Interactional Effect of the Influential Parameters on Seismic Behaviour of the Concrete Surface Tanks

Given to the importance of the tanks and their various applications in different industries, studying the seismic behaviour of these facilities is essential. In such structures, obtaining exact theoretical solution for the seismic behaviour of the tanks is very difficult due to the existence of the soil-structure interaction. In this study, seismic behaviour studying has been taken into account and in addition to considering three-dimensional model of finite element model of a surface rectangular tank and its beneath soil given to SSI and FSI effect, we have done required analysis and Drucker–Prager nonlinear model has been used to investigating more exactly to describe soil behaviour. Euler–Lagrange view with optional mesh displacement has been used for modelling tank-water interaction. According to the obtained results from this modelling, soil beneath the tank and soil-structure interaction affect highly on seismic behaviour of the surface tanks. Meanwhile, the response of the structure to the density changes and soil modulus of elasticity is more sensitive and changes in the coefficient of friction coefficient between the foundation surface and the soil and the internal friction angle do not have tangible effect on the response. The results reveal that the liquid containers response is more sensitive to the changes of the density and the soil modulus of elasticity more than friction coefficient between the surfaces and foundation and internal angle friction.

Back-Calculation of Soil Modulus from PFWD Based on a Viscoelastic Model

To improve the accuracy of back-calculation of soil modulus using the portable falling weight deflectometer (PFWD), a viscoelastic method (VEM) overcoming the limitations of the conventional linear elastic method (LEM) was proposed. A quasi-static dynamic analysis technique of Laplace transformation and a modified Gauss–Newton optimization algorithm were adopted in the proposed method. The back-calculation program was compiled with MATLAB. The effectiveness of the proposed method was verified with the in situ plate load test (PLT) conducted on a highway embankment. In situ test results showed that a time lag existed between the peaks of deflection and load, and load-deflection curves were nonlinear, which indicated the viscoelastic nature of the soil. The back-calculated modulus using the LEM and VEM was higher than that using the PLT. In the case of low stiffness soil, the average error of back-calculation using the LEM and VEM was 53.1% and 14.8%, respectively. However, for stiffer soil, the average error of back-calculation using the LEM and VEM method was 12.4% and 4.3%, respectively. Moduli of back-calculation using LEM and VEM methods were used to perform flexible pavement analysis, which showed that with an 8% reduction of modulus, the pavement service life reduced by 25%. More accurate estimation of modulus can save maintenance cost in the future.

The Effect of Mass, Depth, and Properties of the Soil Below the Raft Foundation on the Seismic Performance of R.C. Plane Frames

Soil structure interaction has been the subject of numerous studies. The foundation soil has a definite effect on the performance of structures during seismic excitation. Recent studies show that the effect of soil-structure interaction SSI may be detrimental to the structure during seismic excitation. In this study, the effect of consideration of the soil below foundation and its depth, and the soil modulus of elasticity on the response of structures is investigated. The number of mode shapes considered has an effect on the accuracy of the values of structure response. A structural model consisting of an 8-story reinforced concrete frame resting on raft foundation, and including the soil below the raft is analyzed. The frame is analyzed using SAP2000 software, and time history and modal analysis are carried out with varying values of both soil depth and soil modulus of elasticity. The soil below the foundation is connected to the raft elements by gap links. Gap element links are compression–only members with appropriate stiffness, which are active only in compression. Modal analysis results show that the periods of vibration decrease as the modulus of elasticity of the soil increases. Periods of vibration of the frame without the soil mass consideration are less than those when the soil mass below the raft is considered, and they increase with increased depth of foundation to a certain limit. The structures response in the form of columns shear forces and story displacements are also evaluated under the variable parameters considered.

Kajian Modulus Tanah Berdasarkan Uji Lapangan dan Uji Laboratorium

Penelitian ini mengkaji tentang soil modulus (modulus tanah) yaitu suatu faktor yangmenghubungkan antara besarnya stress/tegangan dan strain/regangan yang terjadi pada tanah. Soilmodulus adalah salah satu parameter utamadalam analisa geoteknik yang menggunakan metodaelemen hingga atau finite elemen method (FEM). Soil modulus biasanya ditentukan melalui ujilaboratorium atau uji in-situ di lapangan.Ada berbagai macam dan ragamsoil modulus, tergantungdari kondisinya antara lain kondisi pembebanannya apakah static atau dynamic, drained atau undrained,level tegangan dan regangan yang terjadi, tegangan keliling dan seterusnya.

EXCEL BASED SETTLEMENT OF BEAMS ON ELASTIC FOUNDATIONS WITH FREE-ENDS AND ARBITRARY LOADING

The deflection of long footings placed on homogeneous and isotropic soils involves soil-structure differential equations models whose solution may not be possible for most practical problems. The analytical solution of beams on elastic foundation problem involves soil modulus of subgrade reaction and simplifying assumptions relative to applied loading. The exact solutions are available in relatively simple cases of loading, uniform cross sectional properties of the footing and constant soil modulus of subgrade reaction. Therefore, the Finite Difference Method (FDM) or Finite Element Method (FEM), are typically used to compute the deformation of beams with variable loading and geometry resting on elastic foundations with variable modulus of subgrade reaction. The finite differences method was used to solve this problem for long beams with arbitrary loading and constant cross-sections using an Excel Workbook to compute beam deflections providing both numerical and graphical output. The foundation is modeled as a long beam with free ends and a constant modulus of subgrade reaction. The proposed solution presents an efficient method involving a complex ordinary differential equation model for beams on elastic foundations encountered in engineering practice.

Effects of Soil Modulus and Flexural Rigidity on Structural Analysis of Water Intake Basins

A water intake basin is a buried box that functions as a water reservoir near shorelines. Number of these structures has been increased in the recent years and for a safe design, it is necessary to know their behaviour under applied loads. In addition to common dead, live and seismic loads, the bottom of such a basin is usually located below sea water level and endures uplift pressure as well as reaction of supporting soils. Uncertainty of these special loads complicates the structural response of this buried basin to the applied loads. Therefore, the unreliability in the soil parameter and in the rigidity of the basin structure is studied in this research by calculating the generated internal bending moments. Different loads and load combinations have been taken into account and finite element analysis is carried out for modelling nonlinear behaviour of different types of supporting soils. It is concluded that the geometry and flexural stiffness of the basin affects the analysis more than the soil parameters because the contribution of the soil modulus in the total stiffness of the system is negligible than the structural rigidity of the basin structure. In addition, inner walls and geometry of the basin should be modelled in detail to obtain acceptable results.