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Reconstruction of the Arsenal in Hvar
Reconstruction of bearing structure of the Arsenal in Hvar RECONSTRUCTION OF THE LOAD BEARING STRUCTURE The construction of Arsenal in Hvar started in the13th century. At first it was a ground-floor structure which served as shed for boat and its equipment. In the course of time it was subject to many changes regarding space usage, but also regarding the size of the structure. The most important issue for the present state is its surroundings, i.e. annexes built on its base volume, on the north, south, and part of the east side. On the north side, in the direction of the Square, the place where low-rises were located earlier was converted for Fontik, with terrace through which entrance to the theatre on the first floor was gained. Along the whole south facade, at the north-eastern corner and on part of the east side, one-storey and two- storey residential buildings were built, adjacent to the Arsenal. Thus, the town block was formed as a separate unit in architectural-structural sense. Alterations on the Arsenal building were significant regarding volume, as well as interaction of parts of the bearing structure. The most significant is the change resulting from construction of the first floor, when transverse stone arches were built about 5,0 m apart, within the ground floor, between longitudinal walls. Parallel to the longitudinal walls and supported by stone arches, wooden beams were placed about 50 cm apart, as floor beams of the first floor. The auditorium of the theatre, occupying the eastern half of the first floor of the Arsenal, is partly located in the parquet circle, partly in boxes, built on two levels, in parterre and on the first floor. The entire bearing structure of the boxes is constructed of wood posts supported by floor beams, and boards dividing the boxes. The floor of the first-floor boxes is constructed as grid, made of wooden beams, leaning on longitudinal walls of the building, posts between the boxes and queen post trusses that carry the edge of the access gallery to the first floor boxes. The bearing structure of the stage is a wooden structure, placed about 1,0 m above the parquet circle of the auditorium, leaning on the east wall of the building and the first adjacent stone arch. The roof is wooden, constructed as purlin roof, with or without collar beams. The western part of the roof had queen post truss with braces that supported the rafters. In later interventions this bearing system was changed by removing the braces and queen post trusses. The eastern part was constructed as purlin roof, with or without collar beams, but everywhere without queen-post trusses. On the part above the stage two double queen-post trusses were constructed, one by the eastern wall and the other above the stage portal, carrying purlins and rafters. The bearing structure of the attic floor consists of wooden beams placed on every other pair of rafters. Due to this, beams on the walls transfer horizontal force from the pair of rafters without connecting beam to the pair with connecting beam, by bending in horizontal plane. The particularity of the ceiling beams in the attic floor above the theatre lies in the fact that they don’t directly lean on longitudinal walls, but below them, at the distance from end walls of the first floor boxes, short beams are placed, leaning on the walls and fixed to the ceiling beams with steel fastenings and screws. The dimensions of ceiling beams above the theatre are not uniform, but are generally of insufficient cross section, so their sinking is easily observed. The floor level is not the same in the eastern half of the attic floor, the one above the theatre. The part above the auditorium is elevated and the remaining part is lower. The reason for this probably lies in positioning of bottom beams that lean on the walls, so ceiling beams had to be placed above them, which resulted in different level of the attic floor. 