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  Number 2/2020

Volume 11 (2020), Nr. 2 - View full issue

Aspecte privind izolarea seismica a bazei
Aspects regarding the seismic base isolation
Zainulabdeen K. Abdulfattah Abdulfattah, Vlad Stefan Niculae, Daniel Stoica

Pentru prezentul studiu s-a dorit analizarea a nouă modele de structuri, diferența intre ele fiind forma și regimul de inălţime. Modelarea structurilor s-a efectuat cu ajutorul programul ETABS realizandu-se o serie de studii pentru clădiri cu structura din b.a. (cadre respectiv duale) clădiri cu formă pătrată in plan (cu 3 regimuri de inălțime: S+P+14, S+P+9, S+P+4), clădire formă dreptunghiulară in plan (cu 3 regimuri de inălțime: S+P+14, S+P+9, S+P+4), clădire formă rotundă in plan (cu 3 regimuri de inălțime: S+P+14, S+P+9, S+P+4), incastrarea suprastructurii considerandu-se la cota planșeului peste subsolul 1. De asemenea s-au realizat modele de calcul cu aceleași tipuri de clădiri, luand in considerare modelarea clasică a interacțiunii teren-structură precum şi modele de calcul cu aceleași tipuri de clădiri, luand in considerare izolarea bazei, cu două tipuri de izolatori seismici de bază (LRB și HDRB). S-au realizat comparaţii intre toate modelele de calcul structural utilizate.

For the present study it was desired to analyze nine models of structures, the difference between them being the height and the height regime. Structural modeling was carried out with the help of the ETABS program, carrying out a series of studies for buildings with a structure from b.a. (respectively double frames) - buildings with square shape in plan (with 3 height regimes: B+15, B+10, B+5), rectangular shaped building in plan (with 3 height regimes: B+15, B+10, B+5), round shaped plan building (with 3 height regimes: with 3 height regimes: B+15, B+10, B+5), the embedding of the superstructure considering at the level of the floor above the basement 1. Also, models of calculation with the same types of buildings were made, taking into account the classical modeling ofthe land-structure interaction as well as models of calculation with the same types of buildings, taking into account consideration of base isolation, with two types of basic seismic isolators (LRB and HDRB). Comparisons were made between all the structural calculation models used.

Studiul reologic și fizico-mecanic al cimenturilor metalurgice pe bază de nano-silice combinate cu zgură de furnal
Rheological and Physic-mechanical study of metallurgical cements based on Nano-silica combined with blast furnace slag
Khaled Bouali, Hakim Daoui Mohammed, Saidi and Brahim Safi

Această lucrare tratează comportamentul reologic și mecanic al cimenturilor metalurgice bazate pe nano-silice (NS) combinate cu zgură de furnal (GBFS). Un studiu experimental a fost realizat cu un raport constant de apă / liant (A / L) de 0,5 utilizat pentru toate mortarele studiate. Pentru a utiliza maximul GBFS și a scădea consumul de ciment, diferitele conținuturi (36% și 66% .wt) GBFS și 3% .wt de NS au fost alese și adăugate la Portland Cement (PC). Au fost efectuate teste reologice pe paste cimentate și au fost efectuate teste mecanice pe mortare elaborate cu ciment metalurgic studiat. Rezultatele obținute arată că pastele de ciment cu 3% NS fără GBFS au fost cele mai puțin vascoase și au un efort de forfecare mai scăzut, cu o workabilitate acceptabilă in comparație cu alte paste de ciment. Cu toate acestea, in prezența GBFS, pastele de ciment devin mai vascoase, ceea ce face ca debitul să fie mai dificil, cu o forță de forfecare mai mare la debit. De asemenea, rezultatele au arătat, in comparație cu mortarele de control GBFS, că incorporarea unei mici cantități de NS in ciment in prezența GBFS crește in mod remarcabil rezistența la compresiune la 28 și 90 de zile. Incorporarea a 3% in greutate NS in pastele de ciment cu un conținut de GBFS de 36% și 66% in greutate a dat valori ale rezistenței la compresie de foarte mare 90 zile (71,70 și 56,30 MPa). NS și LHF pot reduce in mod remarcabil porozitatea matricei de ciment și cresc densitatea acestuia, ceea ce explică de asemenea rezistența ridicată la rezistența la compresiune.

