Seismic C2 Qualification of Anchors: First Decade and Beyond
Presented By: Akanshu Sharma
Affiliation: Purdue University
Description: The seismic C2 qualification for post-installed anchors was introduced with the publication of Annex E of the then European qualification guideline ETAG 001 in 2013. Many anchor products have been qualified accordingly ever since. The ETAG 001 Annex E has been superseded by the EAD 330232 and EAD 330499 in the meantime but the requirements for C2 qualification remained unchanged. The testing conditions and assessment criteria were scientifically substantiated to a level globally unchallenged at that time, and Rolf Eligehausen played a major role in defining them. After more than 10 years of successful application of the C2 qualification requirements in practice and shortly before their introduction in the US within the revisions of the ACI 355.2 and ACI 355.4, it is time for a review. Although C2 qualification is the most advanced seismic qualification protocol, for anchors used in structural and/or seismic strengthening applications, a displacementbased test protocol might be more relevant. This contribution briefly recapitulates the historical and technical background of the development of the C2 qualification and provides some fresh perspectives for future seismic qualification of anchors especially for structural applications.
Anchorage Behavior in the Fully Fastened Haunch Retrofit Solution for Beam-Column Joints
Presented By: Margaritis Tonidis
Affiliation: University of Stuttgart
Description: The Fully Fastened Haunch Retrofit Solution is a relatively low-invasive solution which can be used for the seismic retrofitting of reinforced concrete beam-column joints vulnerable against joint shear failure. The paper presents experimental results on two-dimensional and three-dimensional exterior beam-column joint subassemblies subjected to unidirectional, quasi-static cyclic loads, which have been retrofitted with post-installed steel haunches. The haunch elements were connected to the frame members with post-installed bonded anchors. The paper discusses and compares the performance of the anchorage system between the investigated beam-column joint configurations with respect to global load-displacement behavior, crack pattern in concrete, load distribution among the anchors, haunch axial force and strain profile in diagonal haunch element. The steel haunches led to a significant improvement in the seismic performance of the specimens as long as the anchors were performing well. In the two-dimensional beam-column joint, at relatively high displacement levels associated with large crack widths, the anchors started to fail which initiated a redistribution of loads within the anchor group. In addition, a redistribution of strains has been found along the steel diagonal, which can be used as a failure criterion of the anchorage. Lastly, higher loads were detected in the anchors in the top part of the beam when it was monolithically connected to a slab. In this case, failure was observed in the column above the joint due to column shear and concrete cone breakout of the anchorage.
Discussion on Concrete Break-Out Failure of Hooked and Headed Bars in RC Beam Column Joint
Presented By: ANGELO MARCHISELLA
Affiliation: Politecnico di Milano
Description: The issue of development length (ldh) of steel bars (hook and headed) in Reinforced Concrete 20 (RC) beam-column joint is addressed. In the context of ACI-318, ldh is empirically expressed as a function of the yield strength of the reinforcement, the compressive strength of the concrete and the bar diameter. Additional modifications factors consider the occurrence of different boundary conditions such as light-weighted concrete, epoxy coating, confining reinforcement. Such formulation is based on an experimental characterization which identified three potential
mechanisms: (i) concrete-break out failure (CB); (ii) joint-shear failure (JS); (iii) pullout/splitting failure (PO). However, there is poor agreement on what CB is, even as far as 2 the meaning of that term itself is concerned. In this paper, results of non-linear finite element analyses are used to assess the mechanical behavior of selected experimental tests. In some cases what was originally defined as CB failure reveal to be JS failure. For the sake of completeness, numerical results are compared to simple analytical expressions.
The Coefficient Alpha Setup in High-Strength Concrete
Presented By: Nilde Maci
Affiliation: University of Stuttgart
Description: Many studies have been conducted to find the coefficient alpha setup for adhesive anchors. This paper focuses on the determination of alpha setup in high-strength concrete. For this purpose, tests with an epoxy adhesive system were performed under both confined and unconfined setup at the Institute of Construction Materials (University of Stuttgart). Two different steel elements were considered, namely threaded rods and reinforcing bars with a diameter of 12 mm, respectively. The impact of various parameters including embedment depth, support diameter, and bond length, was observed. The findings indicate that alpha setup varies between 0.57 and 0.92 with an average value of 0.75, which coincides with the recommended value as stated in the current guidelines.
Performance of Anchorages Under Predominant Moment Loading: An Experimental Investigation
Presented By: Gaurav Somnath Chobe
Affiliation: Purdue University - West Lafayette
Description: Post-installed mechanical and chemical anchors offer a large flexibility for the design of connections in concrete structures. Such fastening systems are extensively used to connect structural or non-structural elements to concrete. Moreover, they are used to join new structural elements to existing structures in earthquake retrofit schemes.
Frequently anchorages are subjected to predominantly moment loading either alone or in combination with axial or shear loads. Some of the examples include anchorages used to form column-foundation connections, beam-column connections, beam-wall connections, wall-foundation connections, etc. Current design guidelines such as EN1992-4 and fib Bulletin 58 consider the positive influence of bending moment on the anchorage capacity through the factor ????=1.0. However, the formulations provided in the guidelines are rather limited in applications. For example, when the anchorage is positioned close to the edge, this factor assumes a value of 1.0. For the cases with more than 2 anchors in a row or biaxial moment, the rules for determining the behavior of anchorages under predominant moment loading are not clear.
This paper presents the results of an experimental program, executed to investigate the behavior of anchorages under predominant moment loading. The tests are conducted on column-foundation joint sub-assemblies formed by connecting a steel column to concrete foundation using 2 x 2 anchor groups of post-installed anchors. The sub-assemblies are loaded monotonically under lateral loading at a pre-defined lever arm representing the point of contra-flexure of a frame of a structure under lateral loads. Columns are located close to and away from the edge and tested under loading towards the edge and away from the edge. The test results clearly bring out the differences in the behavior of different sub-assemblies subjected to predominant moment loading.
The New Approach for Qualification and Design of Post-Installed Reinforcing Bars in Europe – Background and Explanations
Presented By: Akanshu Sharma
Affiliation: Purdue University
Description: The qualification and design of post-installed reinforcing bars have seen a major paradigm shift in Europe over the past few years. This is attributed to the new European Assessment Documents (EAD) and the Technical Report (TR) 069 being issued by the European Organisation of Technical Approvals (EOTA). The author of this paper played a pivotal role in the development of the new test and qualification methods as well as the design provisions. The development of the documents took place in steps with the first step as establishing the equivalence of post-installed reinforcing bars with the cast-in bars under seismic loads, second establishing the higher performance of post-installed bars compared to the cat-in bars under static and eventually for seismic loads. A new test specimen (modified beam-end specimen) was developed for conducting the tests, a new method was developed to evaluate the results for establishing the influence of various parameters on the performance of post-installed bars, a new displacement-based testing protocol was developed for the seismic qualification tests, while a hierarchy-based approach was developed to design the structural connections formed using post-installed reinforcing bars. This paper presents the background research that went into development of new formulations, provides the justifications for the design of test specimen and test protocol, and explains the design concept along with the limitations and scope of applications.