Construction Engineering Volume 3, 2015 www.seipub.org/ce Doi: 10.14355/ce.2015.03.002
Comparative Analysis of Mechanical Properties of Composite Walls Filled with Different Ecological Materials M. Zhang*1, W. Huang 1, Z.K. Yang 1,2 College of Civil Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, China College of Civil Engineering, Henan Polytechnic University, Jiaozuo 454000, China *1
mzhangsjz528@163.com; 266149154@qq.com; 394027203@qq.com
Abstract As a new system, eco‐composite wall structure is mainly constructed with pre‐cast eco‐composite wall, concealed frame and floor by means of assembling and casting. Since the existing filling materials are unable to meet the needs of research, various choices of ecological material filled in the ecological composite wall structure have become a key problem the group needs to solve. This paper mainly describes the preparation craft and the uniaxial compressive constitutive model of the building materials. Five kinds of materials filled within eco‐composite wall are analyzed and compared and the application range in the ecological composite wall structure system is given. Studies show that: ceramic blocks can be used in middle‐high rise buildings; aerated blocks and foam concrete blocks can be used in multi‐storey buildings; grass tiles can be used in low‐rise buildings; while the plaster, due to its poor ductility and durability, is not recommended for the structural system. Keywords Aerated Concrete Block; Ceramic Block; Foam Concrete Block; Gypsum Block; Grass Brick; Twin Shear Unified Strength Theory; Constitutive Relationship
Introduction In order to adapt to the Chinaʹs basic conditions, and to satisfy the wall material innovation and building energy requirements, the group developed a new building structural system ‐ new composite wall structure which is characterized by low weight , energy‐saving, good seismic, ecological and environmental protection, energy dissipation damping, fast construction, and practically (shown as Fig.1). It is mainly constructed with precast eco‐ composite wall, concealed frame and floor by means of assembling and casting. As one of the main bearing components, the eco‐composite wall is made up of two parts, a concealed frame and a eco‐composite wall. Linking and restraining the eco‐composite wall, the concealed frame is composed of end frame columns and concealed beams. The eco‐composite wall is prefabricated with reinforced concrete frame grids and filler blocks. The beams and columns of reinforced concrete frame grids, which are called ribbed beams and ribbed columns, are small in section and reinforcement (shown as Fig.2).Along with the development of the new ecological material, the filling material of which has been changed to ecological blocks which are made by industry and agriculture wastes. Concealed beam Floor End frame column Or Connecting column
Composite slab Connecting column
FIG.1 ECO‐COMPOSITE WALL STRUCTURE SYSTEM FIG.2 CONSTRUCTION DETAIL OF THE NEW COMPOSITE WALL
5
www.seipub.org/ce Construction Engineering Volume 3, 2015
The construction process of the precast eco‐composite wall is shown in Fig.3. Based on early study, several kinds of ecological materials filled within composite wall have been developed and implicated [1]. But, due to the deepening and improvement of the subject, the existing fill materials have been unable to meet the needs of research. The diversified choices of materials filled in the ecological composite wall structure have become the key issue the group needs to solve. The paper mainly describes the preparation of their crafts, the uniaxial compressive constitutive model. Through the comparison of the five kinds of materials filled within composite wall, the application range in the ecological composite wall structure system is given.
(a) place the blocks (b) bind the steel bar (c) set up template (d) pouring concrete FIG.3 CONSTRUCTION PROCESS OF THE PRECAST ECO‐COMPOSITE WALL TAB.1 1M3 CONCRETE MIX PROPORTION (KG)
Intensity level LC30
Cement 340
Fly ash 50
Sand 525
Aggregate 975
Admixtures 5.9
Water 160
Experimental procedure Aerated Concrete Block The design mix of the material is shown in Tab.1. The preparation process of aerated concrete block is shown in Fig. 4. The constitutive model of the aerated concrete block (bulk density of 5.8 KN/m3) is obtained [2, 3], shown as Fig. 5 . 1 .2
Preparation of siliceous material Preparation of calcium material
Conditioning agent, & Foaming agent
JQK-1 JQK-2 JQK-3 Fitting curve
1 .0 0 .8 0 .6
Mixing& Stirring
Casting& Foaming
Stand for a certain length of time & perform the cut
Steam with high temperature and high pressure
0 .4 0 .2 0 .0
0
1
2 3
4
5
FIG.4 PREPARATION PROCESS OF AERATED CONCRETE BLOCK FIG.5 CONSTITUTIVE RELATION OF AERATED BLOCKS
The mathematical expression of stress‐strain relationship of aerated block is obtained:
b [1.12( 0 [1.40( 0 [4.16 6.63(
) 0.03] b
0 b (1)
2 ) 3.15( ) 0.75] 0 0
b 0 (2)
) 4.91( ) 2 1.75( )3 0.30( ) 4 0.02( )5 ] 0 u (3) 0 0 0 0 0
where b 0.75MPa , 0 1.75MPa , b 0.0005 , 0 0.0025 , u 0.004 , b , 0 are scale limit stress and peak stress of aerated block respectively; b , 0 and u are the size limit stress and peak stress of aerated block respectively. Ceramsite Block The design mix of the material reference literature [4]and[5].
