내진보강용 폴리우레아로 보강된 철근콘크리트 기둥의 내진성능 평가에 대한 유사동적실험 연구

The seismic performance evaluation and retrofit process are very important in damaged bridges. If the result is not appropriate, then retrofit process are required. In this paper, to validate the seismic performance of retrofitted bridge experimentally, an experimental study was conducted to verify the application and efficiency of the jacket retrofit method to ensure seismic performance of damaged reinforcement concrete (RC) bridge piers. A total of 4 RC bridge piers was made and then 3 piers were pre-loaded under the range of service load to be damaged. These piers were retrofitted and repaired using a carbon fiber reinforced polymer (CFRP), steel plate, and fiber steel composite (FSC) plates. These retrofitted and repaired piers were subjected to monotonic loading. Hysteresis and ultimate behaviors of the 3 RC piers were evaluated and compared with those of 1 non-damaged pier (standard specimen). As a test result, the retrofitted and repaired RC bridge piers applied by the jacket retrofit method were ensured under the targeted displacement ductility and ultimate load. The ultimate load and displacement ductility of the pier retrofitted and repaired by FSC plate were higher than those of other piers by CFRP and steel plates and also the pier by FSC plate showed better energy dissipation capacity than others. Generally, RC bridge pier retrofitted and repaired with the jacket retrofit method has low ductility but it was found that the pier retrofitted and repaired by FSC plate combined with CFRP and steel wire had overcome effectively this disadvantage through ductility evaluation based on the concept of energy numerically. This experiment showed that one could improve the safety margin and targeted ductility by repairing the cracks, spalls, etc. of the damaged RC bridge piers appropriately and then retrofitting them with the high ductile materials. The responses of existing damage bridges are compared with those of retrofitted bridge by jacket method for earthquake of target level, and also seismic performances are evaluated. By the test and analysis results it can be concluded that the proposed seismic retrofit method was found to be valid.

This paper presents some quasi-static tests for 4 mixed columns composed of CFST column and RC column. The seismic performance and failure mode were studied under low-cyclic revised loading. The failure mode was observed under different axial compression ratios. The hysteretic curve and skeleton curve were obtained. The effects of axial compression ratio on yield mechanism, displacement ductility, energy dissipation, stiffness and strength attenuation were analyzed. The results indicate that the failure behavior of CFST-RC mixed column with archaized style is mainly caused by bending failure and accompanied by some shear failure. The axial compression ratio performs a control function on the yielding order of the upper and lower columns. The yielding mechanism has a great influence on the ductility and energy dissipation capacity of specimens. Based on the experiment, finite element analysis was made to further research the seismic performance by ABAQUS software. The variable parameters were stiffness ratio of upper and lower columns, axial compression ratio, yielding strength of steel tube, concrete strength and rebar ratio. The simulation results show that with the increase of stiffness ratio of the upper and lower columns, the bearing capacity and ductility of specimens can correspondingly increase. As the axial compression ratio increases, the ductility of the specimen decreases gradually. The other three parameters both have positive effect on the bearing capacity but have negative effect on the ductility. The results can provide reference for the design and engineering application of mixed column consisted of CFST-RC in Chinese archaized buildings.

합성 교각의 설계에서 요구 내진성능을 만족하기 위한 철근상세 규정이 명확하지 않은 측면이 있다. 합성 교각은 단면치수를 감소시키고 지진하중하에서 기둥의 연성을 개선하기 위해 제안되었다. 이 논문에서는 400mm 직경을 가진 단일 강재를 콘크리트에 매입한 합성기둥 부재를 5기 제작하여 합성기둥의 내진성능을 연구하였다. 진동대 실험과 유사동적 실험이 수행되었는데 근단층지반운동을 고려한 축소모형의 구조적 거동이 평가되었다. 실험 변수는 횡철근의 간격, 주철근의 겹침이음, 매입 강재 단면으로 설정하였다. 진동대 실험에 의해 평가된 변위연성도가 유사동적 실험에 비해 적게 나타났고 한정연성설계, 주철근의 겹침 이음 50%를 가진 부재가 기준 부재에 비해서 낮은 연성도를 보였다. 강재비는 극한강도에 영향을 미치고 겹침이음과 횡철근 비의 감소는 변위능력을 감소시켰다. 합성 교각의 상세에 따른 에너지 소산능력의 차이는 뚜렷하게 나타나지 않았다. For the design of composite bridge piers, detail requirements for the reinforcements is not clear to satisfy the required seismic performance. Composite bridge piers were suggested to reduce the sectional dimensions and to enhance the ductility of the columns under earthquake loadings. In this paper, five specimens of concrete encased composite columns of 400mm diameter with single core steel were fabricated to investigate the seismic performance of the composite columns. Shaking table tests and a Pseudo-Dynamic test were carried out and structural behavior of small-scaled models considering near-fault motions was evaluated. Test parameters were the pace of the transverse reinforcement, lap splice of longitudinal reinforcement and encased steel member sections. The displacement ductility from shaking table tests was lower than that from the pseudo-dynamic test. Limited ductile design and 50% lap splice of longitudinal reinforcement reduced the displacement ductility. Steel ratio showed significant effect on the ultimate strength. Lap splice and low transverse reinforcements reduced the displacement capacity. The energy dissipation capacity of composite columns did not show significant difference according to details.

