Seismic strengthening of structures

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“Seismic Strengthening Of Structures with Exterior Retrofitting”

“Seismic Strengthening Of Structures with Exterior Retrofitting”

Many existing structures located in seismic regions are inadequate based on current seismic design codes. In addition, a number of major earthquakes during recent years have underscored the importance of mitigation to reduce seismic risk. These types of buildings were found to be very vulnerable to unexpected earthquakes. It was observed that some modifications to structural configurations and material properties showed

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FRP Seismic Strengthening of Concrete Structures

FRP Seismic Strengthening of Concrete Structures

Seismic strengthening of reinforced concrete (RC) frames represents an important challenge for engineers in countries with seismic risk. Since the 1995 Kobe earthquake, FRP composites started being used extensively for the repair and strengthening of RC members in seismic zones (Priestley, 1995; Seible, 1997). Unique properties of these materials, such as high strength, light weight, corrosion resistance, ease of fabrication and application, have attracted the attention of many engineers involved in the strengthening design (Hollaway,1999). However, there are concerns regarding the ability of FRP composites to dissipate energy. This concern is misguided since FRP materials are normally used to confine concrete columns (Fig.1) rather than provide flexural reinforcement. For a confinement material, the objective is to prevent the lateral dilation of concrete and, hence, the lack of ductility of FRP is not necessarily an issue (Triantafillou, 2001; Priestley, 1995).
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A Study of Seismic Strengthening of Multi Storey Building

A Study of Seismic Strengthening of Multi Storey Building

Various analysis methods, both elastic (linear) and inelastic (nonlinear), are available for the analysis of existing concrete buildings. Elastic analysis methods include code static lateral force procedures, code dynamic lateral force procedures and elastic procedures using demand capacity ratios. The most basic inelastic analysis method is the complete nonlinear time history analysis. Simplified nonlinear analysis methods, referred to as nonlinear static analysis procedures, include the Capacity Spectrum Method (CSM) that uses the intersection of the capacity (pushover) curve and a reduced response spectrum to estimate maximum displacement; the displacement coefficient method that uses pushover analysis and a modified version of the equal displacement approximation to estimate maximum displacement; and the secant method that uses a substitute structure and secant stiffness. Although an elastic analysis gives a good indication of the elastic capacity of structures and indicates where first yielding will occur, it cannot predict failure mechanism and account for redistribution of forces during progressive yielding. Inelastic analysis procedures demonstrate how building really behave by identifying modes of failure and the potential for progressive collapse. The use of inelastic procedures for design and evaluation is an attempt to help engineers better understand how structures will behave when subjected to major earthquakes, where it is assumed that the elastic capacity of the structure will be exceeded. This resolves some of the uncertainties associated with code and elastic procedures.
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Vulnerability assessment and feasibility analysis of seismic strengthening of school buildings

Vulnerability assessment and feasibility analysis of seismic strengthening of school buildings

The key point concluded from studying the derived fragility curves is the significant uncertainties emanating from the present damage state definitions. More specifically, the lower limit (‘series system’) seems overly conservative, whereas the upper limit leads to damage thresholds associated with very high (and arguably unrealistic) levels of seismic excitation. This is attributed to the special response characteristics of URM buildings, wherein damage is not evenly distributed along all structural elements (as in R/C structures with regular configuration) but rather localizes in certain regions. It is noted here that most of the previous similar studies (e.g. Kappos et al., 2006) are focused on planar (2D) models, where the uncertainties in the definition of damage levels are fewer compared to the present three- dimensional analysis (i.e. 2D models result in a few translational modes dominating the response, they ignore out-of plane failure, and so on).
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Seismic Retrofitting of Reinforced Concrete Structures

Seismic Retrofitting of Reinforced Concrete Structures

reasons responsible for the destruction to life and property in large numbers. In order to mitigate such hazards, it is important to incorporate norms that will enhance the seismic performance of the structures. Earthquake loads are required to be carefully modeled so as to assess the real behavior of structure with a clear understanding that damage is expected but it should be regulated. Seismic Retrofitting is the modification of existing structures to make them more resistant to seismic activity, ground motion, or soil failure due to earthquakes. In this project our aim is to analyze an existing building using STAAD Pro v8i, with and without the provision of seismic retrofitting. The structure is analyzed in STAAD Pro v8i and the bending moment was chosen as the criteria for selecting the weak member. RC jacketing was selected as the retrofitting technique employed to the weak member andlater the member in the structure was compared with the bending moment value before and after providing retrofitting. It was determined that RC jacketing strengthened the structure, which was vulnerable to seismic activity.
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A Review on Study on Strengthening of Soft Storey Building for Seismic Resistance

