f [1Adhesive2[2]

Adhesive failure is the inability of an adhesive to stick to a surface. During this type of failure, the adhesive fails to hold together two surfaces and as a result, separates from the substrate [a]. There are several types of adhesives which include mortar, cement, epoxy, methacrylate, etc. Epoxy and methacrylate are considered structural adhesives. In this case, structural adhesives are synthetic adhesives with strong load-bearing capabilities.

These types of adhesive failures can be caused by shear or tension forces. However, in most cases, these types of failures occur due to incorrect processes used for initial production.  Adhesive production organizations sometimes fail to differentiate between bond strength and durability [b]. When standard tests are performed, it may be evident that the bond strength is adequate, however, these tests fail to verify that the adhesive will be durable throughout its services. As a result, structures are left vulnerable to adhesive failure.

In order to attempt to prevent these types of failures, steel substrates are cleaned thoroughly and then covered in a protective coating. In terms of concrete surfaces, excess moisture vapor in or below the concrete slab is usually the cause for adhesive failures. To prevent this, the concrete mix should use low water to cement ratios, apply a vapor barrier, and adequately cure the concrete slab so that maximum strength and low permeability can be reached. [c]

Alkali Silica Reaction (ASR)



Alkali Silica Reaction (ASR) is the most common form of alkali-aggregate reaction (AAR) in concrete; the other, much less common, form is alkali-carbonate reaction (ACR). ASR and ACR are therefore both subsets of AAR. ASR is caused by a reaction between the hydroxyl ions in the alkaline cement pore solution in the concrete and reactive forms of silica in the aggregate (eg: chert, quartzite, opal, strained quartz crystals). A gel is produced, which increases in volume by taking up water and so exerts an expansive pressure, resulting in failure of the concrete. [a]

Typical indicators of ASR are random map cracking and, in advanced cases, closed joints and attendant spalled concrete. ASR requires water for the chemical reaction and so cracking usually appears in areas with a frequent supply of moisture, such as close to the waterline in piers, near the ground behind retaining walls, near joints and free edges in pavements, or in piers or columns subject to wicking action. A thin section petrographic examination can conclusively identify ASR. [b]

There are a few ways to prevent ASR. One would be to reduce the amount of reactive aggregate in the concrete mix. Another way is through the use of pozzolans which reduce the alkalinity of the pore fluid. [c]

If concrete is affected by ASR then it may be possible to treat it with soluble lithium salts that mitigate the ASR. A main difficulty is getting it into concrete within the concrete’s lifetime. [d]


[1 ; from left: Visible structural deterioration due to ACR and ASR in New Jersey; Cracking within aggregates in reactive carbonate aggregates surrounded by high-alkali cement.]

First observed in Ontario in 1957, the alkali-carbonate reaction (ACR) is the less well understood of two expansive reactions that can occur between alkalis and certain aggregates when mixed to form concrete. The primary source of alkalis in concrete is thought to be cement; however, alkalis are also present in groundwater, seawater, and fertilizers [1]. The alkali content of cement varies widely across North America. ACR causes expansion within the aggregates due to the breakdown of dolomite [2].
Because the expansion occurs within aggregates, ACR can result in localized aggregate cracking or, if the reaction occurs on a large enough scale, cracking and deterioration of the concrete mass overall. The scale and severity of the reaction depend on (1) the alkali content of the concrete mixture, in particular the cement and (2) the chemical composition of the aggregates used.
Characteristics of ACR are often not visible except on a microscopic scale, and laboratory testing may be required to confirm ACR [1].
ACR is less common in modern construction due to careful aggregate selection [2].

(1). In eastern Canada, where ACR is known to cause significant problems, the alkali content of cement has been found to exceed 1.5% in some cement manufacturing plants; in Virginia, where ACR is less of an issue, the alkali content of most cements ranges from 0.55 to 0.70%. Changes in cement production methods are thought to have increased the amount of alkalis in cement [1].
(2) The aggregates associated with ACR are of impure dolomitic limestone [1]. However, alkali-silica reaction (ASR) can also occur within dolomitic limestone aggregates.
The proposed chemical mechanism of ACR is

CaMg(CO3)2 + 2 NaOH → CaCO3 + Na2CO3 + Mg(OH)2

Brucite (Mg(OH)2) is thought to be the direct cause of expansion in the aggregate [3].

Gitanjali Bhattacharjee

brittle-vs-ductile  art4  0512-is-2

[1, 2, 3]

Brittle fracture is the rapid propagation of cracks through a material. This usually occurs so quickly that no plastic deformation takes place before fracture occurs [a]. In building failures, brittle fracture usually causes a failure in structural integrity. Because of the rapid nature of this failure, it often leads to catastrophic failure as there is little indication between the start of failure and full rupture.

Brittle fracture is caused by impurities in a material, whether that is due to manufacturing inconsistencies, small notches in design, or fractures that occur during service [b]. These small impurities cause a small crack which then initiates the rapid propagation of other cracks throughout the material.

Many non-metal construction materials are brittle, or lacking ductility, and as such are subject to brittle fracture. Glass at normal operating temperatures is particularly subject to brittle failure [b]. Metals which undergo brittle fracture are usually high-strength or stiffened in some way [b]. This increased stiffness causes a decrease in ductility which prevents plastic deformation from occurring before fracture. Yet if there is a stress concentration, a tensile stress, and relatively low temperature, brittle fracture can occur in normally ductile materials as well [b].

In buildings, reinforced concrete beams must be designed such as to avoid brittle fracture which occurs due to over-reinforcing. When a beam is over reinforced, the concrete crushes in compression before the steel reaches its full yield point [c]. This is an undesirable mode of failure (as opposed to a gradual ductile failure due to under-reinforcing) because rupture occurs without warning [c].

[a] http://www.sv.vt.edu/classes/MSE2094_NoteBook/97ClassProj/exper/ballard/www/ballard.html

[b] http://www.tec-eurolab.com/en/doc-220-1.aspx

[c] http://www.amazon.com/Reinforced-Concrete-Design/dp/007014110X/ref=sr_1_1?s=books&ie=UTF8&qid=1391117661&sr=1-1&keywords=007014110X pg 113

buckle  buckling

[1], [2]

Buckling is a form of deformation as a result of compression forces. This bending of the column occurs due to the instability of the column. This mode of failure is quick, and hence dangerous[3]. Length, strength and other factors determine how or if a column will buckle.

Long columns compared to their thickness will experience elastic buckling similar to bending a spaghetti noodle. This buckling will occur at stress level less than the ultimate stress of the column[3]. The Euler equation,


explains this phenomena[4]. The ‘L’ in this equation symbolizes length and ‘P’ symbolizes the allowable load before buckling. As the length increases, the allowable load decreases. With shorter columns compared to its thickness, one can infer from the same equation above that the allowable stress on a column before buckling increases as length decreases.

