35 | P a g e
FINITE ELEMENT METHOD USING SOIL
STRUCTURE INTERACTION ON MULTI-STOREYED BUILDING WITH RAFT FOUNDATION
M. Shanmuganathan
#1, P. Paramaguru
#2#1Post Graduate Student, #2Assistant professor & Ponnaiyah Ramajayam Institute of Science and Technology (PRIST Deemed to be University)
Structural Engineering Division, Department of Civil Engineering & Ponnaiyah Ramajayam Institute of Science and Technology (PRIST Deemed to be University), Thanjavur-613403, Tamilnadu, India
ABSTRACT
The behaviour of multi storey structure considering soil structure interaction i.e. interaction between substructure of the building and soil is presented. For this purpose a sample of 5 storey RC frames is analysed in conventional method with incremental static analysis for various load combinations and determines the parameters displacement, shear force and bending moment. Then a same 5 storey RC frame is analysed in numerical analysis using Finite Element Method (FEM) with raft foundation by assigning the soil properties to substructure and determine the parameters displacement, shear force and bending moment.
According to the analysis results the parameters displacements, shear force and bending moment varies from conventional analysis to numerical analysis. Displacements of the structure increases, shear forces of the structure decreases and bending moment of the structure decreases at some points and increases at some points from conventional method of analysis to numerical method of analysis.
Keywords: Soil Structure interaction, Conventional Method of Analysis, Numerical Method of Analysis, Displacement, Shear Force, Bending Moment
INTRODUCTION
The majority of the civil engineering structures involve some type of structural element with direct contact with ground.
When the exterior forces, such as earthquakes, achieve on these systems, neither the structural displacements nor the ground displacements, are self-sufficient of
36 | P a g e each other. The process in which the
response of the soil influences the motion of the structure influences the reaction of the soil is termed as soil-structure interaction (SSI) Analytical methods effects are well established. When there is more than one structure in the medium, because of interference of the structural responses through the soil, the soil structure responses through the soil, soil structure predicament progress to a cross interaction difficulty among multiple structures.
The development in which the response of the soil influences the movement of the structure and the motion of the structure influences the response of the soil is term as soil-structure interaction. Conventional structural design methods neglect the SSI effects. Investigations of soil structure interaction have shown that the dynamic response of a structure supported on flexible soil may differ significantly from response of the same structure when supported on rigid base. One of the significant purposes behind this distinction is that piece of the vibration vitality of adaptable mounted structure is disseminated by radiation of stress waves in the supporting medium and by hysteretic activity in the medium itself. Expository techniques to figure the dynamic soil- structure communication impacts are settled.
At the point when there is more than one structure in the medium, in light of obstruction of the basic reactions through the dirt, the dirt structure reactions through the dirt, soil structure issue develops to a cross connection issue between different structures. It has expectedly been viewed as that dirt structure communication beneficially affects the seismic reaction of a structure.
Many plan codes have recommended that the impact of SSI can sensibly be dismissed for the seismic investigation of structures. This legend about SSI clearly comes from the bogus observation that SSI decreases the by and large seismic reaction of a structure, and subsequently, prompts improved security edges. A large portion of the plan codes use distorted structure spectra, which accomplish consistent quickening up to a specific period, and from that point diminishes monotonically with period. Considering soil- structure communication makes a structure progressively adaptable and in this manner, expanding the characteristic time of the structure contrasted with the comparing inflexibly bolstered structure. Additionally, considering the SSI impact builds the successful damping proportion of the framework. The smooth romanticizing of structure range proposes littler seismic
37 | P a g e reaction with the expanded common time
frames and successful damping proportion due to SSI. With this presumption, it was generally been viewed as that SSI can advantageously be ignored for preservationist plan. Moreover, dismissing SSI massively lessens the difficulty in the examination of the structures which has enticed originators to disregard the impact of SSI in the investigation.
RELATED WORK
In [1] H.S. Chore, R.K. Ingle, and V.A.
Sawant et al presents the investigation of two categories of piles subjected to creative loads incorporating the non-linear activities of soil.
The finite element research is suppose for express out the parametric modify of the pile compilation. The quantity is idealize as a one dimensional beam constituent, the pile restrict as two dimensional plate elements and the soil as non-linear elastic springs using the p-y curves urbanized. Two groups of piles well-established in a consistent soil, involving two and three piles in succession and parallel grounding thereof are calculated.
