|عنوان فارسی مقاله||ظرفیت باد در ساختمان های بلند|
|عنوان انگلیسی مقاله||Wind Loading on Tall Buildings|
|رشته های مرتبط||مهندسی عمران، سازه و مدیریت ساخت|
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بخشی از ترجمه فارسی مقاله:
7 تنطیم جریان هوا
8 تکنیک های محاسبه دینامیک مایع
بخشی از مقاله انگلیسی:
The damping in a mechanical or structural system is a measure of the rate at which the energy of motion of the system is dissipated. All real systems have some form of damping. An example is friction in a bearing. Another example is the viscous damping created by the oil within an automotive shock absorber. In many systems, damping is not helpful and it has to be overcome by the system input. In the case of wind sensitive structures such as tall buildings, however, it is beneficial, as damping reduces motion, making the building feel more stable to its occupants. Controlling vibrations by increasing the effective damping can be a cost effective solution. Occasionally, it is the only practical and economical means of reducing resonant vibrations. Types of damping systems that can be implemented include, passive, active and semi-active dampers. Some examples of passive dampers are: • Tuned Mass Damper (TMD) (an example is given in Fig. 8) • Distributed Viscous Dampers • Tuned Liquid Column Dampers (TLCD), also known as Liquid Column Vibration Absorbers (LVCA) • Tuned Sloshing Water Dampers (TSWD) • Impact Type Dampers • Visco-Elastic Dampers • Friction Dampers Examples of active and hybrid dampers include: • Active Tuned Mass Damper (ATMD) • Active Mass Driver (AMD) Examples of semi-active dampers include : • Variable Stiffness Dampers • Hydraulic dampers • Controllable Fluid Dampers • Magneto-Rheological (MR) Dampers • Electro-Rheological (ER) Dampers • Variable Friction Dampers While general design philosophy tends to favour passive damping systems due to their lower capital and maintenance costs, active or semi-active dampers may be the ideal solution for certain vibration problems. More details about passive and active systems to control vibrations are given by Soong and Costantinou (1994).
8 COMPUTATIONAL FLUID DYNAMICS TECHNIQUES
In a number of fields, numerical simulation by means of CFD (Computational Fluid Dynamics) is becoming a promising and powerful tool for predicting the behaviour of structures in practical engineering cases. This includes applications involving fluidstructure interaction. CFD techniques may be used for determination of wind effects where Standards are sometimes not directly or as easily applicable, for instance when designing tall buildings and non conventional structures. Some examples of CFD studies conducted at the University of Melbourne are given below. A typical 1: 400 scale model of a 40 m x 40 m x 300 m building is shown in Figure 9 and Figure 10. The maxi mum wind speed at the top of the building is 40 m/s (in the prototype). The turbulence intensity follows the Australian code terrain category 2 wind. This analysis was conducted using program CFX10. The turbulence model is SST (shear stress transport).
9 CONCLUDING REMARKS
This paper has considered a number of key factors associated with the design of tall buildings to the effects of wind loading. The general design requirements for structural strength and serviceability assume particular importance in the case of tall building design as significant dynamic response can result from both buffeting and cross-wind wind loading excitation mechanisms. Serviceability with respect to occupier perception of lateral vibration response can become the governing design issue necessitating the introduction of purpose-designed damping systems in order to reduce these vibrations to acceptable levels. Dynamic response levels also play an important role in the detailed design of façade systems. State of the art boundary layer wind tunnel testing, for determining global and local force coefficients and the effects of wind directionality, topographical features and nearby structures on structural response, is recognized as being particularly useful to tall building design. The emerging use of CFD codes, particularly at the concept design stage, is also noted as assuming increasing importance in the design of tall buildings.