Span
[edit] Introduction
In structural engineering and architecture, ‘span’ is the term given to the length of a structural component – eg beam, floor, roof or floor truss – that extends (or ‘spans’) between two supports. Thus, a beam may be supported at either end, in which case it is said to span between the two points, and a floor may span between two (or three or even four) continuous supports.
A general engineering principle is the longer the span, the deeper the structural component will have to be to safely support its self-weight and whatever it must carry, eg a floor.
[edit] Span-to-depth (STD) ratio
Span-to-depth ratio (or span/depth ratio, also known as slenderness ratio L/h) is the ratio of the span length divided by the depth (or vertical height) of a component. It is an important parameter as it can affect structural behaviour, construction costs and aesthetics.
A 250mm-deep beam that spans 4m has a span/depth ratio of 16. If the span/depth ratio is less than two, the beam is considered to be ‘deep’. Eurocode 2 gives span/depth rules for designing reinforced concrete beams and slabs.
More dramatic span/depth ratios can be provided by space frames: a rectangular space frame may have a span/depth ratio of up to 40, while this can be as high as 60 for a skew space frame.
Span/depth ratios are useful in limiting the deflection of a member under service loads. Damage may result if limits are exceeded, eg cracking of plaster, partitions and supporting brickwork. If limits are exceeded wildly, catastrophic structural failure accompanied by potential loss of life may result.
In bridge design, span/depth ratio is an important parameter. The ratio relates the length of the bridge’s span to its girder depth. To ensure that design does not deviate substantially from past successful practice, the ratio is commonly chosen on the basis of experience and the typical values used on past bridges. A typical starting point for estimating bridge construction depths is to take an STD ratio of 20.
[edit] Related articles on Designing Buildings Wiki
Featured articles and news
Top 50 firms awarded 52bn of projects in the last year
New engineering data shows.
Enhancing construction site reporting efficiency
Through digitisation and the digital revolution.
Noise in the built environment
BSRIA guide TG 20/2021.
17,000 people suffer conditions as a result of exposure to excessive noise at work.
Turning down the noise: Auditory health
A pervasive risk with far-reaching consequences.
UK Construction Week, London is here !
Debuting major international pavilions and much more.
Getting the most out of heat pumps and heating
How heat pumps work and how they work best.
Plumbing and heating for successful retrofit and renovation
Low temperature underfloor systems and heat pumps.
Cost-of-living crisis and home improvement plans
Starting on the right footing and top tips for projects.
Delays on construction projects
Types, mitigation and the acceleration of works.
From Chaucer to Fawlty Towers.
Electrotechnical excellence, now open for entries.
Net zero electricity grids BSRIA guide NZG 5/2024
Outlining the changes needed to transition to net zero.
CIOB Global Student Challenge 2024
Universitas Indonesia wins for second year running.
ECA 2024 Apprentice of the Year Award
Entries open for submission until May 31.
Comments
[edit] To make a comment about this article, click 'Add a comment' above. Separate your comments from any existing comments by inserting a horizontal line.