• Steel and Composite Structures
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• v.11 no.3
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• pp.207-223
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• 2011

The results of an experimental investigation are presented in this paper for retrofitting of shear damaged reinforced concrete beams by using U shaped CFRP strips. The experimental program is consisted of seven shear deficient T cross sectioned 1/2 scale simply supported beam specimens. One beam was used as reference specimen, and the remaining six specimens were tested in two stages. At the first stage, specimens were shear damaged severely, and then were retrofitted by using CFRP strips with or without fan type anchorages. Finally, retrofitted beams were tested up to failure. Three different CFRP strip spacing were used such as 125 mm, 150 mm, and 200 mm. The effect of anchorages on shear strength and behavior of the retrofitted specimens is investigated. CFRP strips without anchorages improved the shear strength, but no flexural failure mode was observed. Specimens showed brittle shear failure due to peeling of CFRP strip from RC beam surface. Shear damaged specimens retrofitted with anchoraged CFRP strips showed improved shear strength and ductile flexural failure. Maximum strains at anchoraged strips were approximately 68% larger than that of strips without anchorages.

• Structural Engineering and Mechanics
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• v.82 no.5
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• pp.557-569
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• 2022

The retrofit of existing structures in high seismic zones is a crucial issue in the earthquake engineering field. The interest of the research community is particularly high for the structures that do not respect current seismic codes and present structural deficiencies such as poor detailing and lack of capacity design provisions. A reinforced concrete (RC) school building is used as case study to show the influence of different knowledge levels on the seismic retrofitting cost assessment. The safety assessment of the case study building highlights deficiencies under both vertical and seismic loads. By considering all the possible knowledge levels defined by the Italian such as by the European codes in order to derive the mechanical properties of the school building constitutive materials, the retrofit operations are designed to achieve different seismic safety thresholds. The retrofit structural costs are calculated and summed up to the costs for in-situ in tests. The paper shows how for the case study building the major costs spent for a large number of in-situ tests allows to save a consistent amount of money for retrofit operations. The hypothesis of demolition and reconstruction of the building is also compared in terms of costs with all the analyzed retrofit options.

• Steel and Composite Structures
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• v.52 no.5
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• pp.543-555
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• 2024

This study examines the seismic vulnerability of vertically irregular reinforced concrete (RC) frame buildings, focusing on the effectiveness of retrofitting techniques such as rocking walls (RWs) in mitigating soft story mechanisms. Utilizing a seven-story residential apartment as a prototype in a high-seismicity urban area, this research performs detailed nonlinear simulations to evaluate both regular and irregular structures, both before and after retrofitting. Pushover and nonlinear time history analyses were conducted using OpenSees software, with a suite of nine ground motion records to capture diverse seismic scenarios. The findings indicate that retrofitting with RWs significantly improves seismic performance: for instance, roof displacements at the Collapse Prevention (CP) level decreased by up to 23% in the irregular structure with retrofitting compared to its non-retrofitted counterpart. Additionally, interstory drift ratios were more uniform post-retrofit, with Drift Concentration Factor (DCF) values approaching 1.0 across all performance levels, reflecting reduced variability in seismic response. The global ductility of the retrofitted buildings improved, with displacement ductility ratios increasing by up to 29%. These results underscore the effectiveness of RWs in enhancing global ductility, mitigating soft story failures, and providing a more predictable deformation pattern during seismic events. The study thus provides valuable insights into the robustness and cost-effectiveness of using rocking walls for retrofitting irregular RC buildings.

• Journal of the Korea Concrete Institute
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• v.18 no.6 s.96
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• pp.737-742
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• 2006

Strengthening concrete structures with fiber reinforced polymer materials have grown to be a widely used method over most parts of the world today, which FRP was developed in 1960. A method to apply prestressing force to FRP is developed newly in these days, which can use the maximum performance of FRP materials. This paper presents the results of a study on improvement in flexural capacities of RC beams strenthened with near surface mounted prestressed CFRP rod and plate. Experimental variables include type of CFRP, prestressing level. Tests show that prestressed beams exhibit a higher crack-load as well as a higher steel-yielding load compared to non-prestressed strengthened beams.

• Journal of the Earthquake Engineering Society of Korea
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• v.23 no.3
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• pp.183-190
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• 2019

Recent changes in the construction method of piles to minimize noise, along with the development of high-strength reinforcement, have provided an economical high performance RC pile development to compensate for the disadvantages of existing PHC piles. In this study, a methodology for the development of cross - section details of high performance RC piles of various performances is presented by freely applying high strength steel and concrete. This study suggested a technique for calculating bending moments for a given axial force corresponding to the allowable crack widths and this can be used for serviceablity check. In calculating the design shear force, the existing design equation applicable to the rectangular or the I section was modified to be applicable to the hollow circular section. In particular, in the limit state design method, the shear force is calculated in proportion to the axial force, and the procedure for calculating PV diagram is established. Last, the section details are determined through PM diagrams that they have the similar flexural and axial-flexural performances of the PHC pile A, B and C types with a diameter of 500 mm. To facilitate the application of the selected standard sections to the practical tasks, the design PM diagram and design shear forces are proposed in accordance with the strength design method and limit state design method.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.4
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• pp.79-86
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• 2008

Four RC shear wall specimens with a/d of 2.2 are designed. And a flexural retrofitting is performed for one specimen by both enlarging wall section and adding additional vertical reinforcements. Also the effectivity of jaketting wall sides is evaluated for the two methods using only steel plate or welded wire mesh with enlargement of section. Cyclic loads are applied to the retrofitted specimens according to the loading history proposed by ACI under constant axial force. Test result showed that the strength and ductility of specimen were improved where the section was enlarged after the installation of additional vertical reinforcements. Confining the ends of wall by U shape W.W.F. with enlargement of section showed most excellent structural capacity regarding to the strength and ductility. Retrofitting by using steel plate was much effective not only to protect the abrupt decrease of strength after yield but also to improve the deformation capacity.

