Experimental Study On Out-of-plane Behavior Of Tilt-up Recycled Concrete Walls

Tilt-up building system began before World War I and emerged after World War II.It is widely used in large-scale warehouses,factories,supermarkets and other buildings in North America,and then spread to more than 100 countries such as Australia and New Zealand.Tiltup wall is used as the main force-bearing component in the Tilt-up building system,and its height-to-thickness ratio is generally between 30 and 50,so Tilt-up wall is also called a slender wall.According to the damage to Tilt-up buildings caused by earthquakes in some parts of the America in recent decades,the manifestation of the damage of the slender wall under the action of the earthquake is mainly out-of-plane bending damage.There are few studies on Tilt-up building system in china,and the experimental study on out of plane behavior of Tilt-up concrete wall is rare.In this paper,with reference to the tests of Tilt-up wall and theoretical researches at home and abroad,combined with the related researches of recycled concrete,the test on out-of-plane behavior of Tilt-up recycled concrete walls was designed.The test used airbags to simulate the effects of earthquakes and wind loads,and used a lever mechanism to simulate the vertical eccentric load transmitted by the roof.The experiment designed five recycled concrete walls with variable height-to-thickness ratio,reinforcement form,and vertical eccentric load,and studied the load-deflection curve,out-of-plane deformation,longitudinal reinforcement strain,second-order effect,etc.The test of Tilt-up recycled concrete walls and the test of Tilt-up ordinary concrete walls completed by the research group in the early stage were compared and analyzed,and the similarities and differences of the two kinds of walls in the out-of-plane behavior were explored.In addition,based on the experimental data in this paper,formulas for calculating the cracking moment and deflection of Tilt-up recycled concrete walls was proposed.The main conclusions are as follows:(1)Recycled concrete wall exhibited out-of-plane bending failure in the test,and multiple horizontal cracks appeared in the middle of the wall.After the wall cracked,the rigidity of the wall decreased significantly,and the deflection growth of the wall changed from slow to fast during the deformation process.The load-deflection curve of the wall is approximately bilinear.(2)The height-to-thickness ratio has little influence on the cracking deflection and initial stiffness of the recycled concrete wall,but reducing the height-to-thickness ratio will obviously increase the cracking load and the flexural bearing capacity of the wall.Increasing the vertical eccentric load can increase the bearing capacity of the wall to a certain extent,but the influence of vertical eccentric load on bearing capacity is small,while the use of double-row reinforcement will significantly increase the bearing capacity of the wall.(3)The longitudinal reinforcements on the compression side of the double-row reinforced recycled concrete wall will change from the compression state to the tension state during the continuous bending process of the wall.Since they are close to the neutral axis and the moment arms are short,they have only a small contribution to the bearing capacity,and they can only be considered as structural reinforcements.(4)Tilt-up recycled concrete wall will deform greatly due to the force,so the second-order effect has a great influence on the out-of-plane deformation,and the use of double-row reinforcement can significantly reduce the influence of the second-order effect.(5)The recycled and ordinary concrete walls were compared and analyzed in many aspects,such as load-deflection curve,out-of-plane deformation,longitudinal reinforcement strain,second-order effect,etc.The results indicate that they are close to each other in out-of-plane behavior,and recycled concrete walls can be used in actual projects.(6)Based on the experimental data,this paper proposes formulas for calculating the cracking moment and deflection of Tilt-up recycled concrete walls.The moment-deflection curve obtained from the formulas is close to the experimental data,which can provide a certain reference for the design of Tilt-up recycled concrete walls.