Comparative analysis of conventional and new seismically isolated structure

Extensive analytical and experimental research has been done by the authors directed to mitigation of the effects of earthquakes on structures. The research results mainly represent parts of the realized several related international projects. A selected part of the analytical studies directed to comparison between conventional and seismically isolated frame structures is presented in this paper. The responses of the applied newely developed advanced seismic isolation system HC-RMS-GOSEB to the simulated input excitation of three representative earthquakes of intensity 0.50g, have shown that it is very effective for construction of vibro-isolated and seismically resistant buildings, providing activated multistage seismic response and globally optimized seismic energy balance. Its application achieves an increase in the vibration period of the structure, far enough from the dominant period of seismic excitation. The results of the research confirm that this system is a potential solution for achieving low-cost and highly efficient protection of buildings.

Compressive strength of green concrete with low cement and high filler content

It is estimated that by the end of the current decade, about 26% of clinker will be replaced by suitable alternative materials, among which limestone filler probably has the greatest potential due to its wide availability and relatively low price. Although codes allow as much as 35% of clinker to be replaced by limestone filler, the amounts used in practice are far lower and average only 6-7% globally. In order to use the great potential of fillers, it is necessary to know the key parameters that affect the properties of green concrete with low cement and high filler content in fresh and hardened states. Therefore, thorough literature review was conducted, followed by design of 18 concrete mixtures, in order to analyze the effects of the percentage of cement replacement, water-cement ratio, but also the particle size of the applied filler. The results of experimental research show that at the same w/c ratio there is an increase in compressive strength with increasing percentage of cement replacement and that it is possible to make medium-strength concrete with significantly reduced amount of cement 180 kg/m3 compared to traditional concrete. Thus, economic benefits can be achieved, but also the negative impact of the concrete industry on the environment can be reduced. Unfortunately, the workability of such mixtures can be impaired to the extent that their practical application is prevented, so it is necessary to take further steps to solve this problem.

Performance of RC frames in 26.11.2019. Albania earthquake: Effects of irregularities and detailing

The collapse and damage of large number of buildings during the November 26, 2019 (Mw 6,4) Albania earthquake caused 51 fatalities and injuries to at least 910 people. Most of collapsed or heavily damaged buildings were RC frame buildings. Although RC frame system is considered as very ductile seismic force-resisting system, its behaviour during earthquake highly depends on: (1) regularity in plan and elevation, and (2) global and local ductility. Based on the authors' visit to the earthquake-affected area on behalf of the Serbian Association of Earthquake Engineering and observations of collapsed and damaged buildings, it was concluded that among main reasons for underperformance of these flexible systems were inadequate analysis of interaction between infill walls and RC frames and reinforcement detailing of RC members.

Review of research in the function of structural engineering development in Serbia

Research at faculties in Serbia after WWII, even though they were fruit of individual efforts, resulted in significant theoretical contributions. Organized, mostly applied research was conducted within institutes with participation of scholars and researchers of the faculties. Since 1952, the Association of Yugoslav Laboratories (AYL) consolidated the research, thus providing a considerable contribution to the structural engineering in Serbia. This contribution in the field of theory and practice was the basis for the notable achievements that glorified our structural engineering worldwide. Theoretical contributions contained in the doctoral dissertations in the field of Theory of structures and Geotechnics are significant, so they were listed in the paper. Majority of these studies became a part of research project as late as in 1976, and they are briefly presented in the paper. The synthesis of project results from fundamental and technological development research was published in numerous monographs, articles, papers and proceedings of scientific and professional meetings and some of them are commented in this paper. The necessity to introduce technical regulations which have already been adopted in the EU countries EN 1990 to 1999, i.e. the Eurocode, was emphasized. There is a brief discussion of several research directions which are topical nationwide as well as worldwide.

The new buckling curves for cold-formed stainless steel equal-leg angle columns

The design rules for centrically compressed stainless steel equal-leg angle members are not explicitly stated in the current European standard SRPS EN 1993-1-4. This paper summarizes the results of extensive research conducted on this type of structural elements aiming to define recommendations for their design. Based on a systematic experimental investigation, a detailed numerical analysis was performed, and a database of columns' resistances were defined. Material and geometric nonlinear analysis included three key stainless steel alloys, austenitic, ferritic and duplex. The design curves for flexural and flexural-torsional buckling check have been proposed in accordance with European codified procedures.

