Soil springs in sap2000

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Soil springs in sap2000

At the bottom I need to assign spring supports for soil interaction. So, I defined an elastic support, split the bottom beam into nodes and assigned this support to them. Now, when I run the analysis, this error appears.

Kindly see article 5. Use a "fixed but" support, and assign it as compression only because your soil doesn't take tension.

Soil Temperature Maps by Depth

As an aside, SAP has the option to provide spring supports under a beam without defining individual nodes. The beam is broken up into nodes during analysis and the actual nodal spring values are assigned on a basis of tributary length. It's very handy when looking at grade beams. I have attached a screenshot below.

I am modelling only a unit length of culvert for analysis purpose, so I will obviously assign member sizes with width as 1meter and some assumed depth. So, my question is, to calculate a spring constant, as shown in attached image, shall I use width 2. How to get a correct spring constant? Site Search User.

soil springs in sap2000

Product Communities More. Sign in. Can we do Spring supports to line beam element? Or is there any other way? I am also not sure about the procedure that I followed to assign these supports. Could you plz help to sort this out? At first instance, is it okay to assign spring support to nodes on a beam and not to the nodes forming a plate?

Reply Cancel Cancel. Up 0 Down Verify Answer Cancel. Thank again in advance for your help.!Because of its complexity and unpredictability, engineers often require the use of sophisticated analysis techniques, including specialized software.

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Modulus of subgrade reaction K s is one of the key parameters used in mat or raft foundation design. It approximately represents soil response at any given point underneath a mat foundation. This key parameter is very useful for FEM-based mat foundation design. A mat foundation is often analyzed using a constant value of K s. Many argue this approach is over-simplified and may yield erroneous output for the sake of convenience. This article addresses this complex issue by first briefly discussing the theory and then providing a solution for FEM based mat foundation analysis.

A new method Settlement Profile Convergence Method has been developed by the author to calculate and distribute K sand apply spring supports at all supporting points. As the term suggests, contact pressure is the base pressure between the bottom of the foundation slab and the supporting subgrade medium.

In other words, contact pressure is the subgrade reaction on the footing base due to the application of load on top of the foundation. From observations, one can easily conclude that a loaded foundation will deflect and, as a result, the supporting subgrade medium will settle. The magnitude and the profile of the settlement will depend on soil characteristics, foundation properties, and loading. Determination of the contact pressure is crucial for foundation design, yet calculations can be very complicated.

For larger foundations, like mats or rafts, determination of contact pressure can be even more complex. The theory of subgrade reaction is primarily based on the following two assumptions:. It is important to note that the assumptions mentioned above are considered erroneous as the real contact pressure significantly differs from these simplified assumptions. A uniformly loaded flexible foundation on a perfectly elastic material of clay will have uniform base pressure and will take the shape of a bowl or trough.

A foundation will suffer the maximum deflection at the center and will gradually reduce towards the edge Figure 1. Figure 1. Contact pressure and settlement on flexible foundation.

As discussed above, modulus of subgrade reaction is the ratio between the contact pressure q and its corresponding settlement s. Figure 2. Subgrade modulus of a uniformly loaded flexible foundation. It is known as variable modulus of subgrade reaction, which is part of the broader topic of Soil-Structure interaction SSI. The current practice is to use a commercially available FEM program to analyze mat foundations. The foundation is typically modeled as bending plates, and the supporting soil is modeled as discrete compression-only springs connected to plate nodes.

Those springs are known as Winkler springs. It is a popular modeling paradigm because of its simplicity. Winkler idealized a soil model consisting of closely spaced identical but mutually independent linear springs.Test Problem Name:.

Foundation in Sap2000

On this page:. Joint-spring stiffness is determined from tributary area and the line- or area-spring stiffness which is assigned to the object. As a result, joint springs which support interior joints are stiffer than those at corner joints. Since contact pressure is proportional to joint-spring deformation and the displacement of those joints to which springs are attached, users may obtain contact pressure through the product of spring-stiffness constant and displacement, available for output in both graphic and tabular format.

The example model, attached for reference, contains two area objects 2m x 2m and 1m x 1meach auto-meshed into four area objects, two frame objects 2m and 1meach auto-meshed into two frame objects, and one point object.

A link LIN1 is assigned to the area objects as an area spring, to the frame objects as a line spring, and to the point object as a joint link. UZ displacement of 1m at all joints indicates consistency between applied loading and assigned stiffness.

The stiffness of automatically created internal springs could be indirectly determined by dividing joint reaction by its displacement. These values are available in the output tables. The software automatically creates equivalent joint springs which represent those line and area springs which are assigned to an object. All rights reserved. Powered by Atlassian. Test Problems.

