GFRP 복합보로 보강된 철근콘크리트 보의 장기거동에 관한 연구

박익현,이형주,변상민,최열 대한건축학회지회연합회 2017 대한건축학회연합논문집 Vol.19 No.3

최근 GFRP 복합재로 보강된 철근콘크리트(RC)보의 시간경과 계수에 대한 연구가 진행되고 있다. 본 연구에서는 5개의 RC 보에 대하여 두 가지 극한하중을 가한 정적 실험을 진행하였다. GFRP 복합재 보강 여부에 따라 크기 400mm (W) × 600mm (D) × 6,000mm (L) 의 RC 보를 제작하였다. 10개월 및 12개월을 통한 장기 거동 시험 결과, 극한하중의 30% 및 50%의 하중이 가해졌을 경우 GFRP로 보강한 보는 보강하지 않은 보에 비하여 25.33% 및 28.60% 낮은 처짐값을 보였다. 또한 본 실험의 결과를 통하여 GFRP 복합재는 보의 순간 처짐을 감소시킬 뿐만 아니라 지속하중에 대한 장기 처짐에도 효과적임을 알 수 있다. The present study reports the results of long-term behavior of reinforced concrete (RC) beams strengthened by glass fiber-reinforced polymer (GFRP) composite beams. In this study, a total of five RC beams are fabricated, and tested under the two different long-term loads which obtained from the short-term static tests. The RC specimen had dimensions of 400mm (width) × 600mm (depth) × 6,000mm (length), and tested with or without strengthening of GFRP composite beam. Test results showed that the long-term deflection at 10 and 12 months period of strengthened beam were approximately 25.33% and 28.60% lower than those of un-strengthened beams for 30% and 50% of loading levels, respectively. Furthermore, test results showed that strengthening of GFRP composite beams not only reduced the instantaneous deflection of RC beam but it was also more effective in controlling the long-term deflection of RC beam under long-term loads.

An innovative experimental method to upgrade performance of external weak RC joints using fused steel prop plus sheets

Ali Kheyroddin,Ali Khalili,Ebrahim Emami,Mohammad K. Sharbatdar 국제구조공학회 2016 Steel and Composite Structures, An International J Vol.21 No.2

In this paper, the efficiency and effectiveness of two strengthening methods for upgrading behavior of the two external weak reinforced concrete (RC) beam-column joints were experimentally investigated under cyclic loading. Since two deficient external RC joints with reduced beam height and low strength concrete were strengthened using one-way steel prop and curbs with and without steel revival sheets on the beam. The cyclic performance of these strengthened specimens were compared with two another control external RC beam-column joints, one the standard RC joint that had not two mentioned deficiencies and another had both. Therefore, four halfscale RC joints were tested under cyclic loading.The experimental results showed that these innovative strengthening methods (RC joint with revival sheet specially) surmounted the deficiencies of weak RC joints and upgraded their performance and bearing capacity, stiffness degradation, energy absorption, up to those of standard RC joint. Also, results exhibited that the prop at joint acted as a fuse element due to adding steel revival sheets on the RC beam and showed better behavior than that of the specimen without steel revival sheets. In other words by stiffening of beam, the prop collected all damages due to cyclic loading at itself and acted as the first line of defense and prevented from sever damages at RC joint.

SY 비탈형 보거푸집의 내하성능에 관한 실험적 연구

배규웅 ( Kyu-woong Bae ),부윤섭 ( Yoon-seob Boo ),황윤국 ( Yoon-koog Hwhang ),신상민 ( Sang-min Shin ) 한국구조물진단유지관리공학회 2021 한국구조물진단유지관리공학회 논문집 Vol.25 No.5