The type of end connections for the column is another important factor in determining buckling stress. From pinned-pinned to fixed-fixed to fixed-pinned connection, they are each represented in the Euler equation with different values of ‘n.’ The fixed-fixed connection increases the allowable stress before buckling more than any of the other end connections[3].

In construction, buckling occurs differently for different materials. This factor of material is captured in the Euler’s equation with ‘E” and ‘I,’ different material properties[4]. In steel columns, buckling occurs elastically. This differs for reinforced concrete. In the image below, the steel rebar is bent outward and the concrete is broken apart. With a more brittle material, the buckling is more sudden.

carbonation pic 1 [1]     passivating layer [2]     horizontal[2]     bad [2]

The mode of structural failure termed carbonation is a natural process which occurs in concrete.  The main concern for carbonation is in the application of reinforced concrete.  Carbonation starts as soon as the concrete is exposed to air.  Carbon dioxide begins to penetrate the surface and react with calcium hydroxide within the concrete to form calcium carbonate.  The carbon dioxide and the moisture from pores also produce a dilute carbolic acid which reduces the alkalinity of the concrete (the alkalinity of concrete is usually high, e.g. a pH of 12 to 13).  The carbonation may advance 1mm to 5mm per year depending on the concrete’s porosity and permeability. [2]

The initial consequence of carbonation is the hardening and strengthening of the concrete.  However, the alkalinity of the concrete continues to decrease and the carbon dioxide invades deeper.  Soon the carbon dioxide reaches the passivating layer and begins to break it (the passivating layer is the protective layer surrounding the reinforcing steel as a result of the concrete’s alkalinity).  Once the passivating layer is broken, the reinforcing steel is exposed to the effects of air and water.  The steel then begins to rust and expand putting pressure on the concrete and causing cracks and spalls.  Once carbonation has begun to affect the steel, the chance of failure in the reinforced concrete member rises dramatically. [2]  Increasing the density and, therefore, decreasing the porosity and permeability of the concrete will reduce and delay the effects of carbonation.  Another effective way of preventing carbonation is to use commercial chemicals such as Flexcrete’s Cementitious Coating 851 [3].  “Flexcrete offer[s] a range of cementitious anti-carbonation coatings that have been proven to prevent the ingress of carbon dioxide given the equivalent of a minimum additional 80mm of cover to prevent carbonation in concrete. [3]”  These products not only prevent carbonation, but they can actually reverse the process if coated over concrete already attacked by carbonation.

Image 1Image 2 Image 3

Chloride attack is one of the most important aspects for consideration when we deal with the durability of concrete. Statistics have indicated that over 40% of failure of structures is due to corrosion of reinforcement [a]. Chloride attack poses a significant threat to reinforced concrete especially for structures in marine environments or those that are likely to be exposed to high concentrations of salts. The net result of chloride attack is the corrosion of steel reinforcement, leading to cracking and spalling of concrete and in some cases catastrophic structural failure as the load bearing capacity of the concrete is compromised [b].

The mode of attack relies on salts and other corrosive substances, carried by moisture, being absorbed into the concrete via its pores and micropores through capillary action. Once absorbed, these substances act to reduce the PH value of the concrete thereby eliminating its passive oxide layer which would otherwise provide protection to the steel reinforcement. Corrosion takes place as the chloride ions meet with the steel and the surrounding passive material to produce a chemical process which forms hydrochloric acid. The hydrochloric acid eats away at the steel reinforcement [b].

Whilst cracking and spalling of concrete accompanied by rust staining is indicative of chloride attack, high strength dense concrete may suffer damage to reinforcement without exhibiting such obvious symptoms until substantial loss of steel has occurred. Where spalling has taken place, an inspection of the exposed reinforcement will typically reveal black colored rusting and pitting of the steel where the aggressive hydrochloric acid has ‘eaten’ the reinforcing material [b].

An engineer may employ several different methods or remedies to prevent corrosion induced by chloride intrusion. The simplest way to reduce corrosion is to increase the cover over rebar. Adding just an extra inch of concrete cover could double the life of a structure. Rebar modifications such as utilizing Epoxy coated rebar, stainless steel-clad rebar, or cathodic protection, can also serve to prevent the rate of deterioration. Another way to prevent chloride intrusion is to reduce the permeability of concrete [c]. Moreover, the addition of an anodic inhibitor to the concrete recipe for structures prone to chloride attack is one measure that may increase service life or time to necessary expensive repair [d].



The mixture of concrete is a very precise science. If the appropriate proportions of cement, fine and coarse aggregate, and water are not properly mixed together, various concrete failures can result and cause structural problems for the project. Concrete bleeding, one of these failures, “is a form of segregation where some of the water in the concrete tends to rise to the surface of the freshly placed material” [2]. Bleeding is primarily the result of a too high water saturation level in the mixture, such that the aggregate particles cannot absorb the excess moisture. Instead of soaking into the rocks and sand, the water floats up towards the surface of the recently poured concrete because it has the lowest density of all the ingredients in the mix [2].

Concrete bleeding can have multiple negative repercussions on a project: it can prolong construction, cause poor bonding between layers of poured concrete, and make the mixture harder to pump [3]. As far as safety is concerned, the poor bonding between layers is the greatest structural problem from bleeding. There are, however, some remedies that can be attempted or preemptively enacted when bleeding occurs.

The first remedy is adding more fine aggregate. Smaller particles have larger relative surface areas and are more likely to have a larger percent of their pores exposed, making smaller aggregates like sand much more absorbent than larger rocks. Adding more fine aggregate to the mixture ensures that excess water will be absorbed rather than allowed to float up to the top of the poured layer. Conversely, reducing the water content of the mix would also prevent concrete bleeding [3].

Another way to prevent bleeding in concrete is to entrain the concrete mixture with air bubbles [4]. These pockets of air allow for water to be absorbed into when temperatures drop below freezing (thus preventing the concrete from cracking) but also allow for excess water to be trapped in the mix rather than separated from it.

A microscopic view of creep deformation

A microscopic view of creep deformation

The Big Dig ceiling collapse caused by creep

The Big Dig ceiling collapse caused by creep

Creep is a time-dependent permanent (plastic) deformation under a certain applied load.  Generally, creep occurs at high temperature (thermal creep) but can also happen at room temperature depending on the  material (e.g. lead or glass), although this happens at a much slower rate. As a result, the material undergoes a time-dependent increase in length, which could become quite dangerous while in use [1]. The rate of deformation is called the creep rate. It is the slope of the line in a creep strain vs. time curve (see below) [2].

