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Seismic retrofit of beams in buildings for flexure using concrete jacket
Abstract
To prevent disaster in future earthquakes, one way of retrofitting the members in reinforced concrete buildings is concrete jacketing. The present study investigates the effect of jacketing on the flexural strength and performance of beams. First, slant shear tests are conducted to study the interface between old and new concrete. Second, beam specimens are tested to study the effect of jacketing on the positive bending of the span region. Third, beam-column-joint sub-assemblage specimens are tested to study the effect of jacketing on the positive bending of the beams adjacent to the joint. Further, analytical investigations are carried out to predict the experimental results. A layered approach is used for the prediction of the moment versus rotation curves for the retrofitted beam specimens. An incremental nonlinear analysis is adopted to predict the lateral load versus displacement behaviour for the retrofitted sub-assemblage specimens. Finally, guidelines are provided for the retrofitting of beams by concrete jacketing.
... While the techniques for gravity loads are well known, the same cannot be used reliably for seismic loads. Hence it is necessary to verify the efficacy of various techniques with respect to their ease, cost and efficiency and the resulting enhancement in seismic performance [5]. ...
New materials and structural systems are being introduced in construction profession every day either to replace conventional materials whose availability is becoming scarce or to improve the efficiency of construction. New systems are also being introduced to cater to new demands in functionality and aesthetics. While Indian researchers have kept pace with the theoretical aspects of earthquake resistant design, the practical aspects are hardly touched upon since they require testing and implementation in practice. The current codes are prescriptive about the general requirements for strength and detailing and so are inadequate to define and assess the performance objectives of specific structural systems. Consequently, the gap between academics and profession has been widening and has reached extreme proportions and there is an urgent need to revive applied research in earthquake engineering to evaluate seismic performance of practical systems. In this paper, the work carried out by the author and his students at IIT Madras on seismic design and tests carried out on masonry, reinforced concrete, structural steel, steel-concrete composite, cold-formed steel, semi-rigid frames of steel and composite construction and industrial rack systems are reviewed. The importance of understanding the details of the seismic behaviour of these system towards improving the performance is emphasized.
... Numerous manuscripts have been published about retrofitting RC beams. Narayanan et al. [4] investigated the seismic retrofitting of beams using concrete jackets. A number of experiments were performed to investigate the interaction between new and old concrete. ...
... Investigation on the effect of jacketing on flexural strength and performance of the columns and beams has also been done in the past [14,15]. Firstly, the interface between the old and new concrete were tested by slant shear tests. ...
Whenever a member of a structure becomes structurally deficient, it becomes vulnerable to the existing load and for the additional loads that it may be subjected to in the coming future. Since columns are the most important structural element, the structural retrofit of columns, relative to other structural elements is of prime importance. This study intends to investigate the performance and behaviour of an RC column jacketed with Reinforced Concrete columns under axial loads. The objective of this paper is to find out the efficiency of RC jacket in enhancing the strength of an existing RC column. A mathematical design based upon Indian Standards codes has been designed to identify the behaviour of jacketed RC columns. This has been followed by a finite element based numerical simulation using the same material properties as used in the process of designing. The simulation has been done in ABAQUS software with appropriate contact modelling. The analytical model considers that there is no bond slippage between the existing and new concrete surface i.e. the bond between the existing and new concrete is assumed to be perfect. This perfect bond between the surfaces has been modelled by using appropriate constraints in ABAQUS software. The finite element models show fair agreement with the designed values in terms of ultimate capacity and failure mode. The load bearing capacity enhancement of the RC jacketed column has been found to increase substantially. The enhancement capacity results obtained from the finite element software differs about 16-25% from the design values.
... Alanwar et al [2] used U-shape jacketing mesh and steel bars, showed the increase in both flexural and shear capacity of reinforced concrete beam after retrofit. Narayanan et al [3] introducing additional continuous bottom bars. For an effective Krishna [4], Soliman [5], and Ramana [6]. ...
