Double⁃Shear Experiments of Cold⁃Formed Steel Stud⁃to⁃Sheathing Connections at Elevated Temperatures

The behavior of cold⁃formed steel(CFS)stud⁃to⁃sheathing connections at elevated temperatures is an important parameter for the fire resistance design and modeling of mid⁃rise CFS structures.In this paper,three kinds of sheathings,namely,medium⁃and low⁃density calcium⁃silicate boards and oriented strand board,were selected for double⁃shear experiments on the mechanical properties of 253 screw connections at ambient and elevated temperatures.The effects of the shear direction,screw edge distance and the number of screws on the behavior of the connections were studied.The results showed that the shear direction and the screw edge distance more significantly influenced the peak deformation,while their impacts on the peak load varied with the type of sheathings.Compared with the single⁃screw connections,the peak loads of the specimens with double⁃screw connections obviously increased but did not double.Finally,a simplified load⁃displacement curve model of stud⁃to⁃sheathing connections at elevated temperature was generated first by establishing the prediction formula for characteristic parameters,such as the peak load,the peak deformation and the elastic stiffness,and then by considering whether the curves corresponded to stiffness increase phenomena.The present investigation provides basic data for future studies on the numerical modeling of CFS structures under fire conditions.

Optical screw-wrench for microassembly

For future micro-and nanotechnologies,the manufacturing of miniaturized,functionalized,and integrated devices is indispensable.In this paper,an assembly technique based on a bottom-up strategy that enables the manufacturing of complex microsystems using only optical methods is presented.A screw connection is transferred to the micrometer range and used to assemble screwand nut-shaped microcomponents.Micro-stereolithography is performed by means of two-photon polymerization,and microstructures are fabricated and subsequently trapped,moved,and screwed together using optical forces in a holographic optical tweezer set-up.The design and construction of interlocking microcomponents and the verification of a stable and releasable joint form the main focus of this paper.The assembly technique is also applied to a microfluidic system to enable the pumping or intermixing of fluids on a microfluidic chip.This strategy not only enables the assembly of microcomponents but also the combination of different materials and features to form complex hybrid microsystems.