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Bearing Structure-FMEA
Guideline
Bearing Structure-FMEA:
Preventive Quality Control in Civil Engineering
Werner Seim, Tobias Vogt
Timber Engineering and Building Rehabilitation, 18.07.2011
2
Table of contents
1. Introduction
1.1 Preliminary note
1.2 Terms and definitions
2. Proceedings Bearing-FMEA
2.1 Classification of the construction in the risk categories
2.2 Bearing structure design and preliminary measurement
2.3 Classification of the building in robustness categories
2.4 Classification of the building in FMEA-categories
2.5 Description of the global load bearing
2.6 Error analysis
2.7 Risk evaluation
2.8 Optimization
2.9 Documentation of the events
2.10 Monitoring of the further planning and execution
2.11 Error categories and error causes
2.12 Error types and discovery measures
List of references
3
1 Introduction
1.1 Preliminary Note
In civil engineering the proceedings to prepare static calculations is determined by standards and
regulations. In addition, it is stipulated in which way the impacts on a building are to be considered
by giving the appropriate load assumptions. The necessary guarantees are regulated by the semi-
probable safety concept. But these only relate to the uncertainty on the part of impacts and
resistance of the construction elements. To control the static calculations concerning the correct
application of the standards and regulations as well as the correctness of the bearing concept and
the calculations, one counts on the inspection of a qualified inspection engineer or, for smaller
construction projects, on a not specified, intern quality mechanism. However, this inspection takes
place without a generally accepted system and, thus, is not sufficiently traceable. Besides, mistakes
are so only found at a later date; consequently, the repair is often time-consuming and expensive.
The Failure Mode and Effects Analysis (FMEA) is used to secure the quality of products. Possible
mistakes are to be found in an early stage to prevent these from happening beforehand respectively
to minimize their consequences by taking the appropriate measures. FMEA is already used for
several decades in the field of mechanical engineering, especially in the area of aeronautics, as well
as in the automobile industry and there, it proved its worth in many ways. In the mean time, there, it
forms an important foundation for all projects especially in the development phase. For the
automobile companies, for example, the execution of a FMEA is required for a mutual cooperation
with their suppliers. Also insurance companies call increasingly for a FMEA respectively they contract
clearly better conditions to businesses that execute such ones.
The article “The role of the inspection engineer in the system of a preventive hazard control” by
Dressel [Dre09] gives further reasons for the necessity of an optimized quality control. A good survey
concerning the state of the art respectively the FMEA can be found in the booklet FMEA – Failure
Mode and Effect Analysis.
For the first time, the available guideline states the regulations to perform a FMEA in civil
engineering. In the process, the level of difficulty and the robustness of a building are defined as
parameter for the FMEA.
1.2 Terms and definitions
FMEA-types Mechanical Engineering / Aerospace industry
Framework-FMEA: It examines interaction between the frameworks and the framework
elements and provides the transparency of the whole system.
Construction FMEA: It steps further into the framework and analyses the framework in
detail. The error causes of the framework-FMEA are considered as error types and their
causes are traced.
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Process-FMEA: It studies the errors that can develop during construction.
FMEA-types Civil Engineering
Bearing-FMEA: It is performed after planning and design (work phase 2 and 3) and is used to
prevent fundamental errors in an early stage.
Construction-FMEA: It follows the approval and the detailed planning and aims at securing
the correct the final static calculations and engineering drawings.
Fulfilment-FMEA: It should guarantee the correct performance and prevent errors in this
phase.
Utilisation-FMEA: Its goal is to observe the critical areas and the durability of buildings in the
utilisation phase.
Application Framework-FMEA
Structure analysis: All framework elements as well as their cutting points (connections,
correlations and dependencies) are recognised, analysed and documented. A description is
documented in an appropriate form.
Operational analysis: The respective functions of the framework elements are analysed and
assigned to the different points of the hierarchy.
Error analysis: An error is defined as “failure to perform an operation”. Hence, an error can
be defined for each operation. Additionally, its cause and consequences can be described in
this step. The analysis follows heuristic, i.e. intuitive and based on experience.
Risk evaluation: To estimate the actual risk, 3 criteria with numerical values between 1 and
10 each are reviewed in the most used form of risk evaluation. These are the importance (B)
of the error consequences, the occurrence probability (A) of the error cause as well as the
discovery probability (E) of the error respectively the error cause. The risk priority number
(RPZ) states the risk based on an error and is calculated by the multiplication of the
evaluation numbers:
RPZ = B*A*E.
