These formulations give the total soil springs stiffness for three translational and. Predictive relations to find soil spring stiffness. It is also found that relative connectivity between the soil and piles skin, highly affects the spring s stiffness. Below are the steps how to create a point spring based on soil profile and isolated column footing dimension. Estimation of the static vertical subgrade reaction. Modulus of soil reaction, e the modified iowa formula includes a term referred to as the modulus of soil reaction, e, and is defined as an empirical value used to express the stiffness of the embedment soil in predicting flexible pipe deflection. Numerical study for soilspring stiffness of pile group. Calculation of stiffness of vertical springs spring method. Pile lateral stiffness, lateral springs stiffness, soil pile interaction, lateral springs stiffness. Overview of soil structure interaction principles jonathan p.
Calculate of soil spring stiffness free download as excel spreadsheet. Integral bridge design derivation of the spring constant for modelling the soil structure interaction sergei terzaghi behons, mipenz gillian sisk beng phd miei ceng synopsis integral bridges present a challenge for load distribution calculations because the bridge deck, piers, abutments, embankments and soil must all be considered as a. Scribd is the worlds largest social reading and publishing site. If you are not familiar with these topics, you are.
It assumed that the material is elastic and isotropic i. What i need to know is what to use as spring stiffness when modelling the ground as spring supports. The chapter continues by describing the interaction between structure and soil. Soil stiffness constitutive model parameters for geotechnical. The use of a spring constant for the design and analysis of raft and pileraft foundations has many limitations, related to the proper estimation of the spring constant magnitude and the soil structure interaction. For example, preloaded clay actually has a variation of stiffness with respect to depth as shown in figure 4a. Covered in part 2 are the use of springs in a planeframe structural analysis, ansiasae ep486.
The stiffness of soil springs is automatically calculated and entered into point spring supports. Procedure to calculate tributary area and vertical spring. Janbu has promoted this for many years janbu, 1963, also janbu and senesset, 1979, not only because of the modulus issue, but also because the log scale for pressure gives a distorted picture of the soil. The fundamental problem with the use of this model is to determine the stiffness of elastic springs used to replace the soil. Goodling and documented in appendix vii to asme b31. These reactions spring may represent structural elements that resist movement of the pile. Modulus of subgrade reaction which one should be used. The dynamic properties of the soil could be determined in two different ways. Rerun the seismic analysis using the foundation springs calculated from the soi l response program. Structures and stiffness engr 10 introduction to engineering. The predicted pile movement depends heavily on the accuracy of the inputted e value. Beam deflection and stress formula and calculators engineering calculators civil engineering design resources.
The following relationships can be demonstrated for proofs refer to a text on the strength of materials. What are the most reliable equations or predictive relations to find the soil spring. Guidelines for the design of buried steel pipe july 2001. A graphical depiction of this behavior is shown in figure 4. A beam can be loaded at one or more points along its length whinkler soil springs assumption. Lateral soilpile stiffness subjected to vertical and. Springs used to represent soil foundation interaction complexvalued real part represents stiffness imaginary part related to damping combination of real. Interventions aim at increasing the slabtowall connection by a r. Subgrade reaction model of 1 actual soil reaction on pile and 2 elastic spring model of soil reaction after prakash and. At least that is how it is input to my analysis program. The main difficulty with the winkler spring type model is the derivation of an appropriate spring constant.
Initial soil springs stiffness for laterally loaded piles. Pile group stiffness for seismic soilstructure interaction. Pdf backward calculation of soil stiffness from the loading. Select geometry boundaries pile spring supports in the menu tab of the tree menu. D pile shaft diameter, esd soil youngs modulus at a depth of one pile diameter. Spring stiffness is the load in kn needed for a certain deflection in metres. Covered in part 1 were suggestions for spring placement and procedures for calculating spring stiffness and ultimate spring strength. The load combinations specified in aashto seismic 4.
Some popular fe programs do not include the facility of surface support and hence to model soil as elastic support, calculation of vertical spring stiffness at each node of the mesh becomes necessary. Spring constants have been used for example in the design of a mass rapid transit railway station in an oversea project. It is not meant to be a thorough academic discourse but rather a first step in understanding the complex world of soil moduli. Calculate of soil spring stiffness density classical. Stiffness of equivalent spring soil versus distortion of pile between 4 and 11 m of depth. Winklers idealization represents the soil medium as a. The z axial stiffness of the spring was determined experimentally and compared to the manufacturers design specifications.
