DTI: Partners in Innovation Contract: CI 39/3/684, cc2227SEMINAR 26 February 2003
Design Guidelines – Kyriacos Neocleous
Introduction
Research Aims
Simplified Design Method
Stress-Strain Design Approach
Stress-Crack Design Approach
Discussion & Conclusions
OUTLINE
DTI: Partners in Innovation Contract: CI 39/3/684, cc2227SEMINAR 26 February 2003
Design Guidelines – Kyriacos Neocleous
• Lack of general design framework and simple design guidelines perceived as one of the main barriers for the use of waste fibres in concrete construction
• Can existing SFRC design guidelines be adopted for the design of concrete reinforced with waste-tyre steel fibres (SFTRC)?
Introduction
DTI: Partners in Innovation Contract: CI 39/3/684, cc2227SEMINAR 26 February 2003
Design Guidelines – Kyriacos Neocleous
• Develop general design framework for SFTRC
• Design the demonstration slabs
Line-supported drainage slabs
Research Aims
DTI: Partners in Innovation Contract: CI 39/3/684, cc2227SEMINAR 26 February 2003
Design Guidelines – Kyriacos Neocleous
Simplified Design Method
• Based on Hillerborg Strip approach• Each slab consists of a number of strips,
(10 strips, 80mm wide)
• Strip depth same as for prisms• Bending resistance of strips is calculated
using the prism resistance
DTI: Partners in Innovation Contract: CI 39/3/684, cc2227SEMINAR 26 February 2003
Design Guidelines – Kyriacos Neocleous
*Predicted value
Simplified Design Method
Experimental Load (kN) Predicted Load (kN) Slab type Prism Slab Slab
AMATcon (6%) 32 170 256
Scon (2%) 18 141 144
SIScon (17.5%) 37* 297.8 -
DTI: Partners in Innovation Contract: CI 39/3/684, cc2227SEMINAR 26 February 2003
Design Guidelines – Kyriacos Neocleous
• Utilises Eurocode 2 design framework
• Initially developed for Dramix® steel fibres
• Further developed by RILEM TC 162-TDF
• Ultimate limit states for bending and shear
• Serviceability limit state for cracking
Stress-Strain Design Approach
DTI: Partners in Innovation Contract: CI 39/3/684, cc2227SEMINAR 26 February 2003
Design Guidelines – Kyriacos Neocleous
• Standard tests (concrete-cylinder) and deformation-controlled bending tests required for the evaluation of the material properties
• Material Properties for pre-cracking and post-cracking behaviour required for calculations:
Compressive strength, axial tensile strength, flexural strength and equivalent flexural strength
Stress-Strain Design ApproachMaterial Properties
DTI: Partners in Innovation Contract: CI 39/3/684, cc2227SEMINAR 26 February 2003
Design Guidelines – Kyriacos Neocleous
• Rilem adopts a 3-point loading arrangement to evaluate equivalent flexural strength
Stress-Strain Design ApproachMaterial Properties
0.5P 0.5P
P
BMD BMDBMD
Theoretical 3-point Actual (loading spreading) Theoretical 4-point
DTI: Partners in Innovation Contract: CI 39/3/684, cc2227SEMINAR 26 February 2003
Design Guidelines – Kyriacos Neocleous
• Evaluation of equivalent flexural strength
deflection δ (mm) δL
FL area DBZ,2 f F (kN)
0.3 0.35 deflection δ (mm) δL 0.3 2.35
FL area DBZ,3 f
F (kN)
bh
L0.50D
23f 2
sp
fBZ,2
eq,2
= 2sp
fBZ,3
eq,3 bhL
2.50D
23f
=
Stress-Strain Design ApproachMaterial Properties
DTI: Partners in Innovation Contract: CI 39/3/684, cc2227SEMINAR 26 February 2003
Design Guidelines – Kyriacos Neocleous
Stresses in SFRC derived from idealised stress-strain diagram
Stress-Strain Design ApproachDesign Assumptions
σfc,t
0.37 feq,3/γct 0.45 feq,2/γct
0.85 ffcd = 0.85 fck/ γc
σfc (N/mm2)
σfc,t (N/mm2)
εfc (‰)
10 -2 -3.5
γc: partial safety factor for SFRC in compression γct: partial safety factor for SFRC in tension
0.1‰
fctk,ax/γct (axial force) fctk,ax (1600 - d)/1000 γct (axial force & bending) (d in mm) 1600 – d/ 1000 ≥ 1
DTI: Partners in Innovation Contract: CI 39/3/684, cc2227SEMINAR 26 February 2003
Design Guidelines – Kyriacos Neocleous
• Rilem Stress Block
• Simplified block for tensile concrete stress
FS
γ x αfcmax
FC
FC,T zC,T
zS d
x N.A.
εc, t
εc
Strain Diagram
Cross-section
Stress Block
Equivalent Stress Block
b
0.37 feq,3
feq
0.45 feq,2
0.01 εc,t
Stress-Strain Design ApproachDesign for Bending
DTI: Partners in Innovation Contract: CI 39/3/684, cc2227SEMINAR 26 February 2003
Design Guidelines – Kyriacos Neocleous
Stress-Crack Design Approach• Fracture mechanics design approach
Tension softening behaviour
• Draft recommendation for SFRC by RILEM TC 162-TDF
• Ultimate limit states for bending and shear
• Serviceability limit state for cracking
• Approach still under development
P P
P
δ
DTI: Partners in Innovation Contract: CI 39/3/684, cc2227SEMINAR 26 February 2003
Design Guidelines – Kyriacos Neocleous
Stress-Crack Design Approach• Fictitious crack model: propagation of cracks in SFRC
• Stress-crack opening relationship σw(w):
Stresses (carried by the fibres across a tensile crack) described as a function of the crack opening
Fibre bridging σw(w)
process zone
aggregate interlock
fictitious crack
ft w
DTI: Partners in Innovation Contract: CI 39/3/684, cc2227SEMINAR 26 February 2003
Design Guidelines – Kyriacos Neocleous
Discussion
• Existing design approaches generic and rely on simple tests for material characterisation
• Material characteristics of SFTRC similar to SFRC
• Current design framework OK for SFTRC
• 4-point testing is more realistic to evaluate the equivalent flexural strength. However, new deformation limits need to be established based on serviceability requirements
DTI: Partners in Innovation Contract: CI 39/3/684, cc2227SEMINAR 26 February 2003
Design Guidelines – Kyriacos Neocleous
• Hillerborg strip approach can be used for the design of SFRC plate elements, by using the moment characteristics from flexural tests
• Current design guidelines can be used for SFTRC
• It is proposed to use the 4-point bending test for material characterisation
Conclusions
