Structural engineering

Structural engineering

Structural engineering is a field of engineering dealing with the analysis and design of structures that support or resist loads. Structural engineering is usually considered a speciality within civil engineering, but it can also be studied in its own right. [cite web|url=|title=History of Structural Engineering|publisher=University of San Diego|accessdate=2007-12-02]

Structural engineering theory is based upon physical laws and empirical knowledge of the structural performance of different geometries and materials. Structural engineering design utilises a relatively small number of basic structural elements to build up structural systems than can be very complex. Structural engineers are responsible for making creative and efficient use of funds, structural elements and materials to achieve these goals.cite web|url= |title=What is a structural engineer| publisher=Institution of Structural Engineers|accessdate=2007-12-02]

The structural engineer





Structural engineers are licensed or accredited by different learned societies and regulatory bodies around the world (for example, the Institution of Structural Engineers in the UK)cite web|url=|publisher=Institution of Structural Engineers|title=Routes to membership|accessdate=2007-12-25] . Depending on the degree course they have studied and/or the jurisdiction they are seeking licensure in, they may be accredited (or licensed) as just structural engineers, or as civil engineers, or as both civil and structural engineers.

History of structural engineering


Throughout ancient and medieval history most architectural design and construction was carried out by artisans, such as stone masons and carpenters, rising to the role of master builder. No theory of structures existed and understanding of how structures stood up was extremely limited, and based almost entirely on empirical evidence of 'what had worked before'. Knowledge was retained by guilds and seldom supplanted by advances. Structures were repetitive, and increases in scale were incremental.cite web|url=|title=Lecture notes in Structural Engineering|author=Victor E. Saouma|publisher=University of Colorado|accessdate=2007-11-02]


ignificant structural failures and collapses

Structural engineering has advanced significantly through the study of structural failures. The history of structural engineering contains many collapses and failures. Amongst the most significantweasel-inline failures and collapses are:


First Tay Rail Bridge

The Dee bridge disaster was followed by a number of cast iron bridge collapses, including the collapse of the first Tay Rail Bridge on 28 December 1879. Like the Dee bridge, the Tay collapsed when a train passed over it causing 75 people to lose their lives. The bridge failed because of poorly made cast iron, and the failure of the designer Thomas Bouch to consider wind loading on the bridge. The collapse resulted in cast iron largely being replaced by steel construction, and a complete redesign in 1890 of the Forth Railway Bridge. As a result, the Forth Bridge was the first entirely steel bridge in the world.cite book|title=In the Wake of Tacoma: Suspension Bridges and the Quest for Aerodynamic Stabilitya|author=Scott, Richard|date=2001|publisher=ASCE Publications|isbn=0784405425|pages=p.139]

First Tacoma Narrows Bridge The 1940 collapse of Galloping Gertie, as the original Tacoma Narrows Bridge is known, is sometimes characterized in physics textbooks as a classical example of resonance; although, this description is misleading. The catastrophic vibrations that destroyed the bridge were not due to simple mechanical resonance, but to a more complicated oscillation between the bridge and winds passing through it, known as aeroelastic flutter. Robert H. Scanlan, father of the field of bridge aerodynamics, wrote an article about this misunderstanding [K. Billah and R. Scanlan (1991), "Resonance, Tacoma Narrows Bridge Failure, and Undergraduate Physics Textbooks", American Journal of Physics, 59(2), 118--124 [ (PDF)] ] . This collapse, and the research that followed, led to an increased understanding of wind/structure interactions. Several bridges were altered following the collapse to prevent a similar event occurring again. The only fatality was 'Tubby' the dog.cite book|title=In the Wake of Tacoma: Suspension Bridges and the Quest for Aerodynamic Stabilitya|author=Scott, Richard|date=2001|publisher=ASCE Publications|isbn=0784405425]


Ronan PointOn 16 May, 1968 the 22 storey residential tower Ronan Point in the London borough of Newham collapsed when a relatively small gas explosion on the 18th floor caused a structural wall panel to be blown away from the building. The tower was constructed of precast concrete, and the failure of the single panel caused one entire corner of the building to collapse. The panel was able to be blown out because there was insufficient reinforcement steel passing between the panels. This also meant that the loads carried by the panel could not be redistributed to other adjacent panels, because there was no route for the forces to follow. As a result of the collapse, building regulations were overhauled to prevent "disproportionate collapse",clarifyme|date=July 2008 and the understanding of precast concrete detailing was greatly advanced. Many similar buildings were altered or demolished as a result of the collapse.cite book|title=Construction Failure|author=Feld, Jacob; Carper, Kenneth L.|date=1997|publisher=John Wiley & Sons|isbn=0471574775|pages=p.8]


