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Modelling Alternative Load Paths in Platform-Framed CLT Buildings: A Finite Element Approach
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.ORCID-id: 0000-0001-9196-0370
2019 (Engelska)Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Timber has become more popular as a construction material during recent years. Engineered wood products, such as glued laminated timber and cross-laminated timber, have enabled the construction of multi-storey buildings. Tall buildings with many occupants need to resist a disproportional collapse in case of unexpected exposures, e.g. accidents or terrorism. Structural robustness can improve the collapse resistance of a building. The literature about robustness is comprehensive concerning concrete and steel buildings, but it is rather limited regarding timber.

A robust building can mobilise alternative load paths in the structure after the removal of bearing building components. Alternative load paths rely primarily on the connections between components. For timber buildings, few investigations exist to evaluate the alternative load paths after a removal. Analyses usually do not take into account non-linear effects which could influence the capacity of alternative load paths, such as damage of single fasteners, friction,  timber crushing and brittle failure. In particular, the alternative load paths in platform-framed cross-laminated timber buildings are not well understood.

 The goals of this thesis are to i) review the concept of robustness in general and determine the state of the art concerning timber buildings in particular, ii) develop a method to analyse the alternative load paths in a platform-framed CLT building taking into account relevant non-linearities, iii) use the method to elicit the alternative load paths in a building after a wall removal, and iv) study the effects of probabilistic variations of model parameters.

 The thesis first introduces tall timber buildings and then presents a summary of structural robustness in a collapse resistance framework. The summary includes established analysis methods and specific considerations for timber, whereof a detailed review is provided in Paper I. Paper III additionally provides results of a survey on contemporary practices of professionals around the world concerning robustness.

 In the subsequent chapter, the studied 8-storey case building made of platform-framed cross-laminated timber is described including the modelling abstractions. Additionally, the setup of a validation experiment for the modelling approach is described. The following chapter introduces the modelling approach for an alternative load path analysis after a wall removal. The approach is based on the finite element method using the commercial software Abaqus. The deterministic part of the approach includes a non-linear static pushdown analysis of single storeys in a bay and elicits the alternative load paths and their capacity. Finite connector elements in the model substitute single fasteners including their elastic, plastic, damage and rupture behaviour. The 3D models of the walls and floors account for timber crushing, brittle failure and contact friction. A simplified non-linear dynamic model of the entire bay uses the pushdown results as inputs and evaluates the collapse progression among storeys after a sudden element removal. The probabilistic part of the approach models the uncertainty of the input parameters of the dynamic model by varying the parameter values in a Monte Carlo simulation, to evaluate the probability of a collapse.

 Paper II applies the approach for a simple pushdown of a single storey and Paper IV applies the pushdown and the dynamic analysis to elicit the alternative load paths after a single wall removal. The thesis shows furthermore the results of a double wall removal in the example building and the results of the Monte Carlo analysis for the single and double wall removal.

 For the assumed removals, the developed approach could identify the alternative load paths, determine their capacities and estimate the probability of a collapse under probabilistic variations. The approach might be used to classify various removal scenarios in platform-framed multi-storey cross-laminated timber buildings specifically and predetermine design solutions which could provide a desired level of robustness. The approach might be generalised for multi-storey timber buildings of various construction types.

