Dynamic analysis of vibrations in steel staircases induced by walking

I dagens arkitektur och konstruktion ökar ständigt efterfrågan på slanka och lätta strukturer. Möjligheten att använda stål i smala och starka byggelement skapar nya sätt för oss att konstruera våra byggnader och deras komponenter. Det ökade användandet av slanka stålstrukturer leder till nya och oväntade problem i bruksstadiet, som t.ex. vibrationer och buller. De här dynamiska svårigheterna utmanar oss, som ingenjörer, i hur vi borde eller inte borde utforma våra byggelement och akustiska förutsättningar. I det här examensarbetet undersöktes dynamiska effekter i ståltrappor vid gång, i konstruktiva och akustiska avseenden. En fallstudie användes som ett medel för att få en generell förståelse kring de utmaningar som lätta strukturer kan skapa. Fallstudien bestod av en ståltrappa i en kontorsbyggnad där ljudrelaterade problem från vibrationer i trappan identifierats. Ett antal analyser utfördes för att kartlägga trappans dynamiska respons vilket ledde till att slutsatser gällande möjliga och lämpliga förbättringar för det specifika fallet kunde dras. Efter att fallstudien avslutats genomförs i rapporten en generell diskussion om de studerade problemen. Analyserna från fallstudiens allmänna lämplighet diskuteras. Slutligen föreslås några rekommendationer gällande konstruktörers och akustikers tillvägagångssätt i den här typen av fall.In today’s architecture and construction there is an increasing demand for slender and lightweight structures. The possibility to use steel in slender and strong construction elements creates new ways of designing our buildings and their components. The increased use of slender steel structures leads to new and unexpected serviceability problems in structures, such as vibrations and noise. These dynamic issues pose new challenges to how we, as engineers, should or should not design our structural elements and acoustical conditions. This thesis presents an investigation of the dynamic effects in steel staircases due to walking, from both a structural and acoustical point of view. A case study serves as a mean to reach a general understanding of the issues that lightweight structures can produce. The case study consisted of a steel staircase in an office building where a noise related problem due to vibrations in the staircase had been identified. A number of analyses were conducted to map the dynamic response in the staircase leading up to conclusions regarding possible enhancements suitable for the specific structure. After the presentation of the case study a general discussion regarding the studied issues is carried out. The overall suitability of the analyses used in the case study is discussed. Ultimately some recommendations regarding the approach structural and acoustical engineers should have in these matters are proposed.Analysis of vibrations and noise in steel staircases This master thesis was carried out as a joint project between structural mechanics and acoustics. We have analyzed disturbing noise and motion in steel staircases and presented possible measures to avoid these. In construction today there is an increasing demand for slender and lightweight structures. They are perceived as architecturally pleasing and are efficient in material use. Besides this, constructing slender and lightweight structures sometimes leads to vibrations, which may cause discomfort for the user. The discomfort could either be perceived as noise or that the vibrations are discomforting. These problems are investigated in this master thesis, regarding acoustics and structural mechanics. In the thesis we investigated an existing steel staircase where the user had identified noise from walking in the staircase. We performed analyses, both through measurements and computer modeling. First of all sound measurements while using the staircase were performed, to evaluate problematic noise. Furthermore, for example, we conducted measurements by hitting the staircase with a hammer. By measuring the force in the hammer and the motion in the staircase we could find a relation between force and motion. From the different analyses we could find what types of motions occurred and which of these that were probable noise sources when using the staircase. When we had identified the problems in the staircase we could suggest proper alterations. The alterations regarded both the structure itself but also adjustments to the room surrounding the staircase. For example, a structural alteration was adding steel plates to weaker parts of the staircase. In the surrounding room we proposed adjustments such as sound absorbents and screens to experience the sound differently, thus being able to use the room more efficiently. Conclusively we gave our recommendations on steel staircases. The recommendations covered both how to analyze problems when they are observed and how steel staircases and their surrounding rooms should be designed to avoid these problems