The Protection of Masonry Buildings in a Mining Area

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ScienceDirect Procedia Engineering 193 (2017) 184 – 191

International Conference on Analytical Models and New Concepts in Concrete and Masonry Structures AMCM’2017

The protection of masonry buildings in a mining area Dawid Mrozeka,*, Magdalena Mrozeka, Jan Fedorowiczb a

Silesian University of Technology, Akademicka 5, 44-100 Gliwice, Poland b WST Katowice, Rolna 44, 40-555 Katowice, Poland

Abstract The paper includes the principles of protection of existing masonry buildings, located on mining areas. The article contains both a theoretical discussion and a numerical analysis. The effects of mining influence on a subsoil surface are presented as a part of the theoretical discussion. Furthermore, the rules of the procedure and the methodology for static analyses of wall structures located on an active mining area are briefly discussed. The last part of the theoretical considerations is the methodology and the capabilities of using the Finite Element Method in the static analyses. Results of a numerical analysis of a building behaviour subjected to mining impacts are presented. A residential, three-storey masonry building, not adapted to transmit the mining impacts, is analysed. The main problem of the analysis is a proper structure division by dilatations. Calculations are carried out by the FEM with the use of the non-linear-plastic material model with stiffness degradation. Results of the static analysis are obtained from a classical engineering method – the method of Budzianowski. © Published by Elsevier Ltd. This Authors. Published by Elsevier Ltd.is an open access article under the CC BY-NC-ND license © 2017 2017The TheAuthors. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of the International Conference on Analytical Models and New Peer-review responsibility of the scientific committee of the International Conference on Analytical Models and New Concepts in Concrete and Masonry Structures. Concepts inunder

Concrete and Masonry Structures

Keywords: Mining areas; Mining activities revenues; Protection of buildings on a mining area; Numerical analyses; Models of inelastic material degradation

1. Introduction The effects of mining, which appear on a subsoil surface, largely depend on geological conditions. A classification scheme of these effects, which includes continuous and discontinuous deformations and subsoil

* Corresponding author. Tel.: +48-32-237-2118; fax: +48-32-237-2268. E-mail address: [email protected]

1877-7058 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of the International Conference on Analytical Models and New Concepts in Concrete and Masonry Structures

doi:10.1016/j.proeng.2017.06.202

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vibrations could be found in [1-2]. One of these effects is a depression basin (showed in Fig. 1), which appears on the subsoil surface. This basin migrates with the mining front and generates the states of deformations, changing during the mining, in the under subsoil part of a construction. In the engineering practice these deformations are described by the following rates: w, u [m] – vertical and the horizontal displacements of the points, occurred on the subsoil surface, ε [mm/m] – horizontal deformation in the layer of the subsoil surface, Κ, R [1/km, km] – curvature and radius of the curvature of the depression basin profile, T [mm/m] – slope of the land surface. The secondary effect of the mining activities are changes of the soil-water conditions, which, together with ground dehydration, could induce additional depression of the subsoil surface.

Fig. 1. Diagram of transition of a depression basin under a building; 1- lack of the mining influence (w=0), 2 – the convex edge of basin (+Rmjn, +εmax), 3 – extreme slope (Tmax, w=0.5wmax), 4 – the concave edge of basin (-Rmin, -εmax), 5 – after transition of the depression basin (w=wmax).

Values of these parameters could be determined, among others, from the Budryk-Knothe theory [3-5]: • • • • • •

vertical displacements of a point on a subsoil surface: w(x), slope of a basin profile: T(x), curvature of a depression basin profile: K(x), radius of a curvature of a depression basin profile: R(x), horizontal displacements of a point on a subsoil surface: u(x), horizontal deformation in the layer of a subsoil surface: İ(x), where the following is determined in the formulas (Fig. 2): ż coverage radius of the major influences: r ż maximal depression: wmax, ż changes parameter of a coverage radius of the major influences: n, ż angle of a coverage of the major influences: ȕ.

2. Mining resistance of buildings Generally, low intensity mining causes continuous deformations on a subsoil surface. In an engineering practice, it is assumed that discontinuous deformations could be formed after exceeding a certain value of the horizontal deformation, dependent on a geological structure. Based on observations in the Upper Silesian Coal Basin (USCB), it can be estimated at around ε = 9.0 mm/m. - limit of a continuous deformations. An estimation of mining resistance of buildings allows to carry out the activities, which adapt a building for transmission of mining impacts or its strengthening. In the case of existing buildings it could be reached by: • strengthening of foundation and subterranean parts of a building, • partition of a building by setting the expansion joints, • reduction of subsoil impact on a subterranean part of a building, • strengthening of the above-ground parts of a building,

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• strengthening of some building elements and repair of breakdowns. Detailed information about rules and usage conditions of the individual methods could be found in the literature [1,3,6-8]. Figures 2 and 3 present an exemplary, used in this paper, strengthening structure by the reinforced concrete band and steel circumferential anchors on an utmost ceilings level.