1. Inner scaffolds 2. Preparation for grouting of stone walls DAMAGES OF BEARING STRUCTURE Based on the material of various parts of the bearing structure, damages are divided into damages of: stone walls and arches, wooden beams in ceilings of the ground and first floor and wooden roof. Damages of stone walls and arches: Cracks that extend along the transverse stone arches are the most pronounced damages on the stone structure of the Arsenal. Numerical analysis of vertical load effects was performed on three-dimension models of bearing structure for parts by the eastern and western facade and the middle, dividing wall. The obtained deformities and stress state in model test corresponded to the actual damage. The transverse stone arches were consequently built in between the existing longitudinal walls, but the interconnection, which is very important, was barely achieved. Thus, in transfer of load, the transverse stone arches behaved as frames with arch intrados. Due to vertical shift of arch crown, its end points shifted horizontally towards the middle, opening cracks in the upper parts of contact surfaces of longitudinal walls and stone arches. Likewise, the built parts above the arch stone intrados and horizontal top surface of the wall cracked where excess tensile strength of material occurred due to effects of negative bending moments. These typical damages were present on almost all arches. Cracking of stone block occurred on the stone arch below the middle dividing wall on the first floor, in the place of maximum pressure stress, due to its concentration on the marginal zone of cross section. Apart from the said damage, on the first floor wall around the door in the crown centre, there are cracks tracing the shape of relieving arch, which points to yield of the crown zone. This correlates to the position of maximum tensile strain that occur in the crown, exactly as in the model. There is also a crack on the joint of the wall and the north longitudinal wall, as the result of the same cause and poor interconnection. On the inner side of the joint edge of the east and south wall there is a crack that extends from the connecting beam of the double queen-post truss to the stage floor. On the west facade there are cracks in the crown of the big stone arch and on the wall on the north and south side of crown zone. These damages are the result of adjusting of the semicircular arch geometry to the support line, established in the wall plane by the existing openings on the first floor. They are also the result of facade remodelling, which was done after adding the first floor. 1. Works on stone arches Damages of timber: Damages of timber were observed upon tests performed on the spot. Due to sensitivity of the theatre floor in view of structure of the boxes in the parterre and on the first floor, all wooden beams were tested on both supports and in the middle of the span. Thus, extensive damages were observed, in the first place caused by fungi and insects, which weakened to a large extent the cross section of the beams, whose bearing capacity for prescribed loads was doubtful. The remaining floor beams of the first floor are in better condition because they were replaced earlier. Nevertheless, a large number of beams were attacked by insects, which is pronounced in the west facade zone. 2. Replacement of metal structure 3. Staircase to the second floor boxes REPAIR OF DAMAGES ON THE BEARING STRUCTURE: Repair of cracks: All cracks were cleaned of all cracked and loose parts of stone and mortar, blown out with compressed air and well moistened before remoulding or grouting. The cracks on the western facade were repaired by stitching and grouting on the inside with grout compounds, using natural hydrated lime. Stitching was performed after grouting, by placing passive bar anchors of RR 400/500 Ø 16 mm in holes of Ø 24 mm, depth l = 95,0 cm, previously bored in the wall. The holes were bored at an angle of 45 degrees in the direction of the wall face and intersect in the centre of the wall thickness. On the opposite side they are about 5,0 cm far from the external wall. After installation of anchors and protection of the central position in the hole by distance pieces, they were grouted with compound that secures full adhesion and impermeability and protects the anchor from effects of the surrounding walls. The crown grid between two stone blocks will be bridged with stainless steel clamp (4170) of thickness t = 5.0 mm. The clamp will be connected to stone with lead. The cracks on inner transverse stone arches on ground floor will be repaired by stitching with passive stitches, with previous crack filling with stone pieces of adequate size in extended lime mortar, of compound ratio 1 : 3 : 9; white cement : hydrated lime and lime putty: aggregate of grain size 0 to 2 mm. All parts of transverse arches, built with stone, except the intrados stone arch which is built with ashlars, will be grouted with natural hydraulic lime Calx Romana. The crack in the north arch heel on the gallery in the end western part of Fontik (measuring place no.8) will be repaired by stitching, fitting of two crosswise bar anchors (as described earlier) and by grouting of the crack with Calx Romana. 