Hydrostatic Load Combinations

Load combinations containing lateral earth and groundwater pressure loads (H) have been implemented in Sizer Column Mode only.

The following design code clauses are used:

• NBC 4.1.2.1 1), 4.1.3.2 3) , Table 4.1.3.2 note 1,
• NBC Structural Commentaries A12 - Eqn. 2 and 3 and Table A-3 (ultimate limit states)
• NBC Structural Commentaries Commentaries A27 and A28, tables A4 and A5. (serviceability limit states)
• CSA O86-14 5.2.3.1, Table 5.2.4.1 Note * , Table 5.2.4.2 Note * , and Table 5.1

Note that the original CSA O86 01 and the NBCC 1995 use the terminology “Hydrostatic” when referring this load as a type of live load. Although this terminology has been dropped in favour of “lateral earth pressure, including groundwater”, the letter H has remained. In the program these are referred to in the input and output load lists as “Hydrostatic” loads, but the output legend says "H=earth,groundwater" .

The table below gives the load combinations that include H along with load types D, L, S , W, and E. . Refer to the comments at the end of this section to extend this for load combinations with Ds or Ls/Lt loads.

Note that in this table, we do not list all the sub-combinations of combinations – if the combination says “plus D, S, W”, then one would go to the table for Ultimate Limit State combinations and see that D + S; D+ W, and D are also generated.

Dead and Hydrostatic Loads alone

The load factor used for dead and hydrostatic loads alone is 1.25, not the 1.4 factor that is used when dead loads are applied alone. (In both cases, the design standards only indicate that the dead loads are not in combination with live, wind or snow loads.)

Storage Loads

The table does not include Lt or Ls loads. To construct these combinations, add “+ 1.5H” to all the load combinations listed in the tables under Live Storage Load Combinations, except those for earthquake combinations, where “+ 1.0H” is added.

Wind and Earthquake Loads

The situation where the user adds both wind and earthquake are added to the member is not included, as it does not yield new combinations. The combinations created are the ones created if just one of those loads was present. For example, for D + H + W + E, the combinations are derived from those in D + H + E and those in D + H + W.

Dead Loads due to Soil

The load combinations for Dead (soil) load types are arrived at by replacing D with D + Ds in this table, without repeating the load combinations for D only.

Dead-load-resisting-failure load combinations

All the combinations in the above table, except those containing E or Ds, will be replicated using 0.9 as the counteracting load combination factor.

Hydrostatic loads resisting failure

It is possible for H to be oriented in a direction that counteracts other loads, as in wind loads on a retaining wall or moments due to eccentric loads on a column in the other direction as the earth pressure on the column. The design codes indicate that you cannot rely on H loads for resistance to other loads on the structure, as those loads due to groundwater may or may not be present. The program will therefore generate all combinations with and without H, including the dead load resisting failure combinations for D. (The H load may be contributing to failure in a direction other than the one D is resisting it.) The ones in which H resists failure will not be critical, and will be discarded by the design routine.

Serviceability load combinations

The serviceability combinations including H can be arrived at by comparing tables in the Ultimate Limit State combinations and the Serviceability Limit State sections, which do not include H, and making the same changes to this table. In general, this means replacing principal factors (greater than 1.0) by 1.0, while retaining companion factors. An example of the load combinations generated, for D + H + L + W, is 1.0D + 1.0H + 1.0L + 0.4W and 1.0D + 1.0H + 1.0W + 0.5L.

Patterns

Hydrostatic loads apply to columns only thus are not patterned.

The load types referred to here are D=dead W=wind S=snow H=earth,groundwater E=earthquake L=live(use,occupancy) Ls=live(storage,equipment) Lt =live(liquids in tanks) Ds=dead load due to soil.