REHABILITATION OF THE OLD BRIDGE

REHABILITATION OF THE OLD BRIDGE MOSTAR
NEWSLETTER 12 30, June 2003 MOSTAR, BOSNIA AND HERZEGOVINA
Upstream east wall MENDING OF WALLS Surfaces of abutment walls had to be strengthened before assembling of cornices and spandrel walls. Therefore, we repaired all the existing blocks by the edge of the abutment walls (endings of wing walls). They have to be repaired so later inserting of arch blocks between them could be possible. Final chiseling of the wall edges During the injection works, wing wall made of conglomerate stone was repaired, and now we came to the end of this wall, to the edge blocks made of tenelija stone, the same stone that the bridge is made of. Placing in of the new blocks Besides this, in Komos we are also chiseling holes for cramps and dowels. In each stone block, before transporting to the site, (in its down side) the dowel is fixed and poured with the lead. Stone block will be inserted in the previously assembled row on the site, and final pouring of the lead in cramps and dowels will be done on the site as well, but that part we will explain additionally. ASSEMBLING OF THE ARCH BLOCKS Transport of the block to the small platform on centering Procedure for assembling of the arch blocks stays the same as we described it in the previous newsletters. Stone block is transported from Komos to the site with already inserted so called “male” dowel, and placed on the main platform. After that, entire rows of blocks with the crane are displaced from the platform to the “stone wetting pools”. There they have to stay for 24 hours before their assembling in the arch of the bridge. After that time period, blocks are moved with the crane to the small platform on the centering of the bridge. From that place by the portal crane block is precisely placed and fixed on its final place. Assembling of the one block from row Before the block is placed on the previously assembled row of the arch, we are putting the mortar layer over the row with 6mm thick. As regulators for the thickness of the mortar layer we use small lead plates of adequate thickness, over whose layer of mortar is made. Holes for dowels are protected from the mortar and dust with the wooden lids. For the same reason canals for pouring of the lead into the hidden dowels are also protected, with rubber tapes of triangle cross-section. Those rubber tapes are placed into canals by it’s whole length. Before laying down the stone, wooden lids from the holes for dowels are removed and already fixed “male” dowel is inserted in the hole for dowel of previously assembled block. Rubber tapes stay in canals until pouring of lead starts. POURING OF LEAD IN DOWELS Mounting of drying device Procedure of pouring the lead into the dowels started on 17^th of June. This is the one of the most important and the most delicate procedures during the building of the bridge. Lead is poured trough canals to the “hidden” (already inserted) dowels between the rows of the arch. Drying of canals Before pouring of the lead, few preparation works must be done. First of all, rubber tapes from canals, placed just after assembling the next block, have to be pulled out. After that we start with drying of canals with special device, which is designed and made by Mr. Šeparović. Taking of melted lead from vessel Drying of holes has been done with the hot air. Drying device consists of “vacuum cleaner” which has a function of blowing ASSEMBLING OF LOWER CORNICE Prepared places for assembling of cornice After assembling of arch blocks according to the project, the next parts that should be assembled are lower cornices of the bridge. We started with their assembling 24.06. on the left side, upstream and downstream. For this was necessary to adjust blocks of the arch, precisely chisel their curvature, and each of them connect to the next one with cramps and poured them with the lead. Assembling of first block for cornice Blocks for cornice have been prepared in Komos and separately transported to the site. Than they were mounted according to already determined procedure. Blocks of the cornice are wide about 70cm, but 50cm of their width comes in the arch blocks, and 14-20cm stays out of the arch. On the top side they are connected with cramps. Assembled four blocks of cornice on northeast side	First we investigated the condition of each stone; we marked the stones that can stay, those that should be repaired, and those that should be replaced with the new ones. Based on these estimations we started with repairing and chiseling of the blocks, if that was found necessary. We ensured the lateral sides of the wing walls and masonry of the spandrel walls can start now. KOMOS Works in Komos Chiseling of all kinds of the blocks for the bridge continues in Komos. Procedure for chiseling of the big voussoir blocks is following: all 2-5 stone blocks (depending of how many of them should be in the one row according to the project) are placed one next to the other and then, using the old method of connected vessels (we are using transparent pipe), midpoints of the each stone is determined, points on the same level