Counterfort retaining wall, comparison with ETABS

Problem. A reinforced concrete counterfort retaining wall under earth pressure, the weight of the soil on the heel and a surcharge is solved separately with MindFEM and with ETABS. The stem bends in two directions between the counterforts, the counterforts tie the stem to the base slab, and the base rests on subgrade springs. The moments in the stem, heel and toe, the soil pressure and the displacement of the stem top are compared.

Reference document. The reference is the same wall modelled in ETABS 20.1.0 with its own objects. The earth pressure is given in ETABS as a non-uniform area load, the soil weight and the surcharge as uniform area loads.

Numerical model. The stem is 9 m long, 6 m high and 0.30 m thick, the base slab 0.50 m thick, the toe 1 m and the heel 3 m, and four counterforts 0.30 m thick, 3 m apart, taper from 3 m wide at the base to 0.5 m at the top. The base rests on a subgrade of modulus 20 000 kN/m³ vertically and 10 000 kN/m³ horizontally, and the mesh is made of 0.25 × 0.25 m quadrilateral elements.

Counterfort retaining wall#

Independent calculation. ETABS 20.1.0, the same structure modelled with ETABS's own objects

The mid-planes of the stem and the base slab at mid-bay between the counterforts (y = 4.5 m), with the counterfort behind in dashed lines. The reading beside a counterfort is at the same height next to the counterfort at y = 3 m. Dimensions are in metres.

Note. G is the self weight, S the weight of the 6 m of soil on the heel (114 kPa), E the active earth pressure (K = 0.33, γ = 19 kN/m³) and Q a 10 kPa surcharge. The pressures use the coordinates of the mid-planes. The section under the table shows where each row is read. In the stem the horizontal moment spans between the counterforts and the vertical moment bends it as a cantilever. The ETABS moment sign convention is the opposite of MindFEM's, and the table uses MindFEM's sign. The table gives the moment component that governs the design at each point. The small other component at the same node, for example the 3.5 kNm/m horizontal moment at the stem base, differs by 20 to 50 per cent between the two programs and is left out.

Model files#

The ETABS model that produced the results in the table can be downloaded. It opens in ETABS 20 and later with File > Import > ETABS .e2k File.

• Counterfort retaining wall (.e2k)