DETAILED ANALYSIS OF THE DESIGN ISSUES

English

4.3.6 Statistic evaluations concerning the stones in their current condition

This statistical approach is strictly linked to the previous paragraph classification and coding system, and it is aimed to a better, impartial and technical reporting of the current situation for what concern the stones. Stones have been analysed one by one and the reported numbers are reliable, although some insignificant inaccuracies may be present due to the scarce readability of some spandrel areas in the ancient surveys of the former bridge that have been left undefined in the "2000 survey" and that have been determined in the final design (see §2.3.8 for exact numbering).

Recovered stones have been considered as singles even if in the survey book are classified by assembled blocks, and this really help to understand how many elements we have to manage.

Even if this is an impartial statistic it has to be clearly underlined that the following graphics represent the most optimistic combination ever possible: in fact it has been presumed that all the stones that look intact may be reused, that all the stones that are within blocks may be dismantled and reused and that all the load bearing voussoirs may be replaced.

This statistical inquiry will avoid any future evaluation by approximations and terms like "many", "a few", will be conveniently substituted by numbers and percentage which are more desirable for this kind of studies.

The graphics have been divided in 5 different groups:

• Load bearing arch stones SMS-A
• Bridge Stones SMS-B
• Bridge Stones - spandrels SMS-Bsp
• Bridge Stones - cornices SMS-Bcs (both upper and lower: c1+c2)
• Bridge Stones - parapets SMS-Bpa

Globally the elements that composed the former bridge were about 1000 (paving and fill not included) the exact number is 1006, but to this, a group of 82 very small stones, should be added, (considering some left joints of the portions that were not documented in the 1982 survey).

Each group is composed by four graphics:

1. about Recovered, Built-in and Lost stones
2. splits Recovered and Built-in stones in intact and broken ones
3. resumes all the intact stones and compares them with broken and lost ones
4. divides stones among intact located ones and all the others

So the fourth graphic of each group represents the final result of this work and quantifies the maximum possible amount (in the most optimistic case) of the stones that may be reused compared to all the other ones (lost, broken and not located). In this study, the possibility of putting stones in locations different to the original ones, hasn't been examined since it has been considered not acceptable to perform this kind of intervention for the reasons specified in the previous paragraphs.

Trough observations of the statistic graphics it results clear that the amount of the lost stones, is for all the bridge elements, around the 55% and for some smaller pieces it is even 77% (cornices). Analysis held on the videos taken during the bridge shootings have revealed that many of the stones were reduced to dust even before the collapse (refer to §2.3.7). Anyhow it is most likely that some other stones may be found in the river bed with more detailed researches downstream from the spot.

Locating percentages are mostly related to the type, dimensions and global number of the elements: the more they are big (or assembled) the more it is possible to find their former position: for instance none of the small recovered spandrel elements have been repositioned (until now). The percentages may be here next resumed (summing up the values of recovered intact located stones with the built-in intact stones):

 Description class code located intact stones Load bearing arch stones SMS-A 28% Bridge Stones SMS-B 17% Bridge Stones - spandrels SMS-Bsp 18% Bridge Stones - cornices SMS-Bcs (c1+c2) 10% Bridge Stones - parapets SMS-Bpa 20% Global: arch + bridge SMS-A + SMS-B 22%

The highest percentage of located intact stones is related to the most difficult ones to be reused (for structural reasons): the load bearing arch stones.

4.3.7 Stones original positioning and preliminary representation

As it has been anticipated the positioning of the recovered stones in their original location is absolutely a study which requires resources and special expertise with numerical management and data base research, but apart from this, it requires professional ancient pictures of the bridge and professional current pictures of the recovered stones including a six faces full documentation and measures. None of the above has been provided.

Moreover there is a method also for recovering the stones from the river bed, which has been performed in other documented similar cases, and which foresees to file the place from which stones have been picked up. As far as we know the recovering of stones has been performed with no archaeological methodological approach. All the above of course is not of any advantage for the type of analysis here carried out.

Anyhow the procedures followed for the survey 2000 have given their results and trough semiautomatic comparing procedures it has been possible with satisfaction to locate most of the assembled voussoirs, and what is more important to note is that measures surveyed on recovered stones perfectly matched the 2000 survey (most likely survey of the bridge).

Recovered stones of the spandrels were 44 (13%) and being small and not assembled elements with many possible locations (344) gave no result, also because every single stone could easily match more than one position, and it was not possible to determine whether it was a north or south side stone. Also some of the cornices matched more than one position and for this reason couldn't be located.

These results may be improved if there is the willing by the PCU and by the ICE of keeping on with this studies and if some other data are provided.

The graphic representation of the locating result is here next represented: the dark stones are intact and light stones are broken (not reusable). No further comment to the drawing will be exposed: it is self evident that the recovered stones are far from covering most of the lacks.

Moreover from data forwarded to General Engineering by LGA, it results that recovered stones do have the same mechanical characteristics of new quarried ones, but they may have internal micro fractures (not visible) that may not guarantee the integrity. This will compel to more detailed analysis of these "intact" stones that may be instead fractured.

fig.01 - Representation of the positioning of the stones in their original location

CREDITS:

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

author of the text: arch. Manfredo Romeo – other contributes have been mentioned in related paragraphs

© - General Engineering Workgroup -

SOURCE:

Final Design Report