Probabilistic equivalent linear soil spring stiffness. Analysis of pile foundation subjected to lateral and. The fundamental problem with the use of this model is to determine the stiffness of elastic springs used to replace the soil below foundation. The soil spring stiffness is computed using modulus of subgrade reaction. Soil spring stiffness and damping values are generally computed with available formulae for circular rigid foundation on the surface of an elastic, homogeneous and isotropic half space.
A common practice is to use the subgrade stiffness for the soil type. Distribution of soil spring stiffness underneath a three. Derivation of the spring constant for modelling the soilstructure. Understanding and using dynamic stiffness a tutorial. What are the conditions associated with this number. Thus, a single value can be used to represent stiffness. The spring value shall be in forceunit displacement. Calculate of soil spring stiffness density classical mechanics. The following is a background on some of the important influencing factors for soil moduli. The modelling of the soil as springs comes forth out of the winkler foundation model.
Pile group stiffness for seismic soil structure interaction anshuli arya anand s. From the main menu select model boundaries pile spring supports. Ken youssefi engineering 10, sjsu 2 wind turbine structure the support structure should be optimized for weight and stiffness deflection support structure. The stiffness of both structure and soil has an important role when modelling the interaction. Soil stiffness measured in oedometer test stress versus strain, rather than as conventional elog graphs. Modelling a spring stiffness as a support will only yield a reaction force and settlement distance. Aci the modulus of subgrade reaction is an often misunderstood and misused concept for the thickness design of slabsonground. Estimating lateral stiffness foundation engineering. The main issue of existing floors and roofs made of iron girders and flooring blocks is represented by the poor connections of the r. This load should be selected such as to characterize the. Horizontal stiffness an overview sciencedirect topics. In the interest of simplicity, equivalent elastic soil stiffness parameters elastic soil moduli are defined as the ratio of stress along an axis to strain along an axis and often employed in soil characterization and analyses. The entered data can be checked from point spring supports table.
Technical data fc11 2 spring calculations excerpts from. Governing differential equation of a beam on lateral springs is given for a beam along. Horizontal and rotational reaction springs can also be included. This model requires continuity between the individual spring elements in the. Evaluation of pile diameter effects on soil pile stiffness jens wiemann 1, kerstin lesny 2. This method accounts for the effect of soil stiffness in the form of pipe soil spring interaction, and the effect of pipe soil friction which results in a virtual anchor. Analyses of lateral loaded piles with py curves observations on the effect of pile flexural stiffness and cyclic loading ncdot 7th 3geo t2, raleigh, nc, thursday, april 04, 20 session 3b geotechnical ii room. Modelling soil stiffness as spring support structural. In bodies of elastic material the three stiffness moduli e, k and g are related to each other and to poissons ratio n. But, to establish a spring constant i would need to estimate a expected deflection which would coincide with that passive pressure. Effect of soil profile modulus distribution on pile head lateral stiffness. We all know soil can be modeled by springs, and for that, stiffness of soil spring has to be calculated. Regarding constrained thermal expansion, the analysis method was developed by e. The subgrade modulus is used to establish the elastic stiffness of the soil and foundation.
Springs stiffness is correlated to mechanical properties of the soil, shaft diameter, and pile flexibility factor using curve fitting techniques. The problem of a laterally loaded pile embedded in soil is closely related to the beam on an elastic foundation. It is found that spring stiffness is dependent to shaft diameter. The overview of soil condition on that particular site is as shown in fig. The entered data can be checked from point spring supports table from the main menu select model boundaries pile spring supports select geometry boundaries pile spring supports in the menu tab of the tree menu. Components of the pile head stiffness matrix for the soil profiles shown in fig. Soil stiffness, e, is one of important factor to consider in geotechnical finite element analysis. It is also found that relative connectivity between the soil and piles skin, highly affects the springs stiffness. Effect of soil profile modulus distribution on pile head lateral stiffness 3 z z z es es mz es esd zd d esd figure 2. Repeated shear strain may reduce the stiffness of saturated soils.
Soil mechanics and foundation engineering conference in florence was a turning point, at which the importance of soil stiffness to both theoreticians and practising engineers became accepted. Modelling the interaction between structure and soil for. Calculation of stiffness of vertical springs spring. This calculator will determie the spring rates for a foundary placed top various soil conditions soil foundary spring calculator. Instructional materials complementing fema p751, design examples foundation design 2. This will give me a bending moment diagram for the beam which i can use to calculate the reinforcement needed.
