Headed Stud Anchors Installed on the Inside Corner of an Angle
Presented By: Susan Lasecki
Affiliation: Ionic Structures and Design, LLC
Description: Most welded headed-stud anchor tests reported in the literature have investigated connections with studs installed normal to the face of the loaded concrete surface. With respect to the embedded plate surface, test loads are applied normal (tension), parallel (shear), or in a combined fashion. The purpose of this investigation
was to determine the capacity of headed-stud anchors cast into concrete at an edge where the anchor is at a 45° angle to the horizontal and vertical surfaces. This type of installation is common in many cast-in-place, precast, and tilt-up applications. It is also a common detail for armoring the corner edge of concrete.
This program tested four series to determine the headed-stud connection capacity. All headed-stud test specimens consisted of ½ in. dia. x 4 in. (12.7 x 102 mm) long headed studs welded at a 45° angle into the inside corner of a 3 in. x 3 in. x 5/16 in. (76 x 76 x 8 mm) thick structural steel angle. The first test series (Series 1) served as control tests to determine the single-stud capacity. The second and third test series examined a two-stud connection with two separate stud spacings (s1): 5 in. and 9 in. (127 and 230 mm) apart, respectively. The fourth test series (Series 4) was identical to Series 2 with s1 = 5 in. (127 mm), but with the addition of confinement reinforcing steel. Test specimens were cast into an 8 in.-thick (200 mm) slab with a center recess; concrete strength averaged 4,700 psi (32.4 MPa).
The observed concrete breakout failure surfaces were similar to those documented in direct tension tests of headed studs near a concrete free edge. The breakout surface closely represents the 35° failure cone model used in current design standards. The single-stud capacity of Series 1 was almost one half the two-stud
connection capacity of Series 3 having studs spaced at 9 in. (230 mm) center-to-center.
Increasing the Concrete Breakout Capacity by Increasing the Anchor Head Area
Presented By: Neal Anderson
Affiliation: Simpson Gumpertz and Heger
Description: In some instances, cast-in-place single anchors need slightly more tension capacity when concrete breakout controls. One method of increasing capacity is to add a larger plate or washer at the embedded anchor end to increase the base head area where the breakout cracking initiates. The ACI 318-19 Code has a procedure for increasing the breakout area in Section 17.6.2.1.3. The AASHTO bridge code also has a complimentary
procedure to design the bearing plates for post-tensioning anchors. These procedures have the same objective but yield different results. To effectively increase the breakout area, the plate or anchor head must be thick (stiff) enough to uniformly distribute the bearing stress to the concrete.
This paper describes the analysis of previously published concrete tension breakout test data in the literature. The paper also reviews the geometry of headed-stud anchors, the geometries of forged heads, friction welded heads, and mechanical end anchorage devices to anchor either a smooth bar or deformed reinforcing bar. Bearing stresses at the anchor head were calculated, as were cantilever flexural stresses estimated in the plate or added washer at the anchor head. These stresses were then compared to a convenient measure of the stiffness of the anchor head. This information is used to suggest when the embedded plate or head for a single anchor has enough rigidity to uniformly distribute the bearing stress to the concrete without excessive bending
deformation.
Fatigue Behavior of Concrete Anchors in Case of Steel Failure
Presented By: Thilo Frohlich
Affiliation: University of Stuttgart
Description: Fasteners are used to connect steel components to concrete structures, e.g. guide rails of elevators, crane girders and slewing cranes or infrastructure systems, where repeated loads may cause damage within the anchorage system and therefore require a verification against fatigue failure. Steel failure of the fastener is often the governing failure mode at a higher number of load cycles, if the anchors are located far from the concrete edge. As there are only a few systematic studies available until now, the fatigue steel resistance of concrete anchors is considered to be product dependent and no generalized assumptions can be made. This article provides an overview of the results of experimental research on the fatigue behavior of post-installed anchors, headed studs and anchor channels performed at the University of Stuttgart in recent years. The investigations focus on the influence of the static load level, the contribution of the concrete and the impact of alternating shear loads. The findings are compared with the existing knowledge from literature and standardized S-N curves of comparable notch details. It could be shown that the nominal stress concept commonly used for steel structures and composite constructions is also applicable for steel failure of fastenings.
