American Journal of Civil Engineering and Architecture
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Open Access journal
ISSN (Print) 2328-398X - ISSN (Online) 2328-3998
Published by Science and Education Publishing [72 journals]
- Adfreeze Forces on Lightly Loaded Pile Foundations of Solar PV Farms in
Authors: Kibriya T; Tahir L.
Pages: 109 - 117
Abstract: Renewable energy generation through utility scale ground mounted solar photo-voltaic systems has gained steady popularity with increasing number of such facilities being constructed in various regions worldwide. Solar PV systems are very popular in the province of Ontario in Canada and strong growth in this sector is led by the popular initiatives of the Government of Ontario which offers extremely attractive rates for generation of renewable energy through Ontario Hydro’s popular Feed-In Tariff (FIT) Program. Many other countries offer incentives on such generation of renewable energy while many governments aim at increasing the percentages of renewable energy in their systems tremendously. Most ambitious plan has recently been launched by the state of Hawaii to deploy 100% of renewable energy in their grid by 2045. Solar PV systems are a cheap source of renewable energy as the energy released by the sun is harnessed as electricity by the solar photo-voltaic panels which is fed to the main transmission systems after raising its voltage. The costs of solar photo-voltaic panels meanwhile have also kept downward trends while the manufacture of various types of solar panels has multiplied rapidly. These renewable energy generation facilities are fully sustainable being completely recyclable on completion of their design/ contract period. Typical utility scale ground mounted solar PV facilities usually comprise of solar PV panels mounted on series of racking tables supported on foundations mostly comprising of partially embedded steel pipes. The governing loads for the foundations of these lightly loaded solar PV structures are usually frost loads in areas facing extremely cold winters. In fine grained soils like silty/ clayey soils, large adfreeze stresses develop due to penetrating frost deep into the soil resulting into uplift of foundation piles. Typical winter conditions in Ontario are harsh with extreme frost conditions in most areas which poses unique issues for design and construction of such foundations. Being a relatively newer technology, codes and standards for design and testing of such lightly loaded solar PV structures are still in the formulation stages. Frost heaving and its effects often create adverse conditions for these structures thereby affecting the production and continuous supply of renewable energy. Due to larger depths of frost penetration in extreme winter conditions, understanding the action of frost and related development of adfreeze stresses on these lightly loaded pile foundations is extremely important. Calculating reasonable frost depths and thereby the design loads is an important part of pile design for such facilities while the contractors tend to save on pile lengths to save on costs and compromising the structural design. Many such Solar PV facilities have experienced frost uplift of foundation piles either during the construction phase or during its lifetime. Since frost heave is more of a serviceability related issue, unfactored adfreeze loads without any factor of safety is a usual tendency by the EPC contractors. This paper investigates the frost depths and adfreeze stress related issues with the foundation piles of solar PV facilities hence the governing design forces on these piles and suggests appropriate frost related design stresses for the foundation piles. The authors have been heavily involved in design/ design reviews, pile selection/ design and pile load testing in the majority of the solar PV farms in Canada and US along with rehabilitation of piles affected by frost [1,2,3].
Issue No: Vol. 3, No. 4 (2015)
- Traditional vs FEA Based Analysis/Design of Baseplates for Tall
Telecommunication & Transmission Poles
Authors: Tahir Kibriya; Leena Tahir
Pages: 118 - 128
Abstract: Various shapes of steel poles are commonly used in the telecommunications and transmission industry for carrying telecommunication equipment to transmit signals for communication equipment or wires and power equipment like transformers etc. for power transmission purposes. These poles vary from 50’ to almost 500’ heights with winds being the governing loads in addition to superimposed equipment loads and snow/ice loads and hence require careful design. The poles vary from being round in geometry to 8/12/16/24/28 sided shapes. With large base diameters and appreciable moments and direct loads, typically the pole baseplates are round, hexagonal or square with/without stiffeners and either rest on the supporting anchor rod base nuts or on grout over the base support, all of which require different analysis/ design procedures. From the literature, one can observe that while baseplate analysis and design for large poles structures has not been amply investigated, limited investigations and testing carried out on base plates designed by various methods and most test results have indicated most procedures to be under designing plates. While AISC and ASCE 48 codes provide limited guidance on design of these various types of pole baseplates, ANSI/EIA/TIA 222F & 222G codes merely refer to AISC for design of these different configurations of baseplates. Many proprietary base plate analysis/design worksheets commercially available produce different results. With the availability of advanced structural analysis techniques like FEA, a comparison is made between the baseplates designed by typical methods using commercially available baseplate worksheets and those designed by using the FEA techniques. The analysis results vary appreciably between the traditional methods and the FEA based method. This paper analyses few pole base plates based on FEA and compares them with the baseplates designed by traditional methods and suggests appropriate improvements in the current design/ analysis procedures so as to reduce the appreciable differences between the both procedures.
Issue No: Vol. 3, No. 4 (2015)