• Journal of the Korea institute for structural maintenance and inspection
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• v.7 no.4
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• pp.191-199
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• 2003

The inelastic response of many structural steel and reinforced concrete structures subject to extreme loadings can be characterized by elastoplastic behaviors. Although excursion beyond the elastic range is usually not permitted under normal conditions of service, the extent of permanent damage a structure may sustain when subjected to extreme conditions, such as severe blast or earthquake loading, is frequently of interest to the engineer. A blast is usually the result of an explosion defined as a "sudden expansion". This paper discusses the basic concept that defines blast loadings on structures and corresponding elastoplastic structural response (displacement, velocity, and acceleration) and try to explain a crack propagation of concrete in sudden expansion. According to nonlinear finite element analysis, the crack forms of static and dynamic states displayed different in RC structural members. This paper also provides useful data for the dynamic fracture analysis of RC frame structures.

• Journal of the Korea Concrete Institute
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• v.20 no.6
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• pp.697-704
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• 2008

This paper presents an analytical prediction of Nonlinear characteristics of prestressed concrete bridges by strengthened of externally tendon considering construction sequence, using unbonded tendon element and beam-column element based on flexibility method. Unbonded tendon model can represent unbounded tendon behavior in concrete of PSC structures and it can deal with the prestressing transfer of posttensioned structures and calculate prestressed concrete structures more efficiently. This tendon model made up the several nodes and segment, therefore a real tendon of same geometry in the prestressed concrete structure can be simulated the one element. The beam-column element was developed with reinforced concrete material nonlinearities which are based on the smeared crack concept. The fiber hysteresis rule of beam-column element is derived from the uniaxial constitutive relations of concrete and reinforcing steel fibers. The formulation of beam-column element is based on flexibility. Beam-column element and unbonded tendon element were be involved in A computer program, named RCAHEST (Reinforced Concrete Analysis in Higher Evaluation System Technology), that were used the analysis of RC and PSC structures. The proposed numerical method for prestressed concrete structures by strengthened of externally tendon is verified by comparison with reliable experimental results.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.3D
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• pp.421-431
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• 2011

In this paper, actual bridges constructed with SMA (Stone Mastic Asphalt) deck pavement and virtual bridges substituted the deck pavement with polymer concrete under the same conditions were statically analyzed to investigate applicability of the thin polymer concrete bridge deck pavements. PSC (prestressed Concrete) girder bridge, steel box girder bridge, PSC box girder bridge, and RC (Reinforced Concrete) rahmen bridge constructed with the SMA deck pavement were analyzed and compared to evaluate various types of the bridge. The bridge deck and pavement were assumed to be fully bonded and the stress and deformation during the construction were ignored while those due to pavement weight and vehicle loading were analyzed. According to the analysis results, the stress and deformation of the bridges using the polymer concrete due to the pavement weight were smaller than those using the SMA because of smaller self weight due to lighter unit weight and thinner thickness of the pavement. The stress and deformation of the bridges using the polymer concrete due to the vehicle loading were larger than those using the SMA because of the smaller area moment of inertia due to the thinner pavement thickness. In case that the pavement weight and vehicle loading applied simultaneously, the stress and deformation of the bridges using the polymer concrete were smaller because effect of self weight reduction was more dominant. Investigation of performance of the bridge deck pavement and analysis of economical efficiency are warranted.

• Journal of the Korea Concrete Institute
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• v.26 no.5
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• pp.627-634
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• 2014

In this study, standoff detonation tests and static beam tests on $160{\times}290{\times}2200mm$ RC beams were conducted to investigate the effect of local damage on the flexural strength and ductility index. And also, blast resistance of RC beams strengthened with steel fiber and FRP sheet were evaluated by these tests. The standoff detonation tests were performed with charge weight of 1kg and standoff distance of 0.1m. After the tests, crater diameters and loss weights of specimens were measured to evaluate the local damage of specimens. Flexural strength and ductility index were measured by conducting the static beam tests on the damaged and undamaged specimens. As a test results, normal concrete specimen(NC) showed relatively large crater and spall diameters that caused weight loss of 23.5kg as a local damage. Whereas, steel fiber reinforced concrete specimen(SFRC) and FRP sheet retrofitted specimens(NC-F, NC-FS) showed higher blast resistance than NC by reducing crater size and weight loss. Flexural strength and ductility index were decreased in case of local damaged specimens by detonation. Especially, large decrease of flexural strength was shown in NC as compared with intact specimen and brittle failure was occurred due to buckling of compressive reinforcement. In case of specimens strengthened with steel fiber and FRP sheet, residual flexural strength and ductility index were increased as compared with NC. In these results, it is concluded that critical local damage can be occurred unless enough standoff distance can be assured even if the charge weight is small. and it is verified that strengthening method using steel fiber and FRP sheet can increase blast resistance.