PRORAČUN ARMIRANO-BETONSKIH OKVIRA ISPUNJENIH ZIĐEM S OTVORIMA

Reinforced-concrete (R/C) frames infilled with masonry wall, especially with the presence of an opening, are insufficiently explored structural elements. We have experimentally investigated influence of the opening’s type and position to the lateral response of reinforced-concrete frames with masonry infill. Correction factors, that take into account influence of the opening’s type and position in the masonry infill in relation to frame without infill, are defined as an improvement of the equivalent diagonal compression strut model. This improvement enables use of R/C frames with masonry infill, with or without openings, as structural element. Its use would result in better seismic assessment of the masonry infilled R/C frames.Armirano-betonski okviri sa zidanim ispunom, naročito uz prisustvo otvora, nedovoljno su istraženi konstruktivni elementi. Eksperimentalno smo istražili utjecaj vrste i položaja otvora na seizmički odgovor armirano-betonskih okvira sa zidanim ispunom. Uvedeni su korekcijski faktori kojima se u obzir uzima utjecaj vrste i položaja otvora u zidanom ispunu u odnosu na okvir bez ispuna, u svrhu poboljšanja modela zamjenske tlačne dijagonale. Poboljšanje omogućava uporabu a-b okvira sa zidanim ispunom, s i bez otvora, kao konstruktivnog elementa. Primjena će omogućiti kvalitetniji seizmički proračun a-b okvira sa zidanim ispunom

Influence of openings, with and without confinement, on cyclic response of infilled R-C frames: an experimental study

This article presents the experimental results of a study on reinforced-concrete frames infilled with masonry with openings. The frames were designed according to current European codes. They were built in a scale 1:2.5 and infilled with masonry walls. Mid-size window and door openings were located centrically and eccentrically and were executed with and without tie-columns around them. Presence of masonry infill, although not accounted for in design, improved the system behavior (increase in stiffness, strength and energy dissipation capacity) at drift levels of up to 1%. During the test, openings did not influence the initial stiffness and strength at low drift levels. Their presence became noticeable at higher drift levels, when they lowered the energy dissipation capacity of the system. The infill wall had a multiple failure mechanism that depended on the opening height and position. Tie-columns controlled the failure type, independent of the opening type, prevented out-of-plane failure of the infill, and increased the system’s ductility. Negative effects of the infill on the frame were not observed. The infill’s contribution could be deemed positive as it enhanced the overall Structural Performance Level. Analytical expressions commonly used for infilled frames underestimate the infill’s contribution to strength and stiffness and overestimate the contribution of the bare frame

NAPREZANJA KUTNOG PROFILA USLIJED DJELOVANJA POPREČNE SILE VAN CENTRA POSMIKA

Angle or L-section bars are commonly used as non-structural elements in modern buildings, such as carriers of massive and expensive glass walls. While they are commonly loaded with shear forces, they can nonetheless be subjected to significant torsion, which occurs from loading outside the shear center, and can be omitted. This omission may result in lack of shear bearing capacity. Shear and additional normal stresses were investigated due to torsion and without one. Analytical calculations in the linear-elastic domain showed a significant increase in shear stresses due to torsion. In addition, we compared the results with numerical models to test the accuracy of the analytical calculations and the suitability of numerical models.Kutne ili L profile primjenjujemo najčešće kao nekonstrukcijske elemente, naprimjer pri gradnji nosača teških i skupocjenih staklenih stijena. Pritom oni, iako izloženi isključivo poprečnom opterećenju, mogu biti pod značajnim utjecajem St. Venantovog uvijanja koje nastaje zbog djelovanja van centra posmika, a koje se može previdjeti. Posljedica toga može biti nedovoljna nosivost na posmik. Istražena su posmična te dodatno normalna naprezanja u slučaju s i bez uvijanja. Analitički proračuni u linearno-elastičnom području pokazali su značajan utjecaj uvijanja na razinu posmičnih naprezanja. Rezultati su dodatno uspoređeni s rezultatima numeričkih proračuna radi provjere točnosti i prikladnosti

