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CIVIL & STRUCTURAL ENGINEERING STRUCTURAL ASSESSMENT APPROACH AND CASE STUDIES
CIVIL & STRUCTURAL ENGINEERING
STRUCTURAL ASSESSMENT APPROACH AND CASE STUDIES
Company presentation
JOSE ANTONIO CRESPO - Civil Engineer, MSc - Working in SILGA since 1989 - Currently General Manager of the Company and Middle East Regional Manager
SILGA is a consulting company specialized in engineering projects, mainly focused on civil, industrial and building structures.
SILGA was established in 1989 around a small but highly specialized group of professionals with experience in structural projects. Since then, SILGA has grown both in human and material resources in order to meet the clients’ requirements with the highest level of excellence. Projects have included bridges, industrial structures and building facilities.
WHO WE ARE
Haramain High Speed Rail viaducts. Jeddah Al Azizia Viaducts. Riyadh
SILGA has worked in over 20 countries worldwide. In some cases through clients in
Spain and in others thanks to our own commercial action and associated companies. WHO WE ARE
What we do
The areas where SILGA has been providing
consultancy services are classified in the
following groups:
DESIGN DESIGN
REVIEW
SUPPORT FOR
TENDERING
ASSISTANCE TO
CONSTRUCTION MAINTENANCE
BRIDGE
CONSTRUCTION
EQUIPMENT
STRUCTURAL ASSESSMENT
CASE STUDIES
DEFINITION
APPROACHES TO STRUCTURAL ASSESSMENT
LOAD RATING
KING SALAM BRIDGE. KHOBAR
PRINCESS NOORAH UNIVERTSITY VIADUCT. RIYADH
BR42 UNDERPASS. DAMMAM
STRUCTURAL ASSESSMENT
CASE STUDIES
DEFINITION
APPROACHES TO STRUCTURAL ASSESSMENT
LOAD RATING
KING SALAM BRIDGE. KHOBAR
PRINCESS NOORAH UNIVERTSITY VIADUCT. RIYADH
BR42 UNDERPASS. DAMMAM
Structural assessment is defined as the process for establishing the condition of a structure, based on information collected.
The assessment seeks answers to the following questions:
- Does the structure have the necessary structural safety?
- If some pathologies have been observed, what is the origin?
- Are urgent remedial measures to be taken, or can the structure continue in operation until repair works are taken?
- Are the damages observed critical for safety?
- Is it necessary to strengthen or are only repair works enough?
- Are damages “alive”, meaning that they are progressing or stabilized?
- How long can the intervention wait until the safety is compromised?
ASSESSMENT
DEFINITION APPROACHES LOAD RATING
CASE STUDIES
KING SALAM BRIDGE. KHOBAR PRINCESS NOORAH UNIVERTSITY VIADUCT. RIYADH BR42 UNDERPASS. DAMMAM
STRUCTURAL ASSESSMENT. DEFINITION
ASSESSMENT
DEFINITION APPROACHES LOAD RATING
CASE STUDIES
KING SALAM BRIDGE. KHOBAR PRINCESS NOORAH UNIVERTSITY VIADUCT. RIYADH BR42 UNDERPASS. DAMMAM
STRUCTURAL ASSESSMENT. DEFINITION
The information needed to complete the process is:
- Collection of all available information (as-built drawings, records of previous inspections..)
- Site inspection including registry of anomalies, damages, geometry, bearing condition..
- Testing (destructive and non-destructive)
The safety of the structure is assessed through structural analysis, load testing or both.
ASSESSMENT
DEFINITION APPROACHES LOAD RATING
CASE STUDIES
KING SALAM BRIDGE. KHOBAR PRINCESS NOORAH UNIVERTSITY VIADUCT. RIYADH BR42 UNDERPASS. DAMMAM
STRUCTURAL ASSESSMENT. DEFINITION
The reasons for undertaking a structural assessment are multiple:
- Observation of defects which rise suspicions of structural anomalies (excessive deflections, cracking, vibrations)
- Documented records of anomalies related to inadequate use of local materials
- Damages due to fire or impacts
- Observed damages due corrosion
- Changes in the use or loads of the structure
- Chemical changes in the concrete
The structural assessment of any structure I normally done through the concept of Limit States. This is stated in all modern
codes with different denomination for the variables. The following is extracted from AASHTO LRFD
ASSESSMENT
DEFINITION APPROACHES LOAD RATING
CASE STUDIES
KING SALAM BRIDGE. KHOBAR PRINCESS NOORAH UNIVERTSITY VIADUCT. RIYADH BR42 UNDERPASS. DAMMAM
STRUCTURAL ASSESSMENT. APPROACHES
The safety format is same for all limit states, and it means that a structure is safe if the effect of the loads is smaller than the
established limit of the response of the structure. This limit takes different meanings depending on the Limit State. Can be
stresses, deflections, resistance..
