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1.
Modeling of a geocell-reinforced pavement
Samo Peter Medved, Bojan Žlender, Stanislav Lenart, Primož Jelušič, 2016, izvirni znanstveni članek

Opis: This article details how the serviceability of a flexural pavement structure is improved by incorporating the Cellular Confinement System (geocells). For this purpose, two different pavement structures, with and without embedded geocells, were manufactured in a laboratory and an accelerated traffic type of loading was applied. The vertical and horizontal cyclic loads were applied simultaneously to simulate the effect of principal stress rotation. A comparative study between the conventional flexible pavement and the geocell-reinforced flexible pavement is presented. Additionally, numerical models of the laboratory tests were built and the results were compared. The simulation of the experimental tests using the Traffic Load Simulator (TLS) are carried out using the FEM and advanced models that describe the permanent strain behavior of the unbound granular material. The development of permanent deformation within the pavement structure, with and without the geocells, is also presented through the numerical model, which was verified by the experimental results.
Ključne besede: flexible pavement, reinforcement, geocell, traffic load simulator, permanent deformation, numerical modeling
Objavljeno: 18.06.2018; Ogledov: 355; Prenosov: 42
.pdf Celotno besedilo (1,39 MB)
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2.
The stability of the excavation face of shallow civil and mining tunnels
Pierpaolo Oreste, 2011, izvirni znanstveni članek

Opis: The stability of the excavation face of shallow tunnels excavated in difficult ground conditions is currently a relevant problem in the sector for tunnelling and mining. Even though face-reinforcement interventions with fibreglass dowels have proved to be efficient, there is still no reliable analysis and dimensioning method available. A new calculation procedure is illustrated in this paper for the analysis of the face static condition in shallow tunnels, also when reinforcement interventions with fibreglass dowels are used. The procedure is based on the limit-equilibrium method applied to the ground core ahead of the face. The main result of the calculation is that the safety factor of the excavation face is also obtained in the presence of reinforcements and from this it is then possible to proceed with the dimensioning of the intervention. The procedure has been applied to two real cases and satisfactory results have been obtained.
Ključne besede: fibreglass dowels, face reinforcement, surface tunnel, limit equilibrium method, factor of safety
Objavljeno: 13.06.2018; Ogledov: 319; Prenosov: 68
.pdf Celotno besedilo (213,90 KB)
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3.
New trends in rock mass characterisation for designing geotechnical structures
Drago Ocepek, 2005, izvirni znanstveni članek

Opis: The investigation on designing supporting measures for geotechnical structures consists of the proper selection of the input data for the stress – strain analysis of the excavation process and the selection of retaining measures. In the preliminary phase of investigation the area must be geologically mapped in detail, and discontinuities precisely measured, boreholes and their “in situ” tests listed and samples for laboratory examinations taken. The new method allows rock mass classification for different rock quality, from soft rocks to mixed rock masses, as well as determination of the geological strength index GSI. The limits for using the suggested method are persistent discontinuities in rock mass which lead to translation or rotation failure mechanisms, either in a single plane or as a wedge. In all cases where discontinuities play a significant role, the rock mass structure must be considered and kinematical analyses performed. In other circumstances, a rock may be uniform and reasonably isotropic due to the geometry of discontinuities and their mutual intersections. The value range of GSI is first determined in the beginning of investigation and later in the excavation phase by considering the disturbance factor D, which expresses disturbances caused by excavation methods and rock mass relaxation. The strength and deformability parameters of rocks of different quality are determined by the generalized Hoek-Brown failure criterion and applied to shallow and deep tunnels or slopes. Before the start of excavations work and after establishing the retaining measures, the analysis results are checked by monitoring. New methods include the determination of post peak strength parameters of rock mass after relaxation, and routine measurements. The newest measurement system however allows direct readings of displacements of the rock mass in both the elastic and post-peak states. With back analyses we determine the softening behavior of the rock mass and a possible need for increasing retaining measures. Such a design method enables the optimization of retaining measures and the reduction of investment costs.
Ključne besede: geological strength index – GSI, simulation of a triaxial large scale »in situ« test, numerical modeling, retaining measures, rock reinforcement, monitoring, back analyses, strain softening, rock mass relaxation
Objavljeno: 16.05.2018; Ogledov: 471; Prenosov: 27
.pdf Celotno besedilo (1,05 MB)
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4.
Experimental investigation of the stability of particulate dispersoid suspensions in aluminium and magnesium melts
Varužan Kevorkijan, 2000, izvirni znanstveni članek