The negligence in construction are usually due to error in replace or calculation of required reinforcement. The mistake known after construction and must be corrected as soon as possible. Some actions should be taken namely, add some pretension, augmented the beam size, use the FRP, and add some external reinforcement. Studies on rehabilitation and retrofitting are gaining importance due to the need for restoration of partially damaged structures due to wind load and earthquake. To prevent any disaster during the future earthquakes, the existing deficient buildings need to be retrofitted. The external tension reinforcement added when the flexural beam capacity inadequate, and the stirrups added when the shear beam capacity inadequate. The adding with external reinforcement also done after some tensile failure or cracks in the beam. In this case some damage of concrete must being consider in reducing stiffness and strength. The objective of this research is studied about the adding of external tensile reinforcement and stirrups after tensile failure and explore the influence of those action to the beam and then compared the strength, stiffness, ductility and crack pattern of beams before and after retrofit. The specimens were 12 original beam, and 12 retrofitted beam. The original beams have dimensions of 15 cm x 15 cm x 100cm, the tensile reinforcement were 4ф6 and compression reinforcement 2ф6. The stirrups were ф6-200 along the beam. Retrofit strategies were adding bottom tensile reinforcement 2ф6 and 3ф6, and adding stirrups ф6-60 in the shear span. The experiment shown the increase of beam ultimate load after retrofitting, but decrease the ductility and stiffness of the beam. The pattern of cracks also changed between original and retrofitted beam.
Natural disasters such as earthquakes have consistently shown current structures vulnerability to seismic effects. Increased service loads, changes in the structure's use, design and/or construction defects, corrosion issues, and seismic retrofits are all examples of engineering challenges. It's obvious that completely rebuilding an entire structure isn't the most cost-effective option. Therefore, retrofitting is used to improve the overall structure's strength. This paper presents general study on beam behaviour and their retrofitting. The retrofitting of RC beams is carried out by using wire mesh and mild steel plates. To carry out the research, a total number of 9 RC beams were casted, 6 beams were retrofitted, each of three were retrofitted with externally bonded mild steel plate and wrapped wire mesh. The analysis under simulated loads was carried out using STAAD pro. The study found that retrofitting a beam with MS plates and wire mesh significantly increases its flexural ability. The behavior of the beams was consistent with the STAAD report. In the case of retrofitted means, the cracking was limited to the retrofitted central portion of the beam. 2. Introduction Cement concrete is made by hardening a cement mixture (binding material) and a predetermined proportion of finely aggregated (sand), coarse compounds (e.g., broken stones (sandstones), gravels etc.) and water. The matrix is thoroughly mixed to produce a functional mixture that can be shaped in different components. In addition to cement from Portland, cement-based materials are commonly used in concrete for economy, reduced hydration heat, enhanced consistency, increased strength and/or improved durability within the expected range. These products are known as admixtures or performance improvers. Concrete attains full strength with age. Plastic concrete hardens as a result of a chemical reaction between cement and water that lasts for a long time. Plain Cement Concrete, or PCC, has a high compressive strength, is less expensive than steel, and is not corrosive or susceptible to other wear effects. It is most commonly used for building foundations and floors. The unit weight of PCC is 24kN/m3. When exposed to stress, it has a low tensile strength and is vulnerable to cracking. As a result, plain cement concrete cannot be used in members or systems that can develop tensile stress. In order to solve this problem, reinforcements in the form of bars, tendons or wires are used in concrete. The composite material formed by combining steel with concrete is reinforced cement concrete or RCC. Structures should be planned and constructed in such a way that resources are adequately used and a positive economic effect is achieved. Various retrofitting or strengthening methods are used to improve the efficiency of an existing structure. Some structural elements, such as columns and beams, may be strengthened to extend the life of the building. A structural element can be retrofitted by adding an accessory, technology, feature, or part.
The structures which are not designed for resisting seismic loads and are constructed in earthquake-prone zones, must be strengthened by adopting different retrofitting techniques in order to resist lateral loads generated due to earthquakes. The retrofitting of such structures enhances their seismic performance and helps in avoiding demolition of such structures. The objective of the present work is to identify the optimum thickness of the reinforced concrete (RC) jacket which is being applied as a retrofitting technique to retrofit RC beams/RC columns present in a structure by considering various thicknesses of the RC jackets that can effectively resist forces or stresses induced due to earthquakes. The optimization of the thickness of the RC Jacket is carried out considering lateral loads acting on the structure produced from an earthquake as well as gravity loads which are acting upon the structure. A numerical analysis is carried out to understand the behaviour of a retrofitted structure subjected to an earthquake, whose structural elements—RC beams/RC columns are strengthened adopting RC jackets having an optimum thickness.
