International Concrete Abstracts Portal

Steel columns are commonly attached to concrete foundations with groups of cast-in-place headed anchors. Recent physical tests and simulations have shown that the strength of these connections can be limited by concrete breakout failure. Four full-scale physical specimens of axially loaded columns attached to a foundation slab were tested, varying the shear reinforcement configuration in the slab. All specimens were governed by concrete breakout failure. The tests suggest that adequately placed distributed shear reinforcement can increase connection strength and displacement capacity. Steep cone failures were observed to limit the beneficial effect of shear reinforcement. Calibrated finite element models were used to investigate critical parameters such as the extent of the shear-reinforced region and bar spacing. A design approach is proposed to calculate connection strength by adding the strength of the concrete and the distributed shear reinforcement. Design detailing is discussed.

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 reinforcing bar lap-spliced 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 post-peak. Current provisions of ACI 318, EC2, and IS 13920 recommend staggered lap-splice detailing in shear walls. However, from the current study, shear walls with different percentages of staggered lap splice show that the staggered lap-splice detailing in shear walls does not improve its seismic performance.

The adequate seismic behavior of slender reinforced concrete (RC) structural walls relies heavily on the effectiveness of the boundary element (BE) in providing stable resistance against combined axial and flexural-shear compression demands resulting from gravity loading and lateral earthquake deformations. The geometric properties of the BE, including thickness and confined length, as well as the arrangement, detailing, and quantity of transverse reinforcement, play crucial roles in achieving a stable compressive response. Laboratory tests on isolated BE specimens subjected to uniform axial compression or cyclic axial tension and compression have been instrumental in understanding the influence of these variables on the compressive behavior of wall BEs. This study uses a database of experimental results from 45 rectangular BE specimens to establish empirical relationships between compressive force and strain, accounting for geometric and transverse reinforcement design parameters. A novel auto-regularizing model is proposed to estimate the compressive behavior within the damaged zone of a BE, based on its geometry and transverse reinforcement.

With a well-thought-out packing theory for sand, fine aggregates, cement, a water-cement ratio lower than 0.2, and steel fibers, ultra-high-performance concrete (UHPC) achieves remarkable mechanical properties. Despite UHPC’s superior mechanical properties compared to conventional concrete, its use remains limited, especially in structural applications, due to factors such as high cost, lack of design standards and guidelines, and inadequate correlation between material properties and structural behavior. By compiling and synthesizing the behavior of 70 structural- or full-scale axial UHPC columns, this research provides a new set of generalized design and detailing guidelines for axial UHPC columns. The study first uses the assembled database to assess and revisit the current ACI 318 axial strength design factors for applicability for UHPC. Next, the behavior trends are carefully analyzed to provide detailed recommendations for proper transverse reinforcement (ρt volume), spacing-to-longitudinal reinforcing bar diameter ratio (s/db, where s represents the centerline-to-centerline spacing between transverse reinforcement), and UHPC steel fiber ratio for best use of confinement.