Ort, förlag, år, upplaga, sidor
Luleå: Luleå University of Technology, 2019.
Serie
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
Nyckelord [en]
timber, robustness, finite element method, alternative load paths, disproportionate collapse
Nationell ämneskategori
Annan samhällsbyggnadsteknik Annan maskinteknik
Forskningsämne
Träteknik
Identifikatorer
URN: urn:nbn:se:ltu:diva-73258ISBN: 978-91-7790-340-6 (tryckt)ISBN: 978-91-7790-341-3 (digital)OAI: oai:DiVA.org:ltu-73258DiVA, id: diva2:1299442
Presentation
2019-06-05, A193, Forskargatan 1, LTU Skellefteå, Skellefteå, 09:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2019-03-27 Skapad: 2019-03-27 Senast uppdaterad: 2019-06-05Bibliografiskt granskad
Delarbeten
1. Structural robustness and timber buildings: a review
Öppna denna publikation i ny flik eller fönster >>Structural robustness and timber buildings: a review
2019 (Engelska)Ingår i: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 14, nr 2, s. 107-128Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Timber buildings are increasing in their dimensions. Structural robustness is imperative for all buildings and specifically important for tall buildings. Lives can be saved if disproportionate collapse can be avoided after a catastrophic event (e.g. accident, terrorism). The literature about robustness is comprehensive concerning concrete and steel buildings, but is rather limited regarding timber. This paper reviews robustness in general and robustness of timber buildings in particular. Robustness is an intrinsic structural property, enhancing global tolerance to local failures, regardless of the cause. A deterministic approach to assess robustness is to remove certain load-bearing elements from the structure and compare the consequences to given limits. Design methods for robustness may be direct by assessing effects of local failure, or indirect by following guidelines. For robust timber buildings, the connections are the key aspects. Usually, metal connectors may provide the required joint ductility. For robust light timber-frame construction, rim beams may be designed. For timber posts and beams and cross laminated timber, guidance regarding robustness is scarce, but in some aspects they seem to be similar to steel frames and precast concrete. Future research should assess the capacity of connections, and evaluate the adequacy of seismic connectors for robust timber buildings.

Ort, förlag, år, upplaga, sidor
Taylor & Francis, 2019
Nyckelord
Robustness, timber, disproportionate collapse, progressive collapse, alternative load path, damage tolerance
Nationell ämneskategori
Annan samhällsbyggnadsteknik Annan maskinteknik
Forskningsämne
Träteknik
Identifikatorer
urn:nbn:se:ltu:diva-67926 (URN)10.1080/17480272.2018.1446052 (DOI)000458549900006 ()2-s2.0-85061480216 (Scopus ID)
Projekt
Vinnova BioInnovation 4.4
Forskningsfinansiär
VINNOVA, BioInnovation 4.4
Anmärkning

Validerad;2019;Nivå 2;2019-02-15 (johcin)

Tillgänglig från: 2018-03-13 Skapad: 2018-03-13 Senast uppdaterad: 2019-03-27Bibliografiskt granskad
2. Assessment of Connections In Cross-Laminated Timberbuildings Regarding Structural Robustness
Öppna denna publikation i ny flik eller fönster >>Assessment of Connections In Cross-Laminated Timberbuildings Regarding Structural Robustness
2018 (Engelska)Konferensbidrag, Publicerat paper (Refereegranskat)
Abstract [en]

Cross-laminated timber makes timber buildings with an increasing number of storeys achievable. Withmore storeys, structural robustness needs more attention to make a building survive unforeseen events (e.g. accidents,terrorism) and save lives. For steel and concrete buildings, design methods for robustness focus on connection details.The assessment of joints in cross-laminated timber buildings regarding robustness is rather limited in the literature. Theobjective of this paper is to conduct an initial assessment of the connectors after the removal of a wall in a platformcross-laminated timber building. We used the finite element method and the component method for the analysis of acase building. The results indicate that the wall-to-wall and the floor-to-floor connectors may fail at low deflectionlevels leading to high shear loads in the floor panel above the removed wall, which might induce cracking. The removalanalysis was only partially completed, but we identified an indication of the deformation behaviour of the case building.Testing and refined modelling of the connections is needed in the future to verify the results. This study may facilitatefuture investigations regarding robustness of multi-storey cross-laminated timber buildings.

Nyckelord
Robustness, Connection, Component method, Cross-laminated timber, Finite element method, Disproportionate collapse
Nationell ämneskategori
Annan samhällsbyggnadsteknik Annan maskinteknik
Forskningsämne
Träteknik
Identifikatorer
urn:nbn:se:ltu:diva-70599 (URN)
Konferens
2018 World Conference on Timber Engineering, Seoul, Republic of Korea, August 20-23 2018
Projekt
Bioinnovation 4.4
Forskningsfinansiär
VINNOVA
Tillgänglig från: 2018-08-27 Skapad: 2018-08-27 Senast uppdaterad: 2019-03-27Bibliografiskt granskad

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