There are the following main limit states:
- Strength: Related to resistance of the structure
- Service: Related to use and functionality
- Fatigue: Applicable under repeated loading causing cracking and rupture
- Durability: Related to the life expectancy of the structure
ASSESSMENT
DEFINITION APPROACHES LOAD RATING
CASE STUDIES
KING SALAM BRIDGE. KHOBAR PRINCESS NOORAH UNIVERTSITY VIADUCT. RIYADH BR42 UNDERPASS. DAMMAM
STRUCTURAL ASSESSMENT. APPROACHES
Semi-probabilistic
This corresponds to the approach to safety
established in all modern codes. Basically consists on
evaluating the inequation shown in the previous
page. For convenience, it is expressed as a safety
factor dividing first and second terms, and the result
should be equal or higher than 1.00. Safety factors to
be used are those established in the codes which
cover the main uncertainties as shown in the following
figure extracted from Eurocode 1990: Basis of
Structural Design
The methods for structural assessment are the following:
Deterministic
The safety of the structure is evaluated as a quotient between the effects of the loads and the limit response of the structure under
those loads. In both cases the parameters are not factored, and the safety of the structure is established if that quotient is higher than
code-established values. This approach requires the collection of an extensive amount of data, and it fails to quantify the
uncertainties in the origin of loads.
Probabilistic
The approach to structural safety can be done by studying the probability of failure based on the collected data. This probability is
expressed as a reliability index, which has to be higher than the values prescribed in the codes
ASSESSMENT
DEFINITION APPROACHES LOAD RATING
CASE STUDIES
KING SALAM BRIDGE. KHOBAR PRINCESS NOORAH UNIVERTSITY VIADUCT. RIYADH BR42 UNDERPASS. DAMMAM
STRUCTURAL ASSESSMENT. APPROACHES
LOAD RATING
Another concept for approaching the structural assessment is
through load rating. In principle, this means reaching a number
which indicates which percentage of the design live load can be
taken by the structure before it reaches the limits set in the codes.
For example, for a section designed to comply strictly with design
requirements, the load rating is 1.00. If the section is overdesigned
the factor will be >1.00. In theory not all elements need to be
overdesigned to comply. The structure could have a higher
material strength than the one it was designed for, for example.
The concept of load rating is very useful for establishing bridge
posting. This takes the form of signs preventing vehicles over a
certain weight not to cross the bridge. Not all bridges with load
ratings under 1.00 need to be posted. If the first approach yields
values below 1.00, the codes make provisions for things like actual
loads likely to occur. It is well known that all bridges are designed
for conservative live load configurations. However, the
characteristics of a specific bridge can make the occurrence of
such high loads very unlikely. Also, having more direct information
about actual material strength values can help reduce the material
safety factors. All these relaxations are included in codes like
AASHTO.
ASSESSMENT
DEFINITION APPROACHES LOAD RATING
CASE STUDIES
KING SALAM BRIDGE. KHOBAR PRINCESS NOORAH UNIVERTSITY VIADUCT. RIYADH BR42 UNDERPASS. DAMMAM
STRUCTURAL ASSESSMENT. APPROACHES
LOAD RATING
Load rating procedures can be applied also for structures where no as-built drawings are available, and testing does
not provide the full structural information.
Section 8.8 of AASHTO manual for bridge evaluation covers these cases. Rating (and structural assessment) is done
through proof testing (also known as Load Testing).
Provisions for obtaining Load Rating values are included in that section
STRUCTURAL ASSESSMENT
CASE STUDIES
DEFINITION
APPROACHES TO STRUCTURAL ASSESSMENT
LOAD RATING
KING SALAM BRIDGE. KHOBAR
PRINCESS NOORAH UNIVERTSITY VIADUCT. RIYADH
BR42 UNDERPASS. DAMMAM
The bridge at the intersection between King Salman and King Fahd Roads in Khobar is a complex structure made of
composite steel and concrete decks, which accommodate all traffic movements at the intersection except for the
through traffic at King Fadh Rd which is located at grade level.
ASSESSMENT
APPROACHES LOAD RATING
CASE STUDIES KING SALAM BRIDGE. KHOBAR
PRINCESS NOORAH UNIVERTSITY VIADUCT. RIYADH BR42 UNDERPASS. DAMMAM
CASE STUDIES. KING SALMAN BRIDGE. KHOBAR
The bridge is of recent construction and for some time there have been some concerns among users about
serviceability in relation to vibrations. Traffic stops at traffic light while some other directions are flowing. For those
occupants of the stopped vehicles the vibration caused by the passing traffic is a matter of concern.
