Experimental and numerical analysis of the global behaviour of the 1:9 scale model of the Old Bridge in Mostar

Kustura, Mladen,Smoljanovic, Hrvoje,Nikolic, Zeljana,Krstevska, Lidija Techno-Press 2021 Coupled systems mechanics Vol.10 No.1

Composite nature of the masonry structures in general causes complex and non-linear behaviour, especially in intense vibration conditions. The presence of different types and forms of structural elements and different materials is a major problem for the analysis of these type of structures. For this reason, the analysis of the behaviour of masonry structures requires a combination of experimental tests and non-linear mathematical modelling. The famous UNESCO Heritage Old Bridge in Mostar was selected as an example for the analysis of the global behaviour of reinforced stone arch masonry bridges. As part of the experimental research, a model of the Old Bridge was constructed in a scale of 1:9 and tested on a shaking table platform for different levels of seismic excitation. Non-linear mathematical modelling was performed using a combined finite-discrete element method (FDEM), including the effect of connection elements. The paper presents the horizontal displacement of the top of the arch and the failure mechanism of the Old Bridge model for the experimental and the numerical phase, as well as the comparison of the results. This research provided a clearer insight into the global behaviour of stone arch masonry structures reinforced with steel clamps and steel dowels, which is significant for the structures classified as world cultural heritage.

Influence of ductility classes on seismic response of reinforced concrete structures

Nikolic, Zeljana,Zivaljica, Nikolina,Smoljanovic, Hrvoje Techno-Press 2018 Coupled systems mechanics Vol.7 No.2

Reinforced concrete buildings in a seismically active area can be designed as DCM (medium ductility) or DCH (high ductility) class according to the regulations of Eurocode 8. In this paper, two RC buildings, one with a wall structural system and the other with a frame system, previously designed for DCM and DCH ductility, were analysed by using incremental dynamic analysis in order to study differences in the behaviour of structures between these ductility classes, especially the failure mechanism and ultimate collapse acceleration. Despite the fact that a higher behaviour factor of DCH structures influences lower seismic resistance, in comparison to DCM structures, a strict application of the design and detailing rules of Eurocode 8 in analysed examples caused that the seismic resistance of both frames does not significantly differ. The conclusions were derived for two buildings and do not necessarily apply to other RC structures. Further analysis could make a valuable contribution to the analysis of the behaviour of such buildings and decide between two ductility classes in everyday building design.

Seismic resistance of dry stone arches under in-plane seismic loading

Ivan Balic,Nikolina Zivaljic,Hrvoje Smoljanovic,Boris Trogrlic 국제구조공학회 2016 Structural Engineering and Mechanics, An Int'l Jou Vol.58 No.2

The aim of this study is to investigate the seismic resistance of dry stone arches under in-plane seismic loading. For that purpose, several numerical analyses were performed using the combined finitediscrete element method (FDEM). Twelve types of arches with different ratios of a rise at the mid-span to the span, different thicknesses of stone blocks and different numbers of stone blocks in the arch were subjected to an incremental dynamic analysis based on excitation from three real horizontal and vertical ground motions. The minimum value of the failure peak ground acceleration that caused the collapse of the arch was adopted as a measure of the seismic resistance. In this study, the collapse mechanisms of each type of stone arch, as well as the influence of the geometry of stone blocks and stone arches on the seismic resistance of structures were observed. The conclusions obtained on the basis of the performed numerical analyses can be used as guidelines for the design of dry stone arches.

Blood Transfusion Rates as a Primary Outcome Measure: The Use of Predetermined Triggers and Display of Clinical Indications in Providing Accurate Comparative Transfusion Rates

David Skipsey,Felix Allen,Anwar Hussein,Deiary Kader,Tomislav Smoljanovic 대한정형외과학회 2017 Clinics in Orthopedic Surgery Vol.9 No.1

We read with interest the paper by Kamath et al.1) on the efficacy of saline-coupled bipolar sealing devices in simultaneous bilateral total knee arthroplasty (TKA). The use of bipolar sealing and conventional electrocautery was compared in 71 consecutive patients who underwent bilateral TKA. Unfortunately, it must be noted that there are discrepancies in the reported transfusion rates. It was stated in the results section of the abstract that patients treated with the bipolar sealer were 35% less likely to require a transfusion when compared with patients treated with conventional electrocautery. The same percentage (35%) was presented in the conclusion section of the article. In contrast, the authors state that in their discussion that the blood transfusion rates were 33% lower in the experimental bilateral group when compared with the control group. The results section of the article and Table 2 claim that 55% (16 of 29) of patients in the experimental cohort required a blood transfusion, while the rate was 83% (35 of 42) in the control group. Therefore, the difference in transfusion requirements between the two groups would be 28% and not the 35% or 33% stated elsewhere in the paper. The need for blood transfusion was determined in the study based upon clinical need as determined by the surgeon and medical co-management team. This included consideration of pertinent medical comorbidities (e.g., strong history of cardiac disease), clinical symptoms such as lethargy, and hemodynamic parameters such as tachycardia and/or hypotension refractory to initial fluid resuscitation. In general, patients without cardiac history were not transfused for a haemoglobin level greater than 8 g/dL. Fixed, predetermined transfusion triggers were not employed, allowing the need for transfusion to appear vague in nature. As stated as a limitation, the staff and surgeons were not blinded and therefore there was a possibility of bias in the decision making process but the authors state that the criteria for transfusing symptomatic patients was used consistently. It is interesting to note that patients who were treated with the bipolar sealing device when compared with patients in the control group had: matched demographics, similar preadmission haemoglobin level (13.5 g/dL vs. 13.3 g/dL), similar estimated blood loss (100 mL) and nonsignificant increased haemoglobin decline (4.2 g/dL vs. 4.8 g/dL), yet finished with the significantly less transfusion requirements.1) It is unclear why there should be a significant difference in transfusion rates when other parameters were similar. One potential explanation for this could be age. It is known that transfusion requirement after major joint arthroplasty is greater in the elderly.2) We note that the control group probably contained a greater number of more elderly patients compared with the experimental group (63.4 ± 17.9 vs. 59.1 ± 4.1), and it would be interesting to know the ages of those that required transfusions as a possible explanation to account for the differences between the two groups. Another possible explanation could be the contribution of dilutional anaemia, and it would be useful to know if there were any differences in the perioperative use of intravenous fluid between the two groups. The overall transfusion requirements found in this study are different to those experienced in our clinical practice. An analysis of bilateral TKA performed at our institution is presented in Table 1. A saline-coupled bipolar sealing device was not used in any of the cases. Our centre employs a fairly restrictive transfusion policy and is governed by a team of senior intensive care specialists who