ابزار جدید مکانیکی برای پس تنیدگی میلگردهای تقویت شده با فیبر پلیمر
ABSTRACT
A mechanical device specially designed for the application of low-level post-tensioning forces to glass fiber reinforced polymer (GFRP) bars has been developed at the University of Missouri-Rolla. Some of the advantageous features of this device are that it is simple to assemble and the low-level post-tensioning forces can be applied manually and safely without the need for hydraulic jacks or heavy equipment. This device has been conceived with the main objective of retrofitting masonry buildings, some of which remain in service despite large, open cracks leading to considerable instability and serviceability concerns. According to the method derived in this paper, GFRP bars are installed in artificially imposed grooves and then post-tensioned with lowlevel stresses with the main objective to partially close these cracks, such that the serviceability and in-plane capacity of un-reinforced masonry (URM) buildings may be regained. In this paper we describe the mechanical components of this device, along with its advantageous features and potential application for the retrofit of URM walls.
Introduction
In their present forms, traditional methods for posttensioning and anchorage of steel tendons cannot be used directly for fiber reinforced polymer (FRP) bars because of difficulties associated with the gripping of FRP bars in the anchorage region. These may include damage to the FRP bars due to excessive gripping force and/or slippage of the bars out of the anchorage zone caused by low friction between the gripping mechanism and the bars. A variety of anchorage systems have been recently developed to address the poor performance of the anchorage of FRP bars.l-6 These can be divided into three general groups: wedge, resin/grout potted, and spike systems. These systems have inevitable drawbacks in practice, such as potential for local damage to the FRP bars, curing time for resin, field setup time, and special requirement for the bars, among many others. A hand-held device was developed in this research program to address some of these issues. This device features a simple way to simultaneously anchor and apply low-level tensile forces to glass fiber reinforced polymer (GFRP) bars without causing damage to the bars due to creep-rupture. Furthermore, this device can be reused for future applications. In this system, the mechanism used for the anchorage of GFRP bars was developed based on the property of thermoplastic resin, inherent to the GFRP bars produced for use with this particular device. 7'8 Thermoplastic resins were considered for this type of application because when they are reheated they become soft, and may be remolded as necessary to achieve the desired anchorage system. In addition, it can be shown that no permanent damage is caused to the bars. Based on this property, the GFRP bars are reheated by controlling the temperature and, after the resin is softened, a wedge or a nail is driven into the center of the bars from each end to create the desired anchorage mechanism. Thus, by combining the resin's thermoplastic property with this specially designed device, low-level tensile forces may be applied to GFRP bars with the main goals of increasing unreinforced masonry (URM) wall strength and restoring the serviceability by closure of cracks from stressing the bars placed in artificially imposed grooves. The mechanical components of this device, assemblage, and potential application for the retrofit of URM walls are discussed in this paper.
چکیده
مقدمه
تشریح دستگاه
ویژگی ها
اجزای اصلی
سرهم بندی
ارزیابی تجربی
فاز 1: خصوصیات اجزا
فاز 2: مقاوم سازی دیوارهای بنایی
نتیجه گیری
ABSTRACT
Introduction
Device Description
Features
Main Components
Assemblage
Experimental Evaluation
Phase h Component Characterization
Phase Ih Retrofit Applications to Masonry Walls
Conclusions
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