Creep Strain vs. Time Curve

Creep Strain vs. Time Curve

Creep deformation has three stages:

  1. Primary creep  starts rapidly and slows down with time.
  2. Secondary creep progresses at a relatively uniform rate.
  3. Tertiary creep has an accelerated rate of deformation which terminates when the material fails (breaks or ruptures). It is associated with both necking and the formation of grain boundary voids [3].

There are several design strategies that can be adopted to avoid creeping in materials:

  • Reduce the effect of grain boundaries (use single crystal material with large grains).
  • Add solid solutions to fill the voids in the material.
  • Use materials with high melting temperatures.
  • Consult creep test data during materials selection [4].

crazing1             crazing
[1]                                              [2]

Crazing describes the development of a network of fine surface cracks due to rapid shrinkage of the surface layer relative to the underlying concrete [a]. Crazing cracks are typically less than 1/8th inch in depth and do not affect the structural integrity or serviceability of the concrete, but are a significant detriment to the aesthetic quality [b].

Crazing is prone to occur when new pours are exposed to high temperature, low humidity, or high winds that lead the surface layer to shrink faster than the underlying concrete [b]. Furthermore, overfloating or finishing the concrete while bleed water is present on the surface increases the water to cement ratio in the surface layer, therefore, decreasing the strength of the surface paste, making it susceptible to surface cracking [b].

When high evaporative conditions exist, crazing can be prevented by maintaining proper curing techniques. Begin curing as soon as finishing is complete by keeping the surface layer moist for 3 to 7 days [a]Curing can be maintained by either flooding the surface or covering with wet burlap [b].

D-Cracking at a Joint  freeze_cracking

D-cracking is cracking in concrete pavements caused by freeze-thaw cycles deteriorating the aggregate in concrete.  Water naturally accumulates at the base and sub-base layers under concrete.  When this water suffers from freeze-thaw cycles it wears on the durability of the concrete and begins to crack in the aggregate at the base of the concrete working its way to the surface.  Since the cracking begins beneath the surface it is hard to detect D-Cracking before it becomes visible on the surface of the pavement [a].  This kind of cracking is more susceptible to occur in concrete on ground level such as foundations, roadways, and sidewalks.

Preventative measures can be taken to help avoid D-Cracking such as air-entraining.  This is the addition of air within concrete to allow water to easily expand and contract during freeze-thaw cycles without adding strain to the aggregate in the concrete.  However, increasing the air volume within concrete decreases the strength creating a limit to which this can be used.  Other options are selecting aggregates to be used that perform better in freeze-thaw cycles or reducing the particle size of the aggregates to strengthen the concrete [a].

In buildings, wood materials are subject to decay. Decay is defined as the state or process of rotting or decomposition [a]. The most common types of wood rot are brown, white, and soft [b].

Brown Rot
[1] Brown Rot

Brown Rot is characterized by wood color becoming lighter prior to becoming dark brown and by cracks forming in brick shapes across and along grains. When dry, very decayed timber will crumble to dust. The dry-rot fungus is a common species of brown rot. [b]

White Rot
[2] White Rot

White Rot can be observed in forests as the disk-shaped growths protruding from the sides of trees. It can also occur on timber in buildings. Strength losses are not significant until late stages of decay. [c]

Soft Rot
[3] Soft Rot

Soft Rot was first characterized as a soft, decayed surface of wood in contact with excessive moisture. However, soft rots can occur in dry environments and may appear similar to brown rot. Common places for soft rot include fence posts, telephone poles, and window frames; essentially, soft rot can be found wherever timber comes in contact with moisture regularly. Presence of nitrogen in the wood or surrounding environment contributes to the development of soft rot. [b]

Wood rot can be prevented by ensuring that no moisture can get past the skin of the building. Problems occur when moisture gets in and can’t get out. Making sure all wood surfaces are painted or sealed and caulking all seems in windows, doors, and exterior vents. Decay-resistant and pressure-treated lumber is also resilient against wood rot. Dry rot can be treated by epoxy, which kills the fungus and fills in the channels, thus restoring structural integrity.


A defect is a commercially produced and distributed good unfit for its intended use.  It is any characteristic of a production which hinders its usability for the purpose for which it was designed and manufactured [A].  A defect is also a non-conformance of a product with the specified requirements, or non-fulfillment of user expectation including the safety aspects [C].  Product defect arise most prominently in legal contexts, where the term is applied to anything that renders the product not reasonably safe.  The defect can also be dangerous or harmful for normal use; this could be due to defective design, assembly, or manufacture [B].

In the first figure, the rope has weak strands which allow it to break in half easily.  The second picture is a ladder with a faulty step.  The wood used for the ladder could have been rotten or filled with knots making it easy to snap when enough pressure is placed on it.  The third picture is a broken chain link.  The connection of the loop was not welded like the other links to which it broke apart.

Delamination in Reinforced Concrete Delamination - Concrete Delamination of Glulam[1, 2, 3]

Delamination occurs when composite materials begin to separate or break apart. In many cases these separations occur below the surface or in between layers of the material making delamination hard to identify until the material has already been seriously damaged. Delamination is detected by listening to the sound a material makes when it is struck. “Most composites will respond with a loud reverberating sound. A delaminating composite will sound dull on impact, with a low non-reverberating sound [a].”

In layered materials, repeated loading or stresses can cause the bonding agent to fail causing the layers to separate or flake apart [b]. Large changes in temperature and pressure and high humidity also dramatically increase the rate at which the adhesives between layers break down [b].

Delamination can also occur in non-layered composite materials like reinforced concrete. If the reinforcement is not properly protected against corrosion the rebar will oxidize and expand resulting in a separation between the concrete and reinforcement material. Delamination can be avoided in concrete if the mix is poured and cured correctly, most notably during final finishing of the concrete [c].

DEF     DEF1    1-s2.0-S0008884601004665-gr4


Delayed ettringite formation is a consequence of improper heating during the curing process. Ettringite is a normal product in concrete and is delayed when the temperature rises too high for it to form. During this period of high temperatures (above 158°F-176°F), the sulfate in cement paste starts to concentrate for a longer than usual period of time [a]. In respone, the sulfate will react with aluminum and calcium in the paste and start to expand, thus creating gaps that form fully around aggregate [3] [b]. This ultimately leaves an open space in the concrete for visible cracking and displacement to form.

