Port and Starboard Workstations - Structural Substantiation

Introduction

ScopeStatic-strength substantiation

Port and Starboard workstation installations on the DHC-8-100, including primary structure, equipment support provisions and aircraft attachments.

Load environmentFlight + emergency ultimate loads

Critical inertia cases are applied to the installed mass and checked through FEM and targeted classical substantiation.

AcceptancePositive structural margin

Member stresses, stability modes, joints, panels, composite supports and attachment reactions are compared with applicable allowables.

This portfolio case study condenses the structural substantiation of the Port and Starboard workstation installations. The engineering scope covers the governing inertia environment, FEM idealization, primary-member stress and stability, sheet-metal screening, joint/fastener loads, composite supports, and aircraft attachment reactions.

Workstations Assemblies at the PORT and STARBOARD sides of a DHC-8-100 aircraft

Design Assessment

Governing configuration. The Port and Starboard layouts are identical over X274.4–X299.4 and experience the same vertical acceleration environment. Because the Starboard workstation carries the greater equipment mass, it is the governing structural configuration; the Port installation is covered by comparison.

WHY

Analyze the heavier side once. Equal geometry + equal vertical acceleration + higher Starboard mass makes the Starboard model the conservative configuration without duplicating an equivalent FE model.

Load-Path Rationale

I used the heavier Starboard workstation as the governing configuration and retained the complete structural load path from equipment inertia to the aircraft attachments. Equipment and composite-table masses are introduced through RBE3 elements so their inertia is distributed without artificial stiffness; beam and plate elements then carry the loads through the tube frame, skins, braces, gussets, and attachment fittings. The lower seat-track studs provide the primary translational restraint, while the upper attachments restrain lateral and longitudinal motion but leave vertical translation free. This avoids creating an artificial upper vertical load path while preserving the physical support kinematics.

Workstation Tower Assembly of the Starboard Workstation.

Mass & CoG Representation

Load-bearing structure remains explicitly modeled. Equipment is introduced at its CoG, while omitted non-load-bearing details are retained as nonstructural mass so the inertia field remains representative without unnecessary geometric detail.

Modeled structure62.49 lb

Equipment127.14 lb

Nonstructural mass12.16 lb

Composite shelves4.29 lb

Total modeled installation206.08 lb

Combined CoG (X, Y, Z)−7.39, −13.10, 32.03 in

Technical structural-analysis visual. — Payload Weights and their CoG locations.

Allowables & Joint Basis

MATERIALS

Metallic strength allowables are taken from the cited MMPDS data. Local welded 6061-T6 tube properties are reduced to the applicable weld-zone values rather than using parent-material strength.

FASTENERS

Joint capacity is based on the weakest applicable failure path for the actual fastener, insert, sheet and bearing stack—not the isolated fastener catalog strength.

Representative strength values used in the substantiation

6061-T6 tube: Ftu = 38 ksi; Fcy = 34 ksiWeld zone: Ftu = 24 ksi; Fcy = 15 ksi2024-T3 ALCAD: tensile/compressive basis = 62/37 ksi2024-T351 plate: tensile/compressive basis = 63/39 ksiUpper attachment stud shear capacity: 481 lbfFE200744 lower stud shear capacity: 2,000 lbf

Load Cases Formulation

The installation is screened against the applicable flight and emergency-landing acceleration environment. Vertical flight loads are extracted conservatively at X287.99 within the workstation span, and emergency cases are included where they govern.

Load Cases

Load Case Number	Load Factor Direction	Ultimate Load Value ( $\mathbf{N}_{\mathbf{u}}$ ) [g]	Governing basis
1	Up	4.26	Flight
2	Down	6.8	Flight
3	Outboard	3.0	Emergency landing
4	Inboard	3.0	Emergency landing
5	Forward	9.0	Emergency landing
Not required*	Aft	1.5	Covered conservatively by Forward case
* The Aft case is covered conservatively by the 9g Forward case and is not analyzed separately.

Load-Case Selection Rationale

I screened the workstation against the applicable flight and emergency-landing accelerations and retained the governing demand for each direction. The vertical flight cases govern Upward and Downward at 4.26g and 6.80g, while the emergency-landing criteria govern Outboard, Inboard, and Forward at 3g, 3g, and 9g. The 1.5g Aft condition is enveloped by the Forward case, so five distinct ultimate-load cases are sufficient without duplicating a weaker reverse-direction case.