최근 공사 기간 단축과 인건비 절감을 위해 철근 콘크리트 보 및 거더용 비탈용 거푸집의 필요성이 많은 구조물에서 강조 되고 있다. 본 연구의 목적은 타설하중, 시공하중, 적재하중에 따른 새로 개발된 SY Beam의 내하성능을 평가하는 것이다. SY Beam의 표준 단면 형상은 MIDAS GEN 프로그램을 통해, 다양한 두께의 강판 데크 구조 모델링을 수행하였다. 해석 모델링 결과, SY Beam의 크기는 높이와 너비가 각각 600 mm와 400 mm로 결정되었다. 총 3 개의 SY Beam에 대해, 실험변수는 강판 데크의 두께로 고려하였으며, 실제 균일 하중 조건을 모사 할 수 있는 모래, 콘크리트 블록, 철근으로 적재한 하중 하에서 수직 및 수평 변위를 측정하는 실험을 수행하였다. 그 결과, 수직 변위는 두께가 증가할 수록 감소하는 경향을 보였다. 수평 변위에서는 두께에 따른 추세가 명확하게 관찰되지 않았다. 하중 실험에 대한 평가에서 SY Beam은 작업성과 구조적 안전성을 모두 확보 할 수 있는 것으로 판단된다. 특히, SY Beam (1.2 mm)은 수평 변위가 거의 발생하지 않아 하중지지력이 우수하여, 즉시 상용화를 하여도 경쟁력이 있을 것으로 판단한다. Recently, necessities of steel form for reinforced concrete beam and girder have been emphasized in building structures for the reduction of the construction period and the labor cost. SY Beam was developed for the these purposes and is roll-formed using thin steel plate. On this research, we tried to evaluate and verify the performance and behavior of SY Beam under construction loading stage as like pouring in situ concrete. For the standard shape of SY beam, structural modelling with various steel thicknesses has carried out using MIDAS GEN program. From results of modelling, the width and height of SY Beam were determined 600mm and 400mm respectively. For 3 SY Beams, the loading experiment was performed to measure vertical and horizontal displacement under stacking sand, concrete block, and bundle of rebar. As a result , the vertical deflection showed a tendency to decrease as the thickness increased. In the horizontal displacement, the trend according to the thickness was not clearly observed. From the evaluation on the loading experiment, it is considered that the SY Beam can secure both workability and structural safety. In particular, the SY Beam(1.2mm) hardly generates horizontal displacement, so it has excellent load-bearing capacity. So, we judged that the SY Beam with 1.2mm steel plate has excellent performance and consider to be immediately commercially available.

Flexural strengthening of RC beams using externally bonded aluminum plates: An experimental and numerical study

Elsamak, Galal,Fayed, Sabry Techno-Press 2021 Advances in concrete construction Vol.11 No.6

This research investigated the flexural strengthening of RC beams using Aluminum plates (AP). An experimental program including 8 RC beams were carried out. The width and depth of the beam were 150 and 300 mm respectively while the effective span of the beam was 1560 mm. The tensile reinforcement ratios of the beams were 0.38 and 0.548%. The external APs ratios (the cross sectional area of AP to the beam cross sectional area) were 0.10, 0.37 and 0.74% while the AP length to the beam length was 0.93. A Finite element analysis (FEA) was investigated to study many variables that influenced on the ultimate load and the behavior of the AP-strengthened beams such as AP length, using shear connectors, using various techniques of the end anchorages and using anchored/unanchored U-shaped APs. It was noticed that the improvement ratios of the ultimate load and the ductility of strengthened beams with tensile reinforcement ratio of 0.38% was better than the beams with tensile reinforcement ratio of 0.548%. The AP length to the beam span ratio had a significant effect on the ultimate load, the ductility and the failure mode of the beams. The ultimate deflection and the ultimate load of the AP strengthened beams that used shear connectors increased by 165 and 54 % respectively compared to the beam without shear connectors. Using U-shaped AP jacket accompanied with end anchorages enhanced the ultimate load by 109%. The ultimate load of the beams with bolted U-shaped AP jacket increased by 128%.