Eventually it impairs the integrity of the structure and can start to expose inner reinforcement leading to problems like corrosion. DEF is not a common type of failure in concrete because it is easily prevented. One can limit the temperature of the concrete to 158°F while it is curing as well as making sure that no extra water or moisture is brought in from an outside source.

tower_580x  car

“Building failure is a defect or imperfection, deficiency or fault in a building element or component. It may also be as a result of omission of performance. The degree of building failure can therefore be related to the extent or degree of deviation of a building from the “as – built” state which is in most cases represent the acceptable standard within the neighborhood, locality, state or country.”[a]

Deviation is a divergence of the value of a quantity from a standard or reference value. Deviation is generally used to indicate a divergence from what was originally intended. [b] Deviation when referring to building failure could mean multiple things such as ignoring building codes, the building swaying more than it should due to unexpected wind loads, or something as simple as constructing a building and ignoring some small details from the original design. Most building failures are deviations they are circumstances that were not intended or accounted for. 

However, deviation is not all bad. The Leaning Tower of Pisa, as seen in the first picture was not originally intended to lean at an angle, but if the deviation had not occured the tower would not have been as famous as it is today.

Click for Video of Menara Umno’s tower-top  collapse which was later suspected of failing because the architect confessed that he had deviated from the building codes. [c] The Menara Umno’s lightning arrestor and cocrete mast from the top of the 21-story building collapsed as seen in the second picture above.

diagonal corner crack  Cracks 3_0


Diagonal cracking is an inclined crack beginning at the tension surface of a concrete member. Steep diagonal cracks appear in concrete foundation due to point loads that exceed the compressive strength of the concrete. This type of failure, known as settlement, can happen due to “volume changes in clay soils due to fluctuation in their water content, increased pressure on a portion of the foundation, or long term consolidation of compressible clay under the foundation” [a]. If the soil under the footing cannot stand the compression force from the weight of the foundation and house/building, then the structure will sink and any adjacent walls that are adequately supported will resist this movement.

In addition to diagonal cracking caused by external effects, it can also occur from internal problems. Diagonal shrinkage cracks can occur in a concrete wall due to “improper mix or improper curing at the time the concrete was set in place” [b]. It is important to make sure that there is adequate soil to place the foundation/structure, and that the mix and curing of concrete was done properly.


Leaning Tower of Pisa  

Differential settlement is a deceptively destructive failure that commonly occurs when the building site has not been properly analyzed. Differential settlement will occur when “the soil beneath a structure cannot bear the weights imposed. The settlement of a structure is the amount that the structure will ‘sink’ during and after construction,” [a]. A well-known example of differential settlement is the Leaning Tower of Pisa, which leans due to insufficient bearing capacity of the soil beneath one side of the tower [b].

Common signs that differential settlement has occurred would include: windows and doors sticking, roof and basement leaking, bricks or walls cracking, walls bowing, bulging or leaning, drywall separating, and more. For a full list of common symptoms of differential settlement click here. Common causes associated with differential settlement include: (1) drought conditions – particularly an issue with clay based soils that are able to expand with an increase in water content, and contract during a drought; (2) undermining of the foundation – poor drainage can cause soils to be eroded; (3) sinkholes – naturally occurring phenomenon resulting in a collapse of the supporting soil under the foundation. [c]

Differential settlement can be prevented by carefully inspecting the site before construction and using preventative measures. Certain soils primarily composed of sand or rock may not require a pier system, but any soil that is susceptible to expansion and contraction, such as clay soils, would benefit from a pier system such as the Resistance Pier System or Helical Pier System. Another concern may be Earthquakes such as in California or Japan; if the site is on or close to a fault line the earth itself can move by inches or even feet during an earthquake leading to differential settlement of the site. Many locations around the world must take advantage of seismic design principles.

The most dangerous aspect of differential settlement is that the failure mechanism is not visible, and thus is not easy to catch after the building is constructed. Each site should be carefully evaluated before construction begins.

     distress 1 distress 2  distres 3  distress 4


Distress, in the most common sense, can be defined as marks of age and wear, or instances that cause strain. In engineering, distress becomes synonymous with failure, and can lead to failure of the structural integrity. Distress can be caused by inadequacy of design, poor quality of construction and maintenance, or by strains to the material. Common distresses include cracking, potholes, surface deformation, and foundation failures. [a] Manuals exist identifying modes of distress in asphalt and concrete, as depicted by an excerpt seen in Figure 2 from the Distress Identification Manual for the LTPP.

Modes of distress can result from many alterations in the environment surrounding the material. For instance, such as in Figure 1 above,  cracking along an exterior wall can result from building settlement. Cracking in a building’s foundation can result from swelling in the soil below the foundation, causing the foundation to settle and crack such as the Lotus Riverside apartment building in China as seen in Figure 3. In this case, excavation near the existing building caused the stress on the foundation piles to become too much and the cracking and failure of the piles. Potholes, another common distress, develops in asphalt pavements from fatigue cracking. As these fatigue cracks grow, pieces become loose and are picked away by traffic loads as shown in Figure 4. Distress is the indicator that a failure has occurred.

 [1]    [2]

Efflorescence is the a change on the surface of a material to a powdery substance upon exposure to air, as a crystalline substance forms through the loss of water [a]. This crystallization usually appears on masonry or concrete structures as a white powder. This powder is salts left behind when water evaporates from the masonry.

Three conditions must exist in order for efflorescence to occur [a].
1. There must be water-soluble salts present somewhere in the wall.
2. There must be sufficient moisture in the wall in order to render the saline solution.
3. There must be a path for the solution to migrate to the surface of the wall where it can evaporate and leave behind the salts that crystallize to create efflorescence.

Efflorescences can occur in natural and built environments [b]. In built environments, efflorescence can occur as a cosmetic problem, but if left unchecked, can lead to serious structural problems. The salts can begin to react with the cement causing an Alkali-Silica Reaction (ASR) which makes the cement dissolve.

Potential efflorescent problems can be greatly reduced by using low alkali cements, clean washed sands and clean, potable salt free water. Special admixtures can also greatly reduced the risk of concrete, masonry, and/or cement contracting efflorescence.

