Anchorages in Concrete Construction

Anchorage or fastenings in concrete construction refers to the means to connect a structural or non-structural component to a concrete structure. A fastener (also known as anchor) is an element typically made of steel or malleable iron that is installed in concrete by either casting it inside the concrete during construction or post-installed into a hardened concrete member. The fastener is used to transmit the loads applied on a structural or non-structural component to inside the concrete member.

Two different types of fasteners are used to form the connection: Cast-In systems and Post-installed systems. The cast-in system is installed by securing it in a pre-defined location inside the formwork and cast into the concrete. To enable an efficient load transfer, the fastener is so-formed as to develop a mechanical interlock. Post-installed fasteners offer a versatile solution to the problem of anchoring in hard concrete, which typically consist of drilling a hole in the concrete member and installing the anchor. Typical load-transfer mechanisms utilized by post-installed anchors include mechanical interlock, bond and friction (also in combination). Some of the major topics of research on anchorages being pursued by me include:

Anchorages with supplementary reinforcement under tension loading
Anchorages with supplementary reinforcement under shear loading
Anchorages with supplementary reinforcement under combined tension and shear loading
Anchorages under seismic loading
Anchorages of irregular configurations
Anchorages of circular configuration
Computational modeling of anchorages
Advanced methods for modeling and design of anchorages

Anchorages with supplementary reinforcement under tension loading

The presence of supplementary reinforcement has a significant influence on the load-carrying capacity of anchorages subjected to tension loads. The load-bearing capacity of an anchorage with supplementary reinforcement results from the anchorage in the concrete breakout body achieved by means of bond and bearing of a hook or bend. When the anchorage is loaded in tension, first the concrete cracks forming the breakout body, and then the stirrups get activated. If the anchorage length of the stirrups within the concrete breakout body is small, they might reach bond failure prior to yielding resulting in lower resistance than potentially achievable. For stirrups with relatively large anchorage lengths, as in case of closely spaced stirrups, resistance equal to the yield resistance of the stirrup can develop resulting in enhanced load and deformation capacity of the anchorage. However, beyond a certain level of reinforcement, the failure of concrete struts can limit the failure load for the anchorage.

The models included in the current standards and guidelines to evaluate the failure loads for anchorages with supplementary reinforcement subjected to either tension or shear forces are generally very conservative. The existing models do not explicitly consider all three major components that provide resistance to applied forces for anchorages with supplementary reinforcement namely the concrete struts, the tension ties and the nodes. The consideration of only concrete “or” reinforcement resistance as the anchorage resistance generally leads to a very conservative estimate of the failure loads for the anchorage. On the other hand, not recognizing concrete strut failure as a possible failure mode might lead to an over-estimation of the failure loads for anchorages of certain configurations with relatively high amount of supplementary reinforcement.

This project deals with investigating the behavior of anchorages with supplementary reinforcement subjected to tension forces and to develop an analytical model for them. Based on well-instrumented tests, a new model has been developed to predict the failure load and the failure mode for anchorages with supplementary reinforcement under tension loads. The model considers separate contribution of the hook and the bond length of the stirrup to calculate the reinforcement resistance based on modifications to the Schmid model. The concrete and reinforcement resistance is combined based on the readings of strain gauges. The increase in the anchorage resistance due to supplementary reinforcement is capped by the strut failure load based on the modifications to the Berger model.

The research has been funded by Peikko Group Corporation and the work has been carried out along with Prof. Rolf Eligehausen and Dr. Jörg Asmus. Further details of the tests and analytical model can be obtained from the following publications:

Paper Experiments

Paper Analytical model

Anchorages with supplementary reinforcement under shear loading

Experimental studies on anchorages with multiple anchor rows and supplementary reinforcement for shear loads in case of concrete edge failure and development of analytical models for evaluating the failure loads.