Página 1 dos resultados de 129 itens digitais encontrados em 0.002 segundos

## A new proposal of a simple model for lateral-torsional buckling of unrestrained steel i-beams in case of fire: experimental and numerical validation

Vila Real, P.M.M.; Piloto, P.A.G.; Franssen, J.-M.
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
17.17%
The behaviour of Steel I-Beams exhibiting lateral-torsional buckling at elevated temperature has been studied by means of experimental and numerical analysis. The authors in an earlier paper have presented an analytical formula for the buckling resistance moment in the fire design situation. This new proposal, different from the actual proposal of the Eurocode 3 Part 1.2 has been validated in this work by comparison with the results from a set of 120 experimental and numerical tests performed on IPE 100 beams, submitted to temperatures varying from room temperature to 600 °C. The numerical simulations have been based on the measured geometrical dimensions of the cross-sections, the longitudinal imperfections, i. e. the out of straightness of the beams, the residual stresses and the yield strength. The Eurocode simple model promotes ultimate loads that depend mainly on the non-dimensional slenderness of the beams. The analytical results provided by the Eurocode 3, for a certain range of the slenderness, appear to be unsafe when compared with the numerical and experimental results. It is shown that the new proposal is safer than the Eurocode 3 formulas.

## A simple model for the lateral–torsional buckling of steel I-beams under fire conditions: numerical and experimental validation

Vila Real, P.M.M.; Piloto, P.A.G.; Franssen, J.-Marc
Fonte: ACS, ACAI Publicador: ACS, ACAI
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
17.17%
When a beam is bent about its greatest flexural resistance axis it may twist and move laterally, before it reaches its strength limit. Although this problem of lateral-torsional buckling of steel beams at room temperature is well known, the same problem at elevated temperature is not. This paper summarises the results obtained in the scope of a research project entitled “lateral buckling of steel I-beams under fire conditions”, where a set of 120 experimental and numerical tests were performed on IPE 100 beams, submittted to temperatures varying from 20 °C to 600 °C, to validate a new proposal for the buckling resistance moment of a laterally unrestrained beam under tire conditions The numerical and experimental results for the lateral-torsional buckling of steel I-beams have been compared to those from the simple model presented in Eurocode 3, Part 1-2. This Eurocode simple model promotes safety levels that depend mainly on the non-dimensional slenderness of the beams. The analytical results provided by flue Eurocode 3, for a certain range of the slenderness, would now appear to be unsafe when compared with the numerical and experimental results. It will be shown that the new proposal is safer than the Eurocode 3 formulas.

## Stability of pure even-aged conifer stands in Portugal

Nunes, Luís; Tomé, José; Tomé, Margarida
Fonte: University of Trás-os-Montes e Alto Douro Publicador: University of Trás-os-Montes e Alto Douro
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
17.48%
The slenderness coefficient of a tree is defined as the ratio of total height (h) to diameter at 1.3 m above ground (d). For the stand level, the slenderness coefficient is calculated using the quadratic mean diameter and the height of the mean tree as (hg/dg). There is well known that a straight relationship exist between the slenderness coefficient of the stands and the risk of stem breakage or tree fall due to abiotic factors such as the wind or snow. When ignoring or neglecting the aspects related to the stands stability, risks of wood production losses caused by storms can be high. Storms of 1982 and 1999 with wind speeds above 100 Km h-1 have particularly damaged extensive forest areas (mainly conifer stands) in the Central European Plain. As the result of learning from these occurrences, the combined effect of hg/dg coefficient and dominant height was found to be a useful and practical criterion for the diagnosis of the stability situation (wind-firmness) of pure even-aged stands of conifer species. Three stability levels have been considered which could be presented in a simple diagram: optimum, moderate and instable. A stand that is let to grow naturally, without intervention, quickly attains the instability level, being more vulnerable to winds of great strength. In Portugal there have been no meaningful episodes of windthrow in conifer stands where the maritime pine (Pinus pinaster Ait.) is the most representative species. Future climate scenarios forecast an increase in the growth potential in some forest sites. Higher dominant heights may increase the risk of tree damage caused by violent storms. In this study...