Erosion 1  Erosion 2 [1,2] Erosion is the process by which material on the earth’s surface is gradually worn away by the effects of wind, water, and glaciers [a].  The eroded material is often transported away from the erosion sight. Erosion can pose major problems to structures built on hill sides [b], in coastal areas, and near water ways [c].  As the soil on which a foundation is built is eroded away an increased amount of stress is placed on certain parts of the foundation, resulting in cracking and occasionally catastrophic failure. The sand under this beachfront home’s foundation in Delaware (Image 1) was eroded away during a major storm in 1962, causing the foundation to fail [d].  Buildings built in areas particularly vulnerable to erosion are often built on deep peer foundations thereby resting the weight of the structure on rock or soil deep within the earth as opposed to its easily erodible surface [c].

airEntrainers (1)  [1, 2]

The U.S. Dept. of the Interior defines freeze/thaw damage as “damage to concrete caused by extreme temperature variations as noted by random pattern cracking.”[a]

Freeze/thaw damage occurs in concrete when the water molecules in concrete freeze and expand beyond the volume constraints of the concrete.  When the >91% of the pores of concrete are filled with water, the concrete is known to be saturated.  When these water molecules freeze, they expand by 9%, and because there is no room for their increased volume, the concrete distresses.  The freeze can cause the bonds in cement around the aggregate to break and the concrete can crack in those places.  Thus, the higher the water/cement ratio in the concrete, the higher risk it is for freeze/thaw damage.  As the seasons pass, concrete goes through the process of freezing and thawing, wearing out over time.  As winters come and go from year to year, the concrete deteriorates. [b]

Certain measures can be taken to prevent freeze/thaw damage to pavements and any concrete structure.  Prevention measures include adding deicing chemicals to the concrete during the winter in order to decrease the freezing point of precipitation as it falls onto the pavement as well as using high strength, air-entrained concrete.  By reducing the freezing point of the precipitation, chemicals such as sodium chloride, calcium chloride, magnesium chloride, and potassium chloride in high concentrations work to reduce the exposure of the pavement to freeze/thaw cycles. [c]

 [1]   [2]
Frost penetration is the depth at which frost is beneath the pavement or soil, also known as the frost line or frost depth. There are two ways to calculate frost penetration: theoretically or using field tests. Typically during the theoretical method, information from a freeze index is used. Results from a field test, however, tend to be more accurate. [a]

If frost is present beneath pavement, it can damage the concrete and cause cracking and other failure. Freezing is caused by an increase in moisture content, ice expanding, and ice lenses. Ice lenses are layers of solid ice parallel to the surface of the soil below surface level. They can cause the greatest magnitude of displacement in pavement structures. In order to avoid or minimize damage and frost penetration, drainage systems and optimized thermal properties of the structure should be put in place. [b]

by Nathan Simmons


[1, 2]

Functional failure is when a component or system does not perform the intended function expected of it by the designer.[A] This means that the system or component is unable for some reason to serve its intended purpose. This does not mean that this failure will pose a threat to the health and safety of the occupants of the building. For example, let us say a house has settled a little bit. Because of this, a door is unable to close completely. This would count as a functional failure because the door (the system or component, in this case) is unable to serve its intended purpose (which in this case is being able to close). It does not directly threaten the safety and lives of the occupants, but it does show itself to be quite the defect and deviation from its main purpose.

Functional failure is a type of failure, meaning that it is a category of a difference between expected performance and actual performance. [A] Functional failure in building may be caused by a lack of maintenance. Keeping up general maintenance over time can prevent or functional failure caused by aging in general degenerating of material or degeneration due to overuse. Functional failure can also be caused due to lack of oversight by engineers over the workers during construction. [B] Liability can lie one the engineers, the workers, or even the owner for failure to maintain the component or system. [B]

[A]“Failure Mechanisms in Building Construction.” David H. Nicastro.The American Society of Civil Engineers. Print.


Lateral torsional buckling occurs when an applied load causes both lateral displacement and twisting of a member. This failure is usually seen when a load is applied to an unconstrained, steel I-beam, with the two flanges acting differently, one under compression and the other tension. ‘Unconstrained’ in this case simply means the flange under compression is free to move laterally and also twist [a]. The buckling will be seen in the compression flange of a simply supported beam.

The best way to prevent this type of buckling from occurring is to restrain the flange under compression, which prevents it from rotating along its axis. Some beams have restraints such as walls or braced elements periodically along their lengths, as well as on the ends [b].

This failure can also occur in a cantilever beam, in which case the bottom flange needs to be more restrained than the top flange [b].

The location of the applied load is a major concern. If the load is applied above the shear center of a section it is considered a destabilizing load, and the beam will be more susceptible to lateral torsional buckling. Therefore loads applied at or below the shear center is a stabilizing load, with little risk of the buckling occurring [a].


[1] Mortar crack in brick facade


[2] Expansion joint in concrete

All porous materials expand to some extent when they absorb water. This kind of deformation is generally reversible when the material dries out, except in such materials as concretes. mortars, and plasters [a]. In other words, the expansion and swelling remains in the material even after ordinary drying has completed. When a material expands, the swelling can cause cracking of both the material and it’s facade, examples of which can be seen in the figures above [1,2].

For ceramics, most expansion will occur in the first 10-12 weeks after production but can continue, at a decreasing rate, for many years [b]. The majority of volumetric changes due to moisture release or evaporation in concrete occur within the initial casting and curing phases, making precast concrete materials advantageous [a]. The small cracks that inevitably form in concrete allow moisture to penetrate into the specimens, making these specimens particularly susceptible to moisture expansion deformation [c]. This cracking allows for more moisture to enter the material, thus propagating the damage into the future.

Moisture expansion can result from any physical or chemical process which creates voids in a material. There are various preventative methods that exist to avoid the negative effects of expansion in construction materials. In brick masonry, expansion joints (unobstructed openings through the brick wythe that are filled with compressible material) can be added to allow joints to close as the brick expands [d]. Similarly, as seen in figure [3], concrete isolation joints provide relief from the tensile stresses that cause uncontrolled cracking in concrete slabs by allowing the concrete to move freely as it shrinks or expands [e].



[3] Expansion joint detail

les_mom_necking_1    les_mom_necking_2 [1, 2, 3] Necking is local deformation that “begins at a tensile point or ultimate stress point” [a]. After ultimate stress is reached, the cross-sectional area of a small portion of the material decreases. This is a result of uniaxial tension or stretching [b].  This newly smaller area has very large amounts of strain and is seen as an instability, called the “neck”. The act of necking can be shown on a stress-strain diagram.  It is the range on the graph from the ultimate stress point to the point of fracture of the material [a]. Necking takes place after a material passes through the elastic, yielding, and strain hardening region of a material test [c]. Necking is mostly associated with ductile materials, and is common during experimentation of steel in tension in many materials labs. The necking region can take on a cup or cone-like shape in ductile materials. In brittle materials, there is no necking region. The material will simply fracture with a relatively flat plane at the fracture area. Necking has criterion as determined by Considère in 1885: 1) During tensile deformation, the material has a decrease in cross-sectional area, 2) Strain hardening occurs during tensile deformation, and 3) All materials have flaws in their structure [d].


