IS (Part 3) pdf - Download as PDF File .pdf) or read online. IS PART 3 (). LATEST CODE FOR WIND LOAD ANALYSIS. Home · IS (Part 3) pdf. IS (Part 3) pdf. April 7, | Author: maggidiravinder | Category: N/A. DOWNLOAD PDF - MB. Share Embed.
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of Practice for Design Loads (Other than Earthquake) for Buildings and Structures - Part 3: Wind Loads (IS Part 3) + Amendment Foreword. This Indian Standard IS (Part 3). (Third Revision) was adopted by the. Bureau of Indian Standards on. ______(Date), after the draft finalized. IS PART 3 - Free download as PDF File .pdf), Text File .txt) or read online for free. is
Notations have at a distance x down wind from a change in been defined in the text at their first appearance. The categories are increasing fetch length. For the purpose of component of the atmospheric wind speed at different this Code, the gradient height is taken as the height heights above the mean ground level is termed as above the mean ground level, above which the variation velocity profile. The primary cause of wind is traced to earths 4. The height less than 20 m. The wind 4.
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Your Message required. NOTE Evidence on these buidings is fragmentary and any departure from the cases given should be investigated separately.
In order to determine the critical load, the total wind load should be or structure as a whole, and when multiplied by the calculated for each wind direction. F on that particular building or structure. The value of Cf has the to those loads specified in 7.
For rectangular clad following value: The frictional drag force, corrugations or ribs across the wind direction, F', in the direction of the wind is given by the following formulae: For other buildings, the frictional drag has been NOTE Structures that are in the supercritical flow regime, because of their size and design wind velocity, may need further indicated, where necessary, in the tables of pressure calculation to ensure that the greatest loads do not occur at coefficients and force coefficients.
The coefficients are for buildings without 7. The overall force coefficients for rectangular clad 7. However more buildings of uniform section without projections, precise estimation of force coefficients for circular except where otherwise shown shall be as given in shapes of infinite length can be obtained from Fig. When the length is finite the values 7. In the case of buildings whose 7.
To allow for oblique winds, the design shall also be Although this phenomenon is well known in the case checked for net pressure normal to the surface varying of circular cylinders, the same phenomenon exists in linearly from a maximum of 1. The wind load on appurtenances and supports for 7. Allowance members of infinite length. For members of finite shall be made for shielding effects of one element on length, the coefficients should be multiplied by a factor another.
Solid circular shapes mounted on a surface the member and b is the width across the direction of wind. Table 28 gives the required values of K. The The force coefficients for solid circular shapes mounted following special cases must be noted while on a surface shall be as given in Table Cf FIG.
They are denoted by Cfn and Cft obstructed, the ratio shall be taken as infinity and give the forces normal and transverse respectively, for the purpose of determining K.
The the member, the diameter D , the design hourly mean windward frame and any unshielded parts of other wind speed Vd and the solidity ratio. Asub Asub. Where there are more than two frames of similar 7. The loads on the various frames shall or equilateral triangle section with flat-sided be added to obtain total load on the structure. For triangular framed structures or blowing against a face. Allowance may be made for Since the values of IF can vary considerably based on shielding effect from other elements.
The designer is advised that for assigning values of IF for final design 8. If such 8. However, some guidance can be provided for the For intermediate spacing linear interpolation may be purpose of preliminary design. To account for the effect used. Interference effects can be Based on studies on tall rectangular buildings, Fig. The interference gives various zones of interference. Any building or structure which satisfies either of the The interference effect due to buildings of height less above two criteria shall be examined for dynamic than one-third of the height of the building under effects of wind.
It is to be noted that wind induced d oscillations may occur at wind speeds lower than the design where wind speed. The For a structure, the vortex shedding frequency fs shall excitation depends on gust energy available at the resonant be determined by the following formula: The cross-sections horizontal plane which are particularly prone to this type of excitation include the following: Perhaps the most rectangular cross-section: Such element is equal to the frequency of the vortex shedding within energy transfer takes place when the natural frequencies of the range of expected wind speeds.
In such cases, further modes taken individually are close to each other ratio being analysis should be carried out on the basis of special typically less than 2. Flutter can set in at wind speeds publications. Long span suspension bridge decks or are prone to excitations by vortex shedding. Wind tunnel been reported in cases where two or more similar structures testing is required to determine critical flutter speeds and are located in close proximity, for example at less than 20b the likely structural response.
Other types of flutter are apart, where b is the dimension of the structure normal to the single degree of freedom stall flutter, torsional flutter, etc. The value of St decreases slowly as the cooling towers in which the ratio of the diameter or ratio of length to maximum transverse width decreases, the minimum lateral dimension to the wall thickness is of the reduction being up to about half the value, if the structure is order of or more are prone to ovalling oscillations.
Vortex shedding need These oscillations are characterized by periodic radial not be considered if the ratio of length to maximum transverse deformation of the hollow structure.
The across wind design peak base overturning moment and tip deflection shall be where calculated using Level at which action effects are calculated.
Other notations are 1 same as given in A reduced value of 0.