1. Supporting of boxes Vertical cracks on the joint of all transverse stone arches, of both north and south longitudinal wall, will first be filled with pieces of rock in extended lime mortar of ratio 1 : 3 : 9, and walls will be connected with previously described passive stitches at vertical spacing, equal to the thickness of stone arch, i.e. about 75 cm. The crack on the joint between the middle wall on the first floor and the northern longitudinal wall will be repaired in the same way, but the vertical spacing between bar anchors will be about 50.0 cm, due to less thickness of the middle wall. Vertical crack in the corner of the stage, at the joint of the south and north wall, will be repaired with bar anchors, RR - 400/500 Ø 22 mm, installed in holes, previously bored in the wall, of Ø 32 mm, approximately 2.5 m long, vertically apart about 100.0 cm. Installation of bar anchors and grouting will be performed as described earlier. The anchors will be installed in both wall surfaces. The crack will be grouted with Calx Romana. Cracks on the remaining parts of the walls will be repaired as described earlier, but without bar anchors, i.e. only with cleaning, filling with suitable pieces of rock in extended lime mortar, or only with grouting, in case of smaller cracks. Reinforcement of walls and stone arches: In addition to repair of cracks, systems of longitudinal and transverse stirrups will be fitted in the walls, in order to increase their overall resistance, particularly to effects of horizontal load. All steel parts will be of stainless steel 4170 (Inox 1). In the floor of the first floor on the north and south longitudinal wall, iron strip, 20 x 70 mm, of length that corresponds to the wall length, will be placed by the inner face. Connection with longitudinal walls will be performed with anchors, Ø 16 mm, about 1,5 m apart, placed in holes of Ø 26 mm, and grouted with Masterflow 928 compound, with anchoring depth ls = 30 cm. Anchoring at the ends will be done with anchor plate 250 x 300 x 20 mm, placed about 15.0 cm below the external wall face, on the prepared base of fine grained concrete, grain size up to 8.0 mm. Passage through wall will be with 2 holes, Ø 30 mm. 1st class welds will provide connection and continuation of steel parts. The north, middle and south transverse walls will be strengthened with the same steel reinforcement as in longitudinal walls. Anchoring in longitudinal walls will be performed with anchors 2 x 2 x Ø 22 mm, placed in holes in the wall, Ø 32 mm, with grouting with Masterflow 928. Two anchors are placed on the ends of the iron strip 20 x 70 mm. On the top surface of transverse stone arches, steel profiles 2 x Ø 28 mm will be placed by the ceiling beam ends, in side cuts 5 x 5 cm. Connecting the profiles in side cuts with stone walls will be performed with epoxide glue Concresive 1421. Anchoring in longitudinal walls will be performed with anchors 2 x Ø 22mm, placed in Ø 32 mm holes in the wall, and grouted with Masterflow 928. Due to an active crack on the south side of the facade, additional steel stirrup, 20 x 70 mm will be placed and anchored into the south and north wall of the Arsenal. This will be done with anchor profiles 2 x Ø 30 mm and anchor plates 250 x 300 x 20 mm. The stirrup will be anchored in the western wall with anchors Ø 16 mm, about 1.5 m apart, in the way described for longitudinal walls. Regarding height, it will be placed in the place of horizontal cornice, extending above the stone arch crown. Steel stirrups, 3 x Ø 30 mm, will be placed in previously cut side cuts, about 5.0 x 5.0 cm, in the attic floor on top of the longitudinal walls. They will be anchored on external faces of the east and west wall with anchor plates, 250 x 1050 x 20 mm, placed about 15,0 cm below the wall external face, on the prepared base of fine grained concrete, with grain size up to 8.0 mm. Connecting of the profiles in side cuts with stone walls will be performed with epoxide glue Concresive 1421. Reinforcement, steel stirrups 20 x 70 mm, along transverse walls in the attic floor, will completely be performed according to reinforcement in the floor of the first floor. Oblique ends of the middle and cofferdam walls will be reinforced with 2 Ø 25 mm in the middle wall and 3 Ø 25 mm in cofferdam walls, placed in previously cut side cuts, about 5.0 x 5.0 cm, as described earlier. 