Editing Bridge (section)

==Bridge health monitoring==
There are several methods used to monitor the condition of large structures, like bridges. Many long-span bridges are now routinely monitored with a range of sensors, including strain transducers, [[accelerometer]]s,<ref>{{cite web|url=http://www.mnme.com/pdf/smartbridge.pdf|title=The new Minnesota smart bridge|work=mnme.com|access-date=30 January 2012|archive-url=https://web.archive.org/web/20120823002008/http://www.mnme.com/pdf/smartbridge.pdf|archive-date=23 August 2012}}</ref> tiltmeters, and GPS. Accelerometers have the advantage that they are inertial, i.e., they do not require a reference point to measure from. This is often a problem for distance or deflection measurement, especially if the bridge is over water.<ref>{{citation | last1=Bagher Shemirani | first1=Alireza |title = Experimental and numerical studies of concrete bridge decks using ultra high-performance concrete and reinforced concrete | journal=Computers and Concrete |date = 2022 | volume=29 | issue=6 | doi=10.12989/cac.2022.29.6.407 }}</ref>  [[Crowdsourcing]] bridge conditions by accessing data passively captured by cell phones, which routinely include accelerometers and GPS sensors, has been suggested as an alternative to including sensors during bridge construction and an augment for professional examinations.<ref>{{Cite magazine |last=Riordon |first=James R. |date=3 December 2022 |title=Cell phones track bridge integrity |magazine=[[Science News]] |type=Paper |volume=202 |issue=10 |page=8}}</ref>

An option for structural-integrity monitoring is "non-contact monitoring", which uses the [[Doppler effect]] (Doppler shift). A [[laser]] beam from a [[Laser Doppler Vibrometer]] is directed at the point of interest, and the vibration amplitude and frequency are extracted from the Doppler shift of the laser beam frequency due to the motion of the surface.<ref>{{cite web|url=http://www.polytec.com/us/solutions/vibration-measurement/basic-principles-of-vibrometry/|title=Basic Principles of Vibrometry|work=polytec.com|access-date=25 January 2012|url-status=live|archive-url=https://web.archive.org/web/20120610192737/http://www.polytec.com/us/solutions/vibration-measurement/basic-principles-of-vibrometry/|archive-date=10 June 2012}}</ref> The advantage of this method is that the setup time for the equipment is faster and, unlike an accelerometer, this makes measurements possible on multiple structures in as short a time as possible. Additionally, this method can measure specific points on a bridge that might be difficult to access. However, vibrometers are relatively expensive and have the disadvantage that a reference point is needed to measure from.

Snapshots in time of the external condition of a bridge can be recorded using [[Lidar]] to aid bridge inspection.<ref name="omer">{{cite journal | last1 = Omer | display-authors = et. al. | year = 2018 | title = Performance evaluation of bridges using virtual reality | url = https://www.researchgate.net/publication/325194259 | journal = Proceedings of the 6th European Conference on Computational Mechanics (ECCM 6) & 7th European Conference on Computational Fluid Dynamics (ECFD 7), Glasgow, Scotland}}</ref> This can provide measurement of the bridge geometry (to facilitate the building of a computer model) but the accuracy is generally insufficient to measure bridge deflections under load.

While larger modern bridges are routinely monitored electronically, smaller bridges are generally inspected visually by trained inspectors. There is considerable research interest in the challenge of smaller bridges as they are often remote and do not have electrical power on site. Possible solutions are the installation of sensors on a specialist inspection vehicle and the use of its measurements as it drives over the bridge to infer information about the bridge condition.<ref>{{Cite journal|last1=Yang|first1=Y.-B.|last2=Lin|first2=C.W.|last3=Yau|first3=J.D.|date=May 2004|title=Extracting bridge frequencies from the dynamic response of a passing vehicle|journal=Journal of Sound and Vibration|volume=272 |issue=3–5|pages=471–493|doi=10.1016/S0022-460X(03)00378-X|bibcode=2004JSV...272..471Y}}</ref><ref>{{Cite journal|last1=Yang|first1=Y. B.|last2= Yang|first2=Judy P.|date=February 2018|title=State-of-the-Art Review on Modal Identification and Damage Detection of Bridges by Moving Test Vehicles|journal=International Journal of Structural Stability and Dynamics|volume=18|issue= 2|page=1850025|doi=10.1142/S0219455418500256|issn=0219-4554}}</ref><ref>{{Cite journal|last1=Malekjafarian|first1=Abdollah |last2=McGetrick|first2=Patrick J.|last3=OBrien|first3=Eugene J.|date=2015|title=A Review of Indirect Bridge Monitoring Using Passing Vehicles|journal=Shock and Vibration|volume=2015|pages=1–16|doi=10.1155/2015/286139|issn=1070-9622|doi-access=free|hdl=10197/7054|hdl-access=free}}</ref> These vehicles can be equipped with accelerometers, gyrometers, Laser Doppler Vibrometers<ref>{{Cite journal|last1=OBrien |first1=E. J.|last2=Keenahan|first2=J.|date=May 2015|title=Drive-by damage detection in bridges using the apparent profile |journal=Structural Control and Health Monitoring|volume=22|issue=5|pages=813–825|doi=10.1002/stc.1721|hdl=10197/7053|s2cid=55735216 |hdl-access=free}}</ref><ref>{{Cite journal|last1=Malekjafarian|first1=Abdollah|last2=Martinez|first2=Daniel|last3=OBrien|first3=Eugene J.|date=2018|title=The Feasibility of Using Laser Doppler Vibrometer Measurements from a Passing Vehicle for Bridge Damage Detection|journal=Shock and Vibration|volume=2018|pages=1–10|doi=10.1155/2018/9385171|issn=1070-9622|doi-access=free|hdl=10197/9539|hdl-access=free}}</ref> and some even have the capability to apply a resonant force to the road surface to dynamically excite the bridge at its resonant frequency.