This work deals the rheological and mechanical behavior of metallurgical cements based on nano-silica (NS) combined with blast furnace slag (GBFS). An experimental study was conducted with constant water-to-binder ratio (W / B) of 0.5 used for all studied mortars. In order to use the max of GBFS and decrease the consumption of cement, the different contents (36% and 66%.wt) of GBFS and 3%.wt of NS were chosen and added to Portland Cement (PC). Rheological tests were conducted on cementitious pastes and mechanical tests were carried on mortars elaborated with metallurgical cement studied. Obtained results show that that cementitious pastes with 3% NS without GBFS were the least viscous and have a lower shear stress with acceptable workability compared to other cement pastes. However, in the presence GBFS the cement pastes become more viscous which makes the flow more difficult with higher shear stress at the flow. Also, the results showed in comparison with the GBFS control mortars that the incorporation of a small amount of NS in the cement in the presence of GBFS remarkably increases the compressive strength at 28 and 90 days. Incorporation of 3% wt NS in cement pastes with a 36% and 66% wt GBFS content gave respectively very high 90 day compressive strength values (71.70 and 56.30 MPa). NS and LHF can remarkably reduce the porosity of the cement matrix, and increase the density of the latter, which also explains the high resistance of the compressive strength.

Metode de estimare a parametrilor caracteristici fenomenului de flashover
Methods of estimating parameters characteristics of the flashover phenomenon
Alexandru-Florin CHIOJDOIU, Ion ANGHEL, Manuel ȘERBAN, Ștefan TRACHE

In acest studiu este prezentată, pe de o parte, complexitatea fenomenului de flashover, iar pe de altă parte, o serie de metode de estimare a principalilor parametri ai acestui fenomen. Momentul producerii fenomenului de flashover este destul de greu de anticipat de către echipajele sosite la locul intervenției. Acesta prezintă un pericol deosebit atat pentru ocupanții clădirii surprinși de incendiu, cat și pentru forțele de intervenție, datorită faptului că, pe timpul acestui fenomen, valoarea temperaturii in interiorul compartimentului ajunge la 500-600 Ԩ, iar densitatea fluxlui căldurii degajate de incendiu, la nivelul pardoselii compartimentului, la cca 20 ݉/ܹ݇2. De asemenea, au fost folosite trei metode de estimare, prin intermediul FDTs, a fluxului căldurii degajate de incendiu pe timpul manifestării fenomenului de flashover, o metodă de estimare a temperaturii compartimentului de incendiu in faza post-flashover, respectiv o metodă de estimare a severității incendiului.

In this study is presented, on the one hand, the complexity of the phenomenon of flashover, and on the other hand, a number of methods for estimating the main parameters of this phenomenon. The moment of the flashover phenomenon is quite difficult to predict by incoming crews at the site of the intervention. It presents a special hazard for both the occupants of the fire building and the intervention forces, due to the fact that, during this phenomenon, the value of the temperature inside the compartment reaches 500-600 C, and the density of the heat flow emitted from the fire, at the level of the compartment floor, at about 20 kW/m2. Also, three methods were used to estimate, with FDTs, the rate of heat rate released by the fire during the phenomenon of flashover, a method of estimating the temperature of the fire compartment in the post-flashover phase, respectively, a method of estimation of the fire severity.

Comportament flexibil - forfecare a grinzilor de beton armat intărit de diverse rețele de compozite incorporate
Flexural Shear behavior of RC beams Strengthened by various embedded composites grids
Abdelhak Aouadi,Youcef Ghernouti

Această lucrare evaluează comportamentul de forfecare-forfecare a grinzilor de beton armat prin grile de polimer intărit cu fibră de carbon incorporate (grile CFRP) și grile metalice cu ochiuri hexagonale, sub test de indoire in patru puncte. A fost efectuată o investigație experimentală pentru a evalua performanța acestui nou tehnic de intărire, Au fost testate trei fascicule de control și cincisprezece grinzi intărite in forfecare flexibilă cu diferite configurații. Cațiva parametri au fost considerați pentru a evidenția eficiența tehnicii utilizate, cum ar fi; Moduri de incărcare finală, ductilitate și defecțiune. Rezultatele experimentale arată că intărirea grinzilor prin rețelele de carbon și metalice incorporate a oferit o imbunătățire mare a rezistenței, a devierii in timp și a indicelui de ductilitate; de fapt, se observă o influență directă asupra modului de eșec.

This paper evaluate the flexural shear behaviour of reinforced concrete beams strengthening by embedded carbon fiber reinforced polymer grids (CFRP grids) and metallic grids with hexagonal meshes, under four-point bending test. An experimental investigation was carried out to evaluate the performance of this new technical of strengthening, Three control beams and fifteen beams strengthened in flexural shear with different configurations have been tested. Several parameters were considered to highlight the efficiency of the technical used, such as; ultimate load, ductility and failuremodes. The experimental results show that the beams strengthening by embedded carbon and metallic grids offered a great improvement in strength, midspan deflection and ductility index; in effect, an influence directly on the failure mode is observed.

