Masonry Vaults: Domes
Mario Como2016, Springer Series in Solid and Structural Mechanics
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Abstract
Beautiful domes have been built firstly by Mycenaeans and later by Romans and Byzantines; domes were practically neglected in the Middle Ages, later rediscovered by the Renaissance and Baroque architecture. Following the approach outlined in the previous section, this chapter firstly deals with the analysis of membrane stresses occurring in rotational shells that describe, with sufficient accuracy, the initial un-cracked stress state of the masonry dome. Later, the masonry dome probably cracks when the tension stresses in the hoop rings near the springing will reach the masonry's weak tensile strength, usually fading in the course of time. The initial membrane equilibrium is thereby lost and meridian cracks will arise and spread along the dome. The emergence of thrust is the main consequence of cracking of the hemispherical domes. The occurrence of this thrust yields a subsequent deformation of the supporting structures and the dome, as a rule, activates its minimum thrust state. The research of the dome thrust is the main subject of the chapter and it will be searched both by static and kinematic approaches: in this last case as maximum thrust among all the kinematical ones. In addition to the hemispherical dome with constant thickness, four outstanding examples of actual masonry domes are then analyzed in detail: the ancient Mycenaean tholoi, the Pantheon, the dome of St. Maria del Fiore in Florence and the St. Peter dome in Vatican.
Key takeaways
- The widening of the drum at its top is due to thrust activation in the dome.
- The cylindrical drum continues for a distance of about 8.20 m above the dome's springer; the weight of this extra masonry serves to oppose the thrust of the dome.
- The extension of the drum beyond the level of the dome springing strongly deviates the thrust of the dome towards the vertical.
- A Valuation of the mean thrust in the dome The small deformation of the drum produced by the thrusting action yields a small increasing in the dome span.
- By way of definition, the quantities shown in the figure are: S domT thrust transmitted directly by the dome slice, acting at a height of about 18.00 m from the drum base; V vertical load due to the weight of the dome slice alone; C 3 weight of the slice of the attic/drum of thickness equal to the dome base; c distance of the vertical force V from the drum's internal edge, as previously evaluated, c = 2.0 m; h 1 height of the strip of the attic/drum, equal to 18.00 m. The dotted arrow in Fig. 5.79 represents the counter-thrust of the buttress, which was not considered in the foregoing analysis.
