📺Complete Domestic Raft Analysis and Design

Posted on September 23rd, 2020 in Analysis

Summary

The provided excerpts detail the methodology for the finite element analysis (FEA) and design of a raft foundation for a small house incorporating two-story, single-story, and garage sections, using the Master Series software.

The design process involved several key stages:

1. Model Setup and Geometry

• Software and Import: The process began by starting the Master Series software, creating a new file, and importing an AutoCAD drawing as a CAD layer.
• Filtering CAD Layers: Layers such as dimensions, text, and small partitions (Def points related to small partitions) were highlighted and excluded from the display, leaving essential elements like walls and hatching.
• Creating the Slab and Members: The outline of the structure was created using concrete members, initially. Additional lines were added internally to represent wall loading and the centres of drop slabs.
• Openings and Coordinates: A few openings were created, although very small ones might typically be ignored. The model's coordinates were adjusted to bring all points back down to the origin (zero-zero point) for cleanliness. The external members were then converted into the FE slab.

2. Slab Properties and Attached Beams

• Material Specification: The slab surface properties were edited, setting codified material properties (Eurocode). The slab was specified as C30 concrete with a 200 mm thickness. For service cases, a modulus of elasticity of 0.25 was assumed.

• Defining Attached Beams (Thickening): Attached beams were designated around the perimeter and along internal lines.

  • The section was defined as rectangular.
  • The slab thickness was increased from 200 mm to 350 mm in these areas, meaning an additional depth of 150 mm was added.
  • The width of thickening was set to 600 mm (150 mm either side of the 300 mm wall width).
• Beam Design Integration: Later in the design phase, the attached beams were treated as combined plates, where a 600 mm width of the slab was ignored when designing the slab reinforcement spanning in that direction, as the beam was catering for it .

3. Supports and Loading

• Raft Support (Soil Interaction): The foundation was modeled as a raft resting on soil, meaning initially there were no restraints .

  • A subgrade modulus (or subgrade reaction) was set; initially 25,000, deemed reasonable for stiff soil, and later reduced to 10,000 to observe the effect of a broader spread of soil take-up .
  • The soil support was set to compression only, allowing for uplift if required .
  • Additional supports were placed to stabilize the slab horizontally and prevent rotation .

• Loading Application: Various dead and live loads were applied to the surface:

  • Full area loads included dead load (screed) of -1.2 and a live load of 2.5 everywhere . The self-weight of the slab was automatically included .
  • Line loads were applied for walls (e.g., 2-story double leaf wall load was -18 kN, single-story double leaf was -9 kN, and a single leaf load was -4.5 kN) [

Summary with Timestamps

This table summarizes the Finite Element Analysis (FEA) and design process for the raft foundation as detailed in the sources, including the corresponding timestamps.