Frame Structures
		Introduction
Fig. 1 Side view of a frame structure Fig. 2 Front view of a frame structure Fig. 3 Deflection of a frame		Frames are often used in buildings (Fig. 1 and Fig. 2) and bridges and are composed of beams and columns, which are connected employing pin joints or fixed joints. Unlike truss, moments can be applied to the frame and forces can be applied to the middle of the members. Usually the frame structures are indeterminate.
		Deflection of the Frame
		The deflections of the frames are critical in design since they must be limited in order to prevent cracking of attached brittle materials such as concrete. Furthermore, the frame must not vibrate or deflect severely to the safety reasons. If the material of the frame can assumed to be linear elastic, the deflection curves of the frame members can be abtained from elastic theory. Figure 3 is an example which shows the deflections of the frames members under one point load. In this example, there are one roller joint and two fixed joints. The key feature of fixed joint is that it can transfer moment and keep its angle unchanged. Here stiffness method was used to get the deflection curves of the frame members.
		Shear and Moment Diagram of the Frame
Fig. 4 Moment diagram Fig. 5 Shear diagram		The design of frames often requires drawing the shear and moment diagrams for each member. Similar to computing the deflection curves of the frame, stiffness method is used to draw the shear and moment diagrams (Fig. 4 and Fig. 5).
		Comparison of Truss Structure and Frame Structure
Fig. 6 Displacement of the truss nodes		The main difference of the truss and the frame is that the truss cannot resist moment while the frame can. Hence, under the loadings the truss members keep straight and the frame member become curves (Fig. 3 and Fig. 6).