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.

An investigation was conducted to develop information on the time-dependent deformation behavior of concrete in the presence of temperature, moisture, and loading conditions similar to those en-' countered in a prestressed concrete reactor vessel (PCRV). Variables were one concrete strength (6000 psi (41 MPa) at 28 days), three 7 aggregate types (chert, limestone, and graywacke), one cement (Type II), two types of specimens (as-cast and air-dried), two levels of tempera-!, ture during test 73 F and 150 F (23 C and 66 C), and four types of "1, loading (uniaxial, hydrostatic, biaxial, and triaxial). There were 66 test conditions for creep tests and 12 test conditions for unloaded or control specimens. Experimental results are presented and discussed. Comparisons are made concerning the effect of the various test conditions on the behavior of concrete and general conclusions are formulated. Research performed under Int eragency Agreement No. AT-(40-1)-4128 for the Oak Ridge National Laborat ory operated by Un ion Carbide Corporation under contract with the Energy' Research and Deve lopment Administration.

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.

An analytic study was made of the effects of creep andshrinkage in lightly loaded continuous girders and frames by means of computer programs which were developed to simulate the timevarying behavior of a structure under sustained variable loading. Variations in the internal moments with time were found to be very large, a 50 percent increase or decrease in the maximum moment being not unusual. Concrete shrinkage was found to have a much more important effect on long-term moment redistribution than creep. The quantity and distribution of reinforcement also had a critical effect, both on moment redistribution and long-term deflection.