Skip to main content

Structural monitoring

Surveying: ‘The future is here’ – KHL Group – Laser-View | Laser-View

By Construction and Engineering, Editor's Choice, Industrial automation, Sensors, Structural monitoring

The days when surveying meant a group of people holding up poles and measuring angles and distances, marking out a site with yet more poles, are long gone, and the techniques used today are becoming more and more sophisticated all the time. BIM (building information modelling) is a term that was coined only a few short years ago, but is now the key to unlock the data needed on a big project.

Source: Surveying: ‘The future is here’ – KHL Group – Laser-View | Laser-View

Surveying: ‘The future is here’ – KHL Group

By Automation, Editor's Choice, Engineering and construction, Sensors, Structural monitoring, technology

Abdce contex capture copy

The days when surveying meant a group of people holding up poles and measuring angles and distances, marking out a site with yet more poles, are long gone, and the techniques used today are becoming more and more sophisticated all the time.

BIM (building information modelling) is a term that was coined only a few short years ago, but is now the key to unlock the data needed on a big project. And the basic information that allows BIM to hold that powerful position, can be sourced easily from so many different places – even the sky, with drones increasingly playing a part.

However, all these new technologies and the possibilities they offer have to be harnessed.

Elżbieta Bieńkowska, EU Commissioner for Internal Market, Industry, Entrepreneurship and SMEs, wrote in the introduction to the Handbook for the Introduction of Building Information Modelling by the European Public Sector, “Similar to other sectors, construction is now seeing its own digital revolution, having previously benefited from only modest productivity improvements.

“Building Information Modelling is being adopted rapidly by different parts of the value chain as a strategic tool to deliver cost savings, productivity and operations efficiencies, improved infrastructure quality and better environmental performance.”

She said, “The future is here, and the moment has now come to build a common European approach for this sector. Both public procurement – which is accountable for a major share of construction expenditure – and policy makers can play a pivotal role to encourage the wider use of BIM in support of innovation and sustainable growth, while actively including our SMEs – and generating better value for money for the European taxpayer.

In the handbook’s executive summary, it says, “The prize is large: if the wider adoption of BIM across Europe delivered 10% savings to the construction sector then an additional €130 billion would be generated for the €1.3 trillion market.

“Even this impact could be small when compared with the potential social and environmental benefits that could be delivered to the climate change and resource efficiency agenda.”

Roads and bridges

One of the leading companies in this area is US-based Bentley Systems. Santanu Das, senior vice president, design modelling, said that one of the biggest advances in information modelling was its use not only in buildings, but also in transportation and heavy civil engineering projects like roads and bridges.

He said there was increased use in brownfield projects.

“Brownfield projects require some sort of starting data,” he said. In the past, 2D drawings were the starting point, then a 3D model.

“One advancement that came out years ago was point clouds – LiDAR,” said Das. “The issue with LiDAR was two big things – it was quite bulky and expensive, you can only do it once every four or five years. The data that are generated would be in the terabytes sometimes and there was nothing really available to process it properly.”

He said a third problem was classification.

“If you took a point cloud, you had no idea what the hell those points meant. A human can figure out, that’s a wall, that’s a column, but in order to do what we call classification, automatically, was impossible.”

He continued, “So what Bentley’s been working on in the past couple years on its BIM platform is reality modelling, and that’s now all a part of our Connect Edition platform.”

Santanu das gc1 1677

Connect Edition converges Bentley’s platform technology to support a hybrid environment across desktop modelling applications, cloud services, on-premise servers, and mobile apps.

“Every single Connect Edition product we have – from Building Designer to OpenPlant to OpenRoads – uses this fundamental datatype that we create from our ContextCapture piece in there.

“That’s one huge advantage that we have for people who want to start off on brownfield projects.”

Bentley can now process this information in the cloud. Das said that with LiDAR and any type of photogrammetry, the number of pictures captured could be astronomical.

