Procedures for vibration serviceability assessment of high-frequency floors

Manufacturing plants that produce micro-electronic components, and facilities for extremeprecision experimental measurements have strict vertical vibration serviceability requirements due to sub-micron feature size or optical/target dimensions. Failure to meet these criteria may result in extremely costly loss of production or failure of experiments. For such facilities floors are massive but stiff, generally have first mode natural frequencies above 10Hz and are typically classed as ‘high frequency floors’. The process of design to limit in-service vibrations to within specific or generic vibration criteria is termed ‘vibration control’. Several guidance documents for vibration control of high frequency floors have been published, for different applications. These design guides typically propose simplifications of complex floor systems and use of empirical predictive design formulae. A recently published guide uses a more rigorous approach based on first-principle modal analysis and modeling footfalls as effective impulses, but there remain unresolved issues about its application, and this paper addresses these in order to develop an improved methodology. First, the significant but conventionally discounted contribution of resonance well above the conventionally accepted boundary between low and high frequency floors is examined. The level of necessary modeling detail is then considered along with the effect of accounting for adjacent bays in simulation of a regular multi-bay floors. Finally, while it is assumed that contributions of higher modes to impulsive response decrease so that a cut-off frequency can be prescribed, simulations demonstrate that with both effective impulse and real footfall forces, there is not necessarily asymptotic response with rising floor mode frequency. The conclusion is that there are no shortcuts to predicting response of high frequency floors to footfall excitation. Simulations must consider resonant response due to high order harmonics, provide adequate detail in finite element models and adopt a cutoff frequency that depends more on usage than on features of the floor or of the walking

Steel slit shear walls with double-tapered links capable of condition assessment

The concept of using a hysteretic damper as a condition assessment device that functions immediately after a damaging earthquake is realized by making use of the residual out-of-plane deformation of links that are arranged in slit shear walls. According to the proposed inspection procedure, the maximum drift ratio experienced by the slit wall is estimated based on the number of torsionally deformed links whose dimensions are determined so that the links would exhibit notable torsional deformation at the target deformations. The adoption of a double-tapered shape for the links enables us to significantly increase the amount of out-of-plane deformation. The relationship between the dimensions and the torsional deformation of the links is established using numerical simulations. The effectiveness of the proposed condition assessment scenario is verified by using a series of cyclic loading tests for individual links and groups of links. As a hysteretic damper, the strength and stiffness of the links predicted by design equations matched well with test results

Hysteretic Analysis of Steel Plate Shear Walls (SPSWs) and a Modified Strip Model for SPSWs

Steel plate shear walls (SPSWs) have become more and more popular in recent years because of their potential huge energy dissipation capacity and ductility under lateral loads. Due to their low cost and fast construction, SPSWs have potential application in practice. The finite element software ANSYS applied to the analysis of the hysteretic behavior of SPSWs is described in this paper first. It was found that compressive stress existed in SPSWs and the effects became more evident with decreasing height-to-thickness ratio. This was validated by comparing theoretical and experimental test results. Secondly, based on the analytical results, a modified strip model is proposed. In the modified model, the compressive effects in the panel were taken into account and it was then found that the load-carrying capacity and the energy dissipation capacity agreed well with the already carefully validated experimental results