Transferul de căldură prin conducţie termică prin peretele cilindric neomogen cu straturi avand conductivitatea termică variabilă cu temperatura rezolvat in Microsoft Excel
Heat transfer by thermal conduction through inhomogeneous cylindrical wall with layers with variable thermal conductivity with temperature solved in Microsoft Excel
Şef lucr. Dr. ing. Gelu-Adrian CHISĂLIŢĂ

Lucrarea prezintă o modalitate de rezolvare a problemei transmiterii căldurii prin conducţie termică in regim staţionar printr-un perete cilindric neomogen (multistrat) cu straturi avand conductivitatea termică variabilă cu temperatura. Implementarea rezolvării este făcută in aplicaţia software Microsoft Excel pentru a folosi instrumentul Solver cu scopul de a rezolva sistemul de ecuaţii neliniare direct dependent de temperaturile de pe suprafeţele delimitatoare ale straturilor peretelui cilindric.

The paper presents a method for solving the steady-state heat transfer problem through a non-homogeneous / multilayered cylindrical shell having one or all layers with variable thermal conductivity. The Solver tool from Microsoft Excel software application is used for solving the system of nonlinear equations directly dependent on the unknown temperatures on the bounding surfaces of the layers.

Critic of permeability estimation methods for unsaturated soil
Leila Mechkarini, Tahar Messafer, Abderrahim Bali

Exploitation of unsaturated soil permeability data (ku) in some cases requires that this characteristic be estimated by methods not measured by laboratory tests and in this case, it is best to use mathematical models to evaluate this parameter. Evaluation of the unsaturated permeability using different estimation methods as well as the studies of comparisons between the results of these models for different types of soils have been treated by several authors ([1], [2]), however none of these authors have compared the results of these models for identical soils (same type of soil, same extraction site, same percentage of different constituents, ect...). In this article we have presented the views of the authors who have treated this subject, then, we applied some models of estimation of ku to samples of sand and silty clay. Also we took as a special case, identical samples that have been extracted from the SoilVision 003 database [3]. After applying to these samples the models of Kunze & al [4], Campbell [5] and Brooks & Corey [6], we found that all these models can present divergent predictions for samples of the same type of soil and also for identical samples. We deduced therefore that there is no general rule that allows us to choose between ku prediction models and that it is always mandatory to go through a series of comparisons in order to select the model that best applies to a soil sample.

Keywords: unsaturated permeability; SoilVision database, help system, empirical models; statistical models

Reglajul termic mixt (cantitativ-calitativ)
Mixed thermal regulation (quantitative-qualitative)
Florin Iordache

Lucrarea are ca obiectiv descrierea problemei reglarii puterii termice intr-o instalatie de incalzire centrala printr-o combinatie secventiala de reglaj termic cantitativ (de debit de agent termic) cu reglaj termic calitativ (de temperatura a agentului termic). Se prezinta relatiile de reglaj termic generale pe baza carora se stabileste posibilitatea combinarii celor doua tipuri de reglaj termic. Reglajul termic cantitativ se efectueaza pana la diminuarea debitului de agent termic cu cel mult 50% din valoarea nominala. Rezultatul obtinut este prezentat grafic si comentat.

Cuvinte cheie: reglaj termic, agent termic

The objective of the paper is to describe the problem of regulating the thermal power in a central heating installation through a sequential combination of quantitative thermal adjustment (flow of thermal agent) with qualitative thermal adjustment (temperature of the thermal agent). The general thermal adjustment relationships are presented based on which the possibility of combining the two types of thermal adjustment is established. The quantitative thermal adjustment is performed until the thermal agent flow is reduced by a maximum of 50% of the nominal value.The result obtained is presented graphically and commented.