“What we doing out with our new ContextCapture in the cloud is that we have the ability to process hundreds of thousands of these pictures in a very, very quick manner, because we’re using the power of multiple servers.

“Then we stream that information as needed to the BIM platform via our ProjectWise.”

With ProjectWise, what Bentley calls i-models can be combined together with other documents into a single package, so that models and associated content can be accessed on an iPad using Bentley mobile apps.

“Reality modelling classification is huge,” said Das. “The other thing that we are finding in information modelling today and the advancement in BIM is the collaboration aspect.”

While people can work together, share data together, Das said there was a problem of a lack of basic terminology of communication.

“So what we have done is to work really hard to come up with a common terminology for all asset class types. So if we’re talking about a beam in a building, or a beam in a plant scenario, it understands what a beam is.”

Some years ago, Bentley introduced i-models, which Das described as “a sort of pdf for the AEC (architecture, engineering and construction) industry”.

He said, “We’ve taken that to the next level. We’re going to be introducing this thing called the i-model hub, which allows for data to flow from discipline to discipline, and different hierarchies.”

He said there were different levels of detail.

“The hub can filter out the information depending on what your role is, and what your discipline is. It also manages change – which is huge – it’s communicating and constantly keeping that model up to date.”

This communication can be with the products of other companies, too.

“We believe in third party interoperability,” said Das.

The daily visualisation of a jobsite can help minimise construction delays, prevent clashes between the work onsite and the design, eliminate the need for rework, facilitate stakeholder communication and align schedules.

The Pix4D Crane Camera claims to combine hardware and software to help with this. A camera is mounted on a tower crane jib, from where it captures site images. These are transmitted wirelessly to the Pix4D cloud, and processed automatically to be converted into 2D maps and 3D models.

The company behind it said it was designed to monitor any type of construction, and had already been endorsed by some large companies worldwide.

Early adopter

A metro line project in western France was among the early adopters. Dodin Campenon Bernard, part of the Vinci group, was awarded a 14km project that included a tunnel and underground stations.

The station to be monitored was in the heart of the city centre and made drone flights, which was one option, impossible.

At 32m of digging depth and with massive brace frames to support the excavation, the building site was said to be a challenge. However, through the data collected with the crane camera, Dodin Campenon Bernard was able to follow the evolution of the site day by day.

Romain Nicolas, deputy technical director at Dodin Campenon Bernard, said, “Projects are complicated – unforeseen circumstances can happen and delay the project. This kind of projects take a few years to achieve, and meanwhile, can highly perturb the neighbourhood.”

He said it was crucial to communicate progress on the construction site, and share visual updates from the site to local residents and all stakeholders.

In Zurich, Switzerland, it was a railway bridge that was the focus for Pix4D. The capacity of the Zurich rail network and surrounding region was felt to have reached its limit, and Porr Suisse, part of one of the largest Austrian construction groups, was given the job of expanding the railway infrastructure. This included the construction of a 200m bridge and a new track.

Swiss company BSF Swissphoto was in charge of surveying the infrastructure. It used the crane camera to document the current situation of the site, capturing data daily.

The weekly work progress reports produced were said to have improved communication and collaboration between the companies and subcontractors involved.

Pix4 d hospital denmark

A large new hospital complex being built in Denmark covers more than 150,000m2, and had 13 cranes erected.

Pix4D said that with BIM and digital construction technologies, this project was a perfect example of a connected site. The contractors have been continually testing new technologies, and selected the crane camera to be a part of the project.

The results were said to have quickly revealed to be a huge time saver for the project team. Although the project team was based on the work site, the camera was situated on the other side of the site, meaning a long walk to check the building status, which could take a few hours. With a permanent monitoring solution like the crane camera, data has been automatically available when needed, enabling the project team to get information quickly, and make faster decisions when it came to confirming or realigning the schedule.

