Structural Engineering Overview CEE 379 Structural Engineering Overview Notes
What do structural engineers do?
Structural engineers have the responsibility of designing structures and structural components so that they are sufficiently strong, stiff, stable, and safe to meet client needs. For a structure to be sufficiently strong, it must be able to handle normal loads without sustaining noticeable damage. To be sufficently stiff, a structure should not deform under loading in ways that cause discomfort or distress to occupants/users or contents/equipment. Stability is related to strength, but it refers to particular kinds of failure that are not initiated by localized overstressing of material, but rather by phenomena driven by nonlinear feedback between load and deformation, such as buckling or overturning. For a structure to be safe, it should be able to handle extreme loadings in such a way that occupants have time to exit prior to collapse. Structural engineers typically work as part of a team that might include architects, contractors, fabrica- tors, building officials, and numerous other engineering disciplines. Although a great deal of the educational focus for structural engineering revolves around analysis and design code calculations, in practice one must bring to the table an ability to work creatively in a team context to solve problems. Structural engineering requires a great deal of technical depth, but structural engineers are professionals, not technicians. Note that it is possible (and not uncommon) for the structural engineer to perform his or her job well, but for the structure itself to not succeed. A building can be ugly, drafty, or toxic, it can block views, it can go out of style, and so on. Although these kinds of issues are not so much the direct concern of the structural engineer, it is generally wise to be aware of the full range of ramifications of one’s work. CEE 379 Structural Engineering Overview Notes What are the principal technical aspects of structural engineering? WhatCEEdo37st9rInucttrourducaltionengineers do? 2 A structural engineer requires both a means to characterize how a given system or component will behave Structural engineers havine theservreicspe on(ansibilalysis)ity ofanddesignianngabilstruityctutoresselandect anstructud confiralgurcompe systeonentsmssoandthatcomptheyonents to behave well (design). are suffiwcienorktlyitsstrelfongmi,ghstiFtorffb,ebstablelothargely,thesanlodecsafealtasandks,to thmesmalleetteccscalelihnenicalt ,neoredingrins.teeFdrornationienatsstrofalucturthaninkde tolingarge-beabsuscoutffialcei.estrunStlyomectustrresfiongrmsare, aretherelfativollowinely g: it mustlarbegeab(100+le to henandgineele nrormals), andloadsmanywiarethousmt alsulstai(
Static A static analysis ignores the effects of inertia, and implicitly assumes that all change in load- ing/properties happens relatively slowly such that no vibrations are induced. (There is a related class of analysis called quasi-static, which also ignores inertial effects, but requires inclusion of a real time scale to account for time effects for things like material behavior (e.g., creep or relaxation). When inertial effects are included, one is doing a dynamic analysis.
1In contemporary practice, there is a trend toward designing structures to meet various levels of performance, as opposed to the more traditional fail/no fail categories. CEE 379 Structural Engineering Overview Notes
What do structural engineers do?
Structural engineers have the responsibility of designing structures and structural components so that they are sufficiently strong, stiff, stable, and safe to meet client needs. For a structure to be sufficiently strong, • Structuralit must engineersbe able t ohavehand thele n responsibilityormal loads withou of designingt sustainin g noticeable damage. To be sufficently stiff, a structuresstructu andre shoul structurald not deform componentsunder load soin thatg in theyways arethat cause discomfort or distress to occupants/users sufficientlyor conten strongts/equ, stiffipm, enstablet. Stabili, andt ysafeis re tolate meetd to sclienttrength, needs(e.g.,but it refers to particular kinds of failure that are sustainable,not initi economical,ated by localize etc.).d overstressing of material, but rather by phenomena driven by nonlinear feedback between load and deformation, such as buckling or overturning. For a structure to be safe, it should be able Structuralto han engineersdle extreme typicallyloadings inworksuch asa w partay th ofat ao cteamcupan tsthathav mighte time to exit prior to collapse. • Structural engineers typically work as part of a team that might include architects, contractors, fabrica- includetors, architects,building o fficontractors,cials, and numerous fabricators,other engibuildingneering officials,disciplines and. Althou gh a great deal of the educational numerousfocus fotheror structura engineeringl engineerin disciplines.g revolves around analysis and design code calculations, in practice one must Notebr thating toit this epossibletable an (andabilit ynotto wuncommon)ork creatively forin a theteam structuralcontext to solve problems. Structural engineering • requires a great deal of technical depth, but structural engineers are professionals, not technicians. engineerNote to performthat it is hisposs orible her(an djobnot well,uncomm but onfor) ftheor the structurestructural engineer to perform his or her job well, itself butot notfor thesucceed.structure itself to not succeed. A building can be ugly, drafty, or toxic, it can block views, it can go out of style, and so on. Although these kinds of issues are not so much the direct concern of the structural engineer, it is generally wise to be aware of the full range of ramifications of one’s work.