Opis: The rejection of Si3N4,Mg3N2, AlN and Si particles from different slurries consisting of molten aluminum and magnesium alloy with 10% of silicon or pure molten metals was experimentally investigated by measuring changes in the electrical resistance of the slurries before and after rejection occurred. In stirring experiments, only individual powder fractions which passed through a 45 µm sieve screen and remained on a 30 µm screenwere applied. The experiments showed that the rejection of Si3N4 particles from Al-10%Si and Mg-10%Si melts occurs when more than 17-18 vol.% of the ceramic phase is dispersed into the melt, while in pure Al and Mg molten metals spontaneous rejection occurs at 7-8 vol.% of the introduced ceramic phase. A similar tendency of rejection (at 16-18 vol.% of particulate in slurry) was also observed during the introduction of silicon particles into Al-10%Si and Mg-10%Si melts.
Ključne besede: metal matrix composites, particle reinforcement, interface, chemically activated wetting
Objavljeno: 01.06.2012; Ogledov: 1142; Prenosov: 44
.pdf Celotno besedilo (215,84 KB)
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5.
Analysis of timber-framed walls coated with CFRP strips strengthened fibre-plaster boards
Miroslav Premrov, Peter Dobrila, Branko Bedenik, 2004, izvirni znanstveni članek

Opis: This paper provides an experimental analysis of timber-framed walls, coated with carbon fibre-reinforced polymers (CFRP) strengthened fibre-plaster boards, usually used as main bearing capacity elements in the construction of prefabricated timber structures. The tensile strength of the fibre-plaster boards is lower than the strength of timber frame, therefore it is convenient to strengthen boards with high-strength materials in order to gain a higher capacity. It has been shown that the inclusion of CFRP diagonal strip reinforcement on the load-carrying capacity can be quite high and that it is maximized when the carbon strips are connected to the timber frame. On the other hand, the ductility itself was not significantly improved. The test samples proved an important distinction in behaviour in timber frame-fibreboard connecting area, dependant on the boundary conditions between inserted CFRP strips and timber frame. It has been shown that proposed simplified Eurocode 5 methods, applicable for wood-based sheathing boards, could be unsuitable for the problems presented.
Ključne besede: civil engineering, timber structures, panel walls, fibre-plaster boards, steel reinforcement, carbon fibres
Objavljeno: 01.06.2012; Ogledov: 1784; Prenosov: 76
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6.
Approximate analytical solutions for diagonal reinforced timber-framed walls with fibre-plaster coating material
Miroslav Premrov, Peter Dobrila, Branko Bedenik, 2004, izvirni znanstveni članek

Opis: This paper provides approximate analytical solutions for diagonally reinforced timber-framed panel walls usually used as main bearing capacity elements in the construction of prefabricated timber structures. These walls can be mathematically treated as composite elements made of a timber frame and fibre-plaster boards as a coating material. As boards are the weakest part of the system they are reinforced with steel diagonals. The proposed approximate analytical models with the fictitious thickness and width of fibre-plaster boards enable simultaneously to consider the influence of inserted steel diagonals, flexibility of mechanical fasteners between the boards and the timber frame and any appearing cracks in the tensile area of the fibre-plaster boards. The obtained numerical results show good agreement with the measured experimental results.
Ključne besede: civil engineering, timber structures, panel walls, fibre-plaster boards, steel reinforcement, steel diagonals, mathematical modelling
Objavljeno: 01.06.2012; Ogledov: 1530; Prenosov: 62
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7.
Modelling of fastener flexibility in CFRP strengthened timber-framed walls using modified [gamma]-method
Miroslav Premrov, Peter Dobrila, 2008, izvirni znanstveni članek

Opis: The paper provides semi-analytical modelling for prefabricated timber-framed walls using the modified ▫$/gamma$▫-method. The walls are composed of a timber frame and gypsum plasterboards (GPB) which are flexibly connected to the timber frame. Because the tensile strength of the GPB is approximately 10-times lower than the compressive one, it is convenient to strengthen the boards in their tensile diagonal direction with carbon fibre-reinforced polymer (CFRP) strips, which are glued to the boards. Additionally, in the proposed mathematical model the classical beam theory is used taking into account a fasteners' flexibility in the timber frame - GPB connecting area, as well as crack appearing in the GPB and an influence of the inserted CFRP strips. Therefore the CFRP strip contribution is considered with a modified slip modulus which results in the fictive increased stiffness coefficient of the fasteners.
Ključne besede: civil engineering, timber structures, frame walls, fibre-plaster boards, steel reinforcement, CFRP strips, carbon fibre-reinforced polymer, mathematical modelling
Objavljeno: 01.06.2012; Ogledov: 1509; Prenosov: 19
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8.
Mathematical modelling of timber-framed walls strengthened with CFRP strips
Miroslav Premrov, Peter Dobrila, 2008, izvirni znanstveni članek

Opis: This paper provides mathematical modelling for prefabricated timber-framed walls composed of a timber frame and fibre-plaster boards. Because the tensile strength of the fibre-plaster boards is approximately 10-times lower than the compressive one, it is convenient to strengthen the boards in their tensile diagonal direction with carbon fibre-reinforced polymer (CFRP) strips, which are glued to the boards. Based on analysis of experimental research results [7] special approximate mathematical models have been developed. The models enable simultaneously to consider the influence of inserted CFRP strips, flexibility of mechanical fasteners in the connecting areas and any appearing of tensile cracks in the coating boards.
Ključne besede: civil engineering, timber structures, frame walls, fibre-plaster boards, steel reinforcement, CFRP strips, mathematical modelling
Objavljeno: 01.06.2012; Ogledov: 1437; Prenosov: 71
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