Pix4D said that combining crane camera use with drones could ensure the most complete aerial site overview, from the earliest earthwork stages of a project.


Drones go under several aliases – UAS (unmanned aircraft system) and UAV (unmanned aerial vehicle), for example.

Trimble is collaborating with Propeller Aero to distribute its UAS analytics platform. Propeller, based in Australia and the US, said it was a leader in the advanced collection, visualisation and analysis of data from drones.

Trimble said Propeller’s simple automated ground control targets, cloud-based visualisation and rapid analysis platform would also be integrated with Trimble Connected Site solutions to bring “an end-to-end cloud-based UAS solution to civil engineering and construction contractors”.

It said that pairing Propeller’s web-based interface with Trimble Connected Site solutions would allow users to unlock the full value of UAS information.

Texo dsi

Users can get access to simple tools to measure surface geometry, track trends and changes across time, and perform visual inspections. Trimble said that both technical and non-technical professionals were now able to gather insights remotely and collaborate. It added this would drive improvements in safety and efficiency as well as reducing environmental impact across a construction worksite.

Scott Crozier, director of marketing for Trimble Civil Engineering & Construction, said, “Propeller combines ease of use with powerful analysis tools that allow users to view 2D and 3D deliverables and extract valuable information.

“Like Trimble, Propeller understands the value of quality and accurate data for integration with civil engineering and construction workflows.”

Rory San Miguel, CEO of Propeller Aero, said, “We pride ourselves in taking the most trusted, technical data and tools, and wrapping that up in an easy-to-use online platform that is relevant to the entire organisation, not just technical users.

“Integrating our platform into Trimble’s Connected Site solutions will bring a new class of information to construction sites and organisations globally.”

Also working with UAVs, Texo Drone Survey & Inspection (DSI) said that with UAVs, a big part of keeping on top of potential challenges involved talking to clients ahead of them encountering particular issues, and developing bespoke platforms that mee their needs precisely, by engineering solutions from the bottom up.

It said it had been investing in technology that allowed for heavier payloads and enabling its fleet of UAVs to operate under more difficult weather conditions.

The UAVs currently in operation can deal with wind speeds of up to 15m/s, with the flexibility to carry a variety of custom payloads. Texo DSI has permits for operations up to 20kg, which it said was a game changer for the construction sector.

The company said that a standard LiDAR survey, accuracy of data is generally to around 40mm. However, it claimed that through investment and development of its LiDAR UAV fleet and associated survey software, it was achieving accuracy of 1 to 3mm with its survey grade UAV integrated LiDAR system. This system is delivered via a custom-built UAV platform that measures over 1 million points per second.

Topcon Positioning Group has added advanced connectivity options to its DS-200i direct aiming imaging station.

The DS-200i, now with wi-fi access, provides real-time, touchscreen video and photo imaging to capture measured positions.

Ray Kerwin, director of global surveying products, said, “The ultra-wide 5 MP on-board camera provides photo documentation in the field and can now transmit live video using either LongLink or high-speed WLAN as an access point, which allows the FC-5000 or Windows 10 tablets easily to connect.

“The addition of Wi-Fi connectivity offers convenience to the powerful video capabilities of the DS-200i. The system allows for non-prism measurements to be aimed and measured to remote objects – saving time without having to return to the tripod.”

He added, “The live video allows a remote user to know exactly what is being measured.”

Additional standard features include Hybrid Positioning functionality, Xpointing technology for quick and reliable prism acquisition, TSshield telematics security and maintenance technology, and a rating of IP65 for water-resistant construction.

GNSS suported

Leica Geosystems has just released Leica Spider v7.0 software suite, which is now said to support all GNSS (global navigation satellite systems) – GPS, GLONASS, BeiDou, Galileo and QZSS, as well as the GPS-L5 signal for improved network RTK (real time kinematic) correction services.

