Automatic load combination generator
PROKON’s analysis module Sumo features an automatic load combination generator. It currently supports SANS10160-1:2011 and SANS10160-1:2019. The functionality considers three main variable inputs as governed by the code, namely, combination values of variable actions, Ultimate Limit State (ULS) and Serviceability Limit State (SLS) load combinations.
As stated in the code under clause 6 the Combination values of variable action is the product of the combination factor, ψ, the characteristic value, Qk,i, and the partial factor for the leading variable action, γQ,1. The user is required to specify the variable action type (1) and the corresponding combination type (2) from the list provided under the load cases palette. In most cases, the exclusion group (3) should be set to 0. The program then combines the cases exclusively according to the code rules. However, there may be cases where two different load cases cannot occur together, then the exclusion group is used. Load cases with the same exclusion group (excluding 0) are not allowed in the same load combination.
Figure 1: Load cases palette in Sumo
The relevant Ultimate Limit State (ULS) and Serviceability Limit State (SLS) situations can be selected from the options provided in the load combination, Generate Load Combinations dialog box (figure 2). All selected combinations will be combined as stipulated by the code rules.
Figure 2: Generate load combinations
Table 1 provides descriptions of the different combination schemes. The ULS and SLS schemes are governed by clause 7 and 8 of SANS 10160-1:2011&2019, respectively.
Table 1: Combination schemes for ULS and SLS.
| SLS Combinations | |
| Irreversible (remains after removal) | The functioning or damage to the structure or non-structural members, due to permanent and variable actions, is considered when verifying deflections. |
| Reversible (does not remain after removal) | |
| Long-term (over time) | The effects of permanent actions and quasi-permanent values of the variable actions. |
| ULS Combinations | |
| STR and STR-P | Immoderate failure of the structure or structural members. The strength of the structural material is significant in providing resistance. In the case of excessive permanent action use STR-P. |
| EQU | When the structure or part of it loses its static equilibrium due to water pressure or other vertical action, which disregards the strength of construction materials or the ground. |
| GEO | Ground that fails or deforms excessively when the strength of the ground plays an important role in providing resistance. |
| ACC | Limit states associated with accidental and seismic events. |
Ultimate limit states design verification is done as stated by the code (SANS10160-1:20112011&2019, clause 7) it addresses the different ULS situations (as mentioned in table 1), combination schemes, and partial factors. The fundamental combination of actions for use in the verification of the ULS is given by the following equation (see clause 7.3.1.2):
Serviceability limit states design verification is stated by clause 8 in the relevant code.
The combination of actions for irreversible serviceability limit states shall be expressed as (see clause 8.3.1.1):
The combination of actions for reversible serviceability limit states shall be expressed as (see clause 8.3.2):
Combination of actions for long-term serviceability limit state shall be expressed by the equation(s) mentioned above under SLS design.
Where:
γG,j is the partial factor for the permanent action
Gk,j is the characteristic value of permanent action
P is the relevant representative value of the prestressing action
γQ,1 is the partial factor for the leading variable action
Qk,1 is the characteristic value of the leading variable action
γQ,i is the partial factor for the accompanying variable action
Qk,i is the characteristic value of the accompanying variable action
Ψi is the action combination factor corresponding to the accompanying variable action,
Ad is the design value of the accidental action