Hi Cristian, Hope all is well. When calculating influence lines for truss keep in mind that the truss members are affected only by the joint loading, we can therefore obtain the ordinate values of the influence line for a truss member by loading each joint along the deck with a unit load and then using the method of joints or the method of sections to calculate the force in the member.In this case we are using method of sections to calculate the force in member DI as the 1 (one) unit load moves from left to right on each joint based on that we calculate the reaction Ay. When we cut the structure at the location shown in the video we only deal with loads that are on that section, once the unit load is past that point it is no longer belong to that section. Good question Thankyou.
Why is it that you do not count the unit load in the equation when you get past the split???
Hi Cristian,
Hope all is well. When calculating influence lines for truss keep in mind that the truss members are affected only by the joint loading, we can therefore obtain the ordinate values of the influence line for a truss member by loading each joint along the deck with a unit load and then using the method of joints or the method of sections to calculate the force in the member.In this case we are using method of sections to calculate the force in member DI as the 1 (one) unit load moves from left to right on each joint based on that we calculate the reaction Ay. When we cut the structure at the location shown in the video we only deal with loads that are on that section, once the unit load is past that point it is no longer belong to that section. Good question Thankyou.