The Wind-Induced Vibration Response for Tower Crane Based on Virtual Excitation Method
The Dynamics characteristic of Tower Crane is complicated under the wind excitation which complicates the wind-induced vibration response analysis. The random wind-induced response analysis of tower crane is presented based on finite element method and Virtual Excitation Method. The pulsating wind loads are changed into multiple-point correlation stationary excitation. This papers uses Davenport's wind speed spectrum which does not change with height, and considers multiple-point correlation of wind-induction. The Tower Crane is employed as a numerical example, the response spectra and Mean Square Root (RMS) of the tower crane is obtained by wind-induced vibration. The results indicate that the vibration of the tower crane has a large response in low frequency and the One-third Octave acceleration RMS is lower, the influences of the wind-induced vibration on comfort are analyzed.
Wind-induced tower crane vibration and safety evaluation
The maximum wind load direction of tower crane is considered to be perpendicular to its jib. The interference effects of its different segments and across-wind loads are ignored in traditional crane safety evaluation. This study proposes a general scheme for the safety evaluation of tower cranes under fluctuating wind loads. The wind coefficients of a full-scale model of a tower crane were calculated by computational fluid dynamics, and then the time history of wind loads, simulated through the autoregressive method, were applied to the finite element model of a tower crane. The results reveal that the maximum along-wind load direction deflected 30°–60°, and the mean ratio of the absolute value of the across-wind coefficient to the along-wind coefficient of the tower crane was 8.56%, which indicated that the across-wind loads should be taken into account in wind-resistant design. Comparing the wind-induced responses of four typical wind directions, the maximum displacement, the bending stress and the axial stress of the tower crane occurred in the positive direction. Furthermore, the maximum acceleration of the cat-head was 0.028 m/s2, which met the comfort requirements of the operator. Although the tower crane met the strength and static stiffness requirements of design rules, the maximum bending stress at the junctions between the jib and the slewing platform, the counterweight and the counter-jib, exceeded the allowable stress, and the first modal of the tower crane was excited. These results warrant considering the effect of fluctuating wind loads in the safety evaluation of a tower crane.
Legal Process and the Discovery of Better Policies for Fostering Innovation and Growth
Our chapter concerns how legal process can lead to efficient policies for fostering innovation and growth. Future innovation will depend at least as much on how laws are made as on a priori analyses of the optimal content of those laws. Of particular importance is whether U.S. choice of law and choice of forum rules promote an efficient market for law. Our analysis supports three suggestions for improving the law to support growth. First, the rules governing the selection of the jurisdiction whose law governs productive activity can significantly affect growth and innovation. Second, any proposal aimed at increasing growth through a change in law or legal institutions should take account of the existence of multiple jurisdictions and parties’ ability to choose the jurisdiction whose law controls their transactions. Third, we suggest harnessing the power of jurisdictional competition among the states through a federal law enforcing contracting parties’ choice of law except to the extent states legislatively override the choice of law and regulate local transactions. We apply this analysis to several areas of the law that are critical to growth and innovation: non-competition clauses, business associations, the legal profession, internet law, insurance, property law, products liability, and franchise regulation.