Finite Element Analysis of Steel and Steel-Concrete Composite Bridges - Finite Element Analysis and Design of Steel and Steel-Concrete Composite Bridges - page 474

solution accuracy is required or for problems where in-plane bending is
expected. In all of these situations, S4 will outperform element type S4R.
Further details regarding the elements used in modeling steel and metal
structures are found in Ellobody et al. [ 5.1 ] .
As mentioned earlier, steel and steel-concrete composite bridges that
are composed of compact steel sections can be modeled using solid ele-
ments. In addition, reinforced concrete deck slabs in steel-concrete com-
posite bridges can be modeled using either using thick shell elements,
previously highlighted, or more commonly using solid or continuum ele-
ments. Modeling of concrete deck slabs using solid elements has the edge
over modeling the slabs using thick shell elements since reinforcement
bars or prestressing tendons used with the slabs can be accurately repre-
sented. Solid or continuum elements are volume elements that do not
include structural elements such as beams, shells, and trusses. The ele-
ments can be composed of a single homogeneous material or can include
several layers of different materials for the analysis of laminated composite
solids. The naming conventions for solid elements depend on the element
dimensionality, number of nodes in the element, and integration type. For
example, C3D8R elements are continuum elements (C) having 3D eight
nodes (8) with reduced integration (R). Solid elements provide accurate
results if not distorted, particularly for quadrilaterals and hexahedra, as
shown in Figure 5.3 . The triangular and tetrahedral elements are less sen-
sitive to distortion. Solid elements can be used for linear analysis and for
complex nonlinear analyses involving stress, plasticity, and large deforma-
tions. Solid element library includes first-order (linear) interpolation ele-
ments and second-order (quadratic) interpolation elements commonly in
three dimensions. Tetrahedra, triangular prisms, and hexahedra (bricks)
are very common 3D elements, as shown in Figure 5.3 . Modified
second-order triangular and tetrahedral elements as well as reduced-
integration solid elements can be also used. First-order plane-strain, axi-
symmetric quadrilateral and hexahedral solid elements provide constant
volumetric strain throughout the element, whereas second-order ele-
ments provide higher accuracy than first-order elements for smooth prob-
lems that do not involve severe element distortions. They capture stress
concentrations more effectively and are better for modeling geometric
features. They can model a curved surface with fewer elements. Finally,
second-order elements are very effective in bending-dominated prob-
lems. First-order triangular and tetrahedral elements should be avoided
as much as possible in stress analysis problems; the elements are overly stiff