Finite-friction least-thickness self-standing domains of symmetric circular masonry arches

This paper concerns a general aspect, in the mechanics of masonry arches, with reference to symmetric circular geometries, with variable opening, and possible stereotomy with radial joints (to be potentially formed, at failure, within an ideal continuous arch), in a limit least-thickness condition, under self-weight, namely the role that a finite inherent (Coulomb) friction, among the theoretical joints, may play in ruling the self-standing conditions and the mechanical features at incipient collapse, setting a change from purely-rotational modes to mechanisms that may include sliding. The matter is first systematically investigated, by a full analytical treatment, then validated and illustrated through an original Complementarity Problem/Mathematical Programming formulation, and numerical implementation, reconstructing the complete underlying map of thickness-to-radius ratio versus friction coefficient of all arch states, and corresponding collapse mechanisms and relevant characteristic features. This investigation shall clear the issue, of the theoretical influence of finite friction, in the above-stated setting, and contribute to provide a full understanding of fundamental aspects in the methodological description, and physical interpretation, of the mechanics of masonry arches, in terms of natural bearing capacity, as linked to structural form optimization and relying on basic underlying physical properties such as a finite amount of inherent friction, with implications that may come up to appear also in practical terms, once dealing with this traditional and remarkable structures, in real cases, possibly endowed of a historical character and architectural value, to be currently preserved and renewed

Modeling water penetration at dam-foundation joint

When fracture occurs in a concrete dam, the crack mouth is typically exposed to water. Very often this phenomenon occurs at the dam-foundation joint and is driven also by the fluid pressure inside the crack. Since the joint is the weakest point in the structure, this evolutionary process determines the load bearing capacity of the dam. In this paper the cracked joint is analyzed through the cohesive model proposed by Cocchetti et al. [Cocchetti G, Maier G, Shen X. Piecewise linear models for interfaces and mixed mode cohesive cracks. J Engng Mech (ASCE) 2002;3:279-98.], which takes into account the coupled degradation of normal and tangential strength. The water pressure inside the crack, which reduces fracture energy and increases the driving forces, is analyzed through the model proposed by Reich et al. [Reich W, Bruhwiler E, Slowik V, Saouma VE. Experimental and computational aspects of a water/fracture interaction. In: Bourdarot E, Mazars J, Saouma V, editors, Dam Fracture and Damage, The Netherlands: Balkema; 1994. p. 123-31.] and Bruhwiler and Saouma [Bruhwiler E, Saouma VE. Water fracture interaction in concrete. Part II: Fracture properties. Am Concr Inst J 1995;92:296-303; Bruhwiler E, Saouma VE. Water fracture interaction in concrete. Part II: Hydrostatic pressure in cracks. Am Concr Inst J 1995;92:383-90.]. Some numerical results are presented which refer to the benchmark problem proposed in 1999 by the International Commission On Large Dams. During the evolutionary process the horizontal dam crest displacement has been found to be a monotonic increasing function of the external load multiplier. As the fictitious process zone moves from the upstream to the downstream edge a transition occurs in the path of crack formation: the initial phase is dominated by the opening displacement, on the contrary afterwards the shear displacement dominates. Therefore, crack initiation does not depend on dilatancy. On the contrary the load carrying capacity depends on dilatanc

Cohesive crack approach to debonding analysis

Debonding of coatings from substrate due to coating compression occurs in many engineering applications. A simplified analytical approach for the estimation of the ultimate coating compression leading to debonding is developed in this paper, assuming an assigned out-of-plane defect of the coating. The formulation is based on the solution of a beam on a Pasternak (two parameters) elastic foundation, and on the assumption of a Mode I cohesive failure of the coating-substrate interface. The resulting formulas are simple and require the knowledge of a limited number of parameters

Selective mass scaling for distorted solid-shell elements in explicit dynamics: optimal scaling factor and stable time step estimate