Finite Element Analysis (FEA)

The Starboard workstation is modeled in FEMAP and solved using Simcenter Nastran. The model is intentionally mixed-dimensional: beam elements recover member forces efficiently, plate elements capture membrane/bending response, CBUSH elements provide discrete joint reactions, and RBE3 connections distribute equipment inertia without introducing artificial stiffness.

Model & Idealization

IDEALIZATION

Beam elements · tube & braces

Slender members carry load primarily through axial force, shear and bending. Beam idealization preserves section properties and member force recovery with far lower model cost than solid geometry.

IDEALIZATION

Plate elements · sheet structure

Thin panels and brackets are represented by midsurface plates so membrane and bending stresses are recovered directly through the sheet thickness definition.

JOINT MODEL

CBUSH · discrete fasteners

Node-to-node connector elements preserve a discrete load path and enable direct reaction extraction without rigidly tying the joint rotational behavior.

LOAD INTRODUCTION

RBE3 · equipment masses

RBE3 distributes inertia load into surrounding structural nodes without adding artificial stiffness to the supporting panels or tube structure.

MASS MODEL

NSM · omitted nonstructural content

Panels, hardware and small non-load-bearing items are omitted geometrically but retained as distributed nonstructural mass, preserving inertia while avoiding unnecessary mesh/detail.

CONTACT

Non-penetrating interface

The attachment gusset / upper support angle interface transfers compressive contact load without creating an artificial tensile tie across the mating surfaces.

CONSERVATISM

Upper brace omitted

Removing the brace eliminates a potential parallel load path; the remaining modeled structure therefore carries the reaction without credit for that support contribution.

GEOMETRY

Noncritical holes covered

Suppressing holes that do not define the primary load path avoids local numerical peaks and reduces mesh density while retaining structural stiffness at the substantiation scale.

Finite Element Model for the Starboard Workstation.

Loads & Constraints

The lower seat-track studs provide the primary translational restraint. Upper attachments restrain lateral and longitudinal motion while leaving vertical translation free, avoiding an artificial vertical load path through the upper support.

Boundary conditionsLower attachments: Tx, Ty, Tz restrained.
Upper attachments: lateral and longitudinal translation restrained; vertical translation remains free.

Engineering rationale
The constraint set follows the attachment kinematics while avoiding unnecessary upper vertical fixity that would create an artificial load path and over-stiffen the workstation.

Analysis

SIMCENTER NASTRAN

SESTATIC · SOL 101

Linear static analysis is appropriate for the ultimate inertia load cases used for strength substantiation.

Mass is entered in lb_m, density in lb_m/in³ and acceleration in in/s². WTMASS provides consistent mass-to-force conversion so solver forces are recovered in lb_f and stresses in psi.

Governing Results

The full source analysis evaluates each member, panel, joint and equipment support. For portfolio use, the table below retains the governing or representative checks that best demonstrate the structural substantiation method.

Selected governing structural checks

Assessment	Demand / basis	Margin	Status
Welded tube · combined axial + bending interaction	Interaction ratios 0.371 + 0.593	+0.038	PASS
FWD shelf brace · crippling	23.05 ksi allowable / 22.69 ksi demand	+0.016	PASS
2024-T3 ALCAD sheet · principal stress	37 ksi compression basis / 28.30 ksi	+0.31	PASS
2024-T351 plate · principal stress	39 ksi compression basis / 28.09 ksi	+0.39	PASS
6061-T6/T6511 extrusion · principal stress	34 ksi compression basis / 24.35 ksi	+0.40	PASS
Upper attachment stud · shear	481 lbf / (357.70 × 1.15) lbf	+0.17	PASS
Upper seat-track tooth	2,250 lbf / 1,515.5 lbf	+0.48	PASS
Seat-track stud · nonlinear check	0.14 in allowable / 0.0692 in displacement basis	+1.02	PASS
FWD desk panel · Part 1 rivets	428 lbf / 401 lbf shear	+0.07	PASS
Inboard tower skin · rivets	428 lbf / 408.13 lbf shear	+0.05	PASS
Attachment gusset · shear	482 lbf / 432.71 lbf	+0.11	PASS
Desk-to-tower riveted joint · shear	316 lbf / (389.93 / 2) lbf	+0.62	PASS

GOV

Minimum reported margin: +0.016 The forward shelf-brace crippling check is the tightest retained margin in this portfolio summary; all selected checks remain positive.

