Thin RC Research Articles

Experimental response of thin RC walls seismically strengthened with steel plates

In some Latin American countries, and especially in Colombia, the industrialized system of thin and slender walls has been chosen for the construction of residential buildings, thus reducing costs and increasing efficiency of construction processes. However, these walls differ considerably from traditional concrete wall system due to their reduced thickness, reinforcement detailing, and use of nonductile electro-welded reinforcement, which increases their seismic vulnerability, especially in tall buildings and in high seismic hazard zones. Strengthening proposals for walls with these specific characteristics of the industrialized system are scarce; therefore, it is necessary to evaluate alternatives that allow for improving their seismic performance. This article presents the experimental response of a thin wall that was brought to failure and subsequently repaired and strengthened with externally bonded steel plates to evaluate the effectiveness of the repair process and the strengthening. Additionally, the results of two thin walls externally strengthened with steel plates and bolts are presented, and their response is compared with that of the original walls. All the specimens were subjected to the same type of test under cyclical lateral load and constant axial load until failure. The behavior observed in the rehabilitated wall showed that it is possible to restore the stiffness of a wall that has previously been brought to a severe level of damage and increase its displacement capacity with the strengthening. In strengthened walls without previous damage, the displacement capacity was increased between 25 % and 43 %, reaching a roof drift of up to 2.0 % without a significant increase in resistance. A noticeable increase was obtained in the amount of dissipated energy (greater than 80 %), and the rupture of web reinforcement and buckling of longitudinal reinforcement of the boundaries were delayed for average drifts of 43 % and 32 % higher than in the original walls, respectively.

Effect of thickness and CAD-CAM material on fatigue resistance of endodontically treated molars restored with occlusal veneers.

To evaluate the influence of the thickness and type of computer-aided design and computer-aided manufacturing (CAD-CAM) material on the fatigue resistance and failure mode of endodontically treated teeth (ETT) restored with occlusal veneers (OV). Seventy-five (N = 75) ETT were restored with Herculite XRV in the endodontic access. Five experimental groups (n = 15) were tested. Four groups had two different thicknesses (0.6-0.7mm or 1.4-1.6mm) and two different CAD-CAM materials: zirconia-reinforced lithium-silicate (LS/Celtra Duo) and composite resin (RC/Cerasmart). The fifth group (control) did not have occlusal veneers. All the specimens were subjected to accelerated fatigue (5Hz frequency) with an occlusal load increasing up to 1800 N and 131,000 cycles. The number of cycles was recorded when the machine stopped or at the completion of the test. Fatigue resistance was analyzed using the Kaplan-Meier survival test (95% significance level, log-rank post hoc pairwise comparisons). The samples were categorized according to failure mode. The CAD-CAM materials were examined through scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). No differences were found between the thicknesses, regardless of the type of the CAD-CAM material. The thick LS OV outperformed the RC and control groups. The thin RC OV and control groups showed a higher percentage of repairable and possibly repairable failures than the other groups. LS was more homogeneous under SEM, and the EDS analysis detected Si and Zr, but not Li. A larger thickness did not improve the resistance of the CAD-CAM materials. Thick LS showed a higher cumulative survival rate to fatigue than the RC and control groups. The direct composite alone (control) survived similarly to the experimental groups, except for the thick LS.

Shear strength estimation of reinforced concrete walls using support vector regression improved by Teaching–learning-based optimization, Particle Swarm optimization, and Harris Hawks Optimization algorithms

Peak shear strength estimation of RC shear walls is one of the influential parameters on the design of RC shear walls. Considering all models and equations provided by researchers and building design codes, it is still not possible to estimate the peak shear strength of shear walls with high level of accuracy. Therefore, the authors proposed three innovative models to estimate the peak shear strength based on combination of the Support Vector Regression with meta-heuristic optimization algorithms such as Teaching–learning-based optimization (TLBO), Particle swarm optimization (PSO), and Harris Hawks Optimization (HHO). The authors collected a large database containing 228 experimental data of RC shear walls and eight input parameters. One of the best features of this research is providing models for prediction of shear strength for three categories including, squat, cylinder, and thin RC shear walls.Finally, all three models have been compared with each other and with the equations proposed by the design codes and the researchers. The results indicate that the proposed models have good accuracy. As a result, researchers can use these models to estimate the shear strength of RC shear walls, which could increase the accuracy in predicting the behavior of the structure and would reduce the construction costs.