The higher the RPZ the more important it is to perform an optimization for this error, i.e. the
higher the priority to examine this error. The possible results lie between 1 (no respectively
very low risk) and 1000 (very high risk).
Optimization: On this background it is possible to develop in teamwork appropriate
measures to detect respectively to prevent the errors for the identified risks. The defined
measures are considered at the evaluation of the criteria and lead to a reduction of the RPZ.
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2 Proceedings Bearing-FMEA
The complete development of a Bearing–FMEA is shown in illustration 2.1 as a flow chart. Each
process step is shortly explained in illustration 2.2. Additionally, there is a hint to the appropriate
chapters, illustrations and charts.
2.1 Classification of the construction in the risk categories
The building is classified in the appropriate risk category (cf. illustration 2.4) due to the charge zone
(cf. chart 2.1) and the consequence class (cf. illustration 2.3).
charge zone planning requirements
HZ I very low HZ II low HZ III average HZ IV above average HZ V very high
chart 2.1 : charge zones according to HOAI
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Proceeding Bearing-FMEA (complete development)
Planning / Design of the architect
1. Classification of the building in risk categories
↓
2. Developing of an static concept (bearing concept and the pre-sizing
↓
3. Classification of the building in robustness categories
Definition of the necessary extent of the FMEA and preparation of the session
↓
4. Determination of the FMEA-Class
↓
5. Presentation of the global load transfer
↓
6. Error analysis
↓
7. Risk evaluation
↓ Performance of the session for the
error analysis and optimisation
8. If necessary optimisation
↓
9. Documentation of the results
↓
10. Monitoring of the performance according to the assumption agreed on, otherwise adjustment of the FMEA and
if necessary performance of a new session
Control and adaptation during
planning and adaptations
Picture 2.1: Flow chart to demonstrate the total course of action of a bearing-FMEA
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Line Process Step Intention Participants Respective Information
1
Classification of the building in risk categories
Determination of the necessary definition/correct observation at performing
the FMEA
Structural engineers, possibly definition by evaluation authorities
Chapter 2.1
Picture 2.3, 2.4
Chart 2.1
2
Static design and planning
Determination of an appropriate bearing concept
and the necessary dimensions of the
construction elements
Structural engineers
3
Classification of the building in
robustness classes
Determination of the necessary number of
elements to be detected for the performance of the FMEA
Structural engineers, possibly definition by evaluation authorities
Chapter 2.3
--
Chart 2.3, 2.4
4
Classification of the building in FMEA-classes
Determination of the
necessary extension of the FMEA performed
Structural engineers, possibly definition by evaluation authorities
Chapter 2.4
Picture 2.5, 2.6
Chart 2.6, 2.6
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Presentation of the global load
transfer
Support for the determination of the error
consequences to continuative construction elements (error
propagation)
Structural engineers
Chapter 2.5
Picture 2.7, 2.8
--
6
Error analysis
Detection of possible mistakes as well as the
corresponding causes and consequences
Participants of the meeting according to
chapter 2.4 respectively 2.6
Chapter 2.6
--
Chart 2.6, 2.9, 2.10
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Risk evaluation
Determination if the existing
risk observes the defined boundaries
Participants of the meeting according to
chapter 2.4 respectively 2.6
Chapter 2.7
Picture 2.9, 2.10, 2.11
Chart 2.8
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Optimisation
Reduction of the risk when the defined boundaries are
not observed
Participants of the meeting according to
chapter 2.4 respectively 2.6
Chapter 2.8
--
Chart 2.9, 2.11
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Documentation of the incidents
Documentation of the
important information and using these in further phases
Recording participant of the meeting
according to chapter 2.4 respectively 2.6,
confirmation by participants
Chapter 2.9
Picture 2.12
--
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Monitoring of
the further planning and performing
Monitoring, if criteria determined are respected
and if necessary adjustment of the FMEA to new
conditions
Determing a
responsible person, e.g. inspection engineer
Chapter 2.10
--
--
Picture 2.2: Explanations and cross references with regards to the flow chart
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2.2 Bearing structure design and preliminary measurement
Corresponding to the requirements of the risk category (see chart 2.2) a bearing structure design is
developed and the preliminary measurements are performed.
Risk category Necessary complexity of the preliminary measurement
GK 1 / 2 Developing the static design and the preliminary measurements in the usual way
GK 3 Developing the static design and performing an accurate preliminary measurement, preliminary
dimensioning of the attachments and connections. Defining the critical elements by comparative calculation (measurement for a
deficiency of the construction elements).