Primary Tube Structure

Beam-force recovery is converted to axial and bending stress at the tube extremes, with separate parent-material and weld-zone properties. The combined interaction check at the weld is more critical than simple tension and provides the governing tube-structure margin shown below.

Axial Force and Bending Moments contours over the tube structure for the forward case.

Tube Structure Combined Stresses

{{M.S}^{tube} = \frac{1}{R_{A,max}^{tube} + R_{b,max}^{tube}} - 1 = \frac{1}{0.1447 + 0.404} - 1 }{= \boxed{0.823}}

{{M.S}^{weld} = \frac{1}{R_{A,max}^{weld} + R_{b,max}^{weld}} - 1 = \frac{1}{0.371 + 0.593} - 1 }{= \boxed{0.038}}

\boxed{{M.S}^{tube - struc.} = 0.038\ }

→ PASS

Shelf Braces · Strength & Crippling

The shelf-brace extrusions are checked for direct tension/compression and local crippling. The forward brace is the critical member, with the crippling allowable only slightly above the maximum compressive demand.

Axial Force and Bending Moments contours over the FWD Shelf Brace Beam for the forward load case.

{M.S}_{Crippling}^{FWD\ BRACE} = \frac{23.05}{22.69\ } - 1

{M.S}_{Crippling}^{AFT\ BRACE} = \frac{23.05}{21.42} - 1

\boxed{{M.S}^{FWD\ BRACE} = 0.016\ }

→ PASS

\boxed{{M.S}^{AFT\ BRACE} = 0.076\ }

→ PASS

Sheet-Metal Stress Screening

Principal stresses are screened across every load case. Elements outside the source-defined thresholds are flagged for physical review so isolated numerical peaks do not automatically govern without checking their location and structural meaning.

2024-T3 ALCADMS +0.31

2024-T351 plateMS +0.39

6061-T6/T6511MS +0.40

The Flagged Elements within the 2024-T3 ALCAD Sheet that have Principal Stress Values Falling Out of the Set Thresholds.

The Flagged Elements within the 2024-T351 Plates that have Principal Stress Values Falling Out of the Set Thresholds.

Composite Table Supports

The sandwich tables are checked using conservative simply-supported loading under the 6.8g downward case. For the main table plus mission computer, the calculated core shear stress is 2.95 psi versus published short-beam shear allowables of 262/391 psi; the calculated facing bending stress is 1.071 ksi versus published long-beam facing allowables of approximately 58 ksi. The side table is less critical.

Main Tabletop installation

Face Sheet Bending Stress

Aircraft Attachment Load Path

Attachment reactions are extracted directly from the connector model and resolved into tensile/shear demand. The custom upper stud, seat-track tooth and lower seat-track stud are then checked using targeted classical and nonlinear analyses.

Upper stud max shear357.70 lbf

Lower stud max shear374.90 lbf

Lower stud max tension2,150.84 lbf

Upper Attachment Stud.

{M.S}_{fs}^{UpAttStud} = \frac{481}{357.70 \times 1.15} - 1

{M.S}_{fs}^{LowerAttStud} = \frac{2000}{374.90 \times 1.15} - 1

\boxed{{M.S}^{UpAttStud} = 0.17}

→ PASS

\boxed{{M.S}^{LowerAttStud} \gg 1\ \ \ }

→ PASS

{M.S}^{tooth} = \frac{2,250}{1515.5\ } - 1

\boxed{{M.S}^{tooth} = 0.48}

→ PASS

Non-linear analysis for Seat Track Stud

{M.S}^{Seat\ Track\ Stud} = \frac{0.14}{0.0692} - 1

\boxed{{M.S}^{Seat\ Track\ Stud} = 1.02}

→ PASS

Panel Joints & Fastener Load Extraction

Panel membrane resultants, shear flow and transverse shear are converted to discrete edge/fastener loads. The governing panel-joint margins remain positive; representative tight checks include the FWD desk panel rivets (+0.07) and inboard tower-skin rivets (+0.05).

The Inboard Tower Skin Panel and its Rivets.

The Inboard Tower Skin Panel’s (i) Membrane Forces per unit length along x and y-axes, (ii) Shear Flow per unit length, and (iii) Shear Forces per unit length over the x and y faces in the forward load case.

Python-Assisted Plate Post-Processing

The desk-to-tower attachment demonstrates the workflow used where plate resultants must be converted into discrete fastener demand over many elements and load cases.

Python Workflow

The plate-force post-processing was automated to reduce repetitive manual work and improve traceability. The script reads FEMAP-exported element and nodal data, rejects triangular elements, calculates element dimensions, converts membrane resultants to elemental forces, screens all load cases, and writes governing results to a summary workbook.

