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,

Field measurements on two existing reinforced concrete slabs had to show that the chosen strengthening methods were successful. This was done by determining the bending stiffnesses of the two slabs before and after strengthening. The strengthening methods and the measuring equipment are described. The results showed that the sub-sequent strengthening provided an increase of the bending stiffnesses. It was also found that to achieve good quantitatif results a load test is required, whereas the actual floor loading produces only qualitatif results.

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.

Previously published experimental data on the effect of nuclear radiation on the properties of plain concrete are summarized and evaluated. Neutron radiation with a fluence of more than 1 x 1019 n/cm 2 may have a detrimental effect on concrete strength and modulus of elasticity. Thermal coefficient of expansion, thermal conductivity and shielding properties of concrete are little affected by radiation. Radiation damage is mainly caused by lattice defects in the aggregates which cause a volume increase of aggregates and concrete. Different aggregates show different radiation resistance so that the selection of suitable aggregates is the most important parameter in the design of a radiation resistant concrete.

The random behavior of reinforced concrete elements at de-formational limit states and at the ultimate limit state is analyzed by a second moment approximation. The deterministic and stochastic parameters involved, their functional and stochastic dependences, and their experimentally based statistics are discussed. The resulting variances of ultimate carrying capacity and ductility and of crack development are shown. It should be noted that ultimate ductility has an especially strong statistical variation independent of the amount of compressive reinforcement. A two-span beam is analytically modeled to elaborate first order approximations of the means and variances of simultaneously acting live loads and temperature effects which cause different limit states. Imposed deformations do not greatly influence ultimate load-carrying capacity provided that there is sufficient ultimate ductility. However, load-carrying capacity with respect to a limit state of allowable crack width is substan-tially reduced by simultaneously acting imposed deformations.