International Journal of Modern Research in Engineering & Management (IJMREM) ||Volume|| 1||Issue|| 6 ||Pages|| 15-19 || June 2018|| ISSN: 2581-4540
Effect of Planner Aspect Ratio on Vernacular Masonry Building under Earthquakes Jagat Kumar Shrestha Department of Civil Engineering, Pulchowk Campus, Institute of Engineering, TU
--------------------------------------------------------ABSTRACT-------------------------------------------------The behavior of a building during earthquakes depends critically on its planner aspect ratio. This paper deals with an evaluation of the seismic performance of vernacular masonry buildings with different planner aspect ratio. Rubble stone mud mortar masonry building structures are taken as reference building for this work, which are available in the rural area of Nepal. Four different planner aspect ratio's buildings are selected for model with flexible floor diaphragm representing the scenario of the constructed or constructing buildings in rural areas of our country after 25 April 2015 Earthquake in Nepal. A static non-linear (Pushover) analysis was performed. Subsequently, the available capacity spectrums are obtained to the corresponding demand spectrum to demonstrate the pushover responses of the buildings.
KEYWORDS: stone mud mortar building, planner aspect ratio, capacity curve, capacity spectrum, performance point. ----------------------------------------------------------------------------------------------------------------------------- --------Date of Submission: Date, 02 June 2018 Date of Accepted: 11 June 2018 ----------------------------------------------------------------------------------------------------------------------------- ---------
I.
INTRODUCTION
Different stone mud mortar buildings are constructed in rural hill areas of Nepal with varying planar aspect ratios. Stone masonry is a traditional form of construction that has been practiced for centuries in regions where stone is locally available. It is also effective especially in warm areas because the surface of the stone with its light color reflects the heat and direct solar radiation. Stone masonry has been used for the construction of some of the most important monuments and structures around the world. There are broad variations in their shape and the number of stories. Houses in rural areas are generally smaller in size and have smaller openings since they are typically used by a single family. The stone masonry walls mainly consist of irregularly placed undressed stones. However, such buildings are the most vulnerable categories of buildings due to the nature of the material and also the lack of proper construction and maintenance. The main lateral and gravity load-resisting system consists of stone masonry structural walls. The walls are generally uniformly distributed in both orthogonal directions with a wall thickness ranging from 380 mm to 450 mm [1]. Generally, in rural hilly area of Nepal most of the buildings are two room two story building made by locally available rubble stone with mud mortar. The typical floor plan of the building is shown in Figure 1.
Figure 1: Typical floor plan of building in rural hill areas of Nepal
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Effect of Planner Aspect Ratio on Vernacular Masonry… At the entrance, the floors consist out of pressure vaults with timber or bamboo beams. The first floor is composed out of one-way timber with single plank. This model represents the overall scenario of existing and new rebuild masonry buildings in earthquake affected areas of Nepal. The ground floor height of the building is taken as 3 m and first floor made as attic floor is taken as 1.5 m at corner level and 2.3 m at the ridge level. The overall thickness of wall is taken as 450 mm and roof slope varies from 25°-30° with horizontal. Table 1 shows the detail dimension of rubble stone masonry building and structural elements available in the different areas of the country. Table 1: Dimensions of stone mud mortar masonry building SN.
Description
Length
Breadth
Height
1
Lalitpur district, Nallu VDC, 14.5 haat x 10.5 haat Nuwakot district, Urleni VDC,16 haat x 10 haat Okhaldunga district, Ragani VDC, 18.5 haat x 10 haat Ramechhap district, Khimti VDC, 17 haat x 9 haat
22ft. (6.7m)
16 ft. (4.875m)
3.0 m
Planner Aspect Ratio 1.4
24 ft. (7.315 m) 28 ft. (8.534 m)
15 ft. (4.572 m) 15.5 ft. (4.724 m)
3.0 m
1.6
3.0 m
1.8
26 ft. (7.924 m)
13 ft. (3.962 m)
3.0 m
2
2 3
4
Remarks
5 ft. attic wall at end and 7 ft. at center level. Haat is the traditional unit.