Calculation of across wind response is not required for lattice towers. Sl Kind of Structure Damping k No. Turbulence Intensity of 0. NUMBER a Above height hx , the velocities shall be In cases of transition from a low terrain category determined in accordance with the rougher number corresponding to a low terrain roughness to more distant terrain; and a higher terrain category number corresponding to a b Below height hx, the velocity shall be taken rougher terrain , the velocity profile over the rougher as the lesser of the following: In cases of transition from a more rough to a less rough NOTE Examples involving three terrain categories are terrain, the velocity profile shall be determined as shown in Fig.
In such cases, the average value of the terrain upwind of considered to extend 1. Otherwise the feature should be treated a Fig. Examples of typical features are given b Fig. NOTE Where the downwind slope of a hill or ridge is more NOTES than 3, there will be large regions of reduced accelerations or 1 No difference is made, in evaluating k 3 between a three even shelter and it is not possible to give general design rules dimensional hill and two dimensional ridge.
Values of s 0 from Fig. D-1 The wind force on any object is given by: For most shapes, the force coefficient remains approximately constant over the whole range of wind FIG.
However, for objects of circular cross-section, it varies considerably. For a circular section, the force coefficient depends on the way in which the wind flows around it and is dependent upon the velocity and kinematic viscosity of the wind and diameter of the section.
The force coefficient is usually quoted against a non-dimensional parameter, called the Reynolds number, which takes into account of the velocity and viscosity of the flowing medium in this case the wind , and the member diameter. It can be seen that the main effect of free-stream turbulence is to decrease the critical value of the The dependence of a circular sections force coefficient parameter D Vd.
For subcritical flows, turbulence can on Reynolds number is due to the change in the wake produce a considerable reduction in Cf below the steady developed behind the body.
For supercritical flows, this effect At a low Reynolds number, the wake is as shown in becomes significantly smaller. As If the surface of the cylinder is deliberately roughened Reynolds number is increased, the wake gradually such as by incorporating flutes, riveted construction, changes to that shown in Fig.
Member Secretaries Shri S.
The Committee observed that there has been a growing awareness among the consultants, academicians, researchers and practice engineers for design and construction of wind sensitive structures. In order to augment the available limited good quality meteorological wind data and structural response data, it is necessary to conduct full scale measurements in the field.
Thus as emphasized in the previous revision, all individuals and organizations responsible for putting-up of tall structures are encouraged to provide instrumentation in their existing and new structures transmission towers, chimneys, cooling towers, buildings, etc at different elevations at least at two levels to continuously measure and monitor wind data. The instruments are required to collect data on wind direction, wind speed and structural response of the structure due to wind with the help of accelerometer, strain gauges, etc.
It is also the opinion of the Committee that such instrumentation in tall structures shall not in any way affect or alter the functional behaviour of such structures. The data so collected shall be very valuable in evolving more accurate wind loading of structures. The Committee responsible for the formulation of this standard has taken into account the prevailing practice in regard to loading standards followed in this country by the various authorities and has also taken note of the developments in a number of other countries.
In the formulation of this code, the following overseas standards have also been examined: Actions on structures Part The composition of the Committee responsible for the formulation of this Code is given at Annex E. For the purpose of deciding whether a particular requirement of this standard is complied with, the final value observed or calculated, expressing the result of a test or analysis, shall be rounded off in accordance with IS 2: The number of significant places retained in the rounded off value should be the same as that of specified value in this standard.
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Users of Indian Standards should ascertain that they are in possession of the latest amendments or edition by referring to the latest issue of BIS Catalogue and Standards: Monthly Additions. Amend No. Patnaikuni and Sankili Reynold 1. The post cyclonic reports revealed that the telecommunications towers also get damaged even though the recommended design guidelines have been followed according to IS Part-3 code .
In the world, economic losses of the wind damages for the tele communications towers are gradually increasing . The cyclonic wind characteristics such as turbulence intensity and length scales, spectral energy etc. In the dynamic analysis of structures the IS Part 3  recommended the distinct peak factors for approaching upwind velocity fluctuations and resonance conditions.
For safety of structures besides these factors the code  specified the cyclonic importance factor of 1. The offshore wind velocity factor of 1.
Telecommunication towers are tall and self-supporting structures are designed for supporting antennas used for microwave transmission for communication sector and categorized as tri-pole and angular space structures. They act as cantilever space frames designed to carry wind loads predominantly. With the exponential growing subscribers additional towers needed for increased capacity across the urban areas in the coastal region.
The tri pole towers with circular hollow sections as a profile leg members and bracings as flat members are known as a hybrid three legged tower. These towers have less wind drag coefficients when compared to flat members in angular profile towers , hence less material components are required. The objective of this paper is to find the effect of cyclonic importance factor on 40 and 60m high hybrid tri pole telecommunication towers according to Indian Standard codes of IS Part 3 version and make a comparison with version of static analysis with the STAAD Pro 8i version Software .
During the past couple of decades, there seems to have increased the incidence of cyclones  Santhosh Kumar et al  outlined the historical development of introduction to Cyclonic importance factors k4 factor in India. The impact of a k4 factor on A-type and Lean- to roof trusses for static analysis was examined.
It was concluded that there was a substantial increase of internal forces when the k4 factor was 1. During the last 10 years, we have seen an enormous expansion in the population of towers and masts due to the phenomenal growth in the television coverage and mobile phone networks  In the dynamic analysis, even though IS Part3 :  code specified the different gust factor coefficients for background and resonance conditions, cannot guarantee the design of the towers in cyclonic prone areas.