Anchor Head Research Articles

Behavior of Fasteners Loaded in Tension in Cracked Reinforced Concrete

Many reinforced concrete structures are designed under the assumption that the concrete is cracked due to external loods or restraint of imposed deformations (e.g., due to creep, shrinkage, temperaure variations, or suppose settlement). Research shows that fasteners will attrack cracks or even induce cracking. Therefore, the behavior of different types of fastener in cracked reinforced concrete has been studied extensively. Fasteners suitable for use in cracked reinforced concrete such as cast-in situ headed studs or headed anchors, post-installed undercut anchors, and specially designed torque-controlled expansion anchors show a reduction of the concrete cone failure load of about 25 to 35 percent compared to uncracked concrete when located in or close to cracks with a witdh ∼0.3%0.4 mm (0.012 to 0.016 in.). This crack width can be expected in typical concrete members designed with ordinary crock control provisions. The failure load of ordinary torque-controlled expansion, deformation-controlled expansion, and bonded anchors is more influenced by cracks and may be unpredictable, especially if installation inaccuracies that might occur on site are taken into account. Fasteners used in zones with potential concrete cracking must be suitable for this application. A test program to check the effective functioning of fasteners in cracked reinforced concrete is described in mechnical guides by UEAtc and EOTA, a basis for the proposed ASTM specification

Fracture Size Effect: Review of Evidence for Concrete Structures

The paper reviews experimental evidence on the size effect caused by energy release due to fracture growth during brittle failures of concrete structures. The experimental evidence has by now become quite extensive. The size effect is verified for diagonal shear failure and torsional failure of longitudinally reinforced beams without stirrups, punching shear failure of slabs, pull-out failures of deformed bars and of headed anchors, failure of short and slender tied columns, double-punch compression failure and for part of the range also the splitting failure of concrete cylinders in the Brazilian test. Although much of this experimental evidence has been obtained with smaller laboratory specimens and concrete of reduced aggregate size, some significant evidence now also exists for normal-size structures made with normal-size aggregate. There is also extensive and multifaceted theoretical support. A nonlocal finite element code based on the microplane model is shown to be capable of correctly simulating the existing experimental data on the size effect. More experimental data for large structures with normal-size aggregate are needed to strengthen the existing verification and improve the calibration of the theory.

Failure Mechanism of New Bond‐Type Anchor Bolt Subject to Tension

The objective of this study is to investigate the failure mechanism of a new bond‐type anchor bolt under tensile force so that a design method may be established. A conventional headed anchor bolt embedded in a concrete footing normally fails by pulling out a stress cone; however, the bond‐type anchor bolt exhibits a complex failure mode, here referred to as a mixed bond‐cone failure. To date, the theoretical aspects of this failure mechanism have not been established. With the needs of design application in mind, an analytical model to predict the ultimate strength of the bond‐type anchor bolt is presented. Experimental data confirm that this model can be used with acceptable accuracy to assess the ultimate strength and the failure mode of the bond‐type anchorage system.

Load-displacement behaviour at anchor and pile heads (In German)

Load-displacement behaviour at anchor and pile heads (In German)

Strength of Epoxy‐Grouted Anchor Bolts in Concrete

An analysis based on linear and nonlinear finite element computer models of headed anchor bolts epoxied in place in hardened concrete is presented. Two failure theories, the maximum tensile stress criteria and the Mohr‐Coulomb criteria, are applied to the hardened concrete. An approximate expression is developed to predict the ultimate tensile strength of the anchorage system. Results obtained through this analysis are compared to previously reported experimental data.

Suggested method for rock anchorage testing : ISRM Comm on Testing Methods Int J Rock Mech Min SciV22, N2, April 1985, P71–83

(A)This suggested method provides guidelines on a variety of tests for rock anchorages, including design tests and proof tests. In addition, this document suggests equipment, measurements, calculations and records which are suitable for these two classes of tests. The long-term monitoring of anchorages is treated in a separate suggested method. (B) two alternative methods of loading are normally considered in practice. In the co-axial loading method, the rock immediately surrounding the anchor head is used as a bearing surface for the stressing device; thus, rock movement or rock mass failure cannot be tested. Where rock mass failure in the form of a cone, wedge or block is a possibility then the remote loading method is appropriate, whereby the reaction loads are applied via a beam or grillage, to the ground surface remote from the test Anchorage. The span between reaction points must be sufficient to allow rock mass failure, if the rock is weaker than the steel tendon or its bond strength to the rock. For example, if a conical or wedge type of failure is anticipated with an included angle of 45 degrees, the free span should not be less than the total embedded depth. For laminar type failure in horizontally bedded slabby rock, free spans may be increased or decreased depending upon fracture geometry. In cases where the rock is separated from the reaction structure by a considerable thickness of overburden soil, the effect of the overburden's surcharge in restraining rock mass failure must be evaluated. (TRRL)

Design of Headed Anchor Bolts

In current practice the design of base plates is controlled by bearing restrictions on the concrete; shear is transmitted to the concrete largely through anchor bolts, shear lugs or bars attached to the base plate and the tensile anchorage steel is generally proportioned only for direct stress. The embedment requirements for anchorage steel are not clearly defined by most codes and are left largely to the discretion of the design engineer. Also, there are no provisions to prevent a brittle failure in the concrete as opposed to a ductile failure in the anchor bolt, as provided for with a probability-based limit states design or Load and Resistance Factor Design (LRFD) for steel. Larger design forces now mandated in many areas due to the revised seismic and wind loads require design capacities for anchor bolts beyond any existing code values. Therefore, there is a need for a complete design procedure for anchor bolts that will accommodate these larger loads and incorporate the proposed design philosophy, i.e., probability-based limit states design (PBLSD).

Elastoplastic analysis of thick perforated plates with application to prestressing anchor heads

The elastoplastic finite element stress analysis of a prestressing anchor head is described. The anchor head constitutes part of an unbonded tendon system for a prestressed concrete nuclear reactor vessel. The anchor head, which is a thick plate with a central region perforated by a large number of holes, is analyzed using an equivalent homogeneous material with numerically determined effective elastic constants and yield stress. Maximum inelastic tensile strains are calculated as a function of anchor head load level, and related to observed failure modes.

Headed Steel Anchor under Combined Loading

The increasing use of headed steel anchor studs under combined shear and tension loading has resulted in a need for more information on their behavior and strength. Some typical situations where this type of loading is encountered in design are shown schematically in Fig. 1. Anchor studs can provide an efficient method of joining steel and concrete members and can permit greater flexibility in the design of composite steel-concrete systems. The existing criteria for designing headed steel anchor studs with partial embedment in concrete is based on limited test data and various models representing connector behavior. Several empirical relationships have been suggested in the literature. However, a number of factors can affect the ultimate strength of a headed steel anchor stud. They include the embedment length, the development of full or partial concrete shear cones which depends on anchor spacing and boundary conditions, concrete shear strength, shear friction, and the attachment plate thickness.