Oklahoma City bombingOn 19 April, 1995, the nine storey concrete framed Alfred P. Murrah Federal Building in Oklahoma was struck by a huge car bomb causing partial collapse, resulting in the deaths of 168 people. The bomb, though large, caused a significantly disproportionate collapse of the structure. The bomb blew all the glass off the front of the building and completely shattered a ground floor reinforced concrete column (see brisance). At second storey level a wider column spacing existed, and loads from upper storey columns were transferred into fewer columns below by girders at second floor level. The removal of one of the lower storey columns caused neighbouring columns to fail due to the extra load, eventually leading to the complete collapse of the central portion of the building. The bombing was one of the first to highlight the extreme forces that blast loading from terrorism can exert on buildings, and led to increased consideration of terrorism in structural design of buildings. [cite book|title=Abnormal Loading on Structures: Experimental and Numerical Modelling|author=Virdi, K.S.|date=2000|publisher=Taylor & Francis|isbn=0419259600|pages=p.108]

9/11In the September 11 attacks, two commercial airliners were deliberately crashed into the Twin Towers of the World Trade Center in New York City. The impact and resulting fires caused both towers to collapse within two hours. After the impacts had severed exterior columns and damaged core columns, the loads on these columns were redistributed. The hat trusses at the top of each building played a significant role in this redistribution of the loads in the structure. cite web | title = NIST's Responsibilities Under the National Construction Safety Team Act | url = | accessdate - 2008-04-23 ] The impacts dislodged some of the fireproofing from the steel, increasing its exposure to the heat of the fires. Temperatures became high enough to weaken the core columns to the point of creep and plastic deformation under the weight of higher floors. Perimeter columns and floors were also weakened by the heat of the fires, causing the floors to sag and exerting an inward force on exterior walls of the building.cite paper |last=Bažant |first=Zdeněk P. |authorlink=Zdeněk Bažant |coauthor=Jia-Liang Le, Frank R. Greening and David B. Benson |title=Collapse of World Trade Center Towers: What Did and Did Not Cause It? |version=2007-06-22 |publisher=Department of Civil and Environmental Engineering, Northwestern University, Evanston, Illinois 60208, USA |date=2007-05-27 |url= |id=Structural Engineering Report No. 07-05/C605c (page 12)|accessdate=2007-09-17 |format=PDF] [cite journal| last=Bažant| first=Zdeněk P.| coauthors=Yong Zhou| title=Why Did the World Trade Center Collapse?—Simple Analysis|date=2002-01-01| month=January| journal=Journal of Engineering Mechanics| volume=128| issue=1| pages=pp. 2–6| doi=0.1061/(ASCE)0733-9399(2002)128:1(2)| url=| accessdate=2007-08-23| doi_brokendate=2008-06-21 |format=PDF]


Building structures





Structural engineering specialties for buildings include:
*Earthquake engineering
*Façade engineering
*Fire engineering
*Roof engineering
*Tower engineering
*Wind engineering

Earthquake engineering structures



The main objectives of earthquake engineering are:

* Understand interaction of structures with the shaky ground.

* Foresee the consequences of possible earthquakes.


Earthquake engineering or earthquake-proof structure does not, necessarily, means "extremely strong" and "expensive" one like El Castillo pyramid at Chichen Itza shown above.

Now, the most "powerful" and "budgetary" tool of the earthquake engineering is base isolation which pertains to the passive structural vibration control technologies.

