Abstract

Abstract

On the last decades, the aeronatical industry has increased the use of Carbon Fibre Reinforced Polymer matrix composites (CFRP), and at the same time, has kept the use of conventional metals. This has led to the presence of hybrid assemblies in the wingbox, fuselage, etc. Due to their high stiffness and strength, as well as the ease to dissasemble and repair, these assemblies are usually bolted. During its usage, an aircraft is subjected to large thermal jumps (the temperature difference between a landed aircraft and a flying one can reach 140 ºC). Because of the presence of hybrid bolted joints, the materials of the joint undergo different thermal expansion/contraction, which cause significant thermal stresses altering the mechanical behaviour of the joint. Framed in the aeronautical Clean Sky 2 project ‘INNOHYBOX’, this work studies the behaviour of hybrid bolted joints subjected to thermal loads, both numerically and experimentally, following a pyramidal approach. At the coupon level, a hybrid carbon-aluminium single-lap shear specimen with one bolt was used to comprehend and characterise its behaviour under thermal loads. At the substructural level, a subcomponent representative of a wingbox was tested under thermal conditions. Finally, a full wingbox was tested. Furthermore, a computationally efficient finite element model was developed to simulate the complex behaviour of these type of joints without comprimsing the computational cost. The numerical predictions correlate favourably against the experimental data.

Abstract

In this research, an effort was made to evaluate the structural behavior of high-rise buildings constructed in fields near to seismic sources that have sustained severe fire damage on some floors against the upcoming near-field earthquakes. Then, the seismic rehabilitation of these buildings was conducted using the proposed hybrid friction-elastic damper (with ''SMA'' super-elastic wires) to prepare them to resist future earthquakes. Therefore, high-rise special steel moment-resisting frames were designed for the life-safety performance level versus design-basis earthquake (''DBE''). These frames were then subjected to three fire scenarios in either of the lower, middle, or upper two stories until to collapse outset. Then, a rehabilitation approach, using a hybrid friction-elastic damper, was proposed to improve the seismic performance against future earthquakes as well as to reuse these structures. Moreover, a set of 10 near-field records including directivity effects were applied to these rehabilitated frames at both ''DBE'' and ''MCE'' hazard levels. The nonlinear dynamic analysis was then conducted. The results indicated that the proposed diagonal brace equipped with this simply-conformed damper is able to increase the energy dissipation capacity in the fire story during the possible forthcoming ground motions. It also provides a large hysteretic response with a minimal structural mechanism of damaged beams in that story. The application of this rehabilitation approach, in addition to a significant increase in ductility-stiffness and lateral load resistance, provides a proper elastic capacity in the frames. Accordingly, the global maximum relative displacement of the structure is reduced considerably, and the local interaction points of the critical columns in the fire-exposed frames fall inside the failure envelope. It also leads to a significant reduction in the average bending moment and axial force by 16-70% and 29-57%, respectively, applied to the fire-exposed columns.