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| ARCHITECTURAL DESIGN - PART 06 | English
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3.12 Centering release For centering releasing notes, refer to chapter six and eight of current report. Centering is anyhow a temporary structure of which General Engineering may be not considered responsible either for what concern the design of it, either for what concern assembling, disassembling, adjusting and management.
3.13 Drainage, piping and waterproofing
For what concern drainage systems it has been followed the ancient methods with some additional devices that may improve things and allow preservation, durability and avoid any future damage to the structure: surface rain waters drainage: Waters are collected in rain wells located at the extremes lower levels of the pavement: each area has its well and, over the bridge pavement, very small interventions will be carried out next to the borders. Moreover, underneath stone thresholds, at the bridge pavement limits, slots have been foreseen to drain water out towards bigger wells. Existing drain water hole by the south west side has been maintained. Bridge pavement rows, as originally conceived should help water to flow away. rain water piping: Wells will be connected one to each other and towards the river by underground piping. Rain water outlets (r.w.o.) should be provided at least in double ways: in case of obstructions no large puddles will take place and maintenance will not occur so urgently. External rain water outlets should be placed in abutment corners, (as previously located), and external pipes should be made of oxidise copper (when colour gets dark and opaque). At the bottom of vertical piping inspection wells are required. Next to the abutment walls when r.w.o. come out, stone spouts are required. bridge pavement waterproffing: The ancient type of waterproofing may be repeated: bridge stone flooring should be placed on a mortar layer with waterproofing requisites; connection joints of the pavement should be accurately sealed. Mortar type should be defined and approved by laboratory tests, and may be used only if it is proved that this type of device is efficient and water resistant even during time. Other devices should be worked out if the above is not confirmed. adjacent pavement waterproofing: Same technological systems may be applied as the above. abutment walls top ground areas: Same technological systems may be applied as the above, but with additional outlet channels to take water away towards the river. Mortar layer may be applied only under areas protected by Tenelija stone blocks or small natural conglomerate rocks, remaining portions characterised by stable rock areas will be left unchanged. inner bridge lightening voids drainage system: No water is supposed to get in the bridge lightening voids, but in case of any infiltration or any condense phenomena, a waterproofing mortar layer is foreseen on the bottom of the voids to protect the load bearing arch. Water trap drainage channels (one per void) are foreseen. Underground channels should be long enough to reach a ground layer with high permeability (according to CONEX investigations), and channels should be filled with rubble of grain size which gets larger to the bottom.
3.14 Finishing works
For what concern the finishing works on stones refer to §7.11 of this report. The model, that the Company in charge of the rehabilitation works is requested to assemble in real scale, should be taken as a reference during the finishing works, being the one that has been approved by the ICE. Anyhow foreseen finishing works are here next resumed and listed: Finishing works on the stones: Finishing for the stone is aimed at reproducing the same type of worked surface as the one of the ancient bridge for the different elements. Moreover finishing works on the stones is an additional stone work aimed at reducing some ordinary construction imperfections in the assembling which is judged, (by works Supervisor), to exceed the average level that characterised the former bridge. Most probably this work will be needed for the bridge intrados vault. Jutting out stone edges should be smoothed, (as defined in the approved model). Parapets will be the elements that will mostly require a masterpiece of stone cut and stone finishing. Pavement stone carvings: Bridge flooring was probably originally built with no carvings on the stone tiles, and (as Mr. Bessac has noted), these carvings may have been performed later on: like from 50 to 200 years later, when stone got slippery. In the rehabilitation works of the bridge, these carvings will be performed again as they were, without waiting for the flooring to get slippery: this because the objective of the current work is to rehabilitate the monument as it was right before destruction, (a declared scientific copy of the former bridge), and is not to live again the experience of building a similar bridge with same techniques and same construction materials. Refer to drawings RE-01 and SC-09. Sealing of joints: All the bridge joints will have to be sealed, including pavement joints and elevation joints in order that no infiltration gets in the bridge inner structure due to rain water or to floods. Patina: Specification of this work stage is given by stone experts: anyhow "patina" will be a light layer of biologic material that will be sprayed over the stone surface to avoid any unpleasant effect during the first months of life of the structure, being in high contrast to the adjacent historical portions.
