RKALC Structural Engineering

STM Studio

From load path to physical nodal zones

STM Studio keeps the solved analytical truss distinct from the finite concrete geometry used to construct and assess the actual nodal zones.

More than a single-purpose calculator

STM Studio is intended for general D-region modelling rather than one predefined structural arrangement. The engineer develops the structural domain, applies loads and supports, establishes the load path, creates the strut-and-tie model and solves the truss equilibrium before progressing to physical nodal-zone construction and member design checks.

TopoKALC topology optimisation can be used as load-path guidance. The engineer remains responsible for selecting the final STM and for reviewing whether the constructed force paths, nodal zones, struts and ties are physically appropriate for the concrete region.

Integrated design workflow

Interactive 2D structural domain and STM modelling.
Automatic solution of the analytical pin-jointed truss.
TopoKALC topology optimisation for load-path guidance.
Finite nodal-zone construction with designer-controlled geometry.
Physical face editing, merging and frozen nodal geometry.
AS 3600-focused nodal, strut and tie design checks.
Offset physical truss review after nodal-zone construction.
General N-face traction, tensor and local stress-field interpretation.
Engineering calculation report generation.

STM Studio worked example for an outrigger wall in a tall building — Worked example: load-path development and STM design of an outrigger wall within a slender 46-storey building.

Engineering workflow

STM Studio design sequence

Move directly to the principal stages of the modelling and design process.

01 · Load-path guidance

Use topology optimisation to understand the force flow

Topology optimisation can be used as an advisory precursor to the engineer-defined strut-and-tie model.

The worked outrigger example tests alternative load-introduction assumptions using TopoKALC before the analytical STM is finalised. The topology result is used to understand likely compression paths and to guide the designer's truss arrangement rather than to replace engineering judgement.

Purpose Load-path guidance

Output Compression-flow indication

Final STM Engineer selected

Role Advisory precursor

STM Studio TopoKALC topology optimisation examples for an outrigger wall — Alternative topology studies used to review how the outrigger load may transfer through the concrete region.

02 · Analytical STM

Construct and solve the strut-and-tie model

The analytical model remains the governing equilibrium model even after physical nodal geometry and offset member axes are introduced.

The designer establishes the truss using compression struts and tension ties within the concrete domain. STM Studio solves the two-dimensional pin-jointed truss and reports the member axial forces, support reactions and equilibrium residuals.

Nodal-zone construction occurs after this analytical force state is known. Editing a physical node does not rotate or re-solve the original analytical force vectors; instead, it controls where the solved actions enter the finite nodal region.

STM Studio initial strut-and-tie model and provisional nodal zones — Initial analytical STM followed by automatic provisional nodal-zone construction.

03 · Physical nodal zones

Construct, edit, merge and freeze the node geometry

STM Studio separates physical nodal construction from the analytical truss so the finite concrete geometry can be adjusted deliberately.

Provisional nodal polygons are generated from the solved nodal actions. Load and support contacts are treated as authoritative physical faces, while free member faces can be moved, resized or rotated by the designer.

Adjacent member faces may be merged into a single physical face. A member face may also be absorbed into an adjacent load or support face while the external contact geometry remains unchanged. The retained physical face carries the vector sum of the assigned analytical actions.

Freeze & Save preserves a geometrically valid nodal state independently of whether the current strength check is PASS, FAIL or LIMIT REQUIRED.

Designer-controlled geometry Mergeable physical faces Frozen design state

STM Studio nodal-zone editor showing member faces, loads, ties and stress colours — Nodal-zone editing with physical faces, boundary stresses and internal stress visualisation.

04 · Nodal stress review

Check the physical faces and the stress state inside the node

Boundary tractions, nodal strength status and local stress-field plots are presented as separate but complementary parts of the review.

Boundary

Face traction

Review the normal and tangential traction acting on each actual physical face.

Strength

AS 3600 nodal check

CCC, CCT and CTT three-action nodes are automatically classified in the current implementation.

Complex nodes

Designer limit

TTT and more complex nodes use a designer-entered allowable nodal compressive stress.

Interpretation

Stress heat maps

Review principal compression, principal tension, shear and Cartesian stress components.

05 · Offset truss

Translate the analytical truss into a physical force-transfer path

Once the nodal faces are established, members connect between the actual nodal-face application points rather than only between idealised node points.