Dynamic soil-structure analysis of tower-like structures using spectral elements

In this paper general equation system for linear dynamic soil-structure interaction (SSI) in frequency domain is presented. The main objective of the paper is to provide and investigate a possibility to use spectral elements in SSI domain. Spectral elements reduce considerably number of unknowns and in some cases, e.g. in frame structures coupled with analytically obtained impedance functions of sub-grade, produce no modelling errors. Results for two different shallow-founded beam structures with identical foundations excited by harmonic free-field motions are presented

Influence of design and construction on building durability and maintenance

Uzročnik nevaljalog stanja objekta i gradiva nije jedino starost objekta. Postoje drugi čimbenici odnosno pogreške koji uvjetuju nevaljalo stanje objekta i potrebu za dodatnim mjerama održavanja i poboljšanja. Ovi čimbenici izravno su povezani s načinom projektiranja i izvedbe odnosno pogreškama koje pri tome nastaju, a čiji uzročnici su sudionici u gradnji. Ove pogreške vidljive su u obliku pukotina, promjene boje i sastava gradiva te samog urušavanja, vrlo brzo nakon završetka objekta. U radu su prikazani primjeri izbora statičkog sustava objekta s ciljem umanjenja mogućnosti nastanka pogreške u završenom objektu. Dodatno, navedene su i objašnjene najčešće vrste istih te su dane smjernice za njihovo sprječavanjeThe time is not the only factor influencing the poor condition of the building and built in materials. There are other factors or flaws that condition the poor building state and the necessity for increased measures for maintenance and rehabilitation. Those factors are related to design and construction process of the building i. e. to flaws made in it, and they are caused by participants in construction. In a very short time after the building is constructed, those flaws are observed in the form of cracks, changed material structure and color, up to very collapse itself. In this paper an example is given about the proper selection of the structural system with aim to reduce the probability of flaws appearance in complete building. Additionally, the most common types of flaws are stated

BLOCKZIEGELMAUERWERK UND VERBUND AN DER MÖRTELFUGE

Ako se pri izvedbi konstrukcijskog ziđa upotrebljevaju opečni zidni elementi s vertikalnim šupljinama i mort opće namjene, tijekom ispunjavanja sljubnica nastupa prodiranje morta u šupljine zidnog elementa. Otpornost pri posmiku određuje se na jednak način za ziđe od punih ili šupljih opečnih zidnih elemenata te stoga utjecaj međusobnog spoja zidnih elemenata i sljubnica morta nije uzet u obzir. Pomoću prostornih nelinearnih proračunskih modela i usporedbom s odzivom fizikalnih modela provjeren je utjecaj međusobnog spoja šupljih zidnih elemenata i sljubnica morta na posmičnu nosivost.If clay blocks with vertical voids and general-purpose mortar are used in masonry construction, interlocking will occur during placement of units and mortar. Shear strength of the clay block and solid brick masonry is usually determined in the same way, without taking interlocking into consideration. With interlocking, the tensile strength of clay blocks is reached before mortar bed joint sliding occurs. In order to consider the effect of interlocking in nonlinear analyses, three-dimensional design models were built and verified using physical model response. The shear resistance function was adopted to enable proper description of masonry response.Wenn für tragendes Mauerwerk Blockziegel und Allzweckmörtel verwendet werden, kommt es bei der Ausführung zur Verknüpfung von Ziegelsteinen und Mörtel. Der Schubwiderstand wird normalerweise gleicherweise für Mauerwerk aus Hohlziegel und für Vollsteinmauerwerk ermittelt, so dass Einflüsse der gegenseitigen Verbindung nicht berücksichtigt werden. Aufgrund der Verknüpfung wird der Zugwiderstand der Blockziegel erreicht, bevor der Schubwiderstand der Mörtelfuge ausgeschöpft ist. Um den Effekt der Wechselwirkung in nichtlinearen Analysen zu berücksichtigen, wurden dreidimensionale Berechnungsmodelle aufgestellt und aufgrund physischen Modellverhaltens verifiziert. Die Schubwiderstandsfunktion wurde eingeführt, um das Verhalten des Mauerwerks auf geeignete Weise darzustellen