3.15 New intervention marks
In order to declare which are the new interventions a plan has been worked out. The plan may be subdivided in two different sections: declaration of the joint in the pavement trough the use of metal marks and marking of some stones, (trough small and light carvings), in the elevations. Metal marks Joint among new interventions and ancient pavement will be of a double size, (compared to the other joints of the pavement), and metal marks will be applied. Of course the shape of the joint line will vary depending on portions of the former pavement that will be possible to maintain: limit line, in drawings, is therefore indicative. Metal marks will be applied along the connection joint on the corners or every cm 30-40. Shape and dimensions of the joint will be decided trough on site checks by the ICE, as well as any writings on the mark top cap (like date of works). Carved marks New stones of the elevation, (like spandrels stones and cornices), which are adjacent to the ancient ones will be marked with a small and light carving which will be visible only to a very close observation. Shape and dimensions of the carved mark will be decided trough on site checks by the ICE, as well as the type of the carving. In the drawing the carving is symbolically represented and the code SMS-Bmk means: Stari Most Stones – Bridge stones – marked ones. Dotted stones, in the drawing, are the stones of the former bridge, that it has been possible to remount in the original position depending on their state of conservation (drawing shows an hypothetical configuration).
3.16 Bridge pavement remedial works
Additional explanations should be given for what concern the bridge pavement over the abutment walls: in this design, even those portions which prosecute inwards over the abutments, and until the limits of the intervention area, have been called "bridge pavement", being conceived as a walk path made of same construction materials and mounted with an identical layout. Of course these additional floorings, being still on-site and not destroyed, are foreseen to be repaired. The current condition of floorings is quite ruined: some spots have been subsided and some stone elements are damaged or lacking. For what concern preliminary cleaning, dismantling and demolition works refer to §3.6.3 and §3.6.7 of this report. Remedial works are, instead, here next resumed: Bridge pavement remounting: Areas in which pavement has been dismantled, (with detailed survey and classification), due to the bridge and abutment fill removal and strengthening. These portions of flooring should be carefully remounted in the original locations and respecting former layout. Bridge pavement lacks repair: Areas that were covered with reinforced concrete blocks and plinths, that have been demolished and that should be repaired and integrated with new pavement stones of same type and layout of the original ones. Bridge pavement remedial works: Single damaged stones of pavement that should be repaired or substituted with new ones of same type of the adjacent ones respecting the original layout. These damaged stones are sometimes in isolated locations, (quantification is by estimation), and some others are in drawn areas, (refer to drawing RM-01). Remedial works should preserve or repair mortar layer underneath. In any case remedial works of the pavement should preserve and repair the ancient "terra rossa" and mortar layers of protection and waterproofing which are located underneath the stone flooring, (in case they are reached during dismantling works). Continuity of the layers is required to avoid rain water infiltration in the abutment. Bridge pavement is composed by stone rows and stone tiles; layout of them may be worked out from design drawings and not randomly performed, since, as it has been conceived, should help rain water to flow away. Tiles and rows should be assembled carefully on a flat and homogeneous preparation layer making connections as much close as possible and sealing them to avoid rain water infiltration. Pavement row stones should be bevelled and shaped as the ancient ones in order to make the walk easier to the users. Areas in which the pavement is slightly subsided may be left as they are, being the signs of time part of the beauty of this original portions. While, for what concern the areas of the flooring that will be remounted, (junction zone between ancient and new pavement), it has to be noted that in those spots the height of parapets were particularly low, so that even with the fences it may results, nowadays, unsafe, (related to current security norms); therefore a slight adjusting of the height of the remounted pavement, (by lowering it), would be advisable. In design drawings this intervention hasn't been proposed since it will have to be evaluated by the works Supervisor on-site. In design drawings, dashed lines next to doorsteps and access of other buildings mean that works have to be co-ordinated with the design for the Towers and adjacent buildings since in some spots stairs may be reconstructed. Flooring has been quantified anyway. Dismantled krecnjak stone socles, (east side), between bridge pavement and adjacent flooring should be, remounted in the original locations, (elements that are not damaged). Other elements which are lacking should be replaced and integrated with new quarried ones with similar shape, finishing layout and colour to the adjacent ones. Refer to drawing RM-01 and SC-09.
