International Concrete Abstracts Portal

In this study, full-scale loading tests were conducted to investigate web-shear strengths of hollow-core slab (HCS) members strengthened in shear by using practically viable methods. All the HCS units used in the current test program were fabricated by using the individual mold method, not by the extrusion method, and the key experimental variables of the shear test were set as the presence of shear reinforcement, core-filling concrete, topping concrete, and also the magnitude of effective prestress. The shear force-displacement behaviors, crack patterns, and strain response of shear reinforcements were reported in detail. In addition, to identify the shear strength enhancement provided under various strengthening conditions in a quantitative manner, existing shear test results of series specimens, including a naked HCS member and corresponding composite HCS members with cast-in-place (CIP) concrete and/or shear reinforcements, were collected from literature. On this basis, a practical design expression capable of estimating shear strengths of HCSs strengthened with CIP concrete and stirrups was suggested based on the ACI 318 code equation. The proposed method evaluated the shear strengths of the collected specimens with a good level of accuracy, regardless of the presence of corefilling concrete, topping concrete, and shear reinforcements.

An experimental investigation was conducted to evaluate the shear friction capacity of cylindrical pocket connections without reinforcement crossing the interface, which is a common connection detail between precast concrete substructure elements. Current code expressions for shear friction capacity include components for cohesion or aggregate interlock and as well as contribution from steel crossing the interface or a clamping force. These expressions were primarily derived and calibrated based on push-off tests with reinforcement crossing the shear plane, which do not represent the behavior of the shear plane in a cylindrical pocket connection. Thirty-four (34), large-scale specimens were built and tested to investigate the shear friction of the cylindrical pocket connection without reinforcing steel crossing the shear plane. This experimental study showed that current code expressions provided conservative estimates for this connection. A revised proposed theory is presented that more accurately predicts the shear friction capacity of this connection without interface steel.

Although ultra-high-performance concrete (UHPC) is one of the promising materials for precast bridge girder applications due to its advanced properties and durability, its implementation in the precast industry is subject to several potential concerns. To support implementation, this paper presents the development of nonproprietary UHPC mixtures for precast, pretensioned UHPC bridge girder applications. The nonproprietary UHPC mixtures were developed using materials commonly available in the Texas precast industry, with the additional requirement of obtaining a compressive strength of 12 to 14 ksi (83 to 97 MPa) within 24 hours without any heat treatment while maintaining the current precast, pretensioned bridge girder fabrication practices. The fresh, hardened, and durability properties of both laboratory- and plant-made UHPC mixtures were investigated. The research results show that the selected nonproprietary UHPC mixture developed in a laboratory setting can be successfully produced in a precast plant setting with comparable properties.

The results of an experimental program conducted to evaluate the performance of shear-critical post-tensioned I-girders with grouted and ungrouted ducts are presented. The experimental program involved the design, construction, and testing to failure of six fullscale specimens with different duct layouts (straight, parabolic, or hybrid) and using both grouted or ungrouted ducts. All tests resulted in similar failure modes, such as localized web crushing in the vicinity of the duct, regardless of the duct condition or layout. Furthermore, the normalized shear stresses at ultimate were similar for the grouted and ungrouted specimens. The current shear design provisions in the AASHTO LRFD Bridge Design Specifications (AASHTO LRFD) were reviewed, and updated shear-strength reduction factors to account for the presence of the duct in the web and its condition (that is, grouted or ungrouted) were proposed. The data generated from these tests served as the foundation for updated shear-strength reduction factors proposed for implementation in AASHTO LRFD.

This paper describes the experimental testing of a reinforced concrete tessellated shear wall. The wall specimen was tested as part of a National Science Foundation-funded research project designed to demonstrate the concept of tessellated structural-architectural (TeSA) systems. TeSA systems are constructed of topologically interlocking tiles arranged in tessellations, or repeating geometric patterns. As such, these systems are designed with easy repair and reuse in mind. The specimen discussed in this paper is a TeSA shear wall constructed from individually precast I-shaped tiles. This paper presents the results of reverse cyclic loading of the specimen, including load-displacement behavior, crack propagation, and energy dissipation. A simplified analytical model for predicting the wall’s flexural capacity is also discussed.