International Concrete Abstracts Portal

The behavior of laterally loaded flat-plate structures is strongly influenced by the nonlinear deformations at the plate-to-column connections. In this paper, a simple procedure is described for predicting the nonlinear moment-rotation behavior of flat-plate-to-column connections. That behavior is expressed by standardized moment-rotation functions. These functions were derived using a modified Rambert-Osgood function and all available experimental data. The influence of the most significant connection parameters such as the steel ratio, concrete strength, gravity loading, etc., on the connection behavior is incorporated into the functions. A physical model of the column region is described which facilitates the incorporation of the functions into a structural analysis computer program. The accuracy of the functions has been demonstrated for several plate-column connections. The computer analysis program is also described and an example is considered to compare results obtained from the program with those published in the literature.

This paper reviews the development of deflection calculation procedures and comments on the risk of computational errors. It then discusses practical considerations affecting deflection and their limitations. It assesses the effect of nine parameters on the variability of deflection by reference to two example beams. Finally, the paper recommends further laboratory and analytical research and makes suggestions on how design engineers may improve the accuracy of their deflection computations.

Studies are limited on the early age performance of high-strength cold weather concretes and their shear strength interaction in cold weather. This paper presents shear transfer strength characteristics between regular high-strength concrete and (i) methyl methacrylate-based polymer concrete and (ii) magnesium phosphate based concrete in subfreezing temperatures. Analytical expressions were developed based on shear transfer hypothesis and verified by experimental results. The experimental study included tests on cylinders and L-shaped push off specimens to determine the early age shear interlock and shear frictional resistance between high-strength regular portland cement concrete and cold weather high-strength concretes as is experienced in rehabilitation of bridge decks and other infrastructure systems. Studies indicated that at early age of 24 hours, shear transfer strength of 1400 psi can be obtained with the use of appropriate material and shear reinforcement. The study also indicated the ACI 318-89 code limits on the shear-friction strength are too conservative even at early ages for high-strength cold weather concretes.

Concrete bridges in the United States constitute about fifty percent of the total number of highway bridges. Recent studies indicate that many of these bridges deteriorate due to age, corrosion of reinforcement, fatigue, cracking and spalling of concrete, and/or human error. Limited funds are available for rehabilitation, strengthening, and replacement. Therefore, there is a need for methods to identify the parts of concrete girder bridges most sensitive to damage using reliability models. This may help lower the costs of checking, inspection, and repair. Load and resistance sensitivity functions for the ultimate flexural capacity limit state of simply supported bridge girders are included. The study indicates that the reliability of bridge girders depends mostly on the strength and location of steel.

This paper presents the evaluation of seismic performance of a special moment-resisting (SMR) frame building and an intermediate moment-resisting (IMR) frame building designed in accordance with the NEHRP provisions and ACI Code 318-83. The annual limit-state probabilities for both SMR and IMR frames are determined by integrating the seismic hazard curve and structural fragility curve. From the comparison between the calculated annual limit-state probability and the specified acceptable risk levels, the seismic performance of a structure can be evaluated. In the NEHRP provision, if reinforced concrete frames are used to resist earthquake forces, the SMR frame is required for buildings belonging to higher seismic performance categories such as Categories D and E. Even though the SMR frame has a higher ductility than the IMR frame, the SMR frame is only designed for 50 percent of the strength required for the IMR frame. As demonstrated in this study, the IMR frame may perform better than the SMR frame in the event of an earthquake. Thus, the concept employed in the NEHRP provisions to protect high-risk and essential buildings needs careful reexamination.