International Concrete Abstracts Portal

Two large-scale beam-column connections with beam longitudinal headed bars were tested to evaluate their susceptibility to breakout failures. The specimens were designed following the strength and transverse reinforcement detailing provisions in Chapter 15 of ACI 318-19. The variable investigated was the headed bar embedment length, which was determined based on either Chapter 25 of ACI 318-19 or recent research at the University of Kansas, the latter leading to a 22% shorter embedment length. Both specimens exhibited beam flexural yielding, but the specimen with shorter bar embedment length experienced significantly more connection damage followed by a concrete breakout failure. Based on the limited test results, it is recommended that nominal joint shear strength be calculated based on a joint effective depth equal to the headed bar embedment length and a shear stress of 1.0λ√(fc' ) (MPa) [12λ√(fc' ) (psi)]. A method for calculating headed bar group anchorage strength in exterior beam-column connections is proposed, which led to reasonable and conservative strength estimates in the test specimens.

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.

This study investigates the behavior of recycled steel fibers (RSFs) recovered from waste tires and industrial hooked-end steel fibers (ISF) in two single and hybrid reinforcement types with different volume content, incorporating microstructural and macrostructural analyses. Scanning electron microscopy (SEM) is used to study the microstructure and fractures, focusing on crack initiation in the fiber interface transition zone (FITZ). The macrostructural analysis involves using digital image correlation (DIC) software, Ncorr, to analyze the split tensile behavior of plain and fiber reinforced concrete (FRC) specimens, calculating strain distribution and investigating crack initiation and propagation. The SEM study reveals that, due to the presence of hooked ends, industrial fibers promoted improved mechanical interlocking; created anchors within the matrix; added frictional resistance during crack propagation; significantly improved load transfer; and had better bonding, crack bridging, and crack deflection than recycled fibers. RSFs significantly delay crack initiation and enhance strength in the pre-peak zone. The study suggests hybridizing recycled fibers from automobile tires with industrial fibers as an optimum strategy for improving tensile performance and using environmentally friendly materials in FRC.

Corrosion of steel anchors in concrete poses a significant risk, leading to detachment, structural damage, and loss of anchor strength. To enhance the durability of structural elements involving anchors, the use of corrosion-resistant nonmetallic inserts could be a feasible alternative. This study presents an experimental investigation of the tensile and shear concrete breakout strength of a single cast-in fine ceramics insert (FCI). The tensile tests were conducted with FCIs located at the center and edge of concrete blocks, while the shear tests were conducted with inserts positioned at varying distances from the concrete block’s edge. The experimental program comprised 75 specimens of three different FCI diameters (FCI 1/2 in. [12.7 mm], FCI 5/8 in. [16.0 mm], and FCI 1 in. [25.4 mm]) with two different embedment depths for each type. The experimental results showed that FCI anchors performed satisfactorily, providing bearing capacity conservatively satisfying the values calculated by ACI equations for the concrete breakout strength.

The behavior of carbon fiber-reinforced polymer (CFRP) flexurally strengthened reinforced concrete (RC) beams under reversed cyclic loading is not sufficiently studied. In this paper, normal-strength concrete is used with a typical steel ratio (0.5%) to build full-scale rectangular beams strengthened on top and bottom with flexural unanchored and anchored CFRP sheets. Five identical beams were examined under fully reversed cycles up to failure following the AC 125 displacement loading protocol. The first beam was tested as an unstrengthened control specimen. The second and third beams were tested as strengthened specimens using thin sheets with and without fiber anchors. On the other hand, the fourth and fifth beams were tested when strengthened using thick sheets with and without fiber anchors. Specimens with thin sheets underwent higher ductility and lower hysteresis pinching relative to the thick ones. The results are comparatively discussed and compared to a phenomenological cyclic analysis model showing promising correspondence.