دانلود رایگان ترجمه مقاله واکنش چرخه ای تیرهای مقاوم بتن مسلح اصلاح شده با تزریق اپوکسی (سال ۲۰۱۶)

واکنش چرخه ای تیرهای مقاوم بتن مسلح اصلاح شده با تزریق اپوکسی

Cyclic Response of Reinforced Concrete Moment Resisting Beams Repaired with Epoxy Injection

Abstract

This paper presents the results of a quasi-static cyclic test carried out on a reinforced concrete special moment resisting beam in the Earthquake Engineering Center of UET Peshawar to study the efficiency of traditional repair techniques in restoring the strength and stiffness capacity of damaged RC beams. The beam was tested in a cantilever mode and was subjected to a standard loading protocol with increasing amplitude of displacement cycles. The final damage state of the beam consisted of severe cracking and spalling of the cover concrete. The cracks were repaired with low-viscosity injection epoxy and the spalled concrete was repaired with early-strength grout. The repaired specimen was subjected to the same loading protocol as the original specimen to study the efficiency of the repair technique employed. It was observed that epoxy injection is not effective in restoring the stiffness of beams due to bar slip and inelastic extension of longitudinal bars at the support end.

۱ Introduction

Modern seismic design codes [1-3] design buildings with the objective to avoid collapse and save human lives. Structures are designed for seismic forces that are considerably smaller than the design-level forces, and therefore they are prone to damage during designbasis earthquake [4]. Reinforced concrete special moment resisting frames are designed according to the principles of capacity design; which states that damage should be concentrated at fixed locations in beams, often called plastic hinges. The plastic hinges are located at the ends of beams and should be proportioned and detailed to respond primarily in flexure mode rather than brittle modes of response such as shear. This philosophy forms the basis of almost all the modern seismic design codes [1-3]. However, the subject of reparability of damaged reinforced concrete structures, after being subjected to an earthquake, has been addressed rarely. The performance of reinforced concrete moment resisting frames, designed to modern codes, in the recent earthquake of Christchurch (2011) was satisfactory but raised the issue of reparability of reinforced concrete structural components [5-6]. A large number of damaged reinforced concrete frames had to be demolished due to the lack of sufficient experimental evidence to justify the use of traditional repair techniques in restoring the capacity of damaged reinforced concrete structural elements.

This paper addresses the issue of reparability of reinforced concrete structural elements through an experimental program. Since there has been a rampant increase in the construction of reinforced concrete frames around the world, therefore, it is considered necessary to bring the issue of reparability of reinforced concrete beams to the knowledge of concerned authorities and structural design engineers. To achieve this task, it was necessary to conduct an experimental program to study the efficiency of repair techniques and highlight the associated problems with different repair techniques, used locally in Pakistan for the past many years. Quasi-static cyclic testing, as proposed by Ahmad et al., (2016) for testing beams, is conducted on a special moment resisting beam to study the efficiency of epoxy injection and grout patching in restoring the strength and stiffness of a damaged beam. Epoxy injection repair technique was studied herein due to its ease of application and its widespread adaptation in local industry in Pakistan within the context of rehabilitation.