Safety assessment of nuclear fuel reprocessing plant under the free drop impact of spent fuel cask and fuel assembly part I: Large-scale model test and finite element model validation

This paper aims to evaluate the structural dynamic responses and damage/failure of the nuclear fuel reprocessing plant under the free drop impact of spent fuel cask (SFC) and fuel assembly (FA) during the on-site transportation. At the present Part I of this paper, the large-scale SFC model free drop test and the corresponding numerical simulations are performed. Firstly, a composite target which is composed of the protective structure, i.e., a thin RC plate (representing the inverted U-shaped slab in the loading shaft) and/or an autoclaved aerated concrete (AAC) blocks sacrificial layer, as well as a thick RC plate (representing the bottom slab in the loading shaft) is designed and fabricated. Then, based on the large dropping tower, the free drop test of large-scale SFC model with the mass of 3 t is carried out from the height of 7 m–11 m. It indicates that the bottom slab in the loading shaft could not resist the free drop impact of SFC. The composite protective structure can effectively reduce the damage and vibrations of the bottom slab, and the inverted U-shaped slab could relieve the damage of the AAC blocks layer dramatically. Furthermore, based on the finite element (FE) program LS-DYNA, the corresponding refined numerical simulations are performed. By comparing the experimental and numerical damage and vibration accelerations of the composite structures, the present adopted numerical algorithms, constitutive models and parameters are validated, which will be applied in the further assessment of drop impact effects of full-scale SFC and FA on prototype nuclear fuel reprocessing plant in the next Part II of this paper.

Two-way shear strength of reinforced concrete transfer slab-column connections

In high-rise wall-type residential buildings, thick RC transfer slabs have been widely used for parking space or public space. Despite the different behavior from thin RC flat slab, design methods for thin RC flat slab are applied to the thick RC transfer slab, due to the limited literature on the two-way shear behavior of RC transfer slab systems with small shear span-to-depth ratio. In the present study, concentric compression tests were performed on eight RC transfer slabs with small shear span-to-depth ratio to investigate the two-way shear strength. The test parameters were the concrete strength, shear span-to-depth ratio, slab thickness, and reinforcement ratio of the slab. The two-way shear strength, deformation capacity, failure mode, and strain distribution of slab rebars of the slab specimens were evaluated. The test results showed that the use of high-strength concrete or large reinforcement ratio increased the two-way shear strength of the transfer slab specimens. However, the transfer slab specimen having large slab thickness without sufficient reinforcement was susceptible to punching shear failure, showing insignificant strength increment. The two-way shear strengths of the test specimens were compared with the predictions of the current design method and the strut-tie model.

Structural layout that takes full advantage of the capabilities and opportunities afforded by two-way RC floors, coupled with the selection of the best technique, to avoid serviceability failures

Abstract A recently cast two-way rectangular reinforced concrete floor with a span-to-thickness ratio equal to 34.1, which constituted the two stories above ground of an office building under construction, exhibited a totally unsatisfactory deflection performance. The static loading test performed at the end of the construction work demonstrated that the stiffness of the floor was too low. Furthermore, not only the floor that had been loaded for the test, but also the other floor, exhibited excessive increases in deflections with time. The author was entrusted with the task of redesigning the floor, which had to constitute the stories of a further nine buildings of the construction lot, whose floors had been designed equal to the floor that had failed, and neither the spans nor the thickness could be changed. The author designed and constructed a test building whose story was made up of a floor with perimeter, spans and thickness equal to those of the floors that had failed, but with different structural conformation, boundary conditions, and both amount and configuration of steel reinforcement. The new floor was built using a different construction method as well. The loading test carried out on this floor measured very low immediate deflections. The load was left on the floor for three years and the deflections increased only moderately. The test results substantiated all the theoretical analyses that had been previously carried out and confirmed that the structural performance was adequate. On that account, the proposed floor was eventually employed for the nine buildings of the complex that remained to be built. This paper – which is directed at analyzing a structural failure, helping reduce the incidence of serviceability failures, and extending the operating horizons of thin RC floors – explains why the original version of the floor failed, describes the new version of the floor, including the loading test on the prototype and on the nine new buildings, and provides a useable and reproducible recipe for designing and assessing high span-to-thickness ratio rectangular RC floors.

Experimentally-validated modelling of thin RC sandwich walls subjected to seismic loads

Modelling the seismic performance of an innovative structural system consisting in lightly-reinforced concrete sandwich panels is the subject of this paper. Thin shotcrete layers are sprayed on the two surfaces of a polystyrene panel (support panel), after placing on each surface a small-diameter wire mesh. Such a system is appealing for developing countries, as it markedly reduces the construction cost, and provides excellent thermal and structural properties. Formulating a nonlinear model is, therefore, instrumental in investigating the cyclic behaviour of such a system, as required by seismic analysis. The proposed model incorporates a recently-introduced concrete damage model, and is validated through experimental tests, concerning both the force–displacement response and the progression of the damage.