A Review on Study on Strengthening of Soft Storey Building for Seismic Resistance

[2]. Umesh P. Patil et al (2015) analysed the seismic performance of two structures G+15, one made of composite steel concrete material and other one is made up of RCC, situated in the earth quake zone III, having a medium soil were investigated analytically for their performance using ETABS software, Equivalent static and response spectrum method are used for the analysis of RCC and composite structures with soft storey. In this method multiple modes of vibrations are considered where base shear of each mode can be calculated separately. Storey drift is reduced by 10% in composite models compared to RCC in soft storey level.It is possible to control the drift in soft storey by providing 1) Shear walls 2) Bracings 3) Stiffer column 4) Lateral load resisting system. The beams and columns in the soft storey are designed 2.5 times of obtained bending moments and shear forces and shear walls are designed by a factor of 1.5 times the storey shear.
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Use of Grancrete as Adhesive for Strengthening Reinforced Concrete Structures.

Use of Grancrete as Adhesive for Strengthening Reinforced Concrete Structures.

using epoxy resins in strengthening applications. For example, epoxy resins may be toxic and may cause health problems in the work environment. Also, some types of epoxy require a minimum application temperature, often 10° C and using epoxy creates sealed surfaces (diffusion-closed) that may cause freeze/thaw problems for concrete structures. In addition, the curing of the epoxy resins is highly affected by environmental conditions such as high humidity and high temperatures (Badanoiu & Holmgren, 2003)(Taljsten & Blanksvard, 2007). One of the major limitations on the use of epoxy in structural strengthening applications is the possibility of the complete loss of the strengthening system in the case of a fire. When FRP strengthening systems are subjected to a combination of high temperatures and sustained loads, the resin polymer matrix could soften and consequently loose its ability to transfer stresses from the concrete to the fibers. The critical point of the system is reached when any of the components of the system reaches its glass-transition temperature, typically ranging from 140 to 180°F (ACI Committee 440, 2008).
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Rehabilitation and Strengthening of R.C.C. STRUCTURES by using FRP composites

Rehabilitation and Strengthening of R.C.C. STRUCTURES by using FRP composites

The experimental study consists of casting of three sets of reinforced concrete (RC) cylinders of size 150mm diameter and 300mm height. In SET I three cylinders of M- 15 grade of concrete were casted, out of which one is unreinforced and other two were strengthened using continuous fiber reinforced polymer (FRP) sheets. In SET II three cylinders of M-20 grade of concrete weak in shear were casted, out of which one is the unreinforced and other two were strengthened by using continuous fiber reinforced polymer (FRP) sheets in shear. In SET III three cylinders of M-25 grade of concrete weak in shear were casted, out of which one is the unreinforced and other two were strengthened by using continuous fiber reinforced polymer (FRP) sheets in shear. The strengthening of the cylinder is done with varying configuration and layers of FRP sheets. Experimental data on load and failure modes of each of the cylinder were obtained. The change in load carrying capacity and failure mode of the cylinder are investigated as the amount and configuration of FRP sheets are altered. The following chapter describes in detail the experimental study. In this study we have taken four cases for checking the strength of unreinforced concrete cylinders over the reinforced concrete cylinders with FRP (Fiber Reinforced Plastic) sheets. In each case we have taken three sets of concrete cylinders having different grades of concrete. All experimental details given in table below.
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Seismic Response of Equipment Supported on Structures

Seismic Response of Equipment Supported on Structures

Nonetheless, for analyses that require more accuracy in the results, performing a coupled analysis will yield to a more reliable and realistic estimate of the seismic response of secondary systems, especially when the equipment being considered is of flexible nature. Our results show the acceleration curve of the secondary system could be either amplified or reduced, therefore it is highly recommended to include the equipment/secondary system in the structural model in order to obtain specific results for the desired case. It is important to also notice the reduction in acceleration response will be greater when the equipment frequency is tuned with the natural frequency of the primary structure, therefore equipment with other frequencies will not be similarly affected. Results from these examples indicate when the use of generic amplification factors seems to be overly conservative, appreciable benefits could be obtained by considering the coupling models secondary systems into the main structure model. This can be achieved by direct development of coupled models or with the improved approximate procedures developed by several researchers (see for instance, Heredia et al. (2006); Clayton and Medina (2012); and Matta and De Stefano (2015)).
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Advanced Fiber Strengthening Systems for Reinforced Concrete Structures.

