Abstract

The present paper aims at assessing the shape irregularities influence on the collapse conditions of masonry arches subjected to vertical point force. Surveys campaigns on cultural Heritage buildings often reveal masonry elements with irregular shapes. In order to accurately predict their actual behavior the presence of such features cannot be neglected. The reasons for these non-canonical shapes are manifold e.g. the evolution of degradation processes and the constructive laws. As a first analysis attempt, the geometrical uncertainties tied to the building work criteria are taken into account. A random parametric model is proposed to generate two-dimensional geometry of irregular polycentric arches. Monte Carlo simulations allows estimating the probabilistic density function of the collapse load multiplier evaluated by means of the implemented limit analysis method. The outcomes referred to the masonry arch with nominal geometry are compared to those obtained for the random polycentric arch, highlighting the extent of the load-bearing capacity reduction due to presence of such shape irregularities.

Abstract

The adoption of effective strengthening techniques of historical constructions is one of the most widely debated aspects in structural engineering. Within this topic, the application of steel fiber reinforced mortar (SFRM) has been recently proposed as a low invasive and effective way to obtain a considerable structural benefit in the safety of existing masonry structure. To this purpose, in this paper the experimental results obtained on a circular masonry arches are presented. The considered specimens, subjected to a vertical increasing static load, is tested in the unstrengthened and strengthened configurations, and is part of a wider experimental campaign. After presenting and discussing the experimental results, they are compared with those relative to numerical simulations conducted by means of a discrete macro-element (DME) strategy, based on a simple mechanical scheme, able to model the nonlinear behavior of masonry structures with a limited computational effort. Such an approach is here extended to model the SFRM strengthening technique accounting for the main failure mechanisms associated to the combined presence existing masonry and the additional strengthening layer applied at the intrados of the arch. Numerical and experimental results demonstrate the efficacy of the proposed retrofitting strategy both in terms of bearing capacity and increase of ductility.

Abstract

Limit state analysis of masonry arches sets to assess the safety of the structure by determining the minimum thickness that just contains a thrust line. Based on the Heymanian assumptions regarding material qualities and the equilibrium approach to the static theorem it has been explicitly proven for semi-circular arches that both the thrust line and the resulting minimum thickness value is subject to stereotomy (brick or stone laying pattern), while present study demonstrates, that the latter statement holds for pointed-circular arches as well. This is not straightforward, since the number- and arrangement of the hinges at limit state vary subject to the geometry in case of pointedcircular arches, resulting a more complex problem. It is also explicitly shown, that stereotomy might also affect the corresponding (rotational) failure mode (for certain arch geometries). Stereotomy of an existing structure is not always known, hence it is relevant to search for a stereotomy related bounding value of minimum thickness for each of the various failure modes. The potential of the envelope of resultants as a thrust line (resulting from vertical stereotomy) leading to bounding value minimum thicknesses is discussed: as shown elsewhere it bounds the family of thrust lines, hence leads to an upper bound value of minimum thickness in case of semi-circular arches. It is demonstrated however, that this cannot be generalized for other rotational failure modes which occur for circular-pointed arches. The envelope of resultants does not necessarily lead to a bounding value of minimum thickness, and even if it does, it can be either an upper or a lower bound. However, it is found that the range of minimum thickness values is bounded in all possible failure mode types. The necessary conditions are provided for each.

Abstract

A brick arch was loaded under laboratory conditions in three successive loading steps. No cracks were observed but reduction of natural frequencies and stiffness of the arch was experimentally documented. The stiffness was evaluated in a non-destructive test using an impact hammer and only two accelerometers. The proposed identification technique based on known experimental modal analysis theory is tailored to stiffness evaluation of masonry vaults. The results and the applied method are extensively discussed.