Understanding concrete in fire test results
1
Understanding concrete in fire test results student: N. Karamitsios Supervisor: Dr T.J. Stratford Moderator: Prof. A. Usmani INTRODUCTION In this project an effort was made to interpret and investigate the behavior of concrete under thermal loads focusing mainly on concrete slabs. Fire experimental tests were investigated and compared. A square reinforced concrete slab with side dimension 1.40m was simulated in the software Abaqus/CAE for further investigation. The model was subjected to various thermal analyses. The influence of various parameters on concrete response under heat flux loading was investigated, parameters such as coefficient of thermal conductivity, coefficient of thermal expansion, concrete mass density, specific heat, boundary conditions, slab thickness taking into consideration the EC2-part 2,2004 directives. There was an effort to assess and compare each parameter’s influence, trying to answer the question how the variation of these parameters affects the thermal behavior and response of concrete. CONCLUSIONS - Dominant form of slab response is thermal bowing due to restraining effect of boundary conditions to thermal expansion of bottom fibers, as a result of heat flux, as seen in fig.1. - The behavior of concrete is dictated by its constituents mainly, remark met both in literature and analyses. The most influential parameter of the investigated slab proved to be coefficient of thermal expansion both in the analyses with constant values of concrete parameters and the analyses, in which parameters of concrete have temperature dependent values. In the latter, no significant differences in the response of concrete were observed in terms of mid span deflection, except for the case of different coefficients of thermal expansion in terms of the corresponding curves for concrete with siliceous, or calcareous aggregate. (see also fig.2) - The assumption for a planar simulation of the slab was proved to be acceptably accurate , since no significant differences in terms of mid span deflections or stress contours were observed for planar model. RESEARCH OBJECTIVES - interpret and investigate the behavior of concrete under thermal loads focusing mainly on concrete slabs - Discuss and compare experimental fire tests on concrete slabs - Investigate, assess and compare the influence of various parameters, trying to answer the question how the variation of these parameters affects the thermal behavior and response of concrete METHODOLOGY The fire experimental tests were compared on the basis of slab mid span maximum deflection normalized to minimum slab longitudinal side or to the slab thickness A user interactive spreadsheet was programmed and developed, which generated data ready to input in the software Abaqus/ CAE, using Visual Basic for Applications in Microsoft Excel environment. A series of numerical analyses were conducted in software Abaqus/CAE, including thermal analyses with concrete parameters with temperature dependent or independent values and analyses with planar models or space models. The influence of each parameter was estimated on how big mid span deflections could cause for a constant heat flux heating loading, while all other involving parameters were kept constant. RESULTS Table 1. part of comparative table of fire experimental tests from literature review α th.expansion - normalised deflection 100.0000 normalised to max mid span deflection % Fig.1 the physical problem, with restrained displacements in boundaries, but free to rotate. Upper left, planar model with Abaqus QUAD elements and corresponding out of plane deflection. Upper right part, space model with HEX elements and corresponding out-of-plane deflections for 2 mesh schemes Bottom left, temperature distribution near boundaries for 2 mesh schemes. Heat flux loading on the bottom face of slab in upwards direction. λc -normalised deflection 100.0000 normalised to max mid λc - deflection Fig.2 Programmed spreadsheet file for EC2,part2 concrete parameters vs temperature α th.expansion - normalised deflection 0.0000 50.0000 100.0000 0.00000 000 0.00000 500 0.00001 000 0.00001 500 0.00002 000 0.00002 500 A th. expansion normalised to max mid span deflection % λc -normalised deflection 0.0000 50.0000 100.0000 0 0.5 1 1.5 2 2.5 coeff of thermal conductivity normalised to max mid span deflection % λc - deflection MD -normalised deflection 0.0000 50.0000 100.0000 2000 2100 2200 2300 2400 mass density kg/m^3 normalised to max mid span deflection % SH -normalised deflection 0.0000 50.0000 100.0000 0 500 1000 1500 2000 2500 specific heat (J/kgK) normalised to max mid span deflection % slab thickness -normalised deflection 0.0000 50.0000 100.0000 0 200 400 600 800 slab thickness (mm) normalised to max mid span deflection % fig.3 parametric analyses for temperature independent concrete parameters (constant values) fig.4 parametric analysis for temperature dependent concrete parameters (values as functions of rising temperature)
Transcript of Understanding concrete in fire test results
Understanding concrete in fire test results student: N. Karamitsios Supervisor: Dr T.J. Stratford Moderator: Prof. A. Usmani
INTRODUCTION In this project an effort was made to interpret and investigate the behavior of concrete under thermal loads focusing mainly on concrete slabs. Fire experimental tests were investigated and compared. A square reinforced concrete slab with side dimension 1.40m was simulated in the software Abaqus/CAE for further investigation. The model was subjected to various thermal analyses. The influence of various parameters on concrete response under heat flux loading was investigated, parameters such as coefficient of thermal conductivity, coefficient of thermal expansion, concrete mass density, specific heat, boundary conditions, slab thickness taking into consideration the EC2-part 2,2004 directives. There was an effort to assess and compare each parameter’s influence, trying to answer the question how the variation of these parameters affects the thermal behavior and response of concrete.
