Structure load cases ([[load_case]], .ohlslc)#

A structure carries load cases of its own: recipes that say how the loads the line gives at a placed structure act on it. The structure application evaluates them for each placed structure into a load table: per case and point (or member), the transverse, longitudinal and vertical load. Specification: Building structures §2 (decisions 5 to 7).

Status: the recipes, their files, the evaluation and the table's CSV are built, in active development (not approved yet) (apps/structure/ohl-structure-loads). The structure application edits them in the Load recipes and Load table panels (Load cases menu) and solves the table's cases in its FE results panel (Results menu) (The structure application). Open in OHL-Structure… on a placed structure in the line application opens the structure with that place's line values and keeps the values typed over its table with it (Started for a placed structure). XLSX import and export of the table and of the recipes come later; CSV works today.

Recipes#

A load case is a list of loads. Each load says what, how and where:

[[load_case]]
name = "ice, unbalanced"
description = "the ice case's vertical loads × 1.3, and 2 kN along the line at set 1"
line_case = "ice"          # the line's load case giving the values
strength = 0.9             # strength factor of the checks (default 1)
self_weight = 1.0          # factor on the structure's own weight (default 1)

[[load_case.load]]
what = "vertical"          # a value the line gives
factor = 1.3
points = "all"

[[load_case.load]]
value = "2 kN"             # a value of the case itself
direction = "y"
sets = [1]

[[load_case.load]]
what = "tension_max"
one_sided = "40 %"         # 40 % on one side only…
side = "ahead"             # …this one
sets = [1]

[[load_case]]
name = "body wind"

[[load_case.load]]
pressure = "0.6 kPa"       # a surface load on the members' area
direction = "x"
members = "all"

A load gives one of what, value, pressure, and says where. points, sets and phases together pick the points that match all of them. Every key is checked: a mistyped one is refused, naming it.

What the line gives#

Forces in the structure's axes: transverse to the right of the line, longitudinal ahead, vertical down.

The line's structure loads give the first six at every point, in each case the line sends (Criteria › Loads for structures, see Loads for structures): its load cases (all by default) and the weather cases ticked to be sent on their own, named weather: <name>, every factor 1 (factored = unfactored). A recipe names the line's case by that name. A value the line does not give makes a row marked no line value (its force 0); so does every line value of a structure opened on its own. Such values can be typed into the table.

How a load acts#

• A line value without a direction acts along its own axis, signed as the line gives it; a tension acts along the line towards its span (tension_back back, tension_ahead ahead), or towards side.
• A line value with a direction: its size along the direction.
• A value of the case (value): along its direction, signed.
• A pressure: pressure × the member's area along the direction, the total per member, along the direction. The area comes from the section library: the profile's width seen along the direction (in the member's cross-section plane) × the member's length × sin θ (θ between the direction and the member; across the member: width × length). No drag factor. A member whose section is not in the library has no area (the row says why).

The load is the value × factor × one_sided.

The [[load]] tables: case model#

A structure's [[load]] tables (nodal forces at joints, structure axes, z up; Structure analysis) are read as one case named model, its rows at the joints (vertical turned to down). A moment given there is not in the table (the finite-element check reads it from [[load]]).

The load table#

One row per case, load and point (or member, or joint):

Typed values stay as given and are marked typed; the evaluated value is kept beside them. Evaluated again (new line values, a recipe changed), the typed values are put back over the new table. A typed row with no load number is a load of its own (e.g. from a client's load tree).

The structure application keeps the typed values beside the structure file as <name>.loads.csv (type-02.ohls → type-02.loads.csv): the table's CSV with only the typed rows, written when the structure is saved and read when it is opened. Started for a placed structure (say T2), as <name>.T2.loads.csv instead: each place has its own loads (decision 7), and in a project the line application keeps the file in the project with that placed structure (project library kind loads). A table read back from CSV types what it has beyond the evaluation (other values, rows of its own), so a table exported and imported again is the same table.

The table is written and read as CSV with these columns (numbers in N); a spreadsheet with the same columns reads back.

Structure load-case files (.ohlslc)#

The recipes on their own, to export them from one structure and import them into another:

format = "ohl-structure-load-cases"
version = 1
name = "Synthetic example structure load cases"

[[load_case]]
name = "construction"
self_weight = 1.1

[[load_case.load]]
value = "1.5 kN"
direction = "-z"
points = "all"

The same [[load_case]] tables as in the structure file; format and version as in every OpenOHL file. The recipes are also written and read as CSV: one row per load (case, description, line_case, strength, self_weight, load, what, value in N, pressure in Pa, load_line_case, factor, one_sided, side, direction, points, sets, phases, members, note; lists separated by ;).

Examples (invented, not from a design code): examples/synthetic-line/Structures/type-02.ohls (three cases and its [[load]]s) and examples/synthetic-line/structure-load-cases.ohlslc.