The rejoinder of the pile groups is institute to be perceptibly misrepresented by the parameters such as the spacing among the piles, the numeral of piles in an assembly and the direction of the lateral load. From the dissimilarity, it is experimental that the non-
linearity of soil is create to enhance the top displacement of the pile group in the range of 66.4%-145.6%, while lessening the predetermined moments in the collection of 2% to 20% and the positive moments in the selection of 54% to 57%. Further, two arrangements of piles in a group are measured with reference to the lateral load acting on the pile cap. Linear elastic behaviour is supposed for the elements of the pile group such as pile and pile cap, whereas the behaviour of soil is thought to be non- linear-elastic.
In [2] Shehata E. Abdel Raheem, Mohamed M. Ahmed, Tarek M. A. Alazrak et al presents the effects of Soil Structure Interaction might be detrimental to the seismic response of arrangement and neglecting SSI in analysis could guide to un- conservative design. Despite this, the conventional design practice usually involves assumption of fixity at the base of foundation neglect the flexibility of the establishment, the compressibility of soil mass and consequently the consequence of establishment conclusion on additional redeployment of bending instant and shear force demands. The effects of SSI are analyzed for typical multi-story building inactive on raft foundation. Three techniques of examination are used for seismic demands
38 | P a g e assessment of the objective minute resistant
enclose buildings: correspondent static load;
response spectrum methods and nonlinear time narration investigation with suit of nine time history records. Three-dimensional Finite Element illustration is constructing to analyze the belongings of miscellaneous soil conditions and number of stories on the vibration depiction and seismic reaction demands of building structures. Numerical grades obtain using soil structure interaction representation conditions are estimate to those equivalent to fixed-base support conditions. The peak responses of narrative shear, story moment, story displacement, story drift, moments at beam ends, as well as force of inner columns are analyzed. Safety is thus achieved by the victorious integration of analysis, design and building.
In [3] R. R. Chaudhari, Dr K. N. Kadam et al presents Piled-raft foundations for imperative high-rise buildings have proved to be a expensive alternative to conventional pile foundations or mat foundations. The thought of using piled raft foundation is that the combined foundation is able to sustain the applied axial loading with an appropriate factor of protection and that the settlement of the combined foundation at operational load is tolerable. Pile raft foundation behavior is evaluated with lots of researches and the
effect of pile length; pile distance, pile arrangement and cap thickness are determined under vertical or horizontal static and dynamic loading. In the present manuscript manipulate of pile length configurations on behavior of multi-storied are evaluate under vertical loading. In exercise, the foundation loads from structural analysis are attaining without allowances for soil settlements and the foundation settlements are estimated suppose a completely flexible structure. However, the stiffness of the structure can restrain the displacements of the foundations and even miniature discrepancy settlements of the foundations will also change forces of the structural members. Hence, the interaction among structures, their foundations and the soil medium beneath the foundations alter the actual performance of the structure significantly than what is obtained from the deliberation of the structure alone.
In [4] Dr. M. Reza Emami Azadi, Ali Akbar Soltani et al presents the authority of foundation-soil-structure communication on the non-linear active behavior of a cement- storage silo organization is investigate. The effects of structure-soil-structure interaction on the silo's response are also studied during the course of this research work. Both near- field and far-field soil effects are considered.
39 | P a g e The grades demonstrate that inclusion of
soil-structure interaction might have a considerable effect on the dynamic response of the silo structure. In particular, the SSI is shown to have more significant consequence on the base-shear and overturning response of silo structure supported on softer soil. It is also observed that the softer soil as might augment the acceleration response of the silo while reducing the maximum overturning moments at the base. However, the effect on the base shear response is observed to be somewhat mixed depending on the EQ- record and the bearing of seismic wave. It is also observed that SSSI effect might augment the utmost base shear response at silo’s base while dropping the peak overturning moment and the maximum displacement values. Although, the site precise seismic input motion was not generated here due to incomplete scope of the research but the effects of varying ground conditions have been studied jointly with the obtain soil profilesin the Delijan silo’s building site
In [5] Resmi.R Dr. S. Thenmozhi et al presents in most engineering curricula, the structure is analyzed as model or simplified structures without the assistance of being able to contrast their grades to the behavior of real structures. By considering Soil-
Structure Interaction in the analysis it provides grades which are closer to actual behavior of structure. The response of a structure to earthquake shaking is affected by interactions between three linked systems:
which are the structure, the foundation, the soil underlying and nearby the foundation.
Soil-structure interaction analysis evaluates the combined response of these systems to a specified ground motion. Conventional structural design methods neglect the SSI effects. Neglecting SSI is reasonable for light structures in relatively stiff soil such as increase buildings and simple rigid retaining walls. The consequence of SSI, however, becomes well-known for serious structures resting on relatively soft soils for instance nuclear power plants, high-rise buildings and elevated-highways on soft soil.
