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The design and assessment of concrete elements are typically performed at the sectional (1-D element) or point (2-D element) level. This procedure is described in all structural design standards, e.g., the American Concrete Institute’s ACI 318-19, Building Code Requirements for Structural Concrete and Commentary, EN 1992-1-1, Eurocode 2: Design of Concrete Structures, or the International Federation for Structural Concrete (fib) Model Code. All of these standards are used in everyday structural engineering practice. However, it is not always understood that the procedure is only acceptable in areas where the Bernoulli-Navieri hypothesis of plane strain distribution applies (referred to as B-regions). The places where this hypothesis does not apply are called discontinuity or disturbed regions (D-Regions). Examples of B and D regions of 1-D elements are shown in Figure 1.
These include bearing areas, parts where concentrated loads are applied, locations where an abrupt change in the cross-section occurs, openings, etc. In addition, designers meet a lot of other D-Regions, such as walls, bridge diaphragms, corbels, etc., when designing concrete structures.