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

Structural elements should provide sufficient rigidity to limit deflections that reduce the serviceability of the structure. When loading takes place, buildings with low stiffness will displace elastically because of their flexibility, causing the occupants to feel uncomfortable. The importance of stiffness of a structural element makes researchers further investigate the mechanical characteristic of graded concrete (GC) beams. Investigations are conducted to determine the effect of the ratio of cross-sectional dimensions and the ratio of reinforcement to stiffness produced by GC beams. There were eight specimens used in this experimental study. The GC beams were designed using a combination of two concrete mixes, namely 20 MPa and 40 MPa. The cross-sectional dimension ratio used is 0.5 and 0.67 and a shear span ratio of 2.5. The reinforcement ratio used is 1.59% and 4.78% for the maximum reinforcement ratio and 0.35% and 0.49% for the minimum reinforcement ratio. The specimens were tested in flexure at the age of 28 days. The results showed: 1) The use of a deeper dimension ratio can increase the initial stiffness of GC beams by up to 20%; 2) The use of the maximum reinforcement ratio in GC beams can increase the stiffness by more than 150% at the dimension ratio of ½ and increase the stiffness up to 30% at the dimension ratio of 2/3; 3) The design of the GC beam to the minimum steel ratio is recommended to create elements behaviour remain in a ductile condition