Browsing by Author "Strauss, Lourens"
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- ItemModelling of 3D structures in fire as skeletal frames using the Fire Beam Element (FBE) for simplified analysis and design(Stellenbosch : Stellenbosch University, 2021-03) Strauss, Lourens; Walls, Richard Shaun; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: n recent years performance-based designhasbecomemore popular in structural fire engineeringas itoften leads to more cost effective and safe designs. Real incidents,such as the Broadgate fire in 1990,and large-scale experiments, such as the Cardington tests, have shownthat composite structures havesignificantlyhigher resistance in fire than whatis typicallypredicted by prescriptive designs based on isolated members. However, performance-based design tools require significant expertise and computational effort. Simplified tools,such asthe Fire Beam Element (FBE)methodologyandtheSlab Panel Method (SPM),can individually be used to analyse the skeletal frame of a structure in fire or composite floorpanelsrespectively.However, few tools exist for consulting engineers to be able to comprehensively, but efficiently, consider global structuralanalyses for fire. The FBE methodology is based on a finite element that has a movable Neutral Axis (NA) and can consider material and geometric nonlinearity. In this research the FBE methodology is extended toincludea three-dimensional (3D) beam element andisimplemented in a finite element software, OpenSees, so that it could be applied to 3D skeletal composite structures. The SPM is a design tool for composite slabs that considers the concrete deck and unprotected secondary beams as a whole. In theSPM, the ultimate load-carrying capacity is calculated for the slab panel taking into account the Tensile Membrane Action (TMA) mechanism that develops due to large deformationsof the slab panel.In this thesis, a design methodology is proposed linking the FBE methodology with the SPM. In theproposeddesign methodology,the composite slab and the supporting skeletal structureare consideredas two separate systems which are able to interact with eachother. The3D FBEdesign methodology isvalidated withthree-case studies, obtained in literature,which are used to validatethe behaviour of the supporting skeletal structure. The case-studies show that the 3D FBE is able to capture the behaviour of the structure where the Bernoulli-Euler assumption holds, and typically shows good correlations between FBE and literature supplied deformations. The second case study investigated indicatesthat continuity should be taken into account whendetermining the yieldline pattern and load distribution to the support beams.The third case study highlightsalimitation of the FBE analysisthat is applicablewhen the primary support beams losetheirstrength,and the loads are carried through Membrane Action. Lastly, the FBE and SPM design methodology are applied to a ten-storey office building which provides aproofof concept of the overall design methodology. The results obtained from the FBE analysis demonstrated the behaviour of the supporting skeletal structure and the impact that the rest of the structure hason thesupport beams. The ultimate load-carrying capacity of the slab panel arecalculated with the updated edge deflection determined with the FBE analysisIt is highlighted how SPM predictions can be updated based on improved information regarding perimetersupporting beam deflections.