6
Construction Engineering Volume 3, 2015 www.seipub.org/ce
The preparation process is shown as Fig.6. Experimental contrast analysis is done between ceramsite concrete block and ordinary concrete, and a corresponding adjustment of the descent stage of the LWAC constitutive model in Technical specification for lightweight aggregate concrete structures. Comparative analysis showed that ceramsite concrete and ordinary concrete were basic unanimously, except that the normal concrete was destroyed by the interface between coarse aggregate and mortar, while the ceramsite concrete was aggregate fracturing ceramsite concrete. The cause of this phenomenon is that the strength of the ceramsite is much lower than that of coarse aggregate [4]. Ceramsite block constitutive model of rising curve is based on the Technical specification for lightweight aggregate concrete structures (JGJ52‐2002) [5] while the expression of decline curve is based on literature [4].
0 [1.5( 0 (
) 0.5( ) 2 ] 0 0
2 ) 1 b( ) ( ) 0 0 0
0 (4) 0 u (5)
where 0 1.96MPa , 0 =0.0022 , u =0.0038 , and b and can be obtained through experiments, and the higher the concrete strength grade is , the smaller the value , b will be ; 0 , 0 , u are the ceramsite block of peak stress, peak strain, ultimate compressive strain respectively. Fig. 7 shows the comparison between the test fitting constitutive model and the standard model, in which we can see that two models match better in the rising period, but the standard model does not give a decline curve changes, which remains to be further perfect. 1.2
Fly ash & cement
Mixing & Balling
Test data Standard model
1.0
Into the mould
Slag
Binder
High-temperature roasting
Mold release and maintenance
0.8 0.6 0.4 0.2
Ceramsite
0.0
0
2 3
1
4
5
FIG.6 PREPARATION PROCESS OF CERAMIC BLOCK FIG.7 COMPARISON OF EXPERIMENTAL MODEL AND STANDARD MODEL
Lightweight Foam Concrete Block The design mix of the material reference literature [6]. The preparation process of prefabricated foam mixing method is shown in Fig. 8. According to the test data uniaxial compressive stress‐strain fitting curve of foam concrete block can be obtained (shown as Fig. 9) [6]. 1.2
P M -1 P M -2 F itting curve
Preparation of foaming agent Preparation of cement mortar
1.0
Mixing & Stirring
Concreting and vibrating
0.8 0.6
Mold release and maintenance
0.4 0.2 0.0
0
1
2 3
4
5
FIG.8 PREPARATION PROCESS OF LIGHTWEIGHT FOAM CONCRETE BLOCK FIG.9 COMPRESSIVE STRESS –STRAIN CURVE OF FOAM CONCRETE
The compression stress‐strain mathematical expression of foam concrete is given:
= 0 [2(
) 1.1( ) 2 1.7( )3 3.8( ) 4 2( )5 ] 0 0 0 0 0
0 0 (6)
7
www.seipub.org/ce Construction Engineering Volume 3, 2015
0 [5.2 3.7(
)] [1 7.9( )] 0 u (7) 0 0
