James O. Jirsa

A STUDY OF HOOKED BAR ANCHORAGES IN BEAM-COLUMN JOINTS

Twenty-two specimens simulating typical exterior beam-column joints in a structure were tested to evaluate the capacity of anchored beam reinforcement subjected to varying degrees of confinement at the joint. The effects of column axial load, vertical column reinforcement, side concrete cover, and lateral reinforcement through the joint on the performance of standard hooked bars were studied. The tests were conducted using either #7 or #11 beam bars anchored in the columns. Standard 90 or 180 deg hooks conforming to AC1 318-71 specifications were used throughout. Based on observarions of the test specimens, current AC1 318-71 Code specifications are studied and design recommendations for hooked bar anchorages proposed. Comparison of the proposed design recommendations with the measured results indicated that higher stresses could be allowed for hooked anchorages provided that confinement in the form of cover or ties and straight lead embedment before the hook were sufficient.

THE BEHAVIOR OF MULTIPLE LAP SPLICES IN WIDE SECTIONS

In most reinforced concrete catilever retaining walls, construction procedures require some type of splicing of the reinforcing steel. Economics often dictate the use of a lap splice. Since a retaining wall has no redundancy, understanding of splice behavior becomes critical to the design of the structure. In order to investigate the behavior of lap splices of the reinforcing steel in such a structure, twenty-five specimens were tested. The specimens were tested with the splice regions subjected to a constant moment along the length of the splice. This loading produced a stress condition as severe as that in the prototype. The main variables in the test program were the splice length and bar diameter, the ratio of the clear cover to the clear spacing of the splices, the edge splice condition, the amount of transverse reinforcement in the splice region, and the casting position. Cracking patterns, steel strain distributions, and failure modes of the specimens were studied to obtain a basic understanding of the behavior of lap splices in wide sections. /FHWA/

BEHAVIOR OF BENT BAR ANCHORAGES.

The object of the study was to examine some of the factors which influence the anchorage capacities of bent deformed reinforcing bars. Eighty specimens containing bars bent to different geometric configurations were tested to determine the effect of bend length, angle included in the bend, inside radius of bend, and bar diameter on the deformation and strength of hooked bar anchorages. Of primary interest was the measurement of slip between the bar and the concrete at several points along the anchored bar. the load-slip curves obtained were used to compare the performances of different bar geometries. The results indicated that at a given bar stress, the longer the angle of bend or the smaller the radius of bend, the greater will be the slip. Ultimate strength of hooked bar anchorages is about the same as that of straight bars. For practical joint design detailing, the results indicate that 90 deg hooks are preferable to 180 deg hooks. To reduce slip the radius of the hook should be as large as practical. /Author/