3.17 Adjacent areas works
Other spots that are involved in this design work, (and included in site limits), have been defined as "adjacent areas" and may be subdivided as follows:
In the above mentioned zones only small protection and preservation interventions are foreseen. Anyhow some cleaning, dismantling and demolition is required before repair works could take place.
3.17.1 Adjacent areas: dismantling works
Dismantling works are here next resumed: Demolition of concrete blocks: Existing concrete blocks should be demolished; those which are over the pavement should be demolished before pavement remedial works; the others may be demolished at the end of the works once they are not necessary for any provisional work. Demolishing of reinforced concrete blocks should be performed with no vibration and taking care for the adjacent unstable structures. Underground thickness of the blocks has been estimated and quantified. Demolition of underground portions may be not performed if there is any structural risk: to be decided on the Supervisor responsibility. Demolition of masonry walls: Masonry walls that are almost completely ruined should be partially demolished until a good layer is found. There is only one case of demolition of a small masonry wall that is almost completely ruined: it is located at the borders of the works limit by the north-east side (drawing DS-01 position E-10). It should be partially demolished until a good layer is found. Rubble removal and cleaning: Portions of the pavement which are covered by rubbles should be cleaned before flooring remedial works. Dismantling of damaged elements over the abutment walls: Dismantling of damaged elements, either pavement blocks, either natural small conglomerate rocks which are not anchored to the soil; cleaning and preparation of the area for the remedial works.
3.17.2 Adjacent areas: remedial works
Repair works are here next resumed: Adjacent pavement remedial works: Portions of pavement adjacent to the bridge flooring will be reintegrated with new stones of the type of river stones, (small size river pebbles – header layout), similar to small remaining portions still on site in that spot. This remedial work will be performed only after dismantling of the reinforced concrete blocks and plinths which are over the area. Protection pavement over the abutment walls: Pavement in Tenelija blocks (layout and thickness similar to a masonry wall – equal to still remaining portions on site in that spot), is a sort of masonry protection that should be remounted and reinforced with cramps, and should be stuck to the underneath ground by metal anchor bars. Waterproofing and protection from infiltration should be performed by mortar layer use and by accurate sealing of joints. Waterproofing and protection over the abutment walls: Areas adjacent to the intervention spot should be protected from infiltration of rain water in order to avoid future damages to the abutment walls. Protection should be performed following the original traditional devices like the use of a mortar layer underneath stone blocks or settling natural conglomerate rocks. Water channels should be fixed in order to take rain water away. Waterproofing and protection over the abutment walls (out of work limits): There are some areas which should be repaired as the above mentioned ones but in co-ordination with the yard of the Towers and adjacent buildings, being out of the work limits. This intervention should be performed during the restoration works of surrounding buildings. Masonry wall reconstruction: Portion of ruined wall should be partially repaired and reconstructed. Type of masonry, layout and appearance should be as it was before. Shape and height is determined in the reconstruction drawing. There is only one case of a small masonry wall that is almost completely ruined: it is located at the borders of the works limit by the north-east side (drawing RM-01 position E-10).