Advanced Fiber Strengthening Systems for Reinforced Concrete Structures.

adhesive to form a strong bond with the concrete substrata, which can be a very expensive and time consuming process, the near surface mounted technique requires very little surface preparation. The only requirement for the surface preparation is cutting grooves into the concrete, which is a relatively simple process. FRP that is applied using the EB technique is exposed to corrosive environments as well as other potential harmful scenarios that include damage from accidental impact, mechanical damage, and fire (Palmieri, Matthys, & Taerwe 2010). By applying the NSM technique the risk associated with these potentially harmful scenarios is very unlikely. An additional advantage to using NSM in comparison to EB is that the FRP that can be used in the NSM technique can be more easily prestressed (De Lorenzis and Teng 2007). The NSM technique is also more aesthetically pleasing since the grooves are cut into the concrete surface and filled with FRP and adhesive typically leveled with the surface and does not alter the original elevation of the concrete. The grooves can then be painted in a way to completely hide the strengthening system. Using the EB technique, the system will become a visible system that cannot be easily concealed. When Barros, Dias, and Lima (2006) directly compared beams that were strengthened with the externally bonded technique to beams strengthened with the near surface mounted technique, they found that the failure modes were more favorable for the NSM technique than the EB technique and came to the conclusion that NSM is more efficient than the EB techniques. This was confirmed by an experimental program conducted in 2010 that compared reinforced concrete beams strengthened with the EB technique to those strengthened with the NSM technique (Ceroni 2010) and in another similar experimental program (Nurbaiah et al. 2010). It was reported that the measured ultimate loads for members strengthened by using NSM FPR bars were greater than the measured values for EB FRP sheets strengthening systems. There was also greater ductility for the NSM FRP bars than the EB FRP sheets and it was concluded that the NSM technique was the most effective way to strengthen structures in comparison to the EB technique (Nurbaiah et al. 2010).
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Seismic Analysis of Reactor Assembly for Prototype Fast Breeder Reactor

Seismic Analysis of Reactor Assembly for Prototype Fast Breeder Reactor

The basic seismic input data is site dependent design response spectrum (DRS) corresponding to 5% damping (target spectrum). Three uncorrelated synthetic time histories are generated compatible to the target spectrum, to apply 3 mutual perpendicular directions at the base of raft. Subsequently 3D seismic analysis of nuclear island including all the essential buildings and base raft is performed and the acceleration time histories in two horizontal and one vertical directions are extracted at reactor assembly support location. Fig.1 shows the finite element model of nuclear island connected building (NICB). From each of these acceleration time histories, respective floor response spectra (FRS) are derived as per the guidelines recommended in the ASME: Appendix-N [3]. The damping values of 2 % for OBE and 4 % for SSE are used, applicable for analysis of welded structures as per ASME:Appendix-N. Since analysis is axisymmetric, the conservative spectrum is chosen from the two spectra available for the horizontal direction. Fig.3 shows the FRS generated at the reactor assembly support location.
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Seismic risk evaluation method focused on effect of plant management

Seismic risk evaluation method focused on effect of plant management

Japan is located in the high-level earthquake occurrence area of the Pacific Rim, and earthquake is recognized as one of the highest risks to the management of an enterprise. If it relates to the plant facilities, which hold the flammable materials that potentially lead to a fire or an explosion, or toxic materials, the greater impacts on the neighbourhood inhabitants would be expected in case of large earthquake. As a result, the management is required to control those damages and to prevent their extensions, and the seismic risk management over the plant facilities becomes significantly important. Therefore, from the viewpoint of the strengthening against the earthquakes, the method to select the most appropriate seismic strengthening countermeasures using the relationship between the risks to be held for the residual service period of the whole plant facilities and the cost of the strengthening countermeasures, is required.
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Evaluation of Column-Tree Moment Resisting Connection with End Plates and Haunched Beam (RESEARCH NOTE)

Evaluation of Column-Tree Moment Resisting Connection with End Plates and Haunched Beam (RESEARCH NOTE)