Fig. 2. Strengthening of building foundation by a typical reinforced concrete band.

Fig. 3. Details of above-ground part of building strengthening by an external steel anchor in grooves.

The next part of the paper presents the procedure of a building resistance assessment and results of influence of added mining loads analysis for three-storey masonry residential building. Based on the building condition assessment and an estimation of cost-effectiveness of the building renovation, partition of the building by expansion joints on four parts was applied. For each part a reinforced concrete band on a foundation level and external steel anchors on ceilings above basement and the highest storey level have been used. An internal forces analysis was carried out twice, and the results from the classical engineering methods obtained by the spatial FEM model [9], which use the linear-plastic with stiffness degradation material model, were compared. 3. A structure description and geological-mining conditions A subject of analysis is a three-stairway residential building, designed in the twenties of the last century in the traditional technology with different height (three and four storeys). The object is founded on one level and has a basement under the whole structure. In a horizontal projection the building has a C letter shape – Fig. 4. The building is brick masonry with predominant longitudinal load-bearing system. Concrete building foundations are 60100 cm wide. Load-bearing walls of the first two floors have a thickness of 51 cm and 38 cm on the highest floors. The ceiling above basement is beam and block type, the others are wooden. The object is in poor condition - caused by mining impacts transmission.

Fig. 4. A view of the analysed building.

In a geological-mining opinion it was found that primary ratios, which characterise the ground surface deformation for mining operation in the region of analysed building foundation, are amounted to: εmax=2.9 mm/m, T=2.6 mm/m and Rmin=-27.0 km, w=260 mm. A the same time it was stated, that for mining operation, which is planned to the year 2030, the most probable are mining impacts, characterized by ratios equals appropriately: εmax=1.4 mm/m, T=3.3 mm/m, Rmin=41.0 km, w=933 mm [10,13]. The mining was a reason of the ground surface

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decrease about average 260 mm and appearance of substantial failures of bearing walls in the building. Fig. 4 presents the building facade with some damages of bearing walls, which are visible outside the building.

Fig. 5. Analyzed directions of a mining exploitation in view of the object.

Detailed visual inspection of the object allows to estimate its technical condition. It was found that the building condition is poor because of its age and previous damages, caused by the mining. However, an estimation of an object value indicates the profitability of major overhaul. Therefore a numerical analysis of a building structure effort was carried out in view of selection of a proper protecting method against the mining. Taking into account the size and shape of the building (Fig. 5), it was stated that the proper way to protect the building structure is division of the building with the use of expansion joints 4. Numerical analysis of a static behavior of a building structure

Fig. 6. The schemes of walls systems, taken to the calculations: a) the whole building, b) the building after application of two expansion joints, c) the building after application of three expansion joints.

A static analysis of a building structure work was carried out with two methods: A) a classical one – the Budzianowski method [4,5] for subsoil curvature impacts and according to the guidelines [3] related to a horizontal subsoil loosening and B) a numerical method (FEM) with spatial models [11,12]. FEM calculations were conducted thrice. Construction as a whole in actually state (Fig. 6a), divided by the expansion joints on three parts (Fig. 6b) and on four parts – full protection (Fig. 6c) have been analysed. The three design situations have been analyzed with the

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direction (Fig. 5) of mining ȥ equals to 0°, 45° and 90°. In addition to the full building protection, its strengthening by steel anchors on the first and the last floor level and installation of reinforced concrete band on the foundations level were provided. Location of that strengthening was schematically shown in Fig. 6c – dashed lines. Three computational FEM models, shown in Fig. 7a-c, corresponding to the horizontal projections from Fig. 5, were composed. Mesh with quadrangular finite elements with 0,1 m of side dimension is the same in all cases. The following were assumed for the numerical calculations, based on the building documentation: • values of horizontal subsoil deformation resulted from the mining, on the level εmax=3.0 mm/m, • values of strength parameters of subsoil in a place of a building location, estimated according to the documentation and the literature, on the level c=20 kPa, φ=15o, Eo=25 MPa, ν=0.30, • average vertical pressure of the building to subsoil σn=100-200 kPa, • thickness of a basement floor h1=0.15 m. The values of coefficient of the vertical subsoil flexibility Co of whole system, determined according to [3,6], equalled Co=20 kN/m3. Strength parameters of a material, accepted to the calculations, are matched in the table 1.

