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“...countless buildings. In particular, some reinforced concrete (RC) buildings, which compose a large part of the worldwide construction portfolio, presented some deficiencies and poor response when subjected to the seismic actions [1,2]. Past and recent international structural design codes do not consider the structural contribution of the infill masonry walls in the assessment of the global response of structures. Infill panels are widely used in construction for many reasons, including as partition walls, acoustic and thermal purposes, among others. When subjected to earthquakes, the infill walls tend to interact with the surrounding frame providing additional lateral stiffness and strength to the building. However, with the increment of the peak ground accelerations different failure modes can occur such
Published online: 12 March 2018...”
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“...notorious difficulties of the government in implementing building design codes accounting for seismic loads and/or the contribution of the infill masonry walls to the response has been lacking in Nepal. It is worth noting that most of the residential buildings and some important buildings, such as schools or government buildings were not designed according to the most recent seismic design codes. The lack of planning and structural knowledge by the structural designers and community at the time when these buildings were designed resulted in the construction of vulnerable structures when exposed to intense seismic ground shaking due to earthquakes [11].
Shaky a and Kawan [12] reported that most of the damaged RC buildings, after the 2015 Gorkha earthquake, were identified to be non-engineered buildings. According to Gautam et al. [13] and Varum et al. [14], the non-engineered buildings are built spontaneously following traditional building practices, with little to no intervention by engineers...”
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“...International Journal of Civil Engineering
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Fig. 1 Case study building dimensions: a general view; b ground floor building plan; and c front view (dimensions in mm)
transverse reinforcement for all columns consists of 04.75 spaced at 150 mm on center. The beams have cross section of 400 x300mm2 with reinforcing steel consisting 3012 on top and 3012 on the bottom (Fig. 3).
2.2 Numerical Modeling and Calibration
A three-dimensional (3D) numerical model was developed using the software SeismoStruct [15]. This software was developed with the goal of providing the expected behavior of different types of structures when subjected to ground shaking due to earthquake loading. SeismoStruct allows for
Springer...”
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“...for: a concrete; b steel; c infill masonry wall (compression/tension struts); and d infill masonry wall (shear springs)
the use of 3D models and for consideration of geometric and material nonlinearity. In addition, the software has an extensive library of different elements and material models that can be used to model reinforced concrete structures with masonry infills, such as the case study analyzed herein. The 3D model was developed considering the real configuration and geometry of the building as well as the location of the infill walls that were confirmed in situ [16].
The RC structure was simulated through non-linear lumped plasticity beam-column element models that are available in the SeismoStruct element library. A plastic hinge length equal to the largest dimension of the RC cross section was assumed, following recommendations in the literature [17, 18]. It was adopted 200 fibers for each cross section for a better representation of the seismic response of the RC elements.
Two...”
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“...shaking. The vulnerability of the structures
Num: 3.80 Hz Exp: 3.88 Hz
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Num: 4.09 Hz
Exp: 4.02 Hz
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Fig. 5 Numerical model modes of vibrations and natural frequencies: a Mode 1 (transverse); b Mode 2 (longitudinal); and c Mode 3 (torsion)
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is assessed by comparing the engineering response parameter values obtained from nonlinear dynamic time history response analysis with limits imposed by international codes and other recommendations. The structure is considered to be vulnerable if the response parameters exceed the limits proposed in codes. Otherwise, the structural performance is deemed acceptable. If the structure is found to be vulnerable,
Table 3 Numerical model: input material properties adopted for the infill masonry walls
Elasticity modulus Em (GPa) Compressive strength/m0 (MPa) Diagonal tensile strength/, (MPa) Shear stress r0 (MPa) Maximum shear stress hnax (Mpo Coefficient of friction q Maximum stress em Ultimate stress eu Closing strain Al
230 2.3 0.575 0.3 1 0.8 0.012 0...”
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“...linear and the other two non-linear. In the present work, it was assumed that the material non-linearity and non-linear dynamic time history response analyses were the most appropriate tool to assess the seismic vulnerability of the building.
Throughout the following sub-sections, the methodology adopted to assess the seismic vulnerability of the structure will be presented and the results will be presented and discussed in detail.
3.2 Methodology
The seismic assessment methodology used is based on the analysis of the peak inter-storey drift ratios reached by the different floors of the structure during the non-linear time history response analysis. These peak inter-storey drift ratios are compared with global drift ratio limits suggested by international codes and existing literature that are tied to specific structural performance levels or damage state levels.
In this study, the damage scale proposed by Rossetto and Elnashai [26], also known as the Homogenized Reinforced Concrete Scale...”
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“...distribution of the infill masonry walls. It must be mentioned that the irregular mass introduced by the balcony at this level of the structure amplified the torsion mechanism, which exacerbated the poor performance of the structure at this storey;
• Globally, the structure is considered vulnerable to seismic actions and it is considered that urgent interventions are necessary at Storeys 1 and 3 for this building structure. While this is a single-case study, several schools in the country follow similar designs, and the findings here highlight the importance of the review of all school building designs, especially in the urban areas of the Kathmandu Valley as well as in other urban areas in the region.
3.3.3 Capacity Curve and Peak Base Shear
Non-linear static pushover analyses, assuming uniform, triangular and adaptive load patterns, were carried out in two numerical models: (1) considering the RC frame only, and (2) considering both the RC frame and the infill masonry walls. Figure 10 shows...”
