Containerised Inverter Station — Structural Qualification Case Study

The Challenge

A 29.5-tonne steel enclosure. Every extreme load. One qualification study.

The client needed structural qualification of their containerised inverter station for deployment on a large-scale 500 MW photovoltaic plant. The container houses a 16-tonne transformer, 5.6-tonne inverter, ring cabinet, auxiliary panels, and a canopy — approximately 29.5 tonnes of dead load distributed across a welded steel frame supported by 10 columns.

The structure had to be proven safe against a demanding combination of environmental and operational loads: 115 mph wind from four directions, significant snow and ice accumulation, moderate-to-high seismicity with directional horizontal and vertical components, and platform live loads — all per ASCE 7-22 requirements.

The client required both Ultimate Limit State (ULS) and Serviceability Limit State (SLS) verification with full per-column reaction data for downstream foundation design and anchor bolt specification.

The challenge wasn't just solving a stress problem — it was producing a complete, traceable load calculation package that a civil engineer could take directly into foundation design without further interpretation.

Our Approach

Code-driven. Every direction. Every combination.

SIMFORGE built a detailed shell element finite element model of the container's main frame in Ansys Mechanical and systematically evaluated 49+ load sub-cases covering every critical scenario required by ASCE 7-22.

Load derivation followed the code rigorously — wind pressures computed for both the pitched canopy and enclosed frame with four independent wind directions. Seismic forces derived using the component-level Fp method with site-specific spectral parameters.

Load	Value	Method / Source
D	295 kN	Self-weight + all internal equipment
L	4.79 kN/m²	ASCE 7-22 Table 4.3-1 — platforms
S	0.588 kN/m²	Flat-roof snow, Ce = 1.0, Ct = 1.2
Di	2.825 kN/m²	32 cm ice layer
qh	1,376.6 N/m²	V = 51.4 m/s, Kz = 0.85, Kzt = 1.0
Fp (horiz.)	0.536 × Wp	SDS = 0.533 g, Ip = 1.25, CAR = 1.4
Ev (vert.)	0.107 × Wp	0.2 × SDS × Wp

ULS Results

Governing load case: seismic, not wind.

Despite the 115 mph (51.4 m/s) design wind speed, seismic loading governed — confirming that for this product class and site, the seismic combination with horizontal excitation in the transverse direction is the critical design driver.

Load Combination	Max Disp.	Max σ	Util.
1.4D	1.3 mm	107.4 MPa	46%	PASS
1.2D + 1.6L + 0.3S	4.7 mm	184.4 MPa	78%	PASS
1.2D + 1.0S + L	3.2 mm	147.0 MPa	63%	PASS
1.2D + W + L + 0.3S	3.2 mm	152.7 MPa	65%	PASS
0.9D + W (worst dir.)	2.0 mm	92.2 MPa	39%	PASS
1.2D + Ev + Eh + L + 0.15S ← governs	3.6 mm	225.8 MPa	96%	PASS
0.9D − Ev + Eh	3.6 mm	178.1 MPa	76%	PASS

SLS Results

Serviceability: well within limits across all combinations.

All 10 SLS combination families were evaluated across directional sub-cases. Maximum displacement under serviceability loading was 3.0 mm — negligible relative to the container span. Stresses remained well below yield.

SLS Combination	Max Disp.	Max σ
D only	0.9 mm	75.2 MPa	PASS
D + L	3.0 mm	131.0 MPa	PASS
D + 0.6W (worst dir.)	1.3 mm	87.4 MPa	PASS
1.0D + 0.7Ev + 0.7Eh	2.6 mm	162.5 MPa	PASS
All remaining SLS combos	≤ 2.5 mm	≤ 148 MPa	PASS

Foundation deliverable

Per-column Fx, Fy, Fz reaction forces were extracted for all 49+ load cases across all 10 columns — providing the civil/foundation engineer with a complete reaction table for anchor bolt sizing and foundation design, directly traceable to code-compliant load combinations.

Engineering Insights

Three findings that changed the foundation design.

Seismic governs over wind — despite 115 mph

The governing combination was seismic with transverse horizontal excitation (225.8 MPa, 96% utilization) — not the 115 mph wind case. This finding is critical for foundation and anchor bolt sizing: designing to wind alone would have under-designed the anchorage by roughly 50% in the transverse direction.

Transformer asymmetry concentrates load on Columns 2 & 7

The 16-tonne transformer offset to one side means Columns 2 and 7 consistently carried the highest vertical reactions — up to ~183 kN resultant under seismic ULS. Without per-column reaction extraction, a symmetric foundation design would have produced unconservative anchor bolts on the transformer side.

No hold-down anchors required — proven by analysis

Even under the most aggressive roof suction (−1,462.6 N/m² net) combined with the minimum gravity case (0.9D), all columns remained in net compression. This is a significant cost saving: eliminating hold-down anchors from a 500 MW plant deployment across hundreds of units is a meaningful project-level saving.

49+ sub-cases. Single delivery cycle.

The full load matrix — 7 ULS + 10 SLS combination families, each expanded across 4 directional sub-cases — was modeled, solved, post-processed, and delivered in a single engagement. The client received a complete illustrated report with contour plots, reaction tables, and code traceability in one package.

Scope of Services

What was delivered.

Load calculation	ASCE 7-22 dead, live, snow, ice, wind & seismic load derivation — all coefficients and factors traceable to code clauses
FEA model	Shell element model of container main frame in Ansys Mechanical 2024 R2. Welds modeled, column boundary conditions matched to real support conditions
ULS verification	7 combination families × directional sub-cases = 19 ULS runs. Von Mises stress and utilization vs. S235 yield for each
SLS verification	10 combination families × directional sub-cases = 30+ SLS runs. Total deformation checked against serviceability targets
Reaction extraction	Per-column Fx, Fy, Fz for all 49+ load cases — 10 columns × 49 sub-cases = 490 reaction values, formatted for direct use by foundation engineer
Deliverable	Full illustrated simulation report: contour plots (stress + deformation) for every sub-case, load calculation annex, reaction force tables, code compliance summary

Similar studies we scope

→Battery storage container structural qualification
→Substation transformer skid analysis
→Solar tracker frame wind + seismic qualification
→Industrial enclosure seismic bracing
→EPC-required foundation reaction packages

Why SIMFORGE for this type of study

Code-driven methodology with every coefficient traceable to clause. Exhaustive directional analysis — not just "worst assumed case". Column-level reaction outputs ready for direct use. Fixed fee, single delivery cycle.

Structural Integrity Under Extreme Conditions — Containerised Inverter Station

Project Snapshot

49+ load sub-cases. Every one passed.

A 29.5-tonne steel enclosure. Every extreme load. One qualification study.

Code-driven. Every direction. Every combination.

Governing load case: seismic, not wind.

Serviceability: well within limits across all combinations.

Three findings that changed the foundation design.

Seismic governs over wind — despite 115 mph

Transformer asymmetry concentrates load on Columns 2 & 7

No hold-down anchors required — proven by analysis

49+ sub-cases. Single delivery cycle.

What was delivered.

Equipment to qualify. Code to satisfy.
Tell us the loading.

Structural Integrity Under Extreme Conditions — Containerised Inverter Station

Project Snapshot

49+ load sub-cases. Every one passed.

A 29.5-tonne steel enclosure. Every extreme load. One qualification study.

Code-driven. Every direction. Every combination.

Governing load case: seismic, not wind.

Serviceability: well within limits across all combinations.

Three findings that changed the foundation design.

Seismic governs over wind — despite 115 mph

Transformer asymmetry concentrates load on Columns 2 & 7

No hold-down anchors required — proven by analysis

49+ sub-cases. Single delivery cycle.

What was delivered.

Equipment to qualify. Code to satisfy.Tell us the loading.

Equipment to qualify. Code to satisfy.
Tell us the loading.