Non-linear analysis of two-layer timber beams considering interlayer slip and uplift

A new mathematical model and its finite element formulation for the non-linear analysis of mechanical behaviour of a two-layer timber planar beam is presented. A modified principle of virtual work is employed in formulating the finite element method. The basic unknowns are strains. The following assumptions are adopted in the mathematical model: materials are taken to be non-linear and can differ from layer to layer; interacting shear and normal contact tractions between layers are derived from the non-linear shear contact traction-slip and the non-linear normal contact traction-uplift characteristics of the connectors; the geometrically linear and materially non-linear Bernoulli's beam theory is assumed for each layer. The formulation is found to be accurate, reliable and computationally effective. The suitability of the theory is validated by the comparison of the numerical solution and the experimental results of full-scale laboratory tests on a simply supported beam. An excellent agreement between measured and calculated results is observed for all load levels. The further objective of the paper is the analysis of the effect of different normal contact traction-uplift constitutive relationships on the kinematic and static quantities in a statically determined and undetermined structure. While the shear contact traction-slip constitutive relationship dictates the deformability of the composite beam and has a substantial influence on most of the static and kinematic quantities of the composite beam, a variable normal contact traction-uplift constitutive relationship is in most cases negligible

Numerical modelling of behaviour of reinforced concrete columns in fire and comparison with Eurocode 2

The paper describes a two-step finite element formulation for the thermo-mechanical non-linear analysis of the behaviour of the reinforced concrete columns in fire. In the first step, the distributions of the temperature over the cross-section during fire are determined. In the next step, the mechanical analysis is made in which these distributions are used as the temperature loads. The analysis employs our new strain-based planar geometrically exact and materially non-linear beam finite elements to model the column. The results are compared with the measurements of the full-scale test on columns in fire and with the results of the European building code EC 2. The resistance times of the present method and the test were close. It is also noted that the building code EC 2 might be non-conservative in the estimation of the resistance time. (c) 2005 Elsevier Ltd. All rights reserved

Uznemiravanje i predacija tetrijeba na pjevalištima u Alpskom i Dinarskom prostoru

Capercaillie (Tetrao urogallusL.) populations in central and south-east Europe cover fragmented edge habitats and are recorded to decline since 1960ies. Capercaillie leks in Slovenia are present at the south-eastern edge of the Alpine metapopulation and at north-western edge of Dinaric. These populations were monitored at leks in two periods in 1980 (466 monito red leks) and 2000 (599). All leks were monitored by local specialists (hunters and/or foresters) and main causes of observed lek populations decline were addressed to each endangered lek. Special emphasis was given to predation at leks, as suggested by D. Jenkins (2008). The six named reasons in 1980ies af fected 39 leks with logging of old-growth forests (at 71.8% of leks) and con struction of forest roads (7.7%) as most pronounced. In 2000 nine reasons affected 92 leks: (i) mountain tourism (26.1%), (ii) cutting of old-growth fo rests (19.60%), (iii) predators attacks (18.5%), (iv) forest management in spring time (9.8%), (v) pastures of livestock with wire fences in forests (6.5%), (vi and vii) berries picking and overgrowing the last pastures in forest-land scape, (viii) constructions of forest roads and (ix) infrastructure. The most profound change in reasons between 1980 and 2000 mapping data were: pre dation at leks, mountain tourism development, increasing of forest manage ment in spring time, wild pasturage of cattle and sheep in forests, overgrowing the last pastures in forest-landscape. A comparison of the increasing percen tage of leks endangered by predators since 1980 has shown positive correla tions with increasing of the main predator populations’ densities. Population density of martens (Martessp.) and wild boar (Sus scrofa) increased for 150% since 1980, while red fox (Vulpes vulpes) density increased only after 1990. Our results confirmed the assessment of reasons for threats to leks based on descriptions and experiences of observers as a suitable approach for caper caillie habitat risk assessment. Results for past decline and differences regar ding to the negative impacts on lek habitats are important guidelines for foresters and wildlife managers concerning sustainable forest management and maintenance of capercaillie populations.Populacije tetrijeba (Tetrao urogallusL.) u središnjoj i jugois toč noj Europi obuhvaća fragmentirani rub staništa,. Brojnost je u opadanju još od 1960. Staništa (pjevališta) tetrijeba u Sloveniji prisutna su na jugois toč nom rubu alpske metapopulacije i na sjeverozapadnom rubu dinarske me tapopulacije. Te populacije praćene su na pjevalištima u dva razdoblja, u 1980. g. (466 praćenih lokaliteta) i 2000. g. (599). Svi lokaliteti pratili su lo kalni stručnjaci (lovci i / ili šumari). Promatrali su glavne uzroke pada popu lacija u staništima, koje su utvrdili za svaki ugroženi lokalitet. Poseban na glasak istraživanja bila je predacija staništa, kao što je predložio D. Jen kins (2008). Glavni razlozi (od šest) ugrožavanja pjevališta (39 pjevališta) u 1980. g. bili su: sječa starih šuma (na 71,8 % lokaliteta) i izgradnje šumskih cesta (7,7 %) i branja šumskih plodova (7,7 %), dok je u 2000. g. bilo devet razloga na 92 ugrožena lokaliteta: (i) planinski turizam (26,1 %), (ii) sječa starih šuma (19,6 %), (iii) predatori (18,5 %), (iv) šumski radovi tijekom pro ljeća (9,8 %), (v) ispaša stoke u šumama, žičane ograde (6,5 %), (VI i VII) branje šumskih plodova i zaraštanje pašnjaka, (viii) izgradnja šumskih cesta (ix) i ostale infrastrukture. Najznačajniji razlozi promjena i ugrožavanja stani š ta između 1980. i 2000. g. bili su: razvoj planinskog turizma, predatora na staništima, radovi u šumama u proljeće, divlje pašarenje goveda i ovaca u šu-mama, zaraštanje posljednjih pašnjaka u šumskim područjima. Usporedba po većanja postotaka ugroženih lokaliteta od grabežljivaca od 1980 godine pokazala su pozitivne korelacije s povećanjem gustoće populacija glavnih grabežljivaca. Gustoća naseljenosti kuna (Martes spp.) i divlje svinje (Sus scrofa) porasla je za 150 %, dok se gustoća naseljenosti lisice (Vulpes vulpes) povećala od 1990. g. (za 35 %). Naši rezultati potvrđuju ocjenu uzroka nega tivnog utjecaja na pjevališta, a temelje se na opisima i iskustvima promatrača kao prikladan pristup za procjene rizika za staništa tetrijeba. Spoznaje o uzro cima sadašnjeg pada pojavnosti tetrijeba nameću donošenje smjernica koje bi omogućile promjenu načina gospodarenja šumama i divljači u cilju podizanju kvalitete staništa za ovu vrstu

