1,721,419 research outputs found
Numerical and experimental investigation on angle multiple slit bolted connections for precast wall panels
Full text linkFlat Multiple Slit Devices (MSDs) have been introduced in steel constructions located in earthquake-prone areas as compact hysteretic dampers connected to braces, and were further proposed to be employed also in other structural typologies, including aligned precast concrete walls. Nevertheless, similar angle connections needed for horizontal joints of orthogonal walls are not tackled in literature. The shape of MSDs, obtained by selective weakening by removing part of the steel area of flat plates, may allow to attain a highly ductile and stable dissipative behaviour, given local plate buckling is avoided, protecting the bolted joints through capacity design. Laser cutting as an alternative to mechanical milling introduces the possibility to easily optimise the shape of the slits in order to attain better performance under laterally imposed cyclic load. This paper analyses the application of right-angle-bent MSDs for the horizontal connection between orthogonal precast walls typical of panel structures with rigid diaphragms. In particular, bolted angle plates with hourglass-shaped multiple slits obtained after laser cutting are investigated numerically via non-linear finite shell elements and experimentally with original cyclic tests. The effect of the aspect ratio of the plate and of the restraint condition, possibly affecting the performance under imposed shear deformation due to the presence of the bent corner, is investigated by parametric analysis. Finally, general design rules and recommendations are presented
Causes of local collapse of a precast industrial roof after a fire
No full textPrecast roofing systems employing prestressed elements often serve as smart structural solutions for the construction of industrial buildings. The precast concrete elements usually employed are highly engineered, and often consist in thin walled members, characterised by a complex behaviour in fire. The present study was carried out after a fire event damaged a precast industrial building made with prestressed beam and roof elements, and non prestressed curved barrel vault elements interposed in between the spaced roof elements. As a consequence of the exposure to the fire, the main elements were found standing, although some locally damaged and distorted, and the local collapse of few curved barrel vault elements was observed in one edge row only. In order to understand and interpret the observed structural performance of the roof system under fire, a full fire safety engineering process was carried out according to the following steps: (a) realistic temperature time curves acting on the structural elements were simulated through computational fluid dynamics, (b) temperature distribution within the concrete elements was obtained with non linear thermal analysis in variable regime, (c) strength and deformation of the concrete elements were checked with non linear thermal mechanical analysis. The analysis of the results allowed to identify the causes of the local collapses occurred, attributable to the distortion caused by temperature to the elements causing loss of support in early fire stage rather than to the material strength reduction due to the progressive exposure of the elements to fire. Finally, practical hints are provided to avoid such a phenomenon to occur when designing similar structures
Application of the method of parallel sections (MPS) for the assessment of the thermo-mechanical performance of precast prestressed concrete roof/floor members in fire
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Local modelling of cast-in threaded dowel bar connections of precast joints under lateral loading
No full textStructural modelling and probabilistic seismic assessment of existing long-span precast industrial buildings
No full textPrecast concrete frame structures constitute a major construction technology of the industrial built heritage within the Italian territory. Most of these buildings were conceived according to obsolete seismic design criteria with lower hazard than currently recognised standards, whilst the most industrialised areas spread over the Italian territory were declared seismically active since less than 20 years. This paper focuses on seismic performance assessment of long-span flat-roof industrial buildings, representative of modern design technologies. Buildings located in areas with increasing seismic hazard over the Italian territory were designed following an archetype existing building based on standards in force after 1996. Seismic performance is investigated by modal response analysis, non-linear static pushover analysis, and non-linear time-history analysis with a multi-stripe approach. The flexibility of the horizontal diaphragm and the interaction of the resisting frame with the cladding system are addressed by exploring progressively advanced modelling strategies up to a detailed assembly comprising roof members, peripheral panels, and all related connections. Mechanical non-linearities regarding column elements, dowel beam-to-column and slab-to-beam connections, strap tie-back and bracket bearing panel-to-frame connections are modelled with lumped plasticity employing experimentally calibrated constitutive laws. Seismic risk is assessed by estimating via multi-stripe analysis failure rates encompassing performance levels from usability preventing damage to global collapse. The results are site-dependent, and the need for retrofit of these typical precast systems is deemed to be urgent for both buildings designed in areas of average and high seismicity
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