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I received almost one dozen requests that I post my 
Dec. 1994 ASCE Civil Engineering 'Forum' article.  
Thank you!

Since many of you have long since discarded or
recycled this magazine, I have tried to revise my 
pre-edited disk file to reflect the published article.  
It is best to refer to the published article for a 
copy without typos.

The article is enclosed for your general interest.

Please note that I have to get back to both hunting 
for paid work and preparation of a research 
proposal (a longer-term project to be done in my 
spare time).  I am sorry, but I will be unable for 
any discussions that ensue.  (I have already 
received over 50 sets of comments from the original 
publication, so I have a good idea what the 
reactions will be.  The original comments were 
quite positive, especially from our senior 
colleagues!)

Julie
---------------------------------------------------

THE NORTHRIDGE WARNING:  HAS 3-D DESIGN BEEN LOST?

	Underlying the many lessons that have been 
drawn from the Northridge earthquake that struck 
Southern California a year ago next month in one 
critical and fundamental issue:  Structural 
engineering has drifted away from the 3-D, 
comprehensive, systems-oriented thought processes 
involved in its parent profession, architecture.  
	Many structures damaged in the earthquake 
pulled apart in the same manner in which they were 
designed - that is, as an unrelated collection of 
2-D vertical and horizontal planes of framing.  The 
lack of breadth and depth leads to the design of 
structural framing schemes - not 3-D systems - with 
inadequate reliability for safety, both globally 
and locally.  Therefore, it is not possible to 
fully consider soil-structure-nonstructure 
interaction in order to develop adequate building-
specific performance criteria for expected levels 
of ground shaking.
	There are several reasons for this loss of 3-D 
design awareness.  First, current approaches to 
seismic-resistant design are being driven by post-
WWII and particularly post-1960s, structural 
engineering education.  As analytical computations 
became easier, structural engineering students 
became more enamored and even mesmerized by 
computer output, especially when post-processor 
graphics were available.  In the post-1960s are, 
students have never been instructed in the design 
3-D structural framing systems, comparison of 
relative merits, and examination of local issues in 
conjunction with global issues.  As a consequence, 
each succeeding generation of teachers gives their 
students given less and less guidance in design.  
Nowadays, a design course typically includes the 
sizing of beams and columns, and dimensioning of 
details, with the most attention on members, often 
without recognizing the complexities of fabrication 
and construction of connections.  This carries over 
into research and practice, and is reflected in the 
codes and licensing exams.
	To counter this trend, one on short-term 
possibility would be for professors who teach 
structures courses to architects to co-teach a 
course with a structural engineering professor to 
structural engineering undergraduates, perhaps with 
joint enrollment.  This may not be easy, because 
even architecture students, who are supposed to 
automatically think in 3-D, are also being 
adversely affected by the computer and computer-
aided architectural design software.  
	The fascination with computers might be 
overridden by initially excluding them from the 
educational process and concentrating on developing 
strong 3-D visual connections among 2-D structural 
plans and elevations; 3-D structural framing with 
architectural elements and systems; examples of 
gravity-, wind-, and seismic-induced failures; and 
technical discussions of the implications of the 
global and local failures on structural 
performance.  This kind of dual approach, which is 
visual plus technical, was exactly the education I 
received as an architecture student in the early 
1970s, which I brought with me to structural 
engineering and have maintained ever since in spite 
of the pressures literally to think otherwise.
	Research is another contributing factor.  For 
example, research on seismic retrofit techniques is 
being performed by structural engineers without 
considering the integration of supplementary 
seismic-resistant structure into existing 
architecture.  Tight budgets for experimental work 
have led to the use of small specimens, typically 
two-dimensional, one bay wide and on story tall, 
with tributary masses and associated inertia forces 
that are not representative of their placement 
within real buildings.   However, analytical 
studies based on the lab tests do not address where 
and how the seismic-retrofit techniques can be used 
in classes of real buildings.  Also, the load- and 
strain-rate dependencies of materials and 
connections are often neglected experimentally, 
because it is expensive to perform time-dependent 
tests.  Again, analytical studies are following 
directly from experimental work.
	Finally, engineering practice must share the 
blame.  Current approaches to seismic-resistant 
design are also being driven by low fees resulting 
from job competition.  Structural framing schemes 
are designed and quickly as possible.  A code-
compliant structural framing scheme can be and 
often is designed as a collection of 2-D vertical 
and horizontal planes of framing.  Codes can be and 
are being interpreted as maximum standards, rather 
than minimum standards as originally intended.  
Peer-review panels for seismic-retrofit schemes are 
often required by building owners.  I have seen 
quite a few cases in which the panel supported a 
scheme that had never been substantiated 
analytically or experimentally in regard to its 
appropriate and efficient use.  The decisions were 
usually based on cost.
	A 3-D systems point-of-view - that is, a 
comprehensive approach that integrates global and 
local issues - must be taken to ensure safe and 
reliable seismic performance.  This will provide a 
basis for code improvements to ensure that 
structural framing is conceived of and designed in 
3-D, not a collection of 2-D vertical and 
horizontal planes of framing.  Perhaps code changes 
will provide incentives for structural engineers to 
be involved with architects from the earliest 
stages of schematic design, and for engineering 
educators to incorporate 3-D structural systems 
design into undergraduate and graduate curricula.

Julie Mark Cohen, Ph.D., P.E.
CLADDING RESEARCH INSTITUTE
Emeryville, CA

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