• Title/Summary/Keyword: post buckling analysis

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Nonlinear spectral collocation analysis of imperfect functionally graded plates under end-shortening

  • Ghannadpour, S. Amir M.;Kiani, Payam
    • Structural Engineering and Mechanics
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    • v.66 no.5
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    • pp.557-568
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    • 2018
  • An investigation is made in the present work on the post-buckling and geometrically nonlinear behaviors of moderately thick perfect and imperfect rectangular plates made-up of functionally graded materials. Spectral collocation approach based on Legendre basis functions is developed to analyze the functionally graded plates while they are subjected to end-shortening strain. The material properties in this study are varied through the thickness according to the simple power law distribution. The fundamental equations for moderately thick rectangular plates are derived using first order shear deformation plate theory and taking into account both geometric nonlinearity and initial geometric imperfections. In the current study, the domain of interest is discretized with Legendre-Gauss-Lobatto nodes. The equilibrium equations will be obtained by discretizing the Von-Karman's equilibrium equations and also boundary conditions with finite Legendre basis functions that are substituted into the displacement fields. Due to effect of geometric nonlinearity, the final set of equilibrium equations is nonlinear and therefore the quadratic extrapolation technique is used to solve them. Since the number of equations in this approach will always be more than the number of unknown coefficients, the least squares technique will be used. Finally, the effects of boundary conditions, initial geometric imperfection and material properties are investigated and discussed to demonstrate the validity and capability of proposed method.

Seismic isolation performance sensitivity to potential deviations from design values

  • Alhan, Cenk;Hisman, Kemal
    • Smart Structures and Systems
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    • v.18 no.2
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    • pp.293-315
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    • 2016
  • Seismic isolation is often used in protecting mission-critical structures including hospitals, data centers, telecommunication buildings, etc. Such structures typically house vibration-sensitive equipment which has to provide continued service but may fail in case sustained accelerations during earthquakes exceed threshold limit values. Thus, peak floor acceleration is one of the two main parameters that control the design of such structures while the other one is peak base displacement since the overall safety of the structure depends on the safety of the isolation system. And in case peak base displacement exceeds the design base displacement during an earthquake, rupture and/or buckling of isolators as well as bumping against stops around the seismic gap may occur. Therefore, obtaining accurate peak floor accelerations and peak base displacement is vital. However, although nominal design values for isolation system and superstructure parameters are calculated in order to meet target peak design base displacement and peak floor accelerations, their actual values may potentially deviate from these nominal design values. In this study, the sensitivity of the seismic performance of structures equipped with linear and nonlinear seismic isolation systems to the aforementioned potential deviations is assessed in the context of a benchmark shear building under different earthquake records with near-fault and far-fault characteristics. The results put forth the degree of sensitivity of peak top floor acceleration and peak base displacement to superstructure parameters including mass, stiffness, and damping and isolation system parameters including stiffness, damping, yield strength, yield displacement, and post-yield to pre-yield stiffness ratio.

Evaluation of the Lateral Ultimate Strength of Steel Moment Resisting Frames under Axial and lateral Forces (수평력과 축력을 받는 강골조의 최대수평내력 평가)

  • Kim, Jong Sung
    • Journal of Korean Society of Steel Construction
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    • v.11 no.1 s.38
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    • pp.69-78
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    • 1999
  • When the lateral forces are applied to a frame, columns in the frame are usually accompanied with sidesway. If this sidesway is large, the frame is subjected to buckling and an early yielding of members which reduces the overall frame stiffness. In this study, numerical analysis of frames were conducted to evaluate the ultimate lateral strength of steel moment resisting frames permitted to sidesway under axial and lateral forces, and develope the procedure for determining the limits of column slenderness ratios. In the numerical analysis, the effects of the relative stiffness ratio between beam and column, deterioration of overall frame stiffness, slenderness ratio and loading conditions were considered. The elasto-plastic analysis method in which the $P-{\Delta}$effect is implemented, presented by the author previously, was adopted in the analysis. Incremental lateral forces were applied to the frame under constant axial loads and the generalized inverse is employed for the post-ultimate behavior.