Keywords: thermal regulation, thermal agent

Rolul punților termice in perspectiva standardului nZEB
The role of thermal bridges in the perspective of thenZEBstandard
Ioan BOIAN

Reducerea emisiilor de gaze cu efect de seră GES este direct legată de utilizarea mai eficientă a combustibililor fosili ca sursă de energie pentru asigurarea confortului termic alături de imbunătățire performanței termice a anvelopei clădirilor. Efortul depus in ultimele decenii pentru imbunătățirea izolării și pentru etanșarea mai adecvată a clădirilor, mai ales cele rezidențiale și cele din sectorul terțiar trebuie insoțite de eliminarea pe cat posibil a pierderilor suplimentare de căldură survenite prin punțile termice, mai ales că efectul produs de acestea se accentuează odată cu izolarea anvelopei. Atingerea standardului nZEB dezvoltat in cadrul Directivei de Performanță Energetică a Clădirilor implică măsuri și soluții constructive care să conducă la obiectivul stabilit de aceasta. In acest context sunt prezentate cerințele stabilite de standardele romanești C107-2010 și Ordinul 2641/2017, punandu-se in evidență ponderea jucată de punțile termice. Totodată este prezentat și efectul izolării peretelui fără o izolare corespunzătoare a plăcii balconului evidențiindu-se efectul global final, neașteptat de nesemnificativ, ca exemplu de avut in vedere in abordările practice.

Reducing GHG emissions is directly linked to more efficient use of fossil fuels as an energy source to ensure thermal comfort while improving the thermal performance of building envelopes. Efforts in recent decades to improve insulation and make buildings more suitable for sealing, especially residential and tertiary sectors, must be accompanied by the elimination as far as possible of additional heat loss from thermal bridges, especially as their effect is accentuates with tire insulation. Achieving the nZEB standard developed under the Energy Performance of Buildings Directive involves constructive measures and solutions that lead to the goal set by it. In this context, the requirements established by the Romanian standards C107-2010 and Order 2641/2017 are presented, highlighting the weight played by thermal bridges. At the same time, the effect of wall insulation without a proper insulation of the balcony slab is presented, highlighting the final global effect, unexpectedly insignificant, as an example to consider in practical approaches.

Flood risk mappingbased on hydraulic model 2D and GIS, Case study in Draa Ben Khada, Tizi ouzou, Algeria
Abdelghani Leghouchi, Mohammad Djemai, Oussama Derdous, Jamila Tarhouni

Floods caused by rivers areone of the serious, common and natural disasters that many countries are facing. It has caused an immense damage, and a huge proportion of such destruction is associated with the lack of knowledge, resources and coping mechanisms. Therefore, studies and researches on the nature of the rivers are inevitable. Computer models are an effective tool for studying and simulating river behavior with the least possible cost, and one of the measures for the risk reduction is the delineation of flood-prone areas. Flood risk mapping involves modeling the complex interaction of the river flow hydraulics with topographical and land use features of the floodplains. An integrated approach to river flood modeling is the use of GIS and hydraulic models. This paper presents the use of flood frequency analysis integrating with 2D Hydraulic model (HECRAS) and Geographic Information System (GIS) to prepare flood maps of different return periods: 10 years, 20 years, 50 years, and 100 years in Wadi Bougdoura; Wadi SEBAOU and Wadi Sbet at DraaBenKahada City in TiziOuzou. The resulting hydraulic model provides a good representation of the general landscape and it contains additional details, the results indicate that GIS is an effective environment for mapping and analyzing floodplains, they clearly show that this new approach, based on 2D simulation results, allows the stakeholders to have a better appreciation of the consequences of a flood, a design of making a land use and infrastructure development decisions, and emergency measures.

Keywords: Draa Ben Khada; Flood risk mapping; HEC-RAS 2D; GIS

Doua tipuri de schimbatoare de caldura specifice instalatiilor in constructii. Evaluarea caracteristicilor termice
Two types of heat exchangers specific to construction installations. Evaluation of thermal characteristics
Florin Iordache, Alexandru Draghici

Cele doua tipuri de schimbatoare de caldura specifice instalatiilor in constructii la care lucrarea face referire sunt: retelele termice arborescente care alimenteaza instalatiile de incalzire centrala si de preparare a apei calde de consum din cladirile urbane, respectiv schimbatoarele de caldura din cadrul buclelor de utilizare a energiei solare. In lucrare se prezinta procedurile de determinare a caracteristicilor termice (numarul de unitati de transfer termic, NTU si modulul termic, E) prin care se poate evalua transferul de flux termic in cadrul echipamentelor mentionate.

Cuvinte cheie: schimbatoare de caldura, transfer de flux termic

In this paper, two types of heat exchangers specific to the building service systems are studied: the arborescent thermal networks that supply the central heating and domestic hot water preparation systems inside the urban buildings, respectively the heat exchangers connected in loops designed for solar energy use. The paper presents the procedures for determining the thermal characteristics (the number of transfer units, NTU and the so-called thermal module, E) that can be used for evaluating the heat flow transfer within the mentioned equipments.

Keywords: heat exchangers, heat transfer

 
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