Raft Footing
The raft will be used for reasonable consideration. The raft foundation is a variety of collective footing that might cover the complete area under the arrangement supporting several columns in one rigid body. Raft foundations are a great concrete slab which can support a number of columns and walls. The slab is increase out under the complete structure or at least a huge division of it which lowers the contact pressure
40 | P a g e compared to the conventionally used strip or
trench footings.
Prototype observation
Studies of recorded responses of instrumental structures constitute an integral part of earthquake hazard-reduction programs, leading to improved designing or analyzing procedures are done by modelling a prototype structure and those are results are compared with conventional design methods so as to ensure the safety of structure.
Finite Element Modelling
The building models are representation as three dimensional structural solids with element types assigned mechanically by FEA software, ANSYS 17.0. Mesh convergence learning was finished for building and used 300mm element size and for soil a coarser mesh was used. No separation category contact was used among structure and soil elements and bonded contact type connecting structural elements. The soil surface is engaged as the contact surface; that of the structure is taken as the target one, since its inflexibility is overweight than that of the soil
METHODOLOGY
A symmetrical 5 storey building is modelled using STAAD Pro software package with 4 no of bays in X direction and 4 no of bays in Z direction. The span of the columns is 3m
in X direction and 3m in Z direction. The plinth area of the building is 12m x 12m. The total height of the 5 storey building is considered as 15m. The height of each storey is taken as 3m respectively.
Fig 1 Plan view of the structure
Fig 2 Isometric view of the structure Soil Pressure Check
In this subdivision, the soil net weight ought to be checked in every point of the raft foundation. The raft foundation is symmetric around x-axis and y-axis. Moments effects on the raft should be checked to assure that stress of the raft under all columns are less than the net allowable stress which is equal to 215 KN/m2.
Raft Thickness
The depth of the raft will be governed by two way shear at one of the exterior columns. In
41 | P a g e case location of the critical shear is not
obvious, it may be necessary to check all possible locations.
Shear strength of the concrete Tc = 1.36 N/mm2
DEAD LOAD DIAGRAM
LIVE LOAD DIAGRAM
Model data of the Structure
Table 1 Structural Properties of the Structure
Structural Properties
Structure OMRF
No of Storeys 5 Storey Height 3.00 m Type of building
used
Residential
Foundation Type III Material Properties
Grade of concrete used
M 30
Grade of steel used 415 MPA Young’s Modulus of
Concrete
27.38* 106 KN/m2
Density of
Reinforcement Concrete
25 KN/m2
Modulus of
Elasticity of brick masonry
3.50 * 106 KN/m2
Density of brick masonry
19.2 KN/m2
Member Properties Thickness of Slab 0.125 m Beam size 0.45 * 0.23 m Column size 0.45 * 0.45 m Thickness of outer
wall
0.230 m
Thickness of inner wall
0.115 m
Seismic Properties
City Place
Zone III
Response reduction factor
3
Structure Type RC Framed
building Damping Ratio 5 %
Soil Properties
42 | P a g e Type of soil Loose Sand
Soil Bearing
Capacity
215 KN/m2
MODELING PROCESS
A symmetrical 5 storey building with raft foundation is taken with 4 no of bays in X direction and 4 no of bays in Z direction. The span of the columns is 3m in X direction and 3m in Z direction. The plinth area of the building is 12m x 12m. The total height of the 5 storey building is considered as 15m.
The height of each storey is taken as 3m respectively.
SHELL63 Element
In this structure slabs and raft foundation are taken as shell elements.
COMBIN14 Element
COMBIN14 has longitudinal or torsional capability in 1-D, 2-D, 3-D applications. The longitudinal spring damper alternative is a uniaxial tension-compression ingredient with up to three degrees of choice at every node, translations in the nodal x, y and z axis. No bending or axial loads are considered. The spring damper element has no mass. Masses can be added by using the appropriate mass elements. The spring or the damping potential may be disconnected from the constituent. The modulus of sub grade (K) value of soil taken as 12000 KN/m3. This
value is assigned for each spring by multiplying it by area on which the spring is acting.
