Strengthened and rehabilitation of Transylvanian saxon house

Transcription

1 Strengthened and rehabilitation of Transylvanian saxon house GABRIELA GHERGHEL, LASZLO SCHREK Faculty of Civil Engineering Department of Construction University Transilvania Turnului Street No. 5 - Brasov ROMANIA office@vesni.ro, laszlo.schreck@yahoo.com Abstract: - This building dates from 1850 and it stands in a mediocre condition; it has rectangular shape, height semi-basement, ground floor and attic. The strength structure of the basement is masonry (bricks and rocks) with clay binder. The thickness of the wall is variable. The continuous footing is made also from rock masonry with clay binder. The floor is vaulting with ring curve. Eastern wall suffered most important degradation, caused by downstream foundation failure. The eastern wall degradation has as effect it s separation from longitudinal walls and cracks appearance in the cylindrical vault. The ground floor conservation is in a good state, excepting the same eastern zone which has problems to the semi-basement. Walls structure is brick masonry with clay binder. The eastern transversal wall is separated from the longitudinal walls; its movement is in direct connection with basement wall. The floor above the ground has a typical Transylvanian floor structure. The roof is wood framing covered with plain tiles. Consolidation involves underpinning, eastern and northern walls stabilization with concrete coating and steel ties under each floor. Key-Words: - concrete coating, consolidation, cracks, foundations failure, tie-rod, underpinning, wall degradation. 1 Description of initial situation The house is situated on a hill which has a gentle slope, and it takes part from a historical complex. The basement entry is visible from down the valley, from the northern side, at the height of a floor. On the opposite side the basement is underground. The basement structure is masonry (bricks and rocks) with clay binder (fig.1). Wall thickness is variable from 65cm up to 110 cm. Continuous footing are also rock masonry with clay binder; depth of foundation is cm from the basement s loam floor. The building has been constructed in two stages. This stands in different quality of materials put into work, and poor walls bounding. The floor is vaulting with ring curve. The north wall has been thickened in trapezoidal shape using brick masonry; foundation has not been modified. Eastern wall suffered most important degradation, visible from inside and outside. Those degradations were caused by foundation failure, because of insufficient foundation depth. This has been aggravated by water infiltration, and poor quality of the foundation material. Fig.1 Basement plan with damaged indications Because of eastern wall degradation results it s separation from longitudinal walls and cracks appearance in the vault (fig.2 up to fig.4). 109

2 There was a repair attempt in the past: outside the eastern wall has been plated with brick (half thickness) linked with low resistance clay; this work has not improved structure behaviour, and the brick detached itself (fig.5 and fig.6). Fig.2 Eastern wall basement separation from the longitudinal wall (north-east corner): view from inside; Fig.5 Eastern wall-plated bricks detached; overview Fig.3 Eastern wall basement separation from longitudinal wall (north-east corner): view from outside Fig.6 Eastern wall-plated bricks detached; detail In the rest the basement appears in relatively good condition, regarding the age of the building; there weren't noticed any other cracks or visible tears in the walls or vaults. Geotechnical study highlighted these layers: dumped fill -upstream 90cm.depth and downstream 140cm depth; next layer is black clay, consistent and plastic, than a massive horizon of dusted clay, yellow-brown. Continuous footing is: downstream in dumped fill layer, and upstream in dusted clay layer. Ground floor walls structure is brick masonry with clay binder, Exterior walls thickness is 50cm, and interior walls thickness is between 30-35cm (fig.7). Fig.4 Crack in the vault 110

3 Fig.7 Ground floor plan with damaged indications Ground floor conservation is in a good state, excepting the eastern area which has the same problems as the basement. Eastern wall is separated from longitudinal walls, movement is in direct correlation with basement wall (fig.8); it also pulled a part of central east wall, which has also cracks (fig.9). Fig.9 Crack in the median longitudinal wall pulled by eastern wall Fig.10 Southeast wall fissure Fig.8 Eastern wall ground floor separation from longitudinal wall (north-east corner) In the middle southeast wall plane fissure is due to the weakening created by the chimney hole (fig.10). A general observation on the ground floor relates to the interior door openings: diagonal cracks starts from upper edge. After plasterwork removed, it was noted that those doorways had been enlarged, and the arc-form lintel has never been reshaped (fig. 11). Fig.11 Doorway enlarged without reshape the arc lintel 111