The present study proposes a new seismic retrofitting method using a concrete-filled tube modular frame (CFT-MF) system, a novel technique to overcome and improve the limitations of existing seismic strengthening methods. This CFT-MF seismic retrofitting method makes the most of the advantages of both concrete and steel pipes, thereby significantly improving constructability and increasing integration between the existing structure and the reinforcement joints. This method falls into the category of typical seismic retrofitting methods that focus on increasing strength, in which the required amount of seismic reinforcement can be easily estimated. Therefore, the method provides an easy solution to improving the strength of existing reinforced concrete (RC) structures with non-seismic details that are prone to shear failure. In the present study, a full-size two-story test frame modeled from existing domestic RC structures with non-seismic details was subjected to pseudo-dynamic testing. As a result, the effect of the CFT-MF system, when applied to existing RC structures, was examined and verified, especially as to its seismic retrofitting performance, i.e., restoring force characteristics, stiffness reinforcement, and seismic response control. In addition, based on the pseudo-dynamic testing results, a restoring force characteristics model was proposed to implement non-linear dynamic analysis of a structure retrofitted with the CFT-MF system (i.e., the test frame). Finally, based on the proposed restoring force characteristics, non-linear dynamic analysis was conducted, and the results were compared with those obtained by the pseudo-dynamic tests. The results showed that the RC frame (building) with no retrofitting measures applied underwent shear failure at a seismic intensity of 200 cm/s2, the threshold applied in seismic design in Korea. In contrast, in the frame (building) retrofitted with the CFT-MF system, only minor earthquake damage was observed, and even when the maximum seismic intensity (300 cm/s2) that may occur in Korean was applied, small-scale damage was observed. These results confirmed the validity of the seismic retrofitting method based on the CFT-MF system developed in the present study. The non-linear dynamic analysis and the pseudo-dynamic test showed similar results, with an average deviation of 10% or less in seismic response load and displacement.

In the present study, a window-type seismic control system (WSCS) using non-buckling slit dampers (NBSDs) was proposed and developed to address the disadvantages of conventional seismic control systems so that it can be effectively applied to existing reinforced concrete (RC) buildings. Materials testing was also conducted to examine the material performance and energy dissipation capacity of NBSD. A full-scale two-story test frame modeled from existing RC buildings with non-seismic details was subjected to pseudo-dynamic testing. As a result, the effect of NBSD-WSCS, when applied to existing RC frames, was examined and verified, especially as to its seismic retrofitting performance. In addition, based on material testing and pseudo-dynamic test results, a restoring force characteristics model was proposed to implement the nonlinear dynamic analysis of a test building retrofitted with NBSD-WSCS. Based on the proposed restoring force characteristics, nonlinear dynamic analysis was conducted, and the results were compared with those obtained by the pseudo-dynamic tests. Finally, in an attempt to commercialize this NBSD-based WSCS, nonlinear dynamic analysis was conducted on the entire RC building with non-seismic details retrofitted with NBSD-WSCS. The results showed that the RC frame (building) with no reinforcement applied underwent shear failure at seismic intensity of 200 cm/s2, a typical threshold applied in seismic design in Korea. In contrast, in the frame (building) retrofitted with NBSD-WSCS, only minor earthquake damage was expected, and even when the seismic intensity was set to 300 cm/s2, the maximum intensity that had been observed in Korea, only small or moderate seismic damage was expected. These results confirmed the effectiveness of the seismic retrofitting method using NBSD-WSCS developed in the present study.

