ProtaStructure Design Guide Loading Generator

ProtaStructure Loading Generator

Scope

ProtaStructure can automatically generate the load combinations as required by different design codes. To generate load combinations automatically use the Loading Generator under Analysis > Building Analysis > Load Combinations. This document explains the different options in the loading generator.


Dead and Live Load Cases

Dead and live load cases must exist in all projects. That’s why it is not allowed to uncheck these two in ProtaStructure.

Pattern live loads are optional. By default, only odd and even loaded span pattern is used. You can optionally check the other three patterns and include in the combinations.


Separate pattern load cases are generated for each orthogonal direction if “Direction Dependent Pattern Loading” is checked.


Roof Live Load Cases

Generally in codes, it is recommended to define different load cases for Roof Live Loads and it is recommended to include in the loading combinations with different coefficients. Especially these definitions are important in steel structures where roof loading is prominent.

 


By checking these options, you can define individual load cases for  "Roof Live Load (Qr, Lr in ASCE-based specifications)", "Snow Load (S)" and / or "Rain Load (R)" instead of "Live Load State (Q)" to roof level slabs and elements (such as roof cladding, purlin, beam).

For example, if you check the Roof and Snow Load fields, a different set of combinations (in the form of Qr or S or R) will be generated for each of these load cases. 



If you define a load in the "Live Load (Q)" field together with "Roof Live Load (Qr)" for a member at roof level, both of these loads will be applied together. Therefore, a load should not be defined in the "Q" field for such elements, unless specifically preferred.

Construction Stages Load Cases

Dead and live load cases can be defined as a part of construction stage. Optionally, you can have a second independent set prepared for construction stage combinations that will enable you to envelope the results with unstaged cases.



Seismic Loading

Four load cases (Ex +, Ex-, Ey +, Ey-) including positive and negative eccentricities are defined for earthquake loads calculated in accordance with the selected earthquake codes. The "+" and "-" signs in the load case labels indicate the side of the eccentricity with respect to floor mass center. (i.e. rotating the floor CW or CCW)


All seismic codes require to include and additional combination, 0.9G + E, that may yield more critical results where G acts favorably. You can optionally include this in loading generator.

Wind Loading

Generally, two load cases are sufficient for the wind loads for standard buildings where windward and leeward facades are similar. Load combinations are automatically created separately for the positive and negative directions.

However, it is necessary to use different load cases in positive and negative directions to define the wind load, especially for the buildings with different windward and leeward facade areas, the cladding and purlins on the sloping roofs of steel structures, and the girts on their surfaces. For this purpose, you can define 4 load cases by using the "Define Different Negative Load States" option.

In the ASCE-based wind loading definition, 4 load cases (Wx, Wmx, Wy, Wmy) are generated by default since the torsion moment is calculated for each direction. If you use the "Define Different Negative Load Cases" option, you can use 8 load cases by creating separate load cases for the negative directions.



Minimum Horizontal Loading

Especially in non-seismic regions, design codes provision the application of a minimum horizontal load (notional loads) to buildings. By definition, this includes the minimum lateral  loads that can be caused by constructional defects in the structure and is usually calculated as a percentage of the building weight.


Soil Pressure

You can check the “Soil Pressure” load cases to describe the soil pressure effects. (For example, span loads applied to the basement shearwalls, or storey loads defined by storey loads editor)

In case the soil pressure is unilateral, it is sufficient to define one or two load cases. By checking the option for relevant direction, you can create soil pressure load cases and associated combinations.

Design codes suggest different combination coefficients for the soil load cases for situations where the soil pressure is applied favorably or unfavorably  with other horizontal loads. In this case, you must specify the direction in which the load is applied.

For example, if "negative" is selected for the direction of 1, the soil load coefficient will be "0.9" in the earthquake loading in the positive direction, and "1.6" in the earthquake loading in the same negative direction.

However, if you want to define different positive and negative load cases in both directions, you can check the "Define Different Negative Load States" option to create 4 load states (Hx, H-x, Hy, H-y).



Notional Load

In the countries where wind loads or seismic loads do not govern the design, minimum lateral loads, so called the Notional Loads, are applied to the structure at storey levels. The storey loads are usually calculated as a fraction of dead and live load.

This is not straightforward because Notional Load Case coefficients differ for each loading code. Some specify custom coefficients whereas some of the codes, notional loads use the same coefficients with dead and live load cases.

Besides, the DEAD or LIVE Load Fraction that is used to calculate the load magnitude also needs to be customizable.
You can flexibly apply notional loads to any combination type with any load case coefficient.

For more explanation on Notional Load, refer this article: Notional Load and Input


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