Deflection
[edit]
Introduction
Deflection – in engineering terms – is the degree to which an element of structure changes shape when a load is applied. The change may be a distance or an angle and can be either visible or invisible, depending on the load intensity, the shape of the component and the material from which it is made.
Deflection is a crucial consideration in the design of a structure and failure to apply due attention to it can be catastrophic.
Different types of load can cause deflections. These include point loads, uniformly distributed loads, wind loads, shear loads as well as ground pressure and earthquakes, to name but a few. When a load produces a deflection that is too great, the component may fail.
Components and structures that suffer deflection include, beams, columns, floors, walls, bridge decks, tunnel walls, dams and so on. San Francisco’s Golden Gate Bridge can sway by as much as 4m laterally under strong winds.
Non-structural components can also deflect, for example cladding panels on a building may deflect inwards when subject to intense wind loading.
Given the possibility of structural failure, building codes usually determine what the maximum allowable deflection should be to ensure the safety of a building’s users and overall structural integrity. For a beam, this is usually expressed as a fraction of the span, eg the beam’s deflection should not be greater than 1/360th of the span; so, if the span is 5m, the deflection should not be greater than 13.9mm. This will usually be measured at the mid-point of the beam.
A structural element will deflect less under load if its stiffness or rigidity is increased. This can usually be achieved by strengthening its section or increasing its size; the latter may also increase its cost.
The material itself must also be considered. For example, because aluminium is around three times more flexible than steel, it is often designed for deflection rather than strength. In contrast, glass is relatively inflexible: even slight deflections in a steel frame could cause the glass to fracture.
RAAC playbook, published by the Manufacturing Technology Centre and the High Value Manufacturing Catapult in 2024 defines deflection as: ‘the degree to which a part of a longitudinal structural element is deformed laterally (in the direction transverse to its longitudinal axis) under a load.’
[edit] Related articles on Designing Buildings
- Approved Document A.
- Concept structural design of buildings.
- Creep.
- Elements of structure in buildings
- Institution of Structural Engineers IStructE.
- Span.
- Structural principles.
- Structures at the end of their design life.
- Substructure.
- Superstructure.
- The development of structural membranes.
- Tower.
- Types of structure.
Featured articles and news
Deputy editor of AT, Tim Fraser, discusses the newly formed society with its current chair, Chris Halligan MCIAT.
Barratt Lo-E passivhaus standard homes planned enmasse
With an initial 728 Lo-E homes across two sites and many more planned for the future.
Government urged to uphold Warm Homes commitment
ECA and industry bodies write to Government concerning its 13.2 billion Warm Homes manifesto commitment.
Places of Worship in Britain and Ireland, 1929-1990. Book review.
The emancipation of women in art.
CIOB Construction Manager of the Year 2025
Just one of the winners at the CIOB Awards 2025.
Call for independent National Grenfell oversight mechanism
MHCLG share findings of Building Safety Inquiry in letter to Secretary of State and Minister for Building Safety.
The Architectural Technology Awards
AT Awards now open for this the sixth decade of CIAT.
50th Golden anniversary ECA Edmundson awards
Deadline for submissions Friday 30 May 2025.
The benefits of precast, off-site foundation systems
Top ten benefits of this notable innovation.
Encouraging individuals to take action saving water at home, work, and in their communities.
Takes a community to support mental health and wellbeing
The why of becoming a Mental Health Instructor explained.
Mental health awareness week 13-18 May
The theme is communities, they can provide a sense of belonging, safety, support in hard times, and a sense purpose.
Mental health support on the rise but workers still struggling
CIOB Understanding Mental Health in the Built Environment 2025 shows.
Design and construction material libraries
Material, sample, product or detail libraries a key component of any architectural design practice.
Construction Products Reform Green Paper and Consultation
Still time to respond as consultation closes on 21 May 2025.
Resilient façade systems for smog reduction in Shanghai
A technical approach using computer simulation and analysis of solar radiation, wind patterns, and ventilation.