Vernacular building is a category of building based on the local needs, construction materials and reflecting local tradition. Nepalese rural vernacular architecture is as varied as the topography, natural environment and ethnicity of Nepal. The length divided by breadth (both in plan) of a building is termed as its aspect ratio. The behavior of a building during earthquakes depends critically on its planner aspect ratio. Planner aspect ratio of building has a significant impact on sustainability of the building during earthquake. The purpose of this study is to conduct the effect of planner aspect ratio on vernacular stone mud masonry building under earthquakes. II. MODELING AND ANALYSIS This study uses the frame by the macro-elements (FME) method, in which macro-elements dimensions are a function of the global geometry of the aggregate, the dimensions of the stories, openings and the distances between openings [2] [3]. The FME approach reduces the number of degrees of freedom to represent the seismic response of complex masonry structures with a very interesting computational demand. A wall can be divided into three types of elements: Piers, spandrel beams and rigid elements. Pier elements are located at the sides of openings and spandrel beams represent the elements above openings. The remaining parts of the wall form rigid elements (Fig. 1). The previous studies have shown that the behavior of piers and spandrel beams can be expressed as linear elements.
Figure 1: Typical type of micro element.
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Effect of Planner Aspect Ratio on Vernacular Masonry‌ The program TREMURI was used to perform pushover analysis of the building model to assess the earthquake response of the buildings.
III.
RESULTS AND DISCUSSION
The capacity curves and performance level for particular stone mud mortar masonry buildings are obtained from static non-linear analysis (pushover analysis). Fig. 2 shows the push over or capacity curve for building having planner aspect ratio 1.4, 1.6, 1.8 and 2 respectively. The base shear and top displacement of the planner aspect ratio 1.4 are found to be 256kN and 9.87mm in X-direction and 310kN and 9.03mm in Y-direction where X is longer, and Y is sorter direction. Similarly, 332kN & 11.63mm and 288kN & 11.04 mm, 405kN & 10.06mm in X direction and 315kN & 13.67mm, 362kN & 11.22mm and 184kN & 10.52 mm in Y direction are found for planner aspect ratio 1.6, 1.8 and 2 respectively. This relation is obtained by increasing monotonically the horizontal load impact or the horizontal displacement to the structure model in corresponding to its first mode of vibration until it collapses. It is independent of the seismic action, as it is an intrinsic characteristic of the structure, a function of the geometry and resistance characteristics of the materials.
350.00 300.00 250.00 200.00 150.00 100.00 50.00 0.00
forAspect Ratio 1.6
Xdirectio n Ydirectio n
350.00 300.00 250.00 200.00 150.00 100.00 50.00 0.00
Base Shear (KN)
Base Shear (KN)
for Aspect Ratio 1.4
Top Displacement (mm)
Top Displacement (mm)
for Aspect Ratio 2
500.00 400.00 Xdirection
100.00
Ydirection
0.00
Base Shear (KN)
Base Shear (KN)
forAspect Ratio 1.8
200.00
Ydirectio n 0.0010.0020.00
0.00 10.0020.00
300.00
Xdirectio n
400.00 300.00 Xdirectio n
200.00 100.00
0.00 10.0020.00
0.00 0.00 10.0020.00
Top Displacement (mm)
Ydirectio n
Top Displacement (mm)
Figure 2: Push over/Capacity Curve of building having AR 1.4, 1.6, 1.8 and 2. Fig. 3 shows the capacity spectrum for building having planner aspect ratio 1.4, 1.6, 1.8 and 2 respectively. These capacity curves are converted into capacity spectrum by using guidelines of ATC 40 [4]. It is a curve showing the relation between the spectral acceleration and spectral displacement. The spectral acceleration and spectral displacement of the planner aspect ratio 1.4 are found to be 0.25g and 8.23mm in X-direction and 0.3g and 7.53mm in Y-direction. Similarly, 0.32g & 9.69mm and 0.28g & 9.2 mm, 0.35g & 8.38mm X direction and 0.27g & 11.39mm, 0.36g & 9.35mm and 0.19g & 8.77 mm Y direction are found for planner aspect ratio 1.6, 1.8 and 2 respectively.