Fig. 7. A view of computational FEM models: a) the whole building model (I), b) the building after two dilatations application model (II), c) the building after two dilatations application model (III). Table 1. Summary of material parameters, assumed in the calculations. Material

ȡ [kg/m3]

Modulus of elasticity E [GPa]

Compressive strength ıc [MPa]

Tensile strength ıt [MPa]

Ȟ

Wall

1900

2.1

2.1

0.4

0.20

Concrete

2400

30.0

16.0

1.6

0.16

Wood

1200

12.0

18.4

14.4

0.05

In analyses of stress and strain based solution is state obtained in the model (I), where the values obtained from other models were formulated by percentage to the model (I). Obtained results of extreme values of vertical stress σ22, shear stress σ12, strain ε1 and non-dilatational strain ε12 are tabulated (Tab. 2). Table 2. Summary of selected results from the FEM calculations of the building. Longitudinal bending, R=12km, ȥ=0o Model

ı11 share [kPa]

ı12 share [kPa]

İ1 [o/oo]

share

İ12 [o/oo]

share

(I)

685

100%

486

100% 0.419 100% 0.555 100%

(II)

622

91%

412

85%

0.390

93%

0.471

85%

(III)

163

24%

128

26%

0.101

24%

0.147

26%

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Fig. 8. Maps of strain distribution İ1 – longitudinal bending (ȥ=0o in Fig. 5) a) model (I), b) model (II), c) model (III)

Maps of obtained strain distribution are shown in Fig. 8, where selected maps of the building for model (I), (II) and (III) are presented. Detailed analysis of obtained results and values given in Tab. 2 and Fig. 8 point that application of two dilatations reduce the effort of the building compared to the effort of the building in one part at about four times. Non-dilatational strain obtained in the model (III) is much smaller than the strain limit according to [6] of 0.0004 mm/m. 5. The building bending – the Budzianowski method Internal forces in the building without dilatation were calculated also by a classical method – the Budzianowski method in the case of building bending and by the way given in the guideline [14] for impact of the horizontal strain. For this purpose, previously defined data, and the [15], coefficient of the vertical subsoil flexibility Co are used in the formulas of the Budzianowski method [4,5,7] which determine values of internal forces in sections, shown in Fig. 5 for three inclination angles of mining direction ψ. There following were calculated: • changes the vertical stress at a base of the foundation caused by deforming substrate, • value of generalized lateral force in a rigid structure - section Į-Į:

Q1* = ³ σ z ( x, y ) dF1

(1)

• value of bending moment in a rigid structure - section Į-Į: M zg* ,1 = ³ r ⋅ σ z ( x, y ) dF1

(2)

F1

F1

• value of torsional moment in a rigid structure in point U ( xU , yU ) - section Į-Į:

M s*,1 = ³ s ⋅ σ z ( x, y ) dF1 F1

•

(3)

value of limiting radius of curvature - any point A ( xA , y A ) :

Rgr ( A) =

− Co 2 ⋅ σ o ( x, y ) x = x A

y= yA

(4)

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Obtained values of generalized internal forces for Rmax=12 km in selected three sections, shown in Fig. 4, are tabulated (Tab. 3). Table 3. Values of internal forces in a deformable building, calculated by the Budzianowski method in sections shown in Fig. 5 depended on a mining direction ȥ. Section - Į 3

The internal force Q [MN]

0.36

0.08

0.00

90o

Mzg [MN·m]

26.63

47.71

93.61

Msk [MN·m]

29.17

13.96

77.66

0o

45o

Section – Į1

Section - Į 2

Angle ȥ

Q [MN]

2.05

4.69

0.00

Mzg [MN·m]

61.12

472.03

659.12

Msk [MN·m]

132.72

1.89

44.68

Q [MN]

4.24

2.26

0.29

Mzg [MN·m]

91.92

232.01

354.31

Msk [MN·m]

103.12

98.84

185.35

Axial force and bending moment redistributions in separate continuous footing for different values (from 100 to 200 kPa) of the foundation pressure on a subsoil, are obtained. As an example, values of determined axial forces in longitudinal continuous footings from Fig. 6b, are presented in Tab. 4. Table 4. Extreme tension forces of wall in segment building model at horizontal subsoil loosening. Bench at Fig. 6b

Force NA in [MN] with ın=100 kPa

Force NA in [MN] with ın=200 kPa

Axis 1

0.681

1.060

Axis 2

1.288

2.020

Bench at Fig. 6c

Force NA in [MN] with ın=100 kPa

Force NA in [MN] with ın=200 kPa

Axis 1

0.390

0.494

Axis 2

0.657

0.899

Fig. 9. Distribution of variable degradation of tensile elements compared to the existing masonry damage analyzed object.

