Case Study: Minneapolis Bridge Failure

ovariesracialΠολεοδομικά Έργα

25 Νοε 2013 (πριν από 3 χρόνια και 11 μήνες)

68 εμφανίσεις

Case Study: Minneapolis Bridge Failure

Biblical Reference

Suddenly, the walls of Jericho collapsed.

Joshua 6:20

The Minneapolis Bridge Failure


On August 1, 2007, the center section of the
Interstate
-
35W bridge in Minneapolis,
Minnesota, suddenly collapsed
.



The design and engineering processes that
bridges undergo are supposed to ensure
that bridge failures do not happen.

Controlled Experiments


After the
bridge
collapse, investigators
needed to use scientific inquiry to
determine why the bridge failed.


They designed
controlled experiments

to
help them answer questions and test their
hypotheses.


A
controlled experiment

is a scientific
investigation that tests how one factor affects
another
.

Identifying Variables & Constants


A
variable

is any factor that can have
more than one value.


The
independent
variable
, the
factor that
you want to
test, is
changed by the
investigator to observe how it affects a
dependent
variable


The
dependent variable

is the factor you
observe or measure during an experiment.


Constants

are the factors in an experiment
that do not change.


Experimental Groups


A controlled experiment
has at
two groups
:



The
experimental group

is used to study
how a change in the independent variable
changes the dependent variable.


The
control group

contains the same factors
as the experimental group, but the
independent variable is not changed.

Simple Beam Bridges


A beam bridge
has one horizontal beam
across two supports
.


It is the most simple bridge, but…


A disadvantage
is
that they tend to sag in the
middle if they are too long.


Truss Bridges


A truss bridge often spans long distances.


It is
supported only at its two ends, but an
assembly of interconnected triangles, or
trusses, strengthens it.


The I
-
35W bridge was a truss bridge designed
in the early 1960s.

Bridge Failure Observations


After recovering all the pieces of the
collapsed bridge, investigators found
physical evidence they needed to
determine where the breaks in each section
of the bridge occurred.


Investigators also used video footage of the
bridge collapse to help pinpoint where the
collapse began.

Video Footage

Asking Questions


Was the original bridge design faulty?


Was there too much weight on the bridge?


Was there proper bridge maintenance?

Gathering Information & Data


Investigators
collected and analyzed both
qualitative

and
quantitative

data.


Qualitative Data:

Uses words to describe what
is observed.


A thick layer of concrete reinforced the bridge rods.


Quantitative Data:

Uses numbers to describe
what is observed.


Gusset Plate U10 experienced Demand
-
to
-
Capacity ratios ranging from 1.30


1.83.

An Early Hypothesis


The bridge failed, because it was
overloaded.


Normal Traffic


Construction Equipment for Renovations


Sand


Gravel


Water Tanker


Concrete
M
ixer

Computer Modeling


Investigators entered data into a computer
model, which performed mathematical
calculations to determine that the bridge
was not overloaded.


The investigators needed a new Hypothesis

Revising the Hypothesis


Investigators reviewed historical photos
and physical evidence at the time of the
collapse.


Photos showed bowed gusset plates in 1999
and 2003.


Several gusset plates fractured during the
collapse.

New Hypothesis:

The gusset
plates failed, which led to the
bridge collapse.

Testing the Hypothesis

Independent Variable:

Demand on the
bridge at the time of the collapse


Bridge Mass + Occupancy Mass = Demand


Dependent Variable:

Demand
-
to
-
Capacity
Ratio


Values greater than 1.00 indicate a safety
concern

Analyzing Results


The U10 gusset plates should have been
twice as thick to support the bridge and it’s
occupants.

Drawing Conclusions


The bridge failed, because the gusset
plates were not properly designed and
they could not carry the load they were
supposed to carry.


Because the NTSB published and
communicated their results, the scientists
and engineers have valuable information
as they design and build future bridges.

A.

constant

B.

control group

C.

experimental group

D.

independent variable

Which is changed to observe how it affects a
dependent variable?

Pop Quiz

Which refers to data that use words to describe
what is observed?

Pop Quiz

A.

control group

B.

dependent variable

C.

qualitative data

D.

quantitative data

A.

constants

B.

control group

C.

experimental group

D.

variable

Which term refers to any factor that can have
more than one value?

Pop Quiz