What Have Our Complicated Specifications Accomplished?

an Editorial by Milo S. Ketchum, Editor
Structural Engineering Practice - Volume 2, Number 4, 1983-84

Design specifications for both steel and concrete get more and more complicated each year, and there seems to be no let up in the drive of code writing agencies to increase the complication. Every expert in the field wants to incorporate what he considers to be the proper structural action reduced to a long formula. It has gotten so that in many cases it is not possible to solve these equations or algorithms by hand, and computers are necessary.

How far should we go to increase the complications? What have the super specs accomplished. Do we have better structures? Are there fewer failures? Have we balanced the complications against the need to make calculations simple so that we will always understand the structure?

We need to stop and take a look at what the so called increased precision has accomplished. Has it made concrete more competitive? If we feel that the specifications are not accomplishing their purpose, then we should make our opinions known. In the past this has been accomplished when the general feeling was that specifications were getting out of hand. One of the problems is that there is no real input to the decisions of code writing authorities, except to object to the final result.

The following discussion will be mostly confined to the concrete code, but the same reasoning can apply to the structural steel design code, and perhaps the timber code. There have been rumblings in the ACI publications and discussions at conventions, that attempts should be made to reduce the complexity but I have seen no tangible results.

On the plus side, I am sure that the new code gives a better understanding of how concrete acts at failure and this will help your design if you understand what the new specifications are trying to say. Strength design has reduced the amount of reinforcing in beams due to the higher stresses and at the same time has reduced the moment arm of the steel for deeper beams. Strength design is here to stay. The specifications could make it a little more understandable. We are now supposed to check for cracks, but how many of you do that in all cases?

We have many more stirrups now, and this is a good thing. There is no reason for two different formulas for shear. The more complicated one is for special designs, and should be so designated. Torsion design has become more precise provided that you know what the torsional forces are to be. These now have become available through computer analysis, but this complicates the analysis chore for all but the simplest structures.

The requirements for design of flat slabs and flat plates are still a mess. Design by the?equivalent frame method is not a simple process, especially the distribution of moments to the column and middle strips. The trouble is that the writers of this section attempted to combine too many types of structures in one chapter. The two?way slabs with beams should have been separated from flat slabs and flat plates. I prefer to use an equivalent grid computer analysis. It is faster, and give you all of the answers in one package, including the effects of torsion in the beam elements.

One answer to this problem is for someone to write a simple specification that will satisfy the code in all respects, but have much simpler procedures and less elaborate equations. In some cases, it may be necessary to be much more specific, particularly in areas that the present code writers think that every one should know. Some of the ideas in the Commentary to the specifications could be incorporated. Much more discussion could be give in some cases where it is necessary to explain the code. Some examples could be given. In the present codes this, of course, is not permitted.

No committee could do this. If done by an individual, such a document would not have the voice of authority, but if it was well done it would be used by many engineers. It would not be necessary to rewrite all the sections of the code, for example the sections on shell structures, on seismic requirements, the first part on material requirements.

The most important duty of an engineer is to understand the structure he is designing. If this is not accomplished, then there is a risk that there will be mistakes that will cause trouble. Specifications ought to help rather than to hinder this process.

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