4 underpinning. Given the poor quality of the foundations binder, the underpinning operation should be done with great attention. The area was divided in work sections, also indicating the order of performance (fig.14). To support the continuous footing against crumbling there it s necessary to mount metallic elements (insurance angle). They are mounted on a section of work (over a length of about 2m) on the both sides of the foundation. Only after this operation is done it s allowed to dig under the existing foundation. Each section is divided in smaller sections, not longer than 60cm which also represents the digging under foundation. The material for underpinning is C12/15 concrete. The next phase (next section dig) can be done only after concrete has strengthened foundation. The wooden porch is in a fairly advanced state of degradation. The wooden pillars are resting on a cluster of brick and stone, and the joints between wood structural elements are partially compromised (fig.12 and fig.13). Fig.12 The wooden pillars are resting on a cluster of brick and stone Fig.13 Damaged joint in wood structural elements The floor above ground has a typical Transylvanian floor structure -meaning that the ceiling wood beams and attic floor beams are separated. In the attic, the wood beams were covered with rubble and slag; over a brick floor was performed. All those layers have a thickness ranging between cm. The unveiling of rubble and brick layers founds no degradation in the timber floor. Wooden roof structure is in a good condition. It discharges on the ground s floor walls through wall plates, and in the porch area it sits on wood purlins, supported by the wooden pillars there. In some roof areas there is water infiltration, leading to strips deterioration. Fig.14 Underpinning sections Fig.15 Underpinning accomplished. View from inside After the underpinning has been finished it can be proceed to stabilize the eastern and northern basement walls (fig.16). This operation involves concrete coating; simultaneously tie rods are 2 Proposed solutions for consolidation After research and studies the first priority conclusion is for eastern and northern walls 112

5 mounted. After concrete has strengthened tie rods are tighten. Fig.18 Coat concrete wall on the east side Once eastern and northern walls are stabilized, the opened cracks in basement vaults stop growing. Now they will be injected with pointing mortar. The north-eastern corner on the ground floor, which is the most damage, is going to be taken into pieces, than rebuild achieving an appropriate wall-bounding. For repair the median longitudinal walls, at first carefully takeout unbounded bricks, than rebuild with proper wedging. Also tie rods are mounted just under the ceiling (fig.19). Fig.16 Consolidation scheme a) section; b) plan Fig.19 Tie rod mounted under the first floor ceiling Wood lintels will be mounted above door openings. The wooden porch will be completely rebuilt using new wood elements. 3 Conclusion Fig.17 Tie rod mounted in the basement There were respected the age and historical importance of the building. Very important was to analyzing the compliance of structural ensemble, insisting on critical and 113

6 vulnerable areas. Also, understanding the manner of building for the middle of 19 th century was challenging. By considering several hypotheses and possibilities of strengthening, step by step, it could be reached the overall structure's integrity, which leads to the optimal solution, both technically and economically. Concrete consolidation works (underpinning and northern and eastern walls stabilization) were strictly necessary to stop this area collapsing. The tie rods are visible on the interior, under the ceiling, but do not restrict or disturb. The bricks used in the masonry restoration process, were mostly recovered from one partial collapsed neighboring building; the binder (mortar) was made upon a recipe known and kept through time by the local craftsmen. Strengthening and rehabilitation have been made considering and protecting building architectural aesthetics, its feature and personality. References: [1] Arsenie G., Voiculescu M., Ionascu M., Strengthen solutions for earthquakes damaged buildings, Technical Publishing House Bucharest, 1997 [2] Benke I., Technical expertise, july 2009 [3] Fabini H., The world of the fortified churches in Transylvania, Monumenta Publishing House Sibiu, 2009 [4] Nistor C., Troia L., Teodoru M., Minialov H., [5] Buildings strengthening and maintenance, Technical Publishing House Bucharest, 1991 [6] Tologea S., Building s events and damages, Technical Publishing House Bucharest, 1979 [7] Tologea S., Buildings pathology issues, Technical Publishing House Bucharest,