Seismic retrofit of a reinforced concrete flat-slab structure: Part I — seismic performance evaluation

The paper investigates the seismic performance of rectangular RC columns retrofitted by a newly developed 3D Textile Reinforced Mortar (TRM) panel. The 3D-TRM used in this study consists of two components: self-leveling mortar and 3D textiles. Firstly, the flexural capacity of the 3D-TRM panel was investigated through the four-point flexural test. Secondly, a total of five specimens were constructed and experimentally investigated through static cyclic loading tests with constant axial load. One specimen was a non-seismically designed column without any retrofit, while the others were strengthened with either the 3D-TRM panel or conventional Fiber Reinforced Polymer (FRP) sheets. Experimental results in terms of hysteretic behavior, ductility ratio, and energy dissipation are investigated and compared with the cases of specimens with conventional retrofitting methods and without any retrofit. The maximum lateral force, ductility, stiffness degradation, and energy dissipation of RC columns with 3D-TRM panels were significantly improved compared with the conventional RC column. Therefore, it is concluded that the proposed retrofitting method can improve the seismic performance of non-conforming RC columns.

In recent years there have been significant developments in seismic retrofit of building structures. For steel off-shore jacket structures, however, researches on the seismic performance evaluation and retrofit are relatively rare. In this study, the advantages of using Buckling-Restrained Braces (BRBs) in offshore jacket structures and its effect on the seismic performance of the platform are highlighted. The potential failure mechanisms of the structures using both normal braces and BRBs under seismic loads were investigated first. Pushover analyses of fixed jacket offshore platforms comprising the most common types of the platforms in practice were conducted. In those model structures, two different schemes of BRB retrofitting were utilized and compared with the normal bracing case. After that, an example for the seismic assessment of an existing 8 legged service platform located in the Gulf of Thailand was investigated. The model was designed based on loads according to the environmental conditions in Gulf of Thailand. Different retrofitting schemes using normal braces were investigated to improve the seismic performance of the structure and the results were compared with the results of the seismic retrofit using BRBs. The analysis results showed that the seismic performances of the jacket structures were greatly improved when bracing members were replaced with BRBs compared to the case with using normal bracing. Numerical results revealed that the plastic hinges were more uniformly distributed over the structures in case of retrofit using BRB, while they were concentrated at the top of the structures when normal bracings were used.

Real‐time pseudodynamic (PSD) testing is an experimental technique for evaluating the dynamic behaviour of a complex structure. During the test, when the targeted command displacements are not achieved by the test structure, or a delay in the measured restoring forces from the test structure exists, the reliability of the testing method is impaired. The stability and accuracy of real‐time PSD testing in the presence of amplitude error and a time delay in the restoring force is presented. Systems consisting of an elastic single degree of freedom (SDOF) structure with load‐rate independent and dependent restoring forces are considered. Bode plots are used to assess the effects of amplitude error and a time delay on the steady‐state accuracy of the system. A method called the pseudodelay technique is used to derive the exact solution to the delay differential equation for the critical time delay that causes instability of the system. The solution is expressed in terms of the test structure parameters (mass, damping, stiffness). An error in the restoring force amplitude is shown to degrade the accuracy of a real‐time PSD test but not destabilize the system, while a time delay can lead to instability. Example calculations are performed for determining the critical time delay, and numerical simulations with both a constant delay and variable delay in the restoring force are shown to agree well with the stability limit for the system based on the critical time delay solution. The simulation models are also used to investigate the effects of a time delay in the PSD test of an inelastic SDOF system. The effect of energy dissipation in an inelastic structure increases the limit for the critical time delay, due to the energy removed from the system by the energy dissipation. Copyright © 2007 John Wiley & Sons, Ltd.

Quasi-static and pseudo-dynamic testing of infilled RC frames retrofitted with CFRP material

The effectiveness of seismic retrofitting of multi-storey multi-bay reinforced concrete (RC)-frame buildings by converting selected bays into new walls through infilling with RC was studied experimentally at the ELSA facility of the Joint Research Centre in Ispra (Italy). A full-scale model was tested with the pseudo-dynamic (PsD) method and consisted of two four-storey (12 m tall) three-bay (8,5 m long) parallel frames linked through 0,15 m slabs with the central bay (2,5 m) infilled with an RC wall. The frames were designed and detailed for gravity loads only and were typical of similar frames built in Cyprus in the 1970s. Different connection details and reinforcement percentages for the two infilled frames were used in order to study their effects in determining structural response. The results of the pseudo-dynamic and cyclic tests performed on the specimen are presented, and conclusions are drawn.