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Nonlinear response history analysis and collapse mode study of a wind turbine tower subjected to tropical cyclonic winds

  • Dai, Kaoshan;Sheng, Chao;Zhao, Zhi;Yi, Zhengxiang;Camara, Alfredo;Bitsuamlak, Girma
    • Wind and Structures
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    • v.25 no.1
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    • pp.79-100
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    • 2017
  • The use of wind energy resources is developing rapidly in recent decades. There is an increasing number of wind farms in high wind-velocity areas such as the Pacific Rim regions. Wind turbine towers are vulnerable to tropical cyclones and tower failures have been reported in an increasing number in these regions. Existing post-disaster failure case studies were mostly performed through forensic investigations and there are few numerical studies that address the collapse mode simulation of wind turbine towers under strong wind loads. In this paper, the wind-induced failure analysis of a conventional 65 m hub high 1.5-MW wind turbine was carried out by means of nonlinear response time-history analyses in a detailed finite element model of the structure. The wind loading was generated based on the wind field parameters adapted from the cyclone boundary layer flow. The analysis results indicate that this particular tower fails due to the formation of a full-section plastic hinge at locations that are consistent with those reported from field investigations, which suggests the validity of the proposed numerical analysis in the assessment of the performance of wind-farms under cyclonic winds. Furthermore, the numerical simulation allows to distinguish different failure stages before the dynamic collapse occurs in the proposed wind turbine tower, opening the door to future research on the control of these intermediate collapse phases.

Two Dimensional Size Effect on the Compressive Strength of Composite Plates Considering Influence of an Anti-buckling Device (좌굴방지장치 영향을 고려한 복합재 적층판의 압축강도에 대한 이차원 크기 효과)

  • ;;C. Soutis
    • Composites Research
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    • v.15 no.4
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    • pp.23-31
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    • 2002
  • The two dimensional size effect of specimen gauge section ($length{\;}{\times}{\;}width$) was investigated on the compressive behavior of a T300/924 $\textrm{[}45/-45/0/90\textrm{]}_{3s}$, carbon fiber-epoxy laminate. A modified ICSTM compression test fixture was used together with an anti-buckling device to test 3mm thick specimens with a $30mm{\;}{\times}{\;}30mm,{\;}50mm{\;}{\times}{\;}50mm,{\;}70mm{\;}{\times}{\;}70mm{\;}and{\;}90mm{\;}{\times}{\;}90mm$ gauge length by width section. In all cases failure was sudden and occurred mainly within the gauge length. Post failure examination suggests that $0^{\circ}$ fiber microbuckling is the critical damage mechanism that causes final failure. This is the matrix dominated failure mode and its triggering depends very much on initial fiber waviness. It is suggested that manufacturing process and quality may play a significant role in determining the compressive strength. When the anti-buckling device was used on specimens, it was showed that the compressive strength with the device was slightly greater than that without the device due to surface friction between the specimen and the device by pretoque in bolts of the device. In the analysis result on influence of the anti-buckling device using the finite element method, it was found that the compressive strength with the anti-buckling device by loaded bolts was about 7% higher than actual compressive strength. Additionally, compressive tests on specimen with an open hole were performed. The local stress concentration arising from the hole dominates the strength of the laminate rather than the stresses in the bulk of the material. It is observed that the remote failure stress decreases with increasing hole size and specimen width but is generally well above the value one might predict from the elastic stress concentration factor. This suggests that the material is not ideally brittle and some stress relief occurs around the hole. X-ray radiography reveals that damage in the form of fiber microbuckling and delamination initiates at the edge of the hole at approximately 80% of the failure load and extends stably under increasing load before becoming unstable at a critical length of 2-3mm (depends on specimen geometry). This damage growth and failure are analysed by a linear cohesive zone model. Using the independently measured laminate parameters of unnotched compressive strength and in-plane fracture toughness the model predicts successfully the notched strength as a function of hole size and width.

Numerical investigation on seismic behaviors of midrise special moment resistant frame retrofitted by timber-base bracings

  • Ainullah-Mirzazadah, Ainullah-Mirzazadah;Sabbagh-Yazdi, Saeed-Reza
    • Steel and Composite Structures
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    • v.45 no.1
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    • pp.83-100
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    • 2022
  • Timber is one of the few natural, renewable building materials and glulam is a type of engineering wood product. In the present work, timber-based braces are applied for retrofitting midrise Special Moment Resisting Frame (SMRF) using two types of timber base braces (Timber base glulam, and hybrid Timber-Steel-BRB) as alternatives for retrofitting by traditional steel bracings. The improving effects of adding the bracings to the SMRF on seismic characteristics of the frame are evaluated using load-bearing capacity, energy dissipation, and story drifts of the frame. For evaluating the retrofitting effects on the seismic performance of SMRF, a five-story SMRF is considered unretofitted and retrofitted with steel-hollow structural section (HSS) brace, Glued Laminated Timber (Glulam) brace, and hybrid Timber-Steel BRB. Using OpenSees structural analyzer, the performance are investigated under pushover, cyclic, and incremental loading. Results showed that steel-HSS, timber base Glulam, and hybrid timber-steel BRB braces have more significant roles in energy dissipation, increasing stiffness, changing capacity curves, reducing inter-story drifts, and reducing the weight of the frames, compared by steel bracing. Results showed that Hybrid BRB counteract the negative post-yield stiffness, so their use is more beneficial on buildings where P-Delta effects are more critical. It is found that the repair costs of the buildings with hybrid BRB will be less due to lower residual drifts. As a result, timber steel-BRB has the best energy dissipation and seismic performance due to symmetrical and stable hysteresis curves of buckling restrained braces that can experience the same capacities in tension and compression.