Experimental investigation of impact behaviour of shear deficient RC beam to column connection

Murat Aras,Tolga Yılmaz,Özlem Çalışkan,Özgür Anıl,R. Tuğrul Erdem,Turgut Kaya 국제구조공학회 2022 Structural Engineering and Mechanics, An Int'l Jou Vol.84 No.5

Reinforced concrete (RC) structures may be subjected to sudden dynamic impact loads such as explosions occurring for different reasons, the collision of masses driven by rockfall, flood, landslide, and avalanche effect structural members, the crash of vehicles to the highway and seaway structures. Many analytical, numerical, and experimental studies focused on the behavior of RC structural elements such as columns, beams, and slabs under sudden dynamic impact loads. However, there is no comprehensive study on the behavior of the RC column-beam connections under the effect of sudden dynamic impact loads. For this purpose, an experimental study was performed to investigate the behavior of RC column-beam connections under the effect of low-velocity impact loads. Sixteen RC beam-column connections with a scale of 1/3 were manufactured and tested under impact load using the drop-weight test setup. The concrete compressive strength, shear reinforcement spacing in the beam, and input impact energy applied to test specimens were taken as experimental variables. The time histories of impact load acting on test specimens, accelerations, and displacements measured from the test specimens were recorded in experiments. Besides, shear and bending crack widths were measured. The effect of experimental variables on the impact behavior of RC beam-column connections has been determined and interpreted in detail. Besides, a finite element model has been established for verification and comparison of the experimental results by using ABAQUS software. It has been demonstrated that concrete strength, shear reinforcement ratio, and impact energy significantly affect the impact behavior of RC column-beam connections.

Performance of damaged RC continuous beams strengthened by prestressed laminates plate: Impact of mechanical and thermal properties on interfacial stresses

Tahar, Hassaine Daouadji,Abderezak, Rabahi,Rabia, Benferhat,Tounsi, Abdelouahed Techno-Press 2021 Coupled systems mechanics Vol.10 No.2

Strengthening of reinforced concrete beams with externally bonded fiber reinforced polymer plates/sheets technique has become widespread in the last two decades. Although a great deal of research has been conducted on simply supported RC beams, a few studies have been carried out on continuous beams strengthened with FRP composites. This paper presents a simple uniaxial nonlinear analytical model that is able to accurately estimate the load carrying capacity and the behaviour of damaged RC continuous beams flexural strengthened with externally bonded prestressed composite plates on both of the upper and lower fibers, taking into account the thermal load. The model is based on equilibrium and deformations compatibility requirements in and all parts of the strengthened beam, i.e., the damaged concrete beam, the FRP plate and the adhesive layer. The flexural analysis results and analytical predictions for the prestressed composite strengthened damaged RC continuous beams were compared and showed very good agreement in terms of the debonding load, yield load, and ultimate load. The use of composite materials increased the ultimate load capacity compared with the non strengthened beams. The major objective of the current model is to help engineers' model FRP strengthened RC continuous beams in a simple manner. Finally, this research is helpful for the understanding on mechanical behaviour of the interface and design of the FRP-damaged RC hybrid structures.

An experimental investigation of the flexural strengthening of preloaded self-compacted RC beams using CFRP sheets and laminates composites

Lattif, Youssef,Hamdy, Osman Techno-Press 2022 Advances in concrete construction Vol.13 No.4

This paper performs an experimental study on the flexural behavior of preloaded reinforced self-compacted concrete beams strengthened with carbon fiber reinforced polymers CFRP. A group of six preloaded strengthened beams was investigated along with one unstrengthened beam used as a reference beam RB. All beams have the same dimensions and reinforcement details: three beams are strengthened with CFRP laminates against flexural failure and three beams are strengthened with CFRP sheets. For simulating actual conditions, the beams are loaded before strengthening. Then, after strengthening, the beams are tested for flexural strength using 4-point loads where cracked and ultimate load and failure mode, along with load-deflection relation are recorded. To study the different configurations of strengthening, one layer, two layers, and U-wrap formation of laminates and sheets are considered. The results show that strengthing the RC beams using CFRP is an effective method to increase the beam's capacity by 47% up to 153% where deflection is reduced by 5%-80%. So, the beams strengthened with CFRP laminates have higher load capacity and lower ductility in comparison with the beams strengthened with CFRP sheets.