2. Grid of grout tubules Apart from this reinforcement, for the purpose of securing tension zone in the intrados of all transverse stone arches, iron strip, 2 x 5 x 50 mm, is required in the part of the arch that extends from the left to the right point in the span quarter. The reinforcement will be placed by cutting 8 mm wide and 60 mm deep side cuts, 10.0 cm far from ashlar face, in the intrados. 5.0 mm thick stainless steel sheets will be placed in side cuts, after which epoxide glue Concresive 1421 will be grouted. The side cut on the intrados will be closed with MAR GRIP 411 - ZB, of coat thickness 10 mm for levelling the stone intrados. Only on the middle stone arch, below the middle wall in the first floor, three vertical sheets will be placed instead of 2, due to the size of tensile stress. The dimensions of two end sheets are 2 x 5 x 50 mm, as on other arches, while the third, middle sheet is 5 x 70 mm, and the side cut is 8 x 80 mm. As the sheets are semi circular, their exact geometry should be measured on the spot and then sheets should be cut accordingly, interconnected with 1st class welds and inserted in the previously cut side cuts. Apart from reinforcement with steel stirrups, all walls – longitudinal and transverse, should be grouted. Natural hydraulic mortar Calx Romana will be used for this purpose, following the detailed instructions of the manufacturer. The reinforcement works will be performed according to the existing standards, and will require the Contractor’s experience, which is in this case very important, all in agreement with the Designer, Conserver and the Supervising Engineer. There is also the need for remodelling all parts of stone walls and arches, where remodelling or filling with other materials was performed before. This will require removal of the existing material, preparation of base and new building with stone blocks of suitable size, with application of extended lime mortar of the described mix-design. Connection of the new stone blocks and the surrounding walls must be performed with proper masonry binder. The Designer, Conserver, Supervising Engineer and Contractor will agree on the spot about the parts to be remodelled. New floor of the first floor: Based on investigating results of the condition of wooden floor beams of the first floor, it was decided that all floor beams be replaced with new II class oak beams, of cross section 18/22 cm. For the purpose of sufficiently rigid horizontal slab, new wooden compregnated KERTO - Q slabs will be placed over the wooden beams. The slabs will be 69 mm thick and their width corresponds to double spacing between the beams, which is in this case about 100.0 cm. The slabs consist of 13 veneer layers, placed in two mutually perpendicular directions, which provides them with similar bearing capacity in both directions. The slabs and beams are connected with special screws SFS WT - T - Ø 8.2 mm, of length 220 mm. The results of laboratory tests, made on connecting models, were used for dimensioning new T-profiles. Before placing the KERTO – Q slabs, 1,0 cm thick boards will be placed perpendicularly to ceiling beams, for ceiling intrados that will have to be the same as the original. For the purpose of homogenization of fields, bordered with longitudinal and transverse walls, or stone arches, interconnection of new, compregnated beams is performed with 20 mm long stainless steel spikes, Ø 10 mm, that are fitted into previously bored holes Ø 10 mm, of each slab, up to the depth of 100 mm, and glued with epoxide glue Concresive 1421. Due to the impossibility of installation of spikes, interconnection of the last board and the one before in each ceiling field will be performed with stainless steel plates, of dimensions 80 x 600 x 6 mm. Two metal strips intersect at an angle of 90° at the contact of two boards. Each one is fixed to the board with 10 screws, Ø 6 mm l = 60 mm for every leg of the cross. Such connecting crosses are placed about 1 m apart. End boards are similarly connected to longitudinal walls, with steel plates 80 x 600 x 6 mm, but with 19 screws Ø 6 mm I = 60 mm. Steel plates are not built into the wall, but stainless steel anchor profiles, Ø 12 mm, are placed into holes Ø 22 mm, of anchoring length 60 cm, mutually at an angle of 90° and 45° towards the wall face. Everything is grouted with grout compound Masterflow 982. Also, both ends of every board are connected with marginal, transverse walls or with the board from the adjacent field. Connection of boards above stone arches is done with crossed plates, 80 x 1200 x 6 mm with 19 screws, Ø 6 mm I = 60 mm for every leg of the cross. Connecting of plates with bar anchors of Ø 12 mm is performed through full