Use of statistics in civil engineering

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2. Use of Statistics In Civil
Engineering
Presented by:
Engr Habib ur Rehman Chandio
Department of Civil Engineering
University of Wah, Wah Cantt.

3. Applications of Statistic in Civil Engineering
•The following situations are examples from the field of civil
engineering where variation occurs and statistical method
either are or could be applied. In some instances the
current practice may not be very sound based on statistical
theory. These applications are useful for analyzing and
discussing the use of Statistics in the practice of civil
engineering.
Applications of Statistic in Civil Engineering

4. Sanitary Engineering
• Given: A series of samples of wastewater ("water" from a sewer) and results of
biological oxygen demand (BOD) tests
Find: The design BOD, which is the value that corresponds to a certain
probability of not being exceeded. This value would be used to design the
wastewater treatment plant.
Commentary: A deterministic approach would use the mean BOD and apply
some factor of safety.
Applications of Statistic in Civil Engineering

5. Traffic/Transportation Engineering
• Given: An intersection between a residential street and a major artery in a suburban
community. The residential street has a stop sign, but the artery does not.
• An access road for a new recreation area is to have a toll booth. The distribution of
vehicles per minute, the time required to process each vehicle, and the length of
roadway required for each waiting vehicle are given.
• Find: The probability that a vehicle stopped at the stop sign will have to wait more
than a specified period before making a left turn onto the artery.
• The required "storage area", which is the minimum required length of roadway
between the toll booth and the adjacent highway such that the probability of
waiting vehicles extending onto the highway does not exceed a certain value.
Applications of Statistic in Civil Engineering

6. • Commentary: The acceptable probability depends on the consequences of being
exceeded. For example, if the highway is a busy one-lane road, a very low design
value would be used, whereas if it is a low-volume four-lane road, perhaps a higher
probability would be acceptable.
• A similar analysis also could be done based on the probability of exceeding some
maximum acceptable waiting time.
Based on the results of such analyses, we might decided to have more than one toll
booth. If so, how often would both booths need to be in service? (study of waiting
lines)
• If this probability is too high a traffic signal may be warranted. Traffic engineers
perform this kind of analysis to determine where to place traffic signals.
Applications of Statistic in Civil Engineering

7. Surveying and Mapping
• Given: A series of measurements from the field, each of which is made using an
instrument that has a certain precision.
• Commentary: Many measurements in surveying are made using a series of
instrument setups. For example, consider a piece of property whose boundary
consists of 8 line segments. The orientation of one of these segments with
respect to true north is known to a precision of 20" of arc. A surveyor sets up a
"total station" (an instrument that measures angles and distances) at each of
the 8 corners, and measures the angles to a precision of 20" and the distances
to a precision of 0.01 ft. These measurements are then "adjusted" so that
satisfy the rules of geometry.
Find: The precision of the computed orientations of the other property lines. It
is not 20"!
Applications of Statistic in Civil Engineering

8. Coastal and Port Engineering
• Given: Anticipated distribution of cargo ship arrivals at a port in the year 2010,
and the mean time required for a ship to occupy a berth.
Find: The number of berths required so the probability of a ship having to wait
more than a certain number of hours to enter a berth is no more than x.
Commentary: A large amount of construction is currently under way at the ports
in Long Beach and Los Angeles. Portions of this construction would be based on
these kinds of analysis.
Applications of Statistic in Civil Engineering

9. Geotechnical Engineering
• Given: Four soil samples obtained from a certain stratum of soil and the results
of laboratory consolidation tests on each sample. These test results are used to
compute the settlement that will occur if a certain load is placed on this strata.
Find: Considering only variations due to the sample locations (i.e., assuming the
sampling method, testing, and analysis introduce no uncertainty), compute the
probability that the settlement will exceed some specified value.
Commentary: I've seen data that indicate COV values of 0.26 to 0.52 from
multiple samples obtained from "homogeneous" strata. Thus, analyses based on
mean values could produce results that are seriously in error.
Related analysis: Given the cost of sampling and testing, how many samples
should be taken
Applications of Statistic in Civil Engineering

10. Hydrology
• Given: Stream flow records for the Santa Ana River near Corona.
Find: The stream flow (ft^3/s) that corresponds to a particular recurrence interval. This flow can
then be used to design dams, levees, etc.
• Commentary: After a devastating flood in 1938, the Army Corps of Engineers built Prado Dam to
protect Orange County. This dam and its spillway can be seen from the 91 freeway (the spillway
has 1776-1976 painted on it). The reservoir behind this dam is normally empty, and is intended to
capture the excess flood waters in the event of another major flood, thus keeping the stream flow
below the dam at manageable levels. This dam was designed based on the best hydrologic data
and analyses then available. However, subsequent analyses performed in the 1970s and 1980s
found the flood that corresponds to a certain recurrence interval (200 years?) is much greater
than had previously been considered. Such a flood could overtop the dam, causing it to fail, thus
producing massive flooding in Orange County. Because of this, the Army Corps of Engineers is
currently building a massive flood control project along the Santa Ana River, which includes a new
dam upstream of Prado (Seven Oaks Dam), new levees, and the raising of Prado Dam. This is a
massive construction project, all of which is based on a statistical analysis of hydrologic data.
Applications of Statistic in Civil Engineering

11. Environmental Engineering
• Given: A series of groundwater samples obtained at different locations and
depths in an aquifer, and the concentration of a certain chemical in each
sample.
Find: The probability that the concentration at any point in the aquifer
exceeds some specified value.
Applications of Statistic in Civil Engineering

12. Earthquake Engineering/Seismology
• Given: A proposed dam to be built at a certain site, the probability of
earthquakes of various sizes occurring on faults at various locations, the
predicted peak horizontal ground acceleration at the dam site from each of
these earthquakes.
Find: The design peak ground acceleration, which is the one that corresponds
to a certain probability of being exceeded during the design life of the dam.
Applications of Statistic in Civil Engineering

13. • Structural Engineering
• Given: The Uniform Building Code dictates certain design values for the live load on
building elements (live load is that load induced by furniture, inventory, occupants,
moveable objects, etc., as contrasted to dead load (the structure itself), earthquake
load, wind load, etc.). For example, the code-specified design load for classrooms is
40 lb/ft^2.
Find: The probability that this design load will be exceeded.
buildings. I couldn't
• Commentary: I've seen some statistical data on live loads based on actual
measurements in find it in my files, but I think the COV is about 0.10, and the
probability of exceeding is about 0.05.
A design method called "load and resistance factor design" (LRFD), which our
students learn in a junior-level course, uses "load factors" and "resistance factors"
that have been developed from extensive reliability analyses. Although design
engineer simply uses the specified factors in a typical design, it is important to
understand how the building codes developed them.
Applications of Statistic in Civil Engineering

14. Thank you …
… for paying attention