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Atashipour, Seyed RasoulORCID iD iconorcid.org/0000-0002-7191-5609
Publications (10 of 35) Show all publications
Atashipour, S. R., Girhammar, U. A. & Challamel, N. (2018). A weak shear web model for deflection analysis of deep composite box-type beams. Engineering structures, 155, 36-49
Open this publication in new window or tab >>A weak shear web model for deflection analysis of deep composite box-type beams
2018 (English)In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 155, p. 36-49Article in journal (Refereed) Published
Abstract [en]

Deep box-type beams, consisting of framing members and sheathings, are sensitive to shear deformations and hence appropriate refined theories or complicated magnification factors are needed to be used to obtain accurate results. For sheathings or webs between the framing members that are weak in shear, additional shear deformations occur corresponding to the relative axial displacement between the framing members. These sandwich-type or partial interaction-type of in-plane shear behaviour between the framing members, needs to be taken into account, especially when the web shear stiffness is very low. The composite box-type beam treated here is composed of three framing members with sheathings on both sides. To incorporate effects of the sheathings shear deformations between the framing members on the deflection, the sheathings, here called web interlayers, are modelled as shear media with equivalent slip moduli corresponding to a partially interacting composite beam model. Governing equilibrium equations of the model are obtained using the minimum total potential energy principle and solved explicitly. The obtained results are compared with those based on different conventional beam theories and 3-D finite element (FE) simulations. It is shown that the model is capable of predicting accurately the deflection for a wide range of geometry and property parameters. It is demonstrated that the deflection of such deep box-type beams can be expressed as the summation of three different effects, namely bending deformations, conventional shear deformations in the framing members and sheathings, and additional in-plane shear deformations or shear slips of the weak web causing relative axial displacements between the framing members.

Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Other Mechanical Engineering
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-59992 (URN)10.1016/j.engstruct.2017.10.073 (DOI)000419409800004 ()2-s2.0-85033432970 (Scopus ID)
Note

Validerad;2017;Nivå 2;2017-11-13 (andbra)

Available from: 2016-10-27 Created: 2016-10-27 Last updated: 2018-06-11Bibliographically approved
Atashipour, S. R. & Girhammar, U. A. (2018). Influence of Grain Inclination Angle on Shear Buckling of Laminated Timber Sheathing Products. Structures, 13, 36-46
Open this publication in new window or tab >>Influence of Grain Inclination Angle on Shear Buckling of Laminated Timber Sheathing Products
2018 (English)In: Structures, ISSN 2352-0124, Vol. 13, p. 36-46Article in journal (Refereed) Published
Abstract [en]

Recent advances in timber production industries have enabled production of new innovative laminated timber products having layers with grain inclination angle. This paper is aimed to study influence of grain inclination angle in the laminated veneer lumber (LVL) and plywood sheathings on their shear buckling loads. Two extreme edge conditions of simply supported and clamped edges are considered. First, an accurate differential quadrature (DQ) computational code is developed using MAPLE programming software to obtain eigen buckling values and their corresponding eigen mode shapes. Next, for convenience of engineering calculations, approximate algebraic formulae are presented to predict critical shear buckling loads and mode shapes of LVL and plywood panels having layers with grain inclination angle, with adequate accuracy. Furthermore, finite element (FE) modelling is conducted for several cases using ANSYS software to show validity and accuracy of the predicted results for the problem. It is shown that the highest shear buckling loads of LVL sheathings is achievable when the inclination angle of about 30° with respect to the shorter edges is considered for production of LVL panels, whereas the same angle with respect to the long edges of the LVL sheathings results in a relatively lower buckling load. Considering similar inclination angle with respect to any edges of a plywood sheathings will also results in its highest pre-buckling capacity. It is also demonstrated that, under optimal design and certain loading circumstances, LVL shows a higher shear buckling capacity compared to a similar plywood sheathing.

Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Other Mechanical Engineering
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-66675 (URN)10.1016/j.istruc.2017.10.003 (DOI)2-s2.0-85034242984 (Scopus ID)
Note

Validerad;2017;Nivå 2;2017-11-21 (andbra)

Available from: 2017-11-21 Created: 2017-11-21 Last updated: 2018-06-11Bibliographically approved
Atashipour, S. R., Girhammar, U. A. & Al-Emrani, M. (2017). Exact Lévy-type solutions for bending of thick laminated orthotropic plates based on 3-D elasticity and shear deformation theories. Computers & structures, 163, 129-151
Open this publication in new window or tab >>Exact Lévy-type solutions for bending of thick laminated orthotropic plates based on 3-D elasticity and shear deformation theories
2017 (English)In: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 163, p. 129-151Article in journal (Refereed) Published
Abstract [en]

Exact solutions for static bending of symmetric laminated orthotropic plates with different Lévy-type boundary conditions are developed. The shear deformation plate theories of Mindlin-Reissner and Reddy as well as the three-dimensional elasticity theory are employed. Using the minimum total potential energy principle, governing equilibrium equations of laminated orthotropic plates and pertaining boundary conditions are derived. Closed-form Lévy-type solutions are obtained for the governing equations of both theories using separation of variables method and different types of classical boundary conditions, namely simply-supported, clamped and free edge, are exactly satisfied. Thereafter, 3-D elasto-static equations for orthotropic materials are solved for bending analysis of laminated plates using two different approaches. First, the method of separation of variables is utilized and an exact closed-from solution is achieved for simply-supported laminated orthotropic plates. Next, a combined Fourier-Differential Quadrature (DQ) approach is employed to present a semi-numerical solution for bending of laminated orthotropic plates with Lévy-type boundary conditions based on the three-dimensional elasticity theory. High accuracy of the presented solutions are proven and comprehensive comparative numerical results are provided and discussed. Presented comparative numerical results can serve as benchmark for investigating the correctness of new solution methods which may be established in the future.

Place, publisher, year, edition, pages
Elsevier, 2017
National Category
Other Mechanical Engineering
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-60002 (URN)10.1016/j.compstruct.2016.12.026 (DOI)000393931800012 ()2-s2.0-85006741906 (Scopus ID)
Note

Validerad; 2017; Nivå 2; 2017-01-09 (andbra)

Available from: 2016-10-27 Created: 2016-10-27 Last updated: 2018-09-13Bibliographically approved
Atashipour, S. R., Girhammar, U. A. & Challamel, N. (2017). Stability analysis of three-layer shear deformable partial composite columns. International Journal of Solids and Structures, 106-107, 213-228
Open this publication in new window or tab >>Stability analysis of three-layer shear deformable partial composite columns
2017 (English)In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 106-107, p. 213-228Article in journal (Refereed) Published
Abstract [en]

This paper is focused on the effect of imperfect bonding and partial composite interaction between the sub-elements of a box-type column on the critical buckling loads. The box column is modelled as a symmetric three-layer composite structure with interlayer slips at the interfaces, based on the Engesser-Timoshenko theory with uniform shear deformation assumptions. Linear shear springs or slip modulus is considered at the interfaces to model the partial interaction between the sub-elements of the structure. The minimum total potential energy principle is utilized to obtain governing equations and boundary conditions. A direct analytical solution of the original governing equations is presented for obtaining exact buckling characteristic equation of the three-layer partial composite column with different end conditions including clamped-pinned end conditions. Also, the coupled equations are recast into an efficient uncoupled form and shown that there is a strong similarity with those for the two layer element. It is shown that the obtained formulae are converted to the known Euler column formulae when the slip modulus approaches infinity (i.e. perfect bonding) and no shear deformations in the sub-elements are considered. A differential shear Engesser-Timoshenko partial composite model is also employed and critical buckling loads, obtained from an inverse solution method, are compared to examine the validity and accuracy level of the uniform shear model. Comprehensive dimensionless numerical results are presented and discussed

