International Concrete Abstracts Portal

Thirty-nine large-scale reinforced concrete beams were tested under monotonic three-point bending to investigate the use of stirrups with mechanical anchors (heads) or hooks and Grade 80 (550) reinforcing steel. Grade 60 and 80 (420 and 550) No. 3, No. 4, and No. 6 (10, 13, and 16 mm) bars were used as stirrups, which were spaced at one-quarter to one-half of the member effective depth. Other variables included beam depth (12 to 48 in. (310 to 1220 mm)), beam width (24 and 42 in. (620 and 1070 mm)), longitudinal reinforcement strain corresponding to the nominal beam shear strength (nominally 0.0011, 0.0017, or 0.018), and concrete compressive strength (4,000 and 10,000 psi (28 and 69 MPa)). Headed stirrups that (a) engage (are in contact with) the longitudinal bars or (b) have a side cover of at least six headed bar diameters and at least one longitudinal bar within the side cover, produce equivalent shear strengths as hooked stirrups, and both details allow stirrups to yield. The results affirm that beams designed for the same V_n with either Grade 60 or 80 (420 or 550) stirrups exhibit equivalent shear strengths. A nominal shear strength based on a concrete contribution equal to 2√(f_cb_wd may be unconservative when ρtfytm < 85 psi (0.59 MPa) in members with a/d= 3, h≥ 36 in., ρ < 1.5%, and no skin reinforcement.

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.

The first edition of ACI 440.11 Building Code was published in September 2022, where some code provisions were either based on limited research or only analytically developed. Therefore, some code provisions, notably shear and development length in footings are difficult to implement. This study, via a design example, aims at a better understanding of the implications of code provisions in ACI 440.11-22 and compares them with ones in CSA S806-12, thereby highlighting a need for reconsiderations. An example of the footing originally designed with steel reinforcement was taken from the ACI Reinforced Concrete Design Handbook and redesigned with GFRP reinforcement as per ACI 440.11-22, and CSA S806-12. A footing designed as per ACI 440.11-22 requires a thicker concrete cross-section to satisfy shear requirements, however, when designed as per CSA S806-12 the required thickness becomes closer to that of the steel-reinforced concrete (RC) footing. The development length required for a GFRP-RC cross-section designed as per ACI 440.11-22 was 13% and 92% greater than that designed as per CSA S806-12 and ACI 318-19 respectively. Also, the reinforcement area required to meet detailing requirements is 170% higher than that for the steel-RC cross-section. Based on the outcomes of this study, there appears to be a need for reconsideration of some code provisions in ACI 440.11-22 to make GFRP reinforcement a viable option for RC members.

With a well-thought packing theory for sand, fine aggregates, cement, a water-to-cement ratio lower than 0.2, and steel fibers, UHPC achieves remarkable mechanical properties. Despite UHPC's superior mechanical properties compared to conventional concrete, its utilization 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 (ρ_t volume), spacing-to-longitudinal rebar diameter ratio (s/d_b) where s represents the centerline-to-centerline spacing between transverse reinforcement, and UHPC steel fiber ratio for best use of confinement.

Beam-column (BC) joints are crucial components for ensuring the safety of structures during earthquakes. Various standards/ codes (Eurocode 8, ACI 352R-02, and IS 13920:1993) prescribe special reinforcement detailing at the joint region to improve the seismic performance. Although extremely important, execution of the same is challenging due to heavy reinforcement congestion. In this regard, an attempt has been made in this study to develop a strain-hardened, high-performance cementitious composite (SHCC) with improved tension-related performance for seismicresistant BC joints, which can potentially reduce the reinforcement demand. The efficacy of SHCC in improving the gravity-loaddesigned (GLD) BC joints without any additional reinforcement required for ductile detailing is investigated. Full-scale BC joint specimens were developed and subjected to reversed cyclic loading, and the critical seismic performance—such as hysteresis behavior, damage pattern, energy dissipation, shear deformation, and strength/stiffness degradation—were evaluated and compared with GLD specimens with normal concrete. It is observed that the GLD specimens with SHCC at the joint region showed remarkable performance. Without any additional confinement in the joint region, energy dissipation is doubled (100%), and shear deformation is only 40% of the GLD under the same drift demand. The findings of this study will help in developing seismic-resistant BC joints with the minimum reinforcement.