Strength Demand of Hysteretic Energy Dissipating Devices Alternative to Coupling Beams in High-Rise Buildings

Choi, Kyung-Suk,Kim, Hyung-Joon Council on Tall Building and Urban Habitat Korea 2014 International journal of high-rise buildings Vol.3 No.2

A Reinforced concrete (RC) shear wall system with coupling beams has been known as one of the most promising structural systems for high-rise buildings. However, significantly large flexural and/or shear stress demands induced in the coupling beams require special reinforcement details to avoid their undesirable brittle failure. In order to solve this problem, one of promising candidates is frictional hysteretic energy dissipating devices (HEDDs) as an alternative to the coupling beams. The introduction of frictional HEDDs into a RC shear wall system increases energy dissipation capacity and maintains the frame action after their yielding. This paper investigates the strength demands (specifically yield strength levels) with a maximum allowable ductility of frictional HEDDs based on comparative non-linear time-history analyses of a prototype RC shear wall system with traditional RC coupling beams and frictional HEDDs. Analysis results show that the RC shear wall systems coupled by frictional HEDDs with more than 50% yield strength of the RC coupling beams present better seismic performance compared to the RC shear wall systems with traditional RC coupling beams. This is due to the increased seismic energy dissipation capacity of the frictional HEDD. Also, it is found from the analysis results that the maximum allowable ductility demand of a frictional HEDD should increase as its yield strength decreases.

Experimental and Numerical Investigation of Shear Behavior of RC Beams Strengthened by Ultra-High Performance Concrete

Ashraf Awadh Bahraq,Mohammed Ali Al-Osta,Shamsad Ahmad,Mesfer Mohammad Al-Zahrani,Salah Othman Al-Dulaijan,Muhammad Kalimur Rahman 한국콘크리트학회 2019 International Journal of Concrete Structures and M Vol.13 No.1

This paper presents a study on the shear behavior of reinforced concrete (RC) beams strengthened by jacketing the surfaces of the beams using ultra-high performance fiber reinforced concrete (UHPC). The surfaces of the RC beams were prepared by sandblasting and UHPC was cast in situ over the surfaces of RC beams. The beams were strengthened using two different strengthening configurations; (i) two longitudinal sides strengthening (ii) three sides strengthening. The bond between normal concrete and UHPC was examined by conducting splitting tensile strength and slant shear strength tests on composite cylindrical specimens cast using normal concrete and UHPC. The control and strengthened beam specimens were tested using four-point loading arrangement maintaining different shear span-to-depth ratios. The results of tested beams showed the beneficial effects of strengthening the RC beams using UHPC, as evident from enhancement of the shear capacity and shifting of the failure mode from brittle to ductile with more stiff behavior. In addition, a non-linear finite element model (FEM) was developed to examine the sufficiency of the experimental results used to study the shear behavior of control and strengthened beams. The failure loads and the crack patterns determined experimentally matched well with those predicted using the proposed model with a reasonably good degree of accuracy.

Effect of GGBFS on time-dependent deflection of RC beams

M. Shariq,H. Abbas,J. Prasad 사단법인 한국계산역학회 2017 Computers and Concrete, An International Journal Vol.19 No.1

The paper presents the experimental investigations for studying the effect of ground granulated blast furnace slag (GGBFS) on the time-dependent deflection of reinforced concrete (RC) beams due to creep and shrinkage. The RC beams were reinforced with 2-10 mm bars at tension side and subjected to constant sustained two-point loading for the period of 150 days. The amount of cement replacement by GGBFS was varied from 0 to 60% with an increment of 20%. The total deflection was measured at different ages of up to 150 days under sustained loads. The experiments revealed that the time-dependent deflection of the reinforced concrete RC beams containing GGBFS was higher than that of plain concrete RC beams. At 150 days, the average creep and shrinkage deflection of RC beams containing 20%, 40% and 60% GGBFS was 1.25, 1.45 and 1.75 times higher than the plain concrete beams. A new model, which is an extension of authors’ earlier model, is proposed to incorporate the effect of GGBFS content in predicting the long-term deflection of RC beams. Besides validating the new model with the current data with higher percentage of tension reinforcement, it was also used to predict the authors’ earlier data containing lesser percentage of tension reinforcement with reasonable accuracy.