Section Enlargement Research Articles

Experimental and numerical studies on prestressed concrete box girders strengthened with PVA-ECC and external prestressing

To improve the shear capacity and repair shear cracks in prestressed concrete box girders, a novel strengthening method utilizing Polyvinyl Alcohol-Engineered Cementitious Composite (PVA-ECC) was proposed and studied. The integrated method consisted of section enlargement with PVA-ECC and decentralized prestressing using prestressed steel strands, which were embedded in the PVA-ECC after being prestressed and bonded. Field investigations were conducted to study and evaluate the effectiveness of this method under random traffic loads using health monitoring systems. Additionally, based on engineering practices, three finite element models (unreinforced box girder, box girder with strengthened side web only, and box girder with strengthened entire web) representing different construction sequences were established to investigate changes in shear behavior before and after strengthening. Finite element analyses were conducted under various loading conditions, and the results showed that the stress response of the webs decreased by approximately 30–40 % after strengthening. Additionally, the deflection of the top slab decreased by approximately 25–35 %. The results from monitoring data and finite element analyses demonstrated that the proposed strengthening method effectively enhanced the shear performance of the box girder webs. This research can provide a reference for strengthening and evaluating existing prestressed concrete box girders.

Calculation of creep deformation of stiffness-degraded RC beams after strengthening with increased cross-section

The strengthening of existing reinforced concrete beams (RCBs) has mainly focused on short-term mechanical properties such as flexural resistance and shear resistance, while long-term deflection of RCBs has seldom been studied. In this study, six RCBs with different types and degrees of damage were designed and strengthened by the section enlargement method. Mid-span deflection and concrete strain were used to evaluate the influence of stiffness degradation due to fatigue or corrosion damage on the creep behavior of strengthened RCBs (SRCBs). The experiment results revealed that time-varying curves of creep deformation from fatigue or from corrosion-damaged SRCBs were consistent among the six specimens. Creep in a damaged SRCB was found to increase faster than that in an undamaged beam, and to reach over 90 % of final creep in about six months. Based on the mean curvature method and creep models, taking fatigue and corrosion damage as examples of stiffness degradation, a calculation method for creep deformation of SRCBs was established, and sensitivity analysis of stress levels, reinforcement height, consolidation time, and other parameters were carried out. The research results can provide a theoretical basis and guidance for evaluating creep deformation of stiffness-degraded RCBs after reinforcement with increased cross-section.

The Effect of Section Enlargement with Cementitious Grout on the Eccentric Compression Behavior of RC Columns

The Effect of Section Enlargement with Cementitious Grout on the Eccentric Compression Behavior of RC Columns

Seismic performance of a structural concrete pile-wharf connection before and after retrofit

A full-scale precast prestressed concrete (PC) pile-wharf specimen with a T-headed dowel bar connection detail was tested under realistic loading and boundary conditions. The testing program introduced several seismic loading protocols, which were determined from nonlinear dynamic analyses of a typical U.S. port structure subjected to ground motions for various hazard levels. Conventional reversed cyclic loading tests were also conducted on the pile-wharf connection, damaged by seismic loading protocols, before and after retrofit. The specimen showed excellent seismic performance in terms of both strength and ductility. It was confirmed that the lateral drift response of such a PC pile-wharf connection is largely governed by a rigid-body rocking mechanism, with spalling in the pile and deck near the joint region appearing to be a main cause of stiffness degradation. This study also considered a section enlargement technique as an efficient retrofitting method of pile-wharf connections in container port structures. The retrofitted pile-wharf connection (with prior seismic damage) showed higher stiffness and improved capacity, but its deformation capacity (ductility) was inevitably limited by previously accumulated damage along the precast pile (where no strengthening was applied).

The Behavior of Reinforced Concrete Members with Section Enlargement Using Self-Compacting Concrete

The Behavior of Reinforced Concrete Members with Section Enlargement Using Self-Compacting Concrete

Structural Behavior Evaluation of Reinforced Concrete Using the Fiber-Reinforced Polymer Strengthening Method.

