Author(s)

ELWIN C. ROBISON

Abstract

The Roman double trusses of San Paolo fuori le Mura (FLM) are the oldest long-span Roman trusses for which sufficient information exists to perform a structural analysis. Span, spacing, and scantlings of members were recorded previous to the loss of the trusses due to a catastrophic fire in 1823. Wood species type can be inferred from comments by Pliny the Elder regarding other long-span trusses in ancient Rome. While the quality of the wood cannot be determined, the analysis results can be bracketed using allowable stresses from different wood visual grading standards. Dead and live loads can be estimated using loadings developed for current engineering practice. Quantifying the levels of stresses in the trusses of San Paolo FLM indicates a relatively conservative design. Stresses in the rafters, or upper chords, were reduced by the insertion of a collar strut providing an intermediate support to the upper chords. Even if it is assumed that timbers matching visual grade DF/L No. 2 were used, the combined flexural and axial stresses in the upper chords are well within those permitted by modern design standards.

Keywords

Roman double truss, Early Christian basilica, San Paolo fuori le Mura, wood truss design