Review on Shell Foundation

ISSN (Online) 2278-1021 ISSN (Print) 2319-5940 IJARCCE International Journal of Advanced Research in Computer and Communication Engineering PCON-2019 National Conference and Seminar on Innovations in Engineering & Technology Govt Polytechnic College, Palakkad Vol. 8, Special Issue 1, January 2019 Review on Shell Foundation 1 Yogesh R M.Tech Structural Engineering, NSS College of Engineering, Palakkad India 2 Pro. Krishnachandran VN Assistant Professor Dept. of civil engineering NSS College of Engineering, Palakkad India 3 Mahima Ganeshan Research scholar Sri Krishna College of technology Coimbatore. India Abstract: Foundations are structure which is used to transfer the load coming from super structure to soil safely without failure. The Foundations should be structurally strong to resist the distress, bearing capacity failure and excessive settlement due to earthquakes. The performance of shells in roof structures initiated the idea of using shells as foundations. Shallow foundations and deep foundations which are generally the first preference in foundation design under favourable conditions are generally more vulnerable to earthquake damage. Among shallow foundations, shell foundations are expected to perform better as they are an economical alternative to plain foundations where heavy super structural loads are to be transmitted to weaker soils. There are various types of shells used in foundations like hyperbolic paraboloid shell, conical shell, inverted dome, elliptic paraboloid, pyramidal shell, triangular shell, cylindrical shell, inverted spherical shell etc. Shell foundations are economic alternatives to plain shallow foundations in situations involving heavy super structural loads to be transmitted to weaker soils. The development in analysis and design of shell type foundations have led to the understanding that there are more advantages of shell type foundations compared to their conventional footing. In this paper includes, the various shell foundation used in practice, parametric study of shell footing and a comparison of behavior of shell footing with conventional footing and an overview of shell foundation. Keywords: shell foundation, earthquake, plain foundation. I. INTRODUCTION A foundation is that part of a structure which transmits the weight of the structure (include dead load, self-weight of the structure and live load during service condition) to the ground with safely without failure. All structures connected on the land are supported by foundation. A foundation is therefore a connecting link between the structure proper and the ground which support it. Retaining structure is built to restrain the earth as in the case of basement of building. The word “foundation” is derived from the latin word fundare meaning to set or ground on something solid. In other words a foundation is a n artificially laid base on which structure is set or build up. A foundation is required for distributing the load of the super structure on a large area. The foundation should be designed such that  The soil below does not fail in shear.  The load coming from the super structure is less than that of the allowable soil pressure. The pressure which the soil can safely withstand is known as “allowable soil pressure”.  Settlements are within the safe limit [6,9]. The foundation may be broadly classified themselves as, 1. Shallow foundation (a shallow foundation transmits the loads to the strata at a shallow depth. The depth is less compared with other dimension.) 2. Deep foundation (a deep foundation is transmits the load at considerable depth while comparing the depth of foundation is higher than the plan dimensions). 3. Special foundation is used for special structures such as transmission towers, cooling towers and chimneys. Shell foundations are considered cost – effective when heavy loads are to be carried by weak foundation soil. Such situations required large sized foundations because of the low bearing capacity of the soil. If we use bending members such as slabs and beams, the bending moments and shears in them will be large and the sections required will be also be large. Shells which act mostly in tension or compression will be more efficient and economical in such situations. Even in small foundations, the amount of materials i.e. Necessary for a shell to carry a load will be considerably less than that required for bending members such as beams and slabs[1]. However, the labour involved in shell Copyright to IJARCCE IJARCCE 1 IJARCCE ISSN (Online) 2278-1021 ISSN (Print) 2319-5940 International Journal of Advanced Research in Computer and Communication Engineering PCON-2019 National Conference and Seminar on Innovations in Engineering & Technology Govt Polytechnic College, Palakkad Vol. 8, Special Issue 1, January 2019 constructions (in forming the shell surfaces, fabricating steel, super vision, etc.) will be more than that necessary in conventional type of foundations. Thus in such special situations, one can considered the use of shells as foundations. The research on shell foundations can be divided into two main categories: Structural performance and geotechnical performance. The first category concentrates on structural performance of reinforced concrete shell foundations with respect to membrane stresses, bending moment, shear, deflection and ultimate strength of shell. The results of the research in this category bring out the savings of concrete and steel reinforcement as compared to conventional flat foundations. The second category involves the geotechnical behavior of shell foundations to determine the soil