Civil engineering structures


columns |width=200px
col1 =
*Offshore structures
col2=*Power stations
*Retaining structures and walls



Mechanical structures



These works can require mechanical structural engineering:

*Airframes and fuselages
*Boilers and pressure vessels
*Coachworks and carriages
*Marine vessels and hulls

tructural elements









A beam may be:

*cantilevered (supported at one end only with a fixed connection)
*simply supported (supported vertically at each end but able to rotate at the supports)
*continuous (supported by three or more supports)


truts and ties

"Little Belt": a truss bridge in Denmark]












tructural engineering theory




*tension (axial force)
*compression (axial force)
*bending, or flexure (a bending moment is a force multiplied by a distance, or lever arm, hence producing a turning effect or torque)






See also:






The inverse of stiffness is the flexibility.

afety factors





Load cases



: "1.4 x Dead Load + 1.6 x Live Load": "1.2 x Dead Load + 1.2 x Live Load + 1.2 x Wind Load"


: "1.0 x Dead Load + 1.0 x Live Load"

Different load cases would be used for different loading conditions. For example, in the case of design for fire a load case of "1.0 x Dead Load + 0.8 x Live Load" may be used, as it is reasonable to assume everyone has left the building if there is a fire.



Newton's laws of motion


Newton's first law states that "every body perseveres in its state of being at rest or of moving uniformly straight forward, except insofar as it is compelled to change its state by force impressed."

Newton's second law states that "the rate of change of momentum of a body is proportional to the resultant force acting on the body and is in the same direction." Mathematically, F=ma (force = mass x acceleration).

Newton's third law states that "all forces occur in pairs, and these two forces are equal in magnitude and opposite in direction."


* sum vec F = 0 : the vectorial sum of the forces acting on the body equals zero. This translates to ::&Sigma; "H" = 0: the sum of the horizontal components of the forces equals zero;::&Sigma; "V" = 0: the sum of the vertical components of forces equals zero;

tatical determinacy



A statically indeterminate structure has more unknowns than equilibrium considerations can supply equations for (see simultaneous equations). Such a system can be solved using consideration of equations of "compatibility" between geometry and deflections in addition to equilibrium equations, or by using virtual work.


r + b = 2j

It should be noted that even if this relationship does hold, a structure can be arranged in such a way as to be statically indeterminate. [cite book|title=Structural Modeling and Analysis|author=Dym, Clive L.|publisher=Cambridge University Press|date=1997|isbn=0521495369|pages=p.98]



For systems that obey Hooke's Law, the extension produced is directly proportional to the load:: vec{mathbf{F=-kvec{mathbf{x where: "x" is the distance that the spring has been stretched or compressed away from the equilibrium position, which is the position where the spring would naturally come to rest [usually in meters] ,: "F" is the restoring force exerted by the material [usually in newtons] , and: "k" is the force constant (or spring constant). This is the stiffness of the spring. The constant has units of force per unit length (usually in newtons per metre)


Some design is based on the assumption that materials will behave plastically.cite book|title=Structural Analysis: A Historical Approach|author=Heyman, Jacques|publisher=Cambridge University Press|date=1998|isbn=0521622492] A plastic material is one which does not obey Hooke's Law, and therefore deformation is not proportional to the applied load. Plastic materials are ductile materials. Plasticity theory can be used for some reinforced concrete structures assuming they are underreinforced, meaning that the steel reinforcement fails before the concrete does.




If the correct collapse load is found, the two methods will give the same result for the collapse load. [cite book|title=Design of Concrete Structures|author=Nilson, Arthur H.; Darwin, David; Dolan, Charles W.|publisher=McGraw-Hill Professional|date=2004|isbn=0072483059|pages=p.486]

Plasticity theory depends upon a correct understanding of when yield will occur. A number of different models for stress distibution and approximations to the yield surface of plastic materials exist:cite book|title=The Science of Structural Engineering|author=Heyman, Jacques|url=|date=1999|publisher=Imperial College Press|isbn=1860941893]

*Mohr's circle
*Von Mises yield criterion
*Henri Tresca

The Euler-Bernoulli beam equation


(1) continuum mechanics is valid for a bending beam
(4) the beam is composed of an isotropic material

A simplified version of Euler-Bernoulli beam equation is:




Successive derivatives of u have important meaning:

:* extstyle{u}, is the deflection.

:* extstyle{frac{partial u}{partial x, is the slope of the beam.

:* extstyle{EIfrac{partial^2 u}{partial x^2, is the bending moment in the beam.

:* extstyle{-frac{partial}{partial x}left(EIfrac{partial^2 u}{partial x^2} ight)}, is the shear force in the beam.







