# Failure Analysis of a Concrete Anchor under Severe Seismic Action
## 1 Introduction  
Earthquake resistant design standard (DS-0050 [1]) and guidelines of electric power facilities consisted of transmission, substation and distribution facilities have recently been updated. The updated guidelines consider maximum ground acceleration equivalent to 10% of the excess probability over 100, 250, and 500 years (drawn as equidistant lines on a hazard map for Korea). These periods and over-probabilities reflect return periods of 1000, 2400, and 4800 years, respectively. In DS-0050, the zonal factors of earthquakes with return periods of approximately 2400 or 4800 years are determined for both existing and new 765-kV electrical power transmission and distribution facilities, to avoid collapse. The maximum peak ground acceleration (PGA) is 0.286 g (ca. 0.3 g). This reflects recent increases in seismic activity on the Korean peninsula. A wide range of stress redistribution over the plate-to-plate contact zone of the huge East-Japan earthquake is still underway. As major facilities, the design of electrical transmission and distribution centers must now consider higher levels of seismic motion. To ensure that concrete anchors meet the seismic provisions, ductile behavior in tension include designs based on the strength of the attachment, which is liable to ductile or brittle failure, and on anchor strength (also liable to ductile or brittle failure). In brittle anchor failure mode, an overstrength factor (\(\Omega_{0}\)) must be applied to the earthquake component (E) of the factored load [1; 2; 3; 4; 5; 6]. Most structures allow designs that reduce the base shear force by reflecting the beneficial effects of flexible behavior. This concept prevents loss of life in advance and allows serious structural damage. However, special structures such as power facilities or nuclear facilities need to limit this sort of damage. There are structures that have relatively less impact on its own functionalities during/after a seismic action. Thus, the level of restrictionneeds to be applied differently in auxiliary structures apart from the main structures (i.e., electrical power transformer/substation, nuclear reactor vessel, and nuclear waste storage structure). Therefore, acceptable damage levels are commonly defined. The response modification factor, \(R\) consists of an inelastic energy absorption coefficient, \(R_{\mu}\), and an overstrength coefficient \(\Omega_{0}\). The overstrength may be estimated through pushover analysis. However, depending on the various structural types, it is cumbersome to perform pushover analysis every time, so it may be conservatively omitted. The overstrength coefficient of a general structure is in the range of 2-3.5 and may be expressed as half of the response modification factor. The inelastic energy absorption coefficient, \(R_{\mu}\) is affected by ductility, strain hardening, hysteresis loop, soil type, deformable mode, etc., and the method of quantifying this is used in four stages [7; 8; 9; 10; 11]. Since the 45 degrees cone method for anchoring to concrete, described in ACI 349-85 and PCI Design Handbook, was developed in the mid 1970s, experiments on their performance have been conducted intensively, when various types of anchors with embedded depth, edge distance, and anchor group effects. The \(\kappa\) method, introduced in ACI 349 and ACI 355 in the late 1980s was developed as a result of experiments at the University of Stuttgart in Germany [12; 13]. In the 1990s, this method was improved and presented as a CCD (Concrete Capacity Design) method that can be used conveniently by users and an international database of experimental results was also established during the same period. Since then, the current ACI 318 and ACI 349 design methods are based on the CCD method [12; 13; 14; 15; 16]. Along the resisting capacity of the concrete bed, the upper system type is important to determine the response modification coefficient, \(R\).