Slip Behavior of High-Tension Bolted Joints Subjected to Compression Force (압축력을 받는 고장력 볼트 이음부의 미끄러짐 거동)

  • Han, Jin Hee;Choi, Jong Kyoung;Heo, In Sung;Kim, Sung Bo
    • Journal of Korean Society of Steel Construction
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    • v.20 no.2
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    • pp.279-288
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    • 2008
  • In this study, the slip behavior of high-tension bolted joints subjected to compression force is investigated through 3D finite element analysis and experiments. The relation with sliding load, bolt deformation, and failure load are studied with the metal thickness affecting the bolted joint. The post-sliding behavior considering bolt stiffness is presented and compared with the results by finite element and experiments. The finite element model is constructed by solid elements in ABAQUS, in consideration of all the friction effects between metal plates and bolts. The stress-strain relations in the literature are used, and the sliding displacements and axial stresses around the bolt connection are investigated. The flexural buckling of species happened when the plate thickness is less than the bolt diameter. However, the shear failures of bolt occurred in the opposite case.

Analysis of the Correlation between the Thickness of Support Pin of Pipe Support and the Compressive Load (파이프 서포트의 지지핀 두께와 압축하중의 상관관계 분석)

  • Choi, Myeong Ki;Park, Jongkeun
    • Journal of the Korean Society of Safety
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    • v.37 no.4
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    • pp.36-43
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    • 2022
  • Generally, in construction sites, the pipe support installation workers often use support pins of 9~10 mm which are much smaller than the safety standard sizes for work convenience. Although the safety certification standard thickness of the support pins is 11 mm, and the supervisors are often indifferent to this. Hence, products with far lower performance than the pipe support safety certification value of 40,000 N, which is applied in the supporting post-structural review, are used. Accordingly, this acts as a factor causing collapse accidents in the process of pouring concrete at the construction site. Therefore, this study performed compression experiments on new and reused pipe supports to determine how the thickness of the support pins affects the structural compression performance of the pipe support by considering the thickness of the support pins as a critical variable among various factors affecting the pipe support performance. In the course of the study, the compression test of the pipe support (V2, V4) for the new products showed that only 14 (58.3%) of the total 24 samples satisfied the safety certification standard value of 40,000 N, which indicates that more thorough quality control is required in the manufacturing process. Additionally, comparing the thickness of the support pins and their fracture shape shows that the pipes with support length of 4.0 m or longer are much more affected by the buckling of the entire length than the thickness of the support pins. Of the several factors affecting the performance of reused pipe supports, it was found that, similar to the new products, the use of support pins, with thickness of 12 mm rather than 11 mm, can satisfy the safety certification value more appropriately. Therefore, regardless of the state of usage, it could be concluded that it is necessary to use 12 mm products, whose thickness is larger than that of the safety certification standard value of 11 mm, to improve the performance of the pipe supports.

Study on Ultimate Behavior of Steel Transmission Tower with Residual Stress and Initial Imperfection (잔류응력과 초기변형을 고려한 송전철탑의 비선형 극한거동에 관한 해석적 연구)

  • Chang, Jin Won;Kim, Seung Jun;Park, Jong Sup;Kang, Young Jong
    • Journal of Korean Society of Steel Construction
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    • v.20 no.3
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    • pp.421-435
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    • 2008
  • This paper presents an investigation on the ultimate behavior of a transmission tower using nonlinear analyses inconsideration of residual stress and initial imperfection. Main members, such as main post, horizontal member and diagonal member of the transmission tower were modeled using beam element. Moreover, submembers of the transmission tower were modeled using truss element. ABAQUS (2004) program was used to perform finite element analyses. Initial condition options of the ABAQUS program considering initial stress and imperfection were used in this study. Before performing the analysis of the total transmission tower, simple angle section models using beam or plate/shell element w ere investigated to verify the appropriateness of ABAQUS analysis models and options. According to the verification results, the beam element was used for nonlinear analyses of the transmission tower. From nonlinear analyses results, buckling failure was in the main member of the leg part because of ${P-{\triangle}}$ effect at that point. Also, this paper includes significant results to define real structural failure modes and quantitative values. This study should be used in the development of a reasonable and economic design method for transmission towers.