Place, publisher, year, edition, pages
Elsevier, 2017
National Category
Other Mechanical Engineering
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-59983 (URN)10.1016/j.ijsolstr.2016.11.018 (DOI)000392889400018 ()2-s2.0-85007038168 (Scopus ID)
Note

Validerad; 2017; Nivå 2; 2017-01-09 (andbra)

Available from: 2016-10-27 Created: 2016-10-27 Last updated: 2018-09-13Bibliographically approved
Atashipour, S. R. (2016). Structural Analysis of Deep Composite Box-Type Components with application to a proprietary stabilising timber wall element (ed.). (Doctoral dissertation). Paper presented at . Luleå tekniska universitet
Open this publication in new window or tab >>Structural Analysis of Deep Composite Box-Type Components with application to a proprietary stabilising timber wall element
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The stabilising wall element of the Trä8-system is a deep box-type beam/column element which is made of different types of timber composites including framing members of gluedlaminated timber (glulam) and sheathings of laminated veneer lumber (LVL). This element is used as a ―shear wall‖ in multi-storey buildings up to four storeys. To be able to optimise thecomposite stabilising element and use its maximum potential and efficiency, it is necessary to have sufficient fundamental knowledge and information about the structural behaviour and influences of different mechanical properties and geometrical parameters and dimensions of the sub-elements.In this thesis, structural analysis and design principles of the Trä8 stabilising wall element are discussed, including the early stage of erection during assembly to the final usage and residence. A list of required fundamental basic analyses are presented, including accurate deflection analysis for the serviceability limit state, local pre- and post-buckling of the LVL sheathings, global buckling as well as the lateral-torsional buckling of the stabilising element in different design situations. This thesis is then focused on deformations and local instability. For each type of structural problem, accurate, but simple and general methodology is employed to incorporate a large number of effective geometric and property parameters. In this way, a fast evaluation of the influence of different parameters is possible for a wide range of values without needing several time-consuming 3-D finite element (FE) simulations. In several cases, the accuracy and validity of the obtained solutions and formulae are examined and confirmed by comparing their results to those based on the 3-D FE simulations. First, different composite beam theories including shear effects are employed for deflection analysis of the stabilising timber element. Next, an accurate energy-based methodology isdeveloped rendering an explicit formula that gives accurate predictions for the deflection of the stabilising element within a medium range of sheathing or web thicknesses and/or stiffnesses. For weak shear webs, however, this model is not sufficient. Therefore, another new model based on the partial composite interaction theory is developed for accurate deflection predictions of the element having weak shear webs. This model contains simple but accurate formulae for deflection analysis of any similar composite box-type of element with an arbitrary range of geometry and property parameters.Next, shear buckling of the rectangular LVL-panel between the framing members are analysed using differential quadrature (DQ) numerical technique as well as an explicit analytical solution and a formula is established for accurate and fast prediction of the shear pre-buckling of the LVL. This study is extended by considering the effect of each individual lamina of the LVL as well as general orthotropic material properties using a laminated theoryand the DQ solution approach. Further, the post-buckling of the LVL panel is studied based on a simple analytical method with rotating stress fields together with the accurate 3-D FE simulations. A simple formula is then proposed for accurate prediction of the shear post-buckling resistance of the LVL-panel in the stabilising element. As a result of the thesis concerning the two main focus areas, deformations and local instability, explicit analytical formulae are presented for the design of the box-type stabilisingelement with respect to deflections including shear effects in the serviceability limit state and with respect to local shear buckling of the sheathings of the stabilising element including the post-critical area in the ultimate limit state.