The column-tree constructional scheme allows for a reliable and convenient erection of moment resisting steel frames. Strengthening of column-tree connection with a haunch part can significantly improve seismic behavior of beam-column joint. In the current study, behavior of column-tree connections with haunched beams and end plate splices have been investigated. Special attention was paid for evaluation of the effect of haunch section length and presence of the beams bottom flange. Nonlinear finite element analysis has been used for numerical analyses. The results indicate an improvement of the load bearing capacity of specimens when a longer haunch was used and also when beam bottom flange existed in the haunch part. A direct relation between haunch length and the amount of stress in splice plates was also observed. However, all connections showed ductile behavior during cyclic analysis and specimens with longer haunch revealed more desirable behavior. It was concluded that despite some deficiencies observed during the numerical tests, in presence of a longer haunch and also the beam's bottom flange, a noticeable improvement of the general behavior of connection can be achieved.
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Development of fragility curves for use in seismic risk targeting

Development of fragility curves for use in seismic risk targeting

As discussed above, in a risk-targeting approach, seismic risk is calculated by convolving the seismic hazard curve of a given location with a fragility curve for a code-designed structure (ideally derived from structural modelling). The ground-motion level that the structure is designed for is chosen so that the structure has a pre-defined probability of achieving a certain performance level (e.g. non-collapse). Determining fragility curves for structures designed with modern codes for different levels of ground motion is, therefore, a prerequisite for the application of the method. In this section, we briefly summarize previous studies proposing fragility curves for code-designed structures for different levels of design acceleration. Only studies that have derived fragility curves for two or more levels of design acceleration are summarized here. This is because the large dispersion between fragility curves from different studies makes drawing conclusions on the effect of design accelerations on the vulnerability of the structure difficult. For example, if one study presents a fragility curve for a 3-storey RC building designed for a 0.1g peak ground acceleration (PGA) and another study presents a curve for a comparable building but designed for 0.3g, the differences could be due to the design acceleration or they could be due to (minor) differences in the design approach or fragility curve derivation (e.g. selected strong-motion records, damage thresholds and fitting technique).
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Seismic strengthening of severely damaged beam column RC joints using CFRP

Seismic strengthening of severely damaged beam column RC joints using CFRP

“Performance of an RC corner beam-column joint severely damaged under bidirectional loading and rehabilitated with FRP composites.” In: Seismic Strengthening of Concrete Buildings Using [r]

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Analysis and Design of an Earthquake Resistant Structure using STADD  Pro

Analysis and Design of an Earthquake Resistant Structure using STADD Pro

This paper contains detailed information on the methodology to analyze and design a structure on STADD. Pro from model generation, fixation of supports, load analysis and finally building design. Step by step procedure has been explained with the help of diagrams. Further, load calculations have been explained in depth and manual seismic and wind calculations have also been undertaken.

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Geodynamics of Earth’s Deep Mantle

Geodynamics of Earth’s Deep Mantle

EX2 and EX3 have different drops in thermal expansion across the mantle (factor of 3 and 1, respectively) and chemical density profiles compared to EX1. With a comparable HNB these models are qualitatively similar to the reference model. The domes in EX2 are marginally flatter with less edge deformation, and plume activity is also reduced. Conversely, the structures in EX3 stand a little higher from the CMB and have steeper sides. In this model, downwellings more significantly deform the domes. For example, Central American slabs produce sufficient stresses to generate a large circular embayment in the north of the African structure. To a lesser extent, dis- placement of material away from Central America also occurs in EX1 (Fig. 5.4g,h,i). The Boussinesq equivalent of EX1 (BO1) does not produce stable domes (Fig. 5.6). Slabs are stronger in BO1 because they have more thermal buoyancy, and are therefore cooler and more viscous at all mantle depths because the transit time through the mantle is reduced (∼ 50 Myr). The slabs exert large stresses on the side walls of the domes and can slide beneath the high-K structures, further destabilizing them. Ultimately the domes rise off the CMB (Fig. 5.6f). In BO2, we increase the density contrast at the CMB (δρ ch ) whilst retaining the same bulk modulus anomaly. In
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Schadl, Ilona
  

(2011):


	The exclusion of society: the problem of post-conflict statebuilding and the case of afghanistan.


