Interface

▒ Overview

Create a homogeneous or heterogeneous material interface where slip or isolation can happen. It is used to simulate the interface behavior between ground and structural members with a large relative stiffness difference. The interface generation method is classified by the work environment (2D/3D) and the target. The properties must be defined in order to create an interface element. The properties can be directly entered, or can be automatically calculated from the properties of adjacent elements using Wizard.

▒ Methodology

Interface element generation immediately separates the connected nodes of that position and creates an element with specific stiffness in the normal and tangent directions. Hence, because the nodes are left separated for certain steps where the interface element is not used (ex. Initial in-situ ground), the nodes need to be connected by a rigid link to prevent analysis error. Reversely, when the interface element is used, the rigid links need to be removed during analysis. Use the [Create Rigid Link Element] option to automatically create a Link element connecting 2 nodes.

The interface material can be defined using the following equation. Using the stiffness of adjacent elements and nonlinear parameters, the virtual thickness (tv) and strength reduction factor (R) is applied. Interface material stiffness and parameters are applied differently according to the relative stiffness difference between neighboring ground or structural members. The Wizard can be used to simplify this process.

Ex) Kn = Eoed,i / tv

Kt = Gi/tv

Ci = R x Csoil

phi_i = tan-1 (R x tan (phi_soil))

Here, Eoed,i = 2 x Gi x (1-νi)/(1-2 x νi)

(νi =Interface Poisson’s ration=0.45, the interface is used to simulate the non-compressive frictional behavior and automatically calculates using 0.45 to prevent numerical errors.)

tv = Virtual thickness(Generally has a value between 0.01~0.1, the higher the stiffness difference between ground and structure, the smaller the value)

Gi = R x Gsoil (Gsoil = E/(2(1+ νsoil)), R = Strength Reduction Factor

The interface can be created using the following methods, depending on the work environment and comp1nts or shape.

From Element Boundary

Create an interface element at the boundary position between the selected element and adjacent element, as shown in the figure below. Selecting all elements cannot create an interface element because there are not adjacent elements. If the created interface element is within a mesh, the interface element has a wedge shape, as shown.

Manual Node ID Input

Directly input the node ID to create an interface element. The nodes are divided into 2 groups: Side 1 and Side 2 that determine the shape of the interface element. The number of input nodes on Side1 and Side2 must be the same and the shape for each size is as follows.

Convert Element

Convert a general 1D, 2D, 3D element into an interface element. Because general elements do not have a consistent node order, the base reference node needs to be selected additionally.

From Free-Edge

Create an interface element from opposing free surface/edge. The free edges (free surface for 3D) with no node connections need to be selected on each side and if the free edge (free surface) does not exist, use the Connection > Divide function to divide beforehand.

From Truss/Beam (Use plate element)

Create an interface element using the truss/beam element. For 3D, use a plate element. Creating an interface element for structural elements such as truss/beam/plate generates an interface element on both sides of the element. Hence if the interface creation method is truss/beam, set the “add mesh set separately” option for the interface element to separately create the interface element in each direction.

Also, if the ground element connected to the interface element is removed during construction, the interface element is also removed to prevent analysis errors.

From Truss/Beam (T/X-cross type)

The interface elements are created at the location where truss/beam elements cross T or X-shape. Shell elements can be selected in 3D model. The ‘Register Interface Mesh Set Separately’ option isn’t available since interface elements are T or X-shape.

From Mesh-Set (T/X-cross type)

Create an interface element at the T- or X-cross of the selected mesh set. This method can be used when the interface elements intersect, such as in masonry structures.

From Node

Create an interface element between adjacent elements, using the relationship between the selected nodes. For 3D, select a segment point if the interface element is not created properly.