Paper Presentation on " Causes of Structural Failure "

Nadar Saraswathi College of Engineering and

Technology,

Vadapudupatti, Theni - 625 531(Approved by AICTE, New Delhi and Affiliated to Anna University, Chennai)

Report for

Paper Presentation on “Causes of Structural

Failure”By

J Marees Kumar B.E.,MBA.,

Document No.: NSCET/Civil/2011-15/02

RemarksApproved byChecked byPrepared byDate IssueRev.

PrincipalMrs.Suikila Devi (HOD.- Civil Engg.)

J Marees Kumar

(Sr. Lecturer-Civil Engg.)04.02.20141

Causes of Structural FailureDate Issue: 04.02.2014Doc.No. : NSCET/Civil/2011-15/02

Review &Comments

Rejected Comments As Marked-Up / Attached No Comment / Approved

Name & Signature:Date: 04.02.2014

Content

1. Objective & Abstract: 32. Referenes: 3

3. Terminology: 34. Causes for Structural Failure (Technical Study): 3

5. Conclution 8

Approved By / Designation Page2 of 12


1. Objective & Abstract:A structural engineer’s dream is to design structures which arefit for their intended uses. No engineer would want to see astructure collapse or fail, unless that engineer is an engineerresearching in causes of failure. Some common causes of structuralfailure are discussed in this paper. A structural failure may haveadverse consequences on the partiesinvolved in the construction ofthe structure. Learning from Failures is the powerful Educationaltool for all civil and structural engineers.

Engineers do make use of this phenomenon and it is quite common tosee those adopting stiffeners to resist certain amounts of momentat a stanchion base. If engineers adopt structural engineeringknowledge, why is it that there is still failure of structures?.

The aim of the paper is to connect and to synthesize informationon damages or Failure or collapses of structure from differentcountries and Some of the causes of structural failure arediscussed in the suceeding topics

2. Referenes: IS 6403 : Code of practice for determination of bearing

capacity of shallow foundations

IS 8009 : Code of practice for calculation of settlement of

foundations subject to symmetrical static vertical

loads.

Harry, H. West, 1993, Fundamentals of Structural Analysis

Failure Of Structures-By Ir. Tee Horng Hean, B.Eng. (Hons), MSc

(Eng.), MBA, M.I.E.M.

3. Causes for Structural Failure (Technical Study):Structural failure occurs when a structure are a part of structurelosses the ability to support a load. Once the structural loss its



load carrying ability, it deforms completely. There are manyreasons for structural failures. They are

Underestimating Loads / Extra-ordinary loads Bad Design Inconsistent Design, Detailing and Construction Improper Connections Not Considering Elements In Contact With Structure Providing Undersized Members Lack Of Maintenance Overlooking The Third Dimension Constructing An Unstable (Mechanism) Structure Foundation Failure

Structural failure is concerning reduction in the load bearingcapacity of a structural component. Structural Failure iscommenced when the materials is stressed to its upper strengthlimit, thus causing rupture or extreme deformations. The ultimatefailure strength of the constructions element should be carefullyconsidered in the design of structures to prevent failures.

There are six basic mechanisms of failure: failure due toexcessive plastic deformation as the result of static overload orimpact, instability, creep, stress corrosion, fatigue and brittlefracture.

3.1. Underestimating Loads / Extra-ordinary loads Extreme conditions can also result in structural failure. Often these failures are not the result of poor design, but theresult of unexpected events that create extraordinary loadson structures.Sometimes, designers may underestimate the loadthatwould be imposed upon their structure when thestructureis in operation.Various structural elements arelikely to be overstressed when designers underestimate theload that would be imposed on their designed structure.Consequently, their structure is susceptible to collapse.



3.2. Bad Design:Approximately 40 % to 60 % of all structural failures are dueto baddesign. Bad designs can be caused by design errors suchas failure toaccount for load, specifying incorrectmaterials, or not consideringimportant factors and stresses.



3.3. Inconsistent Design, Detailing and ConstructionA structural engineer deals with numbers in hisstructuraldesign, which may be Greek to a layman, adraughtsperson oreven the contractor. In order tocommunicate his design to thecontractor, structuraldrawings are produced. At times, thestructural engineermay not be the one producing thestructural drawingsbut his draughtsperson would be the onedrafting it.Somehow or rather, miscommunication may occur anddesigns donot tally with the drawings. There may betimes when youngengineers may draft the drawings butdrafted them incorrectly.It is quite common to notethat engineers analyse a reinforcedconcrete structureas a pin-joint or simply supported but inhis detail,a fixed support is being provided. The consequenceofproceeding with construction would be similar as thatof thehoarding where a change of structural system mayoccur.Faulty construction is the second most common cause ofstructuralfailure. Construction errors can result from theuse of poor qualitymaterials, poor installation from eithersloppiness or lack of expertise,or a combination of these.

