Life cycle & inspection (Ch. 36) adds degraded strength and MTBF screening calculators—asset-level models only.

Scope

Maintenance, aging, and inspections—how structures perform from commissioning through decades in service. This is asset-level thinking: condition assessment, intervention timing, and documentation—not just ULS checks at handover.

Handbook alignment. Handbook of Structural Engineering (Chen & Lui, 2nd ed.) — Chapter 36 — Life cycle evaluation & condition assessment. Licensed reference; owner procedures and national inspection norms govern operational sites.

Reference check (deterioration → inspection → decision)

  1. Model — Estimate residual capacity from a simple ageing curve (toy calculator)—then calibrate with tests and Bayesian updates in real assessments.
  2. Inspect — Plan visual, NDT, or monitoring intervals using risk—major bridges and industrial assets rely on owner standards.
  3. Act — Repair, strengthen, or replace based on life-cycle cost and safety—often tracked in asset software; see tools.

Structural Engineering — Life Cycle & Inspection

Handbook Ch. 36—maintenance, aging, and inspections tied to life-cycle evaluation and condition assessment.

How this page relates to Chapter 36

Chapter 36 — Life cycle evaluation & condition assessment covers asset management, deterioration modelling, inspection planning, and reliability-based assessment—far more than a short web summary. What follows is a theme list; the two calculators are screening toys (linear strength decay, MTBF from constant hazard).

Illustrations (deterioration)

Corrosion and high-temperature oxidation drive section loss and durability decisions on steel and coatings—highly simplified by the diagrams below.

Gas corrosion of steel with iron oxides
Gas corrosion of steel—participation of iron oxides in the layer. Public domain, Wikimedia Commons
Corrosion of chromium coated steel cross section
Corrosion of Cr-coated steel (polished cross-section). CC0, Wikimedia Commons

What life-cycle and inspection produce

  • Condition grades — Rated observations tied to photos, NDT, and load-capacity estimates.
  • Intervention plans — Repair windows, strengthening schemes, and budget forecasts.
  • Risk registers — Updated failure probabilities when inspection data is incorporated.

Standards and owner practice

National bridge inspection manuals, industrial asset standards, and owner engineering rules often exceed generic building codes. Align remaining capacity with the assessment standard cited in the contract (e.g. bridge load rating or structural reliability annexes).

Notation (on-page calculators)

  • Strength decay — f0 initial relative strength; α loss rate per year; t time (years); fn degraded strength factor.
  • MTBF — λ hazard rate (1/year); MTBF = 1/λ (simple random-failure model).

Introduction

Design sets nominal lives and durability assumptions; reality is corrosion, wear, fatigue cracking, foundation movement, and changed use. Condition assessment turns site observations, tests, and history into decisions on repair, strengthening, or replacement—often with reliability and economic risk framing.

Chapter 36 — Life cycle evaluation & condition assessment (handbook scope)

Themes

  • Life-cycle costing — Initial vs maintenance vs failure-risk costs; discounting and intervention timing.
  • Deterioration — Models for corrosion rate, cracking, loss of section; updating with inspection data (Bayesian methods in advanced practice).
  • Inspection — Visual, NDT, monitoring; risk-based inspection intervals; access and baseline records.
  • Assessment — Load rating, remaining capacity, retrofit design; often parallel to bridge or industrial asset codes and owner standards.

Chapter 36 — calculators (screening)

Linear strength degradation model and mean time between random failures from a constant hazard rate—teaching only.

Calculator — degraded strength factor

fn = f0 (1 − α t)

Aging multiplier (illustrative)

Linear residual strength factor fn = f0(1 − αt) vs time (screening model).

Calculator — MTBF from hazard rate

MTBF = 1 / λ

Random failure model (screening)

Mean time between failures MTBF = 1/λ for a constant hazard rate λ.

Software and asset management

Inspection data, digital twins, and reliability updates are often managed in asset information systems. General structural tools still help re-analyse rated members. Examples (official vendor sites):

  • SAP2000 — re-analysis of as-inspected structural models.
  • STAAD.Pro — analysis and design workflows.
  • RFEM — FEA for refined capacity checks.
  • Autodesk Revit — BIM for as-built documentation.

No endorsement—owner inspection manuals and regulator rules define acceptable methods for each asset class.

Diagram sources

Educational schematics. Files in Images/life-cycle-inspection/ from Wikimedia Commons.