Browsing by Author "Kaitila, Olli"

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Design of Cold-Formed Steel Roof Trusses Using ROSETTE - Connections
(1998) Kaitila, Olli
Helsinki University of Technology | Master's thesis
Finite Element Analysis of Steel Columns in Fire Conditions
(2005) Lignell, Mari
Helsinki University of Technology | Master's thesis
Tässä diplomityössä mallinnetaan elementtimenetelmällä teräspilareiden lämpökehitystä sekä standardin mukaisessa että luonnollisessa palossa. Tarkoituksena on, että luotuja malleja voidaan käyttää parametrisessa tarkastelussa koetulosten laajentamiseksi ilman kalliiden kokeiden teettämistä. Työn yleisempänä tavoitteena on tarkastella elementtimenetelmän, erityisesti ABAQUS/Standard ohjelmiston, soveltumista teräspilarien lämmönkehityksen mallintamiseen tulipalossa. Tässä diplomityössä tarkasteltiin neljää teräspilantyyppiä, joista yksi oli suojaamaton ja loput kotelosuojattuja pilareita. Pilarien ja koteloiden materiaalina käytettiin rakenneterästä ja ruostumatonta terästä. Pilarityypeistä luotiin ensin ABAQUS/Standard-ohjelmistolla kaksidimensionaaliset mallit, jotka kuvasivat pilarien lämmönkehitystä EN 1363-1:1999 (ISO 834) mukaisessa standardipalossa. Malleilla testattiin eri lämmönsiirtoparametreja konvektiolle ja säteilylle. Mallit verifioitiin koetuloksilla, jotka saatiin Euroopan hiili- ja teräsyhteisön tutkimusprojektin "Developments of design rules for the fire behaviour of external steel structures" kokeista. Nämä standardipalolle luodut elementtimallit toimivat hyvin ja niillä saatiin riittävän tarkat arviot tulen konvektio- ja säteilylämmönsiirtoparametreille. Luonnollisen palon mallintamista varten pyrittiin luomaan kolmidimensionaaliset mallit, mutta kotelosuojattujen pilareiden tapausta ei saatu analysoitua. Suurimmat ongelmat syntyivät ontelosäteilyn mallintamisesta ontelossa, jossa on varjostavia pintoja. Tällainen ontelo syntyi kotelon ja pilarin välille. Nykyisellä mallintamistekniikalla ontelo vaatii erittäin tiheän elementtiverkon, joten laskentakapasiteettia tarvittiin huomattavasti ja laskenta-aika kasvoi liian pitkäksi. Suojaamattoman pilarin malli luonnollisessa palossa saatiin kuitenkin analysoitua ja verifioitua samaisen tutkimusprojektin kokeilla. Tätä suojaamattoman pilarin elementtimallia voidaan käyttää parametriseen tarkasteluun laajentamaan koetuloksia. Tarkastelua ei kuitenkaan tehty tämän työn puitteessa, sillä kotelosuojatut pilarit olivat työn pääasiallisen kiinnostuksen kohteena.
Finite Element Modelling of Cold-Formed Steel Members at High Temperatures
(2002) Kaitila, Olli
Helsinki University of Technology | Licentiate thesis
Implications of attention-based businesses
(2023) Kaitila, Olli
School of Business | Bachelor's thesis
The advent of social media has created an increasingly growing ecosystem of digital platforms that rely heavily and capitalize on human attention. The business models of attention-based businesses encourage platform developers to constantly seek new ways of drawing their customers towards their platforms and ultimately to be accessible to advertisers. Therefore, social media platform providers are fighting to teeth over how much time and engagement can they attain from their platform’s users. This study presents a descriptive review of the literature on attention-based business models and discusses the ethical issues concerning the development of persuasive technology. The thesis will focus on examining methods and consequences of attention-grabbing technologies in modern attention-based businesses, namely large social media businesses such as Meta, Twitter, and Alphabet. The review explores existing literature to identify the most topical issues at hand and maps open questions for future research. Theoretical background from psychology and behavioral economics are used to assess research findings from relevant literature related to – and around persuasive technology design and its influences. The literature shows that there are myriad biases and heuristics that social media platform providers are tapping into to maximize user engagement, even with undesirable costs to individuals and communities. Addiction, the spread of misinformation, and polarization are presented as key ramifications that harm users, undermine healthy public discourse, and fuel segregation. This thesis argues that intentionally addicting users for economic gains is wrong and that the harmful effects of persuasive technology outweigh the benefits. It provides an overview of how the current state of the attention economy is unfolding and presents transparency and dissolution of the power imbalance between end users and platform providers as possible alternatives to platforms maximizing engagement.
Web crippling of cold-formed thin-walled steel cassettes
(2004-10-22) Kaitila, Olli
Doctoral dissertation (monograph)
The resistance of cold-formed thin-walled cassettes against local transverse forces, i.e. the web crippling capacity, was investigated. The web crippling of cassettes, or liner trays as they are also called, was studied both experimentally and numerically using finite element modelling. Both unreinforced (flat) cassette webs and webs with longitudinal stiffeners situated on only one side of the web mid-line were studied. The calculation of the web crippling capacity of this type of stiffened webs is not included in current design codes. However, if cassettes are designed as continuous over two or more spans, the resistance against local transverse forces has to be verified. It should be noted that the original purpose of the stiffener in cassette webs is to increase the bending moment capacity by increasing the effective area of the compressed part of the web when cassettes are designed as single-span structures, in which case web crippling does not usually become critical. A total of 52 structural tests were carried out on specially manufactured single cassette web sections and built-up cassette structures. Both interior two-flange and interior one-flange loading were considered. The calculation rules for unreinforced webs given in current design codes were found to be relatively conservative in comparison to the test results. Finite element models were developed and validated on the basis of the test results and very good agreement was achieved. These models were used as a starting point for a parametric study of the influence of different cross-sectional parameters on the resistance against local transverse forces of longitudinally stiffened webs. Also the influence of the load bearing length was included in the study. Recommendations concerning the design of the cassette web section are given based on the results. It was shown that the use of a longitudinal stiffener of the studied type in fact reduces the web crippling capacity by at least 10 % in comparison to a similar cassette with an unreinforced web. Depending on the stiffener's geometry, the reduction can be considerably larger. A reduction factor equal to 0.7 - 0.9 should be used for the type of longitudinally stiffened webs considered in this study in connection with the design code formulae for the resistance of unreinforced webs against local transverse forces, depending on the cross-section geometry.