Numerical Simulation on Dynamic Behavior of a Cold-Formed Steel Framing Building Test Model

A nonlinear dynamic numerical simulation on seismic behavior of a two-story cold-formed steel framing building full-scale shaking table test model was carried out by the way of from components to integral structure. Firstly, refined numerical model of shear wall was established, and restoring force models of screw connections between the framing and sheathings were integrated into the numerical model of shear wall. The refined numerical model of shear wall was verified by tests. Secondly, based on refined numerical model of shear wall and modified exponential “Foschi” skeleton curve, uniform restoring force skeleton curves of two typical shear walls of the shaking table test model were obtained. Then, a simplified numerical model of shear wall was proposed. Finally, a dynamic numerical model of cold-formed steel framing building was established based on the simplified shear wall model and assumption of rigid diaphragm, and nonlinear dynamic analysis was carried out. The results of numerical simulation agreed well with the tests, which indicated that the numerical model of integral buildings can factually reflect the dynamic behavior of cold-formed steel framing building

Piezoelectric cantilever sensors

A piezoelectric cantilever with a non-piezoelectric, or piezoelectric tip useful as mass and viscosity sensors. The change in the cantilever mass can be accurately quantified by monitoring a resonance frequency shift of the cantilever. For bio-detection, antibodies or other specific receptors of target antigens may be immobilized on the cantilever surface, preferably on the non-piezoelectric tip. For chemical detection, high surface-area selective absorbent materials are coated on the cantilever tip. Binding of the target antigens or analytes to the cantilever surface increases the cantilever mass. Detection of target antigens or analytes is achieved by monitoring the cantilever's resonance frequency and determining the resonance frequency shift that is due to the mass of the adsorbed target antigens on the cantilever surface. The use of a piezoelectric unimorph cantilever allows both electrical actuation and electrical sensing. Incorporating a non-piezoelectric tip (14) enhances the sensitivity of the sensor. In addition, the piezoelectric cantilever can withstand damping in highly viscous liquids and can be used as a viscosity sensor in wide viscosity range

Load-carrying Capacity Estimation on Cold-formed Thin-walled Steel Columns with Built-up Box Section

The use of cold-formed thin-walled steel structural members has increased in recent years, and most of their sections are open section with only one symmetrical axis, which would likely fail by twisting and interaction with the others buckling mode, such as local buckling and distortional buckling. To improve the ultimate strength of columns, built-up box section can be used. In this paper, a series of loading capacity tests on high-strength cold- formed steel columns with built-up bo x section are presented, including 21 axially-compressed columns and 19 eccentrically-compressed columns sub- jected to bending moments about weak axis as well as strong axis. The test specimens are built up by two channel sections with two intermediate stiffeners in the web, and they connect at their flanges using self-drilling screws. It was shown that distortional buckling and twisting do not occur and the ultimate load-carrying capacity is 10 to 20 percent higher than the sum of the ultimate load-carrying capacity of each lipped channel section columns. According to the test results and theoretical analysis, an improved method based on the suggestion of current China code ‘Technical code of cold-formed thin-walled steel struct ures’ (GB50018-2002) considering the plate-coupling effect was proposed to estimate the ultimate load-carrying capacity of built-up box section column. With the proposed method, the calculated results are close and conservative to the test results

Flexural vibrations and resonance of piezoelectric cantilevers with a nonpiezoelectric extension

IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 54(10): pp. 2001-2010.A piezoelectric cantilever (PEC) is a flexural transducer consisting of a piezoelectric layer [e.g., lead zirconate titanate (PZT)] bonded to a nonpiezoelectric layer (e.g., stainless steel). A PEC with a thin nonpiezoelectric extension has two distinctive sections, each with a different thickness, different axial density, and elastic-modulus profiles and has been increasingly used as an in-situ biosensor. It has the advantages of dipping only the nonpiezoelectric extension part in an aqueous solution without electrically insulating the piezoelectric section as well as serving as the bonding pad for receptor immobilization. In this study, we examined the effect of the thin nonpiezoelectric extension on the flexural resonance spectrum and resonance vibration waveforms of PEC; in particular, how the length ratio between the piezoelectric section and the nonpiezoelectric extension section affects the resonance frequencies and resonance peak intensities of PEC. Theoretical resonance frequencies and resonance vibration waveforms were obtained using an analytical transcendental equation we derived by solving the flexural wave equation. Both experimental and theoretical results showed that the two-section structure distorted the flexural vibration waveforms from those of PEC without an extension. As a result, the higher-mode resonance peaks of PEC with a nonpiezoelectric extension could be higher than the first resonance peak due to the two-section structure. With PEC that has a piezoelectric section of 0.25-mm thick PZT bonded to 0.07 mm thick stainless steel of various length l1 and a 0.07-mm thick nonpiezoelectric extension of length l2, we showed that the first-mode-to-second-mode resonance peak intensity ratio had a maximum of 5.6 at l1/l2 = 0.75 and the first-modeto- second-mode resonance frequency ratio a minimum of 2.2 at l1/l2 = 1.8. These findings will undoubtedly help optimize the design and performance of PEC

Self-exciting, self-sensing PbZr0.53Ti0.47O3 /SiO2 piezoelectric microcantilevers with femtogram/Hertz sensitivity

Applied Physics Letters, 89(2): pp. 3.Piezoelectric microcantilever sensors (PEMSs) consisting of a piezoelectric layer bonded to a nonpiezoelectric layer offer the advantages of electrical self-actuation and self-detection. Here we report PEMSs 60-300 mu m in length fabricated from 1.5-mu m-thick sol-gel PbZr0.53Ti0.47O3 (PZT). films with a 2 mu m grain size, a dielectric constant of 1600, and a saturation polarization of 55 +/- 5 mu C/cm(2). The PEMSs exhibited up to four resonance peaks with quality factors Q ranging from 120 to 320. In humidity sensing tests, a PEMS with a 60 x 25 mu m PZT/SiO2 section and a 24 x 20 mu m SiO2 extension exhibited 1 x 10(-15) g/Hz mass sensitivity, two orders of magnitude better than the sensitivity of the current PZT PEMS