Welcome to my blog once more. It's a privilege to be back on here after a self-imposed ''sabbatical leave'' I’d embarked upon weeks back. Glad to be here once again. For the past few days I’ve been engaged in some building construction works where I’d served in the capacity of the on-site civil engineer. This is exactly why I’ve been absent on here in addition to my faulty laptop which had prohibited me from employing the little time I could spare during the construction process for blogs. However, having completed a major segment of the building which calls for a brief pause to enable more planning and scheduling towards embarking further on the construction, I’ve thus seized the momentary “pause” to repair my computer and intrigue you with one of the civil engineering phenomena; structural failures precisely.

Well, structural failures are one of the devastating happenings various engineering bodies in my country, Nigeria, are currently battling. These failures often lead to the eventual collapse of buildings which, in turn, lead to lose of lives and valuable properties. The amazing thing about these failures is that they are inevitable in all structures. which means they manifest themselves overtime either the structure is technically sound or not. Even though most buildings are designed to last for a very long time, ranging from 30 years to close to a century, yet failures could manifest themselves earlier than expected. It is essential, therefore, to understand them, be able to identify them and also proffer solutions to them before they escalate in magnitude. This present article hope to address this part of the civil engineering practice. Thus, it is essential to provide you with an overview of what you will be encountering in the subsequent paragraphs that follows. We shall examining what is really meant by structural failure, how they can be detected, types and causes of structural failure, and how they can be mended.

Structural Failures.

Over the years, lives, limbs and valuable properties have been lost to the collapse of buildings, bridges or other civil engineering structures all over the world. The most devastating loss recorded in Banqiao Dam collapse in China, with over 200,000 lives lost to the incident in 1975. Numerous collapse of buildings have been recorded in Nigeria, which include that of the Synagogue church in Lagos and the Uyo Church collapse, killing 44 people and 60 people respectively.

Although it is widely claimed that these incessant collapse buildings witnessed, mostly in the developing countries, is as a result of poor workmanship, but what do one say to the recent collapse of a pedestrian bridge in the United State (a developed country where practices, particularly engineering, are being strictly monitored) claiming 6 lives and injuring as much as 9 people. Or take, for example, a failed power station in China which claimed 74 lives in 2016, or that of Russian military training centre which claimed 23 lives… and so on and so forth.

The purpose of this preceding assertions is to clarify or demystify the claims that all buildings or structural collapses are always as a result of poor workmanship. It is usually more than this even though poor workmanship could sometimes contribute to these calamities. However, all structural collapse are as a result of structural failures. Thus, what are structural failures?

"These are states when a structure or a component of the structure loses its capacity to support or carry load due to the component or the structure itself having been stressed beyond the capacity which it can support/carry load effectively."

All structures, and all engineering products, will eventually fail overtime. Buildings, in particular, are not expected to last for a very long time without periodic maintenance. These periodic maintenance (which may occur for every 6months, a year or more) are carried out to put a check on all structural failures that could have surfaced on the structures during the time of its utilization (for whatever purpose it was built for). Engineers usually recognized the need to attend to failures on time before it results in catastrophes.

Types of Structural Failures

1. Cracks

A Crack in the interior wall of a building.
Image Credit: Wikimedia Commons

Cracks are the most apparent and most common types of failures noticed in the buildings. In fact, all other failures in buildings eventually leads to cracks which would later serve as a warning hint for engineers or personnel around. Thus, I may tend to spend more time explaining this than I would for the others. Cracking could occur as a result of so many reasons ranging from the overloading of the structural elements (this is when an element, e.g beam or column commonly known as pillar, is under-designed, thus placing it in a region where it supports more load than it can withstand) to aging or even corrosion.

Reinforcement steels in concrete could get corroded due to the presence of salts, which contain chlorides which reduces the pH level of the concrete thus exposing the steel rods in the concrete to acidic environment which affects their strengths and shorten their life span altogether. Or carbonation, i.e when air and carbon find their way into the concrete thus corroding the surface of the steel rods in the concrete. When steels rust, they expand to more than 10 times their initial volume, with their strengths falling by same standard. Reinforcement steels are included in concrete to improve its tensile strength. Loss of tensile strength tends to make the concrete vulnerable to cracking and eventual collapse. Thus, these may be one of the reasons why cracks occur.