Potential of Portland pozzolana cement in the stabilization of an expansive soil subjected to alternate cycles of wetting and drying

Cement/lime stabilization of soils is one of the common techniques adopted for improving its geotechnical properties. Lately, the focus of investigation has shifted to blended stabilization with industrial wastes as auxiliary additives. However, the role of blended cement in stabilization of soil has been studied insufficiently despite the fact that it is manufactured under controlled conditions. This investigation deals with the use of Portland pozzolana cement (PPC) instead of ordinary Portland cement (OPC) in the stabilization of an expansive soil subjected to alternate cycles of wetting and drying. Unconfined compression strength (UCS) test specimens of dimensions 38mm x 76mm were cast and cured for periods of 7, 14 and 21 days. Then, the specimens were subjected to 1, 2 and 3 cycles of wetting and drying and the UCS of the specimens were determined. Based on the results of the investigation, it was found that OPC performed significantly better than PPC under normal conditions. However, under conditions of wetting and drying, PPC stabilized soil performed much better than OPC stabilized soil when sufficient binder content was available.

New Eurocode 2 provisions for recycled aggregate concrete and their implications for the design of one-way slabs

A significant amount of research has been performed on recycled aggregate concrete (RAC), both on the material and structural level. This has enabled the formulation of material and structural resistance models that can be safely and reliably used for the structural design of RAC members and the new Eurocode 2 (EC2) will contain an informative annex detailing provisions for the design of RAC. Thus, an increased market uptake of recycled aggregate (RA) can be achieved, leading to potential sustainability improvements of concrete structures. In order to familiarize designers with the new provisions for RAC, this paper presents an example of one-way slab design using varying RA substitution ratios, as well as a parametric study on the implications of RAC provisions on slab slenderness. The results of this study show that RAC one way slabs can be successfully designed using EC2. Although such slabs might require larger depths than natural aggregate concrete slabs, their applicability in the typical slenderness range is possible.

Physical-mechanical properties and durability of ultra-high performance concrete (UHPC)

This paper presents the results of the authors' laboratory testing of physical, mechanical and durability properties of Ultra-high Performance Concrete (UHPC). The short history of development and application of UHPC concrete is presented in the first part of this paper while the second part deals with the experimental investigation, presenting the results of material characterization obtained from physical-mechanical and durability tests. Based on the results shown in the paper, the mean value of compressive strength obtained at 28 days is 114 MPa, with the average density of 2270 kg/m3 in hardened state. The results showed that tested UHPC belongs to the highest class of water impermeability V-III, as well as the highest class MS0 (without visible damage) in a simulated freeze-thaw environment and de-icing salt attack test. Also, the highest class XM3 for abrasion resistance was achieved. Additional tests showed that the tested concrete fulfils the requirements for the highest exposure classes XC4 and XD4, in terms of resistance to carbonation and the penetration of chloride ions. Conclusions and recommendations for further development and possible application of UHPC are presented at the end of paper.

Construction of the shopping center Ada Mall in Belgrade

Ada Shopping Mall is located at the corner of Radnička and Paštrovićeva Street in Belgrade, closed to Lake Ada Ciganlija. The building has a gross area of about 100.000m². It consisted of reinforced concrete structure with three underground and four above-ground levels and a steel roof structure. The foundation pit protection was made by bored and bored secant piles in combination with two different Top-Down methods during construction. The excavation depth was up to 25 m. As the building was built in rock mass, during excavation blasting was applied. During construction a monitoring system was implemented. This paper provides an overview of the construction process of shopping mall.

Harvest residues ash as a pozzolanic additive for engineering applications: A review and the catalogue

Biomass ashes originating from wood and harvest residues combustion may be considered as one of the prospective environmentally friendly candidates for supplementary cementitious materials (SCM) production. In the region of Vojvodina province, biomass waste is becoming increasingly important as ''green'' fuel, thus allowing the reduction of the environmental impact of waste disposal, lowering the expensive fossil fuels application and its subsequent greenhouse gasses emission. In the light of the above, the present paper surveys the experimental studies of harvest residues ash (HRA) as a pozzolanic additive for engineering applications. Thus far conducted research on the HRA possible application in cementitious systems, worldwide and in the studied region, has been summarized and the benefits of such approaches outlined. Finally, locally available types of wheat straw, soya straw, sunflower husk, silo waste, oil rapeseed - based ashes were collected, characterized both physically and chemically, evaluated and presented through catalogue. The reactivity results, depending on the amorphous silica content and the achieved level of fineness, are very promising in terms of the potential reuse of these ashes in cementing systems.