The all-in-one solution is said to offer users working on surveying and mapping, among other tasks, improved positioning accuracy and correction service. Leica said that professionals could now increase productivity while they operated reliably in environments with obstructions, like urban canyons, or at high latitudes, thanks to the higher number of usable satellites from multiple GNSS constellations.

Leica said that for the first time, all important GNSS network information was available in one “convenient and easy-to-access web user interface”. The Leica Spider Business Centre web portal is said to combine all the elements to operate the infrastructure efficiently, including user and access management, and network and rover status monitoring.

Leica spider v7.0

Markus Roland, product manager for GNSS Networks and Reference Stations, said, “Our goal with this new version is to incorporate the latest developments into our solution to continue our history of pioneering in GNSS.

“We strive to deliver reliable productivity improvements for our customers. With the new Spider v7.0, customer benefits are tangible and quality is ensured.”

Another new surveying technology which is increasingly apparent on jobsites is augmented and virtual reality (AR and VR).

In the UK, Scotland’s University of Strathclyde’s Advanced Forming Research Centre (AFRC) and the Advanced Manufacturing Research Centre with Boeing (AMRC) in Sheffield, South Yorkshire, have been working with Glasgow-based design visualisation company Soluis Group and modular building designer and manufacturer Carbon Dynamic.

Together, they claim to have successfully built a demonstrator for the use of AR and VR in the construction industry.

The technology was first trialled on a 2.2m plasterboard wall which, when viewed with a Microsoft HoloLens, showed a 3D rendering of the plumbing and wiring behind the façade.

The system can also be used to examine different wall parts to ensure there are no gaps in insulation before being sent to a construction site.

David Grant, partnership development leader at the AFRC, said, “This new technology has a role to play before, during and after construction of both domestic and commercial properties.”

Strathclyde afrc

Strathclyde afrc 3

He said that before work starts, those involved in a construction project would be able accurately to visualise and walk through a building before the foundations were even dug. He said this would help in identifying any potential issues before they occur.

And a Danish BIM-software company is claiming that for the first time, construction workers will be able to see a mix of reality and digital drawings from their smartphone

Dalux has launched what it says is the world’s first AR technology that works on mobile devices, and shows a mix of construction drawings and reality – based on what is being looked at and the location.

Jakob Andreas Bærentzen, associate professor at the Danish Technical University Compute, said he was impressed that an AR product was mature enough to aid in the construction industry already.

He said, “Dalux’s AR-technology already seems to be useful in practice. This is several years earlier than I expected we would see such solutions.

“It makes the accomplishment even more impressive that the software can handle large amounts of data and is mature for practical use on mobile devices – that are not designed for such tasks in the construction industry as the HoloLens is.”

Dalux co-founder Bent Dalgaard said, “Now, at most large construction projects, a digital BIM model is often created. We can access these drawings through mobile devices, based on the construction worker’s location, and show it as AR.

“The fact that the technology can be used on mobile devices makes the adoption in the construction industry much faster, since everybody has a smartphone or tablet these days, and HoloLens is much more expensive, meaning that not all workers have access to the AR drawings.”

Real-time collaboration

Another company, HoloBuilder, which provides 360° reality capturing of construction sites, is releasing a product featuring new capabilities for real-time collaboration and offline handover for project close-out.

HoloBuilder offers a scalable SaaS (software as a service – licensed on subscription) solution. It is said to be a collection of all features that HoloBuilder offers as a collaborative enterprise package – 360° reality capturing with the JobWalk mobile app, TimeTravel for progress documentation, the measurement tool to measure within 360° images, and annotations.

The company said that users could now collaborate with the whole team and enjoy enterprise level service and security. HoloBuilder lets entire construction project teams contribute to the documentation process.

During project close-out, the project can be downloaded and saved as a view-only deliverable for the owner to keep throughout the lifetime of the building.

How Would They Build the Golden Gate Bridge If They Had To Do It Today?