Assessment of Seismic Performance of High-Rise Thin RC Wall Buildings in Lima, Peru Using Fragility Functions

The actual behavior of thin RC wall high-rise buildings during an earthquake in Lima, Peru, and the associated seismic loss is unknown. This type of building was assessed done using analytical fragility functions. The numerical model was based on full-scale tests done in Lima, Peru. Nonlinear dynamic response analysis was performed using records simulated for Lima. The damage ratio was estimated for four damage states and fragility functions were obtained assuming that the damage ratio followed log-normal distributions. Seismic performance was evaluated by considering the probability of different damage states for three seismic hazard levels. It was found that highrise buildings present a low probability of collapse in severe earthquakes.

Solar updraft power plants: Engineering structures for sustainable energy generation

Solar updraft power technology will generate highly sustainable electricity in world-wide deserts in future. It will overcome certain deficits of present renewable energy technologies. In several countries, such power plants are in pre-design stage, forming an important contribution of structural engineering to future energy supply. The present manuscript starts with the working principles of solar updraft power plants, followed by explaining climatic and wind-technologic design assumptions. Then the central solar updraft chimney – the power tower – is treated in more detail: a thin ring-stiffened RC shell of extreme height, forming the utmost structural challenge of such plants. This part is followed by technical requirements for the collector constructions, by far the largest glass-covered areas ever built, and of the wind-loading on the glazing. Then, further design aspects are extracted by the durability requirements for at least 100years of operation in extreme desert climates. The paper closes with some cost estimates for the generated electricity.

Cyclic behavior of thin RC Peruvian shear walls: Full-scale experimental investigation and numerical simulation

The experimental results of seven full-scale thin RC shear walls subjected to cycling loading are presented. The objective of these experiments is to evaluate the use of electro-welded wire mesh as the main reinforcement instead of a conventional reinforcement. Six walls are equipped with the electro-welded wire mesh, which is made of a non-ductile material, and one wall is reinforced with conventional bars, which are made of a ductile material. A single layer of main reinforcement is used in both directions. The edges of all walls are reinforced with conventional bars. These walls are widely used in low- and mid-rise buildings in central Peru, especially in Lima City. The structural behaviors are examined in terms of strength, stiffness, dissipated energy, and equivalent viscous damping. Finally, the “Three-parameter Park hysteretic model” is calibrated in order to reproduce the behaviors of the thin walls reinforced with the conventional reinforcement and electro welded-wire mesh. The parameters are applied to the results of the other walls reinforced by the electro-welded wire mesh. The results of numerical simulations are in good agreement with experimental results.

Crystal structure of 5,8-dimethyl-6-(p-dimethylaminophenylethynyl)-2,2- diphenyl-2H-1-benzopyran, C33H29NO

C33H29NO, monoclinic, P21/a (no. 14), a =1 6.832(3) A, b =9 .325(2) A, c =1 6.999(3) A, / =1 05.03(6)°, V =2 576.9(9) A 3 , Z =4 , Rgt(F) =0 .0407, wRref(F 2 ) =0 .2999, T =2 93 K. Source of material To as olution of 4-(5,8-dimethyl-2,2-diphenyl-2H-chromen-6yl)-2-methylbut-3-yn-2-ol (201 mg, 0,51 mmol) in dry toluene (10 mL) was adde dt he commercial available 4-bromo-N,Ndimethylamine (112 mg ,0 .56 mmol), and the mixture was degassed under argon. Then, ad eaerated aqueous solution of 5.5N NaOH (10 mL), (C6H5-CH2NEt3)Cl (3.5 mg, 0.015 mmol), Pd(PPh3)4 (2 9m g, 0.02 5m mol) and CuI (4.8 mg, 0.025 mmol) were successively added. Th eh eterogeneous mixture was stirred at 70 °C fo r4 h( Thin Laye rC hromatography (TLC) monitoring: cyclohexane/CH2Cl2 :5 0/50). After complete disappearance of the propargylic alcohol, the crude mixture was cooled down to room temperatur ea nd decanted .T he separate aqueou sl ayers were extracte dw ith Et2 O( 3 %10 mL). Th ec ombined organic layers were washed with as aturated NH4Cl aqueou ss olutio n( 3 %15 mL )u ntil neutralisation, dried over MgSO4 and evaporated under reduced pressure. The crude product was purified by column chromatography (SiO2 ;c yclohexane/CH2Cl2 :1 00/0 to 30/70) to afford the desired compound as aw hite powder (148 mg, yield 64%). Crystals appropriate for data collection were obtained after slow evaporation from hexane/CH2Cl2 solution at 298K.