Whatever the reasons, this matter is not to be taken lightly and just discard it as if was just a matter of personal
sensitivity. The following questions need to be addressed:
- Do vibrations correspond to the structure behaving like it is supposed to behave? In other words, is the vibration as
expected or is it the symptom of structural problems?
- Is the bridge prone to stability problems due to vibrations?. Is it too flexible that resonance phenomena is likely to
occur?
- Are acceleration levels due to vibrations acceptable in terms of international standards?
- Is there any action needed to solve any problem detected as an answer to the questions above?
ASSESSMENT
APPROACHES LOAD RATING
CASE STUDIES KING SALAM BRIDGE. KHOBAR
PRINCESS NOORAH UNIVERTSITY VIADUCT. RIYADH BR42 UNDERPASS. DAMMAM
CASE STUDIES. KING SALMAN BRIDGE. KHOBAR
In order to address these issues the following strategy is followed:
- Perform a visual inspection of the bridge. This is in order to detect possible structural damages that could have an
influence on the dynamic behaviour.
- Create a numerical model of the bridge with an aim at getting a theoretical approach for the vibrational
characteristics of the structure in order to compare the results with the field tests.
- Perform a full dynamic load testing of the bridge.
- Analyse the results of all the observation and field data in order to answer the key questions mentioned earlier in this
Introduction.
ASSESSMENT
APPROACHES LOAD RATING
CASE STUDIES KING SALAM BRIDGE. KHOBAR
PRINCESS NOORAH UNIVERTSITY VIADUCT. RIYADH BR42 UNDERPASS. DAMMAM
CASE STUDIES. KING SALMAN BRIDGE. KHOBAR
Visual inspection
A detailed inspection for the Bridge is important to be carried out to
assess the overall structural condition and identify various defects through
a quantitative and qualitative survey according to AASHTO Bridge
Element Inspection Manual.
The visual inspection included all bridge components, such as:
- Bridge Deck including all joints, wearing surface, drainage system.
- Bridge Superstructure including all floor systems and Bearings.
- Bridge Substructure including Piers, Abutments
ASSESSMENT
APPROACHES LOAD RATING
CASE STUDIES KING SALAM BRIDGE. KHOBAR
PRINCESS NOORAH UNIVERTSITY VIADUCT. RIYADH BR42 UNDERPASS. DAMMAM
CASE STUDIES. KING SALMAN BRIDGE. KHOBAR
Numerical analysis
Finite element models were done, and moving loads applied to obtain the theoretical vibrations of the bridge, so that
they can later be compared with the field results
ASSESSMENT
APPROACHES LOAD RATING
CASE STUDIES KING SALAM BRIDGE. KHOBAR
PRINCESS NOORAH UNIVERTSITY VIADUCT. RIYADH BR42 UNDERPASS. DAMMAM
CASE STUDIES. KING SALMAN BRIDGE. KHOBAR
Dynamic Load Test
The test was done with a 20 tn truck moving at speeds of 20, 40, 60 and 80 km/h. Additionally a test is done with the
truck moving at 80 km and crossing over and obstacle to obtain maximum impact and measure the natural
frequency of the bridge and the damping ratio.
Instrumentation was done with displacement transducers and accelerometers and selected locations
ASSESSMENT
APPROACHES LOAD RATING
CASE STUDIES KING SALAM BRIDGE. KHOBAR
PRINCESS NOORAH UNIVERTSITY VIADUCT. RIYADH BR42 UNDERPASS. DAMMAM
CASE STUDIES. KING SALMAN BRIDGE. KHOBAR
Analysis of results
ASSESSMENT
APPROACHES LOAD RATING
CASE STUDIES KING SALAM BRIDGE. KHOBAR
PRINCESS NOORAH UNIVERTSITY VIADUCT. RIYADH BR42 UNDERPASS. DAMMAM
CASE STUDIES. KING SALMAN BRIDGE. KHOBAR
The bridge is of recent construction and for some time there have been some concerns among users about
serviceability in relation to vibrations. Traffic stops at traffic light while some other directions are flowing. For those
occupants of the stopped vehicles the vibration caused by the passing traffic is a matter of concern.
CONTACT
José-Antonio Crespo · SILGA’s general manager
Mob. Spain: (+34) 639 12 59 64
Mob. Saudi Arabia: (+966) 50 603 9543
Mob. Bahrain: (+973) 351 40 782
Domingo Lorenzo · SILGA’s head office
Calle Luxemburgo 2
28232 Las Rozas, Madrid, Spain
Tlf.: (+34) 91 639 80 50
Mob.: (+34) 606 880 217
THANK YOU
GRACIAS
شكرا
