Influence of Foundation Rigidity on the Structural Response of Mat Foundation

A mat is a type of shallow foundation that is appropriate for structures supported on soil having relatively low bearing capacity or excessive settlement. Structural analysis of a mat foundation can be accomplished by either assuming the mat to be perfectly rigid or by considering the soil-structure interaction. This study researches the relationship between the mat-soil rigidity and structural response in terms of the soil bearing pressure, bending moment, and shear within the mat. To accomplish the objective of the study, 70 different mats are analyzed using a linearly elastic finite element approach. The variables that are considered in the analysis are the number of bays in each direction, center-to-center column spacing, mat thickness, panel aspect ratio, column cross section dimensions, soil modulus of subgrade reaction, and modulus of elasticity of concrete. A dimensionless mat rigidity measure was developed that determines whether a given mat can be reasonably analyzed by assuming it to be infinitely rigid. The developed rigidity factor takes into consideration all parameters that significantly affect the mat structural response. Results of the analysis indicate that there is strong correlation between the developed rigidity factor and critical soil bearing pressure and maximum internal bending moment within the mat. No correlation was observed between the mat rigidity and critical shear force. Relationships between the rigidity factor and the critical soil bearing pressures and bending moments, relative to the response of the infinitely rigid mat, are proposed. A parametric study is included to demonstrate the impact of the variables that affect the rigidity index on the response of the mat.

Influence of Soil-Structure Interaction on the Seismic Response of the Structure on Mat Foundation

The disasters that occur due to seismic activities not only affect the structure but also soil beneath it. Neglecting the effect of Soil-Structure Interaction (SSI) in design leads to unsafe design. This paper focuses on the behavior of the structure under El-Centro earthquake considering soil-structure interaction (SSI). Seismic response of G+10 storied building in various seismic zones of India is obtained using Time-history method. The direct approach i.e., finite element analysis is used to analyze effect of SSI. The model with mat foundation and soil is compared with fixed base model in SAP 2000 v.20. The behavior of the structure is studied by parameters like inter-storey drift ratio, lateral storey displacements, response spectrum curves for spectral acceleration and spectral velocity for various damping and time period of different seismic zones of India. The parameter like inter-storey drift ratio can determine safety of the structures. From inter-storey drift ratios, the buildings in zone IV and zone V were found to be unsafe. The lateral storey drift was found to increase by 47-87% considering SSI in zone II and 60-95% considering SSI in Zone II, IV and V. It also increased with increase in storey number. The spectral acceleration, spectral velocity and time period increased by considering effects of SSI in each seismic zone. The spectral acceleration and spectral velocity found to decrease with increase in damping and increase in seismic zones from zone II to V. Further to reduce the effect of SSI the structures can be equipped with base isolators and various types of dampers. It is clear that from zone III to V, SSI should be included for structures on soft soil and for retrofitting of the structure. Some experimental studies can further be performed and the numerical modelling can include parameters like P-delta, angle of incidence of ground motions and various structural systems can be implemented in this study. Doi: 10.28991/cej-2021-03091752 Full Text: PDF

Parametric Study on Behaviour of Retrofitted Piled Raft Foundation

Mat supported on piles is being increasingly used for high-rise buildings with basements in poor soils. Very little is known about the exact behaviour of piled raft foundations in service. However behaviour of retrofitted piled rafts, which are a hybrid foundation of mat provided as retrofitting solution and failed pile foundations, is non-identical. In order to model the mat for retrofitting, engineer needs to analyze the sensitivity of different parameters to their behaviour. In this paper, a numerical analysis has been carried out to investigate the influence of mat thickness and soil subgrade modulus of uniform and varying values to the behaviour of mat foundation rendered to retrofit a short felled pile foundation executed for a high-raised building in Kerala, by using finite element software SAFE v 16. The soil and the piles are modeled as spring element at discrete position below the mat and the mat foundation is modeled using elastic plate element. The results of the study show that mat thickness and soil subgrade modulus are found to be the governing parameters in designing a safe and economical retrofitting mat foundation. Furthermore, it is recommended to provide exact soil subgrade properties under the mat to perceive actual behaviour of foundation.

PEMILIHAN FIXED HEAD ATAU FREE HEAD DALAM DESAIN FUNDASI TANGKI REAKTOR KAP. 2000 M3 PILOT PLANT BIOGAS POME SETARA 700 KW DI PTPN V RIAU

Kebutuhan energi terbarukan di Indonesia sangatlah penting, saat ini sumber energi terbarukan porsinya relatif kecil. BPPT ( Badan Pengkajian dan Penerapan Teknologi) dalam kegiatannya melakukan pembangunan pilot plant Biogas Pome setara 700 kW berkerjasama dengan PTPN V (PT. Perkebunan Nusantara V) dengan sistim tangki berpengaduk secara kontinu yang mana hasil gas tersebut dimanfaatkan sebagai bahan bakar boiler pabrik PMKS di sei pagar. Metode pemilihan pondasi tangki reaktor dengan kapasitas 2000m3, kami melakukan perbandingan perhitungan antara menggunakan free head atau fix head dengan memakai diameter 50cm dan 60cm dengan melihat banyaknya jumlah, diameter pile dan ketebalan mat yang digunakan. Diameter rencana tangki reactor direncanakan berukuran 16.8m dengan ketinggian 9m, dengan beban tangki sekitar 2174.2ton dan berdasarkan data dari soil test didapat nilai N-SPT di kedalaman 10-15m, untuk itu kami merumuskan bahwa fundasi pile yang kita pilih. Perbandingan fix and free head pada pile ukuran 50cm dimana perbedaan fix and free head 44 berbanding 65, dengan ketebalan mat foundation 1.1m berbanding 0.6m sedangkan dengan mengunakan diameter 60cm jumlah pile 32 berbanding 50 dengan ketebalan mat 1.3m berbanding 0.6m. Dari analisa tersebut dengan memperhatikan kekuatan dan keekonomisan maka dipilih pile dengan diameter 50cm dengan mengunakan free head.

Effect of Shear wall Geometry on Ten Storey Building with Raft and Fixed base Foundation

:Raft foundation is widely used for high-rise buildings where presence of shear wall is very common. Shear Wall resists a major portion of the lateral load of high-rise buildings. So, presence of shear wall on mat foundation causes significant change in pattern and intensity of loading on mat foundation. The present work involved an investigation of effect of shear wall geometry in different seismic zones with and without the presence of raft foundation. Multi storey building with ten storey is analysed for the storey drift, storey displacement and base shear. The analysis of building is done by response spectrum analysis. The different shapes of shear walls C,L,F,I with same plan area is considered. The effect of shear wall geometry is studied in zone II, zone III, zone IV, zone V. Loads and load combinations selected based on IS 456-2000 and IS 875-1987 code. Three types of soil conditions are considered typeI ,typeII, typeIII.Raft foundation is designed by meshing the slab into equal quadrilaterals.Assigning of area springs to the each quadrilateral.Meshing is done inorder to convert the infinite solution into finite solution.The different shapes of the shear walls is analysed in zone V with the raft foundation in type III.The results are compared with and without the raft foundation ,conclusions are drawn that the best shape of the shear wall suits in different seismic zones.