DESIGN AND INSPECTION OF LONG SPAN...
Transcript of DESIGN AND INSPECTION OF LONG SPAN...
1Global director RM Bridge, Bentley Systems Austria GmbH, Graz, Austria 2Senior Product manager, Bentley Systems Austria GmbH, Graz, Austria 3Senior consultant, Bentley Systems Austria GmbH, Graz, Austria 4Product manager, Bentley Systems, Pittsburgh, USA
V.Samec, J.Stampler, H.Sorsky, T.Gilmore. Design And Inspection Of Long Span Suspension Bridges –
Bridge Information Modelling, Proceedings of the Istanbul Bridge Conference, 2014.
Istanbul Bridge Conference August 11-13, 2014
Istanbul, Turkey
DESIGN AND INSPECTION OF LONG
SPAN SUSPENSION BRIDGES – BRIDGE
INFORMATION MODELLING
V. Samec1, J.Stampler2, H.Sorsky3, T. Gilmore4
ABSTRACT
In the design process of long-span suspension bridges the consideration of many challenges
needs to be fulfilled: a highly non-linear behaviour of the structure, the need of optimization
the geometry of suspension cables, when designing the sag-profile as well as optimization of
erection procedure. Additionally wind effect is a major point because the extraordinary
slenderness of these structures yields a considerable susceptibility for wind-induced vibrations.
When design challenges are successfully closed, the bridge needs to be maintained and
inspected over its entire life cycle.
During the lifetime of a bridge a huge amount of data related to all aspects of the bridge is
collected and must be managed. Not every piece of data is necessary for every participator in
bridge management, but there will be overlapping occurrences. Therefore it seems natural to
collect all the data in one well organised data pool, which can be accessed by all persons or
institutes involved in the bridge construction and maintenance.
A corresponding data model which is called BrIM – Bridge Information Modelling – is being
developed by the bridge engineering division of Bentley Systems. Mobile inspection represents
a novel solution, which helps asset owners streamline the process of planning inspections,
collecting and managing inspection data, and complying with government reporting
requirements. The central part of the project is to create a common data interchange interface
for a wide range of design CAD, project management and inspection tools usually applied in
bridge design and construction. The application of such a distributed model eases the
communication of the human network behind such a bridge.
This contribution explains the necessary concepts of data flow and organization from the
viewpoint of the construction design and structural analysis. The data flow will show how the
preliminary design can be used for structural design and ultimately how obtained calculation
results can be incorporated into the following construction process. The same model can be
used for inspection of the bridge over its lifetime allowing for a seamless linkage of information
and allowing for proven asset management techniques to be used.
Design And Inspection Of Long Span Suspension Bridges – Bridge
Information Modelling
V. Samec1, J.Stampler2, H.Sorsky3, T. Gilmore4
ABSTRACT
Long span suspension bridges represent some of the most remarkable, yet most vulnerable,
assets in road networks. Due to their important role in the transportation network, the design,
construction, and the following surveillance and maintenance must be performed very
thoughtfully. During the design process, bridge designers must consider and meet many
challenges: the highly non-linear behaviour of the structure, the optimization of the geometry
of suspension cables, and wind effect. The extraordinary, ultrathin design of these structures
yields significant susceptibility for wind-induced vibrations. When design challenges are
successfully satisfied, the bridge needs to be maintained and inspected over its entire life
cycle. A corresponding data model - called BrIM – Bridge Information Modelling – is being
developed by the bridge engineering division of Bentley Systems. Mobile inspection
represents a novel solution, which helps asset owners streamline the process of planning
inspections, collecting and managing inspection data, and complying with government
reporting requirements.
Introduction
Construction of modern-type suspension bridges dates back more than 125 years and
continue to instil special fascination with engineering elegance combined with a touch of
lightness, destined to become lasting landmarks. For bridge engineers, this fascination is also
derived from the size of these structures,
with allowable spans being longer than for
any other bridge type. Long spans
combined with extraordinarily thin lines
present outstanding challenges for any
bridge designer. Modern construction
techniques and materials, as well as
increasing experience and expertise in
bridge design, allow for the possibility of
increasing span lengths on large bridges.
An example of such an evolution is shown
e.g. in Figure 1.
The thinness and kinematical conditions of these structures result in large displacements due
to the permanent loads. Continuous change of structural systems and form finding processes
prove to be an issue for every bridge design engineer. The form finding process is a complicated
iterative process, where the shape of the suspension cables and the hangers need to be
identified.