The offset truss is a downstream physical interpretation of the solved analytical STM. Struts bear against nodal faces and ties connect to the back of the physical node, producing member axes that reflect the finite dimensions of the nodal zones.

The original analytical truss remains the governing equilibrium model. STM Studio can compare the analytical member actions with the forces associated with the offset physical geometry so the designer can review the consequences of the finite nodal construction.

Comparison of analytical truss and offset physical truss in STM Studio — Analytical centre-line STM compared with the downstream offset physical truss.

06 · Strut design

Review compression capacity and bottle-shaped bursting actions

Strut checks combine the physical member geometry with the adopted force, concrete strength parameters and AS 3600 design requirements.

STM Studio distinguishes between prismatic and bottle-shaped compression fields. The strut review reports the physical length, end widths, effective area, governing strut/tie angle, stress limit, applied compression stress, capacity and utilisation.

For bottle-shaped struts, the workflow also evaluates bursting actions and the associated transverse reinforcement demand where required. The worked example shows cases where bursting reinforcement is not required as well as a strut requiring reinforcement in both orthogonal directions.

STM Studio strut check for a bottle-shaped compression field — Representative bottle-shaped strut review including compression capacity and bursting actions.

07 · Tie design

Size the reinforcement and review development through the node

Tie forces are converted into required reinforcement and checked against the selected bar arrangement and design capacity.

The tie solver reports the adopted ULS tension force, minimum physical tie width, reinforcement strength, required steel area, selected bar diameter, number of bars, provided area, tie capacity and utilisation.

Reinforcement must be fully developed past the nodal zone so that the required design tie force is properly anchored at the node. Where ordinary reinforcement becomes impractical, the worked example notes that high-strength bar systems with suitable anchorage may be considered by the designer.

STM Studio tie reinforcement design and summary — Tie reinforcement sizing and utilisation summary from the worked example.

08 · General N-face nodes

Interpret complex nodes using familiar 2D plane-stress mechanics

The number of nodal faces changes the boundary conditions, not the dimensionality of the stress tensor.

For each physical face, STM Studio divides the assigned resultant by the physical face area to obtain an average traction vector, then resolves that traction into signed normal and tangential components relative to the actual face orientation.

All equilibrated physical-face resultants are then used together to recover a whole-node area-averaged Cauchy stress tensor. The symmetric tensor is used to obtain principal stresses, maximum in-plane shear and principal directions by the ordinary two-dimensional plane-stress relationships.

Because one uniform tensor will not generally reproduce every traction on a complex nodal boundary, STM Studio compares predicted and actual face tractions and can construct a centroid-fan constant-strain-triangle elastic stress field for local heat-map interpretation.

Boundary level Face traction, normal stress & shear

Whole node Average 2D Cauchy tensor

Compatibility Predicted versus actual traction

Local field CST plane-stress reconstruction

STM Studio N-face node editor showing stress heat map, face stresses and principal directions — General N-face node editor with boundary-face stresses, average tensor, principal directions and local stress-field heat map.

Engineering interpretation hierarchy for STM Studio N-face nodal plane-stress reconstruction — The interpretation hierarchy separates boundary traction, whole-node average stress, compatibility and the local reconstructed field.

The analytical STM establishes equilibrium. The physical nodal zones explain how those forces enter, leave and redistribute through the concrete.

STM Studio is built around that separation: solve the force model first, then construct and preserve the finite concrete geometry, review the physical force path and complete the separate strength and detailing checks.

Video walkthrough

STM Studio outrigger wall worked example

Watch the complete walkthrough of the worked example, from global building behaviour and load-path development through nodal-zone construction, strut and tie checks, reinforcement design and the final calculation report.

09 · Learning resources

Worked example and N-face technical paper

Review the complete outrigger-wall design sequence and the formulation used for general N-face nodal construction and stress interpretation.

STM Studio outrigger wall worked example cover page

Worked example · 38 pages

Outrigger wall design using STM Studio

A complete educational example covering building behaviour, load-path selection, STM construction, nodal-zone review, offset truss, strut checks, tie design and the generated calculation report.

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STM Studio general N-face nodal stress method

Technical paper · 22 pages

General N-face nodal construction, checking & stress reconstruction

The formulation behind the analytical-to-physical nodal workflow, face traction resolution, whole-node average tensor, compatibility diagnostics and local centroid-fan CST stress-field reconstruction.

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Worked example preview

STM Studio outrigger-wall design

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Related tools and resources

Continue from load-path exploration into broader analysis and structural design workflows.