Question

(40pts) There are two methods to break a concrete beam to determine its modulus of rupture. One is 3-point loading (top diagram). The other is "3rd point loading" (bottom diagram). In third point loading, two equal loads are applied at the top (and two more at the supports on the ends), dividing the beam into "thirds," hence the name. Determine the shear and moment diagrams for both methods (one is in your notes) and sketch them (check your strengths text, ch 6), what is the advantage of using the machine with the two point loads? Hint: What is the bending moment "profile" for each? 4) L/2 P/2 P/2 P/2 P/2 P/2 P/2

Answer 1

In 3-point loading n varies and v and non-zero in 3rd port point loading n is constant i the middle third portion of the BMD in this region v = 0 thus in third point loading use can check beam pure bending (i.e. shear is zero) where as this is not possible with 3-point loading.