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In short … yes, but the root cause has many different avenues to explore - let me explain.


Designing for Concrete

The top recommendation for the management of concrete cracking is to address it in the design phase of a project and to avoid issues with cracking in the first instance. The structural engineer should be able to specify the following to control the location and size of cracks so as not to detrimentally effect the performance or appearance of the concrete:

· Appropriate selection of reinforcement.

· Use of joints (construction, expansion, day etc.).

· Specification of Concrete classification.

· Good quality site workmanship.


Identifying Cracks

All concrete cracks - appropriate engineering can determine the size and position of these cracks and, if needed, reduce them to micro-cracks that will not be easily seen. If we now consider only non-micro cracks, i.e., visible cracking, they can vary generally and can be classified as either structural, or non-structural in nature:


Structural cracks are of primary concern and can lead to issues which affect the stability and durability of a concrete structure. They can occur from incorrect design, poor construction/ workmanship or overloading of the structure.


Non-structural cracks are formed due to internal (or surface) stresses exceeding the material capacity, resulting in ‘small’ cracks appearing throughout the construction. Whilst these do not have the same implications of structural cracks, they often lead to durability issues whereby the cracks allow ingress of water (and potential corrosive products) into the concrete. These may lead to longer term issues such as corrosion of reinforcement.


To determine the category and severity of any cracking, an experienced and competent structural engineer will be able to inspect, identify and classify the severity of cracking and (if required) suggest an appropriate repair methodology.


Main Causes of Cracking in Concrete Structures

Cracks are mainly caused by:

· Movement or Settlement

· Thermal Expansion and Contraction

· Concrete Shrinkage

· Corrosion of Reinforcement

· Flexural or Shear Failure


Movement / Settlement

By nature, concrete is a cementitious medium that (like natural stone) is excellent in resisting compressive load, but poor in resisting tensile loads. The first contributing factor for concrete cracking is movement of the concrete either by settlement (usually occurring early in the lifecycle) or by physical movement (which can happen at any lifecycle stage). Both will lead to an accumulation of tensile stress in the outer fibre, which can lead to surface cracks.


Thermal Expansion and Contraction

In a similar process as movement, when concrete cures it undergoes an exothermic reaction causing the internal temperature of the concrete to reach a higher temperature than the ambient. Depending on the mass of the pour, this can lead to the external edges cooling faster than the internal mass. The resulting effect is the cooler outer edge of the concrete contracts at a faster rate than the core which generates temporary internal stresses in the face and may ultimately lead to cracking.


Concrete Shrinkage

When concrete beings to cure, the moisture within beings to dissipate which in turn results in global shrinkage of the concrete section. If the concrete was unrestrained and free to shrink, there would be no residual stresses and the section would find equilibrium (and not crack). However, realistically all concrete structures (beams, slabs etc.) will have restraints formed by the method of construction (abutting walls, anchorage points, structural framing etc.). Therefore, to control these shrinkage cracks, adequate reinforcement and specification of control joints should be specified by the engineer.


Corrosion of Reinforcement

The reinforcement within concrete, whilst providing the section with its ‘strength’ is also the area most susceptible to attack by chlorides (i.e., salt). Normally the highly alkaline environment of concrete forms a passive protection film on the bar. However, when this film is compromised (through ingress of chlorides from cracking) the protection layer is depleted and corrosion of the steel bars commences.


The consequential corrosion product (rust) is highly expansive and causes residual tensile stresses in the concrete to increase. The resulting pressure causes the concrete to crack and over time this will lead to spalling of the cover, exposing the corroded reinforcing steel bars and accelerating the damage cycle.


Flexural or Shear Failure

In some instances, cracking can be because of failure of the concrete element or structure normally by being subjected to forces greater than can be resisted. In addition, physical damage can have occurred. Cracking of this nature will require structural assessment to determine severity and risk prior to determining remedial actions. Fortunately, these types of cracks are far less common than those discussed above.


What’s the Crack?

If you have concrete structures that are cracked or damaged, it is vital to understand their nature and whether they present a concern in either the immediate, short or long term.


The key is identifying the likely cause of the cracks and whether they are structural or non-structural. The sooner any issues are identified, the sooner remedial action can be taken to avoid costly issues further down the line. The good news is that we can assist with site inspections, retrospective engineering assessments, structural repairs and remedial recommendations!


Get in Touch!

Do you have a Project that You Want to Discuss? Please get in touch for a no obligation discussion.


solutions@subteno.co.uk


An Insight into Ownership of Structures

In Part 1 of this Blog, we discussed some of the reasons why a ‘change of use’ and in particular, the role that understanding and documenting modifications and maintenance issues plays in protecting your structures.


Condition of Existing Assets

A change of use can only be feasible with a solid understanding of the current physical condition. Whilst many Owner / Operators have a regular inspection programme, it is worth pointing out that the results are only as good as the information on which it is based. For example, recording the level of corrosion of a structural brace is important, but if the brace in question was part of a modification, how do we know the results of the survey are acceptable? Well we don’t, is the simple answer - not without an engineering review.


Take a Proactive Approach!

As can be seen, there are a lot of unknowns lurking below the surface but engaging a structural engineering consultant can pay dividends to the success of your project. Whether you are an asset owner or manage assets on behalf of the owner as a matter of course, we recommend that you:

· Assess the adequacy and suitability of existing designs and modifications to all existing structures.

· Structures that are unchanged need to only comply with the original design specifications, codes and standards.

· Structures that have been modified need to comply with codes and standards applicable at the time of the modification. It is worth highlighting, that generally the whole structure will also be checked in accordance with these standards.

· Collate and file all drawings, calculations and supporting documentation for the asset.

· Establish a proactive monitoring and maintenance program.

· Include structural elements in the asset register database (alongside the equipment that is regularly inspected and maintained).



How We Can Help!

Depending on the structural asset or proposed modification in question, we can arrange for structural inspections, assessments and drawing updates to be carried out. The benefit to having this information reviewed by Structural Engineers is that we can undertake a review with knowledge of the original structure, its current condition, and the future intended use, then identify any critical elements or areas of concern and suggest ‘appropriate’ repairs or remedial actions.


‘Appropriate’ in this sense means that we strongly believe in applying the correct solution for the project. We take our obligation as Engineers seriously and aim to leave the Client with a clear and concise recommendation on any remedial work (if it is required).


Dependant on the project, we can provide:

· An independent review of your structural assets, including site visits, review of drawings, specifications, modification logs, maintenance logs etc.

· Design verification of proposed structural modifications using up to date analysis techniques to appropriate codes and standards.

· Design documentation (reports, drawings etc) to provide updated information for the asset database, ensuring accurate records are maintained.

· Recommendations for preventative maintenance and highlight areas of concern.



Get in Touch!

Do you have a project that you want to discuss? Please get in touch for a no obligation discussion.


solutions@subteno.co.uk


In this blog, Matt Byatt FIStructE and Vice President of the Institution of Structural Engineers, describes Subteno's experience in addressing the Climate Emergency.


[Addressing the Climate Emergency within a small engineering practice - The Institution of Structural Engineers (istructe.org)]