Eurocode 7 Analysis Methods
DeepEX implements Eurocode 7 specifications and load combinations for shoring design and analysis. This section examines and presents the Eurocode 7 specifications.
In the US practice excavations are typically designed with a service design approach while a Strength Reduction Approach is used in Europe and in many other parts of the world. Eurocode 7 (strength design, herein EC7) recommends that the designer examines a number of different Design Approaches (DA-1, DA-2, DA-3) so that the most critical condition is determined. In Eurocode 7 soil strengths are readjusted according to the material “M” tables, surcharges and permanent actions are readjusted according to the action “A” tables, and resistances are modified according to the “R” tabulated values. Hence, in a case that may be outlined as “A2” + “M2” + “R2” one would have to apply all the relevant factors to “Actions”, “Materials”, and “Resistances”. A designer still has to perform a service check in addition to all the ultimate design approach cases. Hence, a considerable number of cases will have to be examined unless the most critical condition can be easily established by an experienced engineer. In summary, EC7 provides the following combinations:
Design Approach 1, Combination 1: A1 “+” M1 “+” R1
Design Approach 1, Combination 2: A2 “+” M2 “+” R1
Design Approach 2: A1* “+” M1 “+” R2
Design Approach 3: A1* “+” A2+ “+” M2 “+” R3
A1* = For structural actions or external loads, and A2+= for geotechnical actions
EQK (from EC8): M2 “+” R1
(The Italian code DM08 uses DA1-1, DA1-2, and EQK design approach methods only).
In the old Nonlinear (version 7 and before), the different cases would have been examined in many “Load Histories”. The term “Load History” has been replaced in the new software with the concept of “Design Section”. Each design section can be independent from each other or a Design Section can be linked to a Base Design Section. When a design section is linked, the model and analysis options are directly copied from the Base Design Section with the exception of the Soil Code Options (i.e, Eurocode 7, DM08 etc).
In Eurocode 7, various equilibrium and other type checks are examined:
STR: Structural design/equilibrium checks
GEO: Geotechnical equilibrium checks
HYD: Hydraulic heave cases
UPL: Uplift (on a structure)
EQU: Equilibrium states (applicable to seismic conditions?)
DeepEX handles a number of STR, GEO, and HYD checks while it gives the ability to automatically generate “all” Eurocode 7 cases for a model. Unfortunately, Eurocode 7 as a whole is mostly geared towards traditional limit equilibrium analysis. In more advanced analysis methods (such as in Nonlinear), Eurocode 7 can be handled according to “the letter of the code” only when equal groundwater levels are assumed in both wall sides. However, much doubt exists as to the most appropriate method to be employed when different groundwater levels have to be modeled.
Ultimate Limit State and LRFD Design for Deep Excavations
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