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# Homework # 5 - CIVL 4080 Concrete Design HW5 Laboratory...

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1 CIVL 4080 Concrete Design Spring 2010 HW5: Laboratory Assignment Assigned: March 19 th , 2010 Due: March 26 th , 2010 PART A: Tensile Strength of Concrete: The (Brazilian) Splitting Test Lab Objectives: 1. To gain an understanding of the Brazilian Splitting Test to calculate the tensile strength of concrete; 2. To use the results of the Brazilian Splitting Test to determine the splitting tensile strength of concrete; Background: Concrete as well as other quasi brittle materials is relatively strong in compression, but is rather weak in tension. Tensile behavior of concrete is difficult to measure and model. As a result, in most of the cases, tensile strength is not directly used in design practice. However, there are situations in which it is important to account for the tensile strength. An example is the calculation of the shear resistance of beams. Brazilian Splitting Test: One test typically used to estimate the tensile strength is the splitting test. In this test, a cylinder or a cube is placed on its side between two thin wooden strips and is compressed. The wooden strips run along the longitudinal direction and transfer a line load to the concrete specimen. This line load causes a tensile splitting force that runs down the middle of the specimen. The splitting force pulls the specimen apart and causes it to fail in tension. This procedure leads to a very brittle failure which makes it difficult to capture post peak behavior. However, it is possible to take the peak load from the test and compute an approximation of the tensile strength under the assumption that fracture propagation prior to the peak load is negligible. This strength is affected by both the specimen’ s geometric properties and the width of the wooden strip. For a cube of side L , one has (Rocco, 1999): 5 2 3 max max 2 2 1 0.0115 t P f ' L (1) where P max = peak load, and β = b/L , where b is the width of wooden strip;

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2 Experimental Procedure for Brazilian Splitting Test: Equipment: 1. 300 kip capacity load frame; 2. Rigid steel loading platens; 3. Narrow wooden strips (2 for each test), with b = 0.3 in; 4. Concrete cubes, with L = 3 in; Lab Procedure (in accordance with ASTM C496 / C496M 04): 1. Attach the steel loading platens to the loading frame. Make sure the platens are clean and free of debris; 2. Cut thin wooden strips out of plywood. The width of the strips should be proportional to the size of the specimen. The ratio of the length of the specimen to the width of the strips should be at least 10:1. Record the width of the strips; 3. Remove concrete specimen from moist storage. Specimens should be kept in a moist environment for as long as possible before the test; 4. Mark the centerline of the specimens. This needs to be done to properly align the wood
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