Experimental Investigation of the Concrete Cone Failure Load of Anchor Groups in Narrow Concrete Members Subjected to Eccentric Tension Load
Presented By: Erik Stehle
Affiliation: IEA Gmbh & Co. KG, Hauptstraße 4
Description: Post-installed anchors arranged in an anchor group and installed in narrow concrete members with two parallel close edges have considerably less concrete available to effectively transfer a tensile force acting on the anchorage to the base material. If the tensile force is additionally acting on the anchorage with an eccentricity, a feasible design solution becomes even more difficult. While supplementary anchor reinforcement can be provided in new buildings to withstand the tensile forces, this is no longer possible in existing buildings where, for example, new components are to be connected to the old structure. In the latter case it is particularly desirable to have design solutions with which the capacity of the described anchorage can be calculated realistically for concrete breakout failure. In order to come up with suitable design solutions, experiments were conducted to investigate the behavior of post-installed bonded anchors in narrow members subjected to eccentric tension load. In this work, the experimental campaign and results are presented and discussed. Finally, the experimental results are used to investigate the suitability of design solutions for centrically loaded anchor groups in narrow concrete members, which were previously proposed by the authors.
Performance of Post-Installed Anchors with Anchor Reinforcement Under Tension
Presented By: Deepak Suthar
Affiliation: Purdue University - West Lafayette
Description: Anchor reinforcement is used around an anchor group to improve its strength and ductility under different loading scenarios like tension, shear, moment, etc. Anchor reinforcement is provided in various forms like stirrups, J-hooks, etc. When concrete cone breakout occurs, anchor reinforcement is intercepted by cracks, and forces are redistributed. Strength contribution from concrete decreases and contribution from anchor reinforcement increases. The new model for cast-in anchorages with anchor reinforcement in Europe allows both the concrete and the anchor reinforcement to contributed to the ultimate capacity with an upper limit of strut failure to prevent unlimited gain from anchor reinforcement. The flexibility provided by post-installed anchors makes them a popular choice for anchoring work. However, the new model is only valid for headed cast-in anchors with cast-in anchor reinforcement, while for post-installed anchors the conservative approach of considering only the concrete resistance or the reinforcement resistance is followed. In this study, the applicability of the new model for cast-in anchorages with anchor reinforcement is experimentally investigated for post-installed anchors with cast-in anchor reinforcement under static tension load. Groups of bonded/adhesive, undercut, and expansion anchors were tested with different levels of anchor reinforcement under static tension load. It was observed that utilizing anchor reinforcement around the post-installed anchor groups yields higher capacity and ductility compared to cases without anchor reinforcement. The applicability of the models was verified and compared with the test results with modified upper limits.
Post-Installed Anchor Reinforcement for Enhancing the Performance of Anchorages Against Concrete Related Failure Modes
Presented By: Norbert Vita
Affiliation: Fischerwerke Gmbh & Co.
Description: Cast-in anchor reinforcement is known to be useful for enhancing the capacity of the anchorages in concrete structures. As the concrete breakout initiates and the cracks intercept the anchor reinforcement, the anchor reinforcement gets activated and provides resistance against applied loads. However, to utilize the benefits of the anchor reinforcement in design, the exact location of reinforcement must be known. Therefore, while cast-in reinforcement anchor reinforcement is useful for new designs, it is difficult to utilize it for new anchorages in existing structures and impossible to use for strengthening of existing anchorages. This paper presents the recent research carried out on enhancing the performance of anchorages using an innovative method using post-installed anchor reinforcement, which is useful for both new and existing anchorages, which might need to be strengthened in order to carry higher loads than they were originally designed for.
The paper describes the concept, summarizes the test results and presents analytical model for calculating the concrete breakout resistance of anchorages with post-installed anchor reinforcement. The analytical model is based on the experimental evidence and takes the cue from the existing models for cast-in-place anchor reinforcement with certain modifications considering the behavior of post-installed bars.