Reinforced concrete (RC) structures age with time, which results in performance degradation and cracks. These performance degradations do not recover easily, but a performance higher than the existing structures can be expected through reinforcement. There are various reinforcement methods for RC structures. This study selected four reinforcement methods: near-surface mounting (NSM), external prestressing (EP), external bonding (EB), and section enlargement (SE). In the past, steel bars were often used as reinforcements. However, this study uses fiber-reinforced polymer (FRP), which is an alternative to steel bars owing to its high tensile strength, and its non-corrosive and lightweight properties. It is a basic strengthening material, along with a carbon-fiber-reinforced polymer (CFRP) and glass-fiber-reinforced polymer (GFRP) in bar and sheet forms. Various strengthening materials such as a CFRP, GFRP, and prestressing (PS) strand are applied to the NSM, EP, EB, and SE methods, followed by flexural experiments. In addition, changes in the ductility of the RC structures were examined. The concrete EP and near-surface mounting prestressing (NSM(P)) methods have a stiffness that is almost double the non-strengthened specimen. However, because the EP and EB methods are brittle, the NSM(P) method with ductile behavior is considered the most effective.

Application Research of Maintenance and Reinforcement Technology for Arch Bridge Foundation

In order to study the application of maintenance and reinforcement technology for arch bridge foundation, taking a reinforced concrete half-through arch bridge and a rigid frame arch bridges as examples, the appearance inspection and disease analysis of the bridge piers and pile foundations were carried out. Based on the modified theoretical calculation model, the analysis method of diseases and the maintenance and reinforcement technology were proposed. The method of the pier section enlargement and adding pile is adopted to strengthen the arch bridge foundation. The results show that according to the modified theoretical calculation model, the actual diseases including the distribution area of cracks and degradation degree are in good agreement with the theoretical calculation results. The reinforcement design of section enlargement and adding pile can provide a reference for the reinforcement of similar arch bridges.

Axial test of full-scale columns strengthened with jacket section

This study examines the effect of different arrangements of transverse reinforcement in the jacket section on the axial performance of full-scale reinforced-concrete columns strengthened with a seismic section enlargement approach. For the jacket section with seismic details, overlapped channel-shape bars and prefabricated bar units were designed as the closed peripheral hoops, and V-ties or segmented cross-ties were used for the supplementary transverse reinforcement. For the compressive tests of full-scale strengthened columns with a 750 mm square section, a steel loading frame with a 40 000 kN capacity hydraulic jack was specially devised. Test results showed that the strengthened columns without supplementary V-ties in the jacket section possessed lower ductility capacity when compared with that of the existing non-seismic column. At the same level of transverse reinforcement index, the axial ductility ratio obtained from the present full-scale columns was typically lower than that compiled from the scaled-down column specimens with a square section of 200–300 mm. However, the strengthened column with prefabricated bar unit hoops including supplementary V-ties exhibited good ductility, which was comparable to the axial ductility ratios obtained in scaled-down columns, although a size effect potentially induced a more rapid decreasing rate at the descending branch of the stress–strain relationship of the concrete.

Axial behaviour of CFST stub columns strengthened with steel tube and sandwiched concrete jackets

This study addresses some key concerns on using steel tube and sandwiched concrete jackets to strengthen intact concrete-filled steel tubular (CFST) columns. The research background lies in engineering cases, in which the functional purpose changes when the structure remains intact. Within the parameters investigated, the load-bearing capacity of columns was enhanced by 114%–199% after being jacketed with steel tube and sandwiched concrete. The observable enhancement depended on section enlargement and the confinement effects of the outer steel tube, the latter of which could account for as large as 19% of the nominal load-bearing capacity. A finite element (FE) model was developed and verified, and the load distribution on components of the strengthened columns was presented. The radial stress between the inner concrete and inner steel tube was validated to increase substantially after the CFST column is jacketed with steel tube and sandwiched concrete. The decrease in the diameter-to-thickness ratio of the outer steel tube contributes to the synchronisation of the inner and sandwiched concrete in reaching peak load and benefits the load increase. A parametric study based on the FE model was conducted, and the effects of estimation error with respect to the properties of existing CFST columns were evaluated. A reasonable match between the outer steel tube grade and sandwiched concrete class was advised.