Place, publisher, year, edition, pages
Luleå tekniska universitet, 2016
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Building Technologies
Research subject
Timber Structures
Identifiers
urn:nbn:se:ltu:diva-17337 (URN)2e3e1b6d-3e9d-4446-8e4b-acbb9fcb2d9b (Local ID)978-91-7583-543-3 (ISBN)978-91-7583-544-0 (ISBN)2e3e1b6d-3e9d-4446-8e4b-acbb9fcb2d9b (Archive number)2e3e1b6d-3e9d-4446-8e4b-acbb9fcb2d9b (OAI)
Note

Godkänd; 2016; 20160217 (rasata); Nedanstående person kommer att disputera för avläggande av teknologie doktorsexamen. Namn: Seyed Rasoul Atashipour Ämne: Träbyggnad/Timber Structures Avhandling: Structural Analysis of Deep Composite Box-Type Components With Application to a Proprietary Stabilising Timber Wall Element Opponent: Professor Per Johan Gustafsson, Avd för byggnadsmekanik, Lunds tekniska högskola, Lunds universitet, Lund. Ordförande: Professor Ulf Arne Girhammar, Avd för byggkonstruktion- och produktion, Institutionen för samhällsbyggnad och naturresurser, Luleå tekniska universitet, Luleå Tid: Fredag 18 mars, 2016 kl 10.00 Plats: F1031, Luleå tekniska universitet

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-06-11Bibliographically approved
Girhammar, U. A. & Atashipour, S. R. (2015). Analysis of shear deflections of deep composite box-type of beams using different shear deformation models (ed.). Paper presented at . Computers & structures, 155, 42-53
Open this publication in new window or tab >>Analysis of shear deflections of deep composite box-type of beams using different shear deformation models
2015 (English)In: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 155, p. 42-53Article in journal (Refereed) Published
Abstract [en]

The deflection of deep box-type elements due to shear deformations is treated. A closed-form expression for the shear correction factor is derived by using an energy approach. The high accuracy and reliability of the developed procedure is demonstrated by comparing its results with accurate 3-D finite element results and also with the results of the conventional theories of Timoshenko with constant shear coefficient and of Reddy–Bickford applied to this kind of cross-section. A comprehensive and comparative parametric study is presented to investigate the effects of various mechanical properties and geometric dimensions for the different models. Unlike the higher-order shear deformation theories, which are accurate only for beams with rectangular cross-sections, there is a very good agreement between the results of the proposed method and the 3-D FE model. Clearly, the proposed energy method is applicable to more complicated cross-sections, including those with abrupt changes in the geometry, e.g. due to holes.

National Category
Building Technologies
Research subject
Timber Structures
Identifiers
urn:nbn:se:ltu:diva-10613 (URN)10.1016/j.compstruc.2015.02.025 (DOI)000356738400005 ()2-s2.0-84930375254 (Scopus ID)97154fbb-2466-4e99-855a-bda802515228 (Local ID)97154fbb-2466-4e99-855a-bda802515228 (Archive number)97154fbb-2466-4e99-855a-bda802515228 (OAI)
Note
Validerad; 2015; Nivå 2; 20150330 (andbra)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Sburlati, R., Atashipour, S. R. & Atashipour, S. A. (2015). Exact elastic analysis of a doubly coated thick circular plate using functionally graded interlayers (ed.). Paper presented at . Archive of applied mechanics (1991), 85(12), 1779-1792
Open this publication in new window or tab >>Exact elastic analysis of a doubly coated thick circular plate using functionally graded interlayers
2015 (English)In: Archive of applied mechanics (1991), ISSN 0939-1533, E-ISSN 1432-0681, Vol. 85, no 12, p. 1779-1792Article in journal (Refereed) Published
Abstract [en]

Development of new coating systems has been an important issue over the years with the motivation of extending the effective life of mechanical elements. For this intent, functionally graded materials have been recently used in a variety of applications as promising replacements for conventional coatings. In the present study, a hybrid coating system taking advantage of graded composition concept is proposed to enhance the through-thickness stress distribution within a double-sided coated circular thick homogeneous plate. The coating system is composed of two main layers: an external homogeneous layer and an interlayer between the external layer and the plate, with graded material composition. All layers are modeled within the context of three-dimensional elasticity theory, and an elasto-static solution is obtained by using suitable potential functions. Accuracy and reliability of the proposed analysis is investigated by comparison with results obtained in the literature, as well as with the results of a three-dimensional finite element simulation. Comparative study shows the inherent advantages of the present hybrid coating system over the conventional homogeneous coating or the functionally graded coating layers.

