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The long-term movements of in-situ reinforced concrete columns in two structures are reported through the construction stage to occupancy and subsequently in service. The columns were extensively instrumented to measure strains, temperature and moisture changes; in addition, a stress meter was incorporated in the second structure at the base of an internal column to relate the field movements and their effects to the load actually carried by the column. The results show that the inelastic movements in concrete cause a gradual load transfer to the steel reinforcement. In one structure steel stresses in excess of the permissible design values were noted. The assumed design dead load components of the working loads were realized in the lower columns of the structure but not in the upper storeys. After nearly five years in service, the concrete in the columns of the second structure were found to carry loads varying from 50% to 80% of the measured load carried by the columns. It is shown that a major proportion of the loads carried by the columns result from dead loads and that only about 10%-20% of the total design loads constitute imposed loads.

The principles are presented for the main types of the dif- . ferentiated, structural fire engineering design systems, in practice at present or anticipated to be applied in the future. Such design systems are generally based on real fire exposure characteristics, given by the gastemperature-time curves of the complete fire process and specified in detail with respect to the influence of fire load and the geometri-cal, ventilation and thermal properties of the fire compartment. The design procedure can be in its entirety analytical or combined analyti-cal and experimental. In the latter case, real fire exposure conditions can be transferred to the heating conditions according to the standard fire resistance test via the concept equivalent time of fire duration. Starting from the present state of knowledge, the possibilities are discussed for a practical application of a complete analytical, diffe-rentiated design in regard to fire exposed, reinforced and prestressed concrete structures. Finally, the various sources and kinds of uncer-tainty in the differentiated design procedure are briefly dealt with within the framework of the structural fire safety problem.

Analytical predictions of thermal and mechanical behaviour of reinforced concrete structures exposed to differentiated complete fire processes including the cooling phase are presented and verified by tests. The modelling of the fire response comprises a heat flow ana-lysis in the first step and a structural analysis in the second step, based on two separate computer programs. The evaluated structural fire response is compared with the measured behaviour in a great number of experimental tests in which, the fire process and the external load level are widely varied. The experimental investigation refers to a well-defined hyperstatic structure, viz. a reinforced concrete plate strip fire-exposed on one side and completely fixed against rotation at both ends while axial movement is free to develop. The outline of the project is built on the philosophy of a functionally based, dif-ferentiated design procedure for fire exposed, load-carrying and separating structures. Such a design procedure refers to performance criteria and postulates that the real physical processes with res-pect to fire exposure, heat transfer and structural behaviour are predicted as far as possible.

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.

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.