Chart 2.2: Complexity of the preliminary measurement in dependence to the risk category
2.3 Classification of the building in robustness categories
The classification of the building in robustness categories results on the basis of chart 2.3. The
robustness number is defined by chart 2.4.
Robustness category Robustness number
1 < 10 2 -10 to +10 3 > 10
Chart 2.3: Proposal for the classification in robustness categories
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characteristics statement applies to
not at all
little average a lot absolutely
Redundancy Bearing
structure
Alternative load path exist
-4 -2 0 +2 +4
There is a static uncertain bearing
structure
-2 -1 0 +1 +2
Local deficiencies do not have huge
effects
-4 -2 0 +2 +4
Redundancy connections
The connections bear even if single
fastener fail
-4 -2 0 +2 +4
The connections can also adjust loads that
are caused by the start-ups of
alternative load paths
-4 -2 0 +2 +4
Construction material / behaviour
The construction elements have a
sufficient ductility to exclude a failure
without an advance notice
-8 -4 0 +4 +8
Security of the construction
elements
There are no construction
elements that are increasingly possible
to fail
-8 -4 0 +4 +8
Easiness to maintain
Construction elements and
connections relevant for maintenance are easy accessible and
monitorable
-6 -3 0 +3 +6
Robustness number RZ = ∑
Chart 2.4: proposal of an evaluation method to define the robustness of bearing structures
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2.4 Classification of the building in FMEA-categories
The classification of the building in FMEA-categories is dependent on the risk and the robustness
category (see picture 2.5). These define in what extend the FMEA has to be carried out (see chart 2.6
and 2.7). A schematic illustration of defining the category of a building is shown in picture 2.6:
Robustness category
Ris
k C
ateg
ory
RK 3 RK 2 RK 1
GK 1
1
2
3r
GK 2
2 2 3r
GK 3
3g 3g 4
Picture 2.5: Defining the FMEA-categories in dependence to risk and robustness categories
FMEA-category
accuracy / depth of consideration
number of elements covered
1 -- -- 2 low low
3g high low 3r low high 4 high high
Chart 2.5: Description of the FMEA-classes
accuracy / depth of consideration
low: In-house error analysis and optimisation meeting, other project participants can be included. Normal preparation of the meeting: establishing the static design and the preliminary measurements. Describing of the global load bearing under consideration of the essential bearing elements. Medium limit for risk priority number (RPZ)
high: Error analysis and optimisation meeting in extended group of people, preferably with the architect, the test engineer, the construction supervisor of the performing company and, if possible, the building owner. Extensive preparation of the meeting: establishing the static design and performing of an accurate preliminary measurement, pre-dimensioning of the connections and contacts. Already before the meeting, description of the critical elements by comparative calculations (measuring for failure of construction elements). Description of the global load bearing under consideration of all bearing elements. Low limit for risk priority number RPZ.
number of elements covered
low: restriction to critical construction elements high: taking all construction elements involved in the load bearing into consideration
Chart 2.6: definition of the terms “low” and “high”
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Consequence Classes according to VDI-RL 6200
(picture 2.3)
Charge Zones according to HOAI
(chart 2.1)
Risk Category (picture 2.4)
Robustness Category (picture 2.3 + 2.4)
FMEA-Categories (picture 2.5)
Picture 2.6: Schematic illustration to define the categories of a building
2.5 Description of the global load bearing
According to the requirements of the FMEA-category, either all or only the essential elements of the
bearing structure are described in a “description of the global load bearing”. In that, the load flow
within the bearing structure is visualized from element to element. On this basis the error
consequences to continuative elements and, thus, the significance of errors within the bearing
structure are illustrated. An example is given in the pictures 2.7 and 2.8.
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2.6 Error analysis
In the context of an error analysis and optimisation meeting, the structural bearing and the individual
construction elements and connections are checked for possible errors that can occur.
The meeting takes place either in-house or with an extended group of people (compare chart 2.6),
according to the requirements of the FMEA-category. In chart 2.7, both group of people mentioned
are defined in a more accurate way.
Possible error causes as well as error consequences are looked for and documented for the found
possible errors (error types). To support this process, support in form of error categories, examples
for error causes and an error catalogue are presented in the next chapters.