nsi         normal vs tempered glass       nickel-sulfide-inclusion

NSI – Nickel Sulfide Inclusions Found In/Failure Concern: Tempered Glass, Curtain Walls Prevention: Glazing, Heat Soak Testing [a] NSI is a Failure Mechanism associated with glass breakage. Inclusions, also known as imperfections in the glass, are a common aspect of glass and appear in the production process of tempering glass. There are many types of imperfections; however NiS inclusions are extremely dangerous, and can cause extensive damage and overall failure in tempered glass[b] [c]. When glass is tempered it is cooled rapidly, however when NiS inclusions are present they remain in a high-temperature state and cool overtime. Thus the glass panels appear to be perfectly fine initially and then after placement or installment as the NiS cools it grows in volume, some 2-4%, causing the glass to crack and appear to explode due to the increase in internal tensile stresses[d].

  image_5  EverdryMichBlogPost

There are many types of organic growth that can occur on a structure. On type deals with foliage on the site including trees, shrubs and ivy. The roots and growth can penetrate open joints in the system causing for displacement of the bricks and stones in walls and cracking in foundations and pavings. The trees can  start to grow and come in contact with the building which starts to put extra loads where in contact with the structure. This can be seen in image one with the tree’s branches starting to push out in between the bricks on the roof.  In some cases the extra load can cause the contact surface to start to shift. Other affects of growth can cause blockage of rainwater drains and shading of surfaces on the building. The excessive shading can cause moisture to be retained on the outer surfaces [a].

To deal with the unwanted growth there are many alternative options. Trimming of the branches and roots before contact is the most successful proactive approach for trees and bushes. Full scale removal of the foliage is an option, but this can have an effect on the soil and under water levels, and in some places is illegal due to environment protections.  If dealing with ivy cutting off a section and letting the main stem die off naturally is acceptable because using  force to removal the ivy stem can lead to displacement and detachment of the building facade [a].

Another type of growth that can occur on the building includes algae, lichens, molds, bacteria, and fungi. This type of growth is common on the exterior of buildings and occurs when there is a prevalent amount of moisture, good lighting, and a suitable temperature [b]. Growth of lichens an mosses on buildings  can actually cause for a pleasant aesthetic look which is present in image two. The moss and lichens shows the age of the marker, and creates a wonderful contrast against the smooth gray of the stone.  But when in contact with metals, Lichens can cause deterioration. Moss if a can cause frost damage on roofs and can restrict moisture evaporation.  Algae, fungi, and bacteria grow on the surfaces and mainly only effect the appearance of the building [a]. Black mold is very toxic for humans with symptoms including respiratory problems, skin inflammation and much more. It grows best in warm conditions with a prolong exposure to moisture. In buildings this is most likely places where there are leaks.The mold can grow on almost any sort of plant, or in areas of high cellulose or low nitrogen level which includes most common building materials. The black mold produces toxins in the air which can take years to break down and can stay inside of homes for a long time [c]. Along with the unpleasant health issues the black mold, as seen in image three, distracts from the beauty of the building leaving awful black marks and stains everywhere.

Regular treatment of the building with surface biocide or algaecide is the best way to remove growth on the surface. Removing the algae and fungi with water will get rid of the problem temporarily but does not have long term effect [b]. There is no cure for black mold symptoms expect for removing from the environment of the black mold altogether.


A procedural failure is defined as a nonphysical factor contributing to failure, such as error.  Procedural failures are most important when determining who is liable or responsible for the failure.  For example, if a part or plant is assembled and later fails, one must determine the cause of said failure whether it be during the method of assembly or if something was manufactured wrong.

A failure at a nuclear power plant was blamed from “procedural and hardware” failures.  24 radioactive rods were dropped while being moved during the assembly process.   This may be deemed as a procedural failure because the cause of the accident was due to something going wrong during the assembly process.  Although no injuries were reported, extra safety precautions have now been put in order to prevent failures like this from occurring.  [A]

Another example of a procedural failure happened at an elementary school. Signs of distress n the concrete formed very early including building wall movements, cracking of finishes, and slab heave.  These issues were reported and legal action was taken by the school to figure out the cause of the problem.  Expansive soil problems related to pyrite were deemed to be the cause of failure.  Because the original soil and land survey was performed poorly, this caused damage for over 40 years to the building.  Multiple repairs, cosmetic and structural, have been made by the school.  [B]

1            2

[1]                                                       [2]



Progressive Collapse is “the collapse of multiple bays or floors of a structure resulting from an isolated structural failure due to a chain reaction or domino effect” [a]. The engineering profession started to investigate such behavior worldwide since it was the main mechanism that completely destructed the World Trade Center Towers in the New York City. Any extreme loading that damages structural components such as support beams and columns are subjected to potential cause for progressive collapse. In the case of 9/11 attacks, airplanes crashed into the buildings and blew out the upper floors which took down the layers below to complete ground level. The mechanics of Progressive Collapse has two phases: “Crush-down, whereby gravity and the immense downward kinetic thrust of floors upon mashed floors successively crushes everything below, gives way to crush-up, the free-falling top floors now piling on top of the wreckage. This second phase further pulverizes the rubble” [b].

The nature of the Progressive Collapse which contains impulsive and dynamic external loads make it difficult to fully predict its random occurrence. As a result, although number of researches have been conducted over the past, there are only few standardized structural designs for resisting collapse.   However, steel reinforcement technology can reduce the pancaking effect by enhancing the ductility and structural integrity. Reinforced concrete structures that close the space of beams and columns, connect top and bottom reinforcement, and limit span lengths provide uniform layout to the structural system [c].


Punching shear is a type of failure of reinforced concrete slabs subjected to high localized forces [a]. This type of failure is catastrophic because no visible signs are shown prior to failure [b]. Punching shear failure disasters have occurred several times in this past decade [b]. An example of punching shear failure can be see in image 2.

A typical flat plate punching shear failure is characterized by the slab failing at the intersection point of the column. This results in the column breaking through the portion of the surrounding slab (as seen in image 1). This type of failure is one of the most critical problems to consider when determining the thickness of flat plates at the column-slab intersection. Accurate prediction of punching shear strength is a major concern and absolutely necessary for engineers so they can design a safe structure [b].

Research has also been conducted in the past to develop an understanding of why punching shear occurs and how to prevent it. In recent years, the finite element method has been applied to analyze punching shear failure problems.  It can be used to develop an analytical model for the punching shear failure analysis of reinforced concrete plates [b]. Furthermore, it has been discovered that punching shear can be prevented by increasing the depth of the concrete floor slabs, or by increasing the diameter of the columns supporting the floor [c].

lotus riverside building failure  sprinkler_head_web

A safety failure is a functional failure that creates a hazard [a]. This type of failure can include structural failures, foundation failures, and the failure of life safety mechanisms.