By Editor's Choice, Engineering and construction, Fabrication and metalworking, Structural monitoring

Ever since the Golden Gate Bridge opened to traffic on May 27, 1937, it’s been an iconic symbol on the American landscape.

By 1870, people had realized the necessity of building a bridge spanning the Golden Gate Strait to connect the city of San Francisco with Marin County. However, it was another half-century before structural engineer Joseph Strauss submitted his bridge proposal. The plans evolved, and the final project was approved as a suspension bridge that ended up taking over four years to build.

 When the Golden Gate Bridge went up, it was the longest suspended bridge span in the world – cables hold up the roadway between two towers, with no intermediate supports. And the setting had a number of inherent challenges. It cost about US$37 million at the time; building the same structure today would cost about a billion dollars. So how has the design held up over the past 80 years – and would we do things differently if we were starting from scratch today?

Longest suspension bridge in the world

The Golden Gate Bridge is a suspension bridge, meaning it relies on cables and suspenders under tension along with towers under compression to cross a long distance without any intermediate supports. The roadway deck hangs from vertical suspenders that connect to the two main cables that run between the towers and the anchors on the end. The suspenders transfer vehicular forces and self-weight to the supporting cables that are anchored to towers and on to solid ground.

The first bridges of this type probably connected two cliffs with flexible ropes to cross a valley or a river. Hundreds of years ago, these ropes were made of plant fiber; iron chains came later. The Brooklyn Bridge in New York City, opened in 1883, was the first to use steel cables, which then became standard.

The towers likely started as a simple rock on each side of a valley; eventually engineers used massive stone or steel piers. The Golden Gate Bridge, for instance, is supported by one abutment on each end and the two towers, which are placed over foundations embedded in the seafloor.

The Golden Gate Bridge’s two supporting cables are about the only thing that has not been changed since the bridge was opened to traffic in 1937. Each main cable is formed by 27,572 steel wires with the approximate thickness of a pencil. Construction crews hung nearly 80,000 miles of wire cablesfrom one side of the bridge to the other.

It’s nearly impossible to manufacture a long, thick cable in one piece with no flaws to do this job. And crucially, if a single big cable was holding the bridge up and something happened to it, there would be a catastrophic failure. Relying on smaller wires means any failure would be slower, leaving time to divert disaster.

Since people first started pondering a bridge in the bay of San Francisco, there was huge concern about the structure’s ability to withstand the location’s strong winds, turbulent waters and possible earthquake forces. San Francisco is located at the intersection of two active tectonic plates – obviously no one wanted to see an earthquake bring down the bridge, which currently carries around 112,000 vehicles per day.

To avoid this problem, the builders also located shock absorbers at each end of the bridge to absorb the energy coming from wind or seismic forces. These specially designed vibration dampers are meter-diameter cylinders made of a lead core covered by rubber. Placed at strategic locations, they absorb energy that could otherwise cause the bridge to collapse.

Keeping it in good shape

Conventional wisdom would suggest an infrastructure project is done soon after its inauguration. But keeping the Golden Gate Bridge in tiptop form requires ongoing stringent maintenance. For 80 years, dedicated maintenance crews have serviced the bridge, repainting and substituting the corroded or broken components where necessary.

This work must be done to exacting standards. For example, when any of the thousands of bolts that connect all the various pieces of the bridge need replacement, no more than two are taken out simultaneously, to keep the bridge safe against strong winds or earthquakes forces.

There are structural maintenance issues, too. Due to the passage of time and ongoing temperature variability, the cables and suspenders elongate or contract, and need periodical checking and retensioning. This type of adjustment is referred to as “tuning” and is similar to how a musician keeps a stringed instrument sounding its best.

What would change if we built it today?

Due to huge upkeep costs, some people have suggested reconstructing the Golden Gate Bridge in a way that would limit ongoing maintenance and operation bills. Setting aside the political feasibility, how would engineers design the bridge if they were going to build it from scratch today?

