Seismic Assessment via EC8 of Modern Heritage Structures: Knowledge of the Structure and Analysis Methodologies

Introduction

The Tower of the Nations is a modern heritage structure, located within the Mostra d’Oltremare urban park in Naples (Siola, 1990). The whole urban park was nominated in 2005 for the inscription in the UNESCO Modern Heritage List (http://whc.unesco.org/en/events/247/), given its relevant expression of the cultural and technical background at the time of design and construction. The Tower of the Nations was designed in 1938 by the architect Venturino Ventura, with the help of Carlo Cestelli Guidi (one of the most important structural engineers at the time) and of Guido Quaroni (architect and painter). The building was completed in 1940. The Tower has two glazed façades without any masonry infill (Figure 1a), and it has the other two façades fully infilled by tuff masonry, covered by white travertine plates, see Figure 1b. In 1940, the building had a basement decorated with low reliefs and a big statue representing the Fascist Victory (see Figure 1b); the provisional chalk version of the low reliefs was destroyed during the Second World War.

Figure 1.

Mostra d’Oltremare complex (a), Tower of the Nations (b)

In the years following its construction, the structure was left to the carelessness. Recently the Tower has been included in a refurbishing project of the entire Mostra d’Oltremare urban park. The project includes the assessment and retrofitting of the Tower.

An example of Eurocode 8 (EC8) based assessment (CEN, 2005) carried out for this modern heritage reinforced concrete (RC) building is herein provided. Notwithstanding the fact that general assessment principles for ordinary RC structures can be easily applied to modern heritage buildings; this kind of buildings can often require specific approaches for structural knowledge, significant modeling efforts, and accurate analysis methodologies.

Therefore, all the assessment steps are reviewed considering the Tower of the Nation as test-bed. Structural knowledge (geometry, details, and materials), dynamic identification, choice of the structural analysis methodology are considered, and specific choices made for the assessment of this modern heritage structure are described. In particular, knowledge of the structure and dynamic identification phases emphasize the role that infills can play in the structural behavior of the building. Thus, infill structural contribution is included in the linear and nonlinear numerical model of the structure. While in the case of ordinary structures the explicit modeling of infill is a best-practice option, in the case of modern heritage it can be a key issue to capture modal properties and to model nonlinear behavior. Finally, the choice of nonlinear dynamic analysis as analysis methodology for EC8 based assessment allows also carrying out fragility curves for the limit states considered. On the other hand, it is also emphasized how code-based nonlinear dynamic analysis not always leads to reliable fragility curves. In fact, fragility curves can be considered reliable only in the case in which demand over capacity ratios (D/C) carried out for the assessment are close to unity.

Background

A first definition of the concept of heritage, and, in turn, of heritage buildings was provided in the Charter of Venice (1964), in which it is stressed, not only the value of the message from the past, but also the common responsibility to their safeguard for future generations, (Vecco, 2010). On the other hand, within heritage buildings, a distinction can be made between historical buildings and monumental buildings. The former are those that can be defined as buildings of artistic or cultural value and which can be found in significant numbers; the latter are those truly unique, (Augusti and Ciampoli, 2000).