International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395 -0056
Volume: 04 Issue: 05 | May -2017
p-ISSN: 2395-0072
www.irjet.net
Analysis of R.C. building frame with raft foundation considering soil structure interaction Venkatesh M. B.1, R. D. Deshpande2 1Post
graduate student, Civil Department, KLS Gogte Institute of Technology, Belagavi, Karnataka, India Assistant professor, Civil Department, KLS Gogte Institute of Technology, Belagavi, Karnataka, India ---------------------------------------------------------------------***--------------------------------------------------------------------“The common design practice for dynamic loading Abstract – “Civil engineering structures such as building 2
assumes the building frames to be fixed at their bases. In reality, supporting soil medium allows movement to some extent due to its natural ability to deform. This may decrease the overall stiffness of the structural system and hence, may increase the natural periods of the system. Such influence of partial fixity of structures at the foundation level due to soilflexibility in turn alters the response. On the other hand, the extent of fixity offered by soil at the base of the structure depends on the load transferred from the structure to the soil as the same decides the type and size of foundation to be provided. Such an interdependent behaviour between soil and structure regulating the overall response is referred to as soil structure interaction.”
must have sufficient safety margin under dynamic loading like earthquake. The dynamic performance of a RCC building can be determined accurately that requires appropriate modelling considering foundation-soil, building-foundation and soil interactions. Building-foundation-soil interactions are complex phenomena requiring advanced mathematical and numerical modelling. The soil-structure interaction plays an important role particularly when subjected to seismic excitation, due to the potentially disastrous consequences of a seismic event. In the present work effectiveness of modelling in software for determination of seismic behavior of the medium rise building over raft considering soil flexibility interaction is studied. Modal analysis of building system is carried out in software. For the analysis, three dimensional multiple bays regular RC building model for eight storeys is considered and the soil beneath the structure is modelled as equivalent soil springs connected to the raft foundation. The response spectrum analysis of the soil-structure model was carried out using the general software STAAD.Pro. In both the cases (fixed base and flexible base) of modelling the structure, the earthquake records have been scaled according to the Indian Standard 1893-2002 for each type of soil (i.e. I, II & III) and applied to the ordinary moment resisting frame with seismic zone III, zone IV and zone V.”
2. LITERATURE REVIEW Bhojegowda V T and K G Subramanya (2015): Present study provides systematic guidelines for determining the natural periods of framed buildings due to the effect of soilflexibility and identification of spring stiffness for different regular and irregular story buildings and various influential parameters are identified. The study were carried out for building with isolated, mat and pile foundations for soft, medium and hard soil conditions. It is observed that framed structure with pile foundation resting on hard, medium and soft soil can be treated as fixed since no much variation in the response of the structure. Famed structure with mat foundation possesses high foundation stiffness than isolated foundation hence base shear for mat foundation has increased and other parameters like displacement, bending moment and time period were reduced.
Key Words: Dynamic soil-structure interaction, Seismic response, STAAD.Pro, Natural period, Spring stiffness, Displacement, Mat foundation.
1. INTRODUCTION “Earlier structures and foundations were dealt in complete isolation, where the structural and geo-technical/foundation engineers hardly interacted. While the structural engineer was only bothered about the structural configuration of the system in hand he hardly cared to know anything more about soil other than the allowable bearing capacity and its generic nature, provided of course the foundation design is within his scope of work. On the other hand the geotechnical engineer only remained focused on the inherent soil characteristics like (c, φ, Nc, Nq, Nγ, eo, Cc, G etc.) and recommending the type of foundation (like isolated footing, raft, pile etc.) or at best sizing and designing the same. The crux of this scenario was that nobody got the overall picture, while in reality under static or dynamic loading the foundation and the structure do behave in tandem.”
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F. Behnamfar, M. Banizadeh (2016): The authors established nonlinear dynamic response of buildings on two different soft soils including soil–structure interaction. For each building on each soil type a suit of 10 consistent earthquake motions were considered and scaled through a rational procedure. Responses of buildings including maximum base shear, story drift, and plastic hinge rotation were calculated. The rotations of plastic hinges of beams and columns of each story were calculated as absolute values of maximum rotations at each point averaged between the 10 associated earthquakes. RCC buildings being 3, 5, 6, 8, 9 stories high, resting on soft and very soft soil types, once with moment resisting and once with concrete shear walls are considered. The analysis is done for both fixed-based and flexible-base buildings. The results show that for a flexible
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