SEISMIC STABILITY OF CLASSICAL TEMPLES

In recent years, major interdisciplinary concern has been building over the seismic resistance of monuments. Monuments like the Stonehenge, the Parthenon, the Coliseum, the Taj Mahal, to name only a few, mark mankind’s perpetual commitment to building grandiose structures. These structures dignify our cultural heritage, and their loss bereaves the world beyond any monetary assessment.

My study focuses—but is not limited—on classical temples such as those found throughout Greece, Southeastern Italy, and Western Turkey. Some of the temples of most interest include the Parthenon situated atop the Acropolis in Athens, the Temple of Apollo Epicurius at Bassai in the Peloponnesus region of Greece, and the Temple of Zeus at Nemea, also in the Peloponnesus region.

Architectural rendition of the Acropolis in Athens.

 

The dynamic response of classical monuments is fundamentally different than that of modern structures. Despite their apparent simplicity and unlike modern monolithic structures, ancient monuments are primarily stone blocks (e.g. of marble or limestone) lying on top of one another without a cohesive agent, such as mortar. These blocky structures perform highly nonlinear rigid block motions, such as sliding, uplifting, rocking, and possibly overturning. The complexity of the dynamic analysis of such structures dwarfs that of modern structures. The problem is highly variable and minor perturbations often result in entirely different response. The structural stability of such a dynamical system is an extremely complicated problem.

The polylithic structure of classical temples provides an effective mechanism for dissipation of energy through sliding and rocking that is uncharacteristic of modern structures. Small-amplitude sliding of individual elements results in a polylithic structure surviving an earthquake that collapses a monolithic structure.

In many classical temple columns, wooden dowel-like components called empolia were used between adjacent column drums. The empolia were used at the center of a column to simply assist in aligning the column drums during erection; not to provide shear resistance. Recent analyses have shown that the presence of wooden empolia has little effect in enhancing or reducing the seismic stability of a multidrum column. The wooden empolia have very small shear resistance.

In modern reconstruction schemes, it has been sweepingly proposed to use titanium empolia to replace the deteriorated wooden empolia installed in ancient times. However, the use of such metallic empolia would actually provide shear resistance and prevent the abovementioned beneficial small-amplitude sliding and rocking induced during strong ground shaking. 

The dynamic analysis of such structures is performed primarily with a combination of in-house developed codes as well as commercially available dynamic simulation software. The program Working Model has been validated. It integrates the equations of motion and their associated constraints to produce results of very high fidelity.

 

Computer-generated model of the Parthenon.

The findings of my research work with Professor Nicos Makris (of University of Patras, Greece; formerly of UC Berkeley) on this topic are presented in the following publications: