Case Study

Penstock platform: awkward site conditions turned into a clean, buildable design package

With four new penstock units to be installed into an existing reservoir inlet opening, Frugal surveyed the site, designed the supporting frame and maintenance platform, and delivered a substantiated package that was installed successfully first time.

Sprint

Water infrastructure

Survey to detail design

Right first time installation

Installed penstock support frame and maintenance platform at the reservoir inlet

Situation

A reservoir inlet upgrade required four new penstock units to be installed into an existing stone-channel opening, mounted on a newly designed support frame, with a newly designed access platform alongside for operation, maintenance, and inspection.

The client had a clear operational objective and a preferred penstock type, but the site-specific geometry, loading basis, and practical installation constraints still had to be established and worked through into a package that could be fabricated and installed with confidence.

The real problem

The challenge was not deciding what was needed in principle, but turning that requirement into a design that would work reliably on a remote real-world site without costly fit-up or installation surprises. The engineering judgement lay in establishing enough dependable dimensional, loading, and interface definition to take the design from concept to fabricated steelwork with confidence.

The real difficulty would be in resolving the interfaces and overall arrangement well enough that the awkward site constraints were properly designed around from the outset. The support frame, penstock units, access platform, and site geometry would all need to work together as one coherent package so the final design remained practical to make, transport, handle, and install.

Constraints

Preselected penstocks: The design had to be built around the end-client’s chosen penstock module, with four units installed in a row.
Remote manual access: Parts had to be carriable roughly half a kilometer over wet ground and assembled on site without large cranes or lifting plant.
Missing design basis: Site dimensions, hydrostatic loading, and key technical requirements had to be established as part of the job.
In-water footing: The platform sat over a sand / silt bed, so footing design, stability, and durability all had to be addressed.
Watertight frame interface: The penstock frame had to seal robustly against old stonework and irregular existing cut-out geometry.
Right-first-time fit: Site rework would have been disproportionately costly, so allowances, interfaces, and assembly logic had to be resolved up front.

Client:

Water infrastructure fabricator / installer

Role:

Mechanical engineering consultant

Period:

2022

Scope:

Site survey +
Penstock support frame +
Access platform design pack

Acceptance basis:

EC3 structural verification +
Fabricator design approval +
End-client structural approval

Key moves

Building the site model

Built an initial 3D site model from photos before visiting, then used it to plan the key survey measurements.
Updated that model after surveying the site to create a dependable geometric basis for the design work.

Exploring design routes

Developed and issued several illustrated concept options early on for fabricator review and feedback.
Used that feedback to steer the job toward a solution that was practical to make and install.

Fixing the operational layout

Set the platform position and height using a simple ergonomic assessment of manual penstock operation.
Developed the frame, penstocks, and platform together so the final arrangement worked as a usable whole.

Choosing the structural architecture

Tested whether the platform and penstock frame should be tied together structurally or kept separate.
Kept them decoupled, giving a cleaner, more robust solution, better suited to the design constraints.

Designing for site fit-up

Built in adjustability, particularly in the interface between penstocks and stone bywash inlet, to cope with site variation.
Surfaced installation issues early through provisional BOMs, risk notes, and an illustrated and annotated installation sequence.

Releasing the final package

Produced full manufacturing-detail 3D models, STEP files, drawings, BOMs, and structural substantiation.
Coordinated connection and footing design input, then delivered a package that was installed successfully first time.

Selected snapshots

Existing site condition at the stone bywash before the new penstock installation

Early concept and survey sketches used to explore the layout and key dimensions