• Computers and Concrete
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• 제24권2호
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• pp.159-172
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• 2019

This paper presents an investigation into the flexural behavior of reinforced concrete (RC) beams retrofitted by ultra-high performance fiber-reinforced concrete (UHPFRC) layers. The experimental study has been conducted in two parts. In the first part, four methods of retrofitting with UHPFRC layers in both the up and down sides of the beams have been proposed and their efficiency in the bonding of the normal concrete and ultra-high performance fiber-reinforced concrete has been discussed. The results showed that using the grooving method and the pre-casted UHPFRC layers in comparison with the sandblasting method and the cast-in-place UHPFRC layers leads to increase the load carrying capacity and the energy absorption capacity and causes high bond strength between two concretes. In the second part of the experimental study, the tests have been conducted on the beams with single UHPFRC layer in the down side and in the up side, using the effective retrofitting method chosen from the first part. The results are compared with those of non-retrofitted beam and the results of the first part of experimental study. The results showed that the retrofitted beam with two UHPFRC layers in the up and down sides has the highest energy absorption and load carrying capacity. A finite element analysis was applied to prediction the flexural behavior of the composite beams. A good agreement was achieved between the finite element and experimental results. Finally, a parametric study was carried out on full-scale retrofitted beams. The results indicated that in all retrofitted beams with UHPFRC in single and two sides, increasing of the UHPFRC layer thickness causes the load carrying capacity to be increased. Also, increases of the normal concrete compressive strength improved the cracking load of the beams.

• Structural Engineering and Mechanics
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• 제48권1호
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• pp.57-75
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• 2013

It is still inadequate for investigating the highly nonlinear and complex mechanical behaviors of single-layer latticed domes by only performing a force-based demand-capacity analysis. The energy-based balance method has been largely accepted for assessing the seismic performance of a structure in recent years. The various factors, such as span-to-rise ratio, joint rigidity and damping model, have a remarkable effect on the load-carrying capacity of a single-layer latticed dome. Therefore, it is necessary to determine the maximum load-carrying capacity of a dome under extreme loading conditions. In this paper, a mechanical model for members of the semi-rigidly jointed single-layer latticed domes, which combines fiber section model with semi-rigid connections, is proposed. The static load-carrying capacity and seismic performance on the single-layer latticed domes are evaluated by means of the mechanical model. In these analyses, different geometric parameters, joint rigidities and roof loads are discussed. The buckling behaviors of members and damage distribution of the structure are presented in detail. The sensitivity of dynamic demand parameters of the structures subjected to strong earthquakes to the damping is analyzed. The results are helpful to have a better understanding of the seismic performance of the single-layer latticed domes.

• Structural Engineering and Mechanics
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• 제26권3호
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• pp.277-295
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• 2007

3-D wall panels are used in construction of exterior and interior bearing and non-load bearing walls and floors of building of all types of construction. Fast construction, thermal insulation, reduced labor expense and weight saving are the most well pronounced advantage of such precast system. When the structural performance is concerned, the main disadvantage of 3D panel, when used as floor slab, is their brittleness in flexure. The current study focuses on upgrading ductility and load carrying capacity of 3D slabs in two different ways; using additional tension reinforcement, and inserting a longitudinal concentrated beam. The research is carried on both experimentally and numerically. The structural performance in terms of load carrying capacity and flexural ductility are discussed in details. The obtained results could give better understanding and design consideration of such prefabricated system.

• Structural Engineering and Mechanics
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• 제59권4호
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• pp.703-718
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• 2016

Masonry arch bridges present a large segment of Iranian railway bridge stock. The ever increasing trend in traffic requires constant health monitoring of such structures to determine their load carrying capacity and life expectancy. In this respect, the performance of one of the oldest masonry arch bridges of Iranian railway network is assessed through field tests. Having a total of 11 sensors mounted on the bridge, dynamic tests are carried out on the bridge to study the response of bridge to test train, which is consist of two 6-axle locomotives and two 4-axle freight wagons. Finite element model of the bridge is developed and calibrated by comparing experimental and analytical mid-span deflection, and verified by comparing experimental and analytical natural frequencies. Analytical model is then used to assess the possibility of increasing the allowable axle load of the bridge to 25 tons. Fatigue life expectancy of the bridge is also assessed in permissible limit state. Results of F.E. model suggest an adequacy factor of 3.57 for an axle load of 25 tons. Remaining fatigue life of Veresk is also calculated and shown that a 0.2% decrease will be experienced, if the axle load is increased from 20 tons to 25 tons.

• Steel and Composite Structures
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• 제29권6호
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• pp.735-748
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• 2018

In this paper, the cyclic behavior of steel beam-concrete encased steel (CES) column joints was investigated experimentally and numerically. Three frame middle joint samples with varying concrete slab widths were constructed. Anti-symmetrical low-frequency cyclic load was applied at two beam ends to simulate the earthquake action. The failure modes, hysteretic behavior, ultimate load, stiffness degradation, load carrying capacity degradation, displacement ductility and strain response were investigated in details. The three composite joints exhibited excellent seismic performance in experimental tests, showing high load-carrying capacity, good ductility and superior energy dissipation ability. All three joint samples reached their ultimate loads due to shear failure. Numerical results from ABAQUS modelling agreed well with the test results. Finally, the effect of the concrete slab on ultimate load was analyzed through a parametric study on concrete strength, slab thickness, as well as slab width. Numerical simulation showed that slab width and thickness played an important role in the load-carrying capacity of such joints. As a comparison, the influence of concrete grade was not significant.

