The Significance of the Structural System Engaged at the Pantheon - Coursework Example

The Pantheon Introduction The Pantheon which was a temple dedicated to Roman gods referred to as Olympian divinities, contains several aspects that are significant regarding structural engineering and architecture (Stamper 259). Hence, the Pantheon was designed in two sections, and which are the dome together with its entrance porch. The Pantheon is built on inlaid marble flooring in order to match a sort of convex contour that drained away rain water. Its initial materialization occurred in 27 BC under the order of Agrippa, who was an in-law of the then Roman Emperor Augustus. However, the initial structure was severely destroyed by fire due to the use of Roman limestone rocks which are susceptible to fire. Its construction then took an extensive period so as to provide the Pantheon concrete sufficient time to heal and achieve strength. The design used is similar to that of a massive circular-shaped barrel with a dome casing on top, including a light-well within the midpoint of the dome. Furthermore, thin brickwork wraps the exterior round-walls even as the main entry contains dual bronze doors, which are a feet high and shielded with an elevated broad porch. The porch contains 16 finely positioned granite columns that hold up the gable-fashioned roof (MacDonald 15). Even though the beams within the roof makeup comprising the porch were initially made of wood, they were replaced with bronze strip-out. The pantheon diameter is approximately one meter more than that of the famous St Peters Basilica and that’s why it had the designers reinforced it using concrete (Moffett, Fazio and Wodehus 14). Interestingly, the dome centre has a circular aperture or oculus that is eight meters transversely and thus not under any load whatsoever. The most outstanding feature of the Pantheon is its slanting shape that makes it discernible from any location a person stands in the vault. Fascinatingly, it was constructed totally with no steel reinforcement rods for defying tensile fracturing, but instead a unique combination of concrete was used that has enabled it to last several centuries later (Baker 30). It is this design using concrete that makes the Pantheon to be an unparalleled structure not practiced in contemporary design standards or structural engineering practices. This is more so due to the designers emphasis on steel reinforcement rods, instead of concrete in reducing tensile cracks. Thus, the aim of this paper is to elaborate on the significance of the Pantheon using the arch and vault system. Background Investigation According to MacDonald, the Pantheon vault system was built on the premise that the coffers should minimize the vaults weight and consequently maintaining the adequate cross-section for shoring up its own weight (14). However, if the vault was constructed through an arched basis and supported by a massive cornice shaped radially, then const the coffers constructive plan was controlled with the aid of molds constructed on the structure itself. Furthermore, such a construction occurred on a floor level through the application of template which defined part of its hemisphere. This leads to the question as to why structural engineers, designers and architects did not execute octagonal floor scheme up to the Pantheon vault, since they applied heptagonal floor plan (Castex 108). Hence, the unexpected change between the floor scheme and the pantheon vault layout appears to be a decision conducted based on constructive intentions rather than on a concept. That is why the soffit slopes comprising the mitered joints and which create the Pantheon coffered ceiling appear to be directed to the floor. The interior slopes comprising the vaults coffered-ceiling and which is a cross-section is interpreted as a sort of radial outline (Gara, El Kady and El Alfy 47). Stamper notes that since the Pantheon vault had to sustain its own weight, especially those arising from the dead-loads, the wind-loads and the live-loads the key structural components of the vault includes the meridians, parallel-hoops, oculus, and the coffers (259). The function of the parallel hoops and the meridians is to compel structural continuity, whereas the coffers intent is to decrease the weight. The oculus served to be some sort of compression ring, and as such, the thickness of the vault segment reduces as it rises but with a balanced segment to endure lateral thrusts. This in the end deters possible collapse. The vault segment covers from 6.5 meters on the base to 1.5 meters on the top, such that the vault endures not just the tensile stresses arising from parallel surface, but also compression stresses from upper-plain surface (Baker 30). The parallel unmovable surface lies at 52º within the hemispherical vault at the very last coffers ring and with an angle of nearly 55º. (Watkin 76). Hence, tensile force of the material and compression force are restricted by