Role of post tensioning in construction of efficient infrastructures

With the advancement in science, our world is evolving and so does the infrastructure. The demand of smart infrastructure has increased in recent decades which demand an upgraded quality of concrete so that the structure can support any load beyond its own dead weight. Many structures have collapsed in past because

• The concrete structure couldn’t bear the oversized load e.g. I-5 Skagit River Bridge accident in 2013

• It was structurally too rigid to withstand the damaging factors like strong winds e.g. I-35W Mississippi River Bridge collapse in 2007

• Frequent accidents where vehicles hit the supporting post like boat colliding with the foundation of the bridge e.g. 14th Street Bridge accident in 1982

• Design errors and material used in the construction e.g. Tacoma Narrows Bridge accident in 1940.

• Earthquakes causing damage to the structure e.g. San Francisco – Oakland Bay Bridge collapse in 1989

We have learned from these accidents that if the design and construction quality of any infrastructure is improved then accidents like bridge failures can be prevented. Post tensioning technique which uses prestressed post tensioned tendons to reinforce concrete structures has revolutionized the construction of infrastructures.  it offers many advantages over regular construction technique. Some of the features of post tensioning are following as

• It offers flexibility to the structure means if the structure tend to sag or deflect under the live load then also the concrete structure won’t crack.

• It has lowered down the material and maintenance cost

• It has also reduced the construction time because it allows longer spans in a structure without building supports.

• It increases the tensile strength and load bearing capacity of the structure thus making it durable and long lasting.

• It can also resist the environmental factors e.g. it can withstand stronger winds or earthquakes as it is structurally flexible.

How post tensioning improves the quality of concrete?

Post tension tendons made from high tensile steel, carbon fibre or aramid fibre is placed within or adjacent to concrete volume to provide flexibility to the concrete structure. When extra pressure is applied by the living load, the post tension tendons share the load and prevent cracking in the concrete member.

Once the concrete is stressed along with tendons, it becomes high strength concrete and can withstand tension forces. Post tension tendons and prestressed concrete is widely used in building huge structures like bridges, skyscrapers, dams, silos and tanks, nuclear containment structures and industrial pavement etc. Prestressed concrete with post tension tendons is much better option than the reinforced concrete because of its improved performance which allows reduced structural thickness and longer span which is essential for building complex structures.

What is the constraint while using post tension tendon in concrete structures?

The biggest advantage of post tensioning is lack of cracking and ability to span large spaces without any support. Post tension slabs can be placed or stamped just like reinforced concrete slab and the surface can be overlaid or stained. It is important to consider that the post tensioned concrete should not be cut or drilled because once a post tension tendon is cut down, it is difficult to repair or replace.

It is very difficult to find any damage to the post tension tendons from the surface as they are deeply embedded inside the concrete member. Infrastructure Preservation Corporation (IPC) provides the first post tension tendon scanning system which utilizes the Electrical Capacitance Tomography (ECT) to perform a MRI like assessment of the post tension tendons. This system is referred as “TendonScan” and it can provide accurate information about any deterioration or section loss like corrosions, voids, bleeding grout and any other problem caused to the tendons so that the decision makers can take appropriate action for repairs, in budget and on time.

To know more about TendonScan, our other products and services, you can visit our website https://www.infrastructurepc.com/ or contact us at info@infrastructurepc.com.

Drones (UAS) for Bridge Inspections A New Approach

Drones The approach to utilizing Unmanned Aerial Systems (UAS) for bridge inspections in regards to incorporating same into the realm of structural bridge inspections is long overdue and is welcomed due to the system’s ability to access areas of bridge which would normally require the archaic and oft utilized approach of requiring the incorporation of travel lane closures, costly under-bridge access equipment, and the requirements of conducting bridge inspections at night as not to interrupt traffic flow.

State by state departments of transportation are researching the viability of drone inspections on our nations infrastructure.  Using a drone for Bridge inspection services add a valuable resource in the bridge inspectors toolbox.

Whereas, for safety reasons, a UAS (being a machine) will never be incorporated and utilized over live traffic, however, its ability to provide stand-off positioning adjacent and parallel to the bridge structure for deck inspections is unsurpassed.

A UAS can be used quickly and efficiently to conduct a full bridge structure inspection, which in turn, will identity areas which might require a more hands-on and thorough inspection of structural deficiencies revealed.   The cost savings enjoyed by the bridge owner who selects an inspection consultant which utilizes a UAS inspection approach and program, versus the under-bridge equipment method, is practically infinite. 

DETAILED REQUIREMENT FOR DRONE USE IN BRIDGE INSPECTIONS 

The UAS will be fitted with high resolution video cameras which will transmit real-time inspection views and inspection progress, infrared thermography (IR) cameras which reveal delamination locations and perimeters of same in concrete surfaces, and a laser-based measuring device which will denote the width of structural cracks discovered.  All the data will be transmitted, via telemetry; to the ground-based Command Center System which will in turn collect and archive all data received for submittal to, and reviewed by, the bridge owner, which will be used for future comparison and reference.

The above information and data will be incorporated into a final bridge inspection report to be submitted to the bridge owner.  At that time, a meeting between the bridge owner and the inspection will be conducted to discuss findings of the UAS inspection, what these findings mean in relation to the Health Index of the bridge, and then further discuss the need for work order-driven repair approaches and requirements.

This information shall be kept and secured by the UAS inspection consultant at all times, and if required and directed by the bridge owner upon their receipt of all bridge inspection related data, the UAS inspection consultant shall delete all files related to the bridge inspection.    

INCORPORATING UAS INTO BRIDGE INSPECTIONS

The incorporation of UASs into viable bridge inspection

procedures is a long overdue and very welcomed approach, since all of us who have been involved in onsite bridge inspection projects for many years know the inherent dangers required for us to perform our duties in regards to maintaining the trust of the traveling public that the nation’s bridges are safe.  Instead of human inspectors risking life, limb and injury to perform their duties in avenues of active traffic, rappelling structural bridge members, and accessing areas on a bridge by massive manlifts and/or under-bridge machines, we now have what was once considered insurmountable, to now having the option of machines performing these duties in our stead.  One can replace a UAS easily, but a human life is irreplaceable. 

In all likelihood, and until the UAS manufacturers can provide a fool-proof and nearly indestructible machine which will be guaranteed to be free of any and all malfunctions, a UAS will not replace the hands-on inspection requirements related to Fracture Critical members of a bridge nor will a UAS be able to access the tight connections within a through-truss bridge nor a deck-truss bridge, but many areas are now within easy reach by utilizing UASs safely. 

For more expert information on bridge inspections using drones contact info@infrastructurepc.com.