response with respect to settlement, ultimate bearing capacity, contact pressure distribution, lateral and vertical stresses and displacements induced with in the soil mass [7,8,9]. II. CLASSIFICATION OF SHELLS The shapes of shells commonly used in civil engineering are shown in fig .1 and flow chart of shell foundation is shown in 2. Fig. 1. Classification of shell Fig.2. Flow chart of classification of shell    III. ADVANTAGES OF SHELL FOUNDATION Pre–casting and pre–stressing are two major advantages shells offer. The ability to construct shell sub–structures like footings, easily transported to site on account of their light weight[2,11]. It would have potentially significant time and cost saving implications for a project. Copyright to IJARCCE IJARCCE 2 IJARCCE ISSN (Online) 2278-1021 ISSN (Print) 2319-5940 International Journal of Advanced Research in Computer and Communication Engineering PCON-2019 National Conference and Seminar on Innovations in Engineering & Technology Govt Polytechnic College, Palakkad Vol. 8, Special Issue 1, January 2019             They were proven to provide higher bearing capacity. Settlement is less. It minimizes the cost of foundations through reducing the ratio of steel reinforcement. Minimizing or even eliminating the tension zone in the folded strip footing. Higher resistance to lateral loads as compared to their conventional flat counterparts. Construction of structure is possible in the case of low bearing capacity soil. IV. DIS ADVANTAGES OF SHELL FOUNDATION Shell when used in foundation structures is undeniably present. High labour costs associated with erection and in terms of constructability, Shells require specialized formwork contractors with skilled and experienced labour force. Shell foundation designers should give serious thought to construction methods involved which have major impact on cost functions at times and under extreme circumstances render unfeasible. present–day unavailability of code for design and construction of all types of shell footings, Unskilled labour, inexperienced and lagging construction methodologies are all major shortfalls requiring well–deserved attention in using shell foundations (Kurian, 2006). V. SUMMARY OF LATEST RESEARCH Over the time, shells have experienced marked development in foundation engineering, especially throughout the past half century from its initial inception in the early nineteen-fifties, particularly in the aftermath of World War II. Intrigued researchers have gained interest in their form as enclosures such as bunkers and refugee strongholds, having withstood the destruction and devastation of the time and found to remain largely intact. In a continued effort to explore the shell’s interesting performance attributes in footing applications, a literature review on shell foundation has been conducted and is presented. The first recognized use of shell foundations dates back to the early 1950’s by the Spanish architect, Felix Candela, regarded as conceptual pioneer and fore father of the shell foundations notion [8]. Experimenting with shell shapes, Candela’s concern for elegance and style were his underlying motivations in opting for a structural shell. This conviction led to an extensive exploration of shell structural forms many of which are still in existences today. The hyperbolic paraboloid or otherwise known as “hypar” shell footing, Jadik and Billington (1995) analyzed gabled hyperbolic paraboloid roofs without edge beams using finite element models. The elimination of the edge beams from the structure seems a valid move when considering the results obtained from finite element analysis [5]. Kurian and Devaki (2005) have done analytical studies on the geotechnical performance of shell foundation. Three configurations of conical, spherical and hypar shells have been taken. The influence of coefficient of friction and different loading conditions were studied. The software NISA (Numerical Integrated elements for System Analysis) was used. It was seen that the bearing capacity increases with increase in interface roughness. Increase of 157 %, 151 % and 200 % from perfectly smooth to rough condition for circular, conical and spherical footings, respectively was obtained. The conical hypar footing in upright position subjected to moments shows decrease in bearing capacity of 68 % and 75 %, respectively. Hypar footing in upright position loaded double eccentrically suffers a 53 % decrease in bearing capacity. Huat and Mohammed (2006) analyzed the geotechnical behavior of triangular shell footing using a nonlinear finite element analysis with the finite element code, PLAXIS. From the finite element results, it is found that the shell footing had a better load carrying capacity compared with slab/flat footing for similar cross sectional area. [3] Huat et al. (2007) studied the performance of upright triangular and inverted triangular shell footings using finite element software LUSAS. Nonlinear Drucker – Prager constitutive law was used to model the soil. The foundation was modeled with von Mises. The finite element analysis showed that the inverted triangular shell footing had higher load carrying capacity compare with other strip footings. The load carrying capacity of the inverted Copyright to IJARCCE IJARCCE 3 IJARCCE ISSN (Online) 2278-1021 ISSN (Print) 2319-5940 International Journal of Advanced Research in Computer and Communication Engineering PCON-2019 National Conference and Seminar on Innovations in Engineering & Technology Govt Polytechnic College, Palakkad Vol. 8, Special Issue 1, January 2019 triangular shell footing was about 15 % and 28 % higher