Tension load capacity of these walls in the basement part could be estimated on the level: N gr = 0.4 ⋅ ( 0.58 ⋅ 3.1 + 1.04 ⋅ 0.6 ) = 0.97 MN

(5)

It means, that application of expansion joints according to the conception from Fig. 6c is completely reasonable

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and allows to transfer tension loads by building walls on the level II of the category of a mining area. In this paper, using the model (I), a static analysis was also performed taking into account the elastic-plasticdamage material model (Barcelona Model [16]). In Fig. 9 an examples of the distribution of variable tensile degradation in masonry construction elements are shown. The degraded elements on the degradation maps are coincided with cracks in the wall which had been observed in the reality. 6. Conclusions Mining activities are often carried out in areas where buildings are unprotected in general, or not enough against additional mining influences. The classical methods of estimation of mining effects and effort in the buildings are time-consuming and obtained results may be underestimated. Using of computational methods in civil engineering allows for reduction of calculating time and more complex structures analyses. The problem in this case is a faithfully reflection of geological and mining conditions and a proper interpretation of obtained results. The results for a residential building analyses, presented in the paper, were the base for taking the decision concerning the protection method of an object against mining influences. It was decided that the optimal solution is a building division into four parts. Each of the separate parts should contain protection elements in a form of steel anchors affixed to the ceiling level of the first and the last floor and peripheral concrete ties at the level of the building foundation. Finally, it was assumed that the analyzed building, after the protection introduction, will be able to transmit the mining influences resulting from the second category of a mining area. Acknowledgements This research was supported in part by PLGrid Infrastructure. References [1] Instruction 364/2000: Technical requirements for buildings constructed in mining areas, the Building Research Institute, Warsaw, 2000 (in Polish). [2] L. Fedorowicz, J. Fedorowicz, Methods of evaluation effort of buildings in mining areas. Scientific Papers of Silesian University of Technology, Series Mining, z 246, Gliwice 2000 (in Polish). [3] H. Kratzsch, Mining Subsidence Engineering, Springer-Verlag 1983. [4] A. Malinowska, Accuracy Estimation of the Approximated Methods Used for Assessing Risk of Buildings Damage Under the Influence of Underground Exploitation in the Light of World’s and Polish Experience–Part 1, Archives of Mining Sciences 58 (3) (2013) 843-853. [5] A. Malinowska, Accuracy Estimation of the Approximated Methods Used for Assessing Risk of Buildings Damage Under the Influence of Underground Exploitation in the Light of World’s and Polish Experience–Part 2, Archives of Mining Sciences 58 (3) (2013) 855-865. [6] Collective work: Protection of buildings in mining areas. Wyd. GIG Katowice 1997 (in Polish). [7] Instructions, Guidelines, Guidance 416/2006. The design of buildings in mining areas. Publisher ITB, Warsaw 2006 (in Polish). [8] M. Kawulok, Mining damages in construction. Publisher ITB, Warsaw 2010 (in Polish). [9] T.J.R. Hughes, The finite element method: linear static and dynamic finite element analysis, Courier Corporation, 2012 [10] R. Hejmanowski, A. Malinowska, Evaluation of reliability of subsidence prediction based on spatial statistical analysis. Int J Rock Mech Min Sci. 46(2) (2009) 432–8. [11] J. Fedorowicz, Contact problem of building - subsoil. Part II. The criteria for creating and evaluating computational models of systems design building - ground mining. Scientific Papers of Silesian University of Technology, Building Series, No 1805, z 114, Gliwice, 2008. [12] L. Fedorowicz, Contact Issues building - subsoil. Part I. Criteria for modeling and analysis of fundamental design issues contact Building subsoil. Scientific Papers of Silesian University of Technology, Civil Engineering Series, No 1729, z 107, Gliwice, 2006. [13] A. Saeidi, O. Deck, T. Verdel, Development of building vulnerability functions in subsidence regions from empirical methods. Engineering Structures. 31 (10) 2009 2275-2286. [14] J. Kwiatek, Protection of buildings in mining areas. Wyd. GIG Katowice (in Polish), 1997. [15] O. Deck, M. Al Heib, F. Homand, Taking the soil–structure interaction into account in assessing the loading of a structure in a mining subsidence area. Engineering Structures. 25 (2003) 435–448. [16] A. Wawrzynek, M. Mrozek, D. Mrozek, Nonlinear analysis of degraded buildings applying plastic-damage material model, Proc. International Conference, Bratislava 2008, pp. 4-5.