• Computers and Concrete
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• 제33권2호
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• pp.121-136
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• 2024

In recent times, there has been a growing need to retrofit and strengthen reinforced concrete (RC) structures that have been damaged. Numerous studies have explored various methods for strengthening RC beams. However, there is a significant dearth of research investigating the utilization of ultra-high-performance concrete (UHPC) for retrofitting damaged RC beams within a concrete frame. This study aims to develop a finite element (FE) model capable of accurately simulating the nonlinear behavior of RC beams and subsequently implementing it in an RC concrete frame. The RC frame is subjected to loading until failure at two distinct degrees, followed by retrofitting and strengthening using Ultra high performance shotcrete (UHPS) through two different methods. The results indicate the successful simulation of the load-displacement curve and crack patterns by the FE model, aligning well with experimental observations. Novel techniques for reinforcing deteriorated concrete frame structures through ABAQUS are introduced. The second strengthening method notably improves both the load-carrying capacity and initial stiffness of the load-displacement curve. By incorporating embedded rebars in the frame's columns, the beam's load-carrying capacity is enhanced by up to 31% compared to cases without embedding. These findings indicate the potential for improving the design of strengthening methods for damaged RC beams and utilizing the FE model to predict the strengthening capacity of UHPS for damaged concrete structures.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 가을 학술발표회 논문집
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• pp.451-456
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• 2002

An experimental study was carried out to investigate the flexural behavior of RC beams strengthened with high-performance carbon fiber bars. Specimens designed with the conventional retrofitting method were also tested to compare load-carrying capacity and ductility. As the results, specimens strengthened with high-performance carbon fiber bars showed much higher load-carrying capacity and ductility compared to specimens strengthened with a steel plate and carbon fiber sheets. The failure mechanism of the specimen strengthened with a high-performance carbon fiber bar was bond-slip, whereas that of the others were interface debonding or rip-off.

• Tribology and Lubricants
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• 제25권5호
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• pp.324-329
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• 2009

In this study a complex design fitness analysis of journal bearings is carried out for the LPLi rotary-vane fuel pump application, as an external and horizontal installation, in LPG vehicles. Bearings considered in the analyses are plain and 3-axial groove journal bearings. Upon reflecting the fact that the primary failure mode of bearings in the application is a premature friction and wear failure of bearing metal due to a very low viscosity of liquid fuel LPG as a bearing lubricant, the performance factors of bearings used in an evaluation process of design fitness are a load carrying capacity and vibration suppression ability relative to a rated speed. At this time the design variables of bearings are a radial clearance and length. Results show that, in terms of both of the load carrying capacity and vibration suppression ability, the plain journal bearings are superior to the 3-axial groove journal bearings and among the plain bearings the smaller the bearing clearance (5>10>$15\;{\mu}m$) is and the longer the bearing length (6<8<10<12<14 mm) is, the better the bearing performance is.

• Earthquakes and Structures
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• 제12권1호
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• pp.23-34
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• 2017

Composite steel plate deep beam (CDB) is proposed as a lateral resisting member, which is constructed by steel plate and reinforced concrete (RC) panel, and it is connected with building frame through high-strength bolts. To investigate the seismic performance of the CDB, tests of two 1/3 scaled specimens with different length-to-height ratio were carried out under cyclic loads. The failure modes, load-carrying capacity, hysteretic behavior, ductility and energy dissipation were obtained and analyzed. In addition, the nonlinear finite element (FE) models of the specimens were established and verified by the test results. Besides, parametric analyses were performed to study the effect of length-to-height ratio, height-to-thickness ratio, material type and arrangement of RC panel. The experimental and numerical results showed that: the CDBs lost their load-carrying capacity because of the large out-of plane deformation and yield of the tension field formed on the steel plate. By increasing the length-to-height ratio of steel plate, the load-carrying capacity, elastic stiffness, ductility and energy dissipation capacity of the specimens were significantly enhanced. The ultimate loading capacity increased with increasing the length-to-height ratio of steel plate and yield strength of steel plate; and such capacity increased with decreasing of height-to-thickness ratio of steel plate and gap. Finally, a unified formula is proposed to calculate their ultimate loading capacity, and fitting formula on such indexes are provided for designation of the CDB.

• 한국공간구조학회논문집
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• 제7권1호
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• pp.63-70
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• 2007

최근 복잡해진 도심지의 토지 이용률을 높이기 위하여 원형 강교각이 건설이 요구되고 있다. 원형강교각의 경우 줄어든 단면으로 좌굴 내하력이 감소하며 이에 대한 방안으로 수직 보강재의 적용을 고려할 수 있다. 그러나 수직보강재를 적용한 원형 강교각의 좌굴 내하력의 증가의 효과에 대해서는 아직 명히 파악되지 않았다. 본 연구에서는 먼저 탄소성 유한요소해석 통하여 보강재를 적용하지 않은 무보강 원형 강교각과 수직보강재가 보강된 원형 강교각에 대해서 좌굴내하력을 검토하였다. 그리고, 형상비(R/t)에 따른 좌굴내하력의 변화를 기존의 실험식과 비교하여 그 효과를 검토하였다. 그리고 원형강교각의 수직 보강재를 적용하여 폭과 두께에 따른 좌굴 내하력을 비교 검토하였다. 그리고 수직 보강재를 적용한 원형 강교각에 대한 내진성능을 검토하였다.