3.4. Improper Connections Surprisingly, research has shown that 30% of structuralfailures are caused by defective detailed design of the



joints between structural members For instance, a simplesystem of hoarding with structural elements being connectedwith undersized bolts may look perfectly sturdy However, dueto the use of undersized bolts connecting the horizontal andvertical structural members, the bolts were sheared off,causing the horizontal elements to be disconnected andresulting in the cantilever effect ). Bearing in mind thatin a ‘cantilever’ system, the stress intensity experienced bythe structure can be as large as four times of that of the‘continuous’ system.This is precisely whathappened to this hoardingand since thebolts weresheared off, the dominoeffect of excessivebendingof the steelhoarding sheet, the structural membersbeingsubjected toexcessive bending and thefooting being pulledoffthe ground occurred.In short, failure ofconnections canlead to achange in the structuralsystem, and in turn,haveadverse effects

3.5. Not Considering Elements In Contact With StructureWhen columns are supported by relatively smallfootings andthe soil surrounding the footings is ofcompressible soil, astructural engineer should analyses the columns as pin-jointed. Similarly, if the soil surrounding the footings isstiff andincompressible, then the structural engineer shouldanalyses the columns as fixed.

3.6. Providing Undersized Members



Though it seldom happens, there are times whenundersizedmembers are used. These undersized memberswould mostdefinitely experience excessive stress. Whencertainstructural members cannotwithstand the forcesthat areimposed upon them, the structurewould beimminent of collapse

3.7. Lack Of MaintenanceMany people have the misconception that structuresdo not needany maintenance. This is totally incorrect.Whatever thestructures are made of, whether steel, timberor reinforcedconcrete, they need constant maintenance.Steel structures,for instance, are susceptible to corrosionwhile timberstructures can be destroyed by a colony oftermites. Withoutmaintaining a structure, slowly butsurely, defects wouldoccur. If these defects are leftunattended, it would lead tofurther serious defects andin the end, a structural collapsemay be possible due tothe weakening of the structuralmembers.

3.8. Overlooking The Third Dimension



All structures,except for space frames, can be analysed anddesigned bysimplifying them into two-dimensional structures.Theremay be the possibility that engineers can overlook oneofthe three dimensions. When this occurs, the structureisonly structurally sound in two dimensions but can failinthe third dimension.

3.9. Constructing An Unstable (Mechanism) StructureThere are times when a structure is erected but isunstable.This is especially frequent in roof trusses. Manya time, thecentre line of the structural members do notmeet and thus,forming a structural system which is not a truss



3.10. Foundation Failure Failure of a structure’s base, orfoundation, is less common than baddesignand faulty construction. However, it canalso lead to significantstructural problems.Foundation failure can be caused by poorsoilconditions, poor installation, afoundation that is not large enough fortheload of the structure, or earthquakes.A well-known example of foundation failure is the LeaningTowerof Pisa in Italy.The tower was built in 1178 onsandy,unstable soil with an inadequate foundation. Th e soilshifted and thetower began to lean almost right aft erconstruction began. Over thecenturies, the tower leaned more andmore. Modern constructionmethods have fi nally slowed down themovement of the tower andreturned it to the angle at which itwas leaning in 1870.Foundation failure is more common in smaller buildings. Cracksin the walls of a house or misaligned doors are oft en theresult of ahouse’s foundation shift ing due to poor soilconditions. However, any structure can shift as a result of apoor foundation.

4. ConclusionThe paper discussed only some of the common factorsas to whystructures fail. There can be lots of other factorsincludingminor mistakes such as dimensioning astructural member longerthan it is supposed to be, usingthe wrong units(imperial/metric), not following theconstruction drawings,mixing of high tensile and mildsteel reinforcements forreinforced concrete structures,reducing the lever arm of areinforced concrete structuralelement when workers step on the



steel reinforcements,providing inadequate anchorage length forreinforcementbars, etc. which can lead to structural failure.

The othercause of possible failure in the structure is misuse oftheerected structure. One of the best ways for young engineerstoavoid making the mistakes discussed in this paper is toascertainthe facts from reliable sources.The fundamentals of engineeringshould be applied inthe design of all engineering structures.Overlooking thedesign of even a minute partof a structure suchasconnections can be disastrous.


Paper Presentation on " Causes of Structural Failure "

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