3.18 Rehabilitation of the abutments walls
As already introduced, (see §3.4.2), The abutments walls are, at the moment, fractured in different points and some of the cracks are also wide, like the one on the west bank – north side, which runs vertically almost along all the abutment. Moreover on the east bank – north side we have many damages due to the shootings that have left wide lacks, cracks and have ruined all the masonry surfaces. The general condition of the south elevation seems to be better, more compact and not so much deteriorated. The condition of the abutment walls prior to the shooting were not bad, and as far as it can be gathered from the scarcely readable photographic documentation, they were mostly compact and only the mentioned wide crack, (on the west bank – north side), was remarkable. But during centuries the abutment walls seem to have been frequently restored, since they still look like a patchwork of different kinds of masonry. The repair works that during centuries have taken place, may have been mostly required by river floods, by drainage problems and by settlements of the abutments. The fact that deterioration is mostly located on the north side, (from where the river flows), and on the lower portions, (where Tenelija surface is partially ruined), lead to think that the river has been the cause of non-structural pre-war damages: Tenelija ashlars are often characterised by non-structural fissures and by detaching of outer stone layers. Structural design for the repairs of the abutment walls is not included in General Engineering assignment, since it is one of the task of CONEX Company, that has been performed with the structural design for the foundations works. Therefore General Engineering has proceeded to the architectural design of the non-structural repairs (surface repair works). Anyhow some general advises for the structural design are given here next; these observations are not to be considered as constraints or limits for the works and no responsibility may be attributed to GE for the following notes:
3.18.1 Theoretical approach to the abutment walls repair works The approach to the abutment walls restoration is mainly aimed at their preservation and long lasting by performing the minimum required intervention necessary to avoid any further deterioration or collapsing. As far as the surface repairs are concerned, the architectural design foresees remedial works only of those masonry lacks that are necessary to avoid river and rain water infiltration in the inner portions of the abutments, and only of those masonry surfaces which are so heavily damaged that deterioration is most likely to proceed. In other words, the global appearance of the abutment walls should remain unchanged and characterised by all the numerous traces of ageing and by all the traces of war damages that are not endangering the structure. ICE, during the 5th Commission has confirmed the will of leaving small damages of the abutment walls still unchanged and therefore the proposed theoretical approach is most likely to be followed during the rehabilitation works. The abutment walls, this way, will not be renewed with a different, homogenous and polished layout, but will maintain their roughness and imperfect appearance which is the beauty and the historical value of a monument that has, during its long life, undergone to many interventions of maintenance and improving to face the strength of the river floods. Current "patchwork layout" and masonry stratification is undoubtedly not only a value to be preserved but also a subject that should be studied by archaeological experts to understand how the bridge, central core of the city, has developed. The importance of the above mentioned research work has been confirmed also by the fact that, during the investigation works performed by CONEX Company, many findings have come to our knowledge, among which, the most surprising was the huge void in the north east abutment wing and another masonry wall, round shaped, behind the current abutment wall. It seems most likely that the north east wing of the abutments have been protected by additional walls during time, since that side is the more exposed to the river flows, that coming slightly from north west discharge their thrusts on that side mostly. But, referring to the aforesaid findings, we should also think about the ancient location of the wooden and suspended bridge, (bequeathed by history), that may have been located not far from that spot and that may have required some stone structures to be anchored to. Another matter that should be stressed, to perform a correct intervention on ancient masonry walls, is that any new masonry stone that it is placed either to restore the huge lacks, either to substitute some heavily damaged ashlar, should have a small carving that may declare this repair work to any future study of those walls. Marking by carvings is something which can be seen by a very close observation of the involved stones and not from any of all the view points in the surroundings. Architectural design foresees the respect of the declaration of the new interventions either by documentation, (drawings and reports), either by small signs on-site according to all the International prescriptions and requisites that are given for this type of rehabilitation on the World Cultural Heritage monuments.
3.18.2 Dismantling works in the abutment walls
Small dismantling works have been foreseen for the abutment walls only for those portions in which masonry is ruined and unstable, cases are here next listed:
Dismantling is aimed only at taking some damaged edge stones away to find a good, compact and coherent masonry layout from which it could be possible to start the new masonry repair work. Stone blocks that are not ruined, (but only detached), may be reused in the original locations during the repair works. After dismantling it is required to remove any rubble and stone powder from the connection surfaces on which it is foreseen to place the new masonry. Cleaning of the connection surfaces is important to allow an efficient grip among adjacent stones. Vegetation should be removed either to allow the performing of the remedial works, either to allow a check of the joints and of the good condition of the whole masonry structure.