What are the principal technical aspects of structural engineering?
A structural engineer requires both a means to characterize how a given system or component will behave in service (analysis) and an ability to select and configure systems and components to behave well (design). For both these tasks, the technical ingredients of thinking about structures are the following: Loads The imposed forces and displacements to which the structure will be subjected. Loads can be applied externally (e.g., a desk on a floor), or they can be an inherent part of the structure itself (self-weight). They can be static (e.g., gravity), quasi-static (e.g., snow, thermal effects), or dynamic (e.g., wind, earthquakes, and traffic). For the most part, loads drive structural design, but they also are typically known with the least certainty. Geometry The spatial location of the material that composes the structure, and the geometry of the environment in which the structure must exist. Supports The nature of the interfaces between structural components, including the interaction of the structure and its foundation system. Topology The form and connectivities that define the structural system. Materials The stuff the structure is composed of, how it behaves mechanically, thermally, acoustically, and chemically. The engineer typically has varying degrees of control over each of these, and the basic idea is to work with the parameters one has control over to address the given issues that define the problem. In this regard, structural engineering is just like any field of engineering practice.
Where do structural engineers work?
Structural engineers typically work in a design office setting, but there is usually the opportunity or necessity for field inspection and problem solving. Meeting with clients and other design and construction team members is also a big part of the job, and this often includes a certain degree of marketing and sales (the design bidding process often includes a set of formal presentations). Depending on the firm one works for, the
1 CEE 379 Structural Engineering Overview Notes
What do structural engineers do?
Structural engineers have the responsibility of designing structures and structural components so that they are sufficiently strong, stiff, stable, and safe to meet client needs. For a structure to be sufficiently strong, it must be able to handle normal loads without sustaining noticeable damage. To be sufficently stiff, a structure should not deform under loading in ways that cause discomfort or distress to occupants/users or contents/equipment. Stability is related to strength, but it refers to particular kinds of failure that are not initiated by localized overstressing of material, but rather by phenomena driven by nonlinear feedback between load and deformation, such as buckling or overturning. For a structure to be safe, it should be able to handle extreme loadings in such a way that occupants have time to exit prior to collapse. Structural engineers typically work as part of a team that might include architects, contractors, fabrica- tors, building officials, and numerous other engineering disciplines. Although a great deal of the educational focus for structural engineering revolves around analysis and design code calculations, in practice one must bring to the table an ability to work creatively in a team context to solve problems. Structural engineering requires a great deal of technical depth, but structural engineers are professionals, not technicians. Note that it is possible (and not uncommon) for the structural engineer to perform his or her job well, but for the structure itself to not succeed. A building can be ugly, drafty, or toxic, it can block views, it can go out of style, and so on. Although these kinds of issues are not so much the direct concern of the structural engineer, it is generally wise to be aware of the full range of ramifications of one’s work.
What are the principal technical aspects of structural engineering?
A structural engineer requires both a means to characterize how a given system or component will behave in serviceA(an structuralalysis) and an engineerability to sele ctrequiresand configur bothe syste msa meansand comp toonen characterizets to behave well (d esign). For b•oth these tasks, the technical ingredients of thinking about structures are the following: how a given system or component will behave in service Loads The imposed forces and displacements to which the structure will be subjected. Loads can be applied external(analysis)ly (e.g., a anddesk onana flabilityoor), or theyto selectcan be an andinher econfigurent part of the strusystemscture itse andlf (self-w eight). They can be static (e.g., gravity), quasi-static (e.g., snow, thermal effects), or dynamic (e.g., wind, earthcomponentsquakes, and traffi toc). Fbehaveor the mos twellpart, (design).loads drive structural design, but they also are typically known with the least certainty. Loads: applied externally (e.g., a desk on a floor), or an Geome-try The spatial location of the material that composes the structure, and the geometry of the environmeinherentnt in whic parth the softructur thee mstructureust exist. itself (self-weight). They can be Supports Thestaticnatu (e.g.,re of th gravity),e interfaces quasi-staticbetween structur al(e.g.,comp snow,onents, includthermaling the effects),interaction orof the structudynamicre and its foun (e.g.,dation wind,system. earthquakes, and traffic). For the most Topology Thepart,form loadsand conn driveectivities structuralthat define thedesign,structural butsyste theym. also are typically Materials knownThe stuff the withstructure theis leastcompos certainty.ed of, how it behaves mechanically, thermally, acoustically, and chemically. The engin- eerGeometrytypically has varyi: ngspatialdegrees locationof control ov eofr e actheh of materialthese, and t hethatbasic composesidea is to work with the parametethers one structure,has control oandver to theaddre geometryss the given i ssuesof thethat environmentdefine the problem . inIn whichthis regard , structural engineering is just like any field of engineering practice. the structure must exist. Where do structural engineers work?