on upstream and downstream side of the block. After that, templates made on transparent paper are attached to the blocks. Blocks are chiseled, using those templates, to necessary dimensions. In that way we can be sure that the geometry of the bridge will not deviate from foreseen plans. Copying of dimensions of the block from template to the stone Chiseling of the blocks is performed by the big group of workers and all blocks from the one row (2-5 of them) are chiseled in the same time. Curved blocks are also chiseled in accordance with templates for curvature of the single blocks. Four rows of the big arch blocks can be chiseled in the same time. Geotechnical measurements Blocks are assembled based on the precisely determined points given by the project and based on the photogrammetric measures of the bridge before its destruction. Before and after assembling of each row a team of geodesists determines and controls these points. In all, but especially in lower rows, precision is of the great importance, because the smallest mistake now can have as a result the enormous mistake at the end of the assembling of the arch. Final chiseling of the assembled row After the row is assembled, controlled by geodesists, and possibly additionally chiseled, we start with its finalization. Cramps are placed in the holes, which are already chiseled in Komos and just finalized after assembling of the block. In them we pour the lead on the spot. After that their surface is treated until it became in line with the surface of the stone of the arch. Canals for pouring of the lead to the dowels are chiseled in situ. Preparation for the next row – mortar and rubber tapes out the air as well as and sucking in the air, and two pipes; one is connected to the gas-bottle leading the gas to the flame, and the other one connected to the “vacuum cleaner”. On its way out the air is warmed on the flame, and by the long cuprum pipe is possible to reach to the dowel and its hole. The hole is dried first, and after that possible impurities are “sucked in”. The air is warmed to the high temperature but this can be controlled so the temperature of the air is not too high so it could cause the damage on the stone. Pouring of lead in canals The stone itself contents certain percentage of water (humidity), and besides that it constantly absorbs the water from mortar that dries really slowly between the rows, as well as it absorbs humidity from the air. Because of the sagging of water from upper to the lower rows of the arch, canals in lower rows of the arch are extremely wet, an they must be dried for nearly one hour. This procedure of canals drying does not provide permanent dryness, but just gives us a short period of time (approximately 10 minutes) for pouring the lead trough the canals. If the canal contains even small amount of the water – there is a threaten of lead explosion, what can damage the stone or harm the worker. Canal is poured with the lead After drying, with the same device, just used in reverse, we are sucking in the dust and all impurities that possibly could be accumulated in canals. In the same time while drying is in process, lead is melted in a special vessel and heated up to temperature of 390ºC, then using the special funnel it is poured in dried canals. Pouring of lead demands certain tempo, not too fast or too slow. Too fast pouring of the lead could stop its equal disposing and winding around the dowel, but too slow pouring could result with a too soon cooling and hardening of lead. Assembling of these first parts of the cornice, on east upstream and downstream side of the bridge with a great precision, is of the enormous importance. They have to be assembled and inserted in the wall very precisely and what’s more - each of them was made by Hajrudin in a different way. Therefore we couldn’t use the same procedure for montage of cornices on both east sides. We escaped that on west side of the bridge because the first five arch rows we didn’t dismantle so the bases of this cornice existed already. Assembled four blocks of the cornice on the southeast side VISITS TO THE SITE Works on the bridge are in full play now; we had an opportunity to host many important visitors. Everybody wanted to know even the smallest detail about the progress of the works on the bridge, and without any exception their impressions were the best possible. Representative of Turkish Parliament, Mr. Bulent Arinc, visited the site on 19.06. He took a tour with his colleagues on the major part of the site and Old Town. 25. 06. Mr. Hasan Basri Aktan – Minister of Finance of Turkish Government visited the site. Probably the biggest media attention took the visit of Mr. Erkan Mumcu, Minister for Culture of Republic Of Turkey, and gentlemen Rusmir Cisic and Tihomir Rozic, Director and Project Manager of Project Coordination Unit gave few words of gratitude to the guests for their arrival and support. Mr. Erkan Mumcu during the visit to the Site And our regular guests, Mr. Lawrence Hannah and Mrs. Vesna Francic from World Bank visited the site on 30.06.2003 - they didn’t hesitate to show their satisfaction.