Experimental Study On The Shear Behavior Of Lightweight Aggregate Concrete Beams Without Shear Reinforcement

The shear mechanism of reinforced concrete beams is so complicated that there ’s no generally accepted unified theory nor design method until now, although its theoretical analysis and tests study started in the early 1900 s. The tests regression based semi-empirical equations, which main parameters differ quite considerably, are still adopted in most current structural concrete design code for shear strength.Lightweight aggregate concrete are divided into sand-lightweight concrete and all-lightweight concrete. In the foreign design code for concrete structures, the influence of lightweight aggregate on the shear strength of the concrete beams is generally considered by introducing a reduction factor into the she ar strength equation for normal concrete beams. The reduction factor in ACI 318-11 is a function of splitting strength, but if there’s no information about the splitting strength, 0.75 is used for all-lightweight concrete and 0.85 for sand-lightweight concrete. Eurocode CE-02 adopts a reduction factor relating to the density of the lightweight concrete.In the 80’s of the 20 th century, a lot of tests on the shear behavior of the lightweight aggregate concrete beams were conducted by a project group in China. Based on the tests results and the characters of the lightweight aggregate, a shear equation, which was similar to that of normal concrete beams, was proposed. The shear equation in Chinese Specification for Design of Lightweight Aggregate Concrete Structures JGJ 12-2006 was obtained by multiplying the item of concrete in the shear equation of Code for Design of Concrete Structures GB 50010-2010 by a reduction factor of 0.85 without distinguishing sand-lightweight concrete and all-lightweight concrete.In order to investigate the influence of aggregate types on shear behavior of reinforced concrete beams without stirrups, 16 simply supported beams, which consist of 8 beams with normal concrete and 8 beams with lightweight aggregate concrete, were tested to shear failure under point load. The main variables in the test are shear span to depth ratio and longitudinal reinforcement ratio. The shear failure pattern, the propagation and development of diagonal cracks, the relative displacements of the critical shear cracks and the shear strength of the lightweight aggregate and normal concrete beams were analyzed and compared. Base the test results and some collected test data, model error analysis was conducted for shear equations of JGJ12-2006, ACI318-11, CSA23.3-04, Zararis’s splitting model, Muttoni’s Critical Shear Crack Theory, and Zsutty’s empirical model. Then a new equation for shear strength of reinforced lightweight concrete beams without stirrups is proposed.