Figure 1. Evolution of span length
of suspension bridges
An even greater challenge is the simulation of the erection process. Asymmetric loading due
to traffic causes large displacements and requires non-linear traffic analyses.
Last but not least, a major engineering challenge posed by long suspension bridges is their
susceptibility to wind-induced vibrations. An important topic in wind analysis is the data
management and information interchange.
After the successful construction of the bridge, maintenance and inspection play an important
role in the bridge life cycle, performed in a timely manner throughout at least 80% of the entire
bridge’s lifetime. Huge amounts of data related to all aspects of the bridge are collected and
then appropriately managed. Not every piece of data is necessary for every participator in
bridge management, but there will be overlapping occurrences. Therefore, it seems natural to
collect all the data in one well-organized data pool, made accessible to all persons or institutes
involved in the bridge construction and maintenance.
The central part of the project is to create a common data interchange interface for a wide range
of design CAD, project management, and inspection tools usually applied in bridge design and
construction. The application of such a distributed model eases the communication of the
human network behind such a bridge.
Because of the complexity of the task, many engineers working in different fields must work
more closely together. In this sense, not only do the analysis methods fill an important role, but
the data storage and interchange model also perform to accomplish an efficient design process.
Behaviour of suspension bridge – analysis and design
During the analysis of long-span bridges, especially for cable-suspended bridges, non-
linear effects often reach magnitudes that make it imperative to include them in their structural
analysis. The basic conundrum presented by such a non-linear structural analysis is how to
consistently combine different non-linear behaviours. Time-effects (if concrete is used as
material) have to be coupled with the continuous change of the structural system, the cable-
sagging, the P-delta effects and the large displacement theory. [1]
The shape of the bridge is a non-linear function of the loading, deviating a great deal from the
hypothetical “stress-less” shape. Due to the high non-linearity of the problem, the usual
straight-forward design approach for conventional structures – i.e. using the desired design
shape in the analysis and compensating the deformations in the erection process by applying
appropriate pre-camber values – is no longer suitable. Therefore, a complicated form-finding
process with taking into account geometrical non-linearities is required.
In addition to the geometric non-linearity, various other non-linear mechanisms generally
occur. They require, on the one hand, the use of special element type and, on the other hand, a
global solution concept, dealing with the different non-linearity types in a comprehensive
approach [2].
Typical problems requiring special element types are for instance [3]:
Cable sagging, requiring special cable elements. These elements describe the non-linear
stiffness due to sagging. A special element type has been developed. It guarantees stable
behaviour even with very large displacements and any imperfection of the stress-less
geometry as shown in Figure 2.
Figure 2. Special cable element for calculating large displacements
Fixing the suspension cable at the top of the pylon generally induces high and excessive
bending moments in the pylon. Therefore, a saddle is usually arranged on the top of the
pylon allowing for slipping of the suspension cable in the erection process. This connection
is modelled by friction elements, where the transmitted horizontal forces are a function of
the vertical redirection force (Figure 3). Special care is taken to simulate additional p-delta
and large displacement effects, which are coupled with moving the saddle at the top of the
pylon.
The lateral gaps between the main girder and the pylon legs are modelled with special gap
elements, which confine the free lateral displacements of the main girder to a certain
amount.
Eccentric hinge elements allow for simulating any distance pieces required in the
construction stage for keeping the individual segments in position without inducing
excessive constraints.
Figure 3. Schematic view of a suspension bridge
The form finding process – i.e. determining the theoretical “stress-less” state of the structural
components – is a backward iteration process, being rather complicated and time consuming.