Structural engineers typically work in a design office setting, but there is usually the opportunity or necessity for field inspection and problem solving. Meeting with clients and other design and construction team members is also a big part of the job, and this often includes a certain degree of marketing and sales (the design bidding process often includes a set of formal presentations). Depending on the firm one works for, the
1 - Supports: The nature of the interfaces between structural components, including the interaction of the structure and its foundation system. - Topology: The form and connectivities that define the structural system. - Materials: The stuff the structure is composed of, how it behaves mechanically, thermally, acoustically, and chemically. CEE 379 Structural Engineering Overview Notes
What do structural engineers do?
Structural engineers have the responsibility of designing structures and structural components so that they are sufficiently strong, stiff, stable, and safe to meet client needs. For a structure to be sufficiently strong, it must be able to handle normal loads without sustaining noticeable damage. To be sufficently stiff, a structure should not deform under loading in ways that cause discomfort or distress to occupants/users or contents/equipment. Stability is related to strength, but it refers to particular kinds of failure that are not initiated by localized overstressing of material, but rather by phenomena driven by nonlinear feedback between load and deformation, such as buckling or overturning. For a structure to be safe, it should be able to handle extreme loadings in such a way that occupants have time to exit prior to collapse. Structural engineers typically work as part of a team that might include architects, contractors, fabrica- tors, building officials, and numerous other engineering disciplines. Although a great deal of the educational focus for structural engineering revolves around analysis and design code calculations, in practice one must bring to the table an ability to work creatively in a team context to solve problems. Structural engineering requires a great deal of technical depth, but structural engineers are professionals, not technicians. Note that it is possible (and not uncommon) for the structural engineer to perform his or her job well, but for the structure itself to not succeed. A building can be ugly, drafty, or toxic, it can block views, it can go out of style, and so on. Although these kinds of issues are not so much the direct concern of the structural engineer, it is generally wise to be aware of the full range of ramifications of one’s work.
What are the principal technical aspects of structural engineering?
A structural engineer requires both a means to characterize how a given system or component will behave in service (analysis) and an ability to select and configure systems and components to behave well (design). For both these tasks, the technical ingredients of thinking about structures are the following: Loads The imposed forces and displacements to which the structure will be subjected. Loads can be applied externally (e.g., a desk on a floor), or they can be an inherent part of the structure itself (self-weight). They can be static (e.g., gravity), quasi-static (e.g., snow, thermal effects), or dynamic (e.g., wind, earthquakes, and traffic). For the most part, loads drive structural design, but they also are typically known with the least certainty. Geometry The spatial location of the material that composes the structure, and the geometry of the environment in which the structure must exist. Supports The nature of the interfaces between structural components, including the interaction of the structure and its foundation system. Topology The form and connectivities that define the structural system. Materials The stuff the structure is composed of, how it behaves mechanically, thermally, acoustically, and chemically. The engineer typically has varying degrees of control over each of these, and the basic idea is to work with the parameters one has control over to address the given issues that define the problem. In this regard, structural engineering is just like any field of engineering practice.
Where do structural engineers work?
