What Does Mean In Freeboard In Civil Engineering?
What Does Mean In Freeboard In Civil Engineering?
In civil engineering, freeboard is the height of the watertight portion of a building or other construction above a given level of water in a river, lake, etc.
It is also an additional amount of height above the Base Flood Elevation used as a factor of safety in determining the level at which a structure’s lowest floor must be elevated or floodproofed to be in accordance with state or community floodplain management regulations.
In an open channel, freeboard is the head measured from the maximum water level to the uppermost watertight portion of the surrounding channel.
The recommended amount of freeboard is 1/6 of the channel depth to account for high variations of swift flow induced by waves, surges, and splashes.
How Is Freeboard Calculated Civil Engineering?
Freeboard is the vertical distance between the crest of a structure, such as a dam or levee, and the water level.
It is used to protect the structure from overtopping due to wave action or other forces. Freeboard calculation is an important part of ship design and helps ensure that the vessel will remain afloat in rough seas.
The conditions for assigning freeboard are outlined in regulations 11 to 26 of the International Convention on Load Lines (ICLL) 1966.
The approach to freeboard calculation as laid out in ICLL 66 is to first calculate the standard freeboard that is attributable to the vessel.
This includes factors such as length, breadth, depth, displacement, and block coefficient. The summer freeboard can then be calculated from this standard freeboard and used to determine the summer loadline of the vessel.
Minimum freeboard must also be provided to prevent overtopping of a structure by wave action that may coincide with an inflow design flood.
In addition, it is preferable for steep channels to have a height of freeboard equal to the flow depth in order to account for swift flow induced by waves, surges, and splashes.
What Are Freeboard Design Principles?
The design of freeboard for civil engineering projects is based on a variety of factors, including road classification, site conditions, and debris potential.
Freeboard is the vertical distance between the design elevation and the water surface elevation.
It is recommended that higher freeboards be used for bridges over waterways with debris potential or requiring clearance for the GIWW.
Lower freeboards may be desirable due to constraints such as approach geometry, but the design elevation should not impinge on the low chord.
The American Society of Civil Engineers (ASCE) provides guidelines for establishing scour and freeboard for bridges in their document “Minimum Design Loads for Buildings and Other Structures”.
This document also includes criteria and guidance for planning and designing concrete gravity dams, retrofitting flood-prone residential structures, and fitting saturated hydraulic conductivity using probability density functions.
Additionally, ASCE/SEI 48-05 provides guidance on designing steel transmission pole structures while ASCE/EWRI 50-08 offers a standard guideline for frost-protected shallow foundations.
Overall, there are many considerations when determining appropriate freeboard requirements in civil engineering projects.
The ASCE provides a range of documents that offer technical criteria and guidance to help engineers make informed decisions.
What Are The Freeboard Requirements?
Freeboard is the vertical distance between the crest of the embankment and the reservoir water surface.
It is typically measured in terms of normal freeboard, which is defined as the difference in elevation between the crest of the dam and the normal reservoir water level as fixed by design requirements, and minimum freeboard, which is defined as the difference in elevation between the crest of the dam and the maximum reservoir water surface that would result should an inflow design flood occur.
Freeboard requirements are typically implemented through a locality’s building code. Typical requirements call for an additional 1-3 ft. above base flood elevation (BFE).
Freeboard is not required by NFIP standards, but communities are encouraged to adopt at least a one-foot freeboard to account for a one-foot rise built into structures.
In open channels, freeboard is recommended to be equal to or greater than 1/6 of channel depth to account for high variations of swift flow induced by waves, surges, and splashes.
In addition, culvert, screen and outfall manual (CIRIA C786) published by CIRIA in 2019 defines freeboard as an allowance for uncertainty in design water level and any other physical processes that may affect it, while Containment systems for prevention of pollution (CIRIA C736) published by CIRIA in 2014 defines freeboard as an allowance for uncertainty in design water level plus any other physical processes that may affect it.
Rules of Thumb Guidelines for Building Services (5th Edition) BG 9/2011 also defines freeboard as the vertical distance in a water tank between maximum design level and its uppermost watertight portion.
Finally, High Speed Rail (Crewe – Manchester) Environmental Statement Glossary Abbreviations & References published by Department for Transport in 2022 defines freeboard allowance as height from maximum design level of a watercourse to soffit (underside) of any culvert or bridge above to reduce risk of blockage by floating debris etc.