Read the FEMAP Excel export and nodal coordinates.
Extract nodal-coordinate values (X-Def, Y-Def, Z-Def).
Filter valid quadrilateral plate elements.
Calculate element dimensions and local force directions.
Recover n_x, n_y, n_xy, q_x, and q_y for every element and load case.
Calculate elemental shear and tensile demand.

N_x=d_xn_x,\quad N_y=d_yn_y,\quad N_{xy,x}=d_xn_{xy},\quad N_{xy,y}=d_yn_{xy}

A conservative in-plane resultant is calculated as:

F_{s,max}=\sqrt{(N_x+N_{xy,y})^2+(N_y+N_{xy,x})^2}

Generate contour maps and a governing-result summary.
- 2D plot of elements and nodes.
- Heat maps for maximum shear load and maximum tensile load for every load case.
- Extract maximum membrane forces, shear, and tensile loads from each load case and save them to a new summary table.

Three-dimensional plate element showing membrane resultants, transverse shear resultants, bending moments, twisting moment, dimensions, and local axes used in the Python post-processing workflow.

Why I automated this stepThe governing plate element was not necessarily the element with the largest individual n_x, n_y, or n_xy component. Automation allowed every valid plate element and load case to be evaluated using one documented equation set, eliminating inconsistent spreadsheet manipulation and preserving a repeatable audit trail.

Nodes and Elements extracted from the FEMAP results file.

Shear Force [lb_f] for all elements in all load cases.

Tensile Forces [lb_f] for all elements in all load cases.

{M.S}_{fs}^{Desk - Tower\ Attachment\ Rivets} = \frac{316}{389.93\ /2} - 1

{M.S}_{ft}^{Desk - Tower\ Attachment\ Rivets} = \frac{115}{71.42/2} - 1

\boxed{{M.S}_{s}^{Desk - Tower\ Attachment\ Rivets} = 0.62}

→ PASS

\boxed{{M.S}_{s}^{Desk - Tower\ Attachment\ Rivets} = 2.22}

→ PASS

Equipment & Secondary Attachments

Secondary attachments are screened using extracted CBUSH or nodal reactions against the governing fastener/insert capacity. These checks retain conservative load assumptions while avoiding unnecessary repetition in the portfolio version.

Representative secondary-attachment checks retained from the full analysis

Installation	Governing extracted demand	Assessment
Keyboard tray	Part 3 shear = 553.22 lbf → 276.61 lbf per two-screw assumption	NAS8602-2 screws pass by observation
Mission computer	172.08 lbf shear; 81.5 lbf tension	NAS1832-3-4 insert governs; pass by observation
Monitor bracket	448.8 lbf shear; 163.26 lbf tension per AN3-15A screw	NAS1834-3-1000 insert governs; pass by observation
Monitor close-out	167.54 lbf max nodal component; conservative combined shear = 201 lbf	NAS8602-2 screws pass by observation
Shelf clips	47.45 lbf max nodal component; conservative combined shear = 61 lbf	MS20426AD4 rivets pass by observation
Cross-brace beam attachment	0.54 lbf maximum extracted load	NAS1801-3-8 screws pass by observation

Mission Computer and Composite Table Attachment Points

The Maximum Shear and Tensile Loads [lb_f] due to the the Mission Computer and the Composite Panel.

The Maximum reaction forces [lb_f] at the Monitor Bracket Attachment Points.

References

Structural Methods & Allowables

MMPDS-15 - Metallic Materials Properties Development and Standardization
Analysis and Design of Flight Vehicle Structures - E. F. Bruhn
Aluminum Design Manual 2010
Stress Analysis Manual - Air Force Flight Dynamics Laboratory, Wright-Patterson
Fastener Design Manual - NASA Reference Publication 1228

Regulatory & Aircraft Load Basis

Federal Aviation Regulations - 14 CFR Part 25
DHC-8-100 Load Cases and Applied Loads

Fasteners & Hardware Data

CherryMax Rivets technical data
NAS528 Fastener Codes
MS24693 technical data
NAS1832 / NAS1834 insert technical data
NAS8602 / NAS1801 fastener technical data

Track, Composite & Fitting Data

ANCRA Aircraft Track technical data
FE200744 stud technical data
40351 / 40352 Threaded Stud specifications
TEKLAM AA207-66-1000 / AA207-33-1000 technical data