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Effect of Planner Aspect Ratio on Vernacular Masonry‌
0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00
Xdirectio n
0.00 5.00 10.00
Capacity Spectrum of Aspect Ration 1.6
Sa (g)
Sa (g)
Capacity Spectrum of Aspect Ratio 1.4
Ydirectio n
0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00
Sd (mm)
Capacity Spectrum of Aspect Ratio 1.8
Xdirectio n Ydirectio n
Capacity Spectrum of Aspect Ratio 2
Sa (g)
Sa (g)
Ydirection 0.00 10.00 20.00
Sd (mm)
0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00
Xdirection
0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00
Xdirection Ydirection
0.00 10.00 20.00
0.00 5.00 10.00
Sd (mm)
Sd (mm)
Figure 3: Capacity Spectrum for aspect ratio 1.4, 1.6, 1.8 and 2. Fig. 4 shows the performance point of building having planner aspect ratio 1.4, 1.6, 1.8 and 2 in both X and Y direction. It represents the state of maximum inelastic capacity of the structure, is found through the cross point of the capacity spectrum and demand spectrum for a given damping ratio. The capacity spectrum developed from the nonlinear analysis cannot satisfy the demand spectrum according to the NBC 105 [1] for medium soil. Hence these types of rubble stone mud masonry building cannot get the performance point without strengthening of structural element of building and reducing the demand spectrum with increasing the coefficient of damping.
Figure 4: Performance point of building along X- and Y- direction.
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Effect of Planner Aspect Ratio on Vernacular Masonry… IV.
CONCLUSION
The non-linear behavior of stone mud mortar masonry building was studied by carrying out pushover analysis under 24 different loading conditions. On the basis of the results, it is concluded that all the seismic parameters, viz. base shear and top displacement increase with the length of wall and number of stories. The higher the length, the higher are values of all these parameters. It is seen that the planner aspect ratio 1.4, 1.6, 1.8 & 2, the aspect ratio 1.4 (close to one) perform better, as they possess lesser values of all these seismic parameters (37% in base shear and 15% in displacement), Therefore, planner aspect ratio which have elongated shape or long narrow diaphragms should not preferred. These types of rubble stone mud mortar masonry building cannot satisfy the demand spectrum. Hence, it needs to be strengthened to satisfy demand spectrum.
REFERENCES [1] [2] [3] [4] [5]
NBC 105- 1994, Seismic design of buildings in Nepal, Department of Urban Development and Building Construction, Ministry of Physical Planning and Works, Government of Nepal, 1994. S. Lagomarsino, A. Penna, A. Galasco and S. Cattari, TREMURI program: An equivalent frame model for the nonlinear seismic analysis of masonry buildings, Engineering Structures, Volume 56, 2013, 1787-1799. A. Galasco, S. Lagomarsino, and A. Penna, On the use of pushover analysis for existing masonry building, Geneva, Switzerland, 2006. ATC, Seismic Evaluation and retrofit of Concrete buildings, Volume 1, ATC-40 Report, Applied Technology Council, Redwood City, California, 1996. U. Camathias, B. Stojadinović, N. Mojsilović and V. Bosiljkov, Seismic Performance Evaluation of a Historic Unreinforced Masonry Building Structure, Ljubljana, 2013.
Jagat Kumar Shrestha. “Effect of Planner Aspect Ratio on Vernacular Masonry Building under Earthquakes.” International Journal of Modern Research in Engineering & Management (IJMREM), vol. 1, no. 6, 6AD, pp. 15–19., www.ijmrem.com. www.ijmrem.com
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