Effect of the Cyclic Crack Opening-Closure during Epoxy-Curing Period of a CFRP Strengthening System Bonded on Concrete Substrate

This article investigates the potential detrimental effects of cyclic load during the installation of externally bonded (EB) carbon fiber-reinforced polymer (CFRP) on a damaged reinforced concrete (RC) structure. Four RC specimens were tested in three point bending to study the consequences of crack cyclic opening-closure during epoxy-curing period. A first RC specimen (without bonded CFRP) was loaded monotonically up to failure to serve as undamaged control sample. The three other specimens were pre-cracked before being subjected to a fatigue loading procedure to simulate service condition of a damaged RC structure. Two of the three pre-cracked specimens were strengthened by EB CFRP. One specimen was repaired before the fatigue test while the other one was repaired during the fatigue test. Finally, remaining capacities of all three pre-cracked specimens were measured through monotonic bending tests until failure. It was found that, although bonding of CFRP reinforcement during cyclic load can induce some interesting features with regard to serviceability, cyclic crack opening and closing alters the cure process of epoxy located below the initial crack and decreases the effectiveness of the strengthening at ultimate state. Extended experimental studies are then needed to assess reliable safety factor for the design of repairing operations in which the bridge has to be maintained in service during CFRP installation.

Structural Health Monitoring of Existing Reinforced Cement Concrete Buildings and Bridge Using Nondestructive Evaluation with Repair Methodology

Sustainable development means the utilization of resources at a rate less than the rate at which they are renewing. In India infrastructure industry is growing rapidly due to globalization and raising awareness. In the present study, challenges faced by countries like India are to sustain the existing expectations with limited resources available. Reinforced Concrete (RC) structure may suffer several types of defects that may jeopardize their service life. This chapter deals with condition assessment and repair of RCC (G+3) building situated at Northern part of the country. There are various techniques available for repair and rehabilitation of reinforced concrete structures. From a maintenance point of view, it is essential to take up the strength assessment of an existing structure. So, to find out the reason behind the deterioration of the concrete structures some of the NDT and partially destructive technique are used. The NDT tests conducted during this study are Rebound Hammer, Ultra-sonic Pulse Velocity, Concrete resistivity Meter, Ferro-scanning and Carbonation, etc. This chapter helps to explains, how identified the different parameters of distress building like strength, density, level of corrosion and amount of reinforcement. On basis of these results, apply a repair methodology to revert back the strength parameters of the buildings.

THEORETICAL ANALYSIS OF EXISTING CONCEPTS TO EVALUATE THE NON-FAILURE OF RC STRUCTURES IN OPERATION

The article presents a theoretical analysis of existing concepts to evaluate the non-failure of RC structures in operation. To perform the analysis, the authors considered a number of scientific works of both Ukrainian and foreign researchers. The main focus was on works in which the model of the stochastic nature of the RC structure operation included random parameters of acting loads, as well as the reserve of its bearing capacity and serviceability (geometric dimensions of cross sections of constructive members, strength and deformation characteristics of materials, etc.). Among others, according to the authors, important problems in terms of analysis of a single work were the volume of statistical selection of random parameters, their number and impact on the study result, as well as rationality of the adopted method of calculating the probability of failure (or non-failure work) of RC structure in operation. Based on the processing of a number of scientific works, the authors highlight the relevance, advantages and disadvantages of the concepts of non-failure assessment proposed there, as well as the formulate the conclusions and recommendations for further experimental and theoretical research in this area.

