PERFORMANCE DETERIORATION OF SLOTTED-BOLTED CONNECTION DUE TO BOLT IMPACT AND REMEDY BY RESTRAINERS
The behaviour of slotted-bolted connections when the maximum slip travel exceed the available slot length is presented. The drastic degradation behaviour of slotted-bolted connections under bolt impact is demonstrated. Remedy by means of the concept of restrainers is proposed, which is also advantageous in suppressing the build-up of resonance motion by virtue of the change in system stiffness at different stages. Nonlinear dynamic analyses were performed on a prototype 6-storey steel building equipped with friction dampers with and without restrainers. Three historical earthquake records from California, i.e. the 1989 Loma Prieta, the 1966 Parkfield, and the 1940 El Centro records, were considered in the analyses. In the worst loading case, dampers with restrainers are superior to that without restrainers, resulting in reduction of the peak inter-storey drift by 16% and the peak slip travel by 15%. The shorter slip travel obviously provides extra safety to the system. Increasing the maximum restraining force is generally beneficial in reducing the peak inter-storey drift. However for steel bracings, the restraining force limit should be kept sufficiently below the buckling capacity to avoid buckling of the bracings. Furthermore, a higher restraining force would induce higher storey base shear. Hence, the adequacy of the foundation has to be properly addressed as well in retrofitting of buildings.
Numerical Simulation and Design of Friction- damped D e Steel Frame Structures
(10 pt) During the last decades, a large number of energy dissipating devices were developed, whereas pioneering work on friction dampers was firstly reported by Pall (1979). Existing numerical models of friction devices are based on hysteretic model that uses elasto-plastic representation and follows the Coulomb’s friction law. However, the structural system with friction devices is highly nonlinear due to the kinematic conditions of slip and stick phases of device behaviour, as well as the transition stages from elastic to slipping (stick-slip phase) and from slipping to failure (slip-lock phase) either in bearing or bolt shearing. To have an accurate model of friction devices, all these behavioural phases should be incorporated. Thus, to overpass the drawback regarding friction damper modelling, an equivalent material is proposed in the OpenSees environment. Nonlinear time-history analyses of a 8-storey MRF building equipped with friction-damped braces are carried out.
Chapter 1 – Nanotechnology: A Toolkit for Cell Behavior
Tissue engineering seeks to effectively manipulate cellular populations to improve the function of damaged or diseased tissues and organs. Many techniques can affect cell behavior; however, in order to maintain desirable function, scientists and engineers design solutions that are as biomimetic as possible. True biomimeticity is very challenging without the incorporation of nanotechnology. Since cells in human tissues are surrounded by a 3D hierarchical tissue extracellular matrix containing numerous nano components, a revolutionary change in tissue engineering is to explore biomimetic nanobiomaterials and advanced 3D nano/microfabrication techniques for creating novel tissue constructs and regulating cell behavior. This chapter will provide an overview of recent nanotechnology in tissue engineering applications. We will put special emphasis on integrating cutting-edge 3D nano/microfabrication techniques with nanobiomaterials for complex tissue and organ regeneration.