than the upright triangular shell footing and conventional flat footing, respectively. The load carrying capacity of shell footings was found to increase by around 15 % when the shell thickness increased from 10 cm to 15 cm, and increased by 20 % with the increase of shell angle from 26° to 45°. Frenando et al. (2011) conducted a laboratory model test on the bearing capacities of conical and pyramidal shell foundations on dry sand. The results were compared with those of circular and square flat foundations, respectively. Two layers of color sand non-color sand have been used to identify the failure pattern of sand. The ultimate capacities of shell foundations are higher than that of their flat counterpart with same plan dimensions. The conical shell footing has better settlement characteristics compared to pyramidal shell footing. Shaligram (2011) examined triangular shell footing as a strip footing resting on two – layered sand, reinforced with geo-textiles. The upper layer of sand is weaker than underlying layer. The models of triangular shell strip footings with 60°, 90°, 120°, 150° and 180° (flat footings) apex angles were used as triangular shell strip footing. The strip footing was placed on homogenous sand, reinforced with geo-textiles at different depth. The result indicated that the ultimate bearing capacity of the flat footing is lowest among all geo-reinforced cases. The ultimate load increases with the provision of shell footing with decrease in apex angle. The geo-textile layer at various levels below the footing shows increase in ultimate bearing capacity and decrease in settlement [15]. Shahbas (2014) investigated the performance of conical shell footings considering spectrum of Kobe earthquake by using FEM softwares MSC.Patran, MSC.Mentat for pre and post processing and MSC.Marc for analysis considering various aspects. From the structural aspect, effect of the rise to radius ratio of conical shell footings has an influence on the seismic resistance. Rise to radius ratio of 0.75 shows better performance under seismic conditions [14]. Sameena (2015) investigated the performance of inverted spherical shell footings considering spectrum of Kobe earthquake by using ANSYS software for analysis. Various aspects considered in the analysis were semi-vertical angle, interface roughness and soil properties. From the structural aspect, effect of the semi-vertical angle of the shell has an influence on the seismic resistance. It was also found that the rise of shell foundation, shell-soil contact condition and soil properties have a greater influence in the performance in terms of reduced settlement and stresses were obtained [13]. W R Azzam, A M Nasr (2015), series of loading test was carried out a model shell foundation with and without reinforcement of single layer. This study compared with flat footing with and without reinforcement. using PLAXIS software he found that the ultimate load carrying capacity of foundation with reinforcement is higher that of unreinforced case. Syed Jalaludeen Shah, Anu Sidhardhanan (2016), This work studies the performance of hyperbolic paraboloid shell footings under static and seismic loading using Finite Element Methods (FEM). The investigation is conducted using the FEM Software ANSYS version 15. Time history analysis is conducted to obtain the response of various parameters studied. The spectrum of Kobe earthquake has been used for the seismic analysis[16]. Sayed Abdel Salam, Mahmoud Amir Elkady (2017), in this paper he was study is minimize of the % steel reinforcement with shape reduction and optimization of the structure using shell foundation. The folded strip footing was used instead of rectangular strip footing. The structural and geotechnical performance are both footing studied and the relative parameters were investigated. The % reinforcement is 26% is reduced and cost of construction was reduced by 18% for shell footing compared with ordinary strip footing [10]. Copyright to IJARCCE IJARCCE 4 IJARCCE ISSN (Online) 2278-1021 ISSN (Print) 2319-5940 International Journal of Advanced Research in Computer and Communication Engineering PCON-2019 National Conference and Seminar on Innovations in Engineering & Technology Govt Polytechnic College, Palakkad Vol. 8, Special Issue 1, January 2019 VI. CONCLUSION Shell foundation is one of the foundations which are used as an alternative of conventional foundation. Shell foundation is used when bearing capacity of soil is less and when loads are heavy. The failure of foundation is avoided while replacement of ordinary foundation with shell shells foundation extreme conditions. Buckingham-Pi theorem, general equations for the ultimate load of conical and pyramidal shell foundations was attained. The increase of height and dimension of soil core (b, H) leads to the increase of ultimate load values of pyramidal and conical shell foundations. This behavior has two reasons First, the influence of increasing friction force between soil core and shell foundation and the second, the increase of soil core size. By increasing the dry unit weight (γ d), angle of shearing resistance (Φ) and relative density (D r) of sand, ultimate load capacity of shell foundations is also increased. The influence of angle of shearing resistance on the ultimate load values is greater than other parameters. In general, using the folded form of isolated footing resulted in lower soil settlements. The soil at the foundation level can be practically formed into the required folding angle to cast the concrete footing directly on the formed soils. Good agreement is reached between the experimental