Graded concrete technology could be the best solution to promote the green building concept in the construction industry. The failure behaviour and flexural strength of a RC beam are influenced by various factors, including beam dimension, number and arrangement of reinforcement bars, the shape of the beam cross-section, properties of steel and concrete, and beam span ratio. In this research, the researchers intend to conduct further studies related to the behaviour of graded concrete (GC) beam using various cross-sectional dimension ratios and rebar ratios. This study used 8 (eight) GC beam specimens which mainly made of two concrete mixes, namely the concrete strength of 40 MPa and 20 MPa. The cross-sectional dimension ratio used is 2/3 and 1/2. Two types of rebar ratios were examined which are minimum rebar ratio (0.35% and 0.45%) and maximum rebar ratio (1.59% and 4.78%). The flexural test was carried out by the four-point bending method. The results show that the change in cross-sectional dimensions from 2/3 to 1/2 increases the ultimate load capacity to 62.47% and the deflection decreases to 48.72%. Furthermore, the change of rebar ratio increases load-carrying capacity up to 118.59% and decreases the deflection up to 52.40% along with the increase in the rebar ratio. In the future, it is recommended to design a GC beam using a ratio of 1/2 in cross-sectional dimensions and using a minimum rebar ratio with the respect to the higher concrete strength as the reference.

Load – Deflection relationship of graded concrete beam on different cross-sectional dimension ratio and reinforcement ratio

Innovation in construction materials continues to grow from year to year. Graded concrete (GC) is a novelty in construction materials designed by combining two different concrete strength in one element. The potential use of GC applied as construction materials in the future makes the researcher intend to review the ductility on various cross-sectional dimension ratios and reinforcement ratios. Ductility is one of the essential characteristics in designing modern structures because it prevents brittle failure due to loading. Furthermore, it ensures the safety of the structural system due to dynamic loads caused by the earthquake. The importance of ductility in a structural system makes it necessary to conduct further investigations on GC beams. The GC beam is composed of two concrete mixes with different strength, namely 40 MPa in compression fibre and 20 MPa in tensile fibre. The beam specimen uses a cross-sectional dimension ratio of 2/3 and 1/2 with a minimum and maximum reinforcement ratio. The GC beam specimen is designed with a shear span of 2.5 and the transversal reinforcement is only installed in the support area. The beam specimens were tested at the age of 28 days with a four-point bending setup. The results demonstrated that the change in the ratio of the cross-sectional dimensions from 2/3 to 1/2 can increase the ductility of the GC beam by more than 200%. The use of a larger reinforcement ratio increases the ductility of the GC beam exceeds 100%. The increase in the ductility of the GC beam provides more resistance to the building during an earthquake. Ductility will make a structure able to maintain its strength and stiffness so that it will not collapse even though it has exceeded the designed safety limit.

Ductility of graded concrete beams on different cross-sectional dimension ratio and steel reinforcement ratio

Reinforced concrete (RC) beams are generally designed with different percentages of flexural tension reinforcement depending on the capacity requirements. The amount of reinforcement provided affects the crack propagation and failure mechanism in RC beams. This paper presents discussion on the minimum tension reinforcement requirement in code provisions for RC beams. Models based on fracture mechanics to evaluate minimum flexural reinforcement are also reviewed. Experimental study has been undertaken to understand the effect of size on the behaviour of lightly RC beams. This paper outlines how the present code provisions can be improved by applying fracture mechanics principles for the design of RC beams. Fracture mechanics approach for design of RC structures considers the energy requirements for crack growth and size effect. It also enables rational procedure to evaluate the optimum amount of steel reinforcement, which ensures safe designs by taking the effect of size and other influencing parameters.

G. Appa Rao

Papers

Evaluation of Minimum Flexural Reinforcement in Design of Reinforced Concrete Beams