S. Selvi Rajan

Experimental Determination of Wind-Induced Response on a Model of Natural Draught Cooling Tower

The detailed and well-publicized documented paper by Bamu and Zingoni in 2005 on cooling-tower collapses accentuates the effect of wind on the performance of cooling towers. As it is well established that wind-tunnel tests on tower models result in a more realistic assessment of wind-induced stresses, wind-tunnel tests are conducted on aero-elastic model of an isolated cooling tower and the cooling tower with surrounding structures. The details of the experimental programme, measurements, analysis, and results for both the isolated and interference cases are presented in this paper. Based on the analysis of experimental data, ring-resonance frequencies, and mode shapes of the model, meridional (Nϕ) and hoop (Nθ) stress resultants and interference factor due to the presence of surrounding buildings are evaluated. The values of Nϕ, Nθ, ring-resonance frequencies, and mode shapes for isolated model are further compared with the values obtained based on finite element analysis.

Interference Factors for Natural Draught Cooling Towers Based on Wind Tunnel Experiments

Wind tunnel experiments were conducted under simulated terrain category 2 for evaluating interference factors using pressure models on four sets of cooling tower models, each when located in tandem. The full-scale dimensions of the cooling towers are 180 m, 165 m, 173m, and 143 m heights with diameters at throat, Dth, of 79 m, 71 m, 70 m and 61 m, respectively. The tower corresponding to 165 m height had a geometric scale of 1:500 and the rest of the models corresponded to 1:300 scale. The model of 165 m tall cooling tower was additionally tested under increased turbulence intensity corresponding to terrain category 3. The tests were conducted for various non dimensionalised spacing, r=a/Dm, ranging from 1.4 to 10, where a is the c/c distance between the models and Dm is the mean diameter, defined as the mean of bottom diameter and Dth. Measurement of pressures was carried out at 30 interval at four levels for all the models. The paper consolidates the data base of experiments conducted at CSIR-SERC to see whether there is a discerning pattern in interference factors that can be recommended for design.

Correlations of aerodynamic pressures for prediction of across wind response of structures

Abstract Correlation length is one of the four important aerodynamic parameters, which is required for prediction of across-wind response of a structure subjected to vortex shedding. Pressure measurement studies on models of three structures with different plan shapes- a circular, an octagonal and an irregular shape, were conducted under simulated open terrain conditions using the boundary layer wind tunnel. This paper presents experimental details and test results on pressure distributions and measurement of correlation lengths. It is shown that for the circular and octagonal models studied, the modified value of rms lift coefficient, C L , V ′ is found to be close to 0.088. Further, for the irregular shaped tower block model also, for the wind angle where the mean across wind force is very small, the value of C L , V ′ is found to be around 0.088. Further research is necessary for validating the value of 0.088 for structures with other cross-sectional shapes.

Stochastic gust response of microwave lattice towers

Abstract Microwave lattice towers of heights up to about 100 m are constructed in large numbers for the requirement of an increasing network of electronic communication systems. Wind load, which is basically dynamic in nature, is the main design force for these free-standing lattice towers. The dynamic response of wind sensitive structures subjected to a random wind force can be computed using stochastic analysis. In this paper, a spectral approach for computation of the along-wind response and the gust response factor of microwave lattice towers is presented. A computer program has been developed for the calculation of the gust response factor, the along-wind response of lattice towers and wind characteristics using this spectral method. The gust response factor computed for a microwave lattice tower of 101 m height by this method is compared with the values calculated using the formulae recommended in the Indian, the Australian, the British and the ASCE Standards.

Alpha-Stable Distribution for Prediction of Negative Peak Wind Pressures on Roofs of Low-Rise Building

In this paper, an attempt is made to study the applicability of alpha-stable distribution for modeling the negative peak wind pressures on low-rise building roofs. The required wind pressure data is obtained from the aerodynamic database of Tokyo Polytechnic University. The generality and flexibility offered by alpha-stable distribution makes it a candidate distribution as a single model for predicting the extreme values of negative peak wind pressure coefficients at different regions on the building roof. The results suggest that for the prediction of extreme negative wind pressure coefficients, alpha-stable distribution is a better candidate distribution than the Gumbel minimum.

Wind Tunnel Investigations on a Tall Building With Elliptic Cross Section

According to a statistics revealed by Council of Tall Building and Urban Habitat [1] that for every 11.5 millions of global population, there is one tall building with 200 m+ in height available globally. Tall building constructions are paving ways for rapid urbanization worldwide including India, especially during the last one decade and will be continued over next few decades. Wind loads are one of the most important loads that govern the design of tall buildings. Published data on pressure and force coefficients for 3-D building with elliptic cross section under boundary layer flows are very scanty. This paper presents the results on mean force coefficients obtained through wind tunnel pressure measurements carried out on a 3-D tall building with elliptic cross section for various angles of wind incidence under suburban terrain. It is found that the mean pressure distributions and force coefficients depend significantly upon the angle of wind incidence.

Estimation of Gust Response Factor for a Tall Building Model with 1:1.5 Plan Ratios

The purpose of structural analysis and design of structures as per the building codes and its corresponding standers is to ensure the safety of structure under maximum loads and remains functional under service load. The structure which is designed under consideration of codes should also satisfy the durability, economy and aesthetics. The primary purpose of this work is to understand and compare design wind loads according with the Gust Response Factor as per codes of practices. The paper is concerned with the calculation of design wind loads on a rectangular building model (1:300gemetric scale) of size 10cm x 15cm x 70cm with an aspect ratio of 1:1.5:7 at eight different levels over the height under sub-urban terrain category for 00 angle and 900 angle wind incidence. The experiment id conducted in an atmospheric boundary layer wind tunnel facility of CSIR-Structural engineering Research centre, Chennai. The measured pressures are integrated to evaluate mean and RMS (Root, Mean, Square). Further the variation of above mentioned loads and response factor along the heights of the building with respect to sub-urban terrain condition are discussed and summarized in addition, the codal values of various international standards [IS-875 part-3 1987, IS-875 part-3 draft, ASCE-07] have also considered for comparison.

Wind Induced Interference Effects on a Row of Three Buildings with Irregular Plan Shape

P. Harikrishna, A. Abraham, S. Selvi Rajan, G. Ramesh Babu, S. Chitra Ganapathi, and Nagesh R. Iyer Principal Scientist, CSIR-Structural Engineering Research Centre, Chennai, TN, India, hari@serc.res.in Senior Scientist, CSIR-Structural Engineering Research Centre, Chennai, TN, India, abraham@serc.res.in Chief Scientist, CSIR-Structural Engineering Research Centre, Chennai, TN, India, sselvi@serc.res.in Principal Scientist, CSIR-Structural Engineering Research Centre, Chennai, TN, India, gramesh@serc.res.in Scientist, CSIR-Structural Engineering Research Centre, Chennai, TN, India, chitrag@serc.res.in Director, CSIR-Structural Engineering Research Centre, Chennai, TN, India, nriyer@serc.res.in