## Geometric and material nonlinear analysis of imperfect circular hollow section (CHS) columns : steeel tubes and concrete filled tubes

Gonçalves, G.; Barros, R.C.; Braz César, M.T.
Fonte: Instituto Politécnico de Bragança Publicador: Instituto Politécnico de Bragança
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
17.96%
The comparison between theoretical predictions and design curve predictions of the critical stresses, for a wide range of slenderness ratio, is valid and useful. For columns made of steel S235 with initial deformations and slenderness below about 60, columns capacity is controlled by elastic-plastic resistant and performance, as the slenderness decreases (until the minimum limit, controlled by crushing or plastic squash). For columns with slenderness above 60, columns capacity tends to be controlled by elastic instability as slenderness increases. For the used steel S235, in the dimensionless plot of critical stress divided by steel yield stress versus slenderness, the parametric effect of the end-eccentricities is only slightly significant for slenderness between 40 to 80. Rankine-Gordon formula provides conservative safe estimates of the resistant column capacity. The results of the tests of composite columns reveal some of the strength advantage of using composite construction over traditional steel constructions. They also show the importance of top end eccentricities in the results, and the need to ascertain their value with accuracy of about 1-2 mm. Some resistant capacity gains as well as some ductility reductions...

## Dynamic axial crushing of short to long circular aluminium tubes with agglomerate cork filler

Gameiro, C. P.; Cirne, J.
Tipo: Artigo de Revista Científica Formato: aplication/PDF
ENG
Relevância na Pesquisa
17.17%
Cork is a complex natural cellular material with quite unknown or not well understood properties. It is available in the natural and in the agglomerate form and it is an ecological and very durable material. That is why it is used today as thermal and acoustic insulator, as a seal and as an energy-absorbing medium in flooring, shoes and packaging, among others. However, the application of agglomerate cork as filler inside structural thin-walled sections, in order to increase the energy absorption, has not been much explored. Dynamic experimental tests were carried out on empty and micro-agglomerate cork-filled tubes with 22 and 50 mm in internal diameter (D) and length (L), respectively, and numerical simulations were performed with the finite element method software LS-DYNATM, showing good agreement in terms of load-displacement curves and deformation patterns. Having validated the numerical model with experiments, the finite element model was used to undertake a systematic study of circular tubular structures impacted at 10 m/s. The load-deformation characteristics, energy-absorption response and collapse mode transitions of empty and cork-filled aluminium tubes with varying diameters and thicknesses (t), lengths of 25, 300 and 350 mm...

## Fire resistance of composite columns made of concrete filled circular hollow sections and with restrained termal elongation

Oliveira, Tiago Ancelmo de Carvalho Pires de
ENG
Relevância na Pesquisa
17.17%
Composite columns made of Concrete Filled Circular Hollow (CFCH) sections or CFCH columns become popular principally in high-rise and industrial buildings as a good solution for fire situation due advantages such as high load-bearing capacity, high seismic resistance; attractive appearance, slenderness, fast construction times and reduced costs. Despite several research studies on fire resistance of CFCH columns, its behaviour in fire is not completely understood. Most of these studies did not consider the restraining to column thermal elongation, important parameter for behaviour of the column on fire when that one is inserted in a structure. This thesis presents the results of a series of forty fire resistance tests on CFCH columns with axial and rotational restraining to thermal elongation. Parameters such as the slenderness of the column, its load level, the stiffness of the surrounding structure, the ratio of steel reinforcement and the degree of concrete filling inside the column, were tested. Circular Hollow Sections (CHS) columns (i.e. steel columns) were tested also for comparison. A three-dimensional nonlinear finite element model developed in ABAQUS (2011) to predict the behaviour in fire of these columns is presented and validated in comparison with the fire tests. The model includes the relevant parameters tested experimentally. The research is complemented with a numerical analysis that includes a range of practical values of load level...

