International Concrete Abstracts Portal

This study used finite element analysis to examine how tendon configuration affects the temperature behavior of post-tensioned concrete structures during fire exposure. The thermal behavior of various tendon configurations was modeled, showing good agreement with experimental data. Parametric studies found that unbonded single-strand tendons (S) and prestressing (pretensioned) strands (R) had lower thermal resistance than bonded post-tensioned tendons (B), unbonded post-tensioned tendons (U), and grouted extruded-strand tendons (G). The S and R specimens stayed at or below the critical temperature for one-way slabs, validating current safety codes. The B, U, and G specimens remained well below critical temperatures, indicating that a thinner concrete cover might suffice. These findings highlight the need to consider tendon configuration in structural fire-resistance evaluation and incorporate heat resistance assessment to ensure the safety and efficiency of prestressed concrete structures during fires.

Lap-splicing of longitudinal reinforcing bars in shear walls is often encountered in practice, and the transfer of forces in lap-spliced reinforcing bars to the surrounding concrete depends on the bond strength. Buildings with shear walls during an earthquake develop plastic hinges in the shear walls, particularly where the reinforcing bars are lap-spliced. Brittle failure is commonly observed in lap-spliced reinforced shear walls, which needs to be minimized by choosing the appropriate percentage of lap-spliced reinforcing bars. Therefore, it is essential to address the detailing of the lap-spliced regions of reinforced concrete (RC) shear walls. Several seismic design codes provide guidelines on lap-spliced detailing in shear walls related to its location, length of lap-splice, confinement reinforcement, and percentage of reinforcing bars to be lap-spliced. In this study, the percentage of reinforcing bars to be lap-spliced at a section is examined with staggered lap-splicing of 100, 50, and 33% of longitudinal reinforcing bars, in addition to a control RC shear wall without lap-splicing. This study tested four half-scale RC shear walls with boundary element (BE), designed as per IS 13920 and ACI 318, under quasi-static reversed cyclic loading. From the experimental study, it is observed that the staggered lap splicing of reinforcing bars nominally reduces the performance of shear walls under cyclic load in terms of the reduced flexural strength, deformation capacity, energy dissipation, and ductility of the shear walls compared to the control shear wall without lap splicing. It is also observed that the unspliced reinforcing bars do not sustain the cyclic loading in staggered lap-splice after the postpeak. Current provisions of ACI 318, Eurocode 2, and IS 13920 recommend staggered lap-splice detailing in shear walls. However, from the current study, shear walls with different percentages of staggered lap-splices show that the staggered lap-splice detailing in shear walls does not improve its seismic performance.

The present study demonstrates the feasibility of using longitudinal hybrid reinforcement in concrete columns in seismic zones. In this research, four concrete columns were constructed and subjected to quasi-static cyclic loading, featuring a combination of steel and glass fiber-reinforced polymer (GFRP) longitudinal reinforcement. Two reference columns were fabricated and reinforced in the longitudinal direction with steel bars. These columns had a 400 x 400 mm (15.8 x 15.8 in.) cross section and 1850 mm (72.8 in.) overall height. All the columns were reinforced with GFRP crossties and spirals in the horizontal direction. The variable parameters were the transverse reinforcement spacing, axial load ratio, and column configuration. The outcomes of this research clearly showed that reinforced concrete (RC) columns that are properly designed and detailed longitudinally with hybrid reinforcement (GFRP/steel) could achieve the drift limitation in building codes with no strength degradation. Further, these hybrid-RC columns displayed enhanced energy dissipation capacity, superior ductility, and improved post-earthquake recoverability compared to columns reinforced longitudinally with steel. The promising results of this study represent a step toward the use of longitudinal hybrid reinforcement in lateral-resisting systems.

This study investigated the serviceability behavior and strength of polypropylene fiber (PF)-reinforced self-consolidating concrete (PFSCC) beams reinforced with glass fiber-reinforced polymer (GFRP) bars. Five full-scale concrete beams measuring 3100 mm long x 200 mm wide x 300 mm deep (122.1 x 7.9 x 11.8 in.) were fabricated and tested up to failure under four-point bending cyclic loading. Test parameters included the longitudinal reinforcement ratio (0.78, 1.18, and 1.66%) and PF volume (0, 0.5, and 0.75% by concrete volume). The effect of these parameters on serviceability behavior and strength of the test specimens is analyzed and discussed herein. All the beams were evaluated for cracking behavior, deflection, crack width, strength, failure mode, stiffness degradation, and deformability factor. The test results revealed that increasing the reinforcement ratio and PF volume enhanced the serviceability and flexural performance of the beams by effectively restraining crack widths, reducing deflections at the service and ultimate limit states, and decreasing residual deformation. The stiffness exhibited a fast-to-slow degradation trend until failure for all beams, at which point the beams with a higher reinforcement ratio and fiber volume evidenced higher residual stiffness. The cracking moment, flexural capacities, and crack width of the tested beams were predicted according to the North American codes and design guidelines and compared with the experimental ones. Lastly, the deformability for all beams was quantified with the J-factor approach according to CSA S6-19. Moreover, the tested beams demonstrated adequate deformability as per the calculated deformability factors.

Reinforced concrete (RC) structure design codes stipulate various design limits to prevent the brittle failure of members, as well as ensure serviceability. In the structural design of RC walls, the maximum shear strength is limited to prevent sudden shear failure due to concrete crushing before the yielding of shear reinforcement due to over-reinforcement. Despite the increase in wall shear strength provided by a compression strut, the maximum shear strength limit for walls in the ACI 318-19 Code is the same as the maximum torsional strength. Consequently, the shear strength of large-sized walls with high-strength concrete is limited to an excessively low level. The ACI 318-19, Eurocode 2, CSA-19, and JSCE-17 standards provide similar equations for estimating wall strength, but their maximum shear strength limits for walls are all different. In this study, experimental tests were conducted on nine RC wall specimens to evaluate the maximum shear strength. The main variables of the specimens were shear reinforcement ratio, compressive strength of concrete, and failure mode. The experimental results showed that the maximum load was reached after yielding of shear reinforcement, even when the shear reinforcement ratio was 1.5 times higher than the maximum shear reinforcement ratio specified in the ACI 318-19 code. In addition, the measured shear crack width of all specimens at the service load level was less than 0.42 mm (0.017 in.). The shear strength limits for walls in the current codes were compared using 109 experimental results failing in shear before flexural yielding or shear friction failure, assembled from the literature. The comparison indicated that the ACI 318-19 Code limit underestimates the maximum shear strength of walls, and it particularly underestimates the maximum shear strength of walls with high-strength concrete or barbell-shaped cross sections. Additionally, this study proposes an equation for estimating the maximum shear strength limit of walls based on the truss model. The proposed equation predicted the maximum shear strength of RC walls with reasonable accuracy.