1. Review of learning from E-book
-Compression structures develop mainly compressive stresses under the action of
external loads. Two common examples of such structures are columns and arches.
-Shear structures, such as reinforced concrete shear walls (Fig. 1.9), are used in
multistory buildings to reduce lateral movements due to wind loads and earthquake
excitations.
-Bending structures develop mainly bending stresses under the action of external
loads. Some of the most commonly used structures, such as beams, rigid frames, slabs,
and plates, can be classified as bending structures.
-Trusses are composed of straight members connected at their ends by hinged
connections to form a stable.
-Two types of connections are commonly used to join members of struc- tures: (1)
rigid connections and (2) flexible, or hinged, connections.
-A rigid connection or joint prevents relative translations and rota- tions of the
member ends connected to it; that is, all member ends con- nected to a rigid joint have
the same translation and rotation.
-A hinged connection or joint prevents only relative translations of member ends
connected to it; that is, all member ends connected to a hinged joint have the same
translation but may have diferent rotations.
-Dead loads are gravity loads of constant magnitudes and fixed positions that act
permanently on the structure.
-Live loads are loads of varying magnitudes and/or positions caused by the use of the
structure.
-The dynamic effect of the load that causes this increase in stress in the structure is
referred to as impact.
-An earthquake is a sudden undulation of a portion of the earth’s surface. Although the
ground surface moves in both horizontal and vertical di- rections during an earthquake,
the magnitude of the vertical component of ground motion is usually small and
does not have a significant e¤ect on most structures.
-A structure is considered to be in equilibrium if, initially at rest, it remains at rest
when subjected to a system of forces and couples. If a structure is in equilibrium, then
all its members and parts are also in equilibrium.
-External forces are the actions of other bodies on the structure under consideration.
-Internal forces are the forces and couples exerted on a member or por- tion of the
structure by the rest of the structure.

2. -The loads tend to move the structures; but supports prevent the move- ments by
exerting opposing forces, or reactions, to neutralize the efects of loads, thereby
keeping the structures in equilibrium.
-A structure is considered to be internally stable, or rigid, if it maintains its shape
and remains a rigid body when detached from the supports.
-An internally stable structure is considered to be statically determinate externally if
all its support reactions can be determined by solving the equations of
equilibrium.
-If a structure is supported by more than three reactions, then all the reactions cannot
be determined from the three equations of equilibrium. Such structures are termed
statically indeterminate externally.
-Degree of external indeterminacy can be written as: ie = r – 3
Ifr < 3, statically unstable externally
r = 3, determinate externally
r > 3, statically indeterminate externally