Restoring the orthostates of the Parthenon west pediment

The Acropolis Restoration News • 17-18 December 2018 View of the Parthenon cella from the East. Photo R. Christodoulopoulou, 2018 V. Eleftheriou, 2017-2018 - The progress of the Acropolis restoration works V. Manidaki, J. Dourakopoulos - Restoring the orthostates of the Parthenon west pediment Ch Pinatsi, C.Koutsadelis, E. Kakogiannou -The stategic plan for the interventions on the Acropolis walls R. Christodoulopoulou, V. Manidaki - Moving and re-arranging the cranes of the Parthenon E. Karakitsou, E. Petropoulou, Activities to promote research and bring the restoration works on the Acropolis monuments to the fore I. Kaimara, A. Leonti, M. Tsiolaki - «A Greek Temple»: A new web application on the architecture of ancient Greek temples E. Petropoulou - News from the Acropolis Restoring the orthostates of the Parthenon west pediment Dismantling orthostates of the west tympanum in previous interventions.1902: ∆ΤΥ1, part of ∆ΤΥ2, part of ∆ΤΥ3, ∆ΤΥ5, ∆ΤΥ8. 2011: ∆ΤΥ10. 2017: ∆ΤΥ4. 1945: Restoring part of ∆ΤΥ6. Study of the orthostates: V. Manidaki, 2015. Surveying design: V. Eleftheriou – V. Manidaki, 2008. The structure of the tympanum The tympanum of the Parthenon’s pediment comprises ten orthostates in the façade (ΤΥ1-ΤΥ10) and a backing wall of fifty-eight blocks of isodomic masonry placed on six courses. From the west pediment eight out of ten orthostates and two great fragments of the 6th orthostate are preserved. Only the 7th orthostate is entirely missing. The cross section of all the four central orthostates, which were obviously the higher and the heavier blocks of the tympanum differ from the others. Their builders resorted to carving part of the invisible side in order to lighten them. It is calculated that from the 5th orthostate (∆ΤΥ5) the removed volume of the marble is about 1m3 and 2.8 ton weight. The three next orthostates on both sides of the tympanum gable are regular, in shape, with a rectangular cross-section. Special attention was given in order to provide additional security to the horizontal connection of the four central orthostates, with the backing wall. It was used a unique and sophisticated system of eight pairs of custom-shaped clamps placed in the middle area of the orthostates height and the upper surface of the middle courses of their backing wall. These clamps have the shape of a twisted double T and are known in the bibliography as twisted-clamps. These clamps are the largest connectors that have been used in the building, reach- ing 80cm in length and exceeding the ordinary clamps, which range between 30-50cm. Early interventions In modern times, the court architect Leo von Klenze, in his general proposals of 1834 for interventions on the Acropolis monuments, included the necessity to conduct repair works on the west pediment. In the period 1836-1842 under the direction of Kyriakos Pittakis, the first repair works took place for the fastening of the central orthostates. The two large orthostates were secured against overturning with the use of large connectors that were anchored on the backing wall. After the earthquake in 1894, Durm, Penrose and Magne expressed their concern about the danger of the pediment’s collapse. Durm, especially, suggested that the most appropriate measure would be the entire restoration of the west pediment, with the use of new marble blocks for filling in the tympanum and its backing wall, as well as the reconstruction of all fallen cornices. In 1902, Nikolaos Balanos intervened on the pediment after completing works in the west side (1900-1902). Balanos’ report on the restoration works he completed at this area is summed-up in a phrase: “the central block of the pediment was placed back on its original position and connected with iron clamps with the marble wall found behind the pediment blocks”. Research revealed though that Balanos had conducted more interventions on the west tympanum. Out of the eight in situ preserved orthostates of the west tympanum three were totally dismantled (∆Τ1, ∆ΤΥ5, ∆ΤΥ8) and parts of two other (∆ΤΥ2 and ∆ΤΥ3), while four large clamping elements of strong profile were placed on the position of the ancient twistedclamps, and sixteen clamps for securing the cracks were added; interventions were also carried out on the horizontal cornices underneath (∆Γ12, ∆Γ13, ∆Γ14, ∆Γ15 and ∆Γ19). Studies on the restoration of the tympanum - Priorities of the rescuing intervention In the recent past, attention has been directed to the structural problems of the west orthostate. In 1997 K. Zambas, civil engineer from the technical office of the Parthenon (1984-2000), mentioned in a report that “deterioration has worsen…and that in some cases there is direct danger of big fragments falling off from the monument…”. In 2015, while examining the tympanum, after the completion of the restoration programmes on the two corners of the Parthenon west side (programme 2011-2015), it was documented the unstable condition of the central orthostates. Multiple crackings throughout the height of the marbles, some of which were caused