The Behavior of Reinforced Concrete Members with Section Enlargement Using Self-Compacting Concrete

This paper presents the experimental results of section enlargement effects on prismatic reinforced concrete members. 125 by 200 mm reinforced concrete members with a compressive strength of 20.3 MPa reinforced with D12 steel bars having a yield stress of 335 MPa situated in the tension and compression area, were produced. Two specimens were prepared, the first functioning as the control element and designated as the Control Beam (CB). The second strengthened with a section enlargement using Self-Compacting Concrete (SCC) marked as the Strengthened Beam (SB). The SCC had a 28-day compressive strength of 23.9 MPa. The dimensions of the enlarged beam were 200 by 300 mm. The two specimens CB and SB were tested with a two-point loading system. Based on the tests data, the load–displacement and moment–curvature relationships characterizing the beams were generated. From the results it was concluded that the enlargement affected the load-carrying capacity and stiffness positively. The SB member had a six times higher moment capacity, while the stiffness performance was enhanced seven times when compared to the CB specimen. On the other hand, it was also demonstrated that the ductility of the SB decreased as a consequence of the increase in span-to-depth ratio. The study was expanded based on the rational analyses to evaluate the influence of the additional tensile steel and concrete strength ratio of the enlarged section. Copyright © 2020 Praise Worthy Prize - All rights reserved.

Structural Strengthening/Repair of Reinforced Concrete (RC) Beams by Different Fiber-Reinforced Cementitious Materials - A State-of-the-Art Review

In the last few decades, premature deterioration of reinforced concrete (RC) structures has become a serious problem because of severe environmental actions, overloading, design faults, and materials deficiencies. Therefore, repair and strengthening of RC elements in existing structures are very important to extend their service life. There are numerous methods for retrofitting and strengthening of RC structural components such as; steel plate bonding, external pre-stressing, section enlargement, fiber-reinforced polymer (FRP) wrapping, and so on. Although these modifications can successfully improve the load-bearing capacity of the beams, they are still prone to corrosion damage resulting in failure of the strengthened elements. Therefore, many researchers used cementitious materials due to its low-cost, corrosion resistance, and resulted in the improvement of the tensile and fatigue behaviors. Different types of cementitious materials such as; fiber-reinforced concrete (FRC), high performance concrete (HPC), high strength concrete (HSC), ultra-high performance concrete (UHPC), steel fiber-reinforced high strength lightweight self-compacting concrete (SHLSCC), fabrics reinforced cementitious material (FRCM) and so on have been used to strengthen structural elements. This paper summarized previously published research papers concerning the structural behaviors of RC beams strengthened by different cementitious materials. Shear behaviors, flexural characteristics, torsional properties, deflection, cracking propagation, and twisting angle of the strengthened beams are explained in the present paper. Finally, proper methods are proposed for strengthening RC beams under various loading conditions.

V-타이와 V-클립을 적용한 단면확대 보강 기둥의 중심축하중 거동 평가

이 연구의 목적은 기둥의 단면확대 보강 기술에서 ㄷ형 겹침 후프의 벌어짐을 방지하기 위한 V-클립 적용성의 기초 검증이다. 이를 위해 실제 크기의 단면을 갖는 기둥의 중심축하중 실험을 수행하였다. 실험결과, 보조 띠철근인 V-타이 및 V-클립이 배근된 보강 기둥은 파괴 시까지 보강 단면에서 외부 띠철근의 벌어짐 또는 V-타이의 뽑힘 현상은 나타나지 않았다. V-타이 및 V-클립이 배근된 보강 기둥의 압축 연성비는 기존 비내진 상세를 갖는 기둥에 비해 1.66배 이상 높았다. 또한 V-클립을 갖는 보강 기둥의 압축연성비는 동일 조건의 V-클립의 배근이 없는 보강 기둥에 비해 약 1.42배 높았다. 결과적으로 이 연구에서 제시된 보조 V-타이 및 V-클립은 설계 기준의 내진상세를 만족하면서 단면확대 보강 기둥의 연성 향상에 매우 효율적이다.