## Análise teórica e experimental do comportamento de modelos de pilares esbeltos de concreto de alta resistência, considerando a ductilidade; Theoretical and experimental analysis of slender high-strength concrete columns, considering the ductility

Aguirre Torrico, Francisco
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Relevância na Pesquisa
27.48%

## Instabilidade lateral de vigas pré-moldadas em situações transitórias; Lateral stability of precast concrete beams during transient situations

Krahl, Pablo Augusto
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Relevância na Pesquisa
27.89%
O objetivo desta pesquisa é apresentar procedimentos de verificação da estabilidade lateral de vigas de concreto em situações transitórias e com eles realizar análises paramétricas. As fases transitórias estudadas são içamento, transporte e pré-serviço com e sem contraventamento nos apoios. As formulações apresentadas contém cálculo de carga crítica de instabilidade lateral, momento crítico e fator de segurança. São apresentados exemplos numéricos e a partir deles realizadas análises paramétricas com intuito de determinar limites de segurança. Os parâmetros variados foram fck, imperfeições geométricas, vão, largura da mesa comprimida e espessura da alma fazendo uma comparação entre vigas I e retangular. Com os resultados, foram obtidas esbeltezes geométricas limite para fases transitórias, relações entre carga crítica e carga devido ao peso próprio e uma relação entre momento crítico elástico e momento último de flexão para a fase transitória anterior à execução do tabuleiro com contraventamento nos apoios, especificamente. Na comparação entre vigas I e retangular, constatou-se que os dois tipos de seção apresentam limites de segurança distintos. As análises mostraram que os limites de esbeltez geométrica recomendados...

## Arquitetura, historia de vida e infestação por lianas em especies arboreas de florestas semideciduas no municipio de Campinas, SP; Architecture, life history and liana infestation of tree species in semideciduous forests from Campinas, SP

Arildo de Souza Dias
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Relevância na Pesquisa
17.48%
Lianas possuem um papel chave na dinâmica de ecossistemas florestais, principalmente no que diz respeito aos efeitos diretos exercidos sobre os forófitos, como diminuição da taxa de crescimento e reprodução e aumento da taxa de mortalidade. Nosso objetivo foi responder a três questões principais: Espécies de árvores têm diferentes susceptibilidades à infestação por lianas? Quais características arquiteturais e de história de vida dos forófitos são correlacionadas com a infestação por lianas? Árvores com 51-100% da copa coberta com lianas apresentam diferenças em alometria e desenho mecânico (fator de segurança e esbelteza do caule), comparadas às árvores congenéricas sem infestação da copa? Utilizamos um conjunto de dados previamente coletados sobre infestação da copa por lianas em 10 fragmentos de florestas semedicíduas no município de Campinas, e acrescentamos informações sobre características arquiteturais e de história de vida para 54 espécies arbóreas. Dezoito espécies apresentaram um número de indivíduos infestados que diferiu significativamente do número médio de árvores infestadas no fragmento. Com base nesses resultados classificamos as espécies em três categorias de susceptibilidade à infestação: alta...

## Phenotypic integration of skeletal traits during growth buffers genetic variants affecting the slenderness of femora in inbred mouse strains

Jepsen, Karl J.; Hu, Bin; Tommasini, Steven M.; Courtland, Hayden-William; Price, Christopher; Cordova, Matthew; Nadeau, Joseph H.
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.48%
Compensatory interactions among adult skeletal traits are critical for establishing strength but complicate the search for fracture susceptibility genes by allowing many genetic variants to exist in a population without loss of function. A better understanding of how these interactions arise during growth will provide new insight into genotype-phenotype relationships and the biological controls that establish skeletal strength. We tested the hypothesis that genetic variants affecting growth in width relative to growth in length (slenderness) are coordinated with movement of the inner bone surface and matrix mineralization to match stiffness with weight-bearing loads during postnatal growth. Midshaft femoral morphology and tissue-mineral density were quantified at ages of 1 day and at 4, 8, and 16 weeks for a panel of 20 female AXB/BXA recombinant inbred mouse strains. Path Analyses revealed significant compensatory interactions among outer-surface expansion rate, inner-surface expansion rate, and tissue-mineral density during postnatal growth, indicating that genetic variants affecting bone slenderness were buffered mechanically by the precise regulation of bone surface movements and matrix mineralization. Importantly, the covariation between morphology and mineralization resulted from a heritable constraint limiting the amount of tissue that could be used to construct a functional femur. The functional interactions during growth explained 56-99% of the variability in adult traits and mechanical properties. These functional interactions provide quantitative expectations of how genetic or environmental variants affecting one trait should be compensated by changes in other traits. Variants that impair this process or that cannot be fully compensated are expected to alter skeletal growth leading to underdesigned (weak) or overdesigned (bulky) structures.

