Nagesh R. Iyer

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.

Seismic Response Measurement of an Under‐Water Model Through High Speed Camera and Feature Tracking

Shake table testing is a viable validation tool for bench-marking the analytically computed seismic response of under-water structural models with fluid–structure interaction effects. Conventional displacement sensors like LVDTs (linearly variable differential transformer) cannot be used for under-water response measurements as they require a stationary platform near the measurement point as a reference. This rather limiting application of LVDTs in several situations warrants the use of high speed camera as a potential measurement tool. This article presents the vision based displacement measurement of an under-water model tested on a shake table. High speed video camera is used to record the motion during shaking. The video images are processed using a special motion tracking algorithm and displacements are measured. The sloshing effect of water on the test model and their free vibration at the end of the shaking are studied to calculate natural frequency and damping. Vital information on the allowable under-water motion of the test model is obtained and discussed.

Seismic protection of critical infrastructures through innovative technologies

Development of new technologies for seismic protection will better support the sustainable urban systems. The paper focuses on development of an innovative technology for seismic protection of bridges using smart materials. The seismic protection of structures with the use of special devices is widely accepted as a very effective technique, both for new constructions and for retrofitting of existing ones. Shape memory alloys show the potential to eliminate the limitations of the present technologies, presenting broader application domain. Damper cum restraining device with recentering capabilities has been developed within the laboratory and shake table experiments were conducted on an equivalent SDOF system for a specific narrow band spectrum. The model was subjected to a strong resonant earthquake ground motion in the horizontal direction and analytical investigations were carried out. The damper is found to be very effective for seismic performance enhancement of critical facilities like bridges offering great benefits for the sustainable development of urban systems.

Numerical Investigations of Aerodynamic Forces on 2-D Square Lattice Tower Section Using Two-Equation Turbulence Models

Wind flow around lattice towers is a complex phenomenon involving interference effect between various leg/bracing members. Wind induced forces on such lattice towers are evaluated by considering overall effect on the grouped members and are related to solidity ratio. Most of the codal provisions on drag coefficient values for lattice towers are based on sectional model studies, carried out in wind tunnel for various solidity ratio values. In the present study, numerical studies on 2-D square lattice tower section have been carried out for different solidity ratio values using various turbulence models, viz. Realizable k–e model, two versions of RNG k-e model and SST k–ω model. The numerically evaluated mean drag coefficient values have been compared with those provided in various international codes to assess the relative performance of these turbulence models.

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

Numerical Assessment of Aerodynamic Forces on 2-D L-Angle Section Using CFD

Numerical simulations of aerodynamic forces on regular shaped bluff-bodies using CFD have been well reported in the literature as part of validation. In the present study, CFD simulations have been carried out on a 2-D Langle section using different Reynolds-Averaged Navier Stokes (RANS) based turbulence models to assess their performance in evaluating drag and lift coefficients for various angles of wind incidence. Mean drag and lift coefficients for the 2-D L-angle section have been evaluated under uniform smooth flow conditions using FLUENT 6.3 software. The performance of these turbulence models are assessed by comparing the numerically evaluated force coefficients of the 2-D L-angle section with the experimental results available in literature and also with the values provided in various international standards. SST k– model is observed to perform better in evaluating the above mentioned aerodynamic coefficients than other turbulence models, which are observed to perform better only in evaluating mean lift force coefficients than mean drag coefficients. Further, comparison of the numerically evaluated mean pressure coefficient distributions on various sides of the 2-D L-angle section have been made to discuss the relative performance and the limitations of the considered turbulence models.

Seismic performance of polymer modified concretes in flexure-modelling

Considerable research has been carried out in the recent years in the development of models to simulate the inelastic responses of reinforced concrete elements. The enhancement of ductility and the post-peak behaviour are of special interest for the seismic design of structures. Polymer modified fibre concretes are found to be ideal for seismic application with its inherent structural characteristics. An experimental investigation has been undertaken to understand the flexural behaviour of the polymer-modified fibre concrete modified with natural rubber latex. The results are compared with the response of normal strength concrete beam. Analytical modelling of the beams were carried out in a user friendly finite element software to accurately predict the monotonic behaviour of the beams which is considered to be the envelope of cyclic curve. The strains developed were found and are compared with the theoretical results.