In-house group of people
- structural engineer, who prepared a static design and performed preliminary measurements
- responsible of the project (supervisor of the structural engineer) - construction engineer - other in-house participants
Additionally in an extended group of people
- test engineer - architect - supervisor of the performing company - other participants at the construction site (e.g. geotechnical expert) - possibly owner of the building
Chart 2.7: definition of the in-house and the extended group of people for an error analysis and
optimization meeting
2.7 Risk evaluation
The risk evaluation caused by possible errors is performed on consensus by the participants of the
error analysis and optimization meeting. The existing risk is described by the risk priority number
(RPZ) that consists of the following three evaluation criteria:
Importance of the error consequence according to chart 2.8
Occurrence probability of the error cause
According to picture 2.9a, a category for the construction element is defined with the help of
the existing experiences of the participants with a certain construction element and the
expected element quality in dependence to the producing place. Together with the
utilization factor calculated of the construction element, there is an evaluation number for
the occurrence probability according to picture 2.9b. This determined number is consistent
with a “tendency number”, an accurate definition is made by the participants of the meeting.
Occurrence probability of the error respectively the error cause
Determination of a bearing structural evaluation number for the discovery probability in
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dependence to the honorary zone and the determined FMEA-category (cf. picture 2.10). This
number is equal to a “tendency number”, an accurate definition is made by the participants
of the meeting.
The evaluation is made with numbers between 1 (“low risk” respectively “good”) and 5 (“high risk”
respectively “poor”). The RPZ is calculated by the multiplication of these evaluation numbers, thus
RPZ = B A E. Hence, it lies in the area between 1 and 125. A schematic illustration of the evaluation
system can be seen in picture 2.11.
description of the error consequences evaluation number
failure of the bearing structure or of a part system 5
huge damages at the bearing structure or at a part system, bearing capacity is not guaranteed anymore, no (economic) restoration possible
4
average damages at the bearing structure or at a part system, bearing capacity is limited, restoration to guarantee the bearing capacity is possible with
medium effort
3
small damages at the bearing structure or at a part system, bearing capacity little effected, small restoration steps are necessary
2
no damage of the bearing structure or a part system 1
Chart 2.8: Evaluation of the meaning of an error respectively the error consequence
quality of fabrication category of construction element
fre
qu
en
cy o
f u
se
prefabricated construction
element
partly prefabricated construction
element
fabrication
on-site
uti
lisat
ion
rat
io
I
II
III
often
I
I
II
1
2
3
barely
I
II
III
60-85 %
2
3
4
for the first time
II
III
III
3
4
5
Picture 2.9: (a) Determination of the category of the construction element; (b) Determination of the
evaluation number for the occurrence probability (“tendency value”)
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FMEA-category
ho
no
rary
zo
ne
4
3g/r
2/1
HZ I/II
1
2
3
HZ III
2
3
4
HZ IV/V
3
4
5
Picture 2.10: Determination of the evaluation number for the discovery probability (“tendency
value”)
meaning of the error consequence
(chart 2.8)
occurrence probability (A) of the error cause
(picture 2.9)
discovery probability (E) of the error respectively of
the FU (picture 2.10)
Risk priority number RPZ = B*A*E
Picture 2.11: Defining of the risk priority number in dependence to the evaluation numbers
2.8 Optimization
When a defined RPZ exceeds a specified risk barrier, an optimization by taking the appropriate steps
is necessary. On the one hand, these can be steps to prevent the error cause and, on the other hand,
steps to detect the errors respectively the error causes. By taking these steps the related evaluation
number is reduced depending on the area improved. If no appropriate measures can be found or the
defined measures are not sufficient, it is also possible to reduce the RPZ with a modified bearing
structural concept. An assortment of possible discovery measures in dependence on the error
categories is shown in chart 2.11.
2.9 Documentation of the events
The results of the analysis, evaluation and optimization are documented in form sheets (cf. picture
2.12). For each step defined, a responsible person is appointed to be in charge of the realization. A
date for the performance has to be stipulated.
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When important points are determined in a meeting that have to be taken into consideration for the
following project phases, it is necessary to document these as directions for the following project
phases. These directions as well as the information about the critical parts will be handed out to the
engineers responsible for the licence and the detailed planning as well as for the building
construction to be pursuit.
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construction element / connection
evaluation of the errors:
- occurrence probability (A) - importance of the error consequence (B)
- discovery probability of the error / the error cause (E) function
possible error consequences
B possible error (error type)
possible error causes
preventive measures
A discovery measures
E RPZ responsible / date
Picture 2.12: Form sheet for the error evaluation in the error analysis and optimization meeting
according to [DIN06]
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2.10 Monitoring of the further planning and execution
During the planning and execution process many modifications occur, be it by planning modifications
by the architect or the realization of alternative proposals by the performing company. When such
modifications occur, they have to be included afterwards into the FMEA. At a certain amount, an
error analysis and optimization meeting is again necessary. Additionally, it has to be monitored if the
assumptions and requirements are observed in the appropriate manner.