## Sex-specific Regulation of Body Size and Bone Slenderness by the Acid Labile Subunit

Courtland, Hayden-William; DeMambro, Victoria; Maynard, Jane; Sun, Hui; Elis, Sebastien; Rosen, Clifford; Yakar, Shoshana
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.17%
Insulin-like growth factor-1 (IGF-1) is a crucial mediator of body size and bone mass during growth and development. In serum, IGF-1 is stabilized by several IGF-1 binding proteins (IGFBPs) and the acid labile subunit (ALS). Previous research using ALS knockout (ALSKO) mice indicated a growth retardation phenotype and clinical reports of humans have indicated short stature and low bone mineral density (BMD) in patients with ALS deficiency. To determine the temporal and sex-specific effects of ALS deficiency on body size and skeletal development during growth we characterized control and ALSKO mice from 4 to 16 weeks of age. We found that female ALSKO mice had an earlier onset reduction in body size (4 weeks), but that both female and male ALSKO mice were consistently smaller than control mice. Interestingly, skeletal analyses at multiple ages showed increased slenderness of ALSKO femora that was more severe in females than in males. Both male and female ALSKO mice appeared to compensate for their more slender bones through increased bone formation on their endosteal surfaces during growth, but ALSKO females had increased endosteal bone formation compared to ALSKO males. This study revealed age and sex-specific dependencies of ALS deficiency on body size and bone size. These findings may explain the heterogeneity in growth and BMD measurements reported in human ALS deficient patients.

## Critérios normativos sobre influência da relação Aw/Af e esbeltez de alma no cálculo da resitência à flexão de vigas esbeltas em elementos de estruturas de aço.; Normative criteria of influence of the Aw / Af and slenderness of soul in the calculation of the resistance to bending of beams slim in elements of steel structures.

FERNANDES, Rodrigo
Tipo: Dissertação Formato: application/pdf
POR
Relevância na Pesquisa
27.48%
This work contains a theoretical analysis of the behavior of plate girders. A plate girder has been calculated based on the criteria of the American standard Manual of Steel Construction Load and Resistance Factor Design (AISC, 1994), and checked by the Brazilian standard NBR 8800: Projeto e execução de estruturas de aço de edifícios (método dos estados limites) (ABNT, 1986), the revision project of the Brazilian standard Projeto de Revisão da NBR 8800: Projeto e execução de estruturas de aço e de estruturas mistas aço-concreto de edifícios (ABNT, 2003), the revision project of the Brazilian standard Projeto de Revisão da NBR 8800: Projeto de estruturas de aço e de estruturas mistas de aço e concreto de edifícios (ABNT, 2007) and the European standard Eurocode 3: Design of steel structures Part 1.1: General rules and rules for buildings (CEN, 1992). PFEIL (1989) has calculated a plate girder by using the Brazilian standard NBR 8800/86. The calculated dimension have been checked by the mentioned standards. NARAYANAN (1992 apud OWENS, KNOWLES E DOWLING, 1992) has dimensioned a plate girder by using the British standard BS 5950: Structural use of steelwork in building. Part 1: Code of practice for design in simple and continuous construction: hot rolled sections (BSI...