I definitely think that the spring stiffness modeled would be affected by the width of the beam if you are trying to establish a bearing pressure acting on your ground beam. Now, almost 20 years on, this paper revisits the issue of stiffness determination, and in particular is concerned with smallstrain stiffness, which was. The three soil profile stiffness models used herein. Limitations of winkler model a number of studies in the area of soil structure interaction have been conducted on the basis of winkler hypothesis for its simplicity. Lateral load capacity of piles transportation research board. The method can be applied to estimate the equivalent spring stiffness for a flexible shallow foundation and then subsequently estimate the k f value for. This model has some drawbacks which are improved by the pasternak foundation model. An integrated method for the estimation of static spring stiffness from cpt has been presented for flexible shallow foundations on cohesionless soils. Integral bridge design derivation of the spring constant. There fore, beamonelasticfoundation theory must be modified to account for variations in the spring stiff ness k.
Foundation analysis and desing foundation design 1. Lateral subgrade modulus and vertical subgrade modulus of soil k. Stiffness is the resistance of an elastic body to deflection or deformation by an applied force and can be expressed as. This paper deals with stiffnesses of pile groups based on single pile stiffness as worked. Horizontal and rotational soil spring stiffnesses of the foundation are needed a to perform the dynamic analysis of gravity platforms and b to obtain characteristic wave loads to be used in the geotechnical design analysis of platforms. The second approach is the back calculation of the soil stiffness based on the soil structureinteraction. Comparisons between the current analysis and several.
In order to calculate bending moments in the piles, the stiffness of the soil must be included. Davisson, department of civil engineering, university of illinois, urbana. Pdf numerical study for soilspring stiffness of pile group. Evaluation of pile diameter effects on soilpile stiffness jens wiemann 1, kerstin lesny 2, werner richwien 3 institute for soil mechanics and foundation engineering, university of duisburgessen.
Analysis of pile foundation simplified methods to analyse the pile foundation under lateral and vertical loads 1kanakeswararao thadapaneni,2sarikonda venkata sivaraju,3ravi teja grandhi 1pg student, lenora college of engineering, rampachodavaram,2pg student, kakinada institute of engineering and technology. Initial soil springs stiffness for laterally loaded piles curtin university. Specifying a series of spring supports behind the abutments and adjacent to the foundation piles to approximate soil behaviour is a commonly used modelling method. Also the settlement calculation that the program uses will be discussed. The first one is the common way using the dispersion of the rayleigh waves on the soil surface and the back calculation to shear wave profiles. Structural element approaches for soilstructure interaction. A number of studies in the area of soil structure interaction have been conducted on the basis of winkler hypothesis for its simplicity. Covered in part 1 were sugges tions for spring placement and procedures for calculating spring stiffness and ultimate spring. Stiffness coefficients of layered soil systems journal of. Ken youssefi engineering 10, sjsu 22 concept of area moment of inertia the area moment of inertia, i, is a term used to describe the capacity of a crosssection profile to resist bending.
This calculation uses these global springs to compute. When back calculating the stiffnesses of vertical springs it is necessary to input a typical load in the frame vertical springs that will serve to the determine the spring stiffnesses. For a layered soil system, the stiffness obtained from an idealization of soils underneath as springs in series gives the same value of stiffness regardless of the location and extent of individual soil layers with respect to the base of the foundation. Assuming that the changes in soil stiffness drive the longterm performance, the average strain next to a pile is a governing criterion and must be preserved in order to ensure similar stiffness degradation in both model and prototype. The material behaviour of the soil is described by nonlinear springs. This load should be selected such as to characterize the structure behavior as close as possible. At this project the spring constant concept was adopted for designing the station raft foundation. The soil definition with the default box checked will be used for the soil properties in the model except where another soil region using a different soil definition is drawn. Soil spring stiffness all springs are assumed to exhibit linearelastic behavior until a point of soil failure is reached, at which point the force in the soil spring stays constant as the spring undergoes additional deformation.
Scholar, university of roorkee, india professor emeritus, university of roorkee, roorkee, india synopsis. Pdf many approaches have been developed to determine the soilspring stiffness and typical values have been. Soil profiles and isolated column footing etabs computers. Pdf backward calculation of soil stiffness from the. Steps to calculate soil stiffness as spring in sap. A series of ninestory, fivebay, elastic frames were analyzed to verify the concept of apparent lateral stiffness of a story. Linearly elastic spring stiffness may be successfully used where lateral.
Covered in this article are suggestions for spring placement and procedures for calculating spring stiffness and ultimate. The analysis also allows a calculation of the soil reactions ky. Effect of soil profile modulus distribution on pile head. The group prepared the guidelines presented in this report, with an emphasis on the fundamental design equations suitable for hand calculations, and where necessary, guidance for finite element. Evaluation of pile diameter effects on soilpile stiffness.
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