3.18.3 Remedial works of the abutment walls
Repair works are here next resumed: Lacks repair inside masonry layout: Remedial works aimed at the reintegration of masonry layout; lacks due to shootings and lacks due to dismantling works; (layout and type of stone should be homogeneous to the adjacent masonry). Lacks repair next to masonry margins: Remedial works aimed at the reintegration of masonry layout; lacks due to shootings and lacks due to dismantling works; (layout and type of stone should be homogeneous to the adjacent masonry). Masonry parapets remedial works: Remedial works aimed at the reintegration of masonry parapets (two front faces: inside and by the river side); lacks due to shootings and lacks due to dismantling works; (layout and type of stone should be homogeneous to the adjacent masonry). Masonry parapets top cornices (sills): Remedial works aimed at the reintegration of masonry parapets top cornices (sills); lacks due to shootings and lacks due to dismantling works; (layout and type of stone should be homogeneous to the adjacent cornices: grey Tenelija). Highly damaged surface repair: Remedial works aimed at the rehabilitation and regeneration of the stone surface; (finishing and appearance of stone should be homogeneous to the adjacent masonry). Structural cracks repair: Remedial works for structural cracks (including tie rods applying, joint sealing trough local dismantling and remounting). Drilling holes repair: Remedial works aimed at filling up of the investigation drillings and at replacing a stone top cap equal (for appearance, finishing and type) to the adjacent masonry. Vegetation: Masonry portions covered by vegetation (to be removed as mentioned in previous paragraph). Joints cleaning and sealing: Recent repair works performed with cement mortar should be removed, joints should be cleaned and sealed again with proper binding agent.
3.18.4 Masonry lacks repair description: In the remedial works lacks have been subdivided in different groups depending on the location of them and on the different foreseen work procedures, (which of course have also a different code in the BoQ). When lacks are located inside masonry layout, the following methodology may be applied to perform the repair works. When lacks are located next to masonry margins, notes are similar to the following ones, but the work is quite easier since the masonry layout has to be prosecuted and not inserted avoiding accurate dimensioning to fit in the gaps and avoiding provisional works to protect higher layers from collapsing. When parapets are lacking, no other notes are foreseen, except from the fact that two worked faces are required with additional finishing layout and accurate work. Similar interventions, (to lacks), should be performed for the repair of the drilling holes, for which it is required the filling up of the holes and the placement of the original "stone caps" with accurate sealing making sure that the stone element is well linked with mortar to the masonry behind.
methodology:
materials to be used and quantification: Materials to be used for the intervention should be worked out trough laboratory tests in order to determine the proper chemical contents and proportions depending on the stones, (Tenelija or natural conglomerate), on the mortars originally used, and on the technical requirements that are foreseen for the work. The worked out products to be used should be tested on small portions before the work is performed extensively on the damaged areas. Approval of tests should wait the time necessary for the products to be matured, and will depend on final result, appearance, colour, grains and efficiency. Quantification and proportions of the products used may be subjected to on-site modifications depending on test results.
3.18.5 Remedial works for the masonry joints description: Current condition of masonry joints is quite heterogeneous, and should be carefully checked to guarantee a long lasting and durability of the abutments, and to allow the injecting procedure wherever it will be foreseen due to structural design requirements according to CONEX Company. When ancient mortar is lacking or is heavily desegregated, it should be removed and reintegrated with proper mortar layer. Mortar layer should be slightly inset, (few millimetres), compared to the outer masonry layer, in order to distinguish the new interventions.
methodology:
materials to be used and quantification: Materials to be used for the intervention should be worked out trough laboratory tests in order to determine the proper chemical contents and proportions depending on the stones, (Tenelija or natural conglomerate), on the mortars originally used, and on the technical requirements that are foreseen for the work. The worked out products to be used should be tested on small portions before the work is performed extensively on the damaged areas. Approval of tests should wait the time necessary for the products to be matured, and will depend on final result, appearance, colour, grains and efficiency. Quantification and proportions of the products used may be subjected to on-site modifications depending on test results.