where 0 1.7 MPa , 0 0.003 , u 0.006 ; 0 is the peak stress of the foam concrete; 0 , u ,are the peak strain and ultimate compressive strain of the foamed concrete respectively. Gypsum Block The design mix of the material reference literature [7]. Different material mixture ratio and volume with different strength grade of gypsum block quality can be prepared, taking the quality volume of 650 kg/m3 of gypsum block [7]as an example: The preparation process is shown in Fig. 10. A reasonable constitutive model of gypsum and its mathematical expression are gotten [8~9].(shown as Fig.11) TAB.2 BASIC PHYSICAL AND MECHANICAL PROPERTIES OF THE GYPSUM BLOCK
Items
Bulk density (kg/m3)
Bending strength (MPa)
Compressive strength(MPa)
Tensile strength (MPa)
Softening coefficient
Performance indicators
650
4.0
9.0
2.0
≥0.5
Thermal Nail Sound insulation conductivity hanging performance (m3∙k/w) load 0.107
45.71
40
1.2
1.0 0.8
Water Gypsum powder Additive
Mixing & Stirring
0.6
Casting & Molding
Mold release
0.4
Stoving and maintenance
0.2
0.0 0.0
0.5
1.0
1.5
2.0
2.5
FIG.10 PREPARATION PROCESS OF GYPSUM BLOCK FIG.11 STRESS‐STRAIN CURVE OF GYPSUM BLOCK
The fitting curve is : 0 [3.04(
4 ) 8.33( )3 7.31( ) 2 2.79( )] 0 u (8) 0 0 0 0
Where, 0 5.0 MPa , 0 0.00166 , u 0.0025 ; 0 , 0 , u are the peak stress, peak strain, ultimate compressive strain of the gypsum block respectively. Grass brick The design mix of the material reference literature [10]. The preparation process is shown in Fig. 12. The uniaxial compression dimensionless constitutive relation curve of grass block is obtained as shown in Fig.13[10]. M G -1 M G -2 M G -3 Fitting curve
Crush cotton straw
Deal straw surface with glue
Mixing with fiber & Into the mold
1.2 1.0 0.8 0.6 0.4
Mold release and cut
Stand for 24 hours with pressure
0.2
Vibrating
0.0 0.0
0.5
1.0
1.5
2.0
2.5
FIG.12 PREPARATION PROCESS OF GRASS BRICK FIG.13 STRESS ‐ STRAIN CURVE OF GRASS BRICK
After getting the uniaxial compression dimensionless constitutive relation curve of grass block, the constitutive relation of the grass brick mathematical formula is obtained:
8
Construction Engineering Volume 3, 2015 www.seipub.org/ce
b [1.46( 0 [0.24(
) 0.014] 0 b (9) b
6 ) 1.82( )5 5.23( ) 4 6.66( )3 2.62( )2 1.49( )] b u (10) 0 0 0 0 0 0
where b 0.7 MPa , 0 1.4MPa , b 0.025 , 0 0.0573 , u 0.1154 ; b and 0 are the proportion limit stress and peak stress of grass brick respectively; b , 0 and u are the elastic limit of compressive strain, the peak strain and ultimate compressive strain of the block respectively. Results and discussion Strength theory, under the complex stress state, generally refers to the regularity of plastic yield or brittle fracture theory, and twin shear stress unified strength theory, starting from the twin shearelement, which will consider the effect of intermediate stress on the material. Its practical significance lies in that the deepening unified strength theory can be applied to different types of materials while the old strength theory only could be applied to a single material strength theory in the past. Based on research, the group provides an effective unity solution for the ecological composite wall structure filled with different materials. Fig. 14 is twin shear element model proposed by Professor Yu Mao‐hong [11,12].
