International Concrete Abstracts Portal

The general purpose of reinforcing bars in slabs-on-ground is to control crack widths at the top surface of a slab. As the amount of reinforcement increases across the joint, the probability of out-of-joint cracking increases, as tighter cracks may occur at closer spacing than the joints. The Q&A provides some guidance on the amount of reinforcement crossing the joint and its role.

The PS=Ø system allows engineers to design post-tensioned (PT) and reinforced concrete members with more restraint releases and without the construction schedule delays of traditional pour strips. With or without temporary PT stressing strips, PS=Ø couplers can be used as restraint relief details in slab-to-slab, slab-to-wall, and beam-to-beam joints.

Mehdi Khorasani, Giovanni Muciaccia, and Davood Mostofinejad Synopsis: The externally bonded reinforcement on grooves (EBROG) technique has been recently shown to outperform its rival techniques of surface preparation (such as externally bonded reinforcement, EBR) employed to delay the undesirably premature debonding of fiber reinforced polymer (FRP) from the concrete substrate in retrofitted structure. However, the behavior of EBROG method under fatigue loading has not been assessed yet, and the present study is the first attempt to achieve the above aim. For this purpose, an experimental program is conducted in which 16 CFRP-to-concrete bonded joints on the concrete slab prepared through the EBROG and EBR techniques are subjected to the single lap-shear test and fatigue cyclic loading. Furthermore, the bond behavior of CFRP strips-to-concrete substrate is investigated in this research in terms of the load capacity, slip, debonding mechanism, and fatigue life. The results showed that the grooving method improved the bond properties of CFRP-to-concrete joints under fatigue loading. By using this alternative technique, the number of cycles until failure (fatigue life) increases incredibly under the same fatigue cycle loading and the service life of strengthened members could be improved under fatigue loading. Furthermore, the effects of different loading levels on the behavior of CFRP-concrete joints installed by EBROG method are evaluated. The results showed that fatigue life of strengthened specimens decreases by increasing fatigue upper load limit. Finally, a new predictive equation was developed based on plotting the maximum applied fatigue load versus fatigue life curves for CFRP-to-concrete bonded joints for the EBROG method.

This paper investigates the use of glass fiber reinforced polymer (GFRP) bars to reinforce the jointed precast bridge deck slabs built integrally with steel I-girders. In addition to a cast-in-place slab, three full-size, GFRPreinforced, precast concrete slabs were erected to perform static and fatigue tests under a truck wheel load. Each slab had 200 mm (7.9 in) thickness, 2500 mm (98.4 in) width normal to traffic, and 3500 mm (137.8 in) length in the direction of traffic and was supported over a braced twin-steel girder system. The closure strip between connected precast slabs has a width of 125 mm (4.9 in) with a vertical shear key, filled with ultra-high-performance concrete (UHPC). Sand-coated GFRP bars in the precast slab project into the closure strip with a headed end to provide a 100 mm (3.9 in) embedment length. A static test and two fatigue tests were performed, namely: (i) accelerated variable amplitude cyclic loading and (ii) constant amplitude cyclic loading, followed by static loading to collapse. Test results demonstrated excellent fatigue performance of the developed closure strip details, with the ultimate load-carrying capacity of the slab far greater than the demand. While the failure in the cast-in-place slab was purely punching shear, the failure mode in the jointed precast slabs was punching shear failure with incomplete cone-shape peroration through the UHPC closure strip, combined with a major transverse flexural crack in the UHPC strip. This may be attributed to the fact that the UHPC joint diverted the load distribution pattern towards a flexural mode in the UHPC strip itself close to failure.

A cast-in-place reinforced concrete footbridge built in 1967 suffering from extensive concrete spalling and rebar corrosion needed to be replaced. The use of a steel Pony-Warren truss combined with thin precast UHPFRC slabs linked by short UHPFRC field-cast joints was selected to build an innovative, durable and aesthetic footbridge minimizing impact on traffic during construction. Material rationalization allowed respective reductions of 64 % and 91 % of concrete and rebar volumes in the slab in comparison to a conventional reinforced concrete slab. The design process was completed with non-linear finite element calculations to obtain an adequate behaviour of the UHPFRC slabs and joints at service and ultimate limit states. A full-size proof specimen was then tested under positive bending moment and confirmed being adequate and fulfilling all the design specifications. Construction of the precast slab was successful and required less time than a conventional slab. The long-term performance provided by the UHPFRC slab will be followed up in the next decades.