3.18.6 Remedial works for stone fissures sealing description: Fissures that are non-structural and that are absolutely "static", (not developing by getting larger or smaller), should be sealed if they are deep and they reach stone inner portions or stone core to avoid further deep deterioration. Maintenance and control of the other fissures is required during time to perform additional interventions that may be necessary due to unforeseen development of deterioration. Sealing layer should be slightly inset, (few millimetres), compared to the outer masonry layer, in order to distinguish the new interventions.
methodology:
materials to be used and quantification: Materials to be used for the intervention should be worked out trough laboratory tests in order to determine the proper chemical contents and proportions depending on the stones, (Tenelija or natural conglomerate), on the mortars originally used, and on the technical requirements that are foreseen for the work. The worked out products to be used should be tested on small portions before the work is performed extensively on the damaged areas. Approval of tests should wait the time necessary for the products to be matured, and will depend on final result, appearance, colour, grains and efficiency. Quantification and proportions of the products used may be subjected to on-site modifications depending on test results.
3.18.7 Remedial works for disgregate stone surfaces description: Tenelija stone blocks, that are characterised by surface degradation, may be re-aggregated only if damages are so developed to present stone powder and surface pulverisation. Maintenance and control of the other cases is required during time to perform additional interventions that may be necessary due to unforeseen development of deterioration. The intervention may be performed, (for Tenelija stone), with proper products based on ethyl silicate or similar ones depending on laboratory and on-site tests. Recent repair works, performed with concrete should be previously removed, and masonry layout should be repaired using original construction materials. Underwater portions of the abutments should be inquired wholly, looking for any damage, during suitable season time in which the water level is low.
methodology:
materials to be used and quantification: Materials to be used for the intervention should be worked out trough laboratory tests in order to determine the proper chemical contents and proportions depending on the stones, (Tenelija or natural conglomerate), on the mortars originally used, and on the technical requirements that are foreseen for the work. The worked out products to be used should be tested on small portions before the work is performed extensively on the damaged areas. Approval of tests should wait the time necessary for the products to be matured, and will depend on final result, appearance, colour, grains and efficiency. Quantification and proportions of the products used may be subjected to on-site modifications depending on test results.
3.18.8 Remedial works for stone protection and waterprotection According to LGA studies and researches, it seems that, on the ancient stones, mysterious "limewash or even adhesive layers" were present, and have been defined by LGA "old enough to be ancient". This lead us to hypothesised that ancient devices were applied on the stone surface in order to protect the masonry from rain water, river and weather, (according to LGA a sort of "linseed based limewash or similar for protection"). Of course this is an extremely interesting matter that absolutely requires further investigations before any protection intervention is performed, also to avoid the loos of precious traces of ancient refined construction techniques. If the above hypothesis is confirmed, it should be carefully evaluated if the ancient devices may be adopted for protecting the stone surfaces, otherwise the following procedure may be followed.
description: Protection of surfaces, (after all the other consolidations have been performed), by spray application of a water-repellent and protective product. Quantification of the product to be applied should be checked on-site. Surfaces to be protected are the ones that are often underwater, mostly subjected to damages due to river flows, and the ones that have been consolidated and repaired. The intervention may be performed, (for Tenelija stone), with proper products based on "alchil alcossi silani" or similar ones depending on laboratory and on-site tests.
methodology:
materials to be used and quantification: Materials to be used for the intervention should be worked out trough laboratory tests in order to determine the proper chemical contents and proportions depending on the stones, (Tenelija or natural conglomerate), on the mortars originally used, and on the technical requirements that are foreseen for the work. The worked out products to be used should be tested on small portions before the work is performed extensively on the damaged areas. Approval of tests should wait the time necessary for the products to be matured, and will depend on final result, appearance, colour, grains and efficiency. Quantification and proportions of the products used may be subjected to on-site modifications depending on test results.
3.19 Final works
After works for the reconstruction of the bridge are over:
Nothing should be discharged in the river during the works and no polluting chemical product should be used for the works. Lead should be used with high care, being extremely toxic, and no fragment or small portion of it should be discharged neither in the river nor in the adjacent areas.
3.20 Safety of workers and of the yard The yard is foreseen to be quite dangerous for the machinery to be used, for the site limited accessibility, for the huge scaffoldings, for the river and for the peculiar works that are planned. It is strongly advisable to work out a safety plan for the workers and for the yard, according to the most recent international standards to avoid on site accidents. General Engineering is not anyway and anyhow responsible of any safety requirements and of any on-site accident. |
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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 |
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