:F=frac{pi^2 EI}{(Kl)^2}

where:F = maximum or critical force (vertical load on column),:E = modulus of elasticity,:I = area moment of inertia, or second moment of area:l = unsupported length of column,:K = column effective length factor, whose value depends on the conditions of end support of the column, as follows.::For both ends pinned (hinged, free to rotate), K = 1.0.::For both ends fixed, K = 0.50.::For one end fixed and the other end pinned, K = 0.70.::For one end fixed and the other end free to move laterally, K = 2.0.



where:sigma = maximum or critical stress:r = the least radius of gyration of the cross section



1. Ultimate strength
2. Yield strength-corresponds to yield point.
3. Rupture
4. Strain hardening region
5. Necking region.]


Common structural materials are:


Wrought iron



Cast iron








The elastic modulus of steel is approximately 205 GPa

Steel is very prone to corrosion (rust).

tainless steel



It is highly resistant to corrosion and staining.










1. Ultimate strength
2. Yield strength
3. Proportional Limit Stress
4. Rupture
5. Offset strain (typically 0.002).]




In aircraft it is gradually being replaced by carbon composite materials.












Other structural materials

*Mud bricks
*Roofing materials

ee also

*Architectural engineering
*Building officials
*Civil engineering
*Earthquake engineering
*Forensic engineering
*List of structural engineers
*Mechanical engineering
*Prestressed structure
*Structural engineer
*Structural failure


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* Feld, Jacob; Carper, Kenneth L. (1997). "Construction Failure". John Wiley & Sons. ISBN 0471574775.
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* Hewson, Nigel R. (2003). "Prestressed Concrete Bridges: Design and Construction". Thomas Telford. ISBN 0727727745.
* Heyman, Jacques (1998). "Structural Analysis: A Historical Approach". Cambridge University Press. ISBN 0521622492.
* Heyman, Jacques (1999). "The Science of Structural Engineering". Imperial College Press. ISBN 1860941893.
* Hognestad, E. "A Study of Combined Bending and Axial Load in Reinforced Concrete Members". University of Illinois, Engineering Experiment Station, Bulletin Series N. 399.
* Hosford, William F. (2005). "Mechanical Behavior of Materials". Cambridge University Press. ISBN 0521846706.
* Hoogenboom, P.C.J. . "Historical Overview of Concrete Modelling".
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* Lewis, Peter R. (2007). "Disaster on the Dee." Tempus.
* MacNeal, Richard H. (1994). "Finite Elements: Their Design and Performance". Marcel Dekker. ISBN 0824791622.
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* Mörsch, E. (Stuttgart, 1908). "Der Eisenbetonbau, seine Theorie und Anwendun, (Reinforced Concrete Construction, its Theory and Application)". Konrad Wittwer, 3th edition.
* Nedwell,P.J.; Swamy,R.N.(ed) (1994). "Ferrocement:Proceedings of the Fifth International Symposium". Taylor & Francis. ISBN 0419197001.
* Newton, Isaac; Leseur, Thomas; Jacquier, François (1822). [|"Philosophiæ Naturalis Principia Mathematica"] . Oxford University.
* Nilson, Arthur H.; Darwin, David; Dolan, Charles W. (2004). "Design of Concrete Structures". McGraw-Hill Professional. ISBN 0072483059.
* Petroski, Henry (1994). "Design Paradigms: Case Histories of Error and Judgment in Engineering". Cambridge University Press. ISBN 0521466490.
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* Schlaich, J., K. Schäfer, M. Jennewein (1987). "Toward a Consistent Design of Structural Concrete". "PCI Journal", Special Report, Vol. 32, No. 3.
* Scott, Richard (2001). "In the Wake of Tacoma: Suspension Bridges and the Quest for Aerodynamic Stabilitya". ASCE Publications. ISBN 0784405425.
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* Whitbeck, Caroline (1998). "Ethics in Engineering Practice and Research". Cambridge University Press. ISBN 0521479444.


See above for references to publications and academic papers.

External links

* [ IABSE (International Association for Bridge and Structural Engineering)]
* [ Institution of Structural Engineers (IStructE)]
* [ Structural Engineering Association - International]
* [ National Council of Structural Engineers Associations]
* [ Structural Engineering Institute] , an institute of the American Society of Civil Engineers

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