• Structural Engineering and Mechanics
• /
• 제75권3호
• /
• pp.389-399
• /
• 2020

An infill wall made of high-performance fiber-reinforced cementitious composites (HPFRCC) was utilized in this study to strengthen the reinforced concrete (RC) frame structures that had not been designed for seismic loads. The seismic performance of the RC frame structures strengthened by the HPFRCC infill walls was investigated through the experimental tests, and the test results showed that they have improved strength and deformation capabilities compared to that strengthened by the RC infill wall. A simple numerical modeling method, called the modified longitudinal and diagonal line element model (LDLEM), was introduced to consider the seismic strengthening effect of the infill walls, in which a section aggregator approach was also utilized to reflect the effect of shear in the column members of the RC frames. The proposed model showed accurate estimations on the strength, stiffness, and failure modes of the test specimens strengthened by the infill walls with and without fibers.

• Earthquakes and Structures
• /
• 제10권6호
• /
• pp.1331-1346
• /
• 2016

Historical masonry structures have an important value for cultures and it is essential for every society to strengthen them and confidently transfer to the future. For this reason, determination of the seismic earthquake response, which is the most affecting factor to cause the damage at these structures, gain more importance. In this paper, the seismic earthquake behaviour of Kaya Çelebi Mosque, which is located in Turkey and the restoration process has still continued after 2011 Van earthquake, is determined. Firstly the dynamic modal analysis and subsequently the seismic spectral analysis are performed using the finite element model of the mosque constructed with restoration drawings in SAP2000 program. Maximum displacements, tensile, compressive and shear stresses are obtained and presented with contours diagrams. Turkish Earthquake Code and its general technical specifications are considered to evaluate the structural responses. After the analyses, it is seen that the displacements and compressive/shear stresses within the code limits. However, tension stresses exceeded the maximum values at some local regions. For this mosque, this is in tolerance limits considering the whole structure. But, it can be said that the tension stresses is very important for this type of the structures, especially between the stone and mortar. So, some additional strengthening solutions considering the originality of historical structures may be applicable on maximum tensile regions.

• Steel and Composite Structures
• /
• 제11권6호
• /
• pp.435-454
• /
• 2011

Bonding composite materials to structural members for strengthening purpose has received a considerable attention in recent years. The major problem when using bonded FRP or steel plates to strengthen existing structures is the high interfacial stresses that may be built up near the plate ends which lead to premature failure of the structure. As a result, many researchers have developed several analytical methods to predict the interface performance of bonded repairs. In this paper, a numerical solution using finite - difference method is used to calculate the interfacial stress distribution in beams strengthened with FRP plate having a tapered ends with different thinning profiles. These latter, can significantly reduce the stress concentration. In the present theoretical analysis, the adherend shear deformations are taken into account by assuming a parabolic shear stress through the thickness of both beam and bonded plate. Numerical results from the present analysis are presented to demonstrate the advantages of use the tapers in design of strengthened beams.

• Steel and Composite Structures
• /
• 제33권5호
• /
• pp.629-640
• /
• 2019

This paper presents a theoretical and finite element (FE) study on the stress intensity factors of double-edged cracked steel beams strengthened with carbon fiber reinforced polymer (CFRP) plates. By simplifying the tension flange of the steel beam using a steel plate in tension, the solutions obtained for the stress intensity factors of the double-edged cracked steel plate strengthened with CFRP plates were used to evaluate those of the steel beam specimens. The correction factor α₁ was modified based on the transformed section method, and an additional correction factor φ was introduced into the expressions. Three-dimensional FE modeling was conducted to calculate the stress intensity factors. Numerous combinations of the specimen geometry, crack length, CFRP thickness and Young's modulus, adhesive thickness and shear modulus were analyzed. The numerical results were used to investigate the variations in the stress intensity factor and the additional correction factor φ. The proposed expressions are a function of applied stress, crack length, the ratio between the crack length and half the width of the tension flange, the stiffness ratio between the CFRP plate and tension flange, adhesive shear modulus and thickness. Finally, the proposed expressions were verified by comparing the theoretical and numerical results.

