مطالعه آزمایشگاهی بررسی رفتار و بهسازی میان‌قاب‌های بلوک سفال در بارگذاری خارج از صفحه با استفاده از الیاف شیشه مقاوم در برابر قلیا

Performance assessment of reinforced concrete frames with clay block infills during recent earthquakes, particularly the devastating 2017 Kermanshah (Sarpol-e Zahab) earthquake, demonstrates the significant vulnerability of these common structural systems. Analysis of the resulting damage indicates that most failures stem from inadequate anchoring or complete lack of proper restraint in the infills. This structural weakness has led to extensive economic damage and in some cases, loss of life. Considering the widespread use of this structural system in existing buildings, developing efficient, economical, and implementable retrofitting solutions to enhance their seismic performance is of high importance. The present research aims to develop and evaluate a novel method for retrofitting clay block infills using alkali-resistant glass fiber technology. The effectiveness of this strengthening technique has been assessed through precise out-of-plane loading tests. The proposed retrofitting approach relies on alkali-resistant glass fibers, selected for their favorable durability characteristics in concrete's alkaline environment, appropriate mechanical properties, and optimal cost-to-performance ratio. In this experimental study, three 1:2 scale reinforced concrete frame specimens were designed, constructed, and subjected to standard loading protocols, consisting of: A concrete frame with clay block infill having a two-centimeter gap from columns on each side (representing typical construction practice), A concrete frame with separator wall posts and clay block infill placed two centimeters from columns (representing an improved conventional method)A concrete, frame with wall posts where the infill section is strengthened with alkali-resistant glass fibers (representing the proposed method), For specimen construction, steel formwork with 2mm thick metal sheets was designed and fabricated in the structural laboratory. All construction phases including cutting, bending, and welding were performed with high precision at 1:2 scale proportional to actual specimens at the Shahrood University of Technology's structural laboratory. Importantly, the specimens were constructed according to common building practices, with concrete pouring sequenced from foundation to columns and finally beams to simulate real construction conditions. Standard perforated clay blocks measuring 25×20×10 centimeters were used without scaling to eliminate potential scale effects on mechanical behavior. All structural design and construction details for the reinforced concrete frame complied with Chapter 9 of the Iranian National Building Code. The main innovation of this study, beyond the strengthening method itself, lies in the approach to specimen construction following actual industry practices, making the results more applicable to real-world conditions. An advanced measurement system including high-precision linear variable displacement transducers (LVDTs) was employed to record the complete response of specimens throughout testing. Analysis of test results demonstrated that the specimen reinforced with alkali-resistant glass fibers showed significant improvement in seismic performance compared to the other two specimens. Specifically, this strengthening system provided: Increased lateral load-bearing capacity by up to 110% compared to specimens with infill with boundary conditions and infill with wall posts Enhanced ductility (displacement capacity) by up to 150% compared to non-strengthened specimens, Transformation of failure behavior from brittle and sudden to soft and ductile failure, Progressive and gradual material deterioration instead of sudden collapse. the proposed strengthening method, given its ease of implementation, reasonable cost, and desirable performance, can serve as an effective solution for retrofitting existing buildings with reinforced concrete frame systems with clay block infills in seismic regions.