[ Building & Construction ]
[ Building & Construction ]
20
20 ° C
200 ° C 400 ° C 600 ° C 20 ° C 200 ° C 400 ° C 600 ° C 20 τ b ( MPa )
15 10 5
B500S
15 10 5
ACX915
0
0
0 1 2 3 4 5 0 1 2 3 4 5 Slip ( mm ) Slip ( mm )
Figure 5 . Adhesion stress-slip curves . τ b ( MPa ) following a fire incident in reinforced concrete structures with stainless steel reinforcements . The experimental campaign entailed executing pullout tests following the requirements outlined in standard EN 10080 Annex D , using unprotected B500S carbon steel bars as a reference and duplex stainless steel bars ACX915 ( EN 1.4362 ). Evaluations were conducted for both 12 mm and 16 mm diameters in both cases . The repeatability achieved in the tests was 2 specimens per temperature and diameter , resulting in the creation of 16 specimens for B500S steel and an additional 16 for ACX915 stainless steel . The concrete mixes were designed with a water-to-cement ratio of 0.44 and targeted a strength of C25 / 30 . This quality was assessed for each test and sample , yielding an average compressive strength value of 35.4 MPa for specimens with B500S steel reinforcement and 35.6 MPa for ACX915 stainless steel specimens .
τ b / f c
0,7
0,6
0,5
0,4
0,3
0,2
0,1
0,0 20 ° C
Figure 6 . Maximum adhesion stress .
Adhering to the specifications of standard EN 10080 Annex D , all fabricated specimens are of cubic form , measuring 200 mm on each side . In this configuration , a 600 mm steel bar is inserted and securely bonded to the concrete at a distance of 5d ( 60 mm for 12 mm diameter bars and 80 mm for 16 mm diameter bars ). A metallic separation sleeve was incorporated to prevent adhesion in the remaining contact zone . After 28 days of concrete curing , the specimens underwent heating in an oven at a rate of 100 ° C / min to the designated temperature ( 200 ° C , 400 ° C , 600 ° C ), and maintained for 3 hours . Subsequently , natural air cooling was initiated until ambient temperature was reached . Several days post-cooling , the specimens were subjected to pull-out testing , employing a controlled force increase of 80 N / s for 12 mm diameter reinforcements and 143 N / s for 16 mm diameter ones . Throughout the test ,
B500S ACX915
200 ° C 400 ° C 600 ° C both the applied load and the penetration of the bar at its free end or slippage were meticulously recorded ( slip = ∆0 – ∆1 ). Examining the tensionslip curves recorded for various test series ( Figure 5 ) shows a clear decrease in the maximum adhesion stress can be identified with the increase in the exposure temperature . This decrease is more pronounced from 400 ° C onwards . It should be noted that the maximum adhesion stress values are closely aligned with the models stipulated in Model Code 2010 and EN 1992 , which estimate this maximum stress according to the following equation : τb , max = 2,5 f cm For an average compressive strength of concrete ( fcm ) of 35.5 MPa , this maximum adhesion stress would result in 14.9 MPa , which , as can be observed , aligns conservatively with the values obtained for 20 ° C and 200 ° C . Figure 6 displays the average values for all tested series , presenting maximum adhesion stress values relative to the compressive strength of concrete ( τb / fc ). Error bars denote the standard deviation across the obtained results . Notably , at room temperature ( 20 ° C ) for ACX915 stainless steel reinforcements , slightly lower average values of maximum adhesion stress are evident compared to those for B500S carbon steel reinforcement . This discrepancy is likely attributed to the distinct corrugation configuration of ACX915 steel . However , following exposure to elevated temperatures , ACX915 reinforcements consistently demonstrate superior adhesive behaviour compared to B500S carbon steel reinforcements .
Conclusions To date , there is no known study on the adhesion of stainless steel reinforcements affected by high temperatures . These temperatures
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