by the oxidations of the 13 clamps used in Balanos intervention, as well as fractures on their footing posed a danger of crumbling that asked for immediate rescuing measures. The restoration of the west pediment orthostates is part of the 4th sub-programme that focuses on the west side of the Parthenon, as it was defined by the “Study for the restoration of the west side of the Parthenon-general organisation of the project and intervention proposals on the two corners of the en- and thoughts of the participants as well as YSMA’s personnel have been published in the Proceedings of the Meeting. The decision concerning the entire or partial completion of the tympanum is pending to be resolved after more urgent matters regarding safety will have been dealt with. In 2016 the following studies were submitted and approved, “Study on the restoration of a tympanum orthostate of the west Parthenon pediment”, by removal of the oxidized clamps from the previous interventions, the stabilisation of each member, and connecting them together by following as much as possible the ancient clamping system. For this reason it was found necessary to dismantle the damaged orthostates and the blocks of the backing wall allowing as such the removal of the clamps used at the Balanos restoration. The intervention for safely consolidating the orthostates of the tympanum in- structural restoration was explored in an implementation study prepared by J. Dourakopoulos (Implementation study for the structural restoration of the orthostates ∆ΤΥ4 and ∆ΤΥ5, September 2018). There was also extensive collaboration with A. Vrouva on studying the seismic behaviour of the pediment. The restoration of the orthostates as structural members is expected to be complete by July 2019, while their repositioning will follow the structural restoration of the backing wall scheduled for the middle of 2020. Implementation study for the structural restoration of the orthostates ∆ΤΥ4 and ∆ΤΥ5 Initially, the design of the necessary reinforcement for the structural restoration of the orthostates, based on static calculations with kinematic considerations, was performed. Then, in order to test the aforementioned results and design the clamping of the orthostates with the backing wall, dynamic analyses according to various seismic scenarios, were conducted. These scenarios were represented by the relevant recorded accelerographs, taken from the accelerographs catalogue which was composed in the context of the research programme entitled “Choosing the right accelerographs for dynamic analyses of the Acropolis monuments” (Psycharis 2014), after having been amplified with the appropriate factors. Finally, the chosen seismic scenarios were applied to the three main directions at the base of the monument. Because of the serious damage observed after the orthostates were dismantled, as it is thoroughly presented in the aforementioned study, according to which the orthostates mainly exhibit cracks throughout their width, vertical along their height and parallel to the geological layers of the marble, it has been suggested that the reinforcements of the structural restoration should traverse horizontally, covering the largest possible length so as to consolidate these cracks and reinforce the ones that have yet to appear on opening fracture surfaces. The study also highlights that special attention should be given to both the south corner of the orthostate ∆ΤΥ5 because of its almost horizontal crack through its width, at a height of about 1.90m from the orthostate base, and to the area at the south and middle footing of ∆ΤΥ4, which after a cannonade it has been broken into many fragments and uneven fracture surfaces. For the first case it has been suggested to place, apart from the horizontal reinforcements, inclined reinforcements in order to strengthen the horizontal crack and avoid a vertical drilling, in parallel, that is, with the Numbering the orthostates and twisted-clamps of the Parthenon tympanum (Code of row, number of the orthostate). Drawing: Manidaki, 2015 tablature” in 2008 by V. Eleftheriou, V. Manidaki and A. Vrouva. This study included information on the structure and pathology of the Parthenon tympanum and also alternative proposals for completing the orthostates with new marble. The study was approved by the Central Archaeological Council in 2008, with a positive decision regarding the entire filling of the tympanum. Since it was expected though to conduct a special study on the sub-programme, the question of whether the tympanum would be entirely or partially completed was raised again in a questionnaire addressed to the participants of the 6th International Meeting for the restoration of the Acropolis monuments in 2013. The two alternative proposals regarding the entire or the partial completion were presented in a poster at the exhibition of the Meeting. The theoretical reflections V. Manidaki and “Structural problems of the orthostates of the west pediment, focusing on the risk of their overturn” by L. Paleologos; according to them priority was given to taking urgent action and to the