International Concrete Abstracts Portal

A detailed investigation was made to study the shear transfer between precast prestressed beams and in situ concrete in a relatively new method of construction of continuous bridge decks where the ends of precast beams are connected to an integral in situ crosshead away from the supports. The main advantages of this method are: Increasing the span length, standardization of the beams, elimination of the deep support girder, obtaining full continuity for the dead and live loads, and possibility for using straight beams in skew and curved bridges. The prestressed beam used in the investigation was an inverted T-section, and it was concluded that: 1) The shear force is transferred from a small length at the end of the beam. 2) The in situ concrete nibs can take this shear force without stirrups. 3) There is no need either to project all the bars into the in situ concrete or to prestress the connection transversely. 4) The shape of top flanges of the prestressed beam had a significant effect on the shear transfer capacity of the connection. 5) For the beams without top flanges, the shear strength of the connection can be modified by using transverse prestressing, web shear connectors, or projection of the bars.

According to the trade literature, the determinations of location, direction, and the cover thickness over a single steel bar in concrete are relatively easy and reliable from a magnetic measurement if the bar diameter is known. The estimation of the bar diameter is also possible if the cover thickness is known, although these results are less reliable. Only recent publications suggest double measurements from which both the cover thickness and the bar diameter can be estimated without previous knowledge of either of them. Unfortunately, the accuracy of diameter determination remains unimproved even with these methods. This paper attempts to present the further improvement of the magnetic determination of bar characteristics. The basic idea is to combine a magnetic device with a computer that calculates, without any previous knowledge about the bar: 1) the thickness of the concrete cover above the bar and, 2) the diameter of the bar. Preliminary data also indicate that distinction can be made whether the tested area is above a single bar or multiple bars, although this is not discussed in this paper. Experimental data obtained on laboratory specimens illustrate the new method.

Presents the results of radar tests conducted in a controlled laboratory environment to provide an independent assessment of the usefulness of the technique for investigating in situ concrete structures. Parameters studied include size and thickness of concrete elements, the presence of voids and steel reinforcement, and the influence of moisture. The use of a commercially available computerized signal enhancement system has also been examined to assess the potential benefits. Results are presented that include typical signal response traces and show the degree of precision that can reasonably be expected from radar measurements under a range of practical circumstances. Results are considered in the light of the basic theoretical factors and a number of important limitations are identified. It is concluded that the method offers considerable potential in a range of structural applications but is subject to a number of practical limitations, and guidance is offered concerning experimental technique and interpretation of results.

Recently, deterioration of reinforced concrete structures has been an issue of concern, such that repair methods and repair practice have been studied by many organizations. In this study the flexural behavior of FRP reinforced concrete beams (FRPC beams) was studied. The experimental values of the tensile stress in the main reinforcement, the concrete crack width, and the center displacement of FRPC beam agreed well with the calculated values. The flexural behavior of repaired reinforced concrete beams (RRC beams) using FRP and polymer mortar was studied. The results showed that tensile stress in the main reinforcement, the concrete crack width, and the center displacement of the beam were decreased after repair work. The elastic theory of reinforced concrete was still effective on the repaired beam. The values of tensile stress in the main reinforcement, and the center displacement of the beam could be calculated.

This paper deals with a new type of semiprefabricated slab. The slab is made of precast thin slab stiffened by a set of folded wire fabric including cast in-situ topping concrete. This study covers both the salient features of design and construction of this flooring system and experimental work carried out to study the flexural behavior of the slabs cast using the system. The results of the experiment showed that composite precast slab consisting of the precast thin slab and in-situ topping concrete can be designed as a monolithic component.