both tensile strength and compressive strength, and as a result, compression leads to local buckling, particularly given that it is a thin shell structure which depends on the breadth and suppleness of the concerned material. The stability of the dome structure is enhanced with the coactions by the meridians together with the parallels. In particular, the coffers extracted weight is rather modest in contrast to vault total weight. Thus, this ensures the structural safeguard of the vault. Notably, the vault weight standing at 2.7 meters in height comes to around 5,000 tones, while its uniform segment of around 1.5 meters and 21.7 meters in radius generates a volume of almost 4,752 cubic meters (MacDonald 45). For that reason, the designers gradually positioned the aggregates ranging from heavy to lighter materials so as to maintain the vaults weight in check. When it comes to a shell structure having rotational symmetry in addition to a vertical axis, the summation of gravitational forces above a particular phase in an angle of 236 is equivalent to the vertical apparatus of the internal forces on that phase, and which in the pantheon comprises the membrane forces along its circumference (Castex 108). Therefore, the extracting vault weight enhances the pantheon safety especially the coffers which minimize the weight to the magnitude of 8% to 9 % and which amounts to nearly 1,400 tones (MacDonald 14). The size of the pantheon coffers was more so determined by their function instead of aesthetic forms. The central axis comprising the octagonal trace of the aula runs projects from Northwards to Southwards at two of the vertices, whereas the other six vertices stretch out at the middle of the niches, in addition to the bisection phase of every octagon of the aedicula (MacDonald 54). Also, the pantheon annular base is wide enough to permit outlining of the perimeter comprising the heptagonal vault (Moffett, Fazio and Wodehus 14). Even though it was feasible to outline the surface of every segments of the octagon and that of the heptagons, they are not in superior dimensions, due to a lack of reliability on how the points-of-intersections among the phases of the heptagon or the octagon could be ascertained. The restriction was that the heptagon had to be figured out from the octagon but within a similar circle (Marder 1660). Thus, the heptagonal plan of the pantheon vault can be attributed to the circle being the outer boundary of the vault, and as such, the outline of every phase of the octagon and the heptagon stretch out on the annular bottom. Hence, the underlying arrangement of the pantheon vault was visualized as part of the constructive progression and which was blended with the vault masonry, and which in the end does not display any trace of it (MacDonald 60). The layout of the pantheon internal and external circle resting on the annular base conforms to the chiseled outlines of the vault. The lower indentation of the pantheon coffers slant steadily at approximately -20º to +20º the length of meridians curvature, whereas the higher recesses incline in a similar manner but at an angle of -90º to +90º (Gara, El Kady and El Alfy 46). The magnification of coffers lowers recesses, amplify its hollow outcome and simultaneously help to maintain them in sight. Therefore, a trouble-free but effective method was to ride up the sunken facets of the coffers, in order to make the coffers lower recesses perceptible from the pantheon floor. In terms of constructive approach, the coffers’ outline and the downward inclining of the lower recesses would have aided in drawing out of the centering-frames devoid of fracturing the concrete. When the coffered vaults are observed from any position on the floor, there is no perspective outcome, but instead a distortion due to the ever-shifting coffers size and outline on the internal vault face. The rotunda wall comprises a sequence of easing arches on three phases with the minimal arches comprising only a solitary band of bipedales. The upper parts are more significant and comprise two to three rings of the bricks that are bipedales and sequipedales (MacDonald 27). Macdonald notes that the barrel vault above the entrance way has a discernible intrados constructed completely of bipedales, and the arches were projected to delineate the loads from the colossal dome towards the sides of its piers linking the massive interior niches (86). Thus, the relieving arches stone Springer-blocks, helps to focus loads at particular sections, especially since they have been used in combination with brick-relieving-arches. This then projects the load clear of the architraves above the niches columns (MacDonald 28). Secondly, the purpose of the Springer blocks is to direct the loads to the channel point but through the formation while fusing the walls, in order to shield them from creep. MacDonald observes that the Pantheon wall can be categorized structurally as being a sequence of concrete piers divided