case these data sources have to be connected to the control points on the ruined parts of the arc (see next).

South side previous and current condition: preliminary photogrammetric elaboration worked out on control points

North side previous and current condition: preliminary photogrammetric elaboration worked out on control points

Control points are necessary to connect the survey in its global geometry, and are used both to verify the existing surveys, and to work out new elaboration of the ancient photo documentation.
Trough the use of these points taken on the ruined parts of the elevations of the bridge (even if they are really small parts), it is possible to obtain useful orthogonazilations of the elevations of the bridge. Moreover, the points are taken in x,y,z coordinates and they are precious for any 3d elaboration, or for relating elevations one to the others, or for determining projection elements.
Some of these points have already been surveyed, and they have been transformed trough rototraslation to locate the plan of the north and south side of the bridge, and for proceeding to the photogrammetric rectification of the elevations.

On site sketches with graphical and numerical references of control points

Numerical table of the taken points during the first surveys on site.

Investigation plans of control points, from on site sketch. Control points are to be taken both on the ruins of the arc, and on the abutments of the bridge.