When cracks occur in buildings, the positions where this is noticed are vital. When they occur under beams or near columns, failure of the reinforcement steels comes to mind. This type of failure can only be remedied by braking down these parts only and adding more reinforcement to these parts after having established that steel failure is manifesting in these parts. The process of adding more columns is known as retrofitting. We shall be discussing that some other time. Aging of concrete could also give rise to cracks. When crack manifest in buildings, they tend to make that part of the building vulnerable to various environmental attack ranging from chemical attacks, such as chlorides and sulphates, to acidic attacks. Thus, these cracks must be tended to as soon as possible to thwart the vulnerability.

2. Delamination

Delamination on a BenchMark on Stone Bridge, Saltney.
Image Credit: Wikimedia Commons

This is another type of failure that occurs when premature finishes are applied on a concrete before it cures. Concrete curing means the controlled loss of moisture in concrete for some given time during which it gradually hardens to achieve a targeted strength according to the ratio in which the aggregates (sand and granite), cement and water are mixed.

Once fresh concrete is poured, it is essential to leave it for some time to allow for the moisture content to be lost gradually and totally before any finishes can be applied to it, such as the application of floor tiles, wall tiles, mortal, or even water-proof membranes. If these are applied too quickly, they are bound to trap water beneath which eventually find way to escape overtime, leaving behind voids. These voids create what we know as weakened zones. Failure of such structural elements begins from these zones. They are often detected by the production of hollow sounds in the zones where they occur. Over time, the finishes peels off and blisters are formed around the region of the delaminated zones.

The widespread of this kind of situation is a serious problem which will eventually lead to premature collapse of the region where they occur. To remedy this kind of structural failure, the finishes and the defective concrete are removed and fresh concrete is then poured into the region. The concrete are leveled and allowances are made for the finishes to level with existing ones.

3. Spalling

Spalling Walls.
Image Credit: Wikimedia Commons

Spalling results from the corrosive tendency of steel which, when it corrodes, expands to up to 10 times its original volume, creating an internal tension on the concrete. Concrete are known to be weak in resisting tensional forces (though are great in withstanding compressional forces). This internal tension created on the concrete by the rusting steel causes the concrete to begin to segregate from the steel, thus falling off, otherwise known as spalling. Spalling is actually a gradual failure that is often caused by seemingly harmless cracks which, at first, make the steel vulnerable to corrosive attacks before spalling begin to result.

Whenever spalling is noticed in structures, it is essential to ensure that the peeled parts are enclosed immediately to prevent further steel corrosion which could lead to fatal catastrophe eventually.

Other Structural Defects That Eventually Leads To Structural Failure Overtime.

Freeze and Thawing

This is phenomenon whereby the moisture content on the surface and in the pores of concrete freezes and unfreezes. Frozen water expands to up to 9% of its original volume. This generates pressure within the pores of the concrete. When this generated pressure exceeds the capability of the concrete to withstand the tensile force of the frozen water, rupture begin to occur from within. Thawing is when the frozen water melts and before unfrozen. This cycle of freezing and un-freezing of water particles in the pores of the concrete can eventually lead to a significant loss in the structural integrity of the concrete, thus resulting in formation of cracks, scaling and even spalling of the concrete elements.

Thus, I regret to announce that here is where we shall be stopping today. Thanks to you, readers, for dropping by and taking your time to read through to the very stage. I hope you’ve learnt something all the way.

Kindly stay tuned while I bring more of Civil Engineering articles to your reading.
Thanks once again, and stay blessed. ;)

References:

1. Wikispace
2. Types and causes of concrete deterioration. A Journal article by the Portland Cement Association.
3. Corrosion of Embedded Material Other Than Reinforcing Steelby Woods H.
4. Wikipedia
5. The Constructor
6. Bright Hub Engineering