Existing building codes do not specify the performance criteria of individual structural members under various levels of shaking during earthquake or ground motions. Thus, several developing and developed countries all across the world have incorporated changes in their seismic codes for practical applications. In India, there is no proper description of the ‘Earthquake-Resistant’ building. Buildings should be clearly categorised and designed according to performance objectives. Strict guidelines must be laid down that all buildings should be designated, designed and offered as ‘Earthquake-Resistant-Collapse Prevention/Life Safety/Immediate Occupancy’. It is interesting to know that India is the only seismic-prone country in the world that has neither its own performance-based seismic design (PSBD) code nor a dedicated hospital design code. Moreover, in the current Indian seismic code, displacements and forces are within the elastic limit, i.e., the assumed behaviour is linear. However, the structural response to the major earthquake is not elastic. The formation of plastic hinges exceeding collapse prevention state occurs in most structural members. Retrofitting had also proved to be uneconomical for the buildings to perform better under severe earthquakes. This paper presents a comparative PBSD analysis of G + 4 regular and all five types of plan irregular RC frames using response spectrum and time history methods in Zone IV and Zone V as per IS 1893:2016. The primary objective of the study is to verify the essential dimensions of primary structural members in the lifeline structures condition of collapse prevention and life safety. The time-history data for Bhuj earthquake was used for this analysis. The pushover analysis is then carried out to study the inelastic behaviour of the structure. The research is very useful for practising structural engineers to determine the minimum dimensions of slabs, beams and columns in different configurations of normal and plan irregular frames to be carried out in the state of life safety and collapse prevention.
Keywords
Performance-based seismic design Plan irregularity Indian standard code Lifeline buildings
One of the major tectonic plates in the world is the Indian tectonic plate bearing an area of 11,900,000 km2. According to the Indian Standard Code of Practice (Bureau of Indian Standards (BIS) (2016) Criteria for Earthquake Resistant Design of Structures, 6th Revisi., vol. 1893, no. December. New Delhi), 60% of India’s geographical land lies under zones III, IV, and V (Murty, What are the Indian Seismic Codes?, IIT Kanpur. pp. 1–2). India has witnessed major earthquakes from time to time, over the past few decades. Over the period, the seismic performance of the existing buildings was assessed using various assessment methodologies. Diverse retrofit methods were experimented on various concrete components and were implemented on the impacted building elements. This paper talks about a detailed investigation of the failure mechanisms of the various reinforced concrete buildings of four major earthquakes spread across the country. The earthquakes spanning from Gujarat (2001, magnitude—7.7) in West to Sikkim (2011, magnitude—6.9) and Imphal (2016, magnitude—6.7) in North-East to Andaman and Nicobar Islands (2004, magnitude—8.7), the southernmost Union Territory of India, saw a similar failure mechanism in moment resisting reinforced concrete-framed buildings, despite lying on various seismic zones. Few retrofitting techniques that were applied to these deformed buildings are discussed in detail. From summarizing the diverse retrofitting approaches, it is found that the technique of concrete jacketing efficiently increased the performance of the buildings across the nation. It is one of the most suitable and common methods used employing local construction materials.
One of the well‐known methods for rehabilitation of insufficient or damaged reinforced concrete (RC) beams is to add a new RC layer. Although RC beams strengthened or repaired in this way have proved themselves under monotonic and repeated loads, the behavior under cyclic loads has not been adequately investigated yet. In this experimental research, beams were strengthened, repaired, or revived (repaired after heavy damage) using familiar RC layer adding methods and tested under reversal cyclic loading. Ten half‐scaled specimens, composed of columns and a beam, were prepared and 18 tests were conducted on these specimens. The obtained results showed that the strengthened and repaired beams mostly could achieve the monolithic behavior. However, sufficient ductility could not be maintained for the revived ones.
This article reviews research on various mechanisms of repairing damaged RC beams (Reinforced concrete). Structures in general, are designed depending on the function, structural and environmental conditions and other requirements. All structural members are designed for predefined requirements. Nowadays the majority of the aged civil structures need repairing for improving the strength, integrity, protection of reinforcement from weathering etc. In some cases, it is less expensive for maintaining the infrastructure at appropriate intermissions than to make a re-construction that will need a repair when exposed to harsh conditions for an extensive period. Numerous types of methods and materials are available for repair of aged/damaged structures. This paper deals with the review of various causes of structural distress and different techniques that are assessed for their efficiency both experimentally and analytically for repair and rehabilitation of RC beams.
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