CONCLUSIONS - Dominant form of slab response is thermal bowing due to restraining effect of boundary conditions to thermal expansion of bottom fibers, as a result of heat flux, as seen in fig.1. - The behavior of concrete is dictated by its constituents mainly, remark met both in literature and analyses. The most influential parameter of the investigated slab proved to be coefficient of thermal expansion both in the analyses with constant values of concrete parameters and the analyses, in which parameters of concrete have temperature dependent values. In the latter, no significant differences in the response of concrete were observed in terms of mid span deflection, except for the case of different coefficients of thermal expansion in terms of the corresponding curves for concrete with siliceous, or calcareous aggregate. (see also fig.2) - The assumption for a planar simulation of the slab was proved to be acceptably accurate , since no significant differences in terms of mid span deflections or stress contours were observed for planar model.
RESEARCH OBJECTIVES - interpret and investigate the behavior of concrete under thermal loads focusing mainly on concrete slabs - Discuss and compare experimental fire tests on concrete slabs - Investigate, assess and compare the influence of various parameters, trying to answer the question how the variation of these parameters affects the thermal behavior and response of concrete METHODOLOGY The fire experimental tests were compared on the basis of slab mid span maximum deflection normalized to minimum slab longitudinal side or to the slab thickness A user interactive spreadsheet was programmed and developed, which generated data ready to input in the software Abaqus/CAE, using Visual Basic for Applications in Microsoft Excel environment. A series of numerical analyses were conducted in software Abaqus/CAE, including thermal analyses with concrete parameters with temperature dependent or independent values and analyses with planar models or space models. The influence of each parameter was estimated on how big mid span deflections could cause for a constant heat flux heating loading, while all other involving parameters were kept constant. RESULTS
Table 1. part of comparative table of fire experimental tests from literature review
α th.expansion - normalised deflection
0.0000
50.0000
100.0000
0.00000000
0.00000500
0.00001000
0.00001500
0.00002000
0.00002500
A th. expansion
norm
alis
ed to
max
mid
sp
an d
efle
ctio
n %
Fig.1 the physical problem, with restrained displacements in boundaries, but free to rotate. Upper left, planar model with Abaqus QUAD elements and corresponding out of plane deflection. Upper right part, space model with HEX elements and corresponding out-of-plane deflections for 2 mesh schemes Bottom left, temperature distribution near boundaries for 2 mesh schemes. Heat flux loading on the bottom face of slab in upwards direction.
λc -normalised deflection
0.0000
50.0000
100.0000
0 0.5 1 1.5 2 2.5
coeff of thermal conductivity
norm
alis
ed to
max
mid
sp
an d
efle
ctio
n %
λc - deflection
Fig.2 Programmed spreadsheet file for EC2,part2 concrete parameters vs temperature α th.expansion - normalised deflection
0.0000
50.0000
100.0000
0.00000000
0.00000500
0.00001000
0.00001500
0.00002000
0.00002500
A th. expansion
norm
alis
ed to
max
mid
sp
an d
efle
ctio
n %
λc -normalised deflection
0.0000
50.0000
100.0000
0 0.5 1 1.5 2 2.5
coeff of thermal conductivity
norm
alis
ed to
max
mid
sp
an d
efle
ctio
n %
λc - deflection
MD -normalised deflection
0.0000
50.0000
100.0000
2000 2100 2200 2300 2400
mass density kg/m^3
norm
alis
ed to
max
mid
sp
an d
efle
ctio
n %
SH -normalised deflection
0.0000
50.0000
100.0000
0 500 1000 1500 2000 2500
specific heat (J/kgK)
norm
alis
ed to
max
mid
sp
an d
efle
ctio
n %
slab thickness -normalised deflection
0.0000
50.0000
100.0000
0 200 400 600 800
slab thickness (mm)
norm
alis
ed to
max
mid
sp
an d
efle
ctio
n %
fig.3 parametric analyses for temperature independent concrete parameters (constant values)
fig.4 parametric analysis for temperature dependent concrete parameters (values as functions of rising temperature)
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