National Category
Building Technologies
Research subject
Timber Structures
Identifiers
urn:nbn:se:ltu:diva-15030 (URN)10.1007/s00419-015-1018-3 (DOI)000363536600003 ()2-s2.0-84945468333 (Scopus ID)e7c520a2-3b33-47a2-9587-10556a241bb4 (Local ID)e7c520a2-3b33-47a2-9587-10556a241bb4 (Archive number)e7c520a2-3b33-47a2-9587-10556a241bb4 (OAI)
Note
Validerad; 2015; Nivå 2; 20150522 (andbra)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Atashipour, S. R. & Girhammar, U. A. (2015). On the Shear Buckling of Clamped Narrow Rectangular Orthotropic Plates (ed.). Mathematical problems in engineering (Print), 2015, Article ID 569356.
Open this publication in new window or tab >>On the Shear Buckling of Clamped Narrow Rectangular Orthotropic Plates
2015 (English)In: Mathematical problems in engineering (Print), ISSN 1024-123X, E-ISSN 1563-5147, Vol. 2015, article id 569356Article in journal (Refereed) Published
Abstract [en]

This paper deals with stability analysis of clamped rectangular orthotropic thin plates subjected to uniformly distributed shear load around the edges. Due to the nature of this problem, it is impossible to present mathematically exact analytical solution for the governing differential equations. Consequently, all existing studies in the literature have been performed by means of different numerical approaches. Here, a closed-form approach is presented for simple and fast prediction of the critical buckling load of clamped narrow rectangular orthotropic thin plates. Next, a practical modification factor is proposed to extend the validity of the obtained results for a wide range of plate aspect ratios. To demonstrate the efficiency and reliability of the proposed closed-form formulas, an accurate computational code is developed based on the classical plate theory (CPT) by means of differential quadrature method (DQM) for comparison purposes. Moreover, several finite element (FE) simulations are performed via ANSYS software. It is shown that simplicity, high accuracy, and rapid prediction of the critical load for different values of the plate aspect ratio and for a wide range of effective geometric and mechanical parameters are the main advantages of the proposed closed-form formulas over other existing studies in the literature for the same problem.

National Category
Other Mechanical Engineering Building Technologies
Research subject
Timber Structures; Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-11803 (URN)10.1155/2015/569356 (DOI)000366424100001 ()2-s2.0-84950135228 (Scopus ID)ad094978-58e0-4440-b932-1c147c7f2fac (Local ID)ad094978-58e0-4440-b932-1c147c7f2fac (Archive number)ad094978-58e0-4440-b932-1c147c7f2fac (OAI)
Note

Validerad; 2016; Nivå 2; 20151218 (rasata)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Atashipour, S. R., Girhammar, U. A. & Challamel, N. (2015). The effect of weak shear webs on the deformations of timber box type beams (ed.). In: (Ed.), J. Kruis; Y. Tsompanakis; B.H.V. Topping (Ed.), Proceedings of the Fifteenth International Conference on Civil, Structural and Environmental Engineering Computing: . Paper presented at International Conference on Civil, Structural and Environmental Engineering Computing : 01/09/2015 - 04/09/2015. Stirlingshire: Civil-Comp Press, Article ID 259.
Open this publication in new window or tab >>The effect of weak shear webs on the deformations of timber box type beams
2015 (English)In: Proceedings of the Fifteenth International Conference on Civil, Structural and Environmental Engineering Computing / [ed] J. Kruis; Y. Tsompanakis; B.H.V. Topping, Stirlingshire: Civil-Comp Press , 2015, article id 259Conference paper, Published paper (Refereed)
Abstract [en]