steel profile 20 x 20 x 150 mm, to which plates and anchor profiles are welded. At the intersection of plates and plates with anchor profiles, the connection is performed by welding, with 1st class weld. By placing the anchor profiles into all marginal walls and by connecting them to compregnated boards, which are interconnected, connection of bearing marginal walls to horizontal rigid plane is provided. This improves the structure behaviour under horizontal load, i.e. contributes to homogenization of the overall bearing structure. All metal parts for interconnecting of compregnated boards and their connection with marginal walls, are of stainless steel 4170 (Inox 1). Regarding replacement of old beams with new ones, the construction of boxes in the theatre auditorium, which are supported by floor beams through wood posts, constitutes another problem. Due to small dimensions of cross section of all parts of the bearing structure of boxes, and due to the need of preservation of their original state, the method of replacing the floor beams with new ones was worked out. The method includes placing and connecting compregnated boards with supporting the floor of boxes on the 1st floor, leaving the parts of the bottom bearing structure of boxes in the parterre hanging, so that old beams could be removed and new ones placed in their place. The support structure scheme with elements that will support the bottom parts and the scheme and sequence of replacement of sections of the floor structure are shown in separate drawings, with construction details which the Contractor must respect. The new attic floor: The existing attic floor beams must be completely stripped of top formwork and floor layers, to provide on the site inspection of the actual state of timber. Based on the Expert Report, it can be presumed that the beams can be preserved with adequate treatment with protective coats against moisture and worm-holes. In case of unfavourable state, the decision about replacement with new beams will be made by the Designer, Conserver, Supervising Engineer and Contractor. As the existing roof will be adapted by construction of queen post truss in one half of the span, the condition in ceiling beams will improve considerably, in the sense of significant reduction of sinking and stress. Due to different levels of part of the attic floor above the theatre, beams will be added to ceiling beams at lower level, for equalization of levels. This is necessary because in both parts of the attic floor horizontal bracing will be performed for the purpose of more favourable transfer of horizontal load to marginal walls for both direction of its possible effect. Floor bracing will be done by placing 4,8 cm thick wooden planks in two layers, at an angle of 90°, and each at an angle of 45° in relation to floor beams. On each half of the attic, marginal reinforcement, connected with screws or nails to two layers of planks and floor beams, together form riveted girders, capable of transferring horizontal load to marginal walls, depending on the direction of its activity. As the planks must be of required length, their extensions are performed by cutting the plank in the middle of its thickness and inserting steel plate, 200 x 480 x 1.5 mm, into both planks. Interconnection is performed with nails on the western half of the attic and with screws on the eastern part. This is required for preserving the original, painted mortar on the theatre ceiling. Reinforcement of marginal, border parts is performed with wood beams, 20 x 60 cm, connected with screws and nails to crosswise placed planks and ceiling beams. Bracing is connected to marginal walls with metal crosses and bar anchors, in the same way as in the floor of the 1st floor. Each ceiling beam will be connected to longitudinal walls with vertical bar anchor of RR - 400/500, Ø 19 mm. The hole in the wall for inserting the bar anchor will be of Ø 26 mm, about 80.0 cm deep. Upon inserting the bar anchor, everything will be grouted with Masterflow 928 compound. For more favourable connection of horizontal bracing of attic floor above the theatre, new horizontal part is required on the south side by the eastern wall. Thus, with two horizontal extensions, the eastern part of the attic floor will have better connection with the eastern, transverse wall. Roof structure: The existing roof structure has a number of flaws, both in view of type and the state of timber. Based on mathematically checked required dimensions of cross sections and state of timber, all parts of the bearing structure will be inspected on the spot and decision will be made regarding their further use or replacement with new timber. The decision will be made by the Designer, Conserver, Supervising Engineer and Contractor. 