In the 1930s, many researchers and engineers were involved to improve the calculating method of reinforced concrete. Why? Engineers didn't have the computers to complete the calculations, and therefore all of the calculating details had to be calculated by hand. However, the original calculating method, Working Stress Design, is based on the mechanics of composite material, and actually the calculating procedures are a little bit complex calculated by hand.
C. S. Whitney proposed a simple calculating method in 1937, and it tried to replace the traditional calculating procedures of composite material. This method has many advantages, fast calculation for the beam member, for example, but it does NOT follow the mechanics of composite materials. As everyone knows, Whitney's method is an approximating method to obtain the inaccurate result, and it is based on the experimental data without any mechanics or theory to support.
In the ACI 318 1971 Code, the WSD method is dropped, and the USD method is adopted to replace it. In 1980s, the personal computers were available to all, but the USD method had replaced the WSD method completely. Actually, nobody calculates the beam, column, wall, or plate by hand except that students must pass the required examinations. Besides, engineers are also possible to calculate the members by hand sometimes, but this is just to complete the double check procedure for the special cases.
In the ACI 318 1963 Code, the thickness of the code is less than 80 pages, and it doesn't have the commentaries to explain the articles. In such kind of situation, engineers had to pay their attention on the calculating examples, and therefore most published books adopted a lot of examples to explain the calculating method of ACI Code. Actually, the ACI 318 1963 Code was not important for engineers, but these calculating examples were more important than it.
In the mechanics of composite materials, the theoretical rules do not permit the members to produce the cracks. In my original concept, I also think the reinforced concrete cannot permit to produce the cracks. However, many houses are designed by the USD method, but the crack problem doesn't affect the structural safety. In other words, the influence of crack problem is very finite for the members, and therefore I change my mind to support the cracks.
I think reinforced concrete should follow the WSD method, and the researchers must continue the researches. If the calculating method is still the USD method, the factor interdependent problem shall have to be solved to avoid the design failure. The factor interdependent problem is a problem of "Chicken or Egg", and I think this problem cannot be solved by computer in limited time for the engineering purposes. Of course, it's possible to become a research topic, but I think everyone still has to face the problem.
References
C. S. Whitney proposed a simple calculating method in 1937, and it tried to replace the traditional calculating procedures of composite material. This method has many advantages, fast calculation for the beam member, for example, but it does NOT follow the mechanics of composite materials. As everyone knows, Whitney's method is an approximating method to obtain the inaccurate result, and it is based on the experimental data without any mechanics or theory to support.
In the ACI 318 1971 Code, the WSD method is dropped, and the USD method is adopted to replace it. In 1980s, the personal computers were available to all, but the USD method had replaced the WSD method completely. Actually, nobody calculates the beam, column, wall, or plate by hand except that students must pass the required examinations. Besides, engineers are also possible to calculate the members by hand sometimes, but this is just to complete the double check procedure for the special cases.
In the ACI 318 1963 Code, the thickness of the code is less than 80 pages, and it doesn't have the commentaries to explain the articles. In such kind of situation, engineers had to pay their attention on the calculating examples, and therefore most published books adopted a lot of examples to explain the calculating method of ACI Code. Actually, the ACI 318 1963 Code was not important for engineers, but these calculating examples were more important than it.
In the mechanics of composite materials, the theoretical rules do not permit the members to produce the cracks. In my original concept, I also think the reinforced concrete cannot permit to produce the cracks. However, many houses are designed by the USD method, but the crack problem doesn't affect the structural safety. In other words, the influence of crack problem is very finite for the members, and therefore I change my mind to support the cracks.
I think reinforced concrete should follow the WSD method, and the researchers must continue the researches. If the calculating method is still the USD method, the factor interdependent problem shall have to be solved to avoid the design failure. The factor interdependent problem is a problem of "Chicken or Egg", and I think this problem cannot be solved by computer in limited time for the engineering purposes. Of course, it's possible to become a research topic, but I think everyone still has to face the problem.
References
- C. S. Whitney（1937）Design of Reinforced Concrete members Under Flexure or Combined Flexure and Direct Compression, Journal of American Concrete Institute, Vol.33, pp.483-498
- S. P. Timoshenko & J. M. Gere（1972）Mechanics of Materials, New York: Van Nostrand Reinhold Co.
- Wikipedia, Chicken or the egg, http://en.wikipedia.org/wiki/Chicken_or_the_egg