Over time, researchers have developed lighter materials. Using Fiber Reinforced Polymers (FRPs) rather than steel or concrete is a way to reduce the weight of a structure of this magnitude. This self-weight is typically responsible for using up 70 to 80 percent of its resistence – that’s the maximum load it can bear before it fails. By reducing it, the bridge’s structure would need less strength, allowing for cheaper and easier options.

For example, designers have started using Fiber Reinforced Composite (FRP) materials in bridges such as the Market Street Bridge in West Virginia. FRP uses a plastic resin to bind together glass or carbon fibers, which give strength to the material. Being four times lighter than concrete, the FRPs are five to six times stronger.

Probably a designer’s first target for change in a substitute Golden Gate Bridge would be the composition of the cables. The steel currently in use is corrosive, heavier by four times than newer materials and can fail in harsh moisture and temperature environments – just like those it encounters in this location. Carbon cables are more inert and already in use around the world.

These lighter-than-steel materials could also be utilized in other elements of the bridge, such as the traffic roadway. Using plastic composite decking could bring the Golden Gate Bridge’s deck self-weight down by a factor of five. That would enable engineers to design and construct a cable-stayed bridge rather than a suspension bridge. The advantage there would be the ability to do away with the suspenders; in a cable-stayed bridge forces are transmitted directly from the deck to the towers by the cables. The first highway cable-stayed bridge with CFRP cables is Switzerland’s Stork Bridge, opened in 1996.

A cable-stayed bridge can have a longer span than a suspension bridge, so its structure between the supports and the shore could be simpler. Also building the towers nearer to the shore, where the waterbed is more shallow, would help alleviate one of the main problems when the Golden Gate Bridge was constructed the first time around: It’s very difficult and expensive to work on the tower foundations in deep water with strong currents.

The damping system could also be addressed with a new design. The lead core-based dampers that were used in the construction of the Golden Gate could be replaced by newer technologies that are better able to resist wind, traffic and seismic forces. This improvement would ensure that a failure such as the one on the Tacoma Narrows Bridge – when wind blew the bridge sideways, it twisted and collapsed – would be prevented.

With all that said, the Golden Gate Bridge is still doing fine. Even with other feasible and cheaper options, no one is realistically working to replace the Art Deco icon and its world famous “international orange” paint job. The Golden Gate Bridge is closely monitored to make sure it does not exceed its stress limits due to traffic, wind and seismic loads. We can look forward to at least another 80 years of this engineering masterpiece.

By  and 

PolyU Develops Sprayable Sensing for Real-time Structural Monitoring

By Editor's Choice, Engineering and construction, Sensors, Structural monitoring

The Hong Kong Polytechnic University (PolyU) research team developed a novel breed of nanocomposites-inspired sensors which can be sprayed directly on flat or curved engineering structural surfaces, such as train tracks and aeroplane structures. The sprayed sensors can be networked, to render rich real-time information on the health status of the structure under monitoring. Due to its light weight and low fabrication cost, large quantities of sensors can be deployed in a sensor network for detecting hidden flaws of structures, paving the way for a new era of ultrasonics-based structural health monitoring.

The nanocomposite sensors developed by the research team from PolyU’s Department of Mechanical Engineering, led by Professor Su Zhongqing and Professor Zhou Limin, adopt an innovative technique of fabrication through spraying which makes installation process for sensors much faster and more efficient compared to conventional means. It also enhances the flexibility of the product to adapt to various types of surface.

Currently, the number of conventional ultrasound sensors, such as those made of lead zirconate titanate (PZT), used for in-situ monitoring is usually limited by the factors related to the sensor’s cost and weight. These sensors are usually stiff (unwieldy to adapting to curved structural surfaces), introducing remarkable weight and volume penalty to a host structure to which the sensor is to be mounted. The nanocomposite sensors developed by the team, however, can be fabricated in large quantities to form a dense sensor network for structural health monitoring at a much lower fabrication cost and weight than using conventional sensors.

