Due to our own negligence we are losing huge amounts of money in Poland

• The durability of a structure constructed using prestressed concrete technology is determined by the quality of workmanship. - Prestressed structures require a much higher technological regime than reinforced concrete structures - points out Prof. Adam Wysokowski, chairman of the Association of Bridge Engineers of the Republic of Poland.
• Our interlocutor also points to the importance of the quality of maintenance of such facilities, and in this context, the need for reliable inspections of such structures. Meanwhile, in public procurement, the dominant criterion is price.
• - According to my estimates, if only about 2 percent of the original investment value was allocated for its systematic maintenance over the 100 years of the facility's operation, most of the bridges could be safely used to this day - says Prof. Wysokowski.

This is a proven and effective solution, but requires high-quality workmanship and maintenance.

Almost half of the bridge structures on the road network managed by GDDKiA were made of prestressed concrete. This technology recently became "famous" after the mayor of Chorzów ordered the closure of the viaduct running through the city due to an expert opinion indicating the risk of collapse of this structure . Is there something wrong with this technology?

- Prestressed concrete technology is a proven and effective solution that provides structures with greater durability than traditional reinforced concrete . The general essence of this technology is the introduction of prestressing forces to concrete elements, counteracting later operational loads - e.g. from vehicle traffic.

Thanks to this, concrete works in the compression range, which limits the formation of cracks and prevents water from penetrating the structure. However, for this technology to fully demonstrate its advantages, a number of key conditions must be met.

What kind?

- Firstly, the above-average execution regime of this type of structures. It should be remembered that these are structures in which the prestressing forces are transferred by tendons (colloquially referred to as "cables") anchored at the ends of reinforced concrete elements. Even a small slippage on the anchors can lead to significant losses of the prestressing force , and yet it is this force that maintains the stability of the entire structure. When the prestressing is weakened, the concrete is no longer adequately compressed and may crack or be destroyed.

Therefore , prestressed structures require a much higher technological regime than reinforced concrete structures . The tendons cannot be contaminated, should not be stored outside in unfavorable weather conditions, and the quality of the materials should be checked before their installation. After the completion of prestressing, it is necessary to perform tests to verify the value of the prestressing force.

In addition, prestressed structures should not be painted in a way that makes it difficult to observe the concrete surface – the ability to quickly detect cracks and other damage is crucial for their safe operation . It is also important to properly design and make expansion joints and effectively protect the anchoring zones against the extremely harmful effects of corrosive factors for this type of structure.

What do expansion joints have to do with anything?

- The anchors I mentioned are located directly above the expansion joints. If they are leaky, water and road salt in the winter penetrate directly into the anchor zones , which leads to their corrosion and weakening of the prestressing system. As a result, the anchors may give way and the structure begins to lose its intended load-bearing capacity.

This is not a problem unique to Poland – a perfect example is the Carola-Brücke bridge disaster in Dresden , which occurred last year. In its aftermath, a discussion about the durability and safety of prestressed structures flared up among bridge engineers. The importance of the quality of workmanship and subsequent maintenance of the structures was primarily pointed out.

In Germany, especially in the southern part of the country, a huge number of prestressed bridges were built in the 1960s and 1970s. Unfortunately, over the years, not enough attention was paid to their proper operation and maintenance, which today results in serious technical problems.

A bridge inspection for 300, 100 or even 60 PLN is a fiction. And such orders are accepted

And what does it look like with us?

- If expansion joints are leaky, and shrubs and even trees grow on sidewalks near the abutments of many bridge structures, it is difficult to talk about proper maintenance of infrastructure structures. Such images indicate serious operational neglect and call into question the safety of the structure . In such conditions, even the best-designed structure has no chance of longevity.

Is it that bad?

-It must be said directly: many bridges in Poland really need help . The loss of their technical efficiency not only threatens safety, but also generates huge financial losses. According to my estimates, if over the course of 100 years of the facility's operation only about 2 percent of the value of the original investment were allocated for its systematic maintenance, most bridges could be safely used to this day .

Unfortunately, we too often forget that the durability of a structure does not depend solely on its design, but also – and perhaps primarily – on the quality and continuity of maintenance activities during operation.

Why is this happening?

- For over 20 years I have coordinated the bridge management in Poland. Under my supervision, a team of specialists developed a nationwide system for recording and inspecting bridges. Recently, together with the Road and Bridge Research Institute, we prepared models and standards for the maintenance of engineering structures introduced for use by the Minister of Infrastructure. That is why today I am observing with great regret the results of tenders for five-year bridge inspections, which are awarded for amounts of around PLN 150 or 100. For comparison - a chimney inspection can cost more, and we are talking about structures worth millions of zlotys.

The market has been liberalized, and the system of qualifications for inspection contractors has been drastically weakened. Today, inspections can be performed by virtually anyone – often even by people without the required qualifications . The dominant criterion of the lowest price in public procurement leads to a situation in which engineers compete with each other in tenders, offering rates that are unrealistic from the point of view of reliable execution of the task. A bridge inspection for PLN 300, 100 or even 60 is a fiction. And yet – such orders are most often carried out and, most disturbingly – accepted.

This is a phenomenon widely known in the community, although it is still somewhat of a "secret". We see the effects with a delay: incorrect or superficial assessments of the technical condition result in decisions to demolish , although often it is only then that we discover that the structures were already in a dying state. The case of the Morandi Bridge in Genoa clearly showed what the lack of proper supervision and ignoring the indications of inspections ends with. In Poland, we are on a similar path, although we are all perfectly aware of it.

Do we have any alternative to prestressed concrete since we have a problem with this technology?

- In many cases, there is really no alternative to prestressed structures. These are very good engineering solutions, which in many cases are simply indispensable - for example, when building high-speed railways. Prestressed structures are massive, heavy and transfer dynamic loads very well, damping them . However, in order to fully use their potential, they must be properly designed, made in an appropriately high technological regime and properly maintained throughout the entire period of use.

Unfortunately, in practice, this is not always the case. Recently, I had the opportunity to perform an expert assessment of a multi-span, post-tensioned concrete viaduct located in a horizontal arch – the structure looked very good, but after a deeper analysis, it turned out that the designer had not anticipated the centrifugal and eccentric forces acting on the arch. As a result, the structure began to crack.

This shows how important a comprehensive analysis is already at the design stage – because even the best technology will not work if it is not used correctly.