at floor echelons by very massive niches that are uniformly spaced beside the internal perimeter. This makes the thick wall to act as buttresses in sustaining thrust arising from the dome (38). Hence, such niches can be observed in the rotunda circular sketch through a collection of axes at key compass position. All the niches are semi-circularly shaped and positioned at the closing stage of the diagonal collection of axes, with the exception of that at the main entrance which is rather square-shaped. The niches, together with the wall openings contain an archway of bricks or relieving arch which shore up the higher wall over the apertures. This relieving arch seeks to allocate upper loads towards the piers, particularly during the curing of the pantheon pozzolan concrete. According to MacDonald, the bricks archway was only intended to be part of the wall and not an extension of the pantheon dome (63). When it comes to the Pantheon dome, it was elevated by around 142 feet while spanning nearly 43.4 meters in diameter spacing (Mark and Hutchinson 24). In effect, since the dome was initially made of wood before addition of concrete, the wooden dome was tough enough to bear several instances of its own weight. The pantheon dome as an example of a shell structure contains dual directions: this is the surface and the undersized extension that is perpendicular or vertical to it (DeLaine 410). Unlike plate structures which contain flat surfaces, shell structures have surfaces which are cambered. That is why shell structures can tolerate loads which are perpendicular to their planes without bending. For that reason, the stability of the Pantheon dome is guaranteed by several features, in particular the application of a thinner concrete at its top, as well as the thicker concrete used near its base (Perucchio 7). Secondly, the concrete applied near the oculus is composed of lighter density whereas the concrete near the pantheon base is heavier. The designers emphasized on the use of lightweight volcanic-stones with an aggregate, but weighty granite stones. Thirdly, the dome bottom was constructed using heavier brickworks on the top so as to act as a form of counterbalance. Hence, the even though the dome is lightened, it still maintains some form of stiffness and rigidity, especially by the ceiling being constructed to be thinner on the rectangular parts or coffering. The oculus is thus a unique component for admitting light and minimizing the dome weight (Marder 1660). Even though masonry with concrete are better suited to conducting compression forces, they are still very restricted in terms of tension. Hence, cracks take place within the matrix as well as in between the stones including the bricks, inside the masonry and amid the aggregates inside the concrete (Goshima, Ohmori and Hagiwara 20). On condition that crack openings remain on range within a millimeter, the compressive forces together with shear forces will be conveyed across them. Hence, the Pantheon as an example of spherical shell with no rigid base will always experience tension stresses particularly on the lower section. These forces are thus conveyed within the circumferential direction resulting to radial cracks. Hence, the structural engineers should have taken into consideration the idea that cracks occur as boundaries comprising structural components. That is the cupola and its sustaining cylindrical-wall, and which can be categorized as a collection of radial arches. Nevertheless, the architects tried to maintain the cracks from widening by positioning buttress walls resting on a southward direction which are on an opposite side of the large porch. Therefore, this acted as some sort of clamping apparatus (Goshima, Ohmori and Hagiwara 21). Even though the Pantheon structural projection seems to make them appears as additional room, they only acted as being a segment of the perceived clamp. For that reason the ring which holds the foundation components together is approximately 10 feet wider and this makes the entire width to be nearly 34 feet, and as such, the floor plane towards the bottom of Pantheon foundation amounts to 15-4" wider (Gara, El Kady and El Alfy 50). The Lightweight caementa in the dome offered the builders a way of controlling the pantheon mass of using stones of dissimilar weights in different sections of the structure. The heaviest Caementa are at the bottom while the lightest caementa made of canic scoria with yellow tuff are at the pinnacle. Notably, the entire dome is not composed of lighter materials as the crown contains light weight materials (Goshima, Ohmori and Hagiwara 20). The Pantheon entrance porch referred to as portico comprises string of stone columns which have been roofed-over with granite beams and stone slabs. The bronze ceiling extends across the gaps linking the rows of hold up columns that are nearly twelve meters (Castex 108). The intention was to steer clear of placing excess weight on the granite roof