“This nanocomposite sensor has blazed a trail for implementing in-situ sensing for vibration, or ultrasonic wave-based structural health monitoring, by striking a balance between ‘sensing cost’, i.e. the cost of sensors, and ‘sensing effectiveness’, the quantity of data acquired by the sensors,” said Professor Su.

Low cost, light weight

PolyU’s innovative sensing technology encompasses a sensor network with a number of the sprayed nanocomposite sensors and an ultrasound actuator, to actively detect the health condition of the structure to which they are fixed, quickly and accurately showing if there is any damage in the structure. When the ultrasound actuator emits guided ultrasonic waves (GUWs), the sensors will receive and measure the waves. If damage, such as a crack is present in the structure, propagation of GUWs will be interfered by the damage, leading to unique wave scattering phenomena, to be captured by the sensor network. Based on wave scattering, the damage can be characterized quantitatively and accurately via an all-in-one system that was developed by the team.

Compared to the conventional ultrasound sensors which costs over US$10 each and weighs few grams, this new breed of nanocomposite sensor costs only US$0.5 and 0.04g for each. As such more sensors can be adopted in one structure, generating more information for analysis, with less weight added to the structure. In addition, Professor Su’s sensor has excellent flexibility and can adapt to curved structure surfaces. That allows a wide range of practical engineering applications. It is also sprayable on the surface of a moving structure to transmit the structural health information in a real-time manner.

Wider frequency range of response

The sensor developed by the team can measure an ultrasound signal from static to up to 900 kHz yet with ultralow magnitude. The acquisition of wave scattering in an ultrasonic regime allows detection of cracks as small as 1 to 2 mm in most engineering materials. That response frequency is over 400 times more than the highest frequency than nanocomposite sensors that are reportedly available (as reported in international journals).

While conventional ultrasound sensor can measure a wider range of ultrasound waves when compared to those developed by the team, the high cost and weight of the conventional sensors make a large quantity application infeasible, limiting the quantity of data acquired. There are lots of limitations in applying the conventional ultrasound sensors to practical applications, especially in aerospace structures.

New technology to cut cost and enhance sensitivity

Made of a hybrid of carbon black (CB), 2D graphene, conductive nano-scale particles, and polyvinylidene fluoride (PVDF), the nanocomposite sensor can be easily and flexibly tailored to different sizes towards various engineering applications.

The secret of its high sensitivity to structural change lies in the optimized nanostructure of the hybrid, which endows the sensor to possess an ability to identify the dramatic changes in piezoresistivity of the nanocomposite. To measure and analyze the dramatic change of piezoresistivity, Professor Su and his team tested numerously on the weight ratio of nanofillers in order to optimize the conductivity of the nanocomposite.

Each sensor is connected to a network via a wire printed on the structure. By analyzing and comparing the electrical signals converted from the electric resistivity, the network can spot the defect in a structure, as well as translate the signals into 3D images.

This new research has recently been published in top-tier journals in this field, including Ultrasonics, Carbon, and Smart Materials and Structures. “Due to its light weight, the novel nanocomposite sensors can be applied to moving structures like trains and aeroplanes. That will help to pave the way for real-time monitoring of these structures in future, enhancing safety of the engineering assets and retrofit the traditional system maintenance philosophy,” said Professor Su.

Press Contact
Professor Su Zhongqing, Department of Mechanical Engineering
Telephone: (852)-2766-7818
Email: [email protected]

SOURCE The Hong Kong Polytechnic University

Innovative bracing for durable structures during a natural disaster

By Editor's Choice, Engineering and construction, Remote monitoring, Structural monitoring

Across the world, severe earthquakes regularly shake entire regions. More than two billion people live in danger zones – many of them in structures not built to withstand an earthquake. Together with partners from industry, researchers at the Fraunhofer Institute for Wood Research WKI are developing building materials designed to prevent buildings from collapsing in a natural disaster.