Fig 3 COMBIN14 Element FLOW CHART
Fig 4 Flow chart
Part Module: Forming the geometry of the structure and soil
Property Module: Generating the property of the structure and soil
Assembly module: Assembly of the structures and soil into common partition
Step Module: Define the analysis type
Interaction Module: Define the interaction between the structure and soil medium
Boundary Condition Module: Define the boundary condition in structure
Mesh Module: Meshing of the structure and soil
Submission Module: Submission of the job for the analysis
Visualization Module: Viewing the result
43 | P a g e NUMERICAL ANALYSIS USING
FINITE ELEMENT METHOD Design Parameters
Parameters Value Yield strength of
steel
415 MPA
Strength of concrete 30 MPA Young modules of
elasticity
2000000
Soil unit weight 17.5 KN/m3 Allowable bearing
stress
215 KN/m2
Raft Modelling and Analysis:
RESULT PROCESS
The displacements, shear force and bending moment of the 5 storey building is compared with conventional design method and numerical method using finite element analysis i.e. without soil structure interaction
and with soil structure interaction. All the above stated parameters are compared in columns in Fy direction for each storey, the columns taken for comparison are peripheral columns and centre columns. It is observed that displacement, shear forces and bending moments varies from conventional design methods to numerical method.
Maximum Displacements
The maximum displacements of 5 storied building for the cases of dead load, live load multiplied with safety factor with soil structure interaction and without soil structure interaction for each storey is presented in table below. The grades are engaged only for intense loading conditions and static loading condition i.e. only dead loads and live loads are considered.
Maximum Shear Forces
The maximum shear forces of 5 storeyed building for the cases of dead load, live load multiplied with safety factor with soil structure interaction and without soil structure interaction for each storey is presented in table below. The outputs are taken only for extreme loading conditions and static loading circumstance i.e. only dead loads and live loads are measured.
Maximum Bending Moments
The maximum Bending Moment of 5 storeyed building for the cases of dead load,
44 | P a g e live load multiplied with safety factor with
soil structure interaction and without soil structure interaction for each storey is presented in table below. The conclusions are taken only for extreme loading conditions and static loading situation i.e. only dead loads and live loads are measured.
LOADS ACTING STRUCTURE
CONCLUSION
The exploration of reciprocated piled-raft foundation of multi-storey building is tremendously demanding since of complexities disturbed in the interaction among the components of building structure and soil field. The investigation of the elevated construction preparation with multifaceted foundation organization in standardized soil field should encompass the interaction of structure-foundation-soil. The displacements, shear forces and bending moments are estimated from conventional design scheme and numerical analysis
method using finite element technique in columns i.e. lacking soil structure cooperation and with soil structure organization. The relocations, Shear powers and twisting minutes are contrast and soil structure connection and without soil structure collaboration. In this development of analysis of structure with soil structure collaboration indicates more elimination than the investigation of structure without soil structure association. Conventional scheme of design is somewhat uneconomical as the organization is design for higher shear forces and superior bending moments, so we can go for a structure calculated by considering soil structure interaction. The estimation of sub grade modulus response (Ks) have been expected 12000 KN/m3.
REFERENCE
1. K. Natarajan and B. Vidivelli 2009 : Effect of column spacing on the behaviour of frame raft and soil systems 2. Haytham Adnan Sadeq, Mohammed
saleem Taha 2009: Structural design of raft foundation with soil structure interaction.
3. H.S Chore , V.A Sawant and R.K Ingle 2012: Non-linear analysis of pile groups subjected to lateral loads.
4. Sushma Pulikanti and Pradeep kumar Ramancharla 2013: SSI Analysis of
45 | P a g e framed structures supported on pile
foundations
5. Vivek Garg and M.S Hora 2012: A review on interaction behavior of structure foundation soil system.
6. R. R. Chaudhari, Dr K. N. Kadam 2013:
Effect Of Piled Raft Design On High- Rise Building Considering Soil Structure Interaction.
7. Gaikwad M.V, Ghogare R.B, Vagessha S.
Mathada 2015: Finite element analysis of frame with soil structure interaction.
8. Lou Menglin, Wang Huaifeng, Chen Xi Zhai Yongmei 2011: Structure soil Structure interaction: literature review.
9. Dr. M. Reza Emami Azadi, Ali Akbar Soltani 2010: Effect of soil structure interaction on dynamic response of Delijan cement storage silo under earthquake loading.
10. D. Daniel Thangaraj and L Ilampathi 2012: Numerical analysis of soil raft foundation and space frame system. 11.
Eduardo Kausel 2010: Early history of soil structure interaction.
12. IS 875 (Part-3)-1987 Indian Standard Code of Practice for “Design of Wind Loads for Buildings and Structures”.
13. IS 456:2000 Indian Standard Code of Practice for “Plain and Reinforced concrete design”.
14. IS 1893 (Part-4)-2002 Indian Standard
“Criteria for Earthquake Resistant Design of Structures”.