Dissertation, LMU München: Sozialwissenschaftliche Fakultät

Schadl, Ilona (2011): The exclusion of society: the problem of post-conflict statebuilding and the case of afghanistan. Dissertation, LMU München: Sozialwissenschaftliche Fakultät

One of the distinguishing features of the task development agencies are set up to accomplish is the fact that they have to operate within an environment, which they neither understand well and nor control. Afghanistan lends itself as an illustrative example for this high-risk aid environment. Arguably, the country provides a particularly opaque and alien environment in comparison to many other, more established recipient countries. Chapter Three has provided some background on the historically complex relationship between a small modern state enclave and a largely autonomous rural society; on the establishment of an overpowering war economy with close ties to the post-Bonn political establishment; on the difficulties of international humanitarian actors during the civil war to navigate their ways around local politics, and of their inability to protect their aid from being used as resources in the war. Twenty years of war had significantly cut ties between Afghanistan and the outside world and the collapse of central government structures meant that the most basic information was not available. At the same time, the rapid military and political developments in late 2001 forced aid agencies to set up programmes very quickly. With the numbers of staff required it would have been impossible to predominantly charge ‘Afghanistan experts’ with setting up the massive assistance programme that had been agreed upon by the international community. The World Bank and the IMF, for example, had not operated in the country since the Communist coup in 1979. They became major donors to the new Afghan Transitional Authority. Chapter 2.1 and 2.2 have given some insights into the difficulties aid actors faced in a situation, in which government counterparts were often an integral part of the war economy, some continuing to maintain
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Retrofiting of Concrete Structure with Fiber Reinforced Polymer

Retrofiting of Concrete Structure with Fiber Reinforced Polymer

In very early 20th century some buildings and bridges that have been build are in deprived state and therefore those structure need to be exchanged or retrofitted. In retrofitting, the structure must be designed for both safety and durable, with responsiveness given to the case of retrofitting construction and post-retrofitting maintenance, as well as overall economy and environment-friendliness. Retrofitting is required for those structures which is not being fitted with the newest criteria of earthquake engineering or have experienced significant damages due to earthquakes. In times of economical limitations and decreasing state budget, replacing old infrastructures is too costly. Over past few years, the enlargement of innovative techniques to strengthen structures allows for low retrofitting cost of those infrastructures. One of the most effective ways to increase the structural performance of these buildings is to use fiber reinforced polymers (FRP). Masonry is a composite material prepared of brick units and mortar that has been used for centuries in building construction. It has an extensive use in seismic-prone areas, especially in the form of infill panels within reinforced concrete (RC) or steel frames [21]. Retrofitting of existing foundations implies changing the structural characteristics of the existing foundations and improving the fundamental soil condition [24]. By proof of identity the most significant factors related to seismic rehabilitation of structures, the important parameters involved in the technique selection of the retrofitting process are introduced and categorized by using the concept of value management, new scheme evaluate for relative advantage of each proposed retrofitting design [25]. The study will be implemented for RC slabs, column, beams, walls etc and sometimes retrofitting is also used in wall thicknesses and the walls will be exposed to different exterior and interior climatic conditions for insulation and energy saving[22].The directives aimed to accelerate the transformation of existing buildings towards net zero energy/emissions buildings [23],Sometimes they need to be retrofitted to have better behavior under earthquakes, Ventilation, heat recovery, low-temperature heating in Retrofitting, energy conservation, environmental impacts and indoor air quality.
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Project of Large Scale Earthquake Testing Facility

Project of Large Scale Earthquake Testing Facility

The purpose of seismic simulation tests of large scale structures is to investigate a three dimensional dynamic response up to collapse and failure mechanism of real structures, and to obtain data for establishment of three dimensional numerical simulations which can assess and predict the dynamic behavior of a structure with sufficient accuracy. For that objective it is necessary to have non linear models for each type of structures (reinforced concrete (RC) frames, masonry, walls, steel structures, etc.) associated with acceptance criteria or damage indicators for different parameters. Furthermore, the experimental result can lead to the assessment of safety margin within re-examination framework or the developments of advanced method for evaluation of the earthquake resisting capacity of structures, the new structure systems which aim at improvement of seismic performance and aseismic reinforcement of the existing structures. To perform test on real size object or large scale models of structures, it is desirable to have the large scale three dimensional shaking table, test could be performed to give new light on the mechanism of dynamic failure using real structures.
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