Life safety mechanisms are tools implemented in buildings to protect and evacuate building occupants, in the case of emergencies such as fires, earthquakes, or power outages [b]. Life safety systems include fire suppression systems such as smoke detectors, automated calls to fire departments, fire sprinklers (image 2), the shutdown of ventilation compartments, electric pumps that provide the required water pressure for a sprinkler and gas-powered electric generators [c]. To be considered a safety failure, these mechanisms only have to not function as intended, rather than suffer a complete malfunction, then lead to a hazardous situation [a]. This distinction is shown by a 2008 case study in which a fire consumed a two-story motel. The deluge system in place activated but was unable to contain the spread of the flames, not functioning as intended, and resulting in the collapse of the roof and $10 million in damages [d].

Structural failure refers to structural members yielding under stress, poor material choice, or construction error [e].  A foundation failure is the cracking or erosion of the foundation, causing damage to the building’s components or the potential collapse of the building [f]. A notable structural failure is the facade failure of the Aon Center in Chicago in which a slab cladding the building detached and smashed into a house below. A notable foundation failure is the Lotus Riverside apartment complex in Shanghai, China, when earth moved from the creation of an underground garage and relocated into an adjacent river led to the collapse of the river bank and the flooding of the Lotus Riverside’s foundation, causing it to collapse (image 1) [h].

The job of ensuring the integrity of a structure is that of the structural engineer [i]. A safety engineer is concerned with the performance of life safety systems, even when their components fail [j].

[a]: “Failure Mechanisms in Building Construction.” David H. Nicastro. The American Society of Civil Engineers. Print.

IMG_007  Image174


Segregation typically refers to the separation of different particles in a mix, usually concrete or asphalt. Segregation creates grain boundaries where an aggregate and a solute in the mix, such as a gravel aggregate and Portland cement, become separated and there are pockets of each material. This causes weaknesses along the grain boundaries that may be unexpected and unaccounted for. In engineering applications, it is typical to strive for a well-graded mix. Segregation causes the mix to be less homogeneous which could amplify the weaknesses of an element in a mixture. [a] Segregation can be caused by improper consolidation, where too much leads to more dense particles sinking to the bottom, and where too little results in a poorly packed mix. Segregation can cause premature wear and tear, especially on roads with high traffic loads. It is very important to understand how segregation effects engineering materials and how to prevent it, so that we can prevent unnecessary damage to our projects.

Other Sources: http://jenike.com/bulkmaterialtesting/segregation/

picture 1  picture 2  picture 3  picture 4
1, 2, 3, 4]

Spall is a term used in engineering to describe the chips or fragments of a material that is broken off a larger object. The process of spalling (or spallation) describes the surface failure that occurs when a material such as concrete, brick, or limestone is subjected to excess moisture, corrosion, weathering, and much more. [a]

The most common source of spalling in brick, for example, is from excess moisture in which water enters into the brick material causing pieces of it to crumble. Causes of excess moisture may include consistent, heavy rainfall coming into contact with outdoor brick, or dark, damp areas such as basements in which the humidity and also salt will affect the walls. [b]

Besides environmental factors, poor installation also induces spall to form in concrete or limestone such as through structural overloading of the stone or not taking care to have the proper mixture of ingredients while pouring the concrete. [a]

Spalling, at a low level, is mainly a cosmetic problem but it can lead to structural damage if not dealt with immediately. If left untreated, damage can occur to the reinforcing bars within the concrete. Also, large enough fragments could fall off which could lead to serious consequences. [c]

Preventing spallation is usually done at the outset of mixing the concrete, by using air-entrained concrete, curing well, and making sure to apply a water-repellant sealer after the slab is cured. The water-repellant sealer is probably the most essential ingredient needed to prevent spallation. After the concrete is done though, one can use a Concrete Treat as a sealer on outdoor and indoor concrete in order to prevent moisture from entering.[c]

SF1  SF4  SF2  SF3
[1, 2, 3, 4]

“Damage or deformity to an object as a result of the device being overloaded or forced to work beyond its maximum load bearing capacity”—this does not necessarily result in overall collapse [a]. A structural component is considered a failure when it does not “behave as intended” while in service [b]. Structural failure occurs in several different ways: overloading, cracking, corrosion, and impact damage (damage caused by impact of equipment or other building materials) [c]. These modes of failure are shown in figures 1, 2, 3, and 4, respectively.

[b] David Fowler, Lecture, University of Texas at Austin, January 31, 2014


Sulfate attack [SO4] on concrete is a common occurrence with compromising effects. Sulfates are present in various sources often in contact with concrete, i.e. the gypsum in cement, in fly ash additives, acid rain, ground water runoff, seawater, clay, sewage, and industrial waste. As most sulfates are soluble in water, there is high probability of sulfate exposure in concrete’s lifespan. [a]

Sulfate exposure causes an expansive ettringite crystallization. The increase in volume causes both superficial  and interior cracking, which could compromise the structural integrity of the concrete. [b] Cracking is most likely to occur near the surface where water exposure is more common, which often results in spalling and crumbling of the exterior. Occupants would also be alarmed, as the surface under attack becomes covered in the white reaction product. As seen in Figures 1 & 3, building foundations exposed to ground water runoff commonly suffer sulfate attack.

Prevention methods mainly aim to decrease the porosity of the concrete exposed. Lower water/cement ratios produce less permeable concrete. Other chemical additives increase strength and thus resistance to cracking. [c]

Thermal Hysteresis1  Thermal Hysteresis Diagram  Marble Under Microscope

Hysteresis [his-tuh-ree-sis] is defined as the lag in response exhibited by a body reacting to changes in the forces affecting it.[a] Relating this idea to building failures, thermal hysteresis is the term used to describe the long-term response that certain types of marble display after years of thermal cycling. The stone is particularly susceptible when cut into thin slabs and used for building facades, leaving it exposed to large variations in temperature and humidity. While marble is a brittle material, it exhibits some plastic behavior over long periods of exposure.[b] Following several years of thermal expansion and contraction, panels will start to permanently bow outward, as seen in Figure 1 above. The exposed side expands at a significantly higher rate than the inside of the panel, which remains cooler and more moist. This ‘cupping’ or ‘pillowing’ increases the porosity of the panel and can reduce its flexural strength by as much as 70%, eventually leading to failure.[b] The effect is illustrated above in Figure 2 while Figure 3 shows the resulting fractures that occur at a microscopic level.

