International Concrete Abstracts Portal

Bonded anchors consist of steel elements (e.g. threaded rods) which are bonded into a drilled hole by a prequalified adhesive mortar. They are designed according to ACI 318 Appendix D “Anchoring to Concrete”. Reinforcing bars post-installed in drilled holes by a suitable mortar behave like cast-in reinforcing bars. They are designed according to ACI 318 Appendix A “Strut-and-Tie-Models” in connection with Chapter 12 “Development and Splices of Reinforcement”. In a connection (e.g. concrete column to a foundation) cast-in or post-installed reinforcing bars transfer the tension force of the connected concrete structural member into the base member. This is also done by bonded anchors if a steel member is connected to a concrete structure. When assuming that the bond strength of cast-in or post-installed bars and of bonded anchors is about the same the required embedment depth of connections with straight reinforcing bars and bonded anchors should be about the same independent, if the connection is designed according to Appendix A or Appendix D. However, in many applications this is not the case. In the paper tests on column-foundation connections under monotonic and cyclic loading performed by the authors at the University of Canterbury are described. Used were cast-in hooked and straight deformed reinforcing bars and post-installed reinforcing bars. The measured failure loads are compared with predictions according to ACI 318, Chapter 12 (development length) and Appendix D (anchorages). Based on the results of the evaluations it is proposed to design connections of concrete members according to Appendix D and to amend the provisions in Chapter 12 and Appendix D to achieve a better agreement of the design results when using the two design models.

Prestressing steel is used as the primary tension element in stay cables and external, post-tensioned tendons on long-span bridges throughout the US. The steel is often encased in plastic duct or pipe, which is filled with grout, to provide two layers of corrosion protection. Nondestructive methods have been used successfully to detect severely damaged tension elements on several bridges, but the reliability of these methods to detect the onset of structural damage has not been documented. The results of laboratory tests are used to demonstrate that the residual tensile strength of a grouted tension element decreases more rapidly with increasing levels of damage than the tensile force under service loads. The grout and duct provide a mechanism for fractured strands to re-anchor along the length. Nondestructive methods that detect damage by approximating changes in the service-level tensile force will underestimate the level of structural damage and overestimate the residual tensile strength of a damaged cable or tendon if this inherent redundancy is not considered. Continuous monitoring with an acoustic system provided a reliable means of tracking damage in near real time for the laboratory specimens, but only damage that occurs while the system is operational can be detected.

The design of beam-column joints in reinforced concrete moment frames is an area where USA and New Zealand standards have diverged for many years. USA design guidelines, and ACI 352 in particular, implicitly accept damage in the form of shear cracking, bar slip and possible column hinging for joints subjected to large lateral load reversals. Since the 1980’s, the New Zealand approach has been to minimize that type of damage and to concentrate the deformations in plastic hinges in the beams by careful detailing of the joint and adjacent beam regions, thus keeping columns essentially elastic. The recent February 22, 2011 Christchurch earthquake and its associated swarm present an excellent opportunity to contrast these approaches in terms of visual performance for a variety of New Zealand structures detailed and built before and after the newer, more stringent joint design guidelines came into effect. The main lesson from the Christchurch experience is the importance of providing both some degree of lateral resistance, e.g. via beam-column joint moment-resisting capacity, and an increased level of displacement capacity in secondary or gravity-frames in order to improve the overall building’s robustness and seismic resilience in response to earthquake demands beyond the code design level.

The paper presents an overview of the study carried out to compare the results of three research programs conducted on hooked bars anchored in beam-column joints in normal strength concrete (NSC) structures at the American University of Beirut (AUB). The specimen simulated the rigid connection of a cantilever beam to a column. In the first program, the beam-column joint was confined externally with carbon fiber reinforced polymer (CFRP) sheets. Confinement of the joint in the second program was provided internally by steel fibers of varying volume fractions incorporated in the concrete mix. Although stirrups were included in the beam and column elements of the specimens of the first two programs, however the column stirrups were not extended in the beam-column joint. In the third program, confinement of the joint was provided internally by different amounts of stirrups. Test results of the three programs indicated positive effect of the different confining modes on the bond strength of the anchored hooked bars and ductility of the load-deflection history of the tested specimens. The objective of the study reported in the paper is to perform a correlation between the positive effects of the three different confining modes of the beam column joint.

Engineering consensus documents in the U.S. on proportioning of reinforced concrete slabs went through creative and contradictory transformations starting in 1900’s until a compromise was reached between mechanics and practice as a result of the Investigation of Multiple‐Panel Floor Slabs carried out in Talbot Laboratory of the University of Illinois, Urbana, from 1957 to 1963. This paper traces the work on reinforced concrete slabs in Urbana that started with Arthur Newell Talbot and continued virtually without interruption to the time of Dr. Jirsa’s arrival in Urbana to deliver the coup de grace.