Exact slip-buckling analysis of two-layer composite columns

A mathematical model for slip-buckling has been proposed and its analytical solution has been found for the analysis of layered and geometrically perfect composite columns with inter-layer slip between the layers. The analytical study has been carried out to evaluate exact critical forces and to compare them to those in the literature. Particular emphasis has been placed on the influence of interface compliance on decreasing the bifurcation loads. For this purpose, a preliminary parametric study has been performed by which the influence of various material and geometric parameters on buckling forces have been investigated. (C) 2009 Elsevier Ltd. All rights reserved

An analytical model of layered continuous beams with partial interaction

Starting with the geometrically non-linear formulation and the subsequent linearization, this paper presents a consistent formulation of the exact mechanical analysis of geometrically and materially linear three-layer continuous planar beams. Each layer of the beam is described by the geometrically linear beam theory. Constitutive laws of layer materials and relationships between interlayer slips and shear stresses at the interface are assumed to be linear elastic. The formulation is first applied in the analysis of a three-layer simply supported beam. The results are compared to those of Goodman and Popov (1968) and to those obtained from the formulation of the European code for timber structures, Eurocode 5 (1993). Comparisons show that the present and the Goodman and Popov (1968) results agree completely, while the Eurocode 5 (1993) results differ to a certain degree. Next, the analytical solution is used in formulating a general procedure for the analysis of layered continuous beams. The applications show the qualitative and quantitative effects of the layer and the interlayer slip stiffnesses on internal forces, stresses and deflections of composite continuous beams

Varnostnik - poklic ali zgolj izhod v sili

Namen prispevka je ugotoviti ali se posamezniki odločijo za delo varnostnika, ker si želijo opravljati poklic varnostnika, pomagati ljudem in ker si želijo ustvariti kariero na tem področju, oziroma ali so se za izbrani poklic odločili le zato, ker druge zaposlitve niso dobili

Državljansko samovarovanje

Predstaviti državljansko samovarovanje, ki je v Republiki Sloveniji zaenkrat še daleč do uresničitve in umestitve v naš varnostni sistem oziroma nacionalno varnostni sistem Republike Slovenije. Cilj prispevka je teoretično predstaviti državljansko samovarovanje v Republiki Sloveniji in svetu ter prikazati nekatere podatke iz raziskave na območju Mestne občine Ptuj z okolico, ki kažejo na to, kako ljudje poznajo državljansko samovarovanje in ali bi bili pripravljeni pri tem prostovoljno sodelovati

Preservation of forest soil and vegetation in the Capercaillie (Tetrao urogallus L.) habitat within the eastern Karavanke region an the eastern Kamnik-Savinja Alps in Slovenia

V študiji smo preuevali talne in vegetacijske razmere na devetih reprezentativnih ploskvah v habitatu divjega petelina (Tetrao urogallus L.) v visokogorju vzhodnih Karavank in vzhodnih Kamniško-Savinjskih Alp. Raziskave so potekale na ploskvah v razlinih gozdovih na rastiših divjega petelina, ki so bile sistematino izbrane glede na geološko podlago, ekspozicijo in stopnjo ohranjenosti gozdov. V drugotnih smrekovjih, ki so nastali na zarašenih pašnikih in porašajo distrina rjava tla na andezitnih grohih in na gnajsih, smo v primerjavi talnih lastnosti z dobro ohranjenim bukovimi gozdovi na podobnih rastiših zasledili znake degradacijskih procesov. V gozdovih na apnencih in dolomitih je bila rastlinska vrstna pestrost mnogo veja kot v gozdovih na nekarbonatnih kamninah. Floristina sestava in struktura vegetacijesta jasno nakazala stopnjo ohranjenosti oz. spremenjenosti gozdov tako na karbonatni kot tudi nekarbonatni matini podlagi.In the high-montane zone of the eastern Karavanke range and the eastern Kamnik-Savinja Alps of Slovenia, the soil and vegetation conditions on nine representative plots in the Capercaillie (Tetrao urogallus L.) habitat were studied. The research was carried out on plots in different forest types within the Capercaillie leks, selected with regard to the different bedrock, exposure and level of forest degradation. By contrast to the well preserved beech forest, degradation processes in dystric soil on andesite tuff and gneiss of secondary spruce forest in the abandoned pastures were detected. In the forests on limestone and dolomite, the plant species diversity is much higher than in the forests on non-carbonate bedrock. On carbonate and non-carbonate bedrock, too, the level of preservation of forests (secondary forest in pastures vs. co-natural forests on permanent forest land) is significantly reflected in the floristic composition and vegetation structure