Earthquakes repeatedly claim too many lives, a fact that experts trace back to a lack of preventative measures – particularly when it comes to construction and the failure to comply with standards. All too often, structures in danger areas are not built to withstand an – a state of affairs that the Center for Light and Environmentally-Friendly Structures of the Fraunhofer Institute for Wood Research, Wilhelm-Klauditz-Institut WKI, is now urgently seeking to address. Working together with the Technical University of Braunschweig’s Organic Building Materials and Wood Materials division from the Institute for Building Materials, Concrete Construction and Fire Protection, as well as industry partners such as the company Pitzl Metallbau from Altheim, the researchers are developing solutions for the construction industry that could save thousands of lives. Currently, the engineers at Fraunhofer WKI are working on ultra-durable bracing that will protect even high-rise buildings during an earthquake. The bracing consists of sensor-controlled steel connectors that provide a high level of rigidity while remaining elastic enough to maintain structural integrity in the face of severe shaking. Numerous tests have demonstrated that the connectors work exactly as intended. In one test, the researchers investigated the nature of the stress being placed on structures by applying static, cyclical and dynamic forces; in another, the structure’s service life was tested using environmental simulation. The approach is based on the successful EU SERIES project, which examined earthquake-resistant structures under dynamic loads.

Structures that sway but do not fall

The earthquake-resistant bracing has been designed for buildings with a mullion-and-transom design, and connects the horizontal beams with the vertical post. When exposed to wind or tremors, the connectors must be rigid enough to keep deformation to a minimum – but also elastic enough to withstand strong earthquakes. If deformation does occur, it does not lead to critical stress – in other words, the sways, but does not collapse.

In an earthquake, the connectors slide over each other, converting kinetic energy into frictional energy – and preventing the building from collapsing. Norbert Rüther, project manager at Fraunhofer WKI, explains: “The trick is using friction to dissipate the force. The individual parts of the connector are pressed against one another applying a significant, pre-defined force. When the specified stress limit is exceeded, they begin to slide over each other.” As a result, it is possible to accommodate structural deformation without compromising structural integrity. Even after a strong earthquake, such a structure maintains the same capacity as before, and is still able to cope with the stress placed on a multistory building. This means that buildings can withstand several quakes without suffering significant damage. In a sense, they surf the earthquake wave. “All the weight-bearing, safety-critical are just the same after the earthquake as they were before it,” says Rüther.

Installing the bracing within a building is a simple task, and it does not require any maintenance. On top of this, the Fraunhofer Institute for Surface Engineering and Thin Films IST has developed pressure and temperature sensors integrated into the connector, which means it is possible to measure the forces and stress associated with an earthquake.

A case for the use of wood in high-rise buildings

Fraunhofer WKI has developed its bracing connectors so that they can be set to accommodate the requirements of the individual application – the way in which bolts are attached and tightened, for instance. It is also possible to adjust the connector geometry to suit the size of the structure and the materials used. Rüther: “Our high-performance connectors are compatible with any material and support structure – including concrete, steel, brick and wood.” He makes a case for using wood in multistory buildings. “Wood is extremely durable, light but still stable, and perfect for earthquakes. In its mechanical properties, it compares very well with highly durable composites – though at a significantly lower material cost.” Most countries are skeptical of using wood in such cases, citing the danger of fire. However, there are already good solutions that counter this threat. Solid elements with large profiles, for instance, are highly resistant to fire and can preserve their load-bearing integrity even after hours of exposure to fire.

The connectors are currently in the prototype stage, and are expected to be ready for full-scale production in one to two years. Currently, the experts are exploring the connectors’ economic viability with a view to testing in real buildings. Since all the other components are exposed to linear-elastic stress, there is no need for any further safety contingency – in turn boosting the overall cost-effectiveness of the .

Explore further: Building taller, sturdier wood buildings