An alternative to the conventional approximate calculation, the Additional Constraint Method
has been provided in the program RM Bridge in order to find and optimize the shape of the
suspension cables and the hangers. The preliminary design usually starts from the final
structural system where the deformation state due to permanent loads is calculated. The stress-
less design geometry is then appropriately modified, if pre-cambering is required. The final
hangers
suspension cable
sag
saddle
anchor block
y
x
Deformed Geometry
(Under the Load)
1
A(xA/yA)
2
3
4
5
6
19 n = 21
20
B(xB/yB)
L, A, q
y
x
F = q L
Start Geometry – Stress Free
L0=EA*L/(EA+N)=konstant
Extremely robust cable
element is developedy
x
y
x
Deformed Geometry
(Under the Load)
Deformed Geometry
(Under the Load)
1
A(xA/yA)
2
3
4
5
6
19 n = 21
20
B(xB/yB)
L, A, q
y
x
F = q L
Start Geometry – Stress Free
1
A(xA/yA)
2
3
4
5
6
19 n = 21
20
B(xB/yB)
L, A, q
y
x
F = q L
1
A(xA/yA)
2
3
4
5
6
19 n = 21
20
B(xB/yB)
L, A, q
y
x
F = q L
Start Geometry – Stress Free
L0=EA*L/(EA+N)=konstant
Extremely robust cable
element is developed
defined stress-less design geometry can then be used for performing a detailed construction
stage analysis, with the option of accumulating permanent loads. This allows for the calculation
of the stressing state and geometry of the structure for all construction stages.
Some aspects of using this method in the design process have been successfully used for the
longest suspension bridge in Norway - Hardanger Bridge. This bridge has been opened in
August 2013 and crosses the Hardanger fjord with a main span of 1310 m, ranking it at no. 10
in the current global list of the longest suspension bridges (Figure 4).
Figure 4. Hardanger Bridge, Norway
The Norwegian road authority, Statens Vegvesen, in close collaboration with TDA Norway
and Bentley Systems Austria team in Graz, the supplier of the software package RM Bridge,
performed the design work.
The form-finding process with using the AddCon method was based on the provisional
assumption of a straight girder. Three sets of constraints were applied to get the required cable
lengths, yielding the desired shape under permanent loading. These constraints are:
vertical displacements of the bottom points of the hangers must be zero.
horizontal displacements of the top points of the hangers must be zero.
the main cable sagging must get the intended value, i.e. vertical displacement of the
central hanger top point must be zero.
The continuous change of structural systems is another major reason for experiencing non-
linear optimization problems. The mechanisms of typical construction sequences produce large
displacement effects due to the installation of new segments and corresponding loadings and
to redistribution of loading already applied to the structure. The second effect is mainly
produced by the main suspended cable moving into the new position – to fulfil global loading
equilibrium. The fact that already applied loading is redistributed to the new structural system
in each change of the structural system (or applying the new loading) does not allow classical
approach in finite element analysis with one “reference” structural system. In reality, each
construction stage has its “own” structural system where the same segments, cables, and
hangers have completely different 3D coordinates and orientation [4].
A further great challenge is the simulation of the erection process. The procedure of connecting
the different girder segments individually to their respective hangers causes continuous,
considerable changes to the sagging curve of the suspension cables in accordance with the
weight of the already mounted segments. This leads to high up and down movements of the
deck segments during erection. Preliminary hinged connections with some spacing have to be
applied between the segments in order to prevent inducing impermissible constraints and
uncontrolled segment movement.
An approximate of the final shape is reached when all segments are mounted. Controlled
removal of the distance pieces closes the gaps between the segments and launches the welding
process. The actual final shape is reached when all segments are snugly welded. Continuous
adaptation of the mathematical model is recommended in the erection phase. Any deviations
from predicted behaviour can be detected in an early stage. In addition, required compensation
measures can easily be fixed by performing appropriate erection control calculations.
Dynamic wind impact: Most of the bridges of such enormous span length are also subject to
strong wind forces due to their exposed placement. Because of their thin design and related
dynamic behaviour, it is no longer sufficient simply to treat wind gusts and other fluctuations
by equivalent static wind forces. Instead, different investigation methods developed for such
extreme situations must be applied to examine the interaction between the bridge and any
oncoming winds.
The first step to the numerical modelling is a careful investigation of the airflow around the
concerned bridge cross sections. This is done by applying a CFD (Computer Fluid Dynamic)
module. The subsequent wind buffeting analysis separates static and dynamic wind force
contributions. The static part can be applied as distributed constant load. The dynamic wind
load can be split into aerodynamic damping and stiffness and contributions due to fluctuating
wind. The structural response is calculated by transforming the equations into modal space and
frequency domain. By providing suitable wind profile data, the excitation power spectrum can
be calculated and the structure peak response can be estimated by statistical methods.
By solving simplified versions of the buffeting and flutter equations, wind checks can be
obtained for galloping, torsional divergence, torsional flutter, and classical flutter phenomena.
According critical wind velocities can be estimated.