implementation, firstly, of the rescuing intervention, which is probably the first and most crucial part of a potential planning for an entire making out. The current restoration programme is part of the wider programme concerning the west pediment, which involves the restoration of the backing wall (study by K. Skaris, 2013). Main points of the proposed rescue intervention The aim of this rescue intervention is, on the one hand, to treat important structural problems of the orthostates, and on the other, to safely connect them then with the backing wall. Treating these structural problems assumes the cludes the dismantling, restoration and repositioning of 4 orthostates (∆ΤΥ4, ∆ΤΥ5, ∆ΤΥ6α, ∆ΤΥ8) and the in situ restoration of the third orthostate ∆ΤΥ3. Out of these 4 orthostates only the 4th orthostate was probably intact since the antiquity. The project also incorporates the restoration of the underlying horizontal cornices of the central area, because these are the blocks on which the central orthostates are standing and fixed with dowels (∆Γ14, ∆Γ15, ∆Γ16, ∆Γ17, ∆Γ19 and ∆Γ21). Commencing the works The restoration of the tympanum started in June 2017 by carrying out the planned dismantling and taking down of the orthostates. Then the clamps of the previous restorations were removed and their fragments were detached. Thus the total extent of the fractures and any other damages could be assessed. Their Orthostates of the west tympanum ∆ΤΥ5 (left) and ∆ΤΥ4 (right), east side. Orthophotographs: V. Kyparissi, 2018 clamp (four in ∆ΤΥ5 and three in ∆ΤΥ4) consists of two parts of bended bars that anchor on undamaged areas of both the ortostate and the relevant block, and which also have threaded edges that will be later used to join them together by using a specially shaped nut. When using the clamp inside the orthostate it is suggested to use dowels, perpendicular to the marble surface, placed in the middle of its width to minimize the possibility of fragmentation because of the narrow width of the marble. Moreover, it was found essential to reposition the Π-shaped connector that was placed by Balanos and joined the orthostate ∆ΤΥ4 with block 4.2 of the backing wall. Orthostates of the tympanum ∆ΤΥ4 (above) and ∆ΤΥ5 (below). Three-dimensional model: Above and below, on left: Different colours indicate the existence of fragments. Above and below on right: reinforcement of structural restoration. Photogrammetry: V. Kyparissi. Model: J. Dourakopoulos crystal layers of the marble. For the second case, regarding the south and middle footing of ∆ΤΥ4, and because of the oblique fracture surfaces, it is suggested that inclined reinforcements should be placed along the width of the orthostate; moreover, some of the fragments, which cannot be joined with the others or held together with reinforcements because of their small size, should be replaced with new marble. its footing that were used originally to set these members and consolidate the metal cantilevers under the pedimental sculptures. It should be pointed out that the correct seating of the orthostates plays an important role for their stability and seismic response, therefore the appropriate works should be conducted in order to secure them without though damaging the ancient surfaces. Moreover dowels should be repositioned on the base of the orthostates. In addition, since the footing of the orthostate ∆ΤΥ4 has been rendered unsafe, even after joining its largest ancient fragments, and because of the uneven fracture surfaces along the narrow width of the orthostate, it is suggested that new marble fillings should be placed in the rectangular notches on Finally, regarding the transverse clamps that join the orthostates with the backing wall, and because the cracks are located in the areas of their anchoring both on the orthostates and the blocks of the wall, it was found unsafe to restore the original geometry of the clamps. For this reason it would be better that every It should be noted that the dynamic analyses conducted in the above-mentioned study assumed that every block of the backing wall has been structurally restored; that is, the individual fragments of the blocks were tightly joined while their original dimensions remained the same. However, while the study was being carried out, and after dismantling the 4th and 5th courses of the backing wall, it was revealed that the blocks of the 3rd course were in bad preservation state exposing the existence of multiple fragments; in addition, there are also indications that many blocks of the 2nd course are in a similar condition. As a result, the preservation state of the orthostates and the blocks of the backing wall does not allow the development of axial forces that correspond to the dimensions of the cross-sections of the ancient transverse clamps. Therefore, it is proposed to use the appropriate decreased cross-sections so as the fracture of the clamp in the area of the marble surrounding the mortise could happen before any marble cracking. Vasileia Manidaki Architect Engineer John Dourakopoulos Dr Civil Engineer Parthenon Restoration Project