## Effects of unreinforced masonry wall slenderness ratio on out-of-plane post-cracking dynamic stability

Derakhshan, H.; Ingham, J.; Griffith, M.
Fonte: NZSEE; New Zealand Publicador: NZSEE; New Zealand
Tipo: Conference paper
Relevância na Pesquisa
27.8%
A large number of time-history analyses were performed on several unreinforced masonry (URM) walls that had different slenderness ratios, and the viability of adopting wall slenderness ratio as a criterion for seismic assessment was investigated. Several combinations of three wall properties were assumed to cover most walls found in New Zealand URM buildings, and 30 representative time-history records were used to perform analyses. Walls were either two-leaf thick with no overburden load applied or three-leaf thick having an overburden load applied equal to the weight of a typical second-storey two-leaf URM wall. Wall behavioural data was obtained based on a previous laboratory based study, and each wall was subjected to ground motion scenarios with increasing peak ground acceleration (PGA). The ground motion record PGA that caused the wall to undergo a displacement limit equal to 60% of wall instability displacement was identified, and the sensitivity of the obtained PGA to wall slenderness ratio was studied for all the used records. It was shown that increasing wall slenderness ratio resulted in the wall being more vulnerable.; H. Derakhshan, J. M. Ingham and M. C. Griffith; Paper 55

## Structural Behaviour of Steel Columns and Steel-Concrete Composite Girders Retrofitted using CFRP

Shaat, Amr Abdel Salam
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado Formato: 10320966 bytes; application/pdf
EN; EN
Relevância na Pesquisa
17.48%
Steel bridges and structures often need strengthening due to increased life loads, or repair due to corrosion or fatigue cracking. This study explored the use of adhesively bonded Carbon Fibre Reinforced Polymers (CFRP) flexible sheets and rigid plates in retrofitting steel columns and girders, through experimental and analytical investigations. The first part of the research program investigated the behaviour of CFRP-strengthened steel columns comprised of square Hollow Structural Sections (HSS). Fifty columns, 175 mm to 2380 mm long (i.e. with slenderness ratios ranging from 4 to 93), were tested under axial compression loads to examine the effects of number and type of CFRP layers, fibre orientation, and slenderness ratio. Transverse wrapping was shown to be suitable for controlling outwards local buckling in HSS short columns, while longitudinal layers were more effective in controlling overall buckling in slender columns. The maximum increases in axial strength observed in the experiments were 18 and 71 percent, for short and slender columns, respectively. An analytical fibre-element model and a non-linear finite element model were developed for slender columns. The models account for steel plasticity, geometric non-linearities...

## Strengthening Damaged Reinforced Concrete Beams and Slender Columns Using Ultra-High Modulus CFRP Plates

Richardson, TIMOTHY
Fonte: Quens University Publicador: Quens University
EN; EN
Relevância na Pesquisa
27.17%
This thesis investigates the application of ultra-high modulus carbon fiber reinforced polymer (CFRP) plates to strengthen damaged reinforced concrete beams and slender columns. In the first phase, two different pre-repair loading histories were simulated in seven 3000x300x150 mm reinforced concrete beams, namely cracking within the elastic range, and overloading in the plastic range. After unloading, the beams were repaired with either high- or ultra-high modulus (210 or 400 GPa) CFRP plates, or a hybrid system, and then reloaded to failure. It was shown that the level of pre-existing damage has an insignificant effect on the strengthening effectiveness and the failure mode at ultimate. The 210 and 400 GPa CFRP of reinforcement ratio ρf = 0.17% increased the ultimate strength by up to 29 and 51%, respectively, despite the 40% lower tensile strength of the 400 GPa CFRP, due to the change in failure mode from debonding to rupture. Doubling ρf of the 400 GPa CFRP to 0.34% resulted in a 63% overall gain in flexural strength, only 8% increase in ultimate strength over ρf = 0.17%, due to change in failure mode from rupture to concrete cover delamination. The beam retrofitted by hybrid CFRP showed remarkable pseudo ductility and warning signs before failure. However...

