Bamboo as a substitute for steel in reinforced concrete wall panels

The paper presents a review of the works done by various researchers on different types of reinforced concrete wall panels. Full scale bamboo reinforced concrete wall panels of three different aspect ratios of 1, 1.204 and 1.515 subjected to one way in-plane loading are considered in this study. Also an attempt is made to compare the ultimate loads estimated using the available equations with the experimental values of bamboo reinforced concrete wall panels. The investigation indicates that steel reinforcement could be replaced by bamboo in concrete wall panels.


Introduction
The increasing demand for high speed, superior quality and cost effective construction led to the development of precast concrete structural elements. Of all the precast concrete structural elements, wall panels are the one that gained more importance in the field of construction to satisfy the housing needs of the ever increasing population.
Wall panels are structural elements subjected to in-plane action having negligible thickness compared to their length and breadth. In order to have sufficient strength to take in-plane loads, they may be reinforced with mild steel, steel fibers or steel fabric mesh. They are economical, not only from the structural design point, but also from the view point of overall construction.
The study presents the review of the works done by researchers on wall panels to determine the effect of various parameters like type and grade of concrete, reinforcing materials and its percentages, slenderness ratio (SR) and aspect ratio (AR). It also includes the comparison of the experimental ultimate loads with that of the loads computed by using the equations proposed by various researchers. It may be noted that the use of bamboo, an environmentally sustainable natural material that could replace the highly energy intensive material like steel in the construction of wall panels.

Experimental Programme
The experimental programme involved the casting and testing of three full scale Bamboo Reinforced Concrete Wall Panels (BRCWP) under one way in-plane loading. Details of the specimens are given in the

Reinforcement
Varnished and sand blasted splints of BambusaBambos of 20mm width were used as wall panels. The properties of bamboo splints used as reinforcement in this study include an average ultimate tensile strength of 120MPa, modulus of elasticity of 6.73x10 compressive strength of culm of 40MPa. Spacing of Code of India-Part 6. Splints were kept at equal spacing in both the horizontal and vertical directions. Figure 1 shows the arrangement of bamboo splints used as reinforcement in concrete wall panels.

Casting of Specimens
The machine mixed concrete was used for the casting of wall panels and the bamboo reinforcement cage was kept at the mid thickness of the mould. Concrete was compacted using needle vi after 24 hours of casting, the panels were cured by covering it with wet gunny bags for 28 days.

Test Set Up for the Testing of Wall Panels
The panels were tested under pinned end conditions at both ends with uniformly distributed load applied at an eccentricity of t/6 to reflect the possible eccentric load in practice. All specimens were tested in the vertical position in a loading frame of 100 tons capacity installed in the Structural Engineering Lab. The wall panels were lifted using the 10 tons capacity. Figure 2 shows the schematic diagram of the test set up. The top and bottom hinged support conditions were simulated by placing a 16mm diameter polished rod in between four 6mm diameter rollers welded to the bearing plates. A stiffened I and another stiffened I-beam was used below the bearing plates to act as support. Figure 3 shows the details of top hinged edge. A plumb bob was used to ensure the ve was done gradually in stages up to failure and the experimental ultimate loads were recorded. Figure 4 shows the experimental test setup. Varnished and sand blasted splints of BambusaBambos of 20mm width were used as reinforcement in wall panels. The properties of bamboo splints used as reinforcement in this study include an average ultimate tensile strength of 120MPa, modulus of elasticity of 6.73x10 4 MPa and an average compressive strength of culm of 40MPa. Spacing of splints was provided as per the National Building Part 6. Splints were kept at equal spacing in both the horizontal and vertical directions. Figure 1 shows the arrangement of bamboo splints used as reinforcement in concrete wall panels. The machine mixed concrete was used for the casting of wall panels and the bamboo reinforcement cage was kept at the mid thickness of the mould. Concrete was compacted using needle vi after 24 hours of casting, the panels were cured by covering it with wet gunny bags for 28 days.