The use of solid-shell elements in explicit dynamics has been so far limited by the small critical time step resulting from the small thickness of these elements in comparison with the in-plane dimensions. To reduce the element highest eigenfrequency in inertia dominated problems, the selective mass scaling approach previously proposed in [G. Cocchetti, M. Pagani and U. Perego, Comp. \& Struct. 2013; 127:39-52.] for parallelepiped elements is here reformulated for distorted solid-shell elements. The two following objectives are achieved: the critical time step is governed by the smallest element in-plane dimension and not anymore by the thickness; the mass matrix remains diagonal after the selective mass scaling. The proposed approach makes reference to one Gauss point, trilinear brick element, for which the maximum eigenfrequency can be computed analytically. For this element, it is shown that the proposed mass scaling can be interpreted as a geometric thickness scaling, obtaining in this way a simple criterion for the definition of the optimal mass scaling factor. A strategy for the effective computation of the element maximum eigenfrequency is also proposed. The considered mass scaling preserves the element translational inertia, while it modifies the rotational one, leading to errors in the kinetic energy when the motion rotational component is dominant. The error has been rigorously assessed for an individual element, and a simple formula for its estimate has been derived. Numerical tests, both in small and large displacements and rotations, using a state-of-the-art solid-shell element taken from the literature, confirm the effectiveness and accuracy of the proposed approach. Copyright {\copyright} 2014 John Wiley \& Sons, Ltd

SOLID-SHELL FINITE ELEMENT MODELS FOR EXPLICIT SIMULATIONS OF CRACK PROPAGATION IN THIN STRUCTURES

Crack propagation in thin shell structures due to cutting is conveniently simulated using explicit finite element approaches, in view of the high nonlinearity of the problem. Solidshell elements are usually preferred for the discretization in the presence of complex material behavior and degradation phenomena such as delamination, since they allow for a correct representation of the thickness geometry. However, in solid-shell elements the small thickness leads to a very high maximum eigenfrequency, which imply very small stable time-steps. A new selective mass scaling technique is proposed to increase the time-step size without affecting accuracy. New ”directional” cohesive interface elements are used in conjunction with selective mass scaling to account for the interaction with a sharp blade in cutting processes of thin ductile shells

Prevalence and Correlates of Sexually Transmitted Infections in Transgender People: An Italian Multicentric Cross-Sectional Study

The burden of sexually transmitted infections (STIs) in the transgender population remains an underestimated issue. The aims of the present study were to evaluate the prevalence of either self-reported and serological STIs and to describe socio-demographic and clinical characteristics of transgender individuals with STIs. A consecutive series of 705 transgender individuals (assigned-male at birth, AMAB n = 377; assigned-female at birth, AFAB n = 328) referring to six Italian gender clinics were included. Sociodemographic and clinical information was collected during the first visit. In a subsample of 126 individuals prevalence of STIs (human immunodeficiency virus, HIV; hepatitis C, HCV; hepatitis B, HBV; syphilis) were evaluated through serology tests. The self-reported prevalence of HIV, HBV, HCV and syphilis infection in the total sample were 3.4%, 1.6%, 2.6% and 2.0%, respectively. In the subsample who underwent serological tests, higher rates of serological prevalence were found (9.5%, 4.0%, 5.6% and 7.9% for HIV, HBV, HCV and syphilis, respectively). When comparing transgender people with or without selfreported STIs, unemployment, previous incarceration, justice problems and sex work resulted more frequent in the first group (p< 0.03 for all). Regarding health status, we observed higher rates of lifetime substance abuse and psychiatric morbidities in trans people with at least one reported STI (p < 0.05). The prevalence of STIs exceeded that reported in general population and STIs correlates underline the importance of stigma and discrimination as determinants of transgender health

Comparison of in-plane and out-of-plane failure modes of masonry arch bridges using discontinuum analysis

This research aims to provide a better understanding of the structural behavior of masonry arch bridges using advanced modeling strategies. Two main contributions are achieved in this article; first, triggering mechanisms for the out of plane failure of spandrel walls are established; second, the influence of soil backfill on the behavior and strength of the bridges is presented through a comprehensive parametric study. Here, masonry arch bridges are modeled using a discontinuum approach, composed of discrete blocks, including also a continuum mesh to replicate infill material, adopting a framework of discrete element modeling. The equations of motion for each block are solved by an explicit finite-difference method, using the commercial software 3DEC. The results of the preliminary analyses are compared with analytical solutions and limit state analysis for validation purposes. Different arch bridge models, representing common geometrical properties in the northwest Iberian Peninsula are analyzed. Transverse effects, damage patterns and collapse mechanisms are discussed under different types of loading. The analysis demonstrated the severe capacity reduction due to spandrel wall failures and the importance of soil backfill in results, only possible by taking advantage of the performed numerical modeling strategy