structure is supporting at a particular instant. The live loads in a structure are transmitted through the various load-bearing  structural  members  to  the  ultimate  support of the earth. Horizontal members provide immediate or direct support for the loads. These in turn are supported by vertical members, which in turn are supported by foundations and/or footings, which are finally supported by the earth. The ability of the earth to support a load is called the soil-bearing capacity.  It is determined by test and measured in pounds per square foot. Soil-bearing capacity varies considerably with different types of soil, and a soil with a given bearing capacity will bear a heavier load on a wide foundation or footing than it will a narrow one. Vertical  Members Columns  are  high-strength  vertical  structural members; in buildings they are sometimes called  pillars. Outside-wall  columns  and  bottom-floor  inside  columns usually rest directly on footings. Outside-wall columns usually extend from the footing or foundation to the roof line. Bottom-floor inside columns extend upward from footings  or  foundations  to  horizontal  members  that support the first floor. Upper floor columns usually are located directly over lower-floor columns. A pier in building construction might be called a short column. It may rest directly on a footing, or it may be simply set or driven in the ground. Building piers usually  support  the  lowermost  horizontal  structural members. In bridge construction a pier is a vertical member that provides intermediate support for the bridge   superstructure. The  chief  vertical  structural  members  in  light-frame construction are called  studs. They  are supported on horizontal members called  sills or sole plates, and are topped by horizontal members called top plates or stud caps. Corner posts  are enlarged studs located at the building corners. In early full-frame construction, a corner post was usually a solid piece of larger timber. Built-up  corner  posts  are  used  in  most  modern construction.  They  consist  of  two  or  more  ordinary studs  nailed  together  in  various  ways. Horizontal   Members In  technical  terminology,  a  horizontal  load-bearing structural member that spans a space and is supported at both ends is called a beam. A member that is fixed at one end is called a cantilever. Steel members that consist  of  solid  pieces  of  regular  structural  steel  shapes are called beams. However, one type of steel member is actually a light truss (discussed later) and is called an open-web steel joist or a bar-steel joist. Horizontal structural members that support the ends of  floor  beams  or  joists  in  wood-frame  construction  are called sills, girts, or girders. The choice of terms depends  on  the  type  of  framing  being  done  and  the location  of  the  member  in  the  structure.  Horizontal members that support studs are called sills or sole plates. Horizontal members that support the wall ends of rafters are called rafter plates or top plates, depending on the type of framing. Horizontal members that support the weight of concrete or masonry walls above door and window  openings  are  called  lintels. Trusses A  beam  of  given  strength,  without  intermediate supports below, can support a given load over only a certain maximum span. If the span is wider than this maximum, the beam must have intermediate supports, such as columns. Sometimes it is not feasible to install intermediate supports. In these cases, a truss may be used instead of a beam. A truss is a framework consisting of two horizontal (or nearly horizontal) members joined together by a number of vertical and/or inclined members to form a series of triangles. The loads are applied at the joints. The horizontal members are called the upper or top chords  and  lower  or  bottom  chords.  The  vertical  and/or inclined members that connect the top and bottom chords  are  called  web  members. WELDED  AND  RIVETED  STEEL STRUCTURES The following paragraphs will discuss welded and riveted steel structures and will give examples of both methods  used  to  make  trusses. WELDED  STEEL  STRUCTURES Generally, welded connections are framed or seated just as they are in riveted connections, which we will discuss later. However, welded connections are more flexible. The holes used to bolt or pin pieces together during welding are usually drilled in the fabrication shop.  Beams  are  not  usually  welded  directly  to columns.  The  procedure  produces  a  rigid  connection 7-4