Reinforced Concrete Membranes Under Shear: Ultimate Behaviour and Influence of Thickness

The main purpose of this article is to study the behaviour of thin RC membranes under compression in one direction and tension in the perpendicular direction. The influence of the thickness on the behaviour of the concrete panel is investigated. To study the behaviour of the panels, an experimental programme was carried out. Six RC panels under pure shear were tested up to failure. As a result, new experimental stress–strain relationships of thin plates under pure shear are presented. Such relationships take into account the reduction of the compressive strength due to perpendicular tensile stresses and the influence of the thickness of the RC panels. The good experimental values obtained from this investigation validate the effectiveness of the low cost testing equipment developed for this study. This was a good achievement, because previous tests on this topic were performed using expensive equipment, which very few laboratories could afford. In general, the values obtained for the stress–strain relationships are approximately within the range proposed by other investigators. It is also shown that the strength capacity predicted by European codes is higher than that obtained from the experimental tests. The values predicted by ACI code are very conservative.

Seismic performance of buildings with thin RC bearing walls

In Latin America there is an urgent need for housing; thus, during the last few years a relevant number of mid-height buildings (usually, up to five stories) with thin RC shear–walls have been constructed for low-cost dwellings in Bolivia, Colombia, Ecuador, Mexico, Peru, Venezuela, and other countries located in seismic-prone regions. These walls are 10 cm thick and their reinforcement consists mainly of a single layer of welded wire mesh. This construction technology offers two main advantages: economy and rapidity of construction. These buildings do not fulfill the international seismic codes but some national regulations are less demanding, not preventing the use of thin bearing walls. These buildings might be vulnerable to earthquakes because of their low ductility, the insufficiency of the experimental information, the absence of observed damages and, in some cases, poor construction quality. This work describes the initial steps of a wider research aiming at providing reliable seismic design guidelines for thin-wall buildings; the initial objectives are analyzing the seismic performance of these buildings, proposing preliminary design criteria and identifying further research needs. This research focuses on buildings located in Peru, being representative of the situations in the other countries. The vulnerability is numerically evaluated by push-over and nonlinear time history analyses; the structural parameters are obtained from available testing information. The obtained results show that the seismic strength of the analyzed buildings is insufficient; however, minor changes in the structural design might improve significantly their seismic performance. Cheap and easy-to-implement design recommendations are issued.

Construction of a merging section of Kariba Tunnel #3 without traffic suspension

The disused section of #3 Kariba Tunnel, in Hokkaido Island, Japan, runs through a coastal area prone to rockfall and collapse. A new tunnel section was built to detour around that dangerous area of cliffs and merge with part of the old tunnel. Because there are no alternative routes in the environs of the tunnel, construction on a section where the new tunnel merges with the existing tunnel was done while the road was kept open to traffic. Reconstruction of the existing tunnel accounts for one-third of the merging section length. In that one-third, one lane was kept open to traffic during construction, which was performed concurrently with the construction of the new tunnel section. It was attempted to reduce the construction duration by completing the merging section before the excavation of the new tunnel section reached the merging section. Construction of the old section employed two methods: use of towed longitudinal/transverse movable protectors and use of concrete lining of high-strength thin precast RC plate. The methods and technologies introduced in this paper were developed as among the best options for maintaining traffic safely while widening an existing tunnel with a comparatively small cross-section and shortening the construction period. They were first used for the #3 Kariba Tunnel and have been effectively applied to other tunnel design and construction projects that have conditions similar to those of #3 Kariba Tunnel. Detailed improvement of the methods will facilitate various uses of the technology. The following are proposals to improve the methods and technologies to facilitate higher operational efficiency based on the experience during construction. Protector: (1) For swifter movement and installation, it is necessary either to install a driving mechanism or to lighten the structure to facilitate manual movement. (2) To meet variations in tunnel width, a width-adjusting capability needs to be added. Precast lining: (1) Lightweight plates of a different shape need to be developed to facilitate swift erection and application to a larger cross-section of tunnel. These methods are expected to be improved to facilitate automated tunnel excavation and high-speed operation, which also offer an improved working environment. To this end, it will be necessary to make these improvements to the protector and precast secondary lining, and to coordinate their operation using a tunnel workstation (TWS) that also has the ability to protect passing vehicles. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.