2.11 Error categories and error causes
To support the determination of errors and their cause, the possible error causes are classified into
categories. At the moment, these are limited to the areas calculation, measurement and design (see
chart 2.9)
2.12 Error types and discovery measures
For an assortment of typical construction elements in the common surface construction, a failure
catalogue with possible error types is presented in chart 2.10. It can be used a basis for the definition
of an in-house or also for a public failure catalogue.
Chart 2.11 includes possible discovery measures that are based on the defined error categories, as
well.
error category possible error causes
conceptual error (global level) hidden kinematics at bearing concept insufficient reinforcement of the building deficient robustness, i.e. insufficient reserves for
smaller failure of construction elements and sensitivity to unplanned disturbances, such as not scheduled impact load or explosions
errors in determing the impacts wrong defined loads non-consideration of a decisive impact non-consideration of the decisive load case combination
error in modelling error at entering the model The model does not correspond with reality (e.g. joint
moment instead of rotating clip,…)
error in calculation and measurement
The cross section determination is wrong. The bearing resistance was calculated wrongly.
error at connections and details The dimensioning of the connections was calculated wrongly.
The details are not realizable.
chart 2.9: possible error causes (exemplary)
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1. bearing structure 2. shear wall
- stability failure (crippling) [s] - compressive failure [d/s] - tension failure (tension support) [d] - bending failure [d/s] - too strong deformation [d] - becomes relocatable (unusual) [d] - shear failure (e.g. short bearings at earth
quakes) [s]
- compressive failure (strut) [s] - tension failure (at the support) [d/s] - too strong deformation [d] - failure at openings [d/s]
3. binding girder 4. top panel
- bending failure [d/s] - shear failure [d/s] - too strong deformation [d] - failure at openings [d/s]
- too strong deformation [d] - bending failure [d/s] - shear failure [d/s] - failure at openings [d/s] - punching shear [d at ductility
reinforcement]
5. wall-like bearing 6. floor panel
- compressive failure (of the strut) [s] - tension failure (in tension zone) [d] - failure at openings [d/s]
- too strong deformation [d] - shear failure [d/s] - failure at openings [d/s] - punching shear [d at ductility
reinforcement]
7. foundation
- bending failure [d/s] - shear failure [d/s] - failure of a tensile bracing (launching of the forces) [d/s] - too little position stability [d/s] - for individual foundation: punching shear [d at ductility reinforcement] (not included are failures concerning the floor like e.g. base failure)
d = ductile material behaviour s = brittle material behaviour
chart 2.10: failure catalogue for possible error types of different construction elements of reinforced
concrete (exemplary)
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error category possible discovery measures
conceptual error (global level) verifying the static design on global level of bearing capacity (1st step of the error analysing and optimization meeting)
error in determing the impacts
verifying the determination of loads and load case combinations by:
- check list with all impacts - inspection of all the relevant load case combinations,
especially on critical places
error in modelling verifying the model after entry by: - anew entry (comparison) - inspection of every joint and element - 2nd engineer (in-house)
error in calculation and measurement
verifying of the assessment of the state of strain and dimensioning by:
- 2nd program or basic hand calculation - 2nd engineer (in-house) - Check list with all necessary documentation
Chart 2.11: Possible discovery measures to reduce the risk (exemplary)
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List of references
[DIN06] DIN EN 60812:2006; Analysetechniken für die Funktionsfähigkeit von Systemen - Verfahren für die Fehlzustandsart- und –auswirkungsanalyse (FMEA). 2006
[Dre09] DRESSEL, B.: Die Rolle des Prüfingenieurs im System der vorbeugenden Gefahrenabwehr. Stahlbau 78, Heft 3, Ernst & Sohn Verlag: 214-220, 2009
[e.V08] e.V., VEREIN DEUTSCHER INGENIEURE (Herausgeber): Entwurf der VDI-Richtlinie 6200: Standsicherheit von Bauwerken – regelmäßige Überprüfung. VDI-Gesellschaft Bautechnik, 2008.
[Var04] VARWIG, J.: FMEA – Fehlermöglichkeits- und Einflussanalyse. Hrsg.: Deutsche Gesellschaft für Qualität e.V. (DGQ), Frankfurt; Beuth Verlag GmbH, 2004
[Vog09] VOGT, T.: Durchführung einer Tragwerk-FMEA für ein Bürogebäude und Erarbeitung von Fehlerkategorien. Projektarbeit. Universität Kassel, Fachgebiet Bauwerkserhaltung und Holzbau (als Download unter www.tragwerk-fmea.de), 2009