This paper deals with deflection analysis of a deep composite box beam due to inplane shear deformations, especially the modelling of the shear deformations in the webs is considered. The beam is composed of three framing members with sheathings on both sides. The sheathings or webs between the framing members are modelled as shear media with equivalent slip moduli corresponding to the partially composite beam model with three separated layers and two interlayer slip areas. The minimum total potential energy principle is employed to obtain the governing equilibrium equations and corresponding boundary conditions. The coupled set of governing equations is recast into an uncoupled form and solved explicitly together with the corresponding boundary conditions. The closed-form solutions obtained are compared to those based on the conventional beam theories. It is shown that the model is capable of predicting accurately the deflections for a wide range of geometry and property parameters, especially for small shear stiffness (slip modulus) values for the webs. The formula for the deflection is reduced to the Timoshenko formula for full composite interaction when the shear slip modulus of the web approaches infinity. Comparative numerical results are presented to show the influence of bending deformations, shear deformations in the framing layers and the in-plane shear deformations in the sheathings

Place, publisher, year, edition, pages
Stirlingshire: Civil-Comp Press, 2015
Series
Civil-Comp Proceedings, ISSN 1759-3433 ; 108
National Category
Building Technologies
Research subject
Timber Structures
Identifiers
urn:nbn:se:ltu:diva-40069 (URN)2-s2.0-85013361038 (Scopus ID)f0cbceb4-5732-4866-babe-a45a27c5e238 (Local ID)f0cbceb4-5732-4866-babe-a45a27c5e238 (Archive number)f0cbceb4-5732-4866-babe-a45a27c5e238 (OAI)
Conference
International Conference on Civil, Structural and Environmental Engineering Computing : 01/09/2015 - 04/09/2015
Note

Godkänd; 2015; 20160511 (andbra)

Available from: 2016-10-03 Created: 2016-10-03 Last updated: 2018-06-11Bibliographically approved
Atashipour, S. A., Sburlati, R. & Atashipour, S. R. (2014). Elastic analysis of thick-walled pressurized spherical vessels coated with functionally graded materials (ed.). Paper presented at . Meccanica (Milano. Print), 49(12), 2965-2978
Open this publication in new window or tab >>Elastic analysis of thick-walled pressurized spherical vessels coated with functionally graded materials
2014 (English)In: Meccanica (Milano. Print), ISSN 0025-6455, E-ISSN 1572-9648, Vol. 49, no 12, p. 2965-2978Article in journal (Refereed) Published
Abstract [en]

In recent years, functionally graded material (FGM) has been widely explored in coating technology amongst both academic and industry communities. FGM coatings are suitable substitutes for many typical conventional coatings which are susceptible to cracking, debonding and eventual functional failure due to the mismatch of material properties at the coating/substrate interface. In this study, a thick spherical pressure vessel with an inner FGM coating subjected to internal and external hydrostatic pressure is analyzed within the context of three-dimensional elasticity theory. Young’s modulus of the coating is assumed to vary linearly or exponentially through the thickness, while Poisson’s ratio is considered as constant. A comparative numerical study of FGM versus homogeneous coating is conducted for the case of vessel under internal pressure, and the dependence of stress and displacement fields on the type of coating is examined and discussed.

National Category
Building Technologies
Research subject
Timber Structures
Identifiers
urn:nbn:se:ltu:diva-3558 (URN)10.1007/s11012-014-0047-2 (DOI)000344354300014 ()2-s2.0-84911953308 (Scopus ID)16330241-6365-467d-8667-58abb5f76ec5 (Local ID)16330241-6365-467d-8667-58abb5f76ec5 (Archive number)16330241-6365-467d-8667-58abb5f76ec5 (OAI)
Note
Validerad; 2014; 20140916 (andbra)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-7191-5609

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