600 mm Boom used to support a 30-kN load. 50 mm d = 20 mm 800 mm Consider the structure shown in Fig., which was designed to support a 30-kN load. It consists of a boom AB with a 30 X 50-mm rectangular cross section and of a rod BC with a 20-mm-diameter circular cross section. The boom and the rod are connected by a pin at B and are supported by pins and brackets at A and C, respectively. draw a free-body diagram of the structure by detaching it from its supports at A and C determine the reaction force at A and C determine force that will develop in AB and AC (internal normal foce) 30 kN 600 mm 50 mm d=20 mm 800 mm 30 kN Considering again the structure of Fig. let us assume that rod BC is made of a steel with a maximum allowable stressall = 165 MPa. Can rod BC safely support the load to which it will be subjected? The engineer's role is not limited to the analysis of existing structures and machines subjected to given loading conditions. Of even greater importance to the engineer is the design of new structures and machines, that is, the selection of appropriate components to perform a given task. As an example of design, let us return to the structure of Fig., and assume that aluminum with an allowable stresso all = 100 MPa is to be used. What will be the adequate diameter? Flat end 40 mm 600 mm FRONT VIEW 50 mm d=25 mm 20 mm TOP VIEW OF ROD BC d-20 mm 800 mm d-20 mm Q-30 kN Flat end d=25mm As an example, let us return to the structure of Fig (top). that we have already considered and let us specify the supports and connections at A, B, and C. As shown in Fig. (bottom), the 20-mmdiameter rod BC has flat ends of 20 X 40-mm rectangular cross section, while boom AB has a 30 X 50mm rectangular cross section and is fitted with a clevis at end B. Both members are connected at B by a pin from which the 30-kN load is suspended by means of a U-shaped bracket. Boom AB is supported at A by a pin fitted into a double bracket, while rod BC is connected at C to a single bracket. All pins are 25 mm in diameter. 0-30 kN END VIEW Determine normal stresses in boom AB and rod BC Determine shearing stresses in various connections Determine Bearing stress 125 mm 20 mm 130 mm CHI 20 mm 125 mm B H TOP VIEW OF BOOM AB d = 25 mm