Axial Behavior of Reinforced Concrete Columns Strengthened with New Section Enlargement Approaches

Axial Behavior of Reinforced Concrete Columns Strengthened with New Section Enlargement Approaches

철근 선조립 공법 기반 단면확대 보강기둥의 중심 축하중 거동 평가

이 연구에서는 기존 기둥의 내진 단면확대 보강에서 적용할 수 있는 주철근과 보조 V-타이를 포함한 폐쇄형 횡보강근의 선조립 공법을 개발하였다. 제안 기술의 구조적 타당성 평가를 위한 기초연구로서 실제 단면크기를 갖는 기둥의 압축실험을 수행하였다. 실험결과, 보강기둥의 파괴 시까지 철근 선조립 유닛을 구성하는 V-타이와 U형 타이의 뽑힘현상은 나타나지 않았다. 보강 기둥의 압축내력은 ACI 318-14의 공칭내력 식보다 약 1.16~1.23배 높았다. 보강 기둥의 압축 연성비는 대형단면의 크기 효과에 의한 연성저하 가능성이 있음에도 불구하고 무보강 기둥에 비해 최소 1.4배 이상 높았다. 결과적으로 철근 선조립 공법에 기반하여 제시된 보강기술은 압축력을 받는 기존 RC 기둥의 강성, 내력 및 연성향상을 위해 적용될 수 있다.

Axial behavior of slender RC square columns strengthened with circular steel tube and sandwiched concrete jackets

Steel tube and sandwiched concrete jacketing has been proved to be effective in improving the load-bearing capacity and ductility of deficient reinforced concrete (RC) stub columns. However, the effectiveness of this technique for slender RC columns remains to be validated due to instability problems. In this study, nine slender specimens, including one reference column and eight retrofitted columns, were tested under axial compression. The experimental results showed that the load-bearing capacity, stiffness and ductility of the slender RC square columns were significantly enhanced. The load enhancement was not only attributed to section enlargement, but also due to the confinement provided by the steel tube. Based on the experimental results, a finite element (FE) model was developed to simulate the structural response of the retrofitted slender columns under axial load. The FE results demonstrated that the sandwiched concrete shared a higher load than the steel tube for the cross-section of this paper, justifying the use of “steel tube and sandwiched concrete jacketing”. Moreover, the confinement effects on the load-bearing capacity of the RC part and the sandwiched concrete part were quantitatively analyzed. A modified formula was subsequently proposed to predict the load-bearing capacity of the retrofitted columns, the results of which agreed well with the experimental and FE results.

Size Effect on the Time-Dependent Closure of Drifts in Callovo-Oxfordian Claystone

In this study, we analyzed the influence of the excavation size and the sequence of excavation on the convergence evolution in drifts excavated in Callovo-Oxfordian claystone. The drifts, which are part of the Underground Research Laboratory of the French National Radioactive Waste Management Agency (ANDRA), had diameters ranging between 0.7 m and 6.3 m. The measurements showed an anisotropic convergence with the maximum and minimum values in horizontal and vertical directions. Using a semi-empirical law, convergence evolution was fitted independently for each drift. The results show that the values for the parameters describing the time-dependent properties of the system rock-support depended upon the time elapsed for the support installation and the rate of excavation. For drifts following the same sequence of excavation, these parameters did not depend upon the size of the excavation. Finally, the analysis of a drift cross section enlargement showed that the convergence evolution was more isotropic and that the values for the parameters describing the time-dependent properties were lower, suggesting that overexcavation could limit the delayed response of the ground.

