Seismic Strengthening Of Existing Buildings Vs Structural Maintenance & Durability

Seismic Strengthening Of Existing Buildings Vs Structural Maintenance & Durability

Strengthening existing buildings to achieve a higher performance in earthquakes is an everyday task for structural engineers in New Zealand.

Three or more main questions arise:

- Is the building capable of resisting the demands of earthquakes under the ULS and SLS stated limits  and fulfilling the current code requirements?

- What is the residual life cycle of the existing structural system?

- Is there a continual deterioration of the existing structure caused by active corrosion, aggressive environmental conditions, or concrete carbonation?

For  most structural engineers, the first question is obvious.  How about the others?

Unfortunately, the answer is that the majority of  structural engineers don’t take into consideration the residual life cycle of the existing structural system and the influence that this may have on the future capacity of the structure.

Current international legislation provides solutions and quality control measures for every aspect related to maintenance, structural integrity and repair.

From simple aspects like paint and humidity control, to more complex ones like concrete restoration, structural strengthening and cathodic protection.

Modern codes like EN 1504 ensure that structural maintenance is now a much more difficult assignment requiring specialist knowledge from structural engineers.

EN 1504 recognises that failure of repairs at any structural level including seismic upgrade and repair can lead to unprecedented dangers affecting not only the repair and the correct  structural analysis, but also the investments and lives of the occupants.

Today structural engineers should be able to substantiate their solutions, assumptions and safety factors via a strict protocol of Maintenance and Durability Analysis. The protocol should be able to safeguard that, ifthere are no specific needs that would eventually compromise the selected solution, (i.e. active corrosion of reinforcement or low alkalinity concrete), then the functional service life of the solution can be well defined through a series of tests.   For example, EN 1542  defines the adhesion of FRP repairs.  This means that every step related to the application of the selected repair method can be warranted via the necessary EN standards.  (There are more than 110 standards accompanying repairs from chemical anchorage to the application of shotcrete.)

In Europe, there were growing concerns for more than 40 years that the performance of any structure was profoundly affected by time and exposure.  In the1990s, these concerns justified the creation of special Task Groups of specialists working on the development of   legislation covering Structural Maintenance.

In 2000, all 10 parts of EN 1504 – Repair and Protection of Concrete Structures - was introduced and is now mandatory across the EU-27.

This means that the only way to add value to existing structures is through  depth of knowledge and by using the latest design tools under international legislation.

Here at Harrison Grierson, by working in conjunction with relative departments (Structural Analysis, Inspection, Material Selection and Quality Control) we ensure that our solutions are the result of the best knowledge available today.

We believe that the New Zealand engineering profession  is mature enough to accept the challenge and incorporate the domestic and international codes for durability and maintenance into their practice.

This thought leadership article by Ioannis Prionas, team leader of Structural engineering at Harrison Grierson, raises questions about  whether New Zealand should be adopting international regulations relating to the structural integrity and life cycle of buildings.and how structural engineers need to look beyond the immediate repairs to the overall health and condition of a building.

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