Finite Element Analysis Results of Reinforced Concrete

Fig. 1: Reinforced concrete mesh

Concentrated loads on a concrete slab can cause structural problems, such as a phenomenon called “punching shear.”  If insufficiently reinforced, loads on a concrete slab can cause shear failure around a supporting column, which can then “punch” through the slab.  With concrete forming such an integral part of so many buildings, it’s vital to understand how it can fail, and how structural engineers prevent that failure.  Using Autodesk™ Simulation Mechanical’s FEA software, we investigated the effectiveness of the Shearfix shear reinforcement, from Ancon Building Products, which uses vertical rebar studs set in the concrete during pouring.  A typical configuration for Ancon’s Shearfix system is shown in the cutaway in Figure 2, below.

Fig. 2: Ancon’s Shearfix punching shear reinforcement system

Setting up the CAD model and FEA mesh

Recently, an academic asked us to perform FEA simulations in order to verify his mathematical modeling of the Shearfix system.  We constructed a 3D CAD model for the concrete slab that would integrate well with Autodesk™ Simulation’s meshing software.  We also took advantage of the slab’s symmetry to break the square slab down into a slice one-eighth of the size, which ultimately reduced our computation time by almost 90%.  The mesh on the inner corner of our one-eighth-sized slice is shown in Figure 1, above.

Nonlinear Analysis

Due to the large area of concrete that was experiencing deformation, we utilized the Mechanical Event Simulation (MES) with Nonlinear Materials analysis type offered by Autodesk™ Simulation Mechanical.

We also ran a mesh refinement study alongside our analysis.  We refined our element sizes from 100% to 70%, 45% and 25%, and ultimately the stress values we saw in the results did not change.  However, the total runtime for meshing and analysis jumped from 6 minutes to over an hour at 25% element size.  Ultimately, our original mesh was just as accurate as the finer meshes, and computed results significantly faster.

Simulation Results

Fig. 3: Shear stress with Shearfix vertical stud reinforcement

Our simulation results showed that the shear reinforcement vertical rebar studs did reduce the shear load on the concrete.  You can see in the Figure 3 above that the rebar studs are green, compared to the blue concrete around them, indicating that they are experiencing a high stress than the concrete; this is ideal, as rebar is stronger in compression and significantly stronger in tension than concrete.  The red area in the image above marks where the corner of the square-shaped supporting column is holding up the slab, though this is still well within concrete’s 20-40 MPa compressive strength.

Finite Element

Decades of work in electronics, materials science, mechanical machinery, and semiconductor technology has provided Glew consultants not only with a depth of knowledge and advanced technical skills, but also with valuable experience that they utilize every case. We also provide advanced modeling and finite element analysis capabilities for all applications.