Wind calculations were performed for the Hardanger Bridge in Norway (Figure 5).
Figure 5. Structural model of Hardanger Bridge, Norway
CFD (Computer Fluid Dynamic)
investigations were performed for the main
girder with traffic. The two driving lanes are
loaded with traffic, according to the sketch
presented in Figure 6.
Figure 6.Cross-section for traffic calculation
Three different cases were considered: with both lanes loaded, only with the left lane and only
with the right lane. Since the application of traffic causes a symmetry break of the cross section
layout, the CFD (Computer Fluid Dynamic) calculations must be performed for wind coming
from the left (-10° to 10°) as well as
from the right (170° to 190°). The
computed results for the case with
both traffic lanes are indicated in
Figure 7. It can be observed that the
slope of the lift coefficient for wind
coming from the left is negative for
negative angles. By evaluating the
Glauert-Den Hartog criterion, slightly
negative values are obtained, which
indicates a tendency for galloping [5].
Figure 7. Steady state coefficients CD
(x), CL (o) and
CM (D) for traffic on both lanes for wind from left (solid) and right (dashed).
Based on this set of basics functions, the buffeting analysis was performed for a wind profile
where the mean wind is given by a logarithmic distribution and the power spectral density is
of Kaimal type. By comparing with results for static wind only, static and dynamic lateral
forces are of same magnitude. The twisting moment is larger for the dynamic wind; due to the
fluctuating vertical wind component, the effective wind incident angle varies more than static
effects only. Thus, the overall twisting of the deck is amplified and the internal moment is
consequently higher (Figure 8).
Figure 8. Internal shear force (left) and longitudinal twisting moment (right) due to lateral wind
Inspection of long span bridges
With a goal of consolidating inspection data into one highly accessible database,
Bentley works closely with their clients to efficiently configure and utilize the web-based BrIM
System during inspection and maintenance via the 3-D visualization tool.
Using 3-D Visualization, Engineers can interactively “fly-through” and zoom throughout the
structure. A variety of views are available which provide multiple angles and viewpoints for
given components. By scrolling over an individual member, users can view the member name
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
-10 -8 -6 -4 -2 0 2 4 6 8 10 [°]
CD
,CL, C
M [
1]
170 174 178 182 186 190
and location quickly. If a particular component requires further review, users can simply click
on that component, and a separate window will appear which displays all of the information
that has been entered relevant to the component. Users can then view ratings, remarks,
properties, historical trends, and recent/historical pictures. The software enables a “drill-down”
feature which involves clicking on a picture to see enlarged views of defects with additional
detail (Figure 9). This tool can be utilized from any computer with a web browser and does not
require expensive CAD software.
Figure 9. Components that return under a specific query light up in a designated color.
With the new Mobile App, users can not only operate the 3-D visualization tool while in the
field, but they can attach photos, video files, and audio clips to individual elements within the
visualization. This unique feature streamlines the entire process and saves a significant amount
of Engineers’ precious time. Inspectors and maintenance crews now have access to the design
information via the actual design and construction files during an inspection. All 3-D design
files are available in the field on a mobile device.
Most clients require a single System that could be easily accessed by its Engineers. Thus, the
System establishes a high-level of consistency in formatting and quality for all inspection and
management users. This consistency is seen across all platforms, including mobile devices used
for data collection and file uploading while in the field. Bentley continues to improve its
System by eliminating errors from redundant data entry and dramatically increasing the
reliability of the information obtained via inspections since the data is utilized to make critical
capital planning and maintenance decisions. Bentley is stepping up their System by offering
the 3-D visualization tool, a clear, interactive visual reference of a bridge and its elements,
linking back to report data, historic data, uploaded and attached files, and other crucial
information. Bentley strives to develop a one-stop location for all bridge data (inspections, as-
built drawings, load ratings, work orders, etc.) and make that information available securely
via the internet from any office or other approved location. The 3-D tool and the new mobile
application help Bentley reach this goal. This integrated BrIM System serves a variety of users
(Executives, Managers, Maintenance Personnel) while providing different permission levels
and functions to meet their unique levels of authority. The permission levels prevent a user
from seeing or accidentally corrupting data they should not have access to in the first place.
Overall, the common goal in Bentley’s System implementation is to dramatically streamline
the inspection and management process for all inventory bridges and save time, costs, and
increase the operating efficiency and safety of the bridges.
