International Concrete Abstracts Portal

The purpose of Closing Remarks is usually to integrate the concepts contained in contributions to a symposium volume with the intention of showing new directions for future work, I hope you will forgive me if I deviate from this pattern, I feel that this symposium volume in memory of our common friend Douglas McHenry should not be concluded without our having paid tribute to the example that he offered us as a researcher, It first occurred to me how advanced McHenry's fundamental approach to research was when in 1965 I attended a lecture by the British biologist and Nobel Prize winner Medawar who analyzed the implications of the rapidly burgeoning quantity of scientific data. He prophesied that researchers, even in specialized fields, would be progressively snowed under by numerical data. The human brain is incapable of storing accessibly such a host of records and thus cannot synthesize the data into new ideas, Medawar therefore emphasized the necessity of replacing the many keys opening doors to single rooms with one master key giving direct access to a whole building. He warned against relying on computer systems for extracting meaning from masses of data. Computers cannot replace insight and creativity. The intention of referring to Medawar's statement is to show that McHenry's work as a researcher was inspired to a large extent by a similar spirit, His famous paper "A New Aspect of Creep in Concrete and its Application to Design" (1), published in 1943, typifies his innovative approach. It is a paper full of new ideas, anticipating future developments, but is at the same time an effort to find the master key the designer desperately needed,

Results of a high-amplitude, destructive-level vibration test of a full-scale, 4-story reinforced concrete bare-frame structure indicated that the dynamic response characteristics remained rela-tively constant at motion amplitudes less than the calculated elastic limit (but above the design capacity of the structure). However, as this limit was exceeded, the structure exhibited nonlinear response behavior that was accompanied by significant variations in the dynamic characteristics, causing major structural damage. Empirical relationships relating inelastic response properties to elastic response values and ductility were developed. Although these relationships were derived from data of this test structure, they may be used to predict the approximate range of inelastic response of reinforced concrete structures from known elastic response properties and expected ductility factors. This paper also compares the structure's response properties resulting from lower-amplitude vibration tests conducted before and after the high-amplitude destructive test (i.e., on the undamaged and damaged structure). The response of the damaged structure to forced vibration appears to be consistent with the response of the undamaged structure except that the damaged structure exhibited larger periods, higher damping ratios, and some deflected shape discontinuities.

A procedure for estimating the inelastic respond\se of reinforced concrete structures to ser\severe ground motion is described. This procedure combines analytical structural engineei\ring methods with interpreitve analyses of response spectra and can be used by practicing engineers without complex computer analysis. The solution results in estimated values for peak structural response, peak ductility demands, equivalent responese periods of vibration, equivalent percentages of creitical damping, and reserve capasities. Examples of the procedure are presented, and their results are compared with data obtained from recorded motion of actual reinforced concrete structures.

The paper presents a model capable of predicting the post-cracking response of reinforced and prestressed concrete members subjected to complex loading. The angles of inclination of the compression diagonals in the walls of the truss model are determined from strain compatibility conditions. These compatibility conditions in conjunction with the equilibrium conditions for the truss and the load-deformation relationships for the members of the truss enable the full response of the model to be determined; i.e. the strain in the longitudinal and web reinforcements as well as the various eformations of the beams at all load levels can be predicted. Experimental results are used to confirm the truss model's predictions. It is shown how the truss model could be used in the design office.

This paper presents details of an analysis for strength at failure of prestressed beams subjected to a complex system of applied loads consisting of combined torsion, shear and bending. It is based on a modified skew bending approach incorporating the use of strain compatibility over the beam cross-section to permit recognition of a "non-flat" yield region typical for cold drawn reinforcement. A significant feature of this analysis is the use of a biaxial strain criterion to recognize that the magnitude of the limiting strain in the compressed concrete at failure varies with different combinations of torsion, shear and bending. Other contributors working on this problem have used either a constant limiting concrete strain of magnitude 0.003 as for pure flexure, or some constant fraction of this amount throughout all possible load combinations involving torsion, shear and bending. Incorp-orated also in the determination of the ultimate strength is the ' recognition of the presence of shear stresses on the uncracked failure surface. Results of tests made on eighty four beams were used to verify this analysis. An excellent and consistent correlation was obtained between theoretical and test values for bending moments and resisting torques.