Structural engineers typically work in a design office setting, but there is usually the opportunity or necessity for field inspection and problem solving. Meeting with clients and other design and construction team Structuralme engineersmbers is also typicallya big part ofworkthe job in, and a designthis often officeincludes setting,a certain butdegree of marketing and sales (the • design bidding process often includes a set of formal presentations). Depending on the firm one works for, the there is usually the opportunity or necessity for field inspection and problem solving. 1 • Meeting with clients and other design and construction team members is also a big part of the job, and this often includes a certain degree of marketing and sales (the design bidding process often includes a set of formal presentations). • Depending on the firm one works for, the work itself might be largely local and small scale, or international and large-scale. • Some firms are relatively large (100+ engineers), many are small (< 10 engineers), and it is not uncommon for structural engineers to work in a firm of one (i.e., to be their own firm). CEE 379 Introduction 2
work itself might be largely local and small scale, or international and large-scale. Some firms are relatively large (100+ engineers), and many are small (< 10 engineers), and it is not uncommon for structural engineers to work in a firm of one (i.e., to be their own firm). This latter scenario usually is only possible after a person has worked at a larger firm for long enough to develop sufficient experience and clientelle to strike out out on one’s own.
What is special about civil structures? Civil structuresCivil structur sharees sh aremanymany commoncommon featu featuresres with an ywithdesigned anyp hdesignedysical device , be it an automobile fender • or an airplane wing, but there are several characteristics of civil structures that are relatively specialized: physical device, be it an automobile fender or an airplane wing, but Civil structures tend to be relatively large in scale. There would not be much use for a nano-bridge or there are several• a nano- characteristicsbuilding, at least as fofar ascivildire ctstructuresuse by people thatgoes. are relatively specialized:The infrastructure of a civilization normally is designed to last indefinitely, and so there are large time • scales, too. Civil structures tend to be relatively large in scale. - The environment must be dealt with on its own terms—one does not construct a bridge with a sticker • - The infrastructuresaying things oflik ae, civilization“Store at room normallytemperature; isav oiddesignedvibration”. to last indefinitely,The andcre ationso thereof infrastru arect urelargehas ptimeolitical scales,and cultu too.ral implications. When an electronics manufacturer • develops a new product, there is no need for public hearings, environmental impact studies, and so on, - The environmentbut almos tmustall civi lbepro dealtjects ha vwithe to pass onth itsrou ghownvariou terms.s kinds of public approval processes. There is no prototyping and full-scale testing with civil structures. Planes, automobiles, toothbrushes, - The creation• and thofe linfrastructureike are designed to b ehasman ufpolitical,actured by social,the hundreds environmentalor thousands or m ore, but civil structures and culturalare implications.generally unique one-offs. You have to get it right the first time. The ramifications of failures can be very expensive or even catastrophic, causing extreme disruption in - There is no• p eprototypingople’s lives or los sandof lif efull-scaleitself. Imagi testingne what lif withe wou ldcivilbe l ike if our bridges, buildings, and water structures.supply systems crashed as often as our computer software. - The ramificationsWhere do esof failuresthis co urcanse befit veryint oexpensivethe over orall evencurr iculum? catastrophic,As sugges causingted above, extremestructural engi disruptionneering course inwork people'stypically islivesorgani orzed lossaround two principal threads: of life itself.analysis and design. This is an analysis course, and so the focus is on determining what kind of demands (e.g., internal stresses, displacements, etc.) a given combination of loads, supports, configuration, and materials places on the structural components and subsystems. Design courses typically focus on determining how to size members and components so they will have sufficient capacity to handle these imposed demands1 . For all but the simplest structures, it turns out that design decisions generally affect the demands, and so practical design tends to involve iteration: choose a configuration, analyze it, check demands and capacities, update the configuration as necessary, re-analyze, and so on. Analysis of structural systems can be further broken down into various categories, depending on the nature of the effects and phenomena that must be accommodated by a design. In this course, we will focus primarily on the simplest class of behavior: namely static, linear, elastic response. Figure 1 shows how this set of modeling options might look relative to more general choices if one had a suitable push-button selector. To understand what these terms imply, it is helpful to consider each one in turn:
Static A static analysis ignores the effects of inertia, and implicitly assumes that all change in load- ing/properties happens relatively slowly such that no vibrations are induced. (There is a related class of analysis called quasi-static, which also ignores inertial effects, but requires inclusion of a real time scale to account for time effects for things like material behavior (e.g., creep or relaxation). When inertial effects are included, one is doing a dynamic analysis.
1In contemporary practice, there is a trend toward designing structures to meet various levels of performance, as opposed to the more traditional fail/no fail categories. CEE 379 Introduction 4
Line Elements
Plate/Shell Elements
Continuum Elements
Figure 2: Representative examples of various types of elements used in structural modeling.