For an inspection, users can choose to pre-load information from the most recent inspection
into the forms. When data is pre-loaded, color coding systems are utilized to clearly show what
data fields are changed and what data has remained the same from the previous inspection.
The other option is for users to utilize blank inspection forms without the pre-loaded data. The
3-D visualization tool can also serve as the primary point of data entry. Users are able to collect
data and enter it directly into the system and access it later for review via the 3-D tool.Data
fields that appear on different forms but reference identical information (i.e. Deck rating) are
automatically linked together within the software. This information only needs to be entered
once and is automatically transferred and entered on all other relevant forms within the System
and eventually transferred to the BrIM. The System includes tools for multiple engineers to
simultaneously enter data, photos, and other resources. Even with the flexibility of the System,
users maintain the highest standards of security and controlled all viewing permissions through
usernames and passwords. Each individual component of the bridge is a unique asset in the
System which allows data to be viewed, stored, and retrieved at a very granular level.
The System supports uploading of pictures, diagrams, and other file types. Adding, labelling,
and organizing pictures, sketches, and other files into reports is traditionally a time-consuming
process for all parties. Using the System, inspectors select the files (pictures, etc.) from their
computer or external device and quickly upload those resources into the inspection forms at
desired locations. After being
uploaded, the pictures appear as
thumbnails and are automatically
created and displayed on the
screen. Descriptions can be added
to the pictures, and those
descriptions can be carried over
into the inspection report and/or
used as an ongoing resource. All
uploading tools are also available
on mobile devices with Bentley’s
Mobile App, allowing users to link
photos, videos, and other files
directly to the report and the 3-D
visual of the bridge (Figure 10).
Figure 10: With the Mobile
application, users can enter data into an inspection report in the field.
Users are able to integrate coding manual pages as PDF files within the System. The coding
manuals can appear as PDF files and eliminate the need to bring hard copies to the bridge site
for reference. This feature integrates hundreds of pages of detailed information in an easily
accessible PDF format. Pictures can also be correlated to condition ratings as a visual tool to
standardize the way that all Inspectors rate different components of the bridge. The 3-D
visualization tool provides another option for viewing PDF files, linking each element in the
bridge directly to historic reports and summary report along with other important data.
Managers are then able to search across any field or combination of fields from the inspection
reports. Results are displayed in grid form and also exported to a number of GIS and 3-D BrIM
tools without the need to install additional, costly software.
Conclusions
Overall, Bentley’s BrIM System will provide the solution for modelling, analysis, design and
maintaining long span bridges and preventing the inevitable deterioration due to dynamic wind,
seismic and traffic. Due to the slenderness of the suspension bridge structures, special attention
has to be turned on wind-induced vibrations, with static and dynamic wind excitations to be
investigated. An integral solution of the different topics related to wind impact is shown in the
paper. As an example, the integrated investigations performed in the Hardanger Bridge project
have been presented. This integrated approach considerably eases and enhances the overall
design process.
The 3-D models, created and completed during the design of the bridge, continue to serve its
users throughout the lifecycle of the bridge. Not only does it help bridge designers visualize
their new architecture, but it also continues to help contractors during construction, inspectors
during bridge inspections, maintenance crews sent to seek out a faulty bridge element, and
other ongoing operations of the bridge. The consistent use of the 3-D visualization tool
provides valuable information to bridge owners, inspectors, and maintenance crews while
increasing the return on investment in the design phase. With the ability for this tool to operate
on mobile devices, the 3-D visualization tool simply increases in value, making all construction
and design files, inspection and maintenance reports, and related photos and files readily
available to users in the field.
References
1. Janjic D., Sorsky H., Consistent Non-Linear Structural Analysis Of Long-Span Bridges, Proceedings: EASEC-Symposium 2006, Bangkok
2. Janjic D., Bokan H., Stampler J., Computer Aided Design & Erection of Long Suspension Bridges, Proceedings: IABSE-Symposium 2007, Vancouver
3. RM Bridge V8i, User Guide, Bentley Systems, December 2012
4. Janjic D., Bong-Gyo J., Hyun-Sok C., Gwangyang Bridge – Numerical Simulation of Construction Sequence, Proceedings: IABSE-Symposium 2010, London
5. Janjic D., Stampler J., Domaingo A., Wind and extremely long bridges – a challenge for computer aided design, Proceedings: IABSE-Symposium 2008, Chicago