## Flexural motions under accelerating loads of structurally prestressed beams with general boundary conditions

Oni,S. T.; Omolofe,B.
Fonte: Associação Brasileira de Ciências Mecânicas Publicador: Associação Brasileira de Ciências Mecânicas
Tipo: Artigo de Revista Científica Formato: text/html
Relevância na Pesquisa
27.17%
The transverse vibration of a prismatic Rayleigh beam resting on elastic foundation and continuously acted upon by concentrated masses moving with arbitrarily prescribed velocity is studied. A procedure involving generalized finite integral transform, the use of the expression of the Dirac delta function in series form, a modification of the Struble's asymptotic method and the use of the Fresnel sine and cosine functions is developed to treat this dynamical beam problem and analytical solutions for both the moving force and moving mass model which is valid for all variant of classical boundary conditions are obtained. The proposed analytical procedure is illustrated by examples of some practical engineering interest in which the effects of some important parameters such as boundary conditions, prestressed function, slenderness ratio, mass ratio and elastic foundation are investigated in depth. Resonance phenomenon of the vibrating system is carefully investigated and the condition under which this may occur is clearly scrutinized. The results presented in this paper will form basis for a further research work in this field.

## Anomalous elastic buckling of hexagonal layered crystalline materials in the absence of structure slenderness

Ren, Manrui; Liu, Jeffernson Zhe; Wang, Lifeng; Zheng, Quanshui
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.67%
Hexagonal layered crystalline materials, such as graphene, boron nitride, tungsten sulfate, and so on, have attracted enormous attentions, due to their unique combination of atomistic structures and superior thermal, mechanical, and physical properties. Making use of mechanical buckling is a promising route to control their structural morphology and thus tune their physical properties, giving rise to many novel applications. In this paper, we employ finite element analysis (FEA), molecular dynamic (MD) simulations and continuum modeling to study the mechanical buckling of a column made of layered crystalline materials with the crystal layers parallel to the longitudinal axis. It is found that the mechanical buckling exhibits a gradual transition from a bending mode to a shear mode of instability with the reduction of slenderness ratio. As the slenderness ratio approaches to zero, the critical buckling strain {\epsilon}cr converges to a finite value that is much smaller than the material's mechanical strength, indicating that it is realizable under appropriate experimental conditions. Such a mechanical buckling mode is anomalous and counter-intuitive. The critical buckling strain {\epsilon}cr predicted by our continuum mechanics model agrees very well with the results from the FEA and MD simulations for a group of typical hexagonal layered crystalline materials. MD simulations on graphite indicate the continuum mechanics model is applicable down to a scale of 20 nm. This theoretical model also reveals that a high degree of elastic anisotropy is the origin for the anomalous mechanical buckling of a column made of layered crystalline materials in the absence of structural slenderness. This study provides avenues for engineering layered crystalline materials in various nano-materials and nano-devices via mechanical buckling.; Comment: 24 pages...

## Low-Mach-number--slenderness limit for elastic Cosserat rods

Baus, Franziska; Klar, Axel; Marheineke, Nicole; Wegener, Raimund
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.48%
This paper deals with the relation of the dynamic elastic Cosserat rod model and the Kirchhoff beam equations. We show that the Kirchhoff beam without angular inertia is the asymptotic limit of the Cosserat rod, as the slenderness parameter (ratio between rod diameter and length) and the Mach number (ratio between rod velocity and typical speed of sound) approach zero, i.e. low-Mach-number--slenderness limit. The asymptotic framework is exact up to fourth order in the small parameter and reveals a mathematical structure that allows a uniform handling of the transition regime between the models. To investigate this regime numerically, we apply a scheme that is based on a spatial Gauss-Legendre collocation and an $\alpha$-method in time.

## Optimum Slenderness Ratio of a Stable Low-Drag Body

Brown, F. Barton
Fonte: California Institute of Technology Publicador: California Institute of Technology
Tipo: Report or Paper; PeerReviewed Formato: application/pdf; application/pdf