The Zagreb (Croatia) M5.5 Earthquake on 22 March 2020

On 22 March 2020, Zagreb was struck by an M5.5 earthquake that had been expected for more than 100 years and revealed all the failures in the construction of residential buildings in the Croatian capital, especially those built in the first half of the 20th century. Because of that, extensive seismological, geological, geodetic and structural engineering surveys were conducted immediately after the main shock. This study provides descriptions of damage, specifying the building performances and their correlation with the local soil characteristics, i.e., seismic motion amplification. Co-seismic vertical ground displacement was estimated, and the most affected area is identified according to Sentinel-1 interferometric wide-swath data. Finally, preliminary 3D structural modeling of the earthquake sequence was performed, and two major faults were modeled using inverse distance weight (IDW) interpolation of the grouped hypocenters. The first-order assessment of seismic amplification (due to site conditions) in the Zagreb area for the M5.5 earthquake shows that ground motions of approximately 0.16–0.19 g were amplified at least twice. The observed co-seismic deformation (based on Sentinel-1A IW SLC images) implies an approximately 3 cm uplift of the epicentral area that covers approximately 20 km2. Based on the preliminary spatial and temporal analyses of the Zagreb 2020 earthquake sequence, the main shock and the first aftershocks evidently occurred in the subsurface of the Medvednica Mountains along a deep-seated southeast-dipping thrust fault, recognized as the primary (master) fault. The co-seismic rupture propagated along the thrust towards northwest during the first half-hour of the earthquake sequence, which can be clearly seen from the time-lapse visualization. The preliminary results strongly support one of the debated models of the active tectonic setting of the Medvednica Mountains and will contribute to a better assessment of the seismic hazard for the wider Zagreb area

Mechanical properties of masonry as required for the seismic resistance verification

Primjena opeke i opečnih blokova je jako raširena u građevinarstvu. Istraživanja mehaničkih svojstava opeke kao materijala i ponašanja ziđa pri djelovanju horizontalnih opterećenja u ravnini nije dovoljno istražena, a rezultati iz drugih izvora su obično generalni i ne mogu se direktno primijeniti te se za svaku pojedinu primjenu trebaju posebno odrediti. Ziđe je anizotropno i za svaku nelinearnu analizu njegova naponskog stanja je potreban niz podataka o mehaničkim svojstvima do kojih se teško dolazi. U radu su izložena proširena istraživanja mehaničkih svojstava glinenih zidnih elemenata i ziđa određena primjenom jednostavnih metoda ispitivanja, na primjeru šuplje blok-opeke kakova se često koristi u Republici Hrvatskoj. Prikazani rezultati mogu se koristiti za složene nelinearne proračune ponašanja ziđa izloženog djelovanju vertikalnog i horizontalnog opterećenja.Despite the extensive use of masonry in different types of construction, this material has not been investigated as much as other materials. Results obtained from different sources are general and for each particular use its characteristics have to be determined separately. Although the stress state in masonry is very complex and cannot be easily simulated in experiments, the properties obtained by simple experiments that investigate the basic failure modes of masonry could be used for a more accurate prediction of its non-linear behavior and failure. The outlined extended testing of masonry mechanical properties in plane has been necessary for obtaining the parameters needed for the non-linear numerical analysis of the masonry behavior under in-plane lateral loading. Presented data could be used as initial required values for masonry as used in Croatia. They represent the main input data for any further analysis of masonry buildings made of hollow-clay blocks and they could be used as a good reference for designers, brick industry and masonry builders in Croatia

The characteristics of 2D and 3D modelling approach in calibration of reinforced concrete frames cyclic behaviour

A 3D FE micromodel of a bare RC frame was developed. The model is based on validated 2D micromodel. The 3D model obtained higher response when compared to its 2D counterpart. Consequently, a calibration of the frame was initiated. Calibration involved modifying parameters that govern the plastic behaviour of the computational model, such as fracture energy, plastic displacement and direction of plastic flow. It was shown that the greatest effect in lowering the response had the direction of plastic flow. Plastic flow direction was selected as -0.1 as it has greatest correlation with the experimental data. Negative value denotes that material volume will decrease due to crushing.publishe