Durable Steel-Reinforced Concrete Structures for Marine Environments

Even in harsh marine environments, concrete structures reinforced with steel can show excellent long-term durability, with little or no reinforcement corrosion. Very few actual reinforced concrete (RC) structures have been closely scrutinized over many years and subject to interpretation using recent state-of-the-art understanding gained from detailed laboratory observations. Such a case is described for an 80-year-old RC structure observed annually over about 30 years in what is essentially an extraordinary long experiment. Despite very high chloride concentrations, field excavation evidence showed that reinforcement corrosion overall remains minimal, except where insufficient concrete compaction permitted air-voids to initiate quite severe, very localized corrosion even with still high concrete pH. It is possible that the use of blast furnace slag as aggregate may have assisted the observed durability. The case study supports other studies that show that it is possible to achieve long-term durable and therefore sustainable RC structures without additives and using only conventional reinforcement steels and conventional cements and aggregates. However, the potential dangers of deep narrow cracking extending to the reinforcement and the potentially deleterious effects of alkali–aggregate reactivity of some aggregates needs to be considered.

Novel Global Interconnect structure with improved Elmore Delay Estimation for Low-Power Applications

With advancements in technology, size and speed have been the important facet in VLSI interconnects. Interconnects are known as the basic building block that provide a connection between two or more blocks and have scaling problems that an IC designer faces while designing. As scaling increases, the impact of interconnect in the VLSI circuits became even more important. It controls all the important electrical characteristics on the chip. With scale-down technology, interconnects not only become closer with each other but their dimensions also change which can directly impact the circuit parameters. Certain RC structures have already been defined to control these parameters but in this paper, authors have proposed a new interconnect structure with improved Elmore delay estimation to reduce delay and power consumption in lumped and distributed interconnect circuits using Pulse and Ramp inputs. Further, the proposed model is estimated and verified theoretically. The linear relationship of power consumption and delay for the RC structure has been observed. The proposed structure with improved Elmore delay estimation shows improvement in delay by 64.25% in lumped circuits and 68.75% in distributed circuits in comparison to existing Elmore delay calculations which help in increasing the overall speed of the interconnect circuit.

Seismic Assessment and Rehabilitation of a RC Structure Under Mainshock-Aftershock Seismic Sequences Using Beam-Column Bonded CFRP Strategy

A mainshock is usually accompanied by a group of ground motions. In many design codes, the effects of the seismic sequences have been neglected or underestimated. Aftershocks can increase structural damage or even cause failure. The current study evaluated the seismic behavior of a rehabilitated and as-built RC structure under real scaled mainshock-aftershocks using nonlinear analysis. Verification was done in two modes. The inter-story drift ratio, maximum residual, and relative displacements were studied. The seismic study of the as-built structure showed that the residual displacement grew, on average, more than 90% under the mainshock-aftershock sequence compared to the mainshock-only record. A beam-column bonded CFRP rehabilitation strategy using six layers of T-700 CFRP was chosen based on the specific performance level. The strategy showed the ability to transfer the plastic strain from the columns to the beams, which could be considered as a change from a weak column-strong beam concept to a strong column-weak beam concept. Compared to the as-built structure under the seismic sequences, the rehabilitated structure showed an average growth of 78% in the first-story drift ratio, which was significant. Unlike the as-built structure, seismic sequences caused no growth drift in the rehabilitated structure. It also was observed that the ratio of aftershock PGA to mainshock PGA could have an intensive effect on the seismic behavior of both rehabilitated and as-built structures.

Fixed and Base Isolated Framed Structures: A Comparative Study

Necessity of constructing multi-storied buildings is increasing these days. But they are more prone to severe damage due to earthquakes. Base isolation is one of the most powerful tools pertaining to the passive structural vibration control technologies. The structure above the ground, is separated from the effects of earthquake forces by introducing a mechanism that helps the structure to hover. This project deals with analysis of 10 storey RCC, Steel and Composite structures of different shapes with and without base isolation in various seismic zones by Response Spectrum Method using ETABS software. Lead rubber bearings designed as per UBC97 was used for base isolation. Plus shape was found to be most suitable for base isolation for RC structure, whereas for steel and composite structures rectangular and hollow shapes were found suitable. It was also observed that concrete structure performs best when base isolated, compared to other structures.