The use of marble as a cladding material for high rise buildings began in the 1960s, “when advances in stonecutting allowed thin slices to be produced.”[c] Seeing it as a “prestigious material,” architects began recommending it to wealthy clients, including Edward Durell Stone, the architect behind the Standard Oil headquarters in Chicago.[c] Later being renamed the Amoco Building and then the Aon Center, the building provides one of the best examples of thermal hysteresis. Clad with nearly 6,000 tons of Carrara marble imported from Italy, the facade lasted less than 15 years before requiring replacement. Suffering a similar fate, the “Chase Lincoln First Bank of Rochester, New York had to strip its 27-story headquarters of its Carrara marble skin in a job that took three years” to complete. “Its cachet notwithstanding, the marble was deemed worthless and dumped in a landfill.”[c]

“Studies seem to indicate that impurities, grain size, veining and other obvious orientation of the stone crystals increase a stone’s susceptibility to experience hysteretic behavior.”[b]  However, thermal hysteresis is tough to predict, necessitating frequent observations. In most cases, once hysteresis sets in, the panels have to be replaced, typically with a material other than marble so the problem does not repeat itself. In cases where a designer is determined to use marble cladding, engineered materials like StonePly – which uses a thin marble veneer fully adhered to an aluminum backing – may provide a successful solution.[d]  As a general rule though, using solid marble slabs on facades should be avoided as it poses serious safety risks and can cost millions of dollars to replace.

[3] Siegesmund, S; Ruedrich, J; Koch, A. “Marble Bowing: Comparative Studies of Three Different Public Building Facades.” Environmental Geology 56, no. 3 (December 2008): 473-494.

[b] Newlin, J; Jimenez, G. A; Hester, D; McIntosh Blank, L. “Thin Marble Facades: History, Evaluation, and Maintenance.” Structures Congress, 2010 ASCE: 1051-1062.


Weathering is the process by which natural elements of nature (such as wind, water, CO2) act upon a rock or mineral composition. [a] The reaction, based on a mechanical or chemical process, causes the rocks or minerals to disintegrate to a sand or soil. [b] Weathering on a building depends on the exposed material of the building and bonding agents used to hold the material together. [c]

Various forms of weathering include:

Physical Weathering – Physical forces, such as ocean waves or high speed winds, are exerted onto the building and breakaway the stone compounds [figure 1, 3]. The process of this weathering can be slow and steady. In the event of a shift in temperature, a condition such as Freeze Thaw can occur. Water in the stone can freeze resulting in the alternation of the physical condition of the stone. [c]

Chemical Weathering – Chemicals found in rainfall interact with the buildings stone at the molecular level causing the material to dissolve or change its substance composition. Acidic rainfall is based off the acid in rainfall and it’s interaction with calcium based minerals such as limestone. In cities with dense pollution, rainfall is acidic enough to dissolve some of the minerals. Salt Weathering results from the travel (through rain or wind) of salt into the holes of the building’s stone [figure 2]. Crystallization with the salt and stone begins making the structure weak [figure 4] [c]

Although considered to be a failure mechanism, weathering can be used as a design choice with the use of weathering steel. Rust is allowed to develop acting as a protective shield on the steel. Weathering steel is popularly used in sculptures.


[a] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.

[b] The American Heritage® Dictionary of the English Language, Fourth Edition copyright ©2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.

Image  Image


Yield of a material is explained as the stress at which a material begins to deform irreversibly. Preceding the yield point, the material will deform elastically, meaning that it will return to its original shape when the applied stress is removed (i.e. no permanent, visible change in the shape of the material). Once the yield point is passed, however, some of the deformation will be permanent and non-reversible. Knowledge of the yield point is important when designing a component since it normally signifies an upper limit to the load that can be applied [A]

Not all materials have a well-defined yield region. In the absence of a distinct yield point, a .2% offset is used to obtain an approximate yield point. All deformation before the yield point is uniform throughout the narrow region of the material. [B]

[A] “Yield (engineering).” Wikipedia. Wikimedia Foundation, 02 Mar. 2014. Web

[B] “YIELD STRENGTH.” Yield Strength Help for Strength, Engineering, Homework Help. TransTutors, 12 July 2008. Web.

5  6
[1 , 2]

Serviceability describes the conditions under which a structure is considered useful. All structures and systems have serviceability limits which, if exceeded, will cause the structure to become unusable. Serviceability limit state design of structures includes factors such as durability, overall stability, fire resistance, deflection, deformation, displacements, cracking and excessive vibration. [3]

Serviceability failures are “physical failures that impair the serviceability of a system but not its structural integrity.” [3]

Excessive vibrations can cause serviceability failures in many structures. For example, severe winds and/or excess pedestrian traffic may cause an excess amount of vibration on a pedestrian walking bridge making it uncomfortable for people to travel across. Even though the vibrations are not effecting the structural integrity of the bridge, it is not meeting its serviceability requirements. A skyscraper swaying in the wind could also lead to a serviceability failure. The skyscraper may not be in danger of collapsing but the building is rendered unusable because it is causing nausea among its occupants.

Cracking, deformations, and leakages can also cause serviceability failures. A cracked concrete floor that is supposed to be smooth and polished for aesthetic quality is an example of a serviceability failure as it is not meeting the aesthetic requirements of its design. Improper construction of a parking garage and/or minor deformations in its structural members may cause water to pool up on some levels of the parking garage. This becomes a serviceability failure as it is inconvenient for the occupants to access their vehicles. A more extreme example of this type of serviceability failure would be water pooling up on a roof that does not drain properly, creating the possibility for water leakage into the building. This water could drip down onto the gypsum ceiling tiles below causing mold to grow and building occupants to become sick.

Serviceability failures can also occur in mechanical systems. For example, an HVAC system that is not adequately supplying air to one or more rooms or regions of a building, thus causing discomfort among its occupants, is a system experiencing a serviceability failure.

Other Sources:  [3] “Failure Mechanisms in Building Construction.” David H. Nicastro. The American Society of Civil Engineers. Print.

Bridge Failure  Fracture
[1, 2]

Fatigue failure occurs when a material fails at loads lower than the determined yield strength and is usually caused by stress from cyclical loading over a period of time. The first sign of fatigue is a crack in an area of concentrated stress, followed by crack propagation, and, quickly thereafter, fracture failure [a]. The progression of cracking to failure is shown in Figure 2. Cyclical loading, like opening doors in a building or traffic on a bridge, is the primary cause of fatigue.

While fatigue occurs in buildings and bridges, bridge fatigue tends to be more catastrophic than building fatigue. The repetitive flow of traffic interrupted by heavy trucks are the primary causes of fatigue in bridges. Because fatigue failure occurs relatively quickly, it is crucial to inspect areas of concentrated stress in bridges to avoid fatigue. In general for buildings, fatigue occurs in small parts and will not cause failure of an entire structure; only the moving parts would need to be replaced. Both concrete and steel, the main building materials for large structures, are susceptible to fatigue. In some areas around the world, “fluctuating” wind loading is constant enough to cause fatigue. [b] Fatigue caused by wind can be very damaging to a lateral bracing system, especially one without redundancy, and cause building failure. Other causes of structural fatigue include earthquake loading and machine vibration. [c]


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