Response Of Reinforced SIFCON-slabs UnderBlast-loading

Abstract

The response of ,,reinforced SIFCON-slabs under static and dynamic loading conditions was experimentally investigated. The bending capacity was determined and iso-damage curves in p-J-diagrams were calculated. The bending capacity as well as the energy absorption capacity proved to be much higher compared to normally reinforced concrete. The increasing brittle behaviour of reinforced concrete slabs with increasing reinforcement was not observed with reinforced SIFCON. As a result reinforced can be used favorably to design highly dynamically loaded structures. INTRODUCTION To improve the response of structures to highly dynamic loading it is important to use a material with large working capacity. (Slurry Infiltrated Fibre Concrete) has high toughness and ductility. In connection with reinforcing steel bars, the so called ,,reinforced SIFCON additionally has strong bending capacity. Reinforced slabs (2,0-0,6-0,1 nf) were subjected to static load and dynamic load in a shock tube. The behaviour of the reinforced was judged in comparison to normally reinforced concrete by its bending capacity under flexural stress. More detailed results are given in the references [1], [2] and [3]. EXPERIMENTAL SET-UP The tests under high dynamic loading conditions were done in a shock tube (Fig. 1) in the reflected mode. A typical load function is shown in Fig. 2. The shock-tube arrangement is about 50 m long, the diameter of the test section is 2,4 m. The tube is air-driven. Blast waves with peak reflected over-pressure Transactions on the Built Environment vol 8, © 1994 WIT Press, www.witpress.com, ISSN 1743-3509 140 Structures under Shock and Impact from 10 kN/nf to 300 kN/nf and positive duration from 10 ms to seconds are possible. RESULTS Material Strength of SIFCQN The material behaviour of is influenced by the fibre volume (Vf), the ratio of the fibre length to the fibre diameter (lf/df) and the fibre shape (OL, M, ZL). The relative effect of the fibre volume is reduced for SIFCON, the fibre shape and the relationship of the fibre length to the diameter dominate [1]. The material strength under bending conditions and compression is displayed in Fig. 3. A typical stress-strain relation between and plain concrete is demonstrated in Fig. 4. In Fig. 5 is the energy absorption of in comparison to fibre concrete, plain concrete and plain cement represented. For the investigated fibre types (OL, M, ZL) and certain slurry mixes, described in [1], the compressive stress (3s of is about four times of the bending tensil stress (4z (Fig. 6). Static behaviour of reinforced The experiment clearly point out the enhancement of the bending capacity of reinforced compared to conventional reinforced concrete (Fig. 7). The enhancement depends on the amount of reinforcing steel bars (p) and the material strength (a,, p,, py, â ). Of interest is that independent of u, with reinforced the ductility was not changed. For low and high reinforcement (u = 0,6 %, u = 2,0 %) the same ductility was achieved (x - = 2,5 • x .J. This is not the case with reinforced concrete (high u, low ductility). For the calculation of the static response the conditions shown in Fig. 8 were used. This means the tensil strength of (o ) is considered (case a) or neglected (case b). As Fig. 9 shows an agreement is reached with o^ = 0,4 • 0^2 . The value o^ ~ 0,4 • cr^ is based on the post cracking strength of (see [4]). In this case the calculated response is lower than the experimental result. On this basic the bending moment of reinforced was determined by the formula with a' = cr /Ps, b = width and h = effective depth. Because P^ = 4 -o^ (Fig. 6), a' becomes a constant value of a' = 0,1. In Fig. 10 the enhancement of the bending moment of reinforced M* to reinforced concrete M*> vs. a normalized reinforcement // dynamic loading, to suppress scabbing effects and to design plastic hinghes. REFERENCES 1. Mayrhofer, Chr.: und spezielle Faserbetone fur extreme dynami- sche Beanspruchungen, E 17/90, Ernst-Mach-Institut, Freiburg i. Br., Dez. 1990 2. Mayrhofer, Chr.: Tragverhalten von SIFCON-Platten bei Druckstofibela- stung, E 12/92, Ernst-Mach-Institut, Freiburg i. Br., Nov. 1992 3. Mayrhofer, Chr.: Tragverhalten druckstofibeanspruchter SIFCON-Platten mit zusdtzlicher Baustahlbewehrung, E 7/93, Ernst-Mach-Institut, Frei- burg i. Br., Aug. 1993 4. Hannant, D.J.: Fibre Cements and Fibre Concretes, Department of Civil Engineering, Univ. of Surrey, John Wiley & Sons, Chichester-New York- Brisbane-Toronto Figure 1: Shock tube Transactions on the Built Environment vol 8, © 1994 WIT Press, www.witpress.com, ISSN 1743-3509 Structures under Shock and Impact 143