N°210. 1991. Behavior and Analysis of Reinforced Concrete. Structures under Alternate Actions Inducing Inelastic Response.

During the second half of the eighties, with its new future Model Code already under full development, the CEB feit that the time had arrived to adjourn and make known its ideas on the broad and rapidly evolving field of non-linear analysis of structures. 

In fact, while the number of applications of non-linear analyses for important and non conventional structures was increasing fast, and recourse to such analyses was explicitly allo wed by the M C, no guidance was available to the designer for the selection of the models more suited to each specific case. 

On the other hand, the existence and the accessibility of a nümber of sophisticated F.E. codes for the non-linear analysis of reinforced concrete structures, was a cause more for concern than · for re lief, because of their lack of validation over a sufficient spectrum of different applications. 

The terms of reference given by the CEB to the new group to be formed stated that it should concern itself with those models and methods of analysis adequate for dealing with genera! load and stress histories. 

This decision was obviously of great consequence, in that involved the exclusion of a number of classica! and well proven models and methÖds, but it was certainly a necessary one: the assumption of a proportional increase of all loads acting on a structure is not only unrealistic but also not conservative in assessing the likelihood of attaining a given limit-state. 

Furthermore, since a fairly large number of real loads fluctuate with time, and some of them may also reverse their action, it was finally decided to characterize the scope of the group's work with the widest of its attributions, by titling it as: "Behaviour and Analysis of Reinforced Concrete Structures under Alternate Actions inducing Inelastic Response". 

From the early discussions on the plan of activity, the members concurred that the first step had to be the preparation of a document of fundamental nature. 

The document would contain a review of the pertinent existing knowledge in the area of constitutive modeling of concrete, steel, bond and of their interaction. It should also discuss the problems encountered in assembling the various elements with the purpose of constructing the model of an element made of reinforced concrete. 

In selecting the material for inclusion, the main criterion would be its ability to reproduce, adequately if crudely, non proportional stress/strain paths, with reversed loading. Whether 

physically or empirically based, very simple or sophisticated, long established or just come out, the models would be presented in framework as rational as possible, certainly accompanied by comments on their advantages and limitations, but without attempts to rank them on the basis of their relative merits. 

Tuis program of work, with the addition of a final part dealing with the solution strategies for the numerical integration of non-linear equations, bas materialized in the present Volume 1. 

Admittedly distant from the immediate needs of professional practice, Volume 1 aims at being a basic, comprehensive and relatively easy-to-read document, hopefully useful as a reference for non specialists wishing a more conscious approaèh to the use of the available sophisticated computational tools.