Hybrid simulation with dynamic substructuring of masonry structures: A numerical study

Hybrid simulation is used to compute the time history response of an emulated system subject to a dynamic excitation by combining a physical and a numerical substructure. The former is tested in the laboratory by means of servo-controlled actuators whist a real-time computer simulates the latter and solves the coupled equation of motion. Hybrid simulation has been extensively applied for seismic response history analysis of steel and concrete frame structures. For these systems, subdomain partitioning follows storey levels and nodal joints among beam/column-like elements. In the case of planar masonry structures, distributed interfaces characterize system subdomains and, in principle, several actuators should be used to impose the correct boundary conditions to the tested specimen. This paper presents a new substructuring method for planar masonry substructures, which aims to reduce the number of actuators necessary to achieve a predetermined coupling accuracy between physical and numerical subdomains. The numerical validation of this procedure is illustrated for a masonry building facade system

Influence of Workmanship on the Compressive Strength of Structural Masonry

Structural masonry is a composite material that consists of brick/block units and mortar. Often, masonry is treated as a homogeneously material. The key mechanical characteristic of structural masonry is its compressive strength perpendicular to the bed joints. Estimating or even predicting this material property is thus an issue of central importance to assessing the reliability of masonry structures. As part of a course on structural masonry taught at ETH in Zurich, students are given an opportunity to do some practical work. During one lecture (one and half-hours) students are divided in smaller groups (five to six students) and each group is asked to build a standard masonry specimen (according to the European testing standard EN-1052-1) in the structural laboratory of the Institute of Structural Engineering. Simultaneously, two professional masons, which are instructing/helping students during the exercise, are asked to build one specimen. Such practical work has been performed every year since 2007, usually with clay block masonry, but also with calcium-silicate and AAC masonry. After the prescribed curing time all specimens are tested and the corresponding results (masonry compressive strength) are discussed with students. This paper presents the results and statistics of these test series. Special attention is paid to the influence of workmanship. Namely, strengths obtained from tests on specimens built by professional masons are, for all series, more or less near the mean values in spite of the fact that almost all students are without any skills as masons. The reasons for such distribution of the results are investigated and the findings are presented.The authors wish to recognize the contribution of Professor Bruno Sudret of ETH Zurich for his constructive discussion and suggestions

Local guidelines for drug treatment of patients with covid-19

© 2020, Serbian Medical Society. All rights reserved. Objective. Until now, there have been no guidelines for the use of drugs in patients with COVID 19 in the Republic of Serbia that have been authorized and published in the professional or scientific literature, or on the official websites of the Ministry of Health or healthcare institutions. The aim of this paper is to present a local guideline for the use of drugs in patients with COVID 19 and the process of its development and adoption. Methods. The guideline proposal was prepared by a working group based on the results of a systematic research of the medical literature, and quality control of found publications from the category “clinical practice guidelines”. The proposal of the working group was considered and adopted at the sessions of the Drug / Therapeutics Committee and the Quality Assurance Committee of the University Clinical Centre Kragujevac. Results. The guideline's recommendations are based on the type of patient, and all have the same degree of recommendation and the same quality of evidence on which they are based. Patient types are formed according to the severity of the disease and the need for respiratory support, as well as according to the risk of secondary bacterial infection. Conclusion. The local guideline to the use of drugs in patients with COVID 19 was developed and adopted in a short period of time, primarily due to the need for its urgent use. A revision of this guide is planned after 6 months from the moment of adoption

Masonry subjected to semi-cyclic compression: Inelastic response modelling

A series of load tests on unreinforced masonry elements (triplets and wallettes with inclined bed joints) subjected to semi-cyclic compression have been performed in order to investigate the response of masonry under such loading conditions. The specimens exhibited inelastic and extremely nonlinear response and substantially different behaviour during the loading, unloading and reloading phases. Further investigations revealed that the observed behaviour was governed by the response of the block-mortar interfaces. A new mechanical model has been developed, which combines the conventional stress–strain model for the masonry with a non-linear model describing the response of the block-mortar interfaces. The model was calibrated using the Monte-Carlo simulation method and validated against the semi-cyclic compression tests on masonry specimens. The model developed is expected to improve significantly the simulation of the force–displacement response of unreinforced masonry walls subjected to seismic loading.ISSN:0950-061

Masonry subjected to semi-cyclic compression: Inelastic response modelling

A series of load tests on unreinforced masonry elements (triplets and wallettes with inclined bed joints) subjected to semi-cyclic compression have been performed in order to investigate the response of masonry under such loading conditions. The specimens exhibited inelastic and extremely nonlinear response and substantially different behaviour during the loading, unloading and reloading phases. Further investigations revealed that the observed behaviour was governed by the response of the block-mortar interfaces. A new mechanical model has been developed, which combines the conventional stress–strain model for the masonry with a non-linear model describing the response of the block-mortar interfaces. The model was calibrated using the Monte-Carlo simulation method and validated against the semi-cyclic compression tests on masonry specimens. The model developed is expected to improve significantly the simulation of the force–displacement response of unreinforced masonry walls subjected to seismic loading.ISSN:0950-061