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This paper presents the results of both experimental and numerical investigations on the overall structural performance of two-equal-span reinforced concrete perforated (castellated) beams subjected to external pre-stressing. First, the effects of providing castellated openings along with the application of external pre-stressing on both the ultimate capacity and the percentage of moment redistribution were investigated experimentally. Then, after validation of the numerical modelling, the effects of controlling the parameters on the percentage of moment redistribution were investigated numerically. Experimental results showed that providing castellated openings accelerated the appearance of both flexural and shear cracks, and decreased the ultimate capacity by about 24% compared to that of a solid beam. Moreover, application of external pre-stressing on the castellated beam compensated for the reduction in ultimate capacity and outperformed it by about 9% compared to that of a solid beam. Based on the numerical results, it appears to be better to increase the amount of main tensile steel and strand eccentricity at the hogging moment zone, as well as increase the effective pre-stressing force, to reduce the percentage of moment redistribution at both sagging and hogging moments.

Fibre-reinforced polymer bars are rapidly becoming an approved alternative to conventional reinforcing steel bars, especially for severely exposed structures such as bridges. This paper reports on an experimental study on the bond characteristics of both sand-coated and ribbed-surface glass-fibre-reinforced polymer bars embedded in high-strength concrete (HSC). A total of 145 pull-out tests were conducted to examine the effect of varying parameters on the bond characteristics, namely embedment length, bar diameter, surface treatment and concrete cover. In addition, 45 pull-out tests were conducted to investigate the effect of providing headed-end anchorage for the sand-coated bars. The experimental results showed that the sand-coated bars exhibited better bond strength than the ribbed-surface bars, which entailed lower development lengths. Thus, based on the experimental results, expressions for the development length of both sand-coated and ribbed-surface bars embedded in HSC were developed and compared against the results of formulae in available design standards. The comparison revealed that ACI 440-1R-06 produced lower conservative results than CAN/CSA S806-12.

Two configurations of closure strips between precast reinforced concrete (RC) slab panels were fabricated and filled with either non-shrink grout or ultrahigh-performance strain-hardening cementitious composite (UHP-SHCC) material. The strips were then strengthened with externally bonded carbon-fibre-reinforced polymer (CFRP) sheets in order to compensate the drawback associated with decreasing the amount of connected steel reinforcing bars required to transfer the bending moment between panels. In total, 12 specimens divided into three groups were cast and tested under short-term non-reversed repeated patch loads simulating wheel load at the central joint. The test results showed that the UHP-SHCC filling material enabled the connected panels to exhibit more ductile behaviour compared with the panels whose closure strips were filled with non-shrink grout. On the other hand, the CFRP strengthening sheets for the first configuration of the closure strip failed to restore the ultimate capacity of the un-strengthened monolithic specimen. However, the second configuration, using UHP-SHCC filling material, enabled the connecting panels to restore lost capacity, with a performance improvement of about 14% compared with the un-strengthened monolithic specimen.

A reinforced concrete beam with a recess is an example of a non-prismatic beam, which develops stress concentrations at the corner of the recess owing to the abrupt change in its depth. This entail...

This paper presents the experimental findings for different strengthening techniques applied on defected reinforced-concrete cantilever slabs to restore lost flexural capacities owing to insufficient bond length of the main tensile steel. The restoration technique was based on compensation of the main tensile steel by near-surface mounted steel bars, externally bonded steel plates or externally bonded carbon fibre-reinforced polymer sheets. In addition, new hybrid techniques are presented, which merge the traditional techniques with a 20 mm thick ultra-high-performance strain-hardening cementitious composites (UHP-SHCC) layer. It was found that the strengthening technique based on the embedded steel bars on the UHP-SHCC overlay enabled the strengthened slab to restore its lost capacity and outperformed it by about 5% compared to that of the properly detailed slab. Nevertheless, this restoration was at the expense of the exhibited ductility. Conversely, the strengthening technique based on the application of externally bonded steel plates on a transition layer of the UHP-SHCC material enabled the strengthened slab to restore the lost capacity by about 96% as well as to outperform its ductility by more than 29% compared to those of the properly detailed slab.

Experimental findings and detailed analyses of the overall structural performance of properly detailed and strengthened reinforced concrete (RC) frame structures with defects are presented. Two strengthening techniques were implemented on the faulty frame structures in order to restore lost capacity due to improper detailing of the main tensile steel for both closed- and open-jointed frame systems. The strengthening techniques implemented were near-surface mounted (NSM) steel bars and external un-bonded prestressed steel bars. Three defects were considered, two of them pertaining to frame structures with closed joints and one pertaining to open-jointed frame structures. In total, 11 RC frame specimens divided into four groups were configured, casted and then tested until complete collapse under monotonic incremental loading. It was found that strengthening based on external prestressed bars had a significant effect on both the ultimate capacity and developed ductility of strengthened open-jointed frame structures, while its effect on closed-jointed frame structures was small. For the closed-jointed frame structures, strengthening with NSM steel bars produced greater enhancement in ultimate capacity than the prestressed bar strengthening technique.

This paper presents an experimental study for different details of a beam–column T-joint made from a concrete-filled steel tube (CFT) system, where both girder and column were CFT type. A total of ten half-scale specimens divided into three groups were studied. Group No. 1 was a control group to obtain a comprehensive overview of the CFT system compared with reinforced concrete, and also to study the effect of shear connectors in both girder and columns on the general behaviour of such a system. The remaining two groups represented two different details of beam to column connection with different strengthening techniques. Global responses such as the peak strength, deformation, strain and ductility achieved were recorded and analysed under the effect of monotonic static loading. The experimental data showed the great influence of the shear connectors and detailing of the joint on the overall behaviour of such joints made from CFTs. In addition, the superiority of the CFT system over the equivalent reinforced concrete system under the same loading conditions is highlighted.