FIG.14 TWIN SHEAR ELEMENT MODEL
The mathematic expression of the unified strength theory is: F 1
F
1 b
b 2 3 t , when 2
1 3 , (1) 1
3 1 , (2) 1 b 2 3 t , when 2 1 1 1 b
where 1 , 2 and 3 are the three principal stress respectively; t / c is the tension‐compression strength ratio;
c and t are the uniaxial compression strength and uniaxial tensile strength respectively; b reflects the material damage impacted by middle main shear stress and normal stress. If the material strength parameters and b is confirmed, then a suitable materialʹs yield criterion can be determined. The strength parameters and b of the five kinds of materials is obtained, as shown in Tab.3. TAB.3 STRENGTH PARAMETERS OF THE ECOLOGICAL BLOCKS
Parameters Blocks Aerated concrete block Ceramic block Foam concrete block Gypsum block Grass brick
fc
ft
/ MPa 4.0~5.0 5.3~8.1 2.5~7.5 8.8~10.0 2.5~3.8
/ MPa 0.4~0.55 0.5~0.85 0.2~0.8 0.6~2.0 0.2~0.35
b
0.1~0.11 0.09~0.1 0.08~0.11 0.06~0.2 0.09~0.1
0.25~0.5 0.25~0.6 0.3~0.5 0.5~0.8 0.3~0.5
Based on the early theory [1,13,14], if the uniaxial constitutive equation of materials is known, the material yield hardening function of expression is obtained, the incremental elastoplastic stress‐strain relationship corresponding to different yield function could be gotten and then the resulting incremental elastoplastic stiffness matrix could also be obtained. The multiaxial elastic‐plastic incremental stress‐strain relation is given:
9
www.seipub.org/ce Construction Engineering Volume 3, 2015
d{ } [ D]ep d{ } (3)
where [ D]ep is incremental elastoplastic stiffness matrix, which can be represented as T Q F [ D] [ D] e e (4) [ D] [ D] ep T F Q A [ D]e
where F or F ' is yield function; Q or Q ' is plastic potential function; A is a function of hardening parameter K ,and K can be represented as plastic deformation of plastic work:
dK 1d 1p 2 d 2p d p d T
A
T
F (5)
F 1 F T F dK (6) K d K
Under uniaxial stress state, A can be calculated by using the slope of uniaxial constitutive model that obtained before: A
d 1 ET (7) d d e d d e 1 ET E d d
Through the preceding analysis and derivation, after hardening function A , the corresponding incremental elastoplastic stress‐strain relationship can be gotten, then the elastoplastic stiffness matrix material can be obtained. Nonlinear numerical analysis Tab.4 is the dimensions, reinforcement of the ABAQUS finite element model( as shown as Fig. 15), the concrete strenght of the frame and the rid grid is C30. TAB.4 STRENGTH PARAMETERS OF THE ECOLOGICAL BLOCKS
dimensions /mm Length, height, thickness of wall Frame Frame Rid Rid /mm beam column beam column 1400×1440×200
100
100
50
Frame reinforcement
Rib grid reinforcement
Frame beam
Frame column
Stirrups
Rid beam
Rid column
Stirrups
4ф6
4ф6
ф4＠100
4ф4
4ф4
ф2＠100
50
Based on unified strength theory, by using ABAQUS UMAT subroutine, the P ‐ Δ curve of ecological composite wall filled with different material is obtained respectively by using finite element analysis. To facilitate the comparison and analysis, the five kinds of wall panels of P ‐ Δ curve are fitted under the same coordinate system (shown as Fig.16). 200 (kN)
Gypsum block Geramic block Foam block Aerated concrete block Grass brick
150
100
50
0
0
5
10
15
20
25
30 (mm)
FIG.15 ABAQUS FINITE ELEMENT MODEL FIG.16 P‐Δ CURVE COMPARISON OF COMPOSITE WALL
10
Construction Engineering Volume 3, 2015 www.seipub.org/ce
Fig. 14 shows that: 1) The P ‐ Δ curve has no obvious turning point calculated by finite element method. It failed to simulate the decline part of the curve effectively due to the large number of cracking destruction in concrete and block in loading late. 2) The composite wall is regard as absolute rigid body in finite element model without taking damage factors in the actual situation , the flat‐fell seam between the blocks and bonding sash ‐ slip effect into consideration, therefore, calculated value tends to be greater than the relevant test value. 3) Having a moderate intensity, ceramsite block, and aerated block, foam concrete block can match the outer sash, and after the combination with outer sash the internal force, deformation development process of composite wall can be simulated truly. As the displacement increases gradually,the curve is more and more gentle, which shows that the stiffness degradation is in conformity with the previous experimental results. According to the requirements of strength, ductility and durability, the applicability of various blocks filled in ecological composite wall structure is shown in Tab. 5. TAB.5 APPLICATION SCOPE OF BLOCK
Materials
Ceramic block
Scope of application
middle‐high level
Aerated concrete block
Foam concrete block
multi‐storey
Grass brick
Gypsum block
low‐rise
—
Conclusions Based on the analytical and experimental investigations presented in this paper, the following conclusions may be made. (1) With the properties of qualitative light, moderate intensity, and matching the outer frame structure performance, ceramic block can be used for middle‐high level ecological composite wall structure; (2) The aerated block and foam concrete block can be used in the multi‐layer ecological composite wall structure based on its strength and ductility requirements; (3) The grass brick, with its strength, durability and geographical limitations, is recommended for low‐rise ecological composite wall structure in villages and towns; (4) Gypsum block is not recommended in the ecological composite wall structure, because of its poor ductility and durability. ACKNOWLEDGMENT
The authors gratefully acknowledge the financial support provided by the National Natural Science Foundation of China (51378416), National Twelfth 5‐year Scientific Support Program(2012BAJ16B02‐04)and Natural Science Foundation of Shaanxi Province of China(2013JK0986). REFERENCES
[1]
G. X. Chen: ‘Analysis on nonlinear damage of ecological composite walls filled with different materials based on the twin shear unified strength theory’, PhD thesis, Xi’an University of Architecture and Technology, Xi’an, China, 2010, 21‐44.