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soil springs in sap2000

Jira links. Created by Ondrejlast modified on Mar 27, Test Problem. Name: Line and area springs Description: This test problem demonstrates and validates the application of line and area springs. Program: SAP Version: Powered by Atlassian Confluence 6. This test problem demonstrates and validates the application of line and area springs.Log In.

Variable Modulus of Subgrade Reaction

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Promoting, selling, recruiting, coursework and thesis posting is forbidden. Students Click Here. Related Projects. Hello, I am trying to model buried pipelines on SAP We use a beam element to model the pipe. I am trying to show the soil structure interaction using line springs, link property. On the spring ends or the pipe? You have fixed restraints on both ends which stops axial displacement. Why would you use an axial line support link on a line which is already axially restrained at both ends?

You didn't use a linear line spring, you used a multi-linear elastic link which may require nonlinear load cases for analysis. I think your local link axes are different than what you think they are.

So it appears that your "axial" link is acting in the vertical direction. Again, please double-check local link axes yourself. In answer to your questions: 1 What do you mean "access" both ends of the spring? Line springs are assigned automatically for internal analysis. In order to review and select them individually you would need to instead draw multiple joint links along the length of pipeline instead of using a line assignment for the link.

You can draw joint links as 1 point or 2 point links. The edit menu replicate feature will facilitate copying multiple joints and links 2 You can assign joint imposed displacements only using joints which are modeled with link supports 3 Using a 1 point spring, your spring will not have a length. It will be the same location as pipe centerline joint where the link was drawn. With a 2 point link you can draw a link to have a length, perhaps assigning an anchor to one end of the link and pipe joint on the other end.

In this 2-point link example, the displacement would be assigned to the anchor end of the link. Imposed displacements can only be assigned to joints which have assigned restraints, links or springs.In this paper, the analysis of a numerical study of pile—soil interaction subjected to axial and lateral loads is presented.

A comparison between the bending moments and lateral displacements along the depth of the pile obtained from the FD solutions and FE was performed. A close correlation is found between the results obtained by the FE models and the FD solution. The results indicated that increasing the amount of clay surrounding the piles reduces the induced bending moments and lateral displacements in the piles and hence increases its capacity to resist lateral loading.

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The soil-structure interaction in general has been a concern; therefore, more research is needed to further understand and better model this interaction Abdel-Mohti and Pekcan abKhodair and Hassiotis The primary purpose of using piles is to transfer the loads from the superstructure and the abutment to a reliable soil, in cases where the soil near the ground surface can not support the applied loads.

Piles can transfer both axial and lateral forces. As the pile is subjected to lateral loads, the soil mass surrounding the pile plays a key-role in providing lateral support for the pile.

soil springs in sap2000

The nature of pile—soil interaction is three dimensional and to complicate the problem further, soil is a nonlinear and anisotropic medium. Therefore, finding a closed form solution to such problem is extremely difficult. Several methods have been used to predict the response of the composite pile—soil system.

The persistent obstacle in such processes is to find a valid approximation for soil representation. The subgrade reaction approach provides the simplest solution for the pile—soil interaction problem. In this approach, the pile is treated as an elastic laterally loaded beam. The soil is idealized as a series of independent springs with constant stiffness, where the lateral stiffness at one point does not affect the lateral stiffness at other points along the depth of the pile.

The spring stiffness, or modulus of subgrade reaction, is defined as the ratio of the soil reaction per unit length of the pile as described in Eq.

The solution for the differential equation are readily available and can be found in Hetenyi The subgrade reaction has been widely accepted in the analysis of soil-structure interaction problems Reese and Matlock ; Broms However, a drawback of the method is its inability to account for the continuity of soil. Additionally, the linear representation of the subgrade reaction for the soil elements along the depth of the pile fails to account for the non-linear nature of the soil.

The p-y approach is another method for handling pile—soil interaction. The only difference between the p-y method and the subgrade reaction method is that the former is based on defining a nonlinear relationship between the soil reaction and the lateral deflection at each point along the depth of the pile. Therefore, a p-y relationship is defined at each distinctive point along the depth of the pile.

The solution to Eq. Appropriate boundary conditions must be imposed at the pile head to insure that the equations of equilibrium and compatibility are satisfied at the interface between the pile and the superstructure.

The concept of a p-y curve was first introduced by McCelland and Focht The development of a set of p-y curves can introduce a solution to the differential equation in Eq.Scientific Research An Academic Publisher. In dynamic analysis of a building structure, the base support condition is very essential for calculating its dynamic behavior useful in estimating structural responses and distribution within structural members.