slabs. Furthermore rather than applying timber beams in holding up the ceiling, they applied bronze pack beams or rectangular tubes by pinning bronze plates jointly. This is because tubes enhance the strength and stability of the beam (DeLaine 410). If one part of a structure rests slightly faster or otherwise lower than adjoining parts, very massive bending stresses occurs at points linking the two parts, and which in the end can fracture the concrete. Hence, the Pantheon engineers and builders were faced with considerable uneven settling, and unlike contemporary engineers who have the capability of lashing piles through clay then towards the bedrock, so as to decisively support building way around, pantheon builders used a rather fixed approach. They constructed a second ring which shored up the initial ring so as to prevent additional cracks from occurring, in addition to providing the clay with additional area for support (MacDonald 46). Conclusion This paper has elaborated on the significance of the Pantheon arch and vault system, together with the structural design of the dome. In addition, the paper has provided structural significances of the Pantheon, in a circle using the arch and vault system. Thus, the precise proportions of the material used, the application of geometry including the arithmetic, together with the exercise of space vastness facilitated a design which mirrors Roman tradition and structural engineering innovation. The arch and vault system made unexpected change between the floor scheme and the pantheon vault layout. This appears to be a decision conducted based on constructive intentions rather than on a concept. The extracting vault weight enhances the pantheon safety especially the coffers which minimize the weight. Furthermore, the pantheon annular base is wide enough to permit outlining of the perimeter comprising the heptagonal vault. Also, the Pantheon dome is a fascinating and complicated feature since its configuration and design was so remarkable on both planes. In particular, the wall was built lighter as elevation increase, something which was an outstanding model of engineering development gradation. The most critical aspect of the dome was grave stress concentrations and which can result in massive structural failures. This is because hoop stresses shifts from tension forces to compression forces leading to points of weaknesses in the reinforced concrete comprising the dome. The cracks take place within the openings inside upper cylindrical dome wall. This then amplifies local tensile-hoop stresses as they extend upwards above the building floor. Graphic Section Source: Salgado, Tomás García. "The Geometry Of The Pantheon’s Vault." 2010. 29 March 2013. . Source: Castex, Jean. Architecture of Italy. ABC-CLIO, 2008. Source:Moffett, Marian, Michael W Fazio and Lawrence Wodehus. World History of Architecture. 2. Laurence King Publishing, 2003. Source: Pear Shaped Productions. "The Pantheon – the Most Exquisite Building in the World! ." Tuesday July 2012. 29 March 2013. . Source: Salgado, Tomás García. "The Geometry Of The Pantheon’s Vault." 2010. 29 March 2013. . Works Cited Baker, William T. Architectural Excellence: In a Diverse World Culture. Images Publishing, 2008. Castex, Jean. Architecture of Italy. ABC-CLIO, 2008. DeLaine, Janet. "Structural experimentation: The lintel arch, corbel and tie in western Roman architecture." Architectural Innovation 21.3 (1990): 407-424. Gara, Gihan L. K, Hala El Kady and Ayman H El Alfy. "Developing A New Combined Structural Roofing System Of Domes And Vaults Supported By Cementious Strawbricks." ARPN Journal of Engineering and Applied Sciences 5.4 (2010): 44-55. Goshima, R, et al. "Investigation of the Cross Section of the Pantheon Dome through Catenary Mechanism." Journal of the International Association for Shell and Spatial Structures 52.1 (2011): 19-23. MacDonald, William Lloyd. The Pantheon: Design, Meaning, and Progeny. 2. Harvard University Press, 2002. Marder, Tod A. "Bernini and Alexander VII: Criticism and Praise of the Pantheon in the Seventeenth Century." Art Bulletin 71.4 (1989): 1599-1667. Mark, Robert and Paul Hutchinson. "On the Structure of the Roman Pantheon." Art Bulletin 68.1 (1986): 24-34. Moffett, Marian, Michael W Fazio and Lawrence Wodehus. World History of Architecture. 2. Laurence King Publishing, 2003. Pear Shaped Productions. "The Pantheon – the Most Exquisite Building in the World! ." Tuesday July 2012. 29 March 2013. . Perucchio, Renato. "The Evolution of Structural Design of Monumental Vaulting in Caementicium in Imperial Rome." Third International Congress on Construction History. New York,: Cottbus, 2009. 1-8. Salgado, Tomás García. "The Geometry Of The Pantheon’s Vault." 2010. 29 March 2013. . Stamper, John W. The Architecture of Roman Temples: The Republic to the Middle Empire. Cambridge: Cambridge University Press, 2005. Watkin, David. A History of Western Architecture. 4. Laurence King Publishing, 2005. Read More