Improving fire resistance of existing concrete slabs by concrete topping

Size: px

Start display at page:

Download "Improving fire resistance of existing concrete slabs by concrete topping"

Laura Cook
5 years ago
Views:

Improving fire resistance of existing concrete slabs by concrete topping Is EN 1992-1-2 annex E telling the truth, and

1 Improving fire resistance of existing concrete slabs by concrete topping Is EN annex E telling the truth, and can it be used? Tom Molkens StuBeCo bvba, Overpelt - Belgium Structures in Fire Forum 12 th April 2016 IStructE HQ London

2 Content What s up? Introduction; building and problem setting Bearing and failure mechanism; some reflections Annex E of Eurocode EN ; briefly for continuous slabs Case study for the Linné-Plantes building Interface between topping and existing slab Numerical approach by SAFIR Conclusions; answers and an open question

3 What s up Main purpose of existing codes = design of new buildings What with existing buildings and in particular their shortcomings? Do we need to think on another way or can we just apply the codes? The most easy way to fix problems in an existing building can be reversed to the solution that we would apply in a new building. In this case study; a leak of concrete cover on the bottom can be solved by an extra in situ reinforced topping

4 Introduction Some images (before the bombs)

5 Lever arm wind load About 40 m = levels Introduction Typical floor layout & section

6 Introduction Preliminary data Level Location h s h 1 Principal reinforcement Transverse reinforcement bar distance cover Rein. R bar distance cover Rein. R mm mm mm mm mm mm²/m mm mm mm mm²/m 1? L2-L L2-L mean L5-L6 194, L5-L L5-L L5-L mean L6-L L6-L L6-L L6-L7 7, mean mean over all

Hidden beam 10/45 Hidden beam 9/35 Principal beam

7 Introduction Discoveries during demolishing works Hidden beam 18/45 Hidden beams 9/35 Hidden beam 9/35 Hidden beam 10/45 Hidden beam 9/35 Principal beam 25/50 + column Principal beam 25/50 + column Hidden beam 10/45

8 Failure mechanisms; some reflections Bending for a continuous slab, deformation < h/2 till max h Rotational spring or hinge Compressive membrane action; compression arch Compressive arch No need for reinforcement at the bottom

Failure mechanisms; some reflections Tensile membrane action, catenary action Cable line Tensile membrane action with compressive ring Same issues as for

9 Failure mechanisms; some reflections Tensile membrane action, catenary action Cable line Tensile membrane action with compressive ring Same issues as for tensile membrane action Need for reinforcement at the bottom + large deflections => Some complexities with position reinforcement, analytical design rules,

10 Annex E of Eurocode EN Shifting the moment line for continuous slabs M Ed,fi = w 2 Ed,fil eff 8 = w Ed,fi( l eff 2 )² 2 M Rd,fi = A s bf y,θ (h 1 c Ø 2 A sbf y,θ 2bf ck i θ Issue of interface not covered

11 Case study for the Linné-Plantes building Slab; M Ed,fi = (2,5+1,5+1, ) 4.7²/8 = knm M Rd,fi,span = 0.87 knm with k s (θ) = 0.07, x = 2+8/2 = 6 mm => 900 C M Rd1,fi = M Rd2,fi = > knm with #150/6+Ø10/150mm? EN graphs: => Equilibrium guaranteed M Rd1,fi = M Rd2,fi = = knm

12 Case study for the Linné-Plantes building Beam of TT-frame; M Ed,fi = ( ) 6.75²/8 = 153 knm With ( )/2 ( ) = kn/m New façade + inner wall + beam = ( )/2 [3.93+( ) 25] = m Principal beam = = 3.13 m M Rd1,fi,max = M Rd2,fi,max = ²/2 = 47 knm M Rd,fi,span > M Ed,fi - M Rd1,fi,max = = 106 knm? => Equilibrium not guaranteed with one level; need for push down M Rd,fi,span = = 74 knm

13 Interface between topping and existing slab Some engineering judgement based on a combination of EN paragraph and EN Reciprocal theorem of shear stresses; we consider that the shear stress perpendicular to the surface is equal to the tensile stress So the reduction of the shear stress at this interface has the same behavior as the reduction of the tensile stress. V Edi,fi = = kn 2 m V Rdi,fi = k ct θ c f ctk,0.05 z b γ i c = ( ) 1000 = 35.96k N m

What happens in a real fire (with gas peak temperature @ 60 min.)?

14 Temperature ( C) Interface between topping and existing slab Is an ISO fire representative enough to deal with this problem? What happens in a real fire (with gas peak 60 min.)? 1200 Temperature-time relation ISO834 Natural fire Surface Reinforcement Interface Time (s)

15 Numerical approach by SAFIR Model = half part X Y Z Diamond 2012.a.0 for SAFIR FILE: Linn1_st NODES: 733 BEAMS: 0 TRUSSES: 0 SHELLS: 224 SOILS: 0 SOLIDS: 0 IMPOSED DOF PLOT DISTRIBUTED LOADS PLOT

16 Numerical approach by SAFIR Cantilever reinforcement: s Diamond 2012.a.0 for SAFIR FILE: Linn1_st NODES: 733 BEAMS: 0 TRUSSES: 0 SHELLS: 224 SOILS: 0 SOLIDS: 0 NODES PLOT SHELLS PLOT IMPOSED DOF PLOT DISPLACEMENT PLOT ( x 10) Component: Combination Structure Not Displaced selected TIME: 7200 sec 0, , , , , , , , ,00000 Z X Y

17 Numerical approach by SAFIR Compressive membrane action reinforcement: s Diamond 2012.a.0 for SAFIR FILE: Linn2_st NODES: 733 BEAMS: 0 TRUSSES: 0 SHELLS: 224 SOILS: 0 SOLIDS: 0 SHELLS PLOT DISPLACEMENT PLOT ( x 10) Component: Combination Structure Not Displaced selected TIME: 7200 sec 0, , , , , , , , ,00000 Z X Y

18 Numerical approach by SAFIR Full option, shutting with a gun is not even better: s Diamond 2012.a.0 for SAFIR FILE: Linn3_st NODES: 733 BEAMS: 0 TRUSSES: 0 SHELLS: 224 SOILS: 0 SOLIDS: 0 SHELLS PLOT DISPLACEMENT PLOT ( x 10) Component: Combination Structure Not Displaced selected TIME: 7200 sec 0, , , , , , , , ,00000 Z X Y

19 Conclusions Missing bearing capacity in case of fire can be solved by adding an extra upper reinforcement in a new in situ concrete topping. The question that an ISO fire would be representative enough to judge the bearing capacity of the interface, couldn t be answered. Location or concentration of the extra upper reinforcement seems to be of lesser importance. Due to the still limited deformations handling as a cantilever moments seems to be the best fit. But also other distributions react well. Model uncertainties still to investigate => without vertical support,

20 Questions, answers, suggestions? Anyway thanks for the opportunity to deal this information. Just for information; StuBeCo operations will be very soon integrated in Sweco Belgium

Design of AAC wall panel according to EN 12602

Design of AAC wall panel according to EN 12602 Design of wall panel according to EN 160 Example 3: Wall panel with wind load 1.1 Issue Design of a wall panel at an industrial building Materials with a compressive strength 3,5, density class 500, welded