International Concrete Abstracts Portal

To investigate the seismic behavior and resilience of reinforced concrete (RC) slit shear walls with either low-bond or debonded high-strength reinforcements, eight shear walls with different cross-sectional forms and types of longitudinal reinforcing bars were fabricated and subjected to both compressive loading and cyclic lateral loading. The experimental results indicate that the test shear walls with anchored infilled steel columns (ISCs) failed in flexure of the subshear walls due to the form of a vertical slit. The use of both low-bond high-strength reinforcing bar (SBPDN reinforcing bar) and an anchored ISC significantly increased the ductility of the shear wall without reducing the stiffness at the early deformation stage or the seismic resistance. Interestingly, the debonding of the longitudinal reinforcing bar reduced the strain of the transverse reinforcement. The debonding and low bonding of the longitudinal reinforcing bar increased the contribution ratio of deformation due to steel-bond slip but decreased the contribution ratio of shear deformation. Moreover, the anchorage of an ISC plays an important role in the contributions of shear and flexural deformation. The models proposed in the current provisions can be used to accurately predict the seismic resistance of shear walls with debonded and low-bond high-strength reinforcing bars.

Conventional anchor bolt-confined flexible formwork concrete walls for gob-side entry retaining have clear inherent technical limitations, including incompatible deformation between steel anchors and concrete, low construction efficiency, and grout leakage. However, existing studies have not fundamentally solved the core mechanical problem of confinement efficiency loss caused by deformation mismatch, nor established a complete theoretical design framework for new high-compatibility confined systems, which severely limit their application in complex underground conditions. This study develops an innovative prefabricated stirrup-confined flexible formwork concrete system, identifies two primary surrounding rock fracture modes via theoretical analysis, establishes corresponding mechanical models for support design, and verifies the system through laboratory tests and full-scale field trials. The high-strength fiber stirrups achieve tensile strength equivalent to deformed steel bars with an elongation of ≤6%, significantly improving deformation compatibility with concrete. Field results show that the optimized system delivers excellent surrounding rock control, with a maximum roof subsidence of 65 mm, wall displacement of 30 mm, and floor heave of 35 mm. This study provides a validated design framework for high-efficiency confined concrete underground support structures.

The influence of axial compression is not incorporated into the design provisions for concrete breakout or pryout strength of anchors under shear. This study experimentally evaluated the shear capacities of anchors subjected to axial compression on a base plate using 10 large-scale specimens. The test variables included axial compression N, edge distances from the anchor shaft in the direction of applied shear, edge distances perpendicular to the applied shear, and the compressive strength of concrete. The results showed little difference in crack initiation and propagation with varying axial compression. However, axial compression significantly improved the concrete breakout strength of anchors in shear. The applied axial compression reached up to 2.5 times the mean concrete breakout strength Vcbgo, as determined by the concrete capacity design (CCD) method, and the average increase in shear strength was approximately 0.6 times the applied compression. In addition, axial compression suppressed concrete pryout failure by preventing the uplift of base plates. Based on the lowest N/Vcbgo ratio used in the tests, if axial compression of at least 0.5Vcbgo is applied to a base plate, pryout failure need not be considered.

This paper presents the behavior of anchorage zones, also known as end zones, with discrete reinforcing bars and continuous meshes. To examine the implications of various reinforcing schemes on the capacity, cracking, and failure of end zones, 50 block specimens are loaded and their responses are analyzed. Test parameters include the types of reinforcing bar materials (steel and glass fiber-reinforced polymer [GFRP]), and the configurations of the reinforcing bars and steel meshes (single and multiple placements). In terms of load-carrying capacity, the specimens embedded with the GFRP reinforcing bars outperform those with the steel reinforcing bars and meshes by 14.0%. The post-peak load drop of the blocks with steel and GFRP reinforcing bars is analogous, due to distributed axial stresses in the unreinforced concrete region, unlike the abrupt drop observed in the specimens with steel meshes that intersect the concrete in orthogonal directions. While concrete splitting originates from local tension generated near the axial compression, the location of cracking is dominated by the path of stress trajectories related to the number of reinforcing bars, which is not recognized in the case of the mesh specimens. The pattern of the isostatic lines of compression clarifies the development of bursting forces that cause cracking in the concrete. A two-stage analytical model is formulated to predict the magnitude of bursting forces and figure out the effects of several parameters on the response of the end zones. The applicability of existing design expressions is assessed and the need for follow-up research is delineated.

Prestressed concrete enables slender, economical, and durable structures, with post-tensioned (PT) precast girders widely used in bridge construction. Accurate design requires precise prediction of prestress losses, among which friction losses, arising from duct curvature, wobble, and anchorage slip, are most significant. Existing codes employ simplified exponential models, yet notable discrepancies persist between predicted and actual field values. This study presents full-scale experimental testing on PT precast girders used in Egypt’s Light Railway Transit (LRT) Project. Prestressing forces were measured using strain gauges to evaluate friction losses along tendon profiles. Results revealed that measured losses consistently exceeded code-based predictions, highlighting the influence of stress level and nonlinear variation along the tendon; factors often ignored by current provisions. Regression analysis yielded refined exponential models with improved accuracy and strong agreement with observations. The proposed refinements enhance predictive reliability and provide a foundation for updating design codes toward safer, more realistic PT concrete structures.