Test Set Up for the Testing of Wall Panels
The panels were tested under pinned end conditions at both ends with uniformly distributed load ied at an eccentricity of t/6 to reflect the possible eccentric load in practice. All specimens were tested in the vertical position in a loading frame of 100 tons capacity installed in the Structural Engineering Lab. The wall panels were lifted using the Electric Overhead Travelling (E.O.T.) crane of 10 tons capacity. Figure 2 shows the schematic diagram of the test set up. The top and bottom hinged support conditions were simulated by placing a 16mm diameter polished rod in between four 6mm rs welded to the bearing plates. A stiffened I-beam was used to apply the load at the top beam was used below the bearing plates to act as support. Figure 3 shows the details of top hinged edge. A plumb bob was used to ensure the verticality of the wall panels. Loading was done gradually in stages up to failure and the experimental ultimate loads were recorded. Figure 4 Sand conforming to 1970 (Reaffirmed 2002) and 12mm coarse aggregate conforming to Table 2 1970 (Reaffirmed 2002) and portable water were used to obtain concrete of M20 grade. M20 mix was designed as per Indian Standard Concrete Mix Proportion Guidelines of IS: 10262-2009. Ratio, reinforcement in wall panels. The properties of bamboo splints used as reinforcement in this study include an average MPa and an average splints was provided as per the National Building Part 6. Splints were kept at equal spacing in both the horizontal and vertical directions. Figure 1 shows the arrangement of bamboo splints used as reinforcement in concrete wall panels.
The machine mixed concrete was used for the casting of wall panels and the bamboo reinforcement cage was kept at the mid thickness of the mould. Concrete was compacted using needle vibrator and after 24 hours of casting, the panels were cured by covering it with wet gunny bags for 28 days.
The panels were tested under pinned end conditions at both ends with uniformly distributed load ied at an eccentricity of t/6 to reflect the possible eccentric load in practice. All specimens were tested in the vertical position in a loading frame of 100 tons capacity installed in the Structural Electric Overhead Travelling (E.O.T.) crane of 10 tons capacity. Figure 2 shows the schematic diagram of the test set up. The top and bottom hinged support conditions were simulated by placing a 16mm diameter polished rod in between four 6mm beam was used to apply the load at the top beam was used below the bearing plates to act as support. Figure 3 shows the rticality of the wall panels. Loading was done gradually in stages up to failure and the experimental ultimate loads were recorded.

Comparison of Earlier Studies
The studies conducted by various researchers on wall panels are summerised in the form of tables. The experimental study on bamboo reinfor various researchers on Reinforced Concrete (RC)wall panels.   Details of SR and AR considered in the study of wall panels by various researchers are presented in Table 3. The studies indicate that panels with two-way in plane action are more rigid and strong than the wall panels supported at the top and bottom edges alone, since their four edges are being supported.

Earlier studies
The review of various investigations concluded that as SR increases, strength of wall panels under one way in-plane loading decreases whereas it increases for wall panels under two way in-plane loading. Limited studies are reported on the effect of AR on the strength of wall panels. It was found that as AR increases, strength of wall panels under one way in-plane loading decreases whereas it increases for the wall panels tested under two way in-plane action. Also it was noticed that the studies on wall panels done by researchers other than Zielinski et al. used scaled down model of wall panels.
Many investigators have proposed formulae to predict the ultimate load (Pu) of wall panels either by modifying the existing wall design formulae or by developing a new formula based on certain assumptions in their study. The formula proposed by various authors is listed in Table 4. Formulae developed by Oberlender and Everard (1977), Pillai and Parthasarathy (1977) and Kripanarayanan (1977), Saheb andDesayi (1989, 1990), IS 456 (2000) and ACI 318 (2008) was limited to NSC where as Saheb and Desayi (1990) had developed separate formula for NSC and HSC wall panels. Ganesan et a0l. (2010Ganesan et a0l. ( , 2012Ganesan et a0l. ( and 2013 proposed formulae to predict the strength of SCC, SFRSCC and GPC wall panels. All these studies have used steel as reinforcement in concrete matrices.
Formulae predicted by Oberlender and Everard (1977), Pillai and Parthasarathy (1977) and Kripanarayanan (1977) to determine the strength of wall panels considered the effect of SR on the strength of wall panels but the contribution of reinforcement was not considered in the study. Even though formulae predicted by Zielinski et al. (1982) and Saheb and Desayi (1989) included the contribution of SR and reinforcement, the contribution of AR was not considered. Saheb and Desayi (1990) predicted a formula considering the contribution of SR, AR and reinforcement on the strength of wall panels but that formula was applicable only for the wall panels with aspect ratio less than 2.  Fragomeni et al. (1994) proposed formulae for determining the strength of NSC and HSC wall panels but it didn't consider the effect of SR, AR and reinforcement. BS8110 (1997), Doh and Fragomeni (2004) and IS 456 (2000) developed formulas to predict the strength of wall panels considering the effect of the effect of SR, and the eccentricity at which load is applied to the wall panels, but the formulae didn't consider the contribution of AR and reinforcement on its strength. Formula suggested for predicting the ultimate strength of wall panels by ACI 318 (2008) included the strength reduction factor (Ф) and effective length factor (k) along with the term h/t for considering the effect of SR, but the formula doesn't consider the effect of AR and the contribution of reinforcement. Formula proposed by Mac Gregor and Wight (2009) does not consider the effect of AR, SR, strength reduction factor (Ф) and percentage of reinforcement hence it may overestimate the strength of wall panels. Ganesan et al. ( , 2012 proposed formulae to predict the strength of SCC, SFRSCC and GPC wall panels considering the contribution of SR, AR and reinforcement.

Test Results
The experimental values obtained for Bamboo Reinforced Concrete Wall Panel and the ultimate loads obtained by using the equations proposed by various researchers for Reinforced Concrete wall panels are given in Table 5.