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“...analyses confirmed the occurrence of mechanisms such as soft-storey (longitudinal direction) due to the layout and distribution of the masonry infill walls. In the transverse direction, vulnerability of Storey 1 and Storey 3 are mainly due to the reduction of the cross section of the RC columns at the base of Storey 3, combined with the irregular distribution infill masonry walls along the height of the building and the eccentricity caused by the staircase and cantilevered balcony at the third floor level. The inadequate performance and undesired modes of damage for this case study building lead to the need for developing retrofit interventions that address the vulnerabilities, especially at the Storeys 1 and
Fig. 9 Non-linear dynamic analysis results of peak inter-storey drift ratio in the longitudinal direction for a Storey 1, b Storey 2, and c Storey 3; and peak inter-storey drift in the transverse direction for d Storey 1, e Storey 2, and f Storey 3
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kb Springer
.........Partial Co...”
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“...construction.
In this solution, the materials and properties defined for infill masonry walls used in the original structure, as summarized in Table 3, are used. Thus, two infill panels are added in Storey 3, in the direction of grid lines F and H shown in Fig. lb.
The main advantage of this solution is that it addresses the issue of the vertical irregularity of stiffness provided by the infill walls. However, the main disadvantage is on the impact of the functionality of the space. In the original building, the space where the walls are introduced corresponds to open space library for the students;
2. RC jacketing of all columns (RCJ): The RC jacketing of columns is a commonly used technique in Nepal as reported by Chaulagain et al. [31]. This retrofit solu-...”
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“...joints, and the possible need of strengthening the foundations [33]. Financially, it is considered to be an expensive solution since it requires high level of workmanship and sometimes requires that foundations also be strengthened. This can correspond to high direct construction costs as well as high indirect costs associated with the needed time for the retrofit and disruption of normal building functionality [34],
Regarding the design of the new cross section for the columns and corresponding reinforcing steel detailing, as the main purpose of the retrofitting technique is to increase the building lateral stiffness, the minimum reinforcing steel requirements and section detailing designs according to Eurocode 8 [35], for example, can be adopted assuming a medium ductility class.
In this case study, the new column section adopted is 500 x500mm2. The added longitudinal reinforcing steel is 16-mm-diameter steel bars, while the transverse reinforcement corresponds to 8-mm-diameter reinforcing...”
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“...International Journal of Civil Engineering
Fig. 12 Distribution of the steel braces adopted for the retrofit: a Storey 1; b Storey 2; and c Storey 3 (dimensions in mm and location of steel braces shown in red)
Table 6 Natural frequencies of the building with and without retrofit solutions (Units in Hz)
Mode Original IIMW RCJ-GF RCJ-TOT SB
Transv. 3.80 3.94 4.15 4.28 4.11
Long 4.09 4.05 4.70 4.89 4.76
Torsion 4.83 4.83 5.35 5.40 5.04
Table 6 presents results for the first three natural frequencies for each of the numerical models developed, with and without consideration of the seismic retrofitting. Figure 13 shows the 5% linear elastic acceleration response spectra corresponding to the average of 21 spectra of acceleration of accelerograms evaluated in this work, and the fundamental
frequency values of numerical models with and without retrofit solutions. It can be observed that all the retrofit strategies did modify significantly the natural frequencies of the structure. The RCJ-TOT model...”
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“...school building in Nepal and study the efficacy of different strengthening solutions to be applied. The analyses for evaluating the building and the respective strengthening solutions were based on state-of-the-art numerical models that consider the non-linear behavior of the structures when subjected to earthquake-induced ground shaking. The assessment methodology consisted of performing both non-linear static and non-linear dynamic analyses. Results from the non-linear dynamic analyses
indicated that the structure had large drift values in Storey 1 for the longitudinal direction, and in the Storeys 1 and 3 for the transverse direction. Additionally, using the data obtained from different analyses performed (pushover and dynamic), it was possible to compare the two methodologies and assess the adequacy of the pushover analysis, reinforcing findings existing in the literature.
From the seismic vulnerability assessment of the original structure, it was concluded that the building proved...”
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“...Innovative Inf Solut 1 (1):1
14. Varum H, Furtado A, Rodrigues H, Dias-Oliveira J, Vila-Pouca N, Arede A (2017) Seismic performance of the infill masonry walls and ambient vibration tests after the Ghorka 2015, Nepal earthquake”. Bull Earthq Eng 15,3, 1185-1212
15. SeismoSoft (2004) SeismoStruc- A computer program for static and dynamic nonlinear analysis of framed structures [online],” ed: Available from URL: http://www.seismosoft.com
16. Bose S et al. (2016) Structural Assessment of a School Building in Sankhu, Nepal Damaged Due to Torsional Response During the 2015 Gorkha Earthquake. In: S. Pakzad and C. Juan (eds) Dynamics of civil structures, Volume 2: Proceedings of the 34th IMAC, A Conference and Exposition on Structural Dynamics 2016. Cham: Springer International Publishing,, pp. 31-41
17. Rodrigues H, Varum H, Arede A, Costa A (2012) A comparative efficiency analysis of different non-linear modelling strategies to
simulate the biaxial response of RC columns. Earthq Eng Eng Vib 11:553-566...”
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