The building base condition will be different depending on the type of supporting ground. Fixed base foundation could be assumed on stiff soil and flexible base foundation on soft soil.

Flexibility of base causes decrease in structural stiffness and increase period of vibration during earthquake ground motion. As a result, in the past the dynamic analysis building on soft soil has gained serious attention in seismic active areas. Wolf [1] and many other authors noted that for structures built on strong foundation such as rock during earthquake motion, the force generated in the form of overturning moment and transfers shear will not cause deformation to the base in turn; the stiffness of structure remains constant.

For a given control of motion, the seismic response of the structure depends only on the properties of the structure, however for soft soils used as base; the base deformation changes the stiffness of structure during earthquake vibration, which in turn affects its response, known as Soil Structure Interaction SSI effect.

Even if, SSI has both kinematic and inertia effect on structure; in this study only inertia effect is considered. Figure 1 illustrates SSI effect on structures [2]. Figure 1. In the past, many studies showed that soil structure interaction SSI has both beneficial and detrimental effect on structure. Because SSI increases flexibility of structure, lengthening of structural vibration period and damping. As a result, in building structures, the base shear decreases; however at the same time displacement increases.

Moreover, excessive deflection of building could lead to collision of nearby structures. Moreover, there are researches those stating that for some special cases fixed base models can lead to an underestimation of seismic response [3] [4] [5].

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According to references [4], the idea of design spectra of the seismic codes along with the increased fundamental period and effective damping due to SSI lead always to reduce forces in the structure is not always true. It is shown that in certain seismic and soil environments, an increase in the fundamental natural period of a moderately flexible structure due to SSI may have detrimental effect on the imposed seismic demand [4] [6]. Additionally, the SSI effect has been included in some seismic codes.

Seismic design of foundation regulation ENPart 5 Extension of EC [10] states that SSI the fundamental period of vibration of the flexibly-supported structure will be longer than that of the fixed-base structure, the overall damping will increase both due to radiation and the internal damping generated at the soil-foundation interface, in addition to the damping associated with the superstructure.

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ENPart 5 [10] states for the majority of common building structures, the effects of SSI tend to be beneficial, since it reduce the bending moments and shear forces in the various members of the superstructure.

In conclusion, the three seismic codes do not provide full recommendation, which requires further study. So far, several SSI study on building report mainly focuses only on period of vibration, displacement, story drift, story shear and geotechnical parameters that affects SSI biased to geotechnical engineering.

In addition, soil-structure interaction SSI effect responses variation along height of building among fixed and flexible bases is studied. For comparative analysis of fixed base and flexible base structures, two residential buildings frame regular in plan and elevation are considered to avoid secondary. Figure 2. The plan is adapted from Chinese Seismic and Concrete Design standards [14] [15] and modified for this study purpose. The 2D model frames here after denoted as, S7 and S12 for 7 and story respectively.

Figure 4 shows typical transverse frames S7 and S12 story with first story height 4. The frames are considered in the short transfer direction and carry tributary area of floor load shown in Figure 3 for 2D regular frame analysis.

Figure 3. Typical floor plan for model residential building S7 and S Figure 4. Typical model building frames S7 and S Furthermore, the beam and column stiffness in the frame are proportioned to behave in shear mode according to [17]. Total dead load transferred on floor beam using tributary area including self-weight is Live load transferred on floor beam 8.They may contain viruses.

Use online scanners here and here to upload downloaded attachment to check for safety. How to assign Spring. View previous topic :: View next topic. I have define Columns and Basement walls in my buildings, then I've got problem on assigning the support at the interface of column,Basement wall and soil interface can any one suggest me to define support on STAAD or SAP Back to top. Refrence Manual. This will tell you with proper comands to define all types of support including Spring Support.

These values have significant impact on Raft--Foundation or Pile-Cap design. Vasudeo Pandya. Thanks Pandey Sir. Joined: 23 Mar Posts: I have read some where that in order to determine the soil spring constant cyclic plate load test as per IS need to be performed. Further I have been observing that times the SBC, on thumb rule basis, is applied as spring constant in Y direction.

I understant this not a dependable proposition. I request Mr. Pandya to put forth his views in the matter.

soil springs in sap2000

Jignesh V. Cost of these tests is never an issue because SER Structural Engineer of Record designing the foundation will not accept the soil-report without results from these tests. It is a liability issue.

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D - The Council of American Structural Engineers CASE defines a structural engineer as: "An engineer with specialized knowledge, training, and experience in the sciences and mathematics relating to analyzing and designing force-resisting systems for buildings and other structures. All times are GMT. Tech B. Tech M.


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