1. View of inside scaffold In view of the big span of floor beams, of 12,5 m, and mostly due to their insufficient cross sections, building in of queen post truss is foreseen on every other pair of rafters, leaning on connecting beams for additional support of connecting beams in the half of the span, by which the state in connecting beams is significantly improved. The existing queen post trusses and collar beams will be replaced with new ones, due to their unfavourable construction details. The new part of the roof structure are longitudinal stabilization bonds in both roof surfaces on longitudinal walls, for taking over the complete horizontal load caused by wind and earthquake, for which they were dimensioned. Stabilization bonds include new longitudinal beams, of cross section 14/18 cm, placed at the connection of collar beam and rafter, to which they are connected with screws. Thus, apart from supporting transverse cofferdam walls, they transfer, through braces, horizontal load to longitudinal walls as vertical and longitudinal horizontal component, while the transverse horizontal components are transferred and balanced in connecting beams. The dimensions of transverse brace are 14/14 cm. The connection with the longitudinal beam is realized with steel fastenings, of sheet thickness t = 6.0 mm and screws M - 14. Purlin, of cross section 12/12 cm, above the theatre stage and constructed as clamps 2 x 8/12 cm on the other part of the roof, is another new part of the bearing structure, intended for improvement of longitudinal connection of all pairs of rafters and also for support of the middle and cofferdam walls in the attic. The connection between the purlin and each pair of rafters is provided with clamps 2 x 4.8/14 cm. The connection of stabilization bond bars for longitudinal walls in the height of the floor structure is foreseen with 6.0 mm thick steel anchor mats. The mats are connected with longitudinal walls through reinforced concrete (Type-20) anchor block of adequate geometry and anchor profiles of RR - 400/500, Ø 14 mm, anchoring depth ls = 60 cm. The connection of wood poles, of dimensions 14/14 cm, is performed with screws M -14. The ends of the new horizontal beams, placed in the joint of purlin and rafters, are connected in similar way, through anchor blocks and anchor plates, to the middle wall and cofferdam walls of the attic. All new parts of the roof will be of class II conifer, while connecting screws and plates will be of steel quality 0361, corrosion protected. 2. Detail of altering the bearing structure – supporting of boxes Stage: In order to relieve the stone arch below the stage, new bearing structure of the stage floor was designed, consisting of steel grid above the stone arch, of cross section 600 x 750 mm, composed of steel bars 90 x 90 mm and fill bars 90 x 45 mm. The grid supports are designed as steel plate, of dimensions 200 x 700 x 8 mm, under which there is a neoprene base, in order to reduce possible horizontal shifts due to dynamic effects. Concrete block, of dimensions 10 x 30 x 75 cm, will be constructed at the top of the stone arch, for load transfer to the bottom arch structure, securing sufficient space under the grid for free sinking. The stage floor is supported by steel trims INP – 20 at a distance of 56.0 cm, over which 2.4 cm thick wooden boards are placed in two layers, at an angle of 45° in relation to the trim axis. All steel parts are of 0361 type steel, protected against corrosion and all parts of the grid are welded with 1st class welds. Foundation: Investigation works of the foundation of the Arsenal and the north annex (Fontik) were performed by the Faculty of Civil Engineering and Architecture in Split, Geotechnics Department, with Head Designer M. Sc Predrag Mišćević, civil eng., R.N. GEO 02/96 and 07/96. Based on the investigation works report, the condition of foundation is satisfactory and it did not cause the existing damages of the bearing structure. All presumptions on which technical documents for reconstruction of the bearing structure were based, will be checked on the spot, by performing all foreseen works. All deviations from these presumptions will be recorded and, if needed and upon agreement with the Designer, Conserver, Supervising Engineer and Contractor, changes of the proposed solutions will be made.

Reconstruction of bearing structure of the Arsenal in Hvar