[2]
H. R. Meng and Q. F. Yao: ‘Study on the performance of infill blocks of multi‐ ribbed panel wall’, Concrete, 2006, 11, 77~79.
[3]
B. Baris: ‘An analytical model for stress‐strain behavior of confined concrete’, Engineering Structures, 2005, 27, 040~1051．
[4]
X. Liu and J. Yin: ‘Experimental study of stress‐strain curves of lightweight aggregate concrete’, Journal of Inner Mongolia University of Science and Technology, 2010, 3, 277~280.
[5]
Technical specification for lightweight aggregate concrete structures(JGJ12‐2006) .
[6]
X. Z. Yan and Q. F. Yao: ‘Experiment study on the mechanical property of foamed concrete’, Industrial Construction, 2007, S1, 962~964.
11
www.seipub.org/ce Construction Engineering Volume 3, 2015
[7]
Q. Q. Wang: ‘Building materials and application of Shi Gaoji’, Chemical Industry Press, 2009, 251~254.
[8]
H. Zang: ‘Analysis of bearing performance on simplified model of fiber‐reinforced plasterboard filled with concrete’, M thesis, Tianjin University, Tianjin, China, 2006, 25‐38.
[9]
Y. Xu: ‘Dynamic Test and Analysis of Seismic Response of an Experimental Building of Composite wallboard Structure’, M thesis ,Tianjin University, Tianjin, China, 2005, 22‐36.
[10] G. X. Chen and W. Huang: ‘Study on mechanical properties of cotton straw blocks’, Building science, 2012, 11, 52~54+51. [11] M. H. Yu: ‘A new system of strength theory: theory, application and development’, Xi ʹan Jiaotong University Press, 2011, 77~83. [12] M. H. Yu: ‘Advances in strength theories for materials under complex stress state in the 20th Century’, Applied Mechanics Reviews, ASME, 2002, 55, 169‐218. [13] W. Huang and C. H. Zhang: ‘Comparative analysis of simplified computation models of a multi‐ribbed slab structure’, Journal of Vibration and Shock, 2009, 07, 187~192+222. [14] G. X. Chen and W. Huang: ‘Analysis of vertical bearing capacity of multi‐ribbed composite wall based on the twin shear unified strength theory’, Industrial Construction, 2008, 01, 28~30+53. M.Zhang , born in Hebei Province on Nov. 6, 1988. She graduated from Huaqing College of Xiʹan University of Architecture and Tecnology, and get a bachelorʹs degree in civil engineering in July 2011; in June 2014, she graduated from Xiʹan University of Architecture and Tecnology, Disaster Prevention & Mitigation and Protection Engineering, received her Master degree. Now, she is Pursuing her Ph.D on Structural Engineering at Xiʹan University of Architecture and Tecnology. She’s current research is the new architecture and new materials. W. Huang , born in Shaanxi Province on Dec. 1, 1975. He graduated from Xiʹan Jiaotong University School of industrial and civil construction force a bachelorʹs degree in engineering in june 1998;In June 2004, he graduated from Xiʹan University of Architecture & Civil Engineering, Structural Engineering, received his Ph.D. Prof.Huang, vice chairman of Shaanxi Province Earthquake Engineering Society of Civil Engineering Professional Committee, had been awarded for National Science and Technology Progress award in 2009 and provincial Science and Technology Progress award in 2008 and 2009. Z.K. Yang , born in Henan Province on Jul. 24, 1983. In June 2006, she graduated from Henan University of Technology School of Civil Engineering Management, Bachelor of Engineering; in June 2009, graduated from Xiʹan University of Architecture and Civil Engineering, Civil Engineering Technology and Management, Master of Engineering; since2013 Sep, she is pursuing a Ph.D on Disaster Prevention & Mitigation and Protection Engineering in Xiʹan University of Architecture and Technology.
12