一葉双曲面RC造冷却塔の構造特性に及ぼす形状不整の影響の分析 : 実測された形状の再現モデルを用いた損傷・耐力評価

In the inland in Europe and America, construction case of many reinforced concrete cooling towers exists mainly on the power plant which is hard to utilize much cooling water. It is long in the history of such tower construction, and many towers constructed in 40〜70's are used at present. In China and India, the construction of towers in the power plants increases. In such situation, it is reoorted that the collapse accidents by the gust repeatedly arose in United Kingdom and France in a past. Investigation of the cause of those accidents and examination of the countermeasure are developing, and the evaluation of the safety of the existing facilities becomes important problem. On the thin RC shells for these towers, the much research analyzes buckling / vibration problem and effect of initial imperfection on structural properties, and the proposal of design guidelines has been made. To begin with, using the initial imperfection of the distribution idealized axisymmetrically and asymmetrically, a useful knowledge on fundamental phenomenon and analysis method were obtained, and the recommendations for the tolerance limit of the initial imperfection magnitude were proposed. It was analyzed that according to the many leading research results. the fluctuation of meridian direction in-plane stress by initial imperfection was inversely proportional to the shell thickness due to dead weight and wind load within elastic stress analysis, and that it largely affects meridian direction in-plane stress and circumferential direction bending stress for the circumferential curvature error. In addition. partial initial imperfections with small amplitudes play a major role in meridian and circumferential stresses. Concerning the characteristic of initial imperfection itself, the probability-statistical technique for simulating the spatial distribution property is examined, and the statistical analysis procedure to simulate the effect of imperfection on the stress and buckling load is proposed. Recently, the effect of material nonlinearity of RC members on the ultimate strength also became remarkable problem by some researches. In this study, the three-dimensional distribution of the geometric error based on the reported measured data in the shell surface is reproduced numerically in detail for the tower which caused the collapse accident in a past, and the spatial distribution characteristic is analyzed. Next, the effect of the geometric imperfection of reoroduced shape on elastic stress distribution due to dead weight is examined, and the effect on the wind resistance performance is examined by the elasto-plastic analysis. In addition, the evaluation on the performance of the tower by the thermal stress is made, and the numerical examination on the reinforcing method of the tower is tried. By this study, some results shown below were obtained. Reproduced geometric imperfection widely exists for the shell full face, and it becomes a waveform which recurs in circumferential and meridian direction, and the complicated distribution in which the component which recurs periodically overlaps with the local component is shown. The peak of the imperfection component exists from N=0(axisymmetric) to N=5 on the circumferential direction and from 0 to 10(cycle/100m)in the height direction. ・ The possibility of changing to tension from compression exists on hoop stress due to dead load within large area by the effect of the imperfection. ・Due to wind load, the bending cracks develop in the windward of the imperfect shell, and next, it leads to the failure of the tower by the tension which arises by the bending of the meridian direction. This situation is similar to the thing for the perfect shell. From the result shown in the model which reoroduced the imperfection, the turbulence of the remarkable section forces existed further than the case of the perfect shell, and the result of predicting the l

Electrochemical aspects of new materials and technologies in microelectronics

Major scaling issues, which need to be addressed to continue scaling according to Moore’s law, include increase of transistor leakage due to use of thin gate oxide (about 1 nm limit for SiO 2), power (reaching 100 W/cm 2) and RC delay (dielectric constant limit is 1 for air and Cu resistivity increases with scaling down the feature sizes). Integration of new materials and technologies will allow us to continue scaling and improve device performance. Examples of new materials include high- k dielectrics and strained silicon in the frond end of wafer processing, low- k carbon-doped oxide and electroplated copper in the back end of wafer processing as well as electroplated bumps, high thermal conductivity interface, heat sink and heat spreader materials in packaging. Electrochemical technologies will play an increasingly important role in silicon technology due to low cost, use of self-assembly processing and self-aligned growth ability. New electrochemical technologies in silicon processing include copper electroplating (replaced Al interconnect to reduce RC delay and increase reliability), bump electroplating (replaced wire bonding to allow increased I/O and improve reliability), and porous silicon for silicon on isolator fabrication (to reduce transistor leakage). Copper electroplating allows a low R, an excellent gap fill capability and superior materials properties with (111) textured Cu films and large grain size, and a stable and controlled process.

A STUDY ON THE OVERLAY METHOD BY THIN PRECAST REINFORCED CONCRETE SLAB

The thin reinforced concrete precast slab overlay method is the new effective rehabilitation method for asphalt concrete pavements. In this method, the small thin RC slabs are made at a yard, and then they are carryed and set on the asphalt concrete pavement. But the mechanistic properties of thin RC slabs are not clear enough. In this study, we investigate the mechanistic properties of slabs by the loading test of the real size slabs. From the results of the test, the RC slab have a enough ability for heavy loads. Then we constructed this thin RC precasted pavement for the heavy truffic road and examined the serveciability of this pavement.