The overhead gas-insulated transmission line (GIL) in ultra-high-voltage converter stations, distinct from traditional buried pipelines, demands a thorough investigation into its seismic behavior due to limitations in existing codes. A refined finite element model is established, considering internal structure, slip between various parts, and the relative displacement at the internal conductor joint. Seismic analysis reveals the vulnerability of the GIL at the corner of the pipeline height change, with two failure modes: housing strength failure and internal conductor displacement exceeding the limit. Furthermore, the acceleration amplification coefficient of the support generally exceeds 2.0. Two retrofit methods, namely increasing the fundamental frequency of all supports and fixing the connections between all supports and the housing, have been proposed. The results indicate the effectiveness of both methods in reducing the relative displacement. Fixing all the supports effectively reduces the stress, whereas the other one yields the opposite effect. The seismic performance of a GIL is determined not by the dynamic amplification of supports, but by the control of relative displacement between critical sections, specifically influenced by the angular deformation of the pipeline’s first-order translational vibration mode along the line direction. Seismic vulnerability analysis reveals a reduction of over 50% in the failure probability of the GIL after the retrofit compared to before the retrofit, with the PGA exceeding 0.4 g.

The prefabricated residential buildings have become one of the most dominating construction methods in the modern construction industry. The seismic behavior of prefabricated components is crucial in the limit state design of the precast structure. This paper investigates the seismic behavior of a new type precast concrete column that has clustered steel reinforcement with grouting connection. Quasi-static tests are carried out on three cast-in-situ columns and seven precast columns. Axial compression ratio, lap length and lap space are the main variables considered. The failure process, hysteresis curve, skeleton curve, stiffness degradation, displacement ductility and energy dissipation are elaborated. The experimental results show that the precast columns with cluster reinforcement have similar seismic behavior to the cast-in-situ columns. Reducing the axial pressure can improve the ductility and energy consumption performance of the cluster-reinforced columns and exert its ductility to improve its seismic performance. During the assembly, a moderate increase in lap length can improve the seismic behavior of precast columns, whereas the lap space has an insignificant effect on the seismic behavior which indicates that the lap space is not an important factor during construction. The research outcome can serve as a reference for further development and application of precast structures.

In the design of bridge piers in seismic area, the ductility requirement is the most important factor. In order to enhance the seismic performance of RC columns, it is necessary to make the ductility of columns larger by covering RC columns with steel tubes or confining RC columns by arranging transverse reinforcements such as hoop ties closely. Using core steel composite columns is useful as one of the reinforcing RC columns. In this paper, quasi-static tests on concrete encased composite columns with single core steel or multiple steel elements were performed to investigate the seismic performance of the composite columns. Eight concrete-encased composite specimens were fabricated. The cross-sections of these specimens are composed of concrete-encased H-shaped structural steel columns and a concrete-encased circular tube with partial in-filled concrete. Test parameters were the amount of the transverse reinforcements, type and number of encased steel member. Through the tests, it was evaluated the ductility of SRC composite specimens. It has become clear from the test results that encased steel elements makes the deformation capacity of the columns to be larger. The displacement ductility and lateral strength of specimen with concrete-encased circular tube were indicated the biggest value.

Seismic retrofitting of exiting building structures is a technical and social issue aimed as earthquake risk mitigation. In this study, a new technique for seismic retrofitting via the attachment of an external steel frame with length-adjustment control box (ESFLC) was developed to strengthen medium-to-low-rise reinforced concrete (RC) buildings. The developed method, categorized as a strength design approach, can be used to perform seismic strengthening construction while residents continue to live within the building, exhibiting excellent constructability because a control box is applied as a length-adjustment device to cope with errors in the field associated with assembly works between the existing structure and reinforcing frame. Two full-size two-story RC frame specimens were designed based on an existing Korean RC building without seismic details; one control specimen and one specimen strengthened with the ESFLC system were used. Pseudodynamic tests were carried out to verify the effects of seismic retrofitting in terms of the maximum response strength, response displacement, and degree of earthquake damage compared with a control RC frame. Nonlinear dynamic analysis was also conducted based on the material properties of the test specimens, including mathematical models that represent the nonlinear hysteresis of the used structural members, to compare the results of the pseudodynamic tests. Test results revealed that the proposed ESFLC strengthening method, externally attached to the existing RC frame, effectively increased the lateral ultimate strength, resulting in reduced response displacement of RC structures under large-scale earthquake conditions. The nonlinear dynamic analysis and test results were in reasonable agreement.