Mech
Materials
Area of practice · Donald W. Parnell, PE
Material selection and specification across structural, geotechnical, electrical, mechanical, and process work, documented through engineering notes, specifications, and reports.
Overview
Material selection as a design responsibility
Nearly every project recorded on this site required the selection and specification of materials, and with it the engineering notes, specification sections, and reports that state what material is to be used, to what standard, and why. Material selection is not a separate task from design but a condition of it: the loads, environment, service life, fabrication method, and cost of a structure or machine are all decided in part by the materials chosen for it. The sections below collect that material-selection work by material family, each tied to the projects where it was exercised, and together they document a general working knowledge of material behavior and specification across the areas of practice on this site.
Concrete
Structural, prestressed, and mass concrete
Concrete was specified across the bridge, foundation, and substation work. The prestressed girders on the Mallard Creek ramp required high-early-strength mixes compatible with the prestressing strand and its release strength; bridge decks and substructures required durable, air-entrained mixes with cover and reinforcing grades set for exposure and scour; equipment pads for autotransformers and breakers required mass placements proportioned for bearing and for heat of hydration; drilled piers for towers required mixes that could be placed through the reinforcing cage and, where groundwater was present, by tremie. Oil-containment structures at substations required low-permeability concrete and sealed joints so that captured oil could not escape through the structure itself. Reinforcing steel grade, bar size, and detailing followed from each element’s design.
Structural Steel
Girders, towers, poles, frames, and enclosures
Structural steel was selected and specified for the Spence–Best overpass girders and their cross-frames, for transmission and communications towers and monopoles, for substation dead-end and bus-support structures, for machine frames and weldments on production-line and equipment work, and for switchgear enclosures. Selection turned on the steel grade and its weldability, the fabrication method, and above all the corrosion environment: hot-dip galvanizing for towers, poles, and substation structures exposed for decades; painted or weathering steel for bridge girders according to the owner’s practice; and stainless or coated steel where process or clean-room conditions required it. Bolting, weld electrodes, and anchor-bolt materials were specified to match the members they joined.
Soils and Aggregates
Earthwork, bearing, and pavement materials
Earthwork and foundation design depended on characterizing the site soils and specifying the materials placed on them: select fill and compaction requirements for substation yards and roadway embankments, allowable bearing values taken from soil reports for footings and mats, lateral soil parameters for drilled piers under overturning, aggregate base and crushed stone for substation yards and gravel access roads, riprap gradations for scour countermeasures and channel work, and asphalt surfacing for the greenway corridor. Interpreting the geotechnical report and translating it into material and placement specifications was a recurring part of the site and foundation work.
Electrical Materials
Conductors, insulators, insulating fluids, and grounding
Substation, transmission, and distribution design required specifying the electrical materials of the system: aluminum and copper bus and conductor sized for ampacity and short-circuit forces; ACSR and other conductor types for transmission and distribution lines; porcelain and polymer insulators and bushings rated for voltage class and contamination; transformer and breaker insulating oil, whose containment drove the SPCC work; copper ground-grid conductor and connectors; and the insulating, arc-resistant, and enclosure materials of switchgear. Each is a material choice governed by electrical performance, mechanical loading, and environmental exposure at once.
Piping Materials
Process, sanitary, and utility piping
Process piping is organized around material classes, and the pharmaceutical, nuclear, wastewater, and petroleum piping work required selecting pipe, fitting, valve, and gasket materials for the fluid carried, its temperature and pressure, and its cleanliness requirements. Pharmaceutical process lines under clean-room isolation called for sanitary stainless steel with polished interior surfaces and hygienic fittings; nuclear penetration and plant piping was governed by the plant’s controlled material specifications; wastewater treatment plant piping used ductile iron, coated steel, and plastics selected for corrosion and abrasion; and municipal water and sewer corridors used ductile iron and PVC under AWWA standards. HVAC ductwork and refrigeration piping carried their own material selections for the sheet-metal and refrigerated production-line work.
Engineering Metals
Machined and fabricated components
Machine design and machining required material selection at the component level: tool steels and hardened alloys for tool-and-die work, aluminum and stainless alloys for semiconductor-equipment and short-run parts where cleanliness and non-contamination governed, and the steels, bearings bronzes, and engineered plastics of production-line mechanisms and textile machinery. Machinability, heat treatment, surface finish, and dimensional stability under the required tolerances were the selection criteria, and were carried on the part drawings and bills of material.
Documentation
Specifications, engineering notes, and reports
Material decisions were recorded, on every project, in the documents that carry them into construction and fabrication: specification sections and material schedules, engineering notes on drawings stating grade, standard, finish, and treatment, and reports justifying the selection where the owner or reviewer required it. Preparing those documents — and reviewing the submittals, certifications, and test reports that came back against them — was part of the design responsibility on the projects recorded across this site, and is the practical form in which material selection knowledge is exercised.
About this record. This site is a working record of professional experience, maintained to verify subject-matter background. Areas of practice are reached from the menu above. The record is expanded as additional work history is documented.
Donald W. Parnell, PE | North Carolina PE No. 33878