Analysis of Stiffening Methods and Effects on Irregular Single-layer Lattice Shell Structures

Local stiffening is often a good solution to mechanical property problems of irregular single-layer lattice shell structures. The effects of three local stiffening methods, namely section enlargement stiffening, planar truss stiffening, and space truss stiffening, on their structural stiffness, strength, and overall stability were analyzed in this study. A practical engineering example showed that these three stiffening methods could effectively reduce the deformation of the lattice shell under vertical and lateral loads, reduce the comprehensive stress ratio, and increase the buckling eigenvalue and ultimate bearing capacity factor. The local space truss stiffening method had the best comprehensive effect. The same stiffening methods were applied to a regular lattice shell and the analysis showed that the stiffening effect on a regular shell is quite different from that on an irregular lattice shell. The three stiffening methods could not reduce its deformation under vertical loading but could reinforce the strength and overall stability of the structure effectively. Proper suggestions are proposed according to the preceding analysis in case a single-layer lattice shell structure cannot meet the demands of the design code.

Air-photo based change in channel width in the Minnesota River basin: Modes of adjustment and implications for sediment budget

The Minnesota River and major tributaries have experienced large increases in discharge over the past century. Aerial photograph-based measurements of channel width were made for the 1938–2015 period at 16 multibend subreaches by digitizing the area between vegetation lines and dividing by centerline length. Results show considerable increases in width for the main stem (0.62±0.10%/y) and major tributaries (0.31±0.08%/y) but are inconclusive for smaller channels (width<25m). Width change for a 146.5-km reach of the lower Minnesota River between 1938 and 2008 is similar to that from the subreach-scale analysis. Widening was associated with lateral centerline movement and temporal change in at-a-station hydraulic geometry for water surface width, indicating that widening is associated with cross-sectional change and not simply upward movement of the vegetation line. Digital elevation model analysis and regional hydraulic geometry show that the main stem and larger tributaries account for the vast majority (~85%) of bankfull channel volume. High-order channels are thus disproportionately responsible for sediment production through cross section enlargement, although floodplains or off-channel water bodies adjacent to these channels likely represent important sediment sinks. Because channel enlargement can play an important role in sediment production, it should be considered in sediment reduction strategies in the Minnesota River basin and carefully evaluated in other watersheds undergoing long-term increases in discharge.

Development of deflection hardening cementitious composites using glass fibres for flexural repairing/strengthening concrete beams: experimental and numerical studies

This paper presents experimental and numerical programmes employed to strengthen concrete beams using glass fibre-reinforced concrete in order to achieve deflection hardening behaviour. Numerous tests were carried out on 270 specimens in the experimental phase in order to characterise mechanical properties of beams reinforced with glass fibre. Three beams were then cast with plain concrete and experimentally tested under flexural load conditions. Based on the experimental results, numerical simulations were conducted and the results were calibrated to the experimental results. Then, the robust-able FE models were used to strengthen concrete beams through numerical simulations. Furthermore, section enlargement method was also used to strengthen the concrete beams. The experimental and numerical results showed that using glass fibre-reinforced concrete layer to strengthen the concrete beams through the section enlargement method significantly improves the load carrying capacity and ultimate deflection.

Laboratory Investigation on Performance of Strengthening Techniques of RCC Beam

Reinforced concrete members are the most abundantly used construction elements in civil engineering. These members are normally designed to sustain various types of loads. But due to several reasons the members experience much more load beyond their capacity. Inadequate attention during design and construction of new additional RCC story in our country has raised question about the performance of existing structures. RCC beam is such an important member which sometimes needs to be strengthened. There are various methods of strengthening that have been studied by the researchers such as section enlargement, use of additional bars, use of FRP and CFRP, use of ferrocement, steel plates, etc. This thesis work aims to study and compare the effect of three distinct strengthening techniques- providing additional steel bars from underneath with U shaped shear reinforcement, use of wire mesh and providing single layer of geo-textile with adhesive. The experimental results show that the percentage increase in ultimate load carrying capacity for the steel, wire mesh and geo-textile were found to be 51.96%, 26.5% and 14.5% respectively with respect to reference beams. The value of deflection at failure were 5.63mm, 6.18mm and 5.83 mm respectively while for reference beam the value was 5.33mm. The performance of geo-textile was very poor. The use of wire mesh provides greater value of deflection at failure compared to other two methods but the increase in load carrying capacity is about half of that for steel bar. The application of additional steel is labor intensive compared to other two methods but in terms of ultimate load, it overweighs the advantages compared to other two strengthening techniques.