Large-diameter reinforcements(maximum 57㎜) and amount of reinforcements (about 0.13 million ton, Shin-gori #3,4 project) are used in Nuclear Power Plant Structures in order to enhance the structural safety and secure the enough durability of structure. But the significant congestion occurs in the structures when a lot of reinforcements are placed, and also it may cause several potential problems during the construction. Because many types of systems and components, such as machine equipment, piping, electrical facilities, measurement equipment, shall be mounted on or penetrated through the Nuclear Power Plant Structures, it is necessary to install the embeded materials, such as embeded plates, embeded sleeves, embeded anchors, around the reinforcing bars. But because of the congestion of reinforcements, there are interference in the installation of the embeded materials and difficulty in pouring concrete. In particular, it is more difficult to pour concrete into structural member joint area than other areas because of the significant interference in hooked bars and embedded materials.
We hope that solve these problems due to the reinforcement congestion by using the large-sized diameter(43㎜ & 57㎜) with high-strength(ASTM A615 Gr.80) headed deformed bars of in Nuclear Power Plant Structures as a alternative of standard hooked bars. For this, it is necessary to find the method how to relax limits on their use while maintaining or improving the anchorage capacity. Therefore, it is required to look into the results of tests planned to evaluate the influence of the restricted variables, such as bar size, yield strength, clear cover thickness. Also the usefulness of relaxed limits has to be checked and new equations for the required design development length of headed deformed bars may be established if necessary.
If it is possible to resolve the problem of the reinforcing bar congestion by replacing standard hooked bars with headed deformed bars in beam-column joints of Nuclear Power Plant Structures, it can paly a prominent part in strengthening global competitiveness of Korean Nuclear Power Plant.
In order to applying the large-Diameter headed deformed bars with high yield strength in Nuclear Power Plant Structures, it is necessary to change the code for concrete containment(ASME Sec.Ⅲ Div.2, KEPIC SNB) and nuclear safety-related concrete structures(ACI 349, KEPIC SNC). Therefore design requirements for development length of the headed deformed bars and technological background of design requirement was considered in several different ways.
First, Lap splice test(2006) & CCT node test (2005, 2006) performed by Thompson and shallow embedment test (1999) & side-blowout test (1998) performed by DeVries were considered briefly and the method how to have been reflected in ASME Sec.Ⅲ. Div.2, ACI 349, KEPIC SNB & SNC code was examined.
Various experimental studies were performed to evaluate the anchorage capacity of headed deformed bars beyond the limit conditions of current design requirements after Thompson and DeVries studies. The list of tests are follows;
(1) Test to evaluate the anchorage capacity of the headed deformed bars placed in TTC node (Hanyang university)
(2) Test to evaluate the anchorage capacity of the headed deformed bars used as lap splice (Mockpo National University, Incheon National University)
(3) Test to compare the anchorage capacity of the headed deformed bars and standard hooked bars developed in exterior Beam-Column Joint (Mockpo National University, Incheon National University, Kansas University)
Secondly, test matrix and results mentioned above were checked and correlations between development length and anchorage capacity affected by transverse reinforcement index, clear cover of reinforcement and confinement terms were analysed.
It is necessary to find out the method how to relax limits on their use while maintaining or improving the anchorage capacity in order to apply the headed deformed bars in Nuclear Power Plant Structures effectively. Therefore, development length equations of the headed deformed bars beyond limit conditions, such as size, yield strength and clear cover thickness of bars were suggested through this study.