and numerical results. Various experimental results showed that the maximum tensile stresses in steel bars decreased for folded isolated footing case when compared with conventional flat ones. This decrease will decrease reinforcement quantities needed to cover the generated stresses. The measured and calculated settlements are in good agreement for both the flat and folded bottom footings. However, settlements for the folded isolated footing is much lower than the settlements for the flat bottom footing indicating lower soil stresses in the folded footing case. The failure shape for the folded isolated footings dictate the use of additional reinforcement in the radial direction or using the ring beam at the edge of the folded isolated footing. From the experiments and analytical results compare to convention foundation the folded foundations are better one i.e. settlement are less, folding angle less, % of tensile reinforcement reduction, ultimate load carrying capacity is increases. From all the experiments the shell foundations shows better performance hence shell foundation can be used as an alternative of conventional foundations. REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] Chehol, E. T. (2009). “A study on the design and advantage of conical type shell foundation using analytical and FEM.” M. Tech. Thesis, Addis Ababa University. Fattah, M. Y., Waryosh, W. A. and Al-Hamdani, A. E. (2015). “Experimental and theoretical study on bearing capacity of conical shell foundations composed of reactive powder concrete.” Acta Geodynamica et Geomaterialia, 12(4), 1-16. [Sept. 25, 2015]. Huat, B. B. K. and Mohammed, T. A. (2006). “Finite element study using FE code (PLAXIS) on the geotechnical behavior of shell footing.” Journal of Computer Science, 2(1), 104-108. IS: 9456 (1980). “Indian Standard Code of Practice for Design and Construction of Conical and Hyperbolic Paraboloidal Types of Shell Foundation.” Bureau of Indian Standards, New Delhi. Jadik, T. and Billington, D. P. (1995). “Gabled hyperbolic paraboloid roofs without edge beams.” Journal of Structural Engineering, ASCE, 121(2), 328-335. K R Arora, (2017), “Soil mechanics and Foundation Engineering”, Geotechnical Engineeing, SPD publishers, 636-670. Kurian, N. P. and Devaki. V. M. J. (2005). “Analytical studies on the geotechnical performance of shell foundation.” Canadian Geotechnical Journal, 42, 562-573. Kurian, N. P. (2006). “Shell Foundations: Geometry, Analysis, Design and Construction.” Alpha Science International Limited. Melerski, E. (1988). “Thin shell foundation resting on stochastic soil.” Journal of Structural Engineering, ASCE, 114(12), 2692-2709. Mahmoud Samir El-kady1, Essam Farouk Badrawi, (2018), “Performance of isolated and folded footings”, Science Direct, Journal of Computational Design and Engineering, 150-157. Paliwal, D. N., Sinha, S. N. and Ahmad, A. (1992). “Hypar shell on Pasternak foundation.” Journal of Engineering Mechanics, ASCE, 118(7), 1303-1316. Rinaldi, R. (2012). “Inverted shell foundation performance in soil.” Ph. D. Thesis., Concordia University, Canada. Sameena, K. (2015). “Seismic behavior of inverted spherical shell foundations.” M. Tech. Thesis, University of Calicut, India. Shahbas, A. (2014). “Seismic investigation of conical shell footings.” M. Tech. Thesis, University of Calicut, India. Shaligram, P. S. (2011). “Behavior of triangular shell strip footing on geo-reinforced layer sand.” Journal of Advanced Engineering Technology, II(II), 192-196. Syed Jalaludeen Shah (2016). “Behavior of hyperbolic paraboloid shell footing under point load”, International conference on developments in construction and structural engineering, ICDSE’16. Copyright to IJARCCE IJARCCE 5 IJARCCE ISSN (Online) 2278-1021 ISSN (Print) 2319-5940 International Journal of Advanced Research in Computer and Communication Engineering PCON-2019 National Conference and Seminar on Innovations in Engineering & Technology Govt Polytechnic College, Palakkad Vol. 8, Special Issue 1, January 2019 BIOGRAPHY Mr. Yogesh R holds a B.Tech from Calicut University and pursuing M.Tech in structural engineering from Kerala Technical University. His research interests include seismic studies, shell foundation and composite shear wall. Mr. Krishnachandran VN is Asst. Prof. in the Dept. of Civil Engineering, NSS College of Engineering, Palakkad. He completed his B.Tech in Civil Engineering from Govt. Engineering College, Thrissur and Post-Graduation in Advanced Construction Management from National Institute of Construction Management and Research, Pune. He also holds an M. Tech degree in Structural Engineering and MBA in Project Management. Currently doing PhD at NIT Calicut. He has worked with Hindustan Construction Co. Ltd. and was associated with mega projects like Bandra Worli Sea link, Interlinking of rivers, various hydro electric projects in Greater Himalayas & North East India. He also worked as Asst. Prof. in Sreepathy institute of Management and Technology for a short period. Mrs. Mahima Ganeshan completed her M.E. degree (Structural Engg.) from Karpagam University, Coimbatore and B. Tech degree (Civil Engg.) from N.S.S. College of Engg, Palakkad. She has 5 years of experience in teaching and 5 years in research. She has undertaken two research projects under TNSCST funding and guided M.E & B.E. projects. She also have assisted two KSCSTE funded project. Currently she's pursuing her Doctoral degree in Structural engineering at Anna University, Chennai. Her area of interest include Geopolymers, Self compacting concrete and mineral admixture based concrete. Copyright to IJARCCE IJARCCE 6