• 한국공작기계학회:학술대회논문집
• /
• 한국공작기계학회 1996년도 춘계학술대회 논문집
• /
• pp.61-66
• /
• 1996

An overall feature to simulate composite behavior and to predict closed solution has been performed for the application to the stress analysis in a discontinuous composite solid. To obtain the internal field quantities of composite, the micromechanics analysis and finite element analysis (FEA) were implemented. For the numerical illustration, an aligned axisymmetric single fiber model has been employed to assess field quantities. Further, a micromechanics model to describe the elastic behavior of fiber or whisker reinforced metal matrix composites has been developed and the stress concentrations between reinforcements were investigated using the modified shear lag model with the comparions between reinforcements were investigated using the modified shear lag model with the comparison of finite element analysis (FEA). The rationale is based on the replacement of the matrix between fiber ends with the fictitious fiber to maintain the compatibility of displacement and traction. It was found that the new model gives a good agreement with FEA results in the small fiber aspect ratio regime as well as that in the large fiber aspect ratio regime. It was found that the proposed simulation methodology for stress analysis is applicable to the complicated inhomogeneous solid for the investigation of micromechanical behavior.

• Earthquakes and Structures
• /
• 제13권2호
• /
• pp.177-191
• /
• 2017

In the present study, exterior beam column sub-assemblages are designed in accordance with the codal stipulations prevailed at different times prior to the introduction of modern seismic provisions, viz., i) Gravity load designed with straight bar anchorage (SP1), ii) Gravity load designed with compression anchorage (SP1-D), iii) designed for seismic load but not detailed for ductility (SP2), and iv) designed for seismic load and detailed for ductility (SP3). Comparative seismic performance of these exterior beam-column sub-assemblages are evaluated through experimental investigations carried out under repeated reverse cyclic loading. Seismic performance parameters like load-displacement hysteresis behavior, energy dissipation, strength and stiffness degradation, and joint shear deformation of the specimens are evaluated. It is found from the experimental studies that with the evolution of the design methods, from gravity load designed to non-ductile and then to ductile detailed specimens, a marked improvement in damage resilience is observed. The gravity load designed specimens SP1 and SP1-D respectively dissipated only one-tenth and one-sixth of the energy dissipated by SP3. The specimen SP3 showcased tremendous improvement in the energy dissipation capacity of nearly 2.56 times that of SP2. Irrespective of the level of design and detailing, energy dissipation is finally manifested through the damage in the joint region. The present study underlines the seismic deficiency of beam-column sub-assemblages of different design evolutions and highlights the need for their strengthening/retrofit to make them fit for seismic event.

• Structural Engineering and Mechanics
• /
• 제71권3호
• /
• pp.233-244
• /
• 2019

Steel jacketing technique is a retrofitting method often employed for static and seismic strengthening of existing reinforced concrete columns. When no continuity is given to angle chords as they cross the floor, the jacket is considered "indirectly loaded", which means that the load acting on the column is transferred partially to the external jacket through interface shear stresses. The evaluation of load transfer mechanism between core and jacket is not straightforward to be modeled, due to the absence of knowledge of a proper constitutive law of the concrete-to-steel interface and to the difficulties in taking into account the mechanical nonlinearities of materials. This paper presents an incremental analytical/numerical approach for evaluating the compressive response of RC columns strengthened with indirectly loaded jackets. The approach allows calculating shear stresses at the interface between core and jacket and predicting the axial capacity of retrofitted columns. A proper constitutive law is proposed for modelling the interaction between the steel and the concrete. Based on plasticity rules and the non-linear behaviour of materials, the column is divided into portions. After a detailed parametric analysis, comparisons are finally made by theoretical predictions and experimental results available in the literature, showing a good agreement.

• 대한건축학회연합논문집
• /
• 제21권1호
• /
• pp.185-192
• /
• 2019

Recently, the frequency and magnitude of earthquakes are increasing worldwide. In Korea, the Gyeongju earthquake (2016) and the Pohang earthquake (2017) caused structural damage to many buildings. Since Korea's seismic design standards were revised to three or more stories in 2005, five-story buildings built before the revision are not designed to be earthquake-resistant. In this situation, if strong earthquake occurs in Korea, there will be great damage. To prevent this, seismic retrofit of buildings should be necessary. The seismic retrofit of classical method is mainly used to reduce the displacement generated in the structure by strengthening stiffness and strength. However, since this method increases the base shear force of the structure, it is difficult to apply it to buildings which have weak foundation. Therefore, in this study, we propose the damper system that reduces the response displacement of buildings and suppresses the increase of base shear force by using high damping rubber and steel. And the seismic performance of the damper system is verified through the experiment and the seismic analysis of the structure.

• Earthquakes and Structures
• /
• 제12권6호
• /
• pp.603-617
• /
• 2017

This paper presents investigation into the behavior of beam-column joints, with the joint region concrete being replaced by steel fiber reinforced concrete (SFRC) and by ultra-high performance concrete (UHPC). A total of ten beam-column joint specimens (BCJ) were tested experimentally to failure under monotonic and cyclic loading, with the beam section being subjected to flexural loading and the column to combined flexural and axial loading. The joint region essentially transferred shear and axial stresses as received from the column. Steel fiber reinforced concrete (SFRC) and ultra-high performance concrete (UHPC) were used as an innovative construction and/or strengthening scheme for some of the BCJ specimens. The reinforced concrete specimens were reinforced with longitudinal steel rebar, 18 mm, and some specimens were reinforced with an additional two ties in the joint region. The results showed that using SFRC and UHPC as a replacement concrete for the BCJ improved the joint shear strength and the load carrying capacity of the hybrid specimens. The mode of failure was also converted from a non-desirable joint shear failure to a preferred beam flexural failure. The effect of the ties in the SFRC and UHPC joint regions could not be observed due to the beam flexural failure. Several models were used in estimating the joint shear strength for different BCJ specimens. The results showed that the existing models yielded wide-ranging values. A new concept to take into account the influence of column axial load on the shear strength of beam-column joints is also presented, which demonstrates that the recommended values for concrete tensile strength for determination of joint shear strength need to be amended for joints subject to moderate to high axial loads. Furthermore, finite element model (FEM) simulation to predict the behaviour of the hybrid BCJ specimens was also carried out in an ABAQUS environment. The result of the FEM modelling showed good agreement with experimental results.

• 대한토목학회논문집
• /
• 제32권4A호
• /
• pp.237-244
• /
• 2012

콘크리트는 재료적으로 인장에 취약하고 변형에 취성이 크다는 태생적 단점을 갖고 있다. 콘크리트 조직에 인장에 강한 작은 섬유를 혼합한 섬유보강콘크리트는 이러한 취약점을 보완할 수 있는 좋은 방법으로 간주되었으며, 많은 종류의 섬유재료와 방법들이 제안되었다. 그러나 이 섬유보강콘크리트에도 아직까지 해결하지 못한 문제로서 균질한 배합이 힘들고 높은 체적비를 갖는 섬유 혼입의 어려움 등이 있다. 최근에 새로운 개념의 규칙적 다공질 금속(periodic cellular metal)이 개발되어 기계 분야에 많이 적용되고 있는 철선으로 직조된 카고메 트러스가 있다. 이 논문은 기존 강섬유보강콘크리트의 현실적 문제점을 해결하기 위한 방법의 일환으로 카고메 트러스의 적용 가능성을 검토하기 위한 기초 실험 연구 결과를 정리한 것이다. 3종류의 카고메 트러스로 보강된 실험체와 동일한 제원의 수직스터럽으로 보강된 보 실험 결과와 비교하였다. 그 결과, 카고메 트러스 보강 실험체에서는 강도와 연성이 보통 스터럽 보강 보 보다 더 우수한 결과를 나타냈으며, 복부 보강재로서 우수한 기능을 할 수 있는 것으로 판명되었다.