Min-Yuan Cheng

Evaluation of Steel Fiber Reinforcement for Punching Shear Resistance in Slab-Column Connections— Part I: Monotonically Increased Load

Results from an experimental investigation aimed at evaluating the effectiveness of steel fiber reinforcement for increasing punching shear strength and ductility in slabs subjected to monotonically increased concentrated load are presented. Ten slab-column connections were tested to failure. The main test parameters evaluated were: 1) fiber geometry (hooked or twisted), 2) fiber strength (1100, 1800, or 2300 MPa [160, 260, or 334 ksi]), 3) fiber volume fraction (1% or 1.5%), and 4) slab tension reinforcement ratio (0.56% or 0.83% in each principal direction). Out of the fiber-reinforced concretes (or mortar) evaluated, those reinforced with a 1.5% volume fraction of either regular strength (1100 MPa [160 ksi]) or high-strength (2300 MPa [334 ksiJ) hooked steel fibers led to the best performance in terms of punching shear strength and deformation capacity. These two fiber-reinforced concretes (FRCs) were therefore selected for further evaluation in connections subjected to lateral displacement reversals, as described in the companion paper.

Shear Strength and Drift Capacity of Fiber-Reinforced Concrete Slab-Column Connections Subjected to Biaxial Displacements

Results from the tests of three large-scale slab-column subassemblies subjected to combined gravity load and biaxial lateral displacements are presented. The main purpose of the experimental program was to investigate the use of randomly oriented steel fiber reinforcement as a means to increase connection punching shear strength and deformation capacity. The connection of Specimen SB1 was reinforced with regular strength (1,100 MPa) fibers, 30 mm long and 0.55 mm in diameter, while the connection of Specimen SB2 featured high-strength (2,300 MPa) fibers, 30 mm long and 0.38 mm in diameter. Both types of fibers were targeted at a 1.5% volume fraction. The connection of Specimen SB3, on the other hand, was reinforced with shear studs, designed according to the 2008 American Concrete Institute Building Code. All three connections were subjected to a gravity shear ratio of approximately 1/2 during application of biaxial lateral displacements. The use of fiber reinforcement in the connection region resulted in...

Implementation of High-Performance Fiber Reinforced Concrete Coupling Beams in High-Rise Core-Wall Structures

Synopsis: Experimental and analytical studies that led to the incorporation of strain-hardening, high-performance fiber reinforced concrete (HPFRC) coupling beams in the design of a high-rise core-wall structure in Seattle, WA, are described. A total of eight HPFRC coupling beams with span-to-depth ratios ranging between 1.75 and 3.3 were tested under large displacement reversals. The tension and compression ductility of HPFRC materials allowed an approximately 70% reduction in diagonal reinforcement, relative to an ACI Building Code (318-08) compliant coupling beam design, in beams with a 1.75 span-to-depth aspect ratio and a total elimination of diagonal bars in beams with a 2.75 and 3.3 aspect ratio. Further, special column-type confinement reinforcement was not required except at the ends of the beams. When subjected to shear stress demands close to the upper limit in the 2008 ACI

Earthquake-Resistant Squat Walls Reinforced with High- Strength Steel

Results are reported from reversed cyclic tests of five large-scale squat wall specimens reinforced with steel bars having a specified yield strength of either 60 or 115 ksi (413 or 792 MPa). Two specimens were designed for a shear stress of 5√fc′ psi (0.42√fc′ MPa) and the other three 9√fc′ psi (0.75√fc′ MPa). Boundary element confining reinforcement complied with the requirements of Chapter 18 of ACI 318-14 in all but one specimen, which had 50% of the required transverse boundary element reinforcement. Specimens constructed with Grade 115 steel had similar strength and exhibited 20% greater drift capacity than those with Grade 60 steel. Use of Grade 115 steel tended to control the softening effect of sliding at the base of the wall and to increase the component of drift due to reinforcement strain penetration into the foundation.

Seismic Design Issue of Corner Slab-Column Connection

Design criteria of slab-column connections in the ACI Building Code [2011] were mostly developed from experimental results of interior connections. When dealing with corner slab-column connections, supplementary documents published by ACI Committee 352 and Committee 421 provide better explanations than the ACI Building Code [2011] and become useful references for practical engineers. However, different design values can be obtained using approaches recommended by different